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SCHOOL  OF  MEDICINE 
LIBRARY 


Transferred  from 
the  College  of  Pharmacy 


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ELEMENTS  OF  CHEMISTRY, 


INCLUDING  THE 


fflSTORY  OP  THE  IMPONDERABLES  AND  THE  INORGANIC  CHEMISTRY 


OF  THE  LATE 


EDWARD  TURNER,  M.D.,  F.KS.  L.  &  E 


SEVENTH    EDITION. 


AND   THE 


OUTLINES  OF  ORGANIC  CHEMISTRY, 

BY  WILLIAM  GREGORY,   M.D.,  &c. 

FKOFESSOR  OF  CHEMISTRY,  UNIVERSITY  OF  EDIITBURG. 

C.-!lforn!a  Co!!ors  c'f  Pharmaor 

WITH  NOTES  AND  ADDITIONS, 

BY   JAMES   B.   ROGERS,   M.D. 

Professor  of  General  Chemistry ,  Franklin  Institute,  and  Lecturer  on  Medical  Chemistry,  SfC. 

AND 

ROBERT    E.    ROGERS,    M.D.    &c. 

Professor  of  Chemistry  and  Materia  Medica,  University  of  Virginia,  S^c. 


PHILADELPHIA: 
THOMAS,  COWPERTHWAIT  &  CO.,  254  MARKET  STREET. 

1846. 


Entered  according  to  Act  of  Congress,  in  the  year  1845,  by 

THOMAS,  COWPERTHWAIT  &  CO., 

In  the  Clerk's  Office  of  the  District  Court  for  the  Eastern  District  of  Pennsylvania. 


Euro  &  Baird,  Pxiitters,  9  George  Street. 


o 


PREFACE 


The  present  blended  re-publication  embraces  the  whole  of  the  Impon- 
derables and  Inorganic  Chemistry  of  Dr.  Turner's  well  known  Elements, 
together  with  the  Organic  Chemistry  of  Professor  Gregory's  Outlines,  and 
the  separate  treatises  on  Mineral  and  Organic  Analysis  by  Mr.  Parnell  and 
Professor  Liebig.  In  the  first  plan  of  the  work  it  was  proposed  simply  to 
re-edit  the  seventh  edition  of  Turner's  Elements,  making  such  additions 
and  emendations  as  the  progress  of  the  science  required,  and  at  the  same 
time  re-moulding  the  part  devoted  to  Organic  Chemistry  in  an  abridged  and 
systematic  shape.  The  opportune  appearance  of  Professor  Gregory's  Out- 
lines greatly  aided  the  accomplishment  of  this  plan  by  furnishing  ready  pre- 
pared, just  such  a  condensed  and  methodical  treatise  on  Organic  Chemistry 
as  was  originally  proposed,  and  the  publishers  availing  themselves  of  so 
valuable  an  aid,  at  once  determined  upon  substituting  the  second  part  of 
the  Outlines  in  place  of  the  intended  abridgment  of  the  Organic  Chemistry 
of  Dr.  Turner's  work.  Of  the  propriety  and  utility  of  this  change,  the 
editors  believe  no  doubt  will  be  entertained,  when  it  is  remembered  that 
the  Outlines  are  from  the  same  pen  that  drew  up  a  large  part  of  the  Organic 
Chemistry  in  the  seventh  edition  of  Turner,  that  they  are  in  reality  com- 
piled of  the  same  materials  with  the  addition  of  some  more  recent  results, 
all  very  skilfully  recast,  and  that  they  conform  in  notation  and  general 
method  with  the  inorganic  portion  of  Dr,  Turner's  work. 

In  the  department  of  Analytical  Chemistry,  the  closing  division  of  the 
work,  the  editors  conceive  that  the  present  publication  will  be  admitted  to 
present  a  very  important  improvement.  This  portion  of  the  Elements 
though  enriched  in  the  seventh  edition  by  an  able  sketch  of  Inorganic 


4  I,  u  4  J 


jy  PREFACE. 

Analysis,  written  expressly  for  it  by  Mr.  Parnell,  contains  no  account  of 
the  methods  of  Organic  Analysis^  a  subject  of  peculiar  and  perhaps  lead- 
ing interest  in  its  connection  with  modern  Chemical  research.  To  remedy 
this  defect  the  editors  have  gladly  introduced  Liebig's  outline  of  the  pro- 
cesses for  analyzing  organic  bodies,  a  treatise  of  the  highest  authority  with 
all  who  are  engaged  in  this  department  of  science,  and  one  happily  adapted 
to  the  wants  of  the  practical  student. 

In  the  first  and  second  parts,  treating  respectively  of  the  Imponderables 
and  of  Inorganic  Chemistry,  the  editors  have  not  felt  at  liberty  to  alter  the 
arrangement,  and  except  where  some  new  fact  or  view  derived  from  recent 
researches  rendered  a  correction  or  interpolation  necessary,  they  have  uni- 
formly adhered  to  the  lucid  language  and  illustrations  of  the  text.  In  the 
department  of  the  Imponderables,  and  especially  under  the  head  of  Caloric, 
they  have  thought  it  expedient  to  make  large  additions,  many  of  them 
relating  to  new  determinations  on  points  of  much  practical,  as  well  as  theo- 
retical interest ;  and  in  doing  so,  they  think  they  have  not  given  to  this 
branch  of  the  subject  greater  relative  importance  than  is  assigned  to  it  in 
the  usual  course  of  chemical  studies  in  this  country.  So  long  as  these 
subjects  continue  to  be  embraced  in  systematic  treatises  on  Chemistry,  and 
to  form  a  part  of  the  reg4ilar  oral  instructions  of  the  chemical  teachers  in 
our  medical  and  other  schools,  it  is  thought  that  a  comprehensive  and 
somewhat  detailed  account  of  them  will  be  deemed  an  essential  part  of 
every  Text  book  of  Chemical  Science. 

Under  the  head  of  Inorganic  Chemistry  many  additions  have  been  made 
of  facts  and  processes  discovered  since  the  publication  of  the  text,  and 
every  effort  has  been  used  to  render  this  as  well  as  the  other  portions  of 
this  work,  a  faithful  picture  of  the  present  condition  of  the  science. 

In  the  Organic  Chemistry  no  important  change  has  been  made  beyond 
the  introduction  at  the  beginning  of  many  of  the  distinct  sections,  of  short 
tabular  views  of  the  principal  compounds  of  each  of  the  leading  radicals. 
This  it  is  thought  will  prove  useful  as  a  means  of  immediate  comparison, 
and  will  help  to  remove  the  seeming  confusion  arising  from  a  great  multi- 
plicity of  details.  ^  ^^j  ^  ^ 

Most  of  the  additions  are  incorporated  in  the  text,  and  are  indicated 
by  enclosing  brackets ;  a  few  are  in  the  form  of  notes  with  the  editor's 
initial. 


i  I 


PREFACE.  V 

In  labouring  to  correct  the  numerous  typographical  errors  of  the  London 
work,  the  editors  have  been  greatly  assisted  by  the  American  reprints  of 
the  former  edition  of  Turner's  Elements,  the  great  accuracy  of  which 
reflects  so  much  credit  on  the  industry  and  attainments  of  their  accomplished 
editor.  In  spite  of  the  care  that  has  been  used,  many  errors  have  no  doubt 
escaped  detection,  some  of  which  have  been  discovered  in  time  to  be 
included  in  the  list  of  errata.  For  others  which  it  is  feared  the  reader  will 
detect,  the  editors  must  claim  his  indulgence  on  the  plea  of  the  very  short 
time  allowed  them  for  the  performance  of  their  task. 

Without  claiming  any  merit  in  the  present  work,  beyond  that  of  a  selec- 
tion of  materials  already  furnished  to  their  hands,  and  some  labour  in 
incorporating  matters  of  recent  discovery,  the  editors  indulge  the  hope 
that  the  compilation  now  offered  to  the  public  will  be  found  well  suited  to 
the  wants  of  the  chemical  student,  and  especially  adapted  as  a  comprehend 
sive  text  book  and  work  of  reference  to  those  who  are  pursuing  their  scien- 
tific studies  in  our  medical  and  other  schools.  Founding  their  opinion 
upon  the  acknowledged  merits  of  the  distinguished  authors  whose  separate 
treatises  they  have  ventured  to  unite  in  one  work,  they  think  that  the 
present  volume  will  be  found  to  embrace  a  larger  body  of  the  facts  and 
principles,  the  processes  and  applications  of  the  science  than  any  other 
elementary  work  which  has  yet  been  published  in  our  language.  They 
may  be  permitted  to  add,  that  an  experience  of  many  years  in  teaching 
Chemistry  has  convinced  them  that,  though  not  without  faults,  the  method 
and  scope  of  Dr.  Turner's  work  are  better  suited  to  the  use  of  the  student 
and  even  for  general  reference,  than  the  more  original,  and  at  the  same 
time  speculative  jgiodes  of  presenting  the  science,  adopted  in  the  very  able 
treatises  which  have  more  recently  issued  from  the  press ;  and  if  they  may 
judge  from  the  great  demands  evinced  for  a  republication  of  the  seventh 
edition  of  the  Elements,  a  demand  in  which  the  present  work  originated, 
they  would  infer  that  a  large  number  of  the  chemical  teachers  of  this 
country  share  with  them  in  this  preference. 

(R.) 

Philadelphia,  November,  1845. 


Digitized  by  the  Internet  Archive 

in  2007  with  funding  from 

IVIicrosoft  Corporation 


http://www.archive.org/details/elemechemistryOOturnrich 


CONTENTS, 


Sect.  I. 


Sect.  II. 
Sect.  III. 
Sect.  IV. 


Paok 

Ikteoduction             ......            1 

PART  I. 

IMPONDERABLE    SUBSTANCES. 

Heat           .......               7 

Communication  of  Heat 

8 

Conduclion             .... 

9 

Radiation 

11 

On  the  Cooling  of  Bodies  . 

18 

Effects  of  Heat 

19 

Expansion              .... 

20 

Tiiermometer  .            . 

25 

Specific  Heat         .... 

31 

Liquefaction     .... 

37 

Vaporization           .            .           ,            . 

41 

Ebullition         .            .            .            . 

42 

Evaporation           .... 

46 

Constitution  of  Gases  with  respect  to  Heat 

.         53 

Sources  of  Heat     .... 

53 

Light    ..... 

55 

Electricity".            .... 

67 

Galvanism       .          •  . 

.82 

PART  II. 

'• 

Sect.  I. 


Sect.  II. 


Sect.  IIL 
Sect.  IV. 


INORGANIC    CHEMISTRY.  Ill 

Affinity        .            .            .            .            .            .            .  115 

On  the  changes  that  accompany  Chemical  Action  .  .118 
On  the  Circumstances  that  modify  and  influence  the  operation 

of  Affinity            ......  120 

On  the  Measure  of  Affinity     .            .            .            .  .125 

On  the  Proportions  in  which  Bodies  unite,  and  on  the  Laws  of 

Combination        ......  126 

On  the  Atomic  Theory  of  Dal  ton        .            .            .  .135 

On  the  Theory  of  Volumes            .             ...  138 

Table  of  Equivalent  Weights  and  Volumes               .  .       144 

Chemical  Symbols            .....  146 

Isomeric  Bodies           .            .            .            ,            ,  .150 

Oxygen      .......  150 

Theory  of  Combustion            .            .            .            .  .154 

Hydrogen. — Water            .....  156 


VIU 


CONTENTS. 


Sect.  VI. 


Sect.  VII. 


Binoxide  of  Hydrogen 
SscT.  V.  Nitrogen     ...... 

On  the  Atmosphere    .... 

Compounds  of  Nitrogen  and  Oxygen.— Protoxide 

Binoxide  of  Nitrogen 

Hyponitrous  Acid 

Nitrous  Acid    ..... 

Nitric  Acid  .... 

Carbon  ..... 

Carbonic  Acid        .... 

Carbonic  Oxide  .... 

Sulphur      ..... 

Compounds  of  Sulphur  and  Oxygen.— Sulphurous  Acid 

Sulphuric  Acid  .... 

Hyposulphurous  Acid 

Hyposulphuric  Acid    .... 

Sulphuretted  Hyposulphuric  Acid 

Bisulphuretted  Hyposulphuric  Acid  . 

Phosphorus  .... 

Hypophosphorous  Acid 

Phosphorous  Acid 

Phosphoric  Acid  .... 

Pyrophosphoric  Acid 

Metaphosphoric  Acid  .... 

Boron — Boracic  Acid 

Silicon  ..... 

Selenium    ..... 

Oxide  of  Selenium,  and  Selenious  and  Selenic  Acids 

Chlorine      ..... 

Hydrochloric  Acid      .... 

Compounds  of  Chlorine  and  Oxygen 

Chloric  and  Perchloric  Acids 

Chloride  of  Nitrogen 

Chlorides  of  Carbon    .         ■    • 

Chloride  of  Sulphur 

Chlorides  of  Phosphorus 

Chloro-carbonic  Acid 

Terchloride  of  Silicon 

Chloride  of  Boron,  and  Chloro-nitrous  Gas 

Nature  of  Chlorine      .... 
Sect.  XIII.       ^  Iodine        ..... 

Hydriodic  Acid  .... 

Oxide  of  Iodine,  lodous  and  Iodic  Acids  . 

Periodic  Acid  .... 

Chlorides  of  Iodine 

Iodide  of  Nitrogen,  &c. 
Shot.  XIV.         Bromine  ..... 

Hydrobromic  Acid 

Bromic  Acid    ..... 

Chloride  of  Bromine 

Bromide  of  Sulphur  and  Phosphorus 

Terbromide  of  Silicon 
Sect.  XV.  Fluorine  ..... 

Hydrofluoric  Acid 

Fluoboric  Acid  .... 

Fluosilicic  Acid      .... 


Sect.  VIII. 


Sect.  IX. 
Sect.  X. 
Sect.  XI. 

Sect.  XH. 


Sect.  I. 
Sect.  II. 


ON  THE  COMPOUNDS  OF  THE  SIMPLE  NON-METALLIC  ACIDIFIABLE 
COMBUSTIBLES  WITH   EACH  OTHER. 

Hydrogen  and  Nitrogen. — Ammonia 

Hydrogen  with  Carbon.— Light  carburelted  Hydrogen,  &c. 


255 
258 


CONTENTS. 


IX 


Page 

Sect.  III.            Compounds  of  Hydrogen  and  Sulphur.— H3'drosulphuric  Acid  263 

Persulphuretted  Hydrogen       .....  265 

Sect.  IV.            Hydrogen  and  Selenium. — Hydroselenic  Acid      .             .  267 

Sect.  V.              Hydrogen  and  Phosphorus      .....  267 

Sect.  VI.            Nitrogen  and  Carbon. — Cyanogen            .            .            ,  ^  271 

Mellon 272 

Sect.  VII.           Compounds  of  Phosphorus  and  Nitrogen             .            .  273 

Sect.  VIII.          Compounds  of  Sulphur  with  Carbon              .            .            .  273 

Compounds  of  Sulphur  with  Phosphorus              .            .  274 

Compounds  of  Selenium  with  Sulphur  and  Phosphorus  1  275 

Compounds  of  Selenium  with  Nitrogen 


METALS. 


General  properties  of  Metals  ....  276 

Sect.  I.  Potassium  and  its  Compounds  with  Oxygen,  Chlorine,  Sul- 

phur, &c.      .  .  .  .  .  .  .291 

Sect.  II.  Sodium  and  its  Oxides,  Chloride,  &c.        .  .  .  299 

Sect.  Ill,  Lithium  and  its  Oxides,  &c.    .....      302 

Sect.  IV.  Barium  and  its  Oxides,  &c.  ....  363 

Sect.  V.  Strontium,  and  its  Oxide,  Chloride,  Sulphuret,  &c.    .  .      306 

Sect.  VL  Calcium  and  its  Oxides,  Chloride,  &c.      .  .  .  308 

Sect.  Vn.  Magnesium  and  its  Oxide,  &c.  .  .  .  .311 

Sect.  VIII.  Aluminium Alumina      .....  314 

Sect.  IX.  Glucinium,  Yttrium,  Thorium,  Zirconium,  and  their  Oxides       318 

Sect.  X.  Manganese,  and  its  Compounds  with  Oxygen,  Chlorine,  &c.       323 

Sect.  XL  Iron,  and  its  Compounds  with  Oxygen,  Chlorine,  Sulphur,  &c.  331 

Carburets  of  Iron. — Steel,  Cast  Iron,  Graphite      .  .  339 

Sect.  XII.  Zinc,  and  its  Compounds  with  Oxygen,  Chlorine,  Sulphur,  &c.  341 

Cadmium  and  its  Oxide     .....  343 

Sect.  Xin.         Cobalt,  Nickel        ....  .345 

Sect.  XIV.         Tin,  and  its  Compounds  with  Oxygen,  Chlorine,  &c.  .      350 

Sect.  XV.  Copper,  and  its  Compounds  with  Oxygen,  Chlorine,  &c.  354 

Sect.  XVL         Lead  and  its  Oxides,  &c.  ....  358 

Sect.  XVII.        Arsenic,  and  its  Compounds  with  Oxygen,  Chlorine,  &c.     .      363 

Tests  for  Arsenious  Acid  .....  364 

Sect.  XVIII.       Antimony,  its  Oxides,  Chlorides,  and  Sulphurets       .  .      372 

Sect.  XIX.  Chromium,  and  its  Compounds  with  Oxygen  .  .      378 

Sesquichloride  of  Chromium        ....  379 

Compounds  of  Chromium  with  Fluorine,  &c.  .  .      382 

Vanadium,  and  its  Compounds  with  Oxygen        .  .  384 

Compounds  of  Vanadium  with  Chlorine,  &c.  .  .      389 

Sect.  XX.  Molybdenum  and  its  Compounds  with  Oxygen    .  .  390 

Tungsten  and  its  Compounds  with  Oxygen  .  .       393 

Columbium  and  its  Compounds  with  Oxygen      .  .  395 

Sect.  XXI.         Uranium  and  its  Oxides     .....  397 

Cerium  and  its  Oxides. — Lantanium  .  .  .      399 

Sect.  XXII.        Bismuth,  and  its  Compounds  with  Oxygen,  Chlorine,  and  Sul- 
phur       ....... 

Titanium  and  its  Compounds  with  Oxygen    . 

Tellurium  and  its  Oxides  .  ,  . 

Sect.  XXIII.       Mercury  and  its  Oxides 

Chlorides. — Calomel  and  Corrosive  Sublimate     . 

Iodides,  Cyanurets,  and  Sulphurets     . 
Sect.  XXIV.       Silver,  its  Oxide,  Chloride,  &c.      . 

Sect.  XXV.        Gold,  and  its  Compounds  with  Oxygen,  Chlorine,  and  Sulphur  416 
Sect.  XXVI.       Platinum,  and  its  Compounds  with  Oxygen,  &c.  .  420 

Sect.  XXVII.     Palladium,  Rhodium,  Osmium,  and  Iridium  .  .      424 

Sect.  XXVIIL    On  Metallic  Combinations.— Alloys  .  .  .  431 


399 
401 
403 
406 
410 
411 
412 


CONTENTS. 


SALTS 


GENERAL  REMARKS  ON  SALTS 


Crystallization 
SicT.  I.  Oxy-salts     . 

Sulphates 

Double  Sulphates    . 

Sulphites 

Hyposulphites  and  Hyposulphates 

Nitrates 

Nitrites 

Chlorates 

Chlorites     . 

lodates 

Phosphates 

Pyrophosphates 

Metaphosphates 

Arseniates 

Arsenites    . 

Chromates 

Borates 

Carbonates 
Sect.  H.  Hydro-salts 

Ammoniacal  Salts 

Phosphuretted  Hydrogen  Salts 
Sbct.  ni.  Sulphur-salts     . 

Hydro-sulphurets    . 

Carbo-sulphurets 

Arsenio-sulphurets 

Molybdo-sulphurets 

Antimonio-sulphurets 

Tungsto-sulphurets 
Sect.  IV.  Haloid-salts 

Hydrargo-chlorides 

Auro-chlorides 

Platino-chlorides 

Palladio-chlorides  . 

Rhodio-chlorides 

Iridio-chlorides,  and  Osmio-chlorides 

Oxy-chlorides  . 

Chlorides  with  Ammonia  . 

Chlorides  with  Phosphuretted  Hydrog' 

Double  Iodides 

Double  Bromides  and  Fluorides 

Boro-fluorides 

Silico-fluorides 

Titano-fluorides 

Ojy-fluorides    . 


-crystallization 


PART  III. 


organic  chemistry. 


Ihtrobuctoiit  .:..... 

General  Doctrines  concerning  Compound  Organic  Radicals 
Theory  of  Types,  and  Doctrine  of  Substitutions 

METAMOnPHOSES  OF  OrOAXIC  CoMPOTTiniS  .       ^  . 

1.  By  Oxidation: — 

,    a.  Direct       ....".,, 


521 
524 
528 

532 
533 


CONTENTS. 


XI 


Combustion 
Eremacausis 
b.  Indirect 

2.  By  the  action  of  Acids 

a.  Of  Nitric  Acid  .... 

b.  Of  Sulphuric  Acid 

c.  Of  Phosphoric  Acid,  &c. 

3.  By  the  Action  of  Bases 

4.  By  the  Action  of  Heat,  or  Destructive  Distillation 

5.  By  the  Action  of  Ferments 
Theories  of  Fermentation 
Fermentation  and  Putrefaction        , 
Putrefaction  of  the  aqueous  solution  of  Cyanogen 
General  views  concerning  the  Organic  Acids 

CoMPOuiTD  Radicals  nisows  ob  admitted 
I.  Amide,  ok  Amidogeu" 
Its  Compounds: 
a.  With  Hydrogen  :  Ammonia,  &c. 
6.  With  Metals  .... 

c.  With  Platinum :  singular  bases  of  Gros  and  Reiset 

II.  Carbonic  Oxide  (Oxaltle) 
Its  Compounds  ; 

a.  With  Oxygen :  Oxalic  Acid 
Oxalate  of  Ammonia,  &c.    . 

b.  With  Amide :  Oxamide 

Oxamic  Acid 

c.  With  Chlorine :  Phosgene  Gas] 

d.  With  Potassium  or  Hydrogen 
Rhodizonic  Acid 
Croconic  Acid 
Mellitic  Acid 
Mellitate  of  Ammonia 
Its  Metamorphoses 

III.  CxANOGEX        .... 

Its  Compounds  : 

a.  With  Hydrogen:  Hydrocyanic^Acid 

b.  With  Oxygen         .  .        "   . 
Cyanic  Acid 

Cyanates       .... 
Urea  (Cyanate  of  Ammonia)    . 
Fulminic  Acid  and  Fulminates 
Cyanuric  Acid  . 
Cyamelide    .... 

c.  With  Nitrogen  :  Mellone 

d.  With  Chlorine     . 

e.  With  Bromine,  Iodine,  and  Sulphur 
/.  With  Metals :  Cyanides  . 
Double  Cyanides 

IV.  FERROCTAITOGElf 

Its  Compounds : 

a.  With  Hydrogen :  Ferrocyanic  Acid 

b.  With  Metals  :  Ferrocyanides 

V.    FERRIDCTAyOGEIT 

Its  Compounds : 
a.  With  Hydrogen :  Ferridcyanic  Acid 
6. 'With  Metals:  Ferridcynides 

VI.    CoBAlTOCYANOGEN     . 

VII.  Chromoctanogen 


Page 
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533 
534 
534 
534 
535 
535 
535 
536 
537 
538 
539 
540 
541 

542 
543 

544 
545 
545 

548 

549 
549 
550 
551 
.551 
552 
552 
552 
553 
553 
553 

554 

555 

558 
558 
559 
560 
561 
562 
563 
564 
564 
565 
565 
567 

567 

567 
568 

570 

570 
570 

570 

571 


XII 


CONTENTS, 


VIII.    PLATINOCTAKOeEW      .  .  . 

IX.  Iridiocyanogeit,  &C.      .... 
Paracyanogen  ..... 

X.    SuLPHOCYAJfOGfEN  .... 

Its  Compounds: 
a.  With  Hydrogen :  Sulphocyanic  Acid     . 
h.  With  Metals :  Sulphocyanides 
Persulphocyanic  Acid  .... 

XI.  Mellowe  ..... 

Its  Compounds  : 
a.  With  Hydrogen  :  Hydromellonic  Acid 
h.  With  Metals :  Mellonides 

Products  of  the  distillation  of  Sulphocyanide  of  Ammonium 

Melam  ....  .  . 

Melamine  ..... 

Ammeline    ....... 

Ammelide  .  . 

Tabular  Views  of  these  products,  and  of  their  relation  to  Cyanuric 
Acid,  &c.  ...... 

Cyanogen  with  Carbonic  Oxide  (oxalyle),  or 

xn.  Uryle  ... 

Uric  Acid     . 
Products  of  its  Oxidation : 

By  Peroxide  of  Lead 

Allantoine 
By  Nitric  Acid  . 

1.  Alloxan 

2.  Alloxanic  Acid 

3.  Mesoxalic  Acid 

4.  Mykomelinic  Acid 

5.  Parabanic  Acid 

6.  Oxaluric  Acid 

7.  Thionuric  Acid 

8.  Uramile 

9.  Uramilic  Acid 

10.  Alloxantine 

11.  Dial  uric  Acid    . 

12.  Murexide    . 

13.  Murexan 
Appendix  to  Uric  Acid : 

Xanthic  or  Uric  Oxide 
Cystic  Oxide 

Xin.  Beitzoyle  .... 

Its  Compounds : 

a.  With  Oxygen :  Benzoic  Acid 

b.  With  Hydrogen  :  Hyduret  of  Benzoyle 

c.  With  Chlorine 

d.  With  Amide :  Benzamide 
c.  Formobenzoilic  Acid 

/.  Benzoate  of  Hyduret  of  B. 
g.  Hippuric  Acid 
Products  derived  from  Benzoyle : 

1.  Hyposulphobenzoic  Acid 

2.  Bromobenzoic  Acid 

3.  Benzoyle  (Benzine)     . 

4.  Sniphobenzide 

5.  Hyposulphobcnzidic  Acid 

6.  Nitrobenzide 

7.  Azobenzide       .... 


Page 
571 


CONTENTS. 


Xlll 


8.  Chloride  of  Benzoyle 

9.  Chlorobenzine 

10.  Benzone 

11.  HydrobenzamiHe 

12.  Benzhydramide 

13.  Azobenzoyle 

14.  Azotide  of  Benzoyle 

15.  Benzamide 

16.  Benzoine     . 

17.  Hydrobenzoniamide     . 

18.  Benzile 

19.  Benzilic  Acid 

20.  Azobenzoide 

21.  Cyanobenzile 

21.  6.  Hyduret  of  Sulphobenzoyle 

22.  Stilbene 

23.  Hyduret  of  Sulphazobenzoyle 

24.  Nitrobenzoic  Acid 

25.  Bromide  of  Benzoyle 

26.  Hydrocyanate  of  Benzoine 

27.  Hydrocyanate  of  Benzile    . 
Appendix  to  Benzoyle : — 

1.  Amygdaline 

2.  Amygdalinic  Acid 

3.  Distilled  Water  of  Bitter  Almonds 

4.  Laurel  Water 
Theory  of  the  Formation  of  the  Compounds  of  Benzoyle 

XIV.  Salictie 

Its  Compounds : 

a.  With  Hydrogen :  Hyduret  of  Salicyle 

b.  With  Oxygen  :  Salicylic  Acid 
Products  derived  from  Salicyle  : — 

c.  With  Chlorine  :   Chlorosalicylic  Acid 

d.  With  Nitric  Acid  :  Nitrosalicylic  Acid 
Appendix  to  Salicyle  : — 

Salicine  .... 

Phloridzine 

XV.  CiarifAMYLE        .... 

Its  Compounds  : 

a.  With  Hydrogen :  Hyduret  of  Cinnamyle 

b.  With  Oxygen  :  Cinnamic  Acid 
Balsam  of  Peru 
Balsam  of  Tolu 

XVI.  Ethtle         .... 

Its  Compounds  : 
a.  With  Oxygen :  Oxide  of  Ethyle 

Alcohol         .  .  .  - 

Vinous  Fermentation    . 
6.  With  Chlorine :  Chloride  of  Ethyle 

c.  With  Bromine,  Iodine,  Sulphur 
Mercaptan 

rf.  Salts  of  Oxide  of  Ethyle 

Acid  Sulphate,  or  Sulphovinic  Acid 
Acid  Phosphate,  or  Phosphovinic  Acid 
Nitrate :  Nitric  Ether 
Hyponitrite  :   Nitrous  Ether     . 
Carbonate :  Carbonic  Ether 
Double  Carbonates 
Oxalate:   Oxalic  Ether 
Acid  Oxalate  :  Oxalovinic  Acid 


XIV 


CONTENTS. 


Oxamate :  Oxamethan        .... 

Sulphocarbonate  ..... 

Bicyanurate  .  .  !  .  . 

Benzoate :  Benzoic  Ether        .  .  .  *. 

Hippurate :  Hippuric  Ether 
Salicylate :  Salicylic  Ether      .... 

Compounds  connected  with  Ethyle : 

Chlorocarbonic  Ether         .... 

Urethan  ...... 

Transformations  of  Ethyle : — 

,  Oil  of  Wine  ..... 

.'Heavy  Oil  of  Wine      ..... 

iEthionic,  Isethionic,  Methionic,  and  Althionic  Acids 
Products  of  the  Oxidation  of  Ethyle  and  its  derivatives 

XVn.     ACETTLB  ...... 

a.  Hydrated  Oxide  of  Acetyle,  or  Aldehyde 

b.  Acetal  ...... 

c.  Acetylous  or  Aldehydic  Acid    .... 
rf.  Acetic  Acid        .     . 

Acetification     *..... 
Acetates      ..... 

Action  of  Chlorine,  &c.  on  Ethyle,  Acetyle,  and  their  derivatives 

1.  On  Oxide  of  Ethyle  .... 

2.  On  Salts  of  Ethyle         ..... 

3.  On  Alcohol              ..... 
Chloral 

4.  On  Acetic  Acid        .  .  .  ... 

Chloracetic  Acid  .  .  .    '        . 

Bromal        ...... 

Compounds  derived  from  Alcohol,  of  uncertain  constitution 

defiant  Gas  ..... 

Oil  of  the  Dutch  Chemists        .... 

Chloride  of  Acetyle  .... 

Chloretheral      ...... 

Sulphacetylic  Acid 

Action  of  Bichloride  of  Platinum  on  Alcohol  . 

Action  of  Heat  on  Acetic  Acid  and  the  Acetates   . 

Acetone  ...... 

Mesitylene   ...... 

Compounds  containing  Arsenic  derived  from  Acetyle 

XVni.  Kakodtle     ...... 

Its  Compounds: 
a.  With  Oxygen :  Protoxide  .... 

Kakodylic  Acid        ..... 

h.  With  Chlorine,  Iodine,  Bromine,  Fluorine,  Sulphur,  Cyanogen 
Compounds  of  Kakodyle  containing  Platinum 
Appendix  to  Ethyle : 
Sugar    . 
1.  Cane  Sugar 
3.  Grape  Sugar 
Metacetone 
Action  of  Nitric  Acid  on  Sugar 
Saccharic  Acid 

3.  Sugar  of  Milk  or  Lactine 
Mucic  Acid 
Modified  Mucic  Acid 
Pyromucic  Acid 

4.  Sugar  of  Mushrooms 
Vinous  or  Alcoholic  Fermentation 
Viscous  FermentalionJ 


CONTENTS. 


XV 


Mannite 
Lactic  Acid 

XIX.  Methtle 

a.  Hydrated  Oxide :  Pyroxilic  Spirit 

b.  Oxide  of  Methyle 

c.  Chloride,  Iodide,  Sulphuret 

d.  Salts  of  Oxide  of  Methyle 
Neutral  Sulphate     .... 
Acid  Sulphate    .... 
Nitrate  ..... 
Oxalate  .... 
Benzoate       ..... 
Acetate               .... 

Other  Compounds  of  Methyle 

Products  of  its  Oxidation  : 

XX.  FORMTXE      ..... 

Formic  Acid  .... 

Formiates  .  .  .  .  , 

Chloride,  Bromide,  Sulphuret,  &c.  of  Formyh 

XXI.  Cetyle      ..... 

Hydrated  Oxide :  Ethal 

XXII.  Amtle  .... 

Hydrated  Oxide  of  Amyle,  or  Oil  of  Potato  Spirit 
Other  Compounds  of  Amyle 

Products  of  its  Oxidation : 
Valerianic  Acid 
Amilene 

XXIII.  Gltcektle 
Hydrated  Oxide  of  Glyceryle  or  Glycerine 

Organic  Acids 

1.  Citric  Acid 
Citrates 

Action  of  Heat  on  Citric  Acid 
Aconitic  Acid 
Itaconic  and  Citraconic  Acids 

2.  Tartaric  Acid 
Tartrates 
Tartar  Emetic 

Action  of  Heat  on  Tartaric  Acid 
Tartralic  Acid 
Tartrelic  Acid 
Anhydrous  Tartaric  Acid 
Pyroracemic  Acid 

3.  Racemic  Acid 
Its  Salts 

4.  Malic  Adid 
Its  Salts 

Action  of  Heat  on  it 
Maleic  Acid 
Fumaric  Acid 

5.  Tannic  Acid    , 
Its  Salts      . 
Its  conversion  into  Gallic  Acid 

6.  Gallic  Acid 
Its  Salts 

Action  of  Heat  on  it 
Pyrogallic  Acid 
Metagallic  Acid      . 
EUagic  Acid 


^^ 


X¥l 


CONTENTS. 


Catechu     . 

7.  Meconic  Acid 
Its  Salts 
Action  of  Heat  on  it 

8.  Comenic  Acid 
Its  Salts 
Py  ro  m  econic^Acid 

9.  Kinic  Acid    '  . 
Its  Salts      . 

Products  of  its  Decomposition 
Kinone,  Hydrokinone.  &c 

10.  Butyric  Acid 
Its  Salts 
Butyramide 
Butyrone    . 
Caproic  Acid  . 
Capric  Acid 
Caprylic  Acid 
Hircic  Acid 
Phocenic  Acid 
Cevadic  Acid 
Veralric  Acid  . 
Crotonic  Acid 

11.  Camphoric  Acid 
Anhydrous 
Camphor 
Borneo  Camphor 
Camphogen    . 
Camphrone 

12.  Valerianic  Acid 

13.  Anisic  Acid 
Nitro  anisic  Acid 
Anisole 

14.  CEnanthic  Acid 
CEnanthic  Ether 

15.  Roccellic  Acid 
J  6.  Cuminic  Acid 

Cumene 
Cuminole    . 
Cumyle 

17.  Eugenic  Acid 
Caryophylline 

18.  Cocinic  Acid 

19.  Myristic  Acid 
Myristine    . 
Palmitic  Acid 
Palmitine    . 
Cetylic  Acid     . 
Margaric  Acid 
Margarine 
Margarates 
Stearic  Acid 
Stearates     . 
Stearine 

Action  of  Nitric  Acid  on  Stearic  Acid 

24.  Suberic  Acid 

25.  Succinic  Acid 
Its  Salts 
Amber 

26.  Oleic  Acid 
Oleates 
Oleine 


20. 

21. 
22. 


23. 


CONTENTS. 

xvii 

Page 

Action  of  Heat  on  Oleic  Acid 

.        672 

27.  Sebacic  Acid             .... 

673 

28.  Elaidic  Acid      .... 

.       673 

Elaidine         ..... 

673 

Action  of  Nitric  Acid  on  Oleic  Acid     . 

.       673 

Pimelic  Acid             .... 

673 

Adipic  Acid        .... 

.       673 

Lipic  Acid                .... 

673 

Azoleic  Acid       .            •            .            . 

.       673 

Acids  of  Castor  Oil             .... 

674 

Palmine              .... 

.       674 

Natural  Fats  and  Fixed  Oils 

674 

Action  of  Heat  on  Oils  and  Fat 

.       674 

Acroleine 

674 

Acryle 

.       675 

Acrylic  Acid 

675 

Action  of  Sulphuric  Acid  on  Fat  Oils 

.       675 

Sulpholeic,  Sulphomargaric,  Metamargaric,  Hydromargaritic,  Metoleic,  a 

nd 

Hydroleic  Acids    .... 

675 

Oleene  and  Elaene        .... 

.       676 

Action  of  Nitrous  (Hyponitrous)  Acid  on  Fat  Oils 

676 

Action  of  Nitrate  of  Mercury  on  Fal  Oils 

.       676 

Elaidine       ...... 

676 

Action  of  Bases  on  Fat  Oils    . 

.       676 

Soaps      ..... 

676 

Plasters         .... 

.       677 

Vegetable  Fats          ..... 

677 

Spermaceti        ..... 

.       677 

Cholesterine  and  Cholesteric  Acid 

677 

Ambreine  and  Ambreic  Acid    . 

.       677 

Wax,  Cerine,  Myricine        .... 

677 

Cerosine               ..... 

. 

. 

, 

.     678 

Athamantine           "..... 

678 

Various  Acids                 .... 

.       678 

Volatile  Oils             ..... 

678 

Nonoxygenated  Essential  Oils 

.       678 

Oil  of  Turpentine    .... 

678 

Dadyle  and  Peucyle 

.       679 

Oils  of  Juniper,  Lemons,  Copaiva,  and  other  Nonoxygenated 

Oil 

s 

679 

Oxygenated  Essential  Oils 

. 

.       679 

Oils  of  Cinnamon,  Anise,  Estragon,  and  other  Oxygen 

atedOils    . 

679,  680 

Draconic  Acid  and  other  derivatives  from  Oil  of  Estra 

gon 

. 

.       680 

Coumarine                 .             .            .       ^      . 

681 

Sulphurated  Essential  Oils 

.       681 

Oil  of  Mustard  and  its  Derivatives 

681 

Thiosinnamine,  Sinnamine,&c. 

.       681 

Sinapoline,  Myrosine,  Sinapisine,  &c. 

682 

Oils  of  Garlic,  Assafetida,  &c. 

.       683 

Concrete  Volatile  Bodies  allied  to  the  Volatile  Oils 

683 

Asarone              .... 

.       683 

Anemorine,  Cantharadine 

683 

Caoutchouc         .... 

.       684 

Action  of  Heat  on  Caoutchouc 

684 

Resins    ...... 

,       684 

Colophony,  Pinic,  and  Sylvic  Acids 

684 

Resins  of  Copaiva,  Elemi,  Benzoin,  Balsam  of  Tolu,  &c. 

.       685 

Benzoene,  Nitrobenzoene 

, 

685 

Styrax,  Guaiacum,  Jalap,  Copal,  and  other  Resins 

.       685 

Varnishes     ..... 

. 

685 

Action  of  Heat  on  Resins 

. 

.       686 

Nonazotized  Colouring  Matters 

686 

Yellow               .... 

.       686 

xvm 


CONTENTS. 


Red  .... 

Blue        ..... 

Green,  Chlorophyle     . 
Bitter  Vegetable  Principles,  nonazotized 
Azotized  Colouring  Matters  and  allied  Substances 

Lecanorine,  Orcine,  Erythrine 

Pseudoerythrine,  Variolarine 

Archil,  Litmus,  Phloridzeine    . 

Indigo         ..... 
White  or  reduced  Indigo 

Action  of  Sulphuric  Acid  on  Indigo 

Oxidation  of  Indigo,  Isatine     . 

Chlorisatine,  Bichlorisatine,  «&c.   . 

Isatyde,  Sulphesalyde,  «fec. 

Indine,  Hydrindene,  &c.    . 

Chlorindopten,  &c, 

Chloranile,  Chloranilic  Acid,  &c. 

Imasatine,  Amasatine,  &c. 

Anilic  or  tndigotic  Acid     . 
Picric,  Nitropicric,  Abazotic  Acid  . 

Action  of  Potash  on  Indigo 

Anthranilic  Acid,  Aniline,  &c. 

Tabular  view  of  the  Series  of  Phenyle 

Chlorinized  and  Broniinized  Bases  from  Aniline 

Carmine  .... 

Action  of  Nitric  Acid  on  Aloes 

Chrysaramic  Acid 

Chrysolepic  Acid 

Organic  Bases  ok  Alkaloids 

1.  Liquid  Volatile  Bases     . 
Aniline,  Leukol 
Nicotine,  Conine,  Quinoline 

2.  Bases  from  Oil  of  Mustard 

3.  Bases  of  Cinchona  Bark 

Quinine,  Cinchonine 
Quinoidine,  Aricine,  &c. 

4.  Bases  of  the  Papaveracea    . 
Morphine  .... 
Codeine          .... 
Thebaine,  Narceine,  &c. 
Narcotine  and  its  Derivatives 
Chelidonine        .... 
Chelerythrine,  &c.    . 

5.  Bases  of  the  Solanaceae,  Strychneoe,  &c. 
Hyoscyamine,  Daturine,  Stramonine,  Atropine 
Solanine,  Veratrine,  Sabadilline,  Colchicine 
Aconitine,  Delphine,  Emetine,  Strychnine 
Brucine,  Jervine 
Other  Bases 
Theobromine,  Caffeine 

.  Indifferent  Nonazotized  compounds 

Starch      .  .  .  •  . 

Dextrine,  Leiocoine 
Inuline,  Lichenine,  Saponine    . 
Gum  ..... 

Arabine,  Mucilage,  Bassorine    . 

Pectine,  Pactic  Acid 

Apime,  Glycyrrhizune    . 
Woody  Fibre  .  .  .  . 

Cellulose,  Cignine 

Decay  of  Wood 

Brown  or  Wood  Coal 


Paae 
686 
687 
687 
687 


721 


CONTENTS. 


XIX 


t 


of  Phenyle 


Naphthaline,  Nomenclature 


Mould  or  Humus 
Humic  Acid,  Geine,  &c. 
Cranio  and  Apocrenic  Acids 
Products  of  the  Distillation  of  Wood    . 

1.  Volatile  products,  soluble  in  Water 
Acetate  Acid,  Pyroxylic  Spirit 
Xylite,  Mesite,  &c.    . 

2.  Oily  products,  insoluble  in  Water 
Creosote 
Picamar,  Capnomor,  Eupion     . 

3.  Solid  products 
Paraffine 
Cedriret,  Pittacal,  Pyroxanthine 

Products  of  the  Distillation  of  Coal 

Carbolic  Acid 

Table  of  Substitutions  in  the  series 

Volatile  bases  of  Coal  Tar   . 

Kyanol  or  Aniline 

Leukol  or  Quinoline 
Volatile  Carbo-hydrogen  in  Coal  Tar 

Naphthaline  . 

Action  of  Chlorine  and  Bromine  on 

Chlonaphtase,  Bronaphtase,  &c. 

Action  of  Sulphuric  Acid  on  Naphthaline 

Action  of  Nitric  Acid  on  Naphthaline 

Nitronaphtalase,  &c. 

Action  of  Sulphuret  of  Ammonium  on  Nitronaphtalase,  &c. 

Naphtalidam  .... 

Anthracene,  Chrysene,  and  Pyrene 

Ampeline  and  Ampelic  Acid     . 

Fossil  Resins,  Fossil  Wax,  Fossil  Oil,  Naphtha,  &c. 

Asphaltum,  Petroleum 

Soot  and  Lamp  Black  .... 

Sulphurized  and  Azotized  Nutritious  and  Animal  and  Vegetable  Com- 
pounds 

Vegetable  Albumen 

Vegetable  Fibrine 

Vegetable  Caseine     . 

Emulsine  or  Synaptase 

Fungine,  Gliadine 

Fermentation  of  Vegetable  Juices 

Diastase,  Malt,  Must,  Beer,  or  Ale,  Wort,  Grain,  and  Potato  Spirit 

Panification        ..... 

Ferment,  or  Yeast    .... 

Caseous  Oxide,  or  Aposepidine 

Animal  Albumen      .  •  .  . 

Serum,  White  of  Egg     .... 

Animal  Fibrine  .... 

Animal  Caseine .  .  .  .  . 

Milk 

Cheese     .  .  .  . 

Animal  Mucus  .... 

Horny  Matter      ..... 
Composition  of  the  preceding  Substances 

Proteine  .  ..... 

Products  of  its  decomposition 

Erythroprotide,  Leucine,  Oxides  of  Proteine,  &c. 

Action  of  Acids  on  Proteine  compounds 
Relation  of  Proteine  to  Sugar  and  Ammonia  . 
Gelatigenous  Tissues  .... 

Gelatine,  Chondrine        ..... 
Sugar  of  Gelatine     ..... 


XX 


CONTENTS. 


Bone      .  .  .  • 

Ivory  Black  .... 

Bile       ...... 

Is  Choleate  of  Soda     . 

Products  of  decomposition  of  Bile 

Choloidic  Acid,  Taurine,  Cholinic  Acid,  &c 

Composition  of  Choleic  Acid 

Biliary  Calculi 
Brain  and  Nervous  Matter 

Cerebric  and  Oleophosphoric  Acids,  Cerebroleine 
Gastric  Juice      .... 
Digestion     .... 
Saliva,  Pancreatic  Juice 
Excrements,  Urine  . 
Guano    ..... 

Animal  Manure 
Urinary  Calculi 
Lymph,  Blood 

Globules  of  the  Blood 

Colouring  Matter  of  the  Blood 

Hematosine 


NuxniTioN  OF  Plants  and  Animals 
Equilibrium  between  the  Animal  and  Vege 


able  Kingdoms 


Page 

751 
751 

751 
752 
753 
753 
754 
754 
755 
755 
755 
756 
756 
757 
758 
758 
758 
759 
759 
760 
761 

761 
766 


PART  IV. 


CHEMICAL    ANALYSIS. 


769 


Mineral  Analysis         ......      769 

Sect.  I.  Manipulations  in  Analytical  processes      .  .  .  770 

Sect.  IF.  Qualitative  Analysis    ......      772 

Sect.  Ill,  Quantitative  Analysis         .....  775 

Sect.  IV.  Analysis  of  Mineral  Waters    .....      779 

Classification  of  Mineral  Waters  .  .  .  780 

Organic  Analysis         ......       783 

General  method  of  proceeding      ....  785 

Special  details  of  the  method  ....      792 

Combustion  of  Volatile  liquids      ....  797 

Combustion  of  substances  rich  in  Carbon  or  containingChlorine  799 

800 
801 
801 
802 
804 
806 
810 
814 
815 
817 


Oxide  of  Copper,  preparation  of 
Chromate  of  Lead,  preparation  of 
Combustion  tubes  . 
Determination  of  Carbon 

the  Hydrogen 

Nitrogen     .... 

Nitrogen  direct 
Methods  of  Control  for  Organic  Analysis 
Determination  of  number  of  Atoms  in  Organic  Compounds 
Examples,  Amygdalic  Acid,  &c. 
Determination  of  the  specific  gravity  of  Volatile  substances  as 
a  means  of  ascertaining  the  number  of  atoms  of  their  Ele- 
ments      .  .  .  .  .  .  •  821 


CONTENTS.  xxi 


APPENDIX. 

Paob 

r.  Table  of  Equivalents  or  Atomic  weights  of  Elements,  &c.     .  .      825 

II.         Table  of  the  elastic  force  of  Aqueous  vapour        .  .  .  826 

ni.       Table  of  the  elastic  force  of  the  vapour  of  Alcohol,  &c.  .  .      828 

IV.  Table  for  the  conversion  of  degrees  on  the  Centigrade  Thermometer 

into  degrees  of  Fahrenheit's  Scale  ,  .  .  '.''*^  829 

V.  Table  of  the  strength  of  Sulphuric  Acid  ....      831 

VI.  Table  of  the  strength  of  Nitric  Acid  ....  832 

VII.  Table  of  the  strength  of  Alcohol  .  .  .  .  .833 

VIII.  Table  of  Specific  Gravities  indicated  by  Baum^'s  Hydrometer      .  834 
Index       .........      835 


ERRATA. 


Page  47,  line  11,  for  or,  read  on. 
«    78,    «    14,   for  Fig.  4,  read  Fig.  7. 
'«    78,    «   36,   for  Fig.  5,  read  Fig.  8. 
«  382,    "    16,    for  CIO,  read  Cr  CI. 

*^  551,    "   3  from  bottom,  for  Carbonic  Acid,  read  Carbonic  Oxide. 
"    31,    Caption  Specific  heat  should  precede  the  paragraph. 


m- 


INTRODUCTION. 


Material  substances  are  endowed  with  two  kinds  of  properties,  physical  and 
chemical ;  and  the  study  of  the  phenomena  occasioned  by  them  has  given  rise 
to  two  corresponding  branches  of  knowledge,  Natural  Philosophy  and  Chemistry. 

The  physical  properties  are  either  general  or  secondary.  The  general  are  so 
called  because  they  are  common  to  all  bodies :  the  secondary,  from  being  observ- 
able in  some  substances  ody.  Among  the  general  may  be  enumerated  extension, 
impenetrability,  mobility,  extreme  divisibility,  gravitation,  porosity,  and  inde- 
structibility. 

Extension  is  the  property  of  occupying  a  certain  portion  of  space  :  a  substance 
is  said  to  be  extended  when  it  possesses  length,  breadth,  and  thickness.  By 
impenetrability  is  meant,  that  no  two  portions  of  matter  can  occupy  the  same 
space  at  the  same  moment.  Every  thing  that  possesses  extension  and  impene- 
trability is  matter. 

Matter,  though  susceptible  of  rest  and  motion^  has  no  inherent  power  either  of 
beginning  to  move  when  at  rest,  or  of  arresting  its  progress  when  in  motion.  Its 
indifference  to  either  state  has  been  expressed  by  the  term  vis  inertias,  as  if  it 
depended  on  some  peculiar  force  resident  in  matter,  whereas  it  arises  from 
matter  being  absolutely  passive,  and  thereby  subject  to  the  influence  of  every 
force  which  is  capable  of  acting  upon  it.* 

Matter  is  divisible  to  an  extreme  degee  of  minuteness.  A  grain  of  gold  may 
be  so  extended  by  hammering  that  it  will  cover  50  square  inches  of  surface,  and 
contain  two  millions  of  visible  points ;  and  the  gold  which  covers  the  silver 
wire,  used  in  making  gold  lace,  is  spread  over  a  surface  twelve  times  as  great. 
A  grain  of  iron,  dissolved  in  nitro-hydrochloric  acid,  and  mixed  with  3137  pints 
of  water,  will  be  diffused  through  the  whole  mass :  by  means  of  the  ferro-cya- 
nide  of  potassium,  which  strikes  an  uniform  blue  tint,  some  portion  of  iron 
may  be  detected  in  every  part  of  the  liquid.  The  grain  of  iron  is  hence  inferred 
to  have  been  divided  into  rather  more  than  24  millions  of  parts;  and  if  the 
dilution  were  carried  still  further,  the  diffusion  of  iron  through  the  whole  liquid 

*  All  the  facts  of  mechanical  and  chemical  science,  show  that  the  particles  and  masses 
of  matter  are  incessantly  acting  on  one  another,  and  it  is  to  these  actions,  referred  to  agents 
distinct  from  the  matter  itself,  that  the  term  Force  is  applied.  Hence,  as  in  the  text,  the 
physical  world  is  usually  conceived  to  be  made  up  of  matter  and  forces;  although,  accord- 
ing to  a  juster  metaphysics  it  may  be  regarded  as  consisting  of  matter  in  a  state  of  incessant 
mutual  action.    (R.) 


^ 


2  INTRODUCTIOxN. 

might  be  proved  by  concentrating  any  portion  of  it  by  evaporation,  and  detecting 
the  raetal  by  its  appropriate  tests. 

A  keen  controversy  existed  at  one  time  concerning  the  divisibility  of  matter, 
some  philosophers  affirming  it  to  be  infinitely  divisible,  while  others  maintained 
an  opposite  opinion.  Owing  to  the  imperfection  of  our  senses  the  question 
cannot  be  determined  by  direct  experiment,  because  matter  certainly  continues 
to  be  divisible  long  after  it  has  ceased  to  be  an  object  of  sense.  The  decision, 
if  effected  at  all,  can  only  be  accomplished  indirectly,  as  an  inference  from  other 
phenomena.  In  favour  of  the  former  view  it  was  urged,  on  mathematical 
grounds,  that  a  surface  admits  of  division  without  limit:  and  that  to  whatever 
degree  matter  is  divided,  it  may  still  be  conceived,  in  possessing  extension  and 
surface,  to  be  susceptible  of  still  further  division.  Plausible,  however,  as  this 
mode  of  reasoning  may  appear,  the  opposite  opinion  is  daily  becoming  more 
general.  It  is  now  commonly  believed  that  matter  consists  of  ultimate  particles 
or  molecules,  which  may  indeed  be  conceived  to  be  divisible,  but  which  by 
hypothesis  are  assumed  to  be  infinitely  hard  and  impenetrable,  and  on  that 
account  to  be  incapable  of  division.  These  ultimate  particles  have  received  the 
appellation  of  afows,  (from  the  privative  a  and  tsfxvtip  to  cut,)  as  expressive  of 
their  nature.  The  arguments  adduced  in  support  of  this  opinion  are  principally 
drawn  from  the  phenomena  of  chemistry,  and  from  the  relations  which  have 
been  observed  to  exist  between  the  composition  and  form  of  crystallized  bodies. 
These  subjects  will  be  considered  hereafter:  it  will  now  suffice  to  state,  in  order 
to  show  the  nature  of  the  argument,  that  the  supposed  existence  of  atoms 
accounts  for  numerous  facts,  which  cannot  be  satisfactorily  explained  on  any 
other  principle. 

All  bodies  descend  in  straight  lines  [perpendicular  to  the  curvature  of  the 
earth  at  the  place  of  their  descent,  and  therefore,  as  the  earth  is  nearly  spherical, 
in  directions  closely  tending  towards  its  centre,]  when  left  at  liberty  at  a  dis- 
tance from  its  surface.  The  power  which  produces  this  effect  is  termed  gravity, 
attraction  of  gravitation^  or  terrestrial  attraction  ,•  and  the  force  required  to  sepa- 
rate a  body  from  the  surface  of  the  earth,  or  prevent  it  from  descending  towards 
it,  is  called  its  weight.  Every  particle  of  matter  is  equally  affected  by  gravity; 
and  therefore  the  weight  of  any  body  will  be  proportionate  to  the  number  of 
ponderable  particles  which  it  contains. 

The  minute  particles  of  which  bodies  consist  are  disposed  in  such  a  manner 
as  to  leave  certain  intervals  or  spaces  between  them,  and  this  arrangement  is 
called  porosity.  These  interstices  may  sometimes  be  seen  by  the  naked  eye, 
and  frequently  by  the  aid  of  glasses;  but  were  they  wholly  invisible,  it  would 
still  be  certain  that  they  exist.  All  substances,  even  the  most  compact,  may  be 
diminished  in  bulk  either  by  mechanical  force  or  a  reduction  of  temperature. 
It  hence  follows  that  their  particles  must  touch  each  other  at  a  very  few  points 
only,  if  at  all ;  for  if  their  contact  were  so  perfect  as  to  leave  no  interstitial 
spaces,  then  would  it  be  impossible  to  diminish  the  dimensions  of  a  body, 
because  matter  is  incompressible  and  cannot  yield,. — When  therefore  a  body 
expands,  the  distance  between  its  particles  is  increased;  and,  conversely,  when 
it  contracts  or  diminishes  in  size,  its  particles  approach  each  other.* 

*  Contact  is  not  necessary  for  the  exertion  of  force  between  particles  or  masses, — and 
probably  all  actions  take  place  through  some  distance.  Physical  contact  is  nothing  more 
than  such  a  proximity  as  brings  into  play  powerful  corpuscular  repulsion.    (R.) 


INTRODUCTION.  *J 

By  indestruciihility  is  meant,  that,  according  to  the  present  laws  of  nature, 
matter  never  ceases  to  exist.  This  statement  seems  at  first  view  contrary  to 
fact.  Water  and  volatile  substances  are  dissipated  by  heat,  and  lost ;  coals  and 
wood  are  consumed  in  the  fire,  and  disappear.  But  in  these  and  all  similar 
phenomena  not  a  particle  of  matter  is  annihilated.  The  apparent  destruction  is 
owing  merely  to  a  change  of  form  or  composition ;  for  the  same  material  parti- 
cles, after  having  undergone  any  number  of  such  changes,  may  still  be  proved 
to  possess  the  characteristic  properties  of  matter. 

The  secondary  properties  of  matter  are  opacity,  transparency,  softness,  hard- 
ness, elasticity,  colour,  density,  solidity,  fluidity,  and  others  of  a  like  nature. 
Several  of  these  properties,  especially  those  last  specified,  depend  on  the  rela- 
tive intensity  of  two  opposite  forces — cohesion  and  repulsion.  It  is  inferred, 
from  the  divisibility  of  matter,  that  the  substance  of  solids  and  liquids  is  made 
up  of  an  infinity  of  minute  particles  adhering  together  so  as  to  constitute  larger 
masses ;  and  that  the  mutual  adhesion  of  these  particles  is  owing  to  a  power 
of  reciprocal  attraction.  This  force  is  called  cohesion,  cohesive  attraction,  or  the 
attraction  of  aggregation,  in  order  to  distinguish  it  from  terrestrial  attraction. 
Gravity  is  exerted  between  different  masses  of  matter,  as  well  as  between  their 
particles,  and  acts  at  sensible  and  frequently  ^t  very  great  distances ;  while 
cohesion  exerts  its  influence  only  at  insensible  and  infinitely  small  distances.  It 
enables  similar  molecules  to  cohere,  and  tends  to  keep  them  in  that  condition. 
It  is  best  exemplified  by  the  force  required  to  separate  a  hard  body,  such  as  iron 
or  marble,  into  smaller  fragments ;  or  by  the  weight  which  twine  or  metallic 
wire  will  support  without  breaking. 

The  tendency  of  cohesion  is  manifestly  to  bring  the  ultimate  particles  of 
bodies  into  immediate  contact ;  and  such  would  be  the  result  of  its  influence, 
were  it  not  counteracted  by  an  opposing  force,  a  principle  of  repulsion,  which 
prevents  their  approximation.  It  is  a  general  opinion  among  philosophers,  sup- 
ported by  very  strong  facts,  that  this  repulsion  is  owing  to  the  agency  of  heat, 
which  is  somehow  attached  to  the  elementary  molecules  of  matter,  causing  them 
to  repel  one  another.  Material  substances  are  therefore  subject  to  the  action  of 
two  contrary  and  antagonizing  forces,  one  tending  to  separate  their  particles,  the 
other  to  bring  them  into  closer  proximity.  The  form  of  bodies,  as  to  solidity 
and  fluidity,  is  determined  by  the  relative  intensity  of  these  powers.*  Cohesion 
predominates  in  solids,  in  consequence  of  which  their  particles  are  prevented 
from  moving  freely  on  one  another.  The  particles  of  a  fluid,  on  the  contrary, 
are  far  less  influenced  by  cohesion,  being  free  to  move  on  each  other  with  very 
slight  friction.  Fluids  are  of  two  kinds ;  elastic  fluids  or  aeriform  substances, 
and  inelastic  fluids  or  liquids.  Cohesion  seems  wholly  wanting  in  the  former; 
they  yield  readily  to  compression,  and  expand  when  the  pressure  is  removed; 
indeed,  the  space  they  occupy  is  chiefly  determined  by  the  force  which  com- 
presses them.  The  latter,  on  the  contrary,  do  not  yield  perceptibly  to  ordinary 
degrees  of  compression,  nor  does  an  appreciable  dilatation  ensue  from  the  removal 
of  pressure,  the  tendency  of  repulsion  being  in  them  counterbalanced  by 
cohesion. 

[This  view  of  the  constitution  of  bodies  is  founded  on  the  idea  that  heat  is  a 
distinct  substance,  capable  of  penetrating  betvireen  the  particles  of  ordinary  mat- 
ter, and  by  its  self-repellancy  changing  the  distances  of  these  particles,  and  thus 
modifying  the  properties  of  the  mass.     But  the  progress  of  investigation  seems 


4  INTRODUCTION. 

by  no  means  favourable  to  this  conception  of  the  nature  of  heat.  It  may,  we 
think,  be  more  philosophically  maintained  that  the  attractions  and  repulsions  of 
particles  are  exclusively  dependent  on  their  relation  as  to  distance,  as  originally 
suggested  by  Boscovitch,  and  that  the  various  states  of  matter,  as  solid,  liquid, 
or  gaseous,  are  the  direct  consequences  of  the  difference  in  the  distance  and 
arrangement  of  the  molecules.] 

Matter  is  subject  to  another  kind  of  attraction  different  from  those  yet  men- 
tioned, termed  chemical  attraction  or  affinity.  Like  cohesion  it  acts  only  at 
insensible  distances,  and  thus  differs  entirely  from  gravity.  It  is  distinguished 
from  cohesion  by  being  exerted  between  dissimilar  particles  only,  while  the 
attraction  of  cohesion  unites  similar  particles.  Thus,  a  piece  of  marble  is  an 
aggregate  of  smaller  portions  attached  to  each  other  by  cohesion,  and  the  parts 
so  attached  are  called  integrant  particles  ;  each  of  which,  however  minute,  being 
as  perfect  marble  as  the  mass  itself.  But  the  integrant  particles  consist  of  two 
substances,  lime  and  carbonic  acid,  which  are  different  from  one  another  as  well 
as  from  marble,  and  are  united  by  chemical  attraction.  They  are  the  component 
or  constituent  parts  of  marble.  The  integrant  particles  of  a  body  are  therefore 
aggregated  together  by  cohesion  ;  the  component  parts  are  united  by  affinity. 

The  chemical  properties  of  bodies  are  owing  to  affinity,  and  every  chemical 
phenomenon  is  produced  by  the  operation  of  this  principle.  Though  it  extends 
its  influence  over  all  substances,  yet  it  affects  them  in  very  different  degrees, 
and  is  subject  to  peculiar  modifications.  Of  three  bodies.  A,  B,  and  C,  it  is 
often  found  that  B  and  C  evince  no  affinity  for  one  another,  and  therefore  do  not 
combine  ;  that  A,  on  the  contrary,  has  an  affinity  for  B  and  C,  and  can  enter 
into  separate  combination  with  each  of  them;  but  that  A  has  a  greater  attraction 
for  C  than  for  B,  so  that  if  we  bring  C  in  contact  with  a  compound  of  A  and 
B,  A  will  quit  B  and  unite  by  preference  with  C.  The  union  of  two  substances 
is  called  combination ;  and  its  result  is  the  formation  of  a  new  body  endowed 
with  properties  peculiar  to  itself,  and  different  from  those  of  its  constituents. 
The  change  is  freqiffintly  attended  by  the  destruction  of  a  previously  existing 
compound,  and  in  that  case  decomposition  is  said  to  be  effected. 

The  operation  of  chemical  attraction,  as  thus  explained,  lays  open  a  wide  and 
interesting  field  of  inquiry.  One  may  study,  for  example,  the  affinity  existing 
between  different  substances;  an  attempt  may  be  made  to  discover  the  propor- 
tions in  which  they  unite ;  and  finally,  after  collecting  and  arranging  an  exten- 
sive series  of  insulated  facts,  general  conclusions  may  be  deduced  from  them. 
Hence  chemistry  may  be  defined  the  science,  the  object  of  which  is  to  examine 
the  relations  that  affinity  establishes  between  bodies,  ascertain  with  precision  the 
nature  and  constitution  of  the  compounds  it  produces,  and  determine  the  laws 
by  which  its  action  is  regulated. 

Material  substances  are  divided  by  the  chemist  into  simple  and  compound. 
He  regards  those  bodies  as  compound,  which  may  be  resolved  into  two  or  more 
kinds  of  ponderable  matter;  those  as  simple  or  elementary,  which  contain  but 
one,  [or  properly  speaking,  the  elementary  bodies  of  the  chemist  are  those  which 
have  as  yet  resisted  all  efforts  to  decompose  them.]  The  number  of  the  latter, 
which  have  been  clearly  ascertained,  amounts  only  to  fifty-four;  and  of  these, 
agreeably  to  our  present  knowledge,  all  the  bodies  in  the  earth  consist.  The 
list,  a  few  years  ago,  was  somewhat  different  from  what  it  is  at  present ;  for  the 
acquisition  of  improved  methods  of  analysis  has  enabled  chemists  to  demon- 


INTRODUCTION.  5 

strate  that  some  substances,  which  were  once  supposed  to  be  simple,  are  in 
reality  compound ;  and  it  is  probable  that  a  similar  fate  awaits  some  of  those 
which  are  at  present  regarded  as  simple. 

The  composition  of  a  body  may  be  determined  in  two  ways,  analytically  or 
synthetically.  By  analysis^  the  elements  of  a  compound  are  separated  from  one 
another,  as  when  water  is  resolved  by  the  agency  of  galvanism  into  oxygen  and 
hydrogen ;  by  synthesis,  they  are  made  to  combine,  as  when  oxygen  and  hydro- 
gen unite  by  the  electric  spark,  and  generate  a  portion  of  water.  Each  of  these 
kinds  of  proof  is  satisfactory;  but  when  they  are  conjoined — when  water  is 
resolved  into  its  elements,  and  then  reproduced  by  their  union — the  evidence  is 
in  the  highest  degree  conclusive. 

The  first  part  of  this  work  comprehends  an  account  of  the  nature  and  proper- 
ties of  Heat,  Light,  and  Electricity, — agents  so  diffusive  and  subtile,  that  the 
common  attributes  of  matter  cannot  be  perceived  in  them.  They  are  altogether 
destitute  of  weight ;  at  least,  if  they  possess  any,  it  cannot  fi  discovered  by 
our  most  delicate  balances,  and  hence  they  have  received  the  appellation  of 
Imponderables.  They  cannot  be  confined  and  exhibited  in  a  mass  like  ordinary 
bodies ;  they  can  be  collected  only  through  the  intervention  of  other  substances. 
Their  title  to  be  considered  material  is  therefore  questionable,  and  the  effects 
produced  by  them  have  accordingly  been  attributed  by  some  to  certain  motions 
or  affections  of  common  matter.  It  must  be  admitted,  however,  that  they  appear 
to  be  subject  to  the  same  powers  that  act  on  matter  in  general,  and  that  some  of 
the  laws  which  have  been  determined  concerning  them,  are  exactly  such  as 
might  have  been  anticipated  on  the  supposition  of  their  materiality.  It  hence 
follows,  that  we  need  only  regard  them  as  subtile  species  of  matter,  in  order  that 
the  phenomena  to  which  they  give  rise  may  be  explained  in  the  language,  and 
according  to  the  principles,  which  are  applied  to  material  substances  in  general ; 
and  I  shall  therefore  consider  them  as  such  in  my  subsequent  remarks. 

The  second  part  comprises  Inorganic  Chemistry.  It  includes  the  doctrine  of 
affinity,  and  the  laws  of  combination,  together  with  the  chemical  history  of  all 
the  elementary  principles  hitherto  discovered,  and  of  those  compound  bodies 
which  are  not  the  product  of  organization.  Elementary  bodies  are  divided  into 
the  non-metallic  and  metallic  ;  and  the  substances  contained  in  each  division  are 
treated  in  the  order  which,  it  is  conceived,  will  be  most  convenient  for  the  pur- 
poses of  teaching.  From  the  important  part  which  oxygen  plays  in  the  economy 
of  nature,  it  is  necessary  to  begin  with  the  description  of  that  principle ;  and 
from  the  tendency  it  has  to  unite  with  other  bodies,  as  well  as  the  importance  of 
the  compounds  it  forms  with  them,  it  will  be  useful,  in  studying  the  history  of 
each  elementary  body,  to  describe  the  combinations  into  which  it  enters  with 
oxygen  gas.  The  remaining  compounds  which  the  non-metallic  substances  form 
with  each  other  will  next  be  considered.  The  description  of  the  individual 
metals  will  be  accompanied  by  a  history  of  their  combinations,  first  with  the 
simple  non-metallic  bodies,  and  afterwards  with  each  other.  The  last  division 
of  this  part  will  comprise  a  history  of  the  salts. 

The  third  general  division  of  the  work  is  Organic  Chemistry,  a  subject  which 
will  be  conveniently  discussed  under  two  heads.  In  this,  derived  from  the  work 
of  Professor  Gregory,  the  several  topics  are  arranged  under  two  heads,  the  one 
comprehending  the  Chemistry  of  the  Compound  Radicals,  the  other  treating  of 
the  influence  of  Life  on  Chemical  Products. 

The  fourth  part  is  a  brief  outline  of  Analytical  Chemistry. 


ELEMENTS  OF  CHEMISTRY. 


PART    I. 

IMPONDERABLE  SUBSTANCES. 


SECTION  I. 

HEAT,  OR  CALORIC. 

The  term  Heat^  in  common  language,  has  two  meanings :  in  the  one  case,  it 
implies  the  sensation  experienced  on  touching  a  hot  body;  in  the  other,  it 
expresses  the  cause  of  that  sensation.  When  used  in  the  latter  sense,  it  is 
synonymous  with  the  word  Chloric  (from  Calor,  heat),  which  is  employed 
exclusively  to  signify  the  cause  or  agent  by  which  all  the  effects  of  heat  are 
produced. 

Heat,  on  the  supposition  of  its  being  material,  is  a  subtile  fluid,  the  particles 
of  which  repel  each  other,  and  are  attracted  by  all  other  substances.  It  is 
imponderable ;  that  is,  it  is  so  exceedingly  light,  that  a  body  undergoes  no 
appreciable  change  of  weight,  either  by  the  addition  or  abstraction  of  heat.  It 
is  present  in  all  bodies,  and  cannot  be  wholly  separated  from  them  ;  for  if  a  sub- 
stance, however  cold,  be  transferred  into  an  atmosphere  which  is  still  colder,  a 
thermometer  placed  in  the  body  will  indicate  the  escape  of  heat.  That  its  parti- 
cles repel  one  another,  is  proved  by  observing  that  it  flies  off  from  a  heated  body  ; 
and  that  it  is  attracted  by  other  substances,  is  inferred  from  the  tendency  it  has 
to  penetrate  their  particles,  and  to  be  retained  by  them. 

Heat  may  be  transfened  from  one  body  to  another.  Thus,  if  a  cup  of  mer- 
cury at  60°  be  plunged  into  hot  water,  heat  passes  rapidly  from  one  into  the 
other,  until  the  temperature  in  both  is  the  same ;  that  is,  till  a  thermometer 
placed  in  each  stands  at  the  same  height.  All  bodies  on  the  earth  are  constantly 
tending  to  attain  an  equality,  or  what  is  technically  called  an  equilibrium,  of 
temperature.  If,  for  example,  a  number  of  substances  of  different  temperature 
be  enclosed  in  an  apartment,  in  which  there  is  no  actual  source  of  heat,  they 
will  very  soon  acquire  an  equilibrium,  so  that  a  thermometer  will  stand  at  the 
same  point  in  all.  Our  varying  sensations  of  heat  and  cold  are  owing  to  a  like 
cause.  On  touching  a  hot  body,  heat  passes  from  it  into  the  hand,  and  excites 
the  feeling  of  warmth  ;  when  we  touch  a  cold  body,  heat  is  communicated  to  it 
from  the  hand,  and  thus  arises  the  sensation  of  cold. 


S  HEAT. 

Heat  is  communicated  in  three  ways,  by  direct  contact,  by  conduction,  and  by 
radiation.  By  direct  contact,  when  the  hot  body  touches  a  cold  one,  so  that  the 
heat  may  pass  directly  from  one  into  the  other,  as  when  it  enters  a  bar  of  iron 
put  into  a  fire,  or  the  hand  plunged  into  hot  water.  By  conduction,  as  when  the 
heat  is  observed  to  travel  from  pok't  to  point  of  the  iron  bar  towards  the  end 
remote  from  the  fire.  By  radiation,  when  the  heat  leaps  as  it  were  from  a  hot  to 
a  cold  body  through  an  appreciable  interval ;  as  when  a  red-hot  ball,  suspended 
in  the  vacuum  of  an  air-pump,  distributes  its  heat  to  surrounding  objects,  or 
when  we  are  warmed  by  standing  at  some  distance  before  a  fire.*  In  studying 
these  phenomena  we  must  regard  both  the  loss  of  heat  in  the  hot  body,  and  the 
gain  of  heat  in  the  cold  one.  The  mode  in  which  a  hot  body  cools  is,  firstly, 
by  giving  off  heat  from  its  surface  either  by  contact  or  radiation,  or  both  con- 
jointly;  and  secondly,  by  the  heat  in  its  interior  passing  from  particle  to  particle 
through  its  substance  to  its  surface.  The  heating  of  a  cold  body  is  effected, 
firstly,  by  heat  passing  into  its  surface  either  by  contact  or  radiation,  or  by  both 
conjointly ;  and,  secondly,  by  the  heat  at  its  surface  passing  from  particle  to 
particle  through  its  interior  portions.  Hence,  in  tracing  the  laws  which  regulate 
the  distribution  of  heat,  we  shall  successively  consider  the  communication  of 
heat  from  one  body  to  another  by  contact,  its  passage  from  particle  to  particle  of 
the  same  substance  or  the  conduction  of  heat,  and  its  transfer  from  a  sensible 
distance  or  radiation, 

COMMUNICATION  OF  HEAT  BY  CONTACT. 

The  principal  conditions  which  influence  the  communication  of  heat  from  one 
body  to  another  by  contact,  are  the  degree  of  contiguity,  and  the  conducting 
power  of  the  substances.  The  more  perfect  the  approximation,  the  more  rapid, 
cseteris  paribus,  is  the  transfer.  The  contact  of  two  solids,  or  of  a  solid  with  a 
gas,  is  in  general  of  a  less  perfect  kind,  and  at  fewer  points,  than  that  between 
a  solid  and  a  liquid  ;  and  hence,  so  far  as  contact  alone  is  concerned,  the  transfer 
is  more  rapid  in  the  latter- case  than  in  the  former.  It  is  still  more  rapid  when 
liquids  are  mixed  with  each  other,  or  gases  with  gases,  owing  to  the  intermix- 
ture of  their  particles.  When  bodies  touch  each  other  at  their  surfaces  only, 
the  question  becomes  one  of  conduction,  the  rapidity  of  transfer  depending  on 
the  velocity  with  which  heat  passes  through  the  substances  in  contact.  Thus, 
if  a  hot  mass  of  iron  and  another  of  marble,  of  equal  size,  form,  and  temper- 
ature, be  plunged  into  equal  quantities  of  cold  water,  the  iron  will  cool  faster 
than  the  marble,  because  heat  passes  more  rapidly  through  the  substance  of  the 
former  than  through  that  of  the  latter.  Were  two  pieces  of  hot  iron  similarly 
plunged,  one  into  mercury,  and  the  other  into  water,  the  piece  in  contact  with 
mercury  would  cool  most  rapidly,  because  that  metal  is  a  better  conductor  than 
water.  Were  the  experiment  made  by  immersing  the  iron  into  mercury,  and  the 
marble  into  water,  the  rapidity  of  cooling  in  the  former  would  very  much  exceed 
that  in  the  latter,  from  two  causes  ; — both  from  heat  passing  more  rapidly  through 
iron  than  through  marble,  and  from  its  being  conveyed  away  more  rapidly  by 
mercury  than  by  water.  The  same  principle  explains  the  unequal  sensation 
caused  by  bodies  of  equal  temperature.     Thus  the  hand  receives  a  more  vivid 

*  Strictly  speaking  the  transfer  of  heat  by  direct  contact  is  a  case  of  radiation,  in  which 
the  surfaces,  though  still  separated  by  an  interval,  are  at  an  insensible  distance.    (R.) 


HEAT.  9 

impression  of  warmth  by  touching  hot  iron  than  from  glass  of  the  same  tem- 
perature ;  because  the  quantity  of  heat  <vhich  in  a  given  time  can  be  brought 
from  the  interior  to  the  surface  of  the  hot  body,  so  as  to  pass  into  the  skin,  is 
much  greater  in  iron  than  in  glass.  In  like  manner,  cold  iron  feels  colder  than 
glass  of  the  same  temperature,  because  the  former  conveys  away  from  the  skin 
more  heat  in  a  given  time  than  the  glass. 

CONDUCTION  OF  HEAT. 

By  this  term  is  expressed  the  passage  of  heat  from  particle  to  particle  through 
the  substance  of  bodies.  Heat  is  said  to  be  conducted  by  them  or  to  pass  by 
conduction^  and  the  property  on  which  its  transmission  depends  is  termed  conduct- 
ing power. 

Heat  obviously  passes  through  bodies  with  different  degrees  of  velocity.  Some 
substances  oppose  very  little  impediment  to  its  passage,  while  it  is  transmitted 
slowly  by  others.  One  cannot  leave  one  end  of  a  rod  of  iron  for  some  time  in 
the  fire,  and  then  touch  its  other  extremity,  without  danger  of  being  burned, 
though  this  may  be  done  with  perfect  safety  with  a  rod  of  glass  or  of  wood. 
The  observation  of  these  and  similar  facts,  has  led  to  the  division  of  bodies  into 
conductors  and  non-conductors  of  heat.  The  former  division,  of  course,  includes 
those  bodies,  such  as  the  metals,  which  allow  heat  to  pass  freely  through  their 
substance ;  a»d  the  latter  comprises  those  which  do  not  give  an  easy  passage  t,o 
it,  such  as  stones,  glass,  wood,  and  charcoal. 

Some  experiftients  have  been  made  by  Despretz,  apparently  with  great  care, 
on  the  relative  conducting  power  of  the  metals  and  some  other  substances,  and 
the  results  are  contained  in  the  following  table.   (An.  de  Ch.  et  Ph.  xxxvi.  422.) 


Gold 

1000 

Tin     . 

303-9 

Silver 

973 

Lead            .        . 

179-6 

Copper 

898-2 

Marble 

23-6 

Platinum    . 

381 

Porcelain     . 

12-2 

Iron 

374-3 

Fine  clay    . 

11-4 

Zinc 

363 

[The  substances  used  in  these  experiments  were  square  prisms  of  equal  size, 
and  similarly  coated  with  a  black  varnish,  to  render  the  loss  of  heat  from  the 
surface  the  same  in  all.  At  equal  intervals  along  the  bars,  small  cavities  were 
formed,  in  which  oil  or  mercury  was  placed,  and  in  which  delicate  thermometers 
were  inserted  to  indicate  the  progress  of  temperature  from  point  to  point.  A 
lamp  applied  at  one  extremity  supplied  the  requisite  heat,  the  constancy  of  which 
was  ascertained  by  the  temperature  of  the  thermometer,  nearest  the  lamp, 
becoming  stationary  and  so  continuing  during  the  experiment.  The  heat  con- 
ducted along  the  bars  gradually  raising  the  temperature  of  the  several  thermome- 
ters, but  to  a  less  and  less  extent  according  as  they  were  more  distant  from  the 
heated  end,  would  thus  be  distributed  along  it  with  more  or  less  equality  accord- 
ing to  the  greater  or  less  conducting  power  of  the  material,  and  the  degree  in 
which  the  different  parts  of  its  surface  permitted  the  heat  to  escape  into  the 
surrounding  space.  When  the  heat  thus  escaping  from  the  surface  at  each  point 
became  equal,  in  virtue  of  the  high  temperature,  to  that  received  by  conduction, 
no  further  change  of  temperature  took  place.  The  thermometers  now  stationary 
presented;  when  compared  together,  in  each  bar  in  receding  from  the  heated  end, 

3 


10  HEAT. 

a  progressively  diminishing  excess  of  temperature  over  that  of  the  apartment. 
From  the  ratio  of  this  series,  as  noted  Tor  each  substance,  and  which  is  obviously 
dependent  upon  the  conducting  power,  the  numbers  of  the  above  table  were 
computed.  The  principle  of  this  mode  of  experiment  and  the  theory  by  which 
the  conducting  powers  may  be  calculated  are  due  to  Fourier.] 

An  ingenious  plan  was  adopted  by  Count  Rumford  (Phil.  Trans.  1792,)  for 
ascertaining  the  relative  conducting  power  of  the  diflferent  materials  employed 
for  clothing.  He  enveloped  a  thermometer  in  a  glass  cylinder  blown  into  a  ball 
at  its  extremity,  and  filled  the  interstices  with  the  substance  to  be  examined. 
Having  heated  the  apparatus  to  the  same  temperature  in  every  instance  by  im- 
mersion in  boiling  water,  he  transferred  it  into  melting  ice,  and  observed  care- 
fully the  number  of  seconds  which  elapsed  during  the  passage  of  the  thermometer 
through  135  degrees. 


Air  alone  required    . 

576" 

Raw  Silk  . 

1284" 

Lint 

1032" 

Beaver's  Fur     . 

1296" 

Cotton  Wool     . 

1046" 

Eider  Down 

1305" 

Sheep's  Wool   . 

1118" 

Hare's  Fur 

1315" 

The  general  practice  of  mankind  is  therefore  fully  justified  by  experiment. 
In  winter,  clothing  of  silk  or  wool  is  used  in  order  to  retain  the  animal  heat ; 
while  in  summer,  cotton  or  linen  stuffs  are  preferred,  that  the  heat  of  the  body 
may  the  more  easily  escape.  » 

[It  should,  however,  be  remembered  that  although,  in  Rumford's  experiment 
the  cooling  is  more  rapid  through  air  alone  than  through  lint  and  the  other 
fibrous  materials,  this  eflfect  is  due,  only,  in  part,  to  the  conducting  power  of 
the  air  and  far  more  to  the  mobility  of  its  particles,  as  explained  under  the  next 
head.  In  fact  air  is  a  much  worse  conductor  than  the  solid  matter  of  these 
fibres,  as  is  proved  by  the  readiness  with  which  they  conduct  heat,  when  com- 
pacted closely  together  by  pressure,  so  as  to  exclude  the  air  from  between  them. 
It  is  thus  that  a  blanket  or  cloth  with  a  long  nap  becomes  a  comparatively  good 
conductor,  when  flattened  down  by  strong  compression ;  and  it  is  because  of  the 
air  between  its  particles  that  snow  preserves  the  earth  beneath  it  from  a  very 
great  reduction  of  temperature.] 

The  conducting  power  of  solid  bodies  does  not  seem  to  be  related  to  any  of 
the  other  properties  of  matter ;  but  it  approaches  nearer  to  the  ratio  of  their 
densities  than  to  that  of  any  other  property. 

Convection  of  Heat  in  Liquids  and  Airs. — Liquids  may  be  said  in  one  sense 
to  have  the  power  of  conveying  heat  with  great  rapidity,  though  in  reality  they 
are  very  imperfect  conductors.  This  peculiarity  is  referable  to  the  mobility  which 
subsists  among  the  particles  of  all  fluids,  and  to  the  change  of  size  which  is 
invariably  produced  by  a  change  of  temperature.  When  any  particles  of  a  liquid 
are  heated  they  expand,  thereby  becoming  specifically  lighter  than  those  which 
have  not  received  an  increase  of  temperature ;  and  if  the  former  happen  to  be 
covered  by  a  stratum  of  the  latter,  these  from  their  greater  density  will  descend, 
while  the  warmer  and  lighter  particles  will  be  pressed  upwards.  If,  therefore, 
heat  enter  at  the  bottom  of  a  vessel  containing  a  liquid,  a  double  set  of  currents 
must  be  immediately  established,  the  one  of  hot  particles  rising  towards  the 
surface,  and  the  other  of  colder  particles  descending  to  the  bottom.  These  cur- 
rents take  place  with  such  rapidity,  that  if  a  thermometer  be  placed  at  the  bottom, 
and  another  at  the  top  of  a  long  jar,  the  fire  being  applied  below,  the  upper  one 


HEAT.  11 

will  begin  to  rise  almost  as  soon  as  the  lower.  [Similar  currents  are  still  more 
rapidly  produced  when  heat  is  applied  to  the  lower  part  of  a  mass  of  atmos- 
pheric air,  or  other  gaseous  matter.]  The  transport  of  hot  particles  by  this 
process  has  been  termed  the  convection  of  heat. 

But  if,  instead  of  heating  the  bottom  of  the  jar  of  liquid,  the  heat  enter  by 
the  upper  surface,  very  different  phenomena  will  be  observed.  The  intestine 
movements  cannot  then  be  formed,  because  the  heated  particles,  from  being 
lighter  than  those  below  them,  remain  constantly  at  the  top :  the  heat  can 
descend  through  the  fluid  only  by  transmission  from  particle  to  particle,  a  pro- 
cess which  takes  place  so  very  tardily,  as  to  have  induced  Count  Rumford  to 
deny  that  water  can  conduct  at  all.  In  this,  however,  he  was  mistaken ;  for  the 
opposite  opinion  has  been  successfully  supported  by  Hope,  Thomson,  and  the 
late  Dr.  Murray,  though  they  all  admit  that  water,  and  liquids  in  general,  mer- 
cury excepted,  possess  the  power  of  conducting  heat  in  a  very  slight  degree. 

[In  the  more  recent  experiments  of  Despretz,  the  conduction  of  heat  in  water 
was  proved  by  applying  a  constant  source  of  temperature  to  the  upper  surface 
of  a  prismatic  column  of  the  liquid,  contained  in  a  vessel  made  of  bad  conduct- 
ing materials.  The  progress  of  the  heat  downwards,  as  in  his  experiments  with 
solids,  was  marked  by  thermometers  placed  at  intervals  along  the  axis  of  the 
column,  their  stems  being  suffered  to  project  horizontally  through  one  of  the 
upright  sides  of  the  vessel.  When  they  had  attained  a  stationary  condition  he 
found  their  excesses  of  temperature,  over  the  temperature  of  the  ambient  air,  to 
follow  the  same  law  as  in  the  case  of  conduction  along  solid  bars.] 

It  is  extremely  difficult  to  estimate  the  conducting  power  of  aeriform  fluids. 
Their  particles  move  so  freely  on  each  other,  that  the  moment  a  particle  is 
dilated  by  heat,  it  is  pressed  upwards  with  great  velocity  by  the  descent  of  colder 
and  heavier  particles,  so  that  an  ascending  and  descending  current  is  instantly 
established.  Besides,  gaseous  bodies  allow  a  passage  through  them  by  radia- 
tion. Now  the  quantity  of  heat  which  passes  by  these  two  channels  is  so  much 
greater  than  that  which  is  conducted  from  particle  to  particle,  that  we  possess 
no  means  of  determining  their  proportion.  It  is  certain,  however,  that  the  con- 
ducting power  of  gaseous  fluids  is  exceedingly  imperfect,  probably  even  more 
so  than  that  of  liquids. 

RADIATION. 

"When  the  hand  is  placed  beneath  a  hot  body  suspended  in  the  air,  a  distinct 
sensation  of  warmth  is  perceived,  though  from  a  considerable  distance.  This 
effect  does  not  arise  from  the  heat  being  conveyed  by  means  of  a  hot  current ; 
since  all  the  heated  particles  have  an  uniform  tendency  to  rise.  Neither,  for 
reasons  above  assigned,  can  it  depend  upon  the  conducting  power  of  the  air ; 
because  aerial  substances  possess  that  power  in  a  very  low  degree,  while  the 
sensation  in  the  present  case  is  excited  almost  on  the  instant.  There  is  yet 
another  mode  by  which  heat  passes  from  one  body  to  another  ;  and  as  it  takes 
place  in  all  gases,  and  even  in  vacuo,  it  is  inferred  that  the  presence  of  a  medium 
is  not  necessary  to  its  passage.  This  mode  of  distribution  is  called  Radiation 
of -lleat,  and  the  heat  so  distributed  is  called  Radiant  or  Radiated  Heat.  It 
appears,  therefore,  that  a  heated  body  suspended  in  the  air  cools,  or  is  reduced 
to  an  equilibrium  with  surrounding  bodies,  in  three  ways ;  first,  by  the  conduct- 


12  HEAT. 

ing  power  of  the  air,  the  influence  of  which  is  very  trifling ;  secondly,  by  the 
mobility  of  the  air  in  contact  with  it ;  and  thirdly,  by  radiation. 

Imws  of  Distribution. — Heat  is  emitted  from  the  surface  of  a  hot  body  equally 
in  all  directions,  and  in  right  lines,  like  radii  drawn  from  the  centre  to  the  sur- 
face of  a  sphere  ;  so  that  a  thermometer  placed  at  the  same  distance  on  any  side 
would  stand  at  the  same  point,  if  the  effect  of  the  ascending  current  of  hot  air 
could  be  averted.  The  calorific  rays,  thus  distributed,  pass  freely  through  a 
vacuum  and  the  air,  without,  in  a  sensible  degree,  being  arrested  by  the  latter  or 
affecting  its  temperature.  When  they  fall  upon  the  surface  of  a  solid  or  liquid 
substance  they  may  be  disposed  of  in  three  different  ways: — 1,  they  may 
rebound  from  its  surface,  or  he  reflected ;  2,  they  may  be  received  into  its  sub- 
stance, or  be  absorbed,'  and,  3,  they  may  pass  directly  through  it,  or  be  trans- 
mitted. In  the  first  and  third  cases,  the  temperature  of  the  body  on  which  the 
rays  fall  is  altogether  unaffected  ;  whereas,  in  the  second,  it  is  increased.  The 
heating  influence  varies  with  the  distance  from  the  radiating  body.  The  rate  or 
iaw  of  decrease,  as  ascertained  by  careful  experiment,  and  as  may  be  inferred 
from  mathematical  considerations,  is,  that  the  intensity  of  heat,  like  that  of  light, 
diminishes  in  the  same  ratio  as  the  squares  of  the  distances  from  the  radiating 
point  increase.  Thus  the  thermometer  will  indicate  four  times  less  heat  at  two 
inches,  nine  times  less  at  three  inches,  and  sixteen  times  less  at  four  inches, 
than  it  did  when  it  was  only  one  inch  from  the  heated  substance. 

The  radiation  of  heat  by  hot  bodies  is  singularly  influenced  by  the  nature  and 
condition  of  their  surfaces,  a  circumstance  which  was  first  examined  by  Leslie, 
to  whose  Essay  on  Heat,  published  in  1804,  we  must  still  refer  for  [much]  of 
our  knowledge  on  this  subject.  It  follows  from  these  researches  that  velocity 
of  radiation  depends  more  on  the  surface  than  the  substance  of  a  radiating  body : 
that  the  most  imperfect  radiators  are  to  be  sought  among  those  bodies  which  are 
highly  smooth  and  bright,  such  as  polished  gold,  silver,  tin,  and  bras^;  but 
that  these  same  metals  radiate  freely  when  their  smoothness  and  polish  are 
destroyed,  as  by  scratching  their  surfaces  with  a  file,  or  covering  them  with 
whiting  or  lamp  black.  A  metallic  surface  seems  adverse  to  radiation  independ- 
ently of  its  smoothness,  since  a  highly  polished  piece  of  glass  radiates  far  better 
than  an  equally  polished  metallic  surface.  Scratching  a  surface  probably  favours 
radiation  by  multiplying  the  number  of  radiating  points. 

[The  results  of  Leslie's  experiments  are  included  in  the  following  table : 

RADIATING  POWERS. 


Lamp  Black  . 

100 

Tarnished  Lead     . 

45 

Writing  Paper 

98 

Clean  Lead    . 

19 

Seahng  Wax  . 

95 

Polished  Iron 

15 

Crown  Glass  . 

90 

Tin 

China  Ink       . 
Red  Lead       . 

88 
80 

^.f  ^         I  polished      . 

Silver        r  ^ 

12 

Plumbago 

75 

Copper 

[The  recent  researches  of  Melloni  have  disclosed  new  facts,  and  suggested 
other  views  respecting  the  conditions  of  surface  which  influence  radiation.  He 
found  that  where  in  polishing  the  surface  of  a  metal,  the  outer  layers  are  ren- 
dered denser  by  the  pressure  used,  the  radiating  power  is  impaired,  and  he 
ascribes  the  effect  of  roughening  a  metallic  surface,  in  Leslie's  experiments,  to 
the  partial  removal  or  breaking  up  of  this  denser  coating.     Cast  silver  which 


HEAT.  13 

is  less  dense  than  hammered  silver,  he  found,  with  the  same  polish  of  surface 
to  have  one  third  more  of  radiating  power.  By  scratching-  the  surface  of  the 
hammered  metal  its  power  of  radiation  was  augmented  in  the  ratio  of  10  to  18. 
Roughening  the  surface  of  the  cast  silver  produced  the  contrary  effect,  lowering 
the  radiating  power  in  the  ratio  of  13.7  to  13.4,  and  a  like  result  was  caused  by 
scratching  a  surface  of  polished  marble.  It  would  seem,  therefore,  that  the 
radiating  power  is  closely  connected  with  the  molecular  structure  of  the  outer 
layer  of  the  mass,  and  has  no  definite  relation  to  the  roughness  or  smoothness  of 
its  surface.    Taylor's  Scientif.  Mem.] 

[Until  recently  it  has  been  very  generally  maintained,  that  the  radiation  of  heat 
was  influenced  by  the  colour  of  the  radiant  surface,  dark  colours  being  supposed 
to  possess  this  property  in  the  highest  degree.  This  seems  to  have  been  hastily 
inferred  from  Leslie's  experiments,  which  placed  lamp  black  at  the  head  of  the 
list  of  the  bodies  used  ;  although  in  the  same  table  writing  paper  and  glass  have 
precedence  of  China  ink  and  plumbago.  The  same  inference  has  been  more 
lately  deduced  from  the  observations  of  Dr.  Starke,  as  referred  to  in  the  London 
edition  of  this  work.  These,  however,  were  not  so  conducted  as  to  isolate  the 
effect  of  radiation  from  other  cooling  influences,  and  could  not  lead  to  any  certain 
conclusion.  The  latest  experiments  on  the  subject,  those  of  Dr.  A.  D.  Bache, 
executed  with  the  greatest  care,  furnished  conclusive  proof  that  colour  alone  has 
no  influence  upon  the  radiating  power  of  a  surf 04^6."^ 

Reflection  of  Heat. — The  existence  of  a  reflecting  power  may  be  shown  by 
standing  at  the  side  of  a  fire  in  such  a  position  that  the  heat  cannot  reach  the 
face  directly,  and  then  placing  a  plate  of  tinned  iron  opposite  the  grate,  and  at 
such  an  inclination  as  permits  the  observer  to  see  in  it  the  reflection  of  the  fire : 
as  soon  as  it  is  brought  to  this  inclination,  a  distinct  impression  of  heat  will  be 
perceived  upon  the  face.  If  a  line  be  drawn  from  a  radiating  substance  to  the 
point  of  a  plane  surface  by  which  its  rays  are  reflected,  and  a  second  line  from 
that  point  to  the  spot  where  its  heating  power  is  exerted,  the  angles  which  these 
lines  form  with  a  line  perpendicular  to  the  reflecting  plane  are  called  the  angles 
of  incidence  and  reflection,  and  are  invariably  equal  to  each  other.  It  follows 
from  this  law,  that  when  a  heated  body  is  placed  in  the  focus  of  a  concave  para- 
bolic reflector,  the  diverging  rays  which  strike  upon  it  assume  a  parallel  direc- 
tion with  respect  lo  each  other  ;  and  that  when  these  parallel  rays  impinge  upon 
a  second  concave  reflector  standing  opposite  to  the  former,  they  are  made  to 
converge,  so  as  to  meet  together  in  its  focus.  Their  united  influence  is  thus 
brought  to  bear  upon  a  single  point. 

It  has  been  known  for  ages  that  the  heat  contained  in  the  solar  rays  admits  of 
being  reflected  by  mirrors,  and  a  like  property  has  long  since  been  recognized  in 
the  rays  emitted  by  red-hot  bodies ;  but  that  heat  emanates  in  invisible  rays, 
which  are  subject  to  the  same  laws  of  reflection  as  those  that  are  accompanied 
by  light,  is  a  modern  discovery,  noticed  indeed  by  Lambert,  but  first  decisively 
established  by  Saussure  and  Pictet,  of  Geneva.  They  first  proved  it  of  an  iron 
ball  heated  so  as  not  to  be  luminous  even  in  the  dark,  and  then  of  a  vessel  of 
boiling  water  (Pictet's  Essai  sur  le  Feu,  p.  65,  1790);  but  for  most  of  our 
knowledge  of  this  subject  we  must  again  refer  to  the  labours  of  Leslie.  He 
demonstrated  that  the  reflecting  power  depends  on  the  nature  and  condition  of 
surfaces,  and  that  those  qualities  which  are  adverse  to  radiation,  are  precisely 
such  as  promote  reflection.  Bright  smooth  metallic  surfaces,  as  polished  silver, 
brass,  or  tin,  which  are  retentive  of  their  own  heat,  are  little  prone  to  receive 


Polished  Gold      . 

.        76 

«        Silver    . 

.        62 

<♦        Brass    . 

62 

Brass,  without  polish  . 

.        62 

14  HEAT. 

heat  from  other  sources,  but  cause  such  rays  to  fly  oflf  from  them ;  while  those 
qualities  of  a  surface  which  facilitate  radiation  from  a  hot  body,  likewise  unfit  it 
for  reflecting  the  rays  which  fall  upon  it  from  surrounding  objects.  His  experi- 
ments, indeed,  justify  the  conclusion  that  the  faculty  of  radiation  is  inversely  as 
that  of  reflection. 

[By  a  reference  to  Melloni's  results,  before  mentioned,  it  will  be  apparent  that 
this  inverse  relation  of  radiation  and  reflection  is  far  from  iJeing  a  general  law. 
Thus  the  polished  surface  of  cast  silver,  used  in  his  experiments,  is  not  only  a 
better  reflector,  but  a  better  radiator  than  the  roughened  one.] 

[The  following  table,  derived  from  the  experiments  of  Buff,  exhibits  the  com- 
parative reflecting  power  of  various  surfaces.  Of  100  rays,  incident  at  an  angle 
of  60°  from  the  perpendicular,  there  are  reflected  by 

Polished  Brass,  varnished  .  41 
Looking  Glass  ...  20 
Glass  Plate,  blackened  on  back  12 
Metal  Plate,  blackened       .  6] 

Absorption  of  Heat. — Every  increase  of  temperature  arising  from  radiant  heat 
is  due  to  its  absorption  or  reception  into  the  body  on  which  it  falls.  If  a  pencil 
of  heat  impinge  on  the  surface  of  a  body,  through  which  no  portion  of  it  is 
directly  transmitted,  it  must  either  be  absorbed  or  reflected  :  those  rays  which 
are  reflected  cannot  be  absorbed ;  and  those  which  are  not  reflected  must  be 
absorbed.  The  number  of  absorbed  rays  is  supplemental  to  that  of  the  reflected 
rays.  It  hence  follows  that  as  the  reflecting  power  is  materially  influenced  by 
the  nature  of  surfaces,  the  absorptive  power  must  be  so  likewise.  Those  quali- 
ties of  a  surface  which  increase  reflection  are  to  the  same  extent  adverse  to 
absorption;  and  those  which  favour  absorption  are  proportionally  injurious  to 
reflection. 

[Conceiving  reflection  and  radiation  to  be  inversely  related,  as  wbs  erroneously 
inferred  from  Leslie's  experiments,  and  seeing  that  reflection  and  absorption  are 
also  thus  related,  it  has  been  usually  maintained,  as  the  general  law,  that  the 
conditions  favourable  to  radiation  and  absorption  are  the  same.  Accordingly  the 
experiments  of  Leslie,  on  this  point,  show  that  a  surface  coated  with  lamp  black 
has  great  power  to  absorb  the  heat  incident  upon  it,  while  one  of  polished  metal 
has  but  little,  and  that  the  latter  is  improved  in  this  respect  by  being  roughened. 
Yet  it  cannot  be  inferred,  as  a  general  fact,  that  absorption  and  radiation  follow 
the  same  law.  A  roughened  surface  of  marble,  or  of  cast  silver,  though,  no 
doubt,  possessed  of  higher  powers  of  absorption  than  when  smooth,  is,  as  we 
have  seen,  inferior  in  radiating  power.] 

[The  colour  of  surfaces,  though,  as  hereafter  to  be  shown,  highly  influential 
in  the  absorption  of  heat  associ?^ed  with  light,  as  in  the  rays  of  the  sun,  appears 
to  be  without  effect  upon  uncombined  or  dark  heat.  It  is  true  that  the  experi- 
ment of  Dr.  Starke,  (see  London  edition  of  this  work,)  have  been  adduced  to 
prove  the  reality  of  such  an  influence ;  but  they  are  open  to  serious  objections, 
some  of  which  have  been  already  hinted  at  under  the  head  of  radiation.] 

An  interesting  connection  has  been  traced  by  Nobili  and  Melloni  between  the 
absorbing  and  conducting  power  of  surfaces.  (An.  de  Ch.  et  Ph.  xlviii.  198.) 
In  their  experiments  variations  of  temperature  were  estimated  by  the  thermo-mul- 
tipliery  and  these  researches,  if  free  from  fallacy,  justify  the  inference  that  the 


HEAT.  15 

radiating  and  absorbing  powers  of  surfaces  for  simple  heat  are  in  the  inverse 
order  of  their  conducting  power. 

Transmission  of  Heat. — Radiant  heat  passes  with  perfect  freedom  through  a 
vacuum.  The  air  and  gaseous  substances  present  but  a  feeble  barrier  to  its  pro- 
gress ;  so  feeble,  indeed,  that  the  degree  of  impediment  which  they  occasion  has 
not  yet  been  appreciated.  Most  transparent  media  of  a  denser  kind,  on  the 
contrary,  such  as  the  diamond,  rock-crystal,  glass,  and  water,  even  in  thin  strata, 
interfere  greatly  with  its  passage.  This  last  remark,  however,  is  only  applicable 
to  simple  radiant  heat,  that  is,  to  heat  unassociated  with  light.  The  solar  rays 
pass  readily  through  glass,  both  heat  and  light  being  refracted  in  their  passage, 
as  is  shown  by  the  action  of  a  burning  glass  or  lens ;  and  though  mucli  of  the 
heat  emitted  by  the  flame  of  a  lamp  or  a  red-hot  ball  of  iron  is  arrested  by  glass, 
many  calorific  rays  are  directly  transmitted  along  with  the  light.  But  the  result 
is  diflferent  when  the  heated  body  is  not  luminous.  A  thin  screen  of  glass  inter- 
posed between  such  an  object  and  a  thermometer  certainly  intercepts  most  of  the 
rays  that  fall  upon  it ;  and  the  sole  question  which  can  be  raised  is,  whether  the 
small  effect  on  the  thermometer  is  caused  by  direct  transmission,  or  by  the  screen 
first  becoming  warm  by  absorbing  the  rays,  and  then  acting  by  its  radiation  on 
the  thermometer.  On  this  point  the  philosophic  world  was  long  much  divided ; 
but  the  question  has  been  at  length  finally  set  at  rest  by  the  masterly  researches 
of  Melloni,  made  with  the  therm o-multiplier  (An.  Ch.  et  Ph.  xlviii.  198,  liii.  5, 
Iv.  337,  Ix.  402).  He  has  proved  that  solids  and  liquids  differ  in  transmissibility 
to  the  rays  of  heat,  just  as  they  differ  in  their  action  on  light.  This  may  be 
expressed  by  the  terms  transcalent  and  intranscaleni  {trans  through,  caleo  I  heat), 
or  diathermanous  and  adiathermanous  (5ta  through,  de^fiaiva  I  heat),  correspond- 
ing to  the  adjectives  transparent  and  opaque  as  applied  to  light.  The  principal 
conclusions  flowing  from  his  researches  are  the  following : — 

1.  Though  transcalent  bodies  are  also  in  general  more  or  less  transparent,  the 
only  known  exceptions  being  opaque  black  glass  and  black  mica,  yet  the  trans- 
calency  and  transparency  of  a  substance  are  not  in  the  same  proportion. 

2.  Radiant  heat  falling  perpendicularly  on  laminae  of  transcalent  bodies  having 
parallel  surfaces  suffers  in  all  the  same  degree  of  reflection,  which  amounts  to 
39-lOOOths  of  the  incident  rays  on  entering,  and  37-1 000th s  on  leaving  the  lamina. 

3.  Transcalent  bodies  differ  in  the  degree  of  their  transcalency.  Rock-salt  is 
the  only  known  substance  which  is  perfectly  diathermanous :  heat  from  any 
source  falling  on  a  lamina  of  pure  rock-salt  with  parallel  faces,  is  not  at  all 
absorbed,  all  the  rays  which  are  not  reflected  being  directly  transmitted  ;  and  this 
is  true  whether  the  laminae  be  thick  or  thin.  The  result  is  different  with  other 
transcalent  bodies,  which  always  absorb  a  portion  of  the  incident  rays. 

[Of  100  rays  of  heat  from  the  same  source,  successively  incident  on  laminae 
of  a  number  of  substances  of  equal  thickness,  there  were  transmitted  through 

Rock-salt         ...        92  Gypsum  ....        20 

Calc  Spar         ...        62  Black  Glass  (opaque)     ,  .        16 

Plate  Glass      ...        40  Alum        .        .        .        .        12 

Of  100  rays  similarly  incident  on  strata  of  liquids,  there  were  transmitted 
through 

...        15 
11 


Chloride  of  Sulphur 

63 

Alcohol 

Bi  Sulphuret  of  Carbon   . 

63 

Water 

Ether       .... 

21 

IC  HEAT. 

Of  100  rays  incident  on  similar  laminae  of  differently  coloured  glasses,  there 
were  transmitted  through 

...       33 

26 


Violet  Glass     .    •  . 

.       53 

Blue 

Red          .        .        . 

47 

Green 

Yellow    . 

34 

It  thus  appears  that  while  rock-salt  is  the  most  transcalent  substance  known, 
clear  glass  arrests  more  than  one  half  of  the  incident  heat ;  and  what  is  still 
more  remarkable,  transparent  alum  and  limpid  water  intercept  more  of  the  rays 
than  the  deepest  coloured  and  even  opaque  glasses.] 

4.  In  glass  and  liquids  those  are  most  transcalent  which  have  the  greatest 
refractive  power  in  regard  to  light.  This  is  shown  in  No.  3,  where  only  11  per 
cent,  of  the  incident  heat  passed  through  water,  and  63  through  a  similar  stratum 
of  bisulphuret  of  carbon.  But  the  law  is  not  applicable  to  chrystalline  bodies  ; 
thus,  as  above,  92  per  cent,  of  the  incident  rays  find  their  way  through  rock-salt, 
and  12  per  cent,  through  a  similar  stratum  of  alum ;  while  their  refractive 
powers  for  light  are  nearly  the  same. 

5.  The  quantity  of  radiant  heat  transmissible  through  glass  varies  with  the 
temperature  of  the  source  from  which  the  rays  emanate. 

[Thus  using  as  sources  of  heat  the  lamp  of  Locatelli ;  a  red-hot  spiral  of 
platinum  wire  ;  a  blackened  copper  plate  at  734° ;  and  the  same  at  212°,  Mel- 
loni  found  the  heat  incident  from  these  various  sources  to  be  transmitted  in  the 
following  proportion,  assuming  100  as  the  measure  of  the  incident  rays : 

Substance.  Lamp.  Hot  Platinum.  Copper  734°.  Copper  212". 

Rock-salt  ...  92                   92                   92                   92 

Calc  Spar  ...  39                   28                     6                     0 

Plate  Glass  ...  39                   24                     6                     0 

Gypsum  ...  14                     5                     0                     0 

Alum  ...  9                     2                     0                     0 

It  thus  appears  that  rock-salt  is  not  only  the  most  transcalent  of  bodies,  but 
iar  equally  so  to  heat  of  all  temperatures. 

But  the  action  of  media  upon  radiant  heat  consists  not  merely  in  stopping  a 
certain  portion  of  it,  but  in  separating  it  into  two  portions,  hence  a  second  plate 
of  the  same  kind  of  substance  intercepts  but  little  of  the  heat  which  has  passed 
through  the  first.  Thus  if  1000  rays  be  incident  upon  a  plate  of  alum,  only  90 
will  pass  through,  but  if  these  90  be  allowed  to  fall  on  a  second  plate  of  the 
same  substance,  81,  or  9-lOths  of  the  whole  will  be  transmitted.] 

Hence  it  should  follow,  as  Melloni  has  proved,  that  comparatively  little  heat 
is  absorbed  by  multiplying  screens  of  the  same  material,  or  increasing  the  thick- 
ness of  one  screen:  it  is  the  first  screen,  or  the  side  of  one  screen,  next  the 
radiating  substance,  by  which  the  principal  absorption  of  heat  is  effected.  The 
quantity  of  heat  arrested  by  increasing  the  thickness  of  a  screen  decreases  in  a 
very  rapid  ratio.  These  facts  establish  between  heat  and  light  new  and  deeply 
interesting  relations,  which  will  be  referred  to  in  the  next  section. 

[It  further  appears  from  these  experiments  that  the  kind  of  heat  thus  trans- 
mitted differs  for  different  media,  and  hence  that  there  are  various  kinds  or  states 
of  radiant  heat,  just  as  there  are  various  kinds  or  states  of  light  as  manifested 
by  its  different  colours.  Calc  Spar,  for  example,  transmits  91  per  cent,  of  the 
heat  which  has  passed  through  alum  and  81  of  that  which  has  passed  through 


HEAT.  17 

gypsum,  while  the  green  tourmaline  transmits  only  1  in  the  100  coming  from 
the  alum,  and  no  less  than  30  which  have  passed  through  black  glass.] 

6.  Melloni  has  established  the  refrangibility  of  heat  by  diathermanous  media. 
Prior  observers  failed  of  obtaining  decisive  evidence  of  this  property,  in  conse- 
quence of  using  prisms  or  lenses  of  glass,  the  feeble  transcalency  of  which 
unfits  it  for  such  an  inquiry ;  but  with  a  prism  of  rock-salt  Melloni  easily  demon- 
strated the  general  principle,  and  proved  that  heat  from  different  sources,  like 
light  of  different  colours,  has  different  degrees  of  refrangibility. 

Polarization  and  double  Refraction  of  Heat. — These  properties  of  radiant  heat, 
which  Melloni  with  all  his  skill  vainly  attempted  to  demonstrate,  have  lately 
been  established  in  regard  to  heat,  both  from  luminous  and  non-luminous  sources, 
by  Forbes, — a  discovery  of  great  interest,  as  drawing  still  closer  the  relations 
of  heat  and  light,  and  for  which  he  has  received  the  well-merited  honour  of  the 
Keith  medal,  awarded  by  the  Royal  Society  of  Edinburgh.  Forbes  has  polarized 
heat  by  all  the  methods  which  polarize  light, — by  reflection,  refraction,  and  dou- 
ble refraction.  He  also  depolarized  heat;  and  as  this  occurs  only  as  a  conse- 
quence of  double  refraction,  he  thereby  proved  the  double  refraction  of  heat. 
The  instrument  used  by  Forbes  was  the  thermo-multiplier,  brought  to  such 
extreme  delicacy  that  it  is  supposed  sensible  to  l-1500ths  of  a  degree  of  Fah- 
renheit's thermometer.     (Phil.  Trans.  Ed.  1835.) 

Theory  of  Radiation, — The  tendency  which  all  bodies  evince  to  attain  an 
equality  of  temperature  by  means  of  radiation,  has  given  rise  to  two  ingenious 
theories,  suggested  respectively  by  Pictet  and  Prevost.  According  to  the 
former,  bodies  of  equal  temperature  do  not  radiate  at  all;  and  when  the  tem- 
perature is  unequal,  the  hotter  give  calorific  rays  to  the  colder  bodies  till  an 
equilibrium  is  established,  at  which  moment  the  radiation  ceases.  Prevost,  on 
the  contrary,  conceived  radiation  to  go  on  at  all  times,  and  from  all  substances, 
whether  their  temperature  were  the  same  or  different  from  that  of  surrounding 
objects  (Recherches  sur  la  Chaleur).  Consistently  with  this  view,  the  tempe- 
rature of  a  body  falls  whenever  it  radiates  more  heat  than  it  absorbs  ;  its  tem- 
perature is  stationary  when  the  quantities  emitted  and  received  are  equal ;  and 
it  grows  warm  when  the  absorption  exceeds  the  radiation.  Of  these  theories  the 
preference  is  very  generally  accorded  to  the  latter. 

Adopting,  then,  the  theory  of  Prevost,  it  will  be  useful  to  examine  a  few 
instances  of  its  application ; — and,  first,  in  regard  to  the  experiments  with  con- 
jugate mirrors.  If  a  metallic  ball  in  the  focus  of  one  mirror,  and  a  thermometer 
in  that  of  the  other,  be  of  the  same  temperature  as  the  surrounding  objects  (say 
at  60°),  the  thermometer  will  remain  stationary.  It  will  indeed  receive  rays 
from  the  ball ;  but  as  it  emits  an  equal  number  in  return,  its  temperature  will  be 
unchanged.  If  the  ball  is  above  60°  the  thermometer  will  rise,  because  it  then 
receives  a  greater  number  of  rays  than  it  emits.  If,  on  the  contrary,  the  ball  is 
below  60°,  the  thermometer,  being  the  warmer  of  the  two  bodies,  emits  more 
rays  than  it  receives,  and  its  temperature  will  fall. 

The  same  mode  of  reasoning  explains  an  interesting  experiment  originally 
performed  by  the  Florentine  Academicians,  and  since  carefully  repeated  by 
Pictet.  He  placed  a  piece  of  ice  instead  of  the  metallic  ball  in  the  focus  of  his 
mirror,  and  observed  that  the  thermometer  in  the  opposite  focus  immediately 
descended,  but  rose  again  as  soon  as  the  ice  was  removed.  On  replacing  the 
ice  in  the  focus,  the  thermometer  again  fell,  and  reascended  when  it  was  with- 

3 


18  HEAT. 

drawn.  It  was  supposed  by  some  philosophers  that  this  experiment  proved  the 
existence  of  fiigorific  rays,  endowed  with  the  property  of  communicating  cold- 
ness ;  whereas,  all  the  preceding  remarks  were  made  on  the  supposition  that 
cold  is  merely  a  negative  quality  arising  from  the  diminution  of  heat.  Nor  is 
the  foregoing  experiment  inconsistent  with  such  an  opinion  :  on  the  contrary,  it 
is  readily  accounted  for  by  the  theory  of  Prevost^  and  might  have  been  antici- 
pated by  its  application.  The  thermometer,  in  fact,  has  its  temperature  lowered, 
because  it  emits  more  rays  than  it  receives  ;  and  it  rises  when  the  ice  is  removed, 
because  it  then  receives  a  number  of  calorific  rays  radiated  by  the  warmer  sur- 
rounding objects,  which  were  intercepted  by  the  ice  while  it  was  in  the  focus. 

An  elegant  application  of  this  theory  was  made  by  Dr.  Wells,  to  account  for 
the  formation  of  Dew,  The  most  copious  deposit  of  dew  takes  place  when  the 
weather  is  clear  and  serene ;  and  the  substances  that  are  covered  with  it  are 
always  colder  than  the  contiguous  strata  of  air,  or  than  those  bodies  on  which 
dew  is  not  deposited.  In  fact,  dew  is  a  deposition  of  water  previously  existing 
in  the  air  as  vapour,  and  which  loses  its  gaseous  form  only  in  consequence  of 
being  chilled  by  contact  with  colder  bodies.  In  speculating,  therefore  about  the 
cause  of  this  phenomenon,  the  chief  object  is  to  discover  the  cause  of  the  reduc- 
tion of  temperature.  The  explanation  proposed  by  Wells,  in  his  excellent 
Treatise  on  Dew,  and  now  universally  adopted,  is  founded  on  the  theory  of 
Prevost.  If  it  be  admitted  that  bodies  radiate  at  all  times,  their  temperature 
can  remain  stationary  only  by  their  receiving  from  surrounding  objects  as  many 
rays  as  they  emit ;  and  should  a  substance  be  so  situated  that  its  own  radiation 
may  continue  uninterruptedly  without  an  equivalent  being  returned  to  it,  its  tem- 
perature must  necessarily  fall.  Such  is  believed  to  be  the  condition  of  the 
ground  in  a  calm  starlight  evening.  The  calorific  rays  which  are  then  emitted 
by  substances  on  the  surface  of  the  earth,  are  dispersed  through  free  space  and 
lost ;  nothing  is  present  in  the  atmosphere  to  exchange  rays  with  them,  and  their 
temperature  consequently  diminishes.  If,  on  the  contrary,  the  weather  be  cloudy, 
the  radiant  heat  proceeding  from  the  earth  is  intercepted  by  the  clouds,  an  inter- 
change is  established,  and  the  ground  retains  nearly,  if  not  quite,  the  same  tem- 
perature as  the  adjacent  portions  of  air. 

All  the  facts  hitherto  observed  concerning  the  formation  of  dew,  tend  to  con- 
firm this  explanation.  Dew  is  deposited  sparingly  or  not  at  all  in  cloudy  weather ; 
all  circumstances  which  promote  free  radiation  are  favourable  to  its  deposition ; 
good  radiators  of  heat,  such  as  grass,  wood,  the  leaves  of  plants,  and  filamen- 
tous substances  in  general,  fall  in  temperature,  in  favourable  states  of  the 
weather,  to  an  extent  of  10,  12,  or  even  15  degrees  below  that  of  the  circumam- 
bient air;  and  while  these  are  drenched  with  dew,  pieces  of  polished  metal, 
smooth  stones,  and  other  imperfect  radiators,  are  barely  moistened,  and  are 
nearly  as  warm  as  the  air  in  their  vicinity. 

Cooling  of  Bodies. — Heated  bodies  cool  by  two  very  different  methods.  When 
a  hot  body  is  enveloped  in  solid  substances,  its  heat  is  withdrawn  solely  by 
communication,  and  the  velocity  of  cooling  depends  on  the  conducting  power. 
Cooling  is  effected  in  a  similar  manner  when  the  heated  body  is  immersed  in  a 
liquid  ;  but  the  velocity  of  cooling  then  depends  partly  on  the  conducting  power 
of  the  liquid,  and  partly  on  the  mobility  of  its  particles.  In  elastic  fluids  tl»6 
cooling  takes  place  both  by  communication  and  radiation ;  and  in  a  vacuum  it  is 
produced  solely  by  radiation. 


HEAT.  19 

The  term  velocity  of  cooling  above  employed,  signifies  the  number  of  degrees 
lost  by  a  hot  body  during  equal  intervals  of  time,  as  one  minute  or  one  second ; 
and  by  the  law  of  cooling  is  meant  the  relation  which  the  velocities  of  cooling 
bear  to  each  other.  The  first  attempt  to  fix  the  law  of  cooling  was  by  Newton. 
Observing  that  the  velocity  of  cooling  in  a  hot  body  diminishes  continually  as 
the  excess  of  its  temperature  declines,  he  conceived  that  the  heat  lost  during 
each  interval  of  time  was  a  constant  fraction  of  its  excess  of  heat  at  the  begin- 
ning of  that  interval,  and  he  inferred  as  a  general  law  of  cooling  that  while  the 
times  of  cooling  form  an  arithmetical  series,  the  velocities  of  cooling  are  in  a 
geometric  progression.  [But,  from  the  admirable  researches  of  Dulong  and 
Petit,  it  appears  that  this  law  is  only  approximately  true  when  the  excess  of  tem- 
perature of  the  hot  body  is  small,  and  quite  inapplicable  in  other  cases.  The 
following  is  the  law  of  cooling  in  vacuo  deduced  from  their  experiments. 
When  a  body  cools  in  vacuo,  the  surrounding  temperature  being  constant,  the 
velocity  of  cooling  for  excess  of  temperature,  in  arithmetical  progression,  in- 
creases as  the  terms  of  a'  geometrical  progression  diminished  by  a  certain 
quantity.] 

EFFECTS  OF  HEAT. 


The  phenomena  that  may  be  ascribed  to  this  agent,  and  which  may  therefore 
be  enumerated  as  its  effects,  are  numerous.  With  respect  to  animals,  it  is  the 
cause  of  the  feelings  of  cold,  agreeable  warmth,  and  burning,  according  to  its 
intensity.  It  excites  the  system  powerfully,  and  without  a  certain  degree  of  it 
tlie  vital  actions  entirely  cease.  Over  the  vegetable  world  its  influence  is  obvious 
to  every  eye.  By  its  stimulus  co-operating  with  air  and  moisture,  the  seed  bursts 
its  envelope  and  yields  a  new  plant,  the  buds  open,  the  leaves  expand,  and  the 
fruit  arrives  at  maturity.  With  the  declining  temperature  of  the  seasons  the 
circulation  of  the  sap  ceases,  and  the  plant  remains  torbid  till  it  is  again  excited 
by  the  stimulus  of  heat. 

The  dimensions  of  every  kind  of  matter  are  regulated  by  this  principle.  Its 
increase,  with  few  exceptions,  separates  the  particles  of  bodies  to  a  greater  dis- 
tance from  each  other,  producing  expansion,  so  that  the  same  quantity  of  matter 
is  thus  made  to  occupy  a  larger  space ;  and  the  diminution  of  heat  has  an  oppo- 
site effect. 

The  form  of  bodies  is  dependent  on  heat.  By  its  increase  solids  are  con- 
verted into  liquids,  and  liquids  are  dissipated  in  vapour;  by  its  decrease  vapours 
are  condensed  into  liquids,  and  these  become  solid.  If  matter  ceased  to  be  under 
the  influence  of  heat,  all  liquids,  vapours,  and  doubtless  even  gases,  would 
become  permanently  solid  ;  and  all  motion  on  the  surface  of  the  earth  would  be 
arrested. 

When  heat  is  accumulated  to  a  certain  extent  in  bodies,  they  shine  or  become 
incandescent.  On  this  important  property  depend  all  our  methods  of  artificial 
illumination. 

Heat  exerts  a  powerful  influence  over  chemical  phenomena.  There  is,  indeed, 
scarcely  any  chemical  action  which  is  not  in  some  degree  modified  by  this  prin- 
ciple ;  and  hence  a  knowledge  of  its  laws  is  indispensable  to  the  chemist.  By 
its  means  bodies  previously  separate  are  made  to  combine,  and  the  elements  of 


20  HEAT. 

compounds  are  disunited.  An  undue  proportion  of  it  is  destructive  to  all  organic 
and  many  mineral  compounds ;  and  it  is  essentially  concerned  in  combustion,  a 
process  so  necessary  to  the  wants  and  comforts  of  man. 

Of  the  various  effects  of  heat  above  enumerated,  several  will  be  discussed  in 
other  parts  of  the  work.  In  this  place  it  is  proposed  to  treat  only  of  its  influ- 
ence over  the  dimensions  and  form  of  bodies,  a  subject  which  will  be  conve- 
niently studied  under  the  three  heads  of  expansion,  liquefaction,  and  vaporization. 

EXPANSION. 

[Assuming  with  the  generality  of  chemists  that  heat  is  a  peculiar  species  of 
matter,  whose  particles  are  strongly  repulsive  of  one  another,  and  attractive  in 
various  degrees  of  the  particles  of  ponderable  bodies,  we  may  readily  conceive 
that  the  entrance  of  heat  into  a  mass  will  have  the  effect  of  removing  the  inte- 
grant molecules  to  greater  distances  from  each  other,  and  that  thus  the  body  will 
be  made  to  occupy  a  greater  space,  or  to  expand.] 

This  effect  of  heat  is  opposed  to  cohesion — that  force  which  tends  to  make 
the  particles  of  matter  approximate,  and  which  must  be  overcome  before  any 
expansion  can  ensue.  Heat,  therefore,  should  produce  the  greatest  expansion  in^ 
those  bodies  which  are  least  influenced  by  cohesion,  an  inference  fully  justified 
by  observation.  Thus  the  force  of  cohesion  is  greatest  in  solids,  less  in  liquids, 
and  least  of  all  in  aeriform  substances ;  while  the  expansion  of  solids  ig  trifling, 
that  of  liquids  much  more  considerable,  and  that  of  elastic  fluids  far  greater. 

It  may  be  laid  down  as  a' rule,  the  reason  of  which  will  now  be  obvious,  that 
all  bodies  are  expanded  by  heat,  and  that  the  expansions  of  the  same  body  in- 
creases with  the  quantity  of  heat  which  enters  it.  But  this  law  does  not  apply, 
unless  the  form  and  chemical  constitution  of  the  body  is  preserved.  For  if  a 
change  in  either  be  occasioned,  then  the  reverse  of  expansion  may  ensue ;  not, 
however,  as  the  direct  consequence  of  an  augmented  temperature,  but  as  the 
result  of  a  change  in  form  or  composition. 

To  prove  the  expansion  of  solids,  we  need  only  take  the  exact  dimensions  i^v 
length,  breadth,  and   thickness,  of  any  substance  when  cold,  and  measure  it 
again  while  strongly  heated,  when  it  will  be  found  to  have  increased  in  eveiy 
direction.     This  dilatation  from  heat  and  consequent  contraction  in  cooling  take 
place  with  a  force  which  appears  to  be  irresistible. 

Expansion  of  Solids. — The  expansion  of  solids  has  engaged  the  attention  of 
several  experimenters,  who  have  endeavoured  to  determine  the  exact  quantity  by 
which  different  substances  are  lengthened  by  a  given  increase  of  heat,  and 
whether  or  not  their  elongation  is  equable  at  different  temperatures.  Their 
expansion,  for  example,  from  the  freezing  point  of  water  to  122°,  is  equal  to 
what  takes  place  betwixt  122°  and  212°.  The  researches  of  Dulong  and  Petit 
(An.  de  C.  et  P.  vii.)  prove  that  solids  do  not  dilate  uniformly  at  high  tempe- 
ratures, but  expand  in  an  increasing  ratio ;  that  is,  the  higher  the  temperature 
beyond  212°,  the  greater  the  expansion  for  equal  additions  of  heat.  It  is  mani- 
fest, indeed,  from  their  experiments,  that  the  rate  of  expansion  is  an  increasing 
one  even  between  32  and  212 ;  but  the  differences  which  exist  within  this  small 
range  are  so  inconsiderable  as  to  escape  observation,  and  for  most  practical  pur- 
poses may  he  disregarded. 

The  subjoined  table  includes  the  most  interesting  results  of  Lavoisier  and 


HEAT. 


2f 


Laplace,  who  have  carefully  investigated  the  linear  expansion  of  solids.    (Biot, 
i.  158.) 


Names  of  Substances. 


Elongation  when  heated 
from  32°  to  212°. 


Glass  tube  without  lead,  a  mean  of  three  specimens           .            jtV?  °^  ^^*  length 

English  flint  glass       .             .             .             .             .             .            T2i5 

Copper 

55T 

Brass — mean  of  two  specimens 

B^^ 

Soft  iron  forged 

BT^ 

Iron  wire 

•          b|i 

Untempered  steel 

• 

"957 

Tempered  steel 

BUT 

Lead    .... 

1 
35T 

Tin  of  India    . 

515 

Tin  of  Falmouth 

4k 

Silver  .... 

sh 

Gold — ^mean  of  three  specimens 

gi^ 

Platinum,  determined  by  Borda 

t/^t 

Knowing  the  elongation  of  any  substance  for  a  given  number  of  degrees  of 
the  thermometer,  its  total  increase  in  bulk  may  in  general  be  calculated  by 
trebling  the  number  which  expresses  its  increase  in  length. 

[According  to  the  curious  observations  of  Mitscherlich,  crystalline  bodies,  of 
certain  forms,  are  differently  affected  by  heat  in  different  directions.  Thus  a 
rhomb  of  calcareous  spar,  while  expanded  in  the  direction  of  its  axis  of  double 
refraction,  or  the  line  joining  its  two  obtuse  summits,  is  contracted  in  all  direc- 
tions at  right  angles  to  this.  Hence  the  angles  of  the  crystal  are  changed  by 
heat,  the  obtuse  ones  diminishing  and  the  acute  ones  enlarging,  so  as  to  approach 
the  figure  more  nearly  to  the  form  of  a  cube.  M.  Fresnel  found  the  effect  on 
a  crystal  of  sulphate  of  lime  to  be  just  the  reverse  of  this,  the  expansion  occur- 
ring chiefly  at  right  angles  to  the  axis.  It  is  doubtless  owing  to  a  similar  cause 
that  glass  and  other  solids,  which  are  liable  to  various  degrees  of  crystalline 
arrangement  of  their  parts,  have  been  found,  when  examined  under  these  dif- 
ferent conditions,  to  possess  different  expansibilities.] 

Expansion  of  Liquids. — The  expansion  of  liquids  is  proved  by  putting  a  com- 
mon thermometer,  made  with  mercury  or  alcohol,  into  warm  water,  when  the 
dilatation  of  the  liquid  will  be  shown  by  its  ascent  in  the  stem.  The  experiment 
is  indeed  illustrative  of  two  other  facts.  It  proves,  first,  that  the  dilatation 
increases  with  the  temperature  ;  for  if  the  thermometer  be  plunged  into  several 
portions  of  water  heated  to  different  degrees,  the  ascent  will  be  greatest  in  the 
hottest  water,  and  least  in  the  coolest  portions.  It  demonstrates,  secondly,  that 
liquids  expand  more  than  solids.  The  glass  bulb  of  the  thermometer  is  itself 
expan(ied  by  the  hot  water,  and  therefore  is  enabled  to  contain  more  mercury 
than  before ;  but  the  mercury  being  dilated  to  a  much  greater  extent,  not  only 
occupies  the  additional  space  in  the  bulb,  but  likewise  rises  in  the  stem.  Its 
ascent  marks  the  difference  between  its  own  dilatation  and  that  of  the  glass,  and 
is  only  the  apparent,  not  the  actual,  expansion  of  the  liquid. 

Different  liquids  do  not  expand  to  the  same  degree  from  an  equal  increase  of 
temperature.  Alcohol  expands  much  more  than  water,  and  water  than  mercury. 
In  being  heated  from  32°  to  212° 


22  HEAT. 

Alcohol  is  increased  in  volume,  by   .  .  .  .  i 

Fixed  Oils        .......  J_ 

1  1 

Water  .  .  .  .  .  .  .  w„L, 

Mercury ^-|j 

From  the  frequency  with  which  mercury  is  employed  in  philosophical  experi- 
ments, it  is  important  to  know  the  exact  amount  of  its  expansion.  This  subject 
has  been  investigated  by  several  philosophers,  but  the  experiments  of  Lavoisier 
and  Laplace,  and  especially  of  Dulong  and  Petit,  from  the  extreme  care  with 
which  they  were  made,  are  entitled  to  the  greatest  confidence.  According  to  the 
former  the  actual  dilatation  of  mercury,  in  passing  from  the  freezing  to  the  boiling 
point  of  water,  amounts  to  ^41%  of  its  volume ;  but  the  result  obtained  by 
Dulong  and  Petit,  who  found  it  ^S^S^,  is  probably  still  nearer  the  truth.  Adopt- 
ing the  last  estimate,  this  metal  dilates,  for  every  degree  of  Fahrenheit's  ther- 
mometer, -Tf-ggji  of  the  bulk  which  is  occupied  at  the  temperature  of  32°.  The 
apparent  expansion  of  mercury  contained  in  glass  is  of  course  less  than  the 
absolute  expansion.  Between  the  limits  of  32°  and  212°,  Lavoisier  and  La- 
place estimate  the  apparent  expansion  at  ^.^^  and  Dulong  and  Petit  at  g|.g  of 
its  volume,  being  xyggj  for  each  degree  of  Fahrenheit's  thermometer. 

[The  most  expansible  of  liquids  are  those  which  have  been  produced  by  the 
condensation  of  certain  gases,  and  those  discovered  by  Sir  D.  Brewster  in  the 
minute  cavities  of  crystals  of  topaz  and  quartz.  Liquified  carbonic  acid  expands 
according  to  Thilorier,  at  the  rate  lyluth  0^  i's  volume,  for  each  degree  of  the 
thermometer ;  which  is  four  times  the  expansion  of  air  and  other  gases.  Accord- 
ing to  Dr.  Mitchell  its  dilatation  is  three  times  that  of  air.  The  liquids  are 
believed  to  be  even  more  expansible,  and  are  probably  in  part  composed  of 
liquified  gases.] 

All  experimenters  agree  that  liquids  expand  in  an  increasing  ratioj  or  that 
equal  increments  of  heat  cause  a  greater  dilatation  at  high  than  at  low  tempera- 
tures. Thus,  if  a  fluid  is  heated  from  32°  to  122°  it  will  not  expand  so  much 
as  it  would  do  in  being  heated  from  122°  to  212°,  though  an  equal  number  of 
degrees  is  added  in  both  cases.  In  mercury  the  first  expansion,  according  to 
Deluc,  is  to  the  second  as  14  to  15  ;  in  olive  oil  as  13*4  to  15  ;  in  alcohol  as 
10-9  to  15  ;  and  in  pure  water  as  4*7  to  15. 

[The  augmenting  expansion  of  mercury,  as  measured  by  Dulong  and  Petit  at 
successive  intervals  of  180°,  is  seen  in  the  following  table  : 

From  32»  to  212° ^-^\jj 

"    212«>to392o ^gi^g- 


"    392"  to  672° 


•55?U 


An  interesting  exception  to  this  law  of  an  increased  rate  of  expansion,  has 
been  found  by  Desprets  in  the  dilatation  of  fused  sulphur,  which  he  observed  to 
expand  in  a  diminishing  ratio  with  equal  successive  additions  of  temperature.] 

There  is  a  peculiarity  in  the  effect  of  heat  upon  the  bulk  of  some  fluids  ; 
namely,  that  at  a  certain  temperature  increase  of  heat  causes  them  to  contract, 
and  its  diminution  makes  them  expand.  This  singular  exception  to  the  general 
eff*ect  of  heat  is  only  observable  in  those  liquids  which  increase  in  bulk  in  pass- 
ing from  the  liquid  to  the  solid  state,  and  is  remarked  only  within  a  few  degrees 
of  temperature  above  their  point  of  congelation.  Water  is  a  noted  example  of 
it.    Ice  swims  upon  the  surface  of  water,  and4herefore  must  be  lighter  than  it ; 


A 


HEAT.  23 

a  convincing  proof  that  water  in  the  act  of  freezing  must  expand.  The  specific 
gravity  of  ice  is  nearly  0*92,  which  gives  the  volume  of  ice  to  that  of  water  as 
1  to  0*92  ;  that  is,  water  expands  by  about  1-1 1th  of  its  volume  in  passing  into 
ice. 

But  it  is  not  only  during  the  act  of  congelation  that  water  expands;  sir^c^  it 
begins  to  dilate  some  time  before  it  actually  freezes.  Dr.  Croune  noticed  this 
phenomenon  so  early  as  the  year  1683,  and  it  has  since  been  observed  by  various 
philosophers.  To  render  this  obvious,  fill  a  flask,  capable  of  holding  three  or 
four  ounces,  with  water  at  the  temperature  of  60°,  and  adapt  to  it  a  cork,  through 
which  passes  a  glass  tube  open  at  both  ends,  about  the  eighth  of  an  inch  wide, 
and  ten  inches  long.  After  having  filled  the  flask,  insert  the  cork  and  tube,  and 
pour  a  little  water  into  the  latter  till  the  liquid  rises  to  the  middle  of  it.  On 
immersing  the  flask  into  a  mixture  of  pounded  ice  and  salt,  the  water  at  first 
contracts,  and  therefore  descends  in  the  tube ;  but  soon  after  an  opposite  move- 
ment ensues,  indicating  dilatation,  though  the  water  witiiin  the  flask  is  at  the 
same  time  yielding  heat  to  the  freezing  mixture  in  which  it  is  immersed. 

To  the  inference  deduced  from  this  experiment  it  was  objected,  that  the  ascent 
of  the  water  in  the  tube  is  not  referable  to  expansion  in  the  liquid,  but  to  con- 
traction of  the  flask,  diminishing  its  capacity.  In  fact,  this  cause  does  operate, 
though  not  to  a  degree  suflicient  to  account  for  the  whole  effect;  and,  accord- 
ingly, it  has  been  proved  by  an  elegant  and  decisive  experiment  of  Dr.  Hope, 
that  water  does  really  expand  previous  to  congelation.  He  believes  the  greatest 
density  of  water  to  be  between  39-5°  40°  ;  that  is,  boiling  water  obeys  the  usual 
law  till  it  has  cooled  to  the  temperature  of  about  40°,  after  which  the  abstraction 
of  heat  produces  increase  instead  of  decrease  of  volume  (Phil.  Trans.  Ed.  v. 
379).  Hallstrom,  who  has  examined  this  point  with  much  care,  estimates  it 
at  39°. 

The  expansion  of  water  at  the  moment  of  freezing  is  attributed  to  a  new  and 
peculiar  arrangement  of  its  particles.  Ice  is  in  reality  crystallized  water,  and 
during  its  formation  the  particles  arrange  themselves  in  ranks  and  lines,  which 
cross  each  other  at  angles  of  60°  and  120°,  and  consequently  occupy  rhore  space 
than  when  liquid.  This  may  be  seen  by  examining  the  surface  of  water  while 
freezing  in  a  saucer. 

Water  is  not  the  only  liquid  which  expands  under  reduction  of  temperature, 
as  the  same  effect  has  been  observed  in  a  few  others  which  assume  a  highly 
crystalline  structure  on  becoming  solid  ; — fused  iron,  antimony,  zinc,  and  bis- 
muth, are  examples  of  it.  Mercury  is  a  remarkable  instance  of  the  reverse  ;  for 
when  it  freezes,  it  suffers  a  very  great  contraction. 

Expansion  of  Gases, — As  the  particles  of  air  and  aeriform  substances  are  not 
held  together  by  cohesion,  it  follows  that  increase  of  temperature  must  occasion 
a  considerable  dilatation  of  them  ;  and,  accordingly,  they  are  found  to  dilate  from 
equal  additions  of  heat  much  more  than  solids  or  (most)  liquids. 

This  subject  had  been  unsuccessfully  investigated  by  several  philosophers, 
who  failed  in  their  object  chiefly  because  they  neglected  the  precaution  of  drying 
the  gases  upon  which  they  operated. 

[The  general  laws  of  their  dilatation  were  detected  by  Dalton  and  Gay  Lussac 
nearly  at  the  same  time,  and  afterwards  still  more  fully  investigated  by  Dulong 
and  Petit. 

The  laws  thus  deduced  are  as  follows  : 

1st.  All  gases  dilate  equally  between  the  same  limits  of  temperature. 


94  HEAT. 

2d.    Each  gas  dilates  uniformly  by  equal  successive  additions  of  temperature. 

3d.  The  dilatation  of  any  one  gas  between  the  same  limits  of  temperature  is 
the  same,  whatever  be  the  degree  of  its  condensation,  provided  the  pressure  be 
maintained  uniform  during  the  expansion.  From  similar  experiments,  the  same 
phi^Mophers  were  led  to  infer  that  steam  and  other  vapours,  apart  from  the 
liquids  that  produce  them,  expand  in  a  ratio  sensibly  the  same  with  the  so  called 
permanent  gases. 

According  to  the  experiments  above  referred  to,  100  parts  of  air  or  other  gas- 
eous matter,  in  being  heated  from  32°  to  212°,  expand  to  137-5  parts.  The 
increase  from  180°  is  therefore  37*5  for  the  100  parts,  or  0-375  for  1  part.  This 
divided  by  180  (^jVif )»  gives  for  the  expansion  of  dry  air  for  each  degree  of 
Fahrenheit's  thermometer  :j|^th  ^^  ^^®  volume  of  the  air  at  32°.  Thus  if  a 
cubic  foot  of  air  at  32°  be  raised  one  degree,  its  volume  will  become  l4g^th  cubic 
feet. 

The  more  recent  and  elaborate  investigations  of  Rudberg,  Magnus  and  Reg- 
nault,  have  proved  the  expansibility  of  atmospheric  air  to  be  somewhat  less  than 
that  above  stated.  According  to  Rudberg  the  mean  expansion  of  dry  air  at  the 
common  pressure  for  each  degree  from  32°  to  212°  is  ^|^rd  of  its  volume  at 
32°  ;  according  to  Magnus  it  is  very  nearly  :j^x3t;  and  according  to  Regnault  a 
little  more  than  :f^xsf] 

This  point  being  established,  it  is  easy  to  ascertain  what  volume  any  given 
quantity  of  air  should  occupy  at  any  given  temperature.  Suppose  a  certain  por- 
tion of  air  to  occupy  20  measures  of  a  graduated  tube  at  32°,  it  may  be  desirable 
to  determine  what  would  be  its  bulk  at  42°.  For  every  degree  of  heat  it  has 
increased  by  4j^th  of  its  original  volume,  (assuming  for  simplicity  the  old  co- 
efficient of  expansion,)  and  therefore,  since  the  increase  amounts  to  ten  degrees, 
the  20  measures  will  have  dilated  by  ^^g^ths.  '^^e  expression  will  therefore  be 
20  -f  20  X  ^y^jj  ==  20-416.  The  volume  which  the  air  occupies  at  32°  is  a  neces- 
sary element  in  all  such  calculations.  Thus,  having  20'416  measures  of  air  at 
42°,  the  corresponding  bulk  for  52°  cannot  be  calculated  by  the  formula  20*416 
-f  20-416^^^;  the  real  expression  is  20-416  4-203^^,  because  the  increase  is 
only  ^j^^ths  0^  ^^®  space  occupied  at  32°,  which  is  20  measures.  A  similar 
remark  applies  to  the  formula  for  estimating  the  effect  of  heat  on  the  height  of 
the  barometer. 

[Hitherto  the  same  co-efficient  of  expansion  ^|^  has  been  considered  applica- 
ble to  all  gases,  and  even  to  steam  and  other  vapours,  and  this  would  obviously 
be  the  case  were  they  all  equally  expansible,  as  affirmed  in  the  first  of  the  above 
laws.  But  Magnus  and  Regnault  have  shown  that  there  are  slight  but  sensible 
differences  in  the  expansibility  of  these  bodies.  The  following  table  from  Reg- 
nault's  memoir,  shows  the  increase  of  volume  of  the  different  gases  when  heated 
from  32°  to  212°  under  ordinary  atmospheric  pressure. 


Air 

0.36650 

Nitrous  Oxide  . 

0.37195 

Hydrogen 

0.36706 

Cyanogen 

0.38767 

Carbonic  Oxide 

.        0.3668S 

Sulphurous  Acid 

0.3902S] 

Carbonic  Acid 

0.37099 

[The  second  law,  though  generally  assumed  as  true  for  all  parts  of  the  scale, 
was  only  tested  by  Gay  Lussac,  between  32°  and  212°.  This  was  done  by 
comparing  the  march  of  a  mercurial  with  that  of  an  air  thermometer,  exposed 
together  to  the  same  successive  temperatures  in  the  apparatus  before  described. 


HEAT.  25 

The  correspondence  between  the  instruments  was  found  to  be  very  exact.  Dulong 
extended  the  comparison  to  lower,  and  to  higher  temperatures,  and  inferre<J  that 
the  two  instruments  agree  in  their  indications  from  64*8  to  212°, — but  that 
above  the  latter  point  the  expansions  of  the  air  diminish  for  successively  equal 
increments  of  temperature,  measured  by  the  mercurial  thermometer.  Nearly  the 
same  results  have  been  deduced  by  Regnault,  excepting  that  he  found  the  point 
at  which  the  air  thermometer  fell  behind  the  mercurial  to  vary  in  different  instru- 
ments, owing  to  the  difference  of  expansion  of  different  kinds  of  glass.  In 
atmospheric  air  and  carbonic  acid,  he  found  the  expansion,  for  a  given  increase 
of  temperature,  to  be  greater  as  the  gas  is  more  condensed.  This  increase  of 
expansibility,  by  augmented  pressure,  was  observed  in  a  still  more  marked 
degree  with  cyanogen  and  sulphurous  acid  gases.  With  the  latter  the  dilatation 
under  1  atmosphere  of  pressure  was  0.3902,  and  under  l^U^  atmosphere,  was 
0.3980. 

These  experiments  would  seem  to  prove  that  the  increase  of  expansibility  as 
the  pressure  is  augmented,  is  most  rapid  in  the  cases  of  those  gases  which 
require  the  least  compression  for  their  liquefaction,  such  as  the  two  last  men- 
tioned. Hence  Regnault  inferred  the  probability  that  the  vapours,  which  are 
even  more  condensible  than  these  gases,  would  be  found  to  possess  expansibili- 
ties exceeding  by  a  still  greater  amount  that  of  atmospheric  air.  Hitherto,  how- 
ever, they  have  been  regarded  as  having  exactly  the  same  expansibility,  and 
hence  been  included  in  the  first  of  the  laws  above  announced. 

It  is  an  interesting  fact,  ascertained  in  these  experiments,  that  hydrogen  gas 
preserves  its  expansibility  0.34706,  unaltered  as  high  as  3|-  atmospheres,  the 
limit  to  which  he  carried  his  experiments  on  this  substance.] 


ON  THE  THERMOMETER. 

The  influence  of  heat  over  the  bulk  of  bodies  is  better  fitted  for  estimating  a 
change  in  the  quantity  of  that  agent  than  any  other  of  its  properties ;  for  sub- 
stances not  only  expand  more  and  more  as  the  temperature  increases,  but  in 
general  return  exactly  to  their  original  volume  when  the  heat  is  withdrawn. 
The  first  attempt  to  measure  the  intensity  of  heat  on  this  principle  was  made 
early  in  the  seventeenth  century,  and  the  honour  of  the  invention  is  by  some 
bestowed  on  Sanctorius,  by  others  on  Cornelius  Drebel,  and  by  others  on  the 
celebrated  Galileo.  The  material  used  by  Sanctorius  was  atmospheric  air.  There 
are,  however,  two  forcible  objections  to  the  general  employment  of  this  ther- 
mometer. In  the  first  place,  its  dilatations  and  contractions  are  so  great,  that  it 
is  inconvenient  to  measure  them  when  the  change  of  temperature  is  considera- 
ble ;  and,  secondly,  its  movements  are  influenced  by  pressure  as  well  as  by  heat, 
so  that  the  instrument  would  be  affected  by  variations  of  the  barometer,  though 
the  temperature  should  be  quite  stationary. 

For  the  reasons  just  stated,  the  common  air  thermometer  is  rarely  employed; 
but  a  modification  of  it,  described  in  1804  by  Leslie  in  his  Essay  on  Heat 
under  the  name  of  Differential  Thermometer.,  is  entirely  free  from  the  last  objec- 
tion, and  is  admirably  fitted  for  some  special  purposes.  This  instrument  was 
invented  a  century  and  a  half  ago  by  Sturmius,  Professor  of  Mathematics  at 
Altdorff,  who  has  left  a  description  and  sketch  of  it  in  his  Collegium  Curiosum, 
p.  64,  published  in  the  year  1676 ;  but  like  other  air  thermometers  it  had  fallen 


M 


HEAT. 


into  disuse,  till  it  was  again  brought  into  notice  by  Leslie.  As  now  made  it  con- 
sists 6f  two  thin  glass  balls  joined  together  by  a  tube,  bent  twice  at  a  right  ano-le, 
Oy^ — \  as  represented  in  the  annexed  figure.  Both  balls  con- 
l  i  tain  air,  but  the  greater  part  of  the  tube  is  filled  with 
""  sulphuric  acid  coloured  with  carmine.  It  is  obvious 
that  this  instrument  cannot  be  affected  by  any  change 
of  temperature  acting  equally  on  both  balls ;  for  as  long 
as  the  air  within  them  expands  or  contracts  to  the  same 
extent,  the  pressure  on  the  opposite  surfaces  of  the 
liquid,  and  consequently  its  position,  will  continue  un- 
changed. Hence  the  differential  thermometer  stands  at 
the  same  point,  however  different  may  be  the  tempera- 
ture of  the  medium.  But  the  slightest  difference  be- 
tween the  temperature  of  the  two  balls  will  instantly 
be  detected ;  for  the  elasticity  of  the  air  on  one  side 
being  then  greater  than  that  on  the  other,  the  liquid  will 
retreat  towards  the  ball  whose  temperature  is  lowest. 
B  '4J        Solid  substances  are  not  better  suited  to  the  construc- 

W  tion  of  a  thermometer  than  gases  ;  for  while  the  expan- 

^^^^^  sion  of  the  latter  is  too  great,  that  of  the  former  is  so 

^^^^^  small  that  it  cannot  be  measured  except  by  the  adapta- 

tion of  complicated  machinery.  Liquids  which  expand  more  than  the  one  and 
lees  than  the  other,  are  exempt  from  both  extremes ;  and,  consequently,  we  must 
search  among  them  for  a  material  with  which  to  construct  a  thermometer.  The 
principle  of  selection  is  plain.  A  material  is  required  whose  expansions  are 
uniform,  and  whose  boiling  and  freezing  points  are  very  remote  from  one  another. 
Mercury  fulfils  these  conditions  better  than  any  other  liquid.  No  fluid  can  sup- 
port a  greater  degree  of  heat  without  boiling  than  mercury ;  and  none,  except 
alcohol  and  ether,  can  endure  a  more  intense  cold  without  freezing.  It  has, 
besides,  the  additional  advantage  of  being  more  sensible  to  the  action  of  heat 
than  other  liquids,  while  its  dilatations  between  32°  and  212°  are  almost  per- 
fectly uniform.  Strictly  speaking,  the  same  quantity  of  heat  does  occasion  a 
greater  dilatation  at  high  than  at  low  temperatures,  so  that,  like  other  fluids,  it 
expands  in  an  increasing  ratio.  But  it  is  remarkable  that  this  ratio,  within  the 
limits  assigned,  is  exactly  the  same  as  that  of  glass  ;  and  therefore,  if  contained 
in  a  glass  tube,  the  increasing  expansion  of  the  vessel  compensates  for  that  of 
the  mercury. 

We  cannot  here  describe  in  detail  the  method  of  constructing  a  mercurial 
thermometer.  This  well  known  instrument  consists  of  a  tube  of  a  uniform 
small  bore,  having  a  ball  blown  at  one  end.  The  ball  and  part  of  the  tube  are 
filled  with  mercury,  the  air  is  expelled  by  boiling  the  mercury,  and  the  tube  is 
hermetically  sealed. 

In  order  to  graduate  the  thermometer,  two  fixed  points  are  required  :  these  are 
obtained  by  immersing  it  first  in  melting  ice,  marking  the  point  at  which  it 
stands;  and  secondly  in  boiling  water,  at  the  level  of  the  sea,  and  under  the 
usual  atmospheric  pressure,  the  point  at  which  it  stands  being  also  marked. 

The  distance  between  these  two  points  may  be  divided  into  any  number  of 
equal  parts  or  degrees.  Fahrenheit,  whose  scale  is  used  in  this  country,  divided 
it  into  180  degrees,  beginning  his  scale  at  a  point  32  of  these  degrees  below 
the  freezing  point  of  water,  which  is  the  lero-of  his  scale.     Celsius,  the  author 


HEAT. 


27 


of  the  centigrade  scale,  most  frequently  employed  on  the  Continent,  placed  his 
zero  at  the  freezing  point,  and  divided  the  distance  between  that  and  the  boiling 
point  into  100  degrees.  Reaumur  adopted  the  same  starting  point  or  zero,  but 
divided  the  same  distance  into  80  degrees  only.  Hence,  the  boiling  point  of 
water,  on  Fahrenheit's  scale,  is  212°,  on  the  centigrade  scale  100°,  and  on  that 
of  Reaumur  80°. 

It  is  easy  to  reduce  the  temperature  expressed  by  one  thermometer  to  that  of 
another,  by  knowing  the  relation  which  exists  between  their  degrees.  Thus, 
180  is  to  100  as  9  to  5,  and  to  80  as  9  to  4 ;  so  that  nine  degrees  of  Fahrenheit 
are  equal  to  five  of  the  centigrade,  and  four  of  Reaumur's  thermometer.  Fah- 
renheit's is  therefore  reduced  to  the  centigrade  scale  by  multiplying  by  five,  and 
dividing  by  nine  ;  or  to  that  of  Reaumur,  by  multiplying  by  four  instead  of  five, 
previously  subtracting  32°,  because  the  zero  of  Fahrenheit  is  32°  lower  than 
that  of  the  others.  The  same  process,  reversed,  enables  us  to  reduce  degrees  of 
the  other  scales  to  those  of  Fahrenheit. 

But,  to  save  the  trouble  of  such  reductions,  I  have  subjoined  a  table  which 
shows  the  degrees  on  the  centigrade  scale  and  that  of  Reaumur,  corresponding 
to  the  degrees  of  Fahrenheit's  thermometer. 


Fahr. 

Cent. 

Reaum.  j 

Fahr. 

Cent. 

Reaum. 

Fahr. 

Cent. 

Reaum. 

212 

100 

80 

113 

45 

36 

14 

-10 

-  8 

203 

95 

76 

104 

40 

32 

5 

-15 

-12 

194 

90 

72 

95 

35 

28 

4 

-20 

-16 

185 

85 

68 

86 

30 

24 

-13 

-25 

-20 

176 

80 

64 

77 

25 

20 

-22 

-30 

-24 

167 

75 

60 

68 

20 

16 

-31 

-35 

-28 

158 

70 

56 

69 

15 

12 

-40 

-40 

-32 

149 

65 

52 

50 

10 

8 

140 

60 

48 

41 

5 

4 

131 

55 

44 

32 

0 

0 

, 

122 

50 

40 

23 

-5 

-4 

f 


The  mercurial  thermometer  may  be  made  to  indicate  temperatures  which  exceed 
212°,  or  fall  below  zero,  by  continuing  the  degrees  above  and  below  those  points. 
But  as  mercury  freezes  at  39  degrees  below  zero,  it  cannot  indicate  temperatures 
below  that  point;  and  indeed  the  only  liquid  which  has  been  used  for  such  pur- 
poses is  alcohol. 

[It  has  been  observed  that  mercurial  thermometers  slowly  change  their  zero, 
which  uniformly  becomes  higher  than  at  the  time  of  graduation.  This  pheno- 
menon due  to  a  diminished  capacity  of  the  ball,  has  been  ascribed  to  the  atmos- 
phere continually  pressing  on  its  exterior,  while  a  vacuum  exists  in  the  interior 
of  the  tube.  As  the  principal  contraction  ensues  after  the  tube  is  sealed,  it  is 
proper  to  allow  some  time  to  elapse  between  the  sealing  and  graduation  of  the 
instrument, 

M.  Person  has  found  that  the  elevation  of  the  zero  is  very  great  when  the 
instrument  has  been  exposed  to  a  high  temperature  for  some  hours.  Former 
observers  have  tried  the  effect  of  a  temperature  as  high  as  300°,  allowing  the 
instrument  to  commence  cooling  immediately  after  reaching  that  point ;  in  this 
case  the  rise  of  the  zero  was  only  about  1°  ;  but  M.  P.  operating  at  440°,  and 
maintaining  that  temperature  for  several  hours,  obtained  an  elevation  of  12°,  15° 


i. 


28  HEAT. 

and  even  17°.  After  such  a  prolonged  heating  he  thinks  that  farther  change  is 
probably  prevented,  especially  if  sudden  fluctuations  be  avoided.  It  is  obvious 
from  these  facts  that  no  mercurial  thermometer,  however  accurate  when  first 
constructed,  can  be  relied  upon  after  long  use,  and  especially  if  exposed  to 
extremes  of  temperature,  unless  its  scale  be  rectified  from  time  to  time  by  experi- 
ment.] 

Register  Thermometer, — For  some  purposes,  especially  in  making  meteorolo- 
gical observations,  it  is  a  very  desirable  object  to  ascertain  the  highest  and 

lowest  temperature  which  has 


I 


i»iiiniiiiiiiiiiiiniiiiiii_iiimii|iinmiiiiiiiyiiin] 


riTiiiJiiiiiiiiiiiiiiiiiitiiiiiiifffflTHTrHTTTTTTTTHTfi 


occurred  in  a  given  interval  of 
time,  during  the  absence  of 
the  observer.  The  instrument 
employed  with  this  intention 
is  called  a  Register  Thermo- 
meter, and  the  most  convenient 
kind  with  w^hich  I  am  acquainted,  is  tjiat  described  in  the  Philosophical  Trans- 
actions of  Edinburgh,  iii.  245,  by  Dr.  John  Rutherford.  The  thermometer  for 
ascertaining  the  most  intense  cold  is  made  with  alcohol,  and  the  bulb  is  bent  at 
a  right  angle  to  the  stem,  so  that  the  latter  may  conveniently  be  placed  in  a 
horizontal  position.  In  the  spirit  is  immersed  a  cylindrical  piece  of  black 
enamel,  a,  of  such  size  as  to  move  freely  within  the  tube.  In  order  to  make  an 
observation,  the  enamel  should  be  brought  down  to  the  surface  of  the  spirit,  an 
object  easily  effected  by  slight  percussion  while  the  bulb  is  inclined  upwards. 
When  the  thermometer  sinks  by  exposure  to  cold,  the  enamel  likewise  retreats 
towards  the  bulb,  owing  to  its  adhesion  to  the  spirit ;  but,  on  expanding,  the 
spirit  passes  directly  beyond  the  enamel,  leaving  it  at  the  extreme  point  to 
which  it  had  been  conveyed  by  the  previous  contraction. 

For  registering  the  highest  temperature,  a  common  mercurial  thermometer  of 
the  same  form  as  the  preceding  is  employed,  having  a  small  cylindrical  piece 
of  black  enamel  ft,  at  the  surface  of  the  mercury.  When  the  mercury  expands, 
the  enamel  is  pushed  forward ;  and  as  the  stem  of  the  thermometer  is  placed 
horizontally,  it  does  not  recede  when  the  mercury  contracts,  but  remains  at  the 
spot  to  which  it  had  been  conveyed  by  the  previous  dilatation.  The  enamel  i» 
easily  restored  to  the  surface  of  the  mercury  by  slight  percussion  while  the  bulb 
is  inclined  downwards  ;  but  this  should  be  performed  with  care,  lest  the  enamel, 
in  falling  abruptly,  should  interrupt  the  continuity  of  the  mercurial  column,  and 
interfere  with  the  indications  of  the  instrument. 

Pyrometers. — The  instruments  for  measuring  intense  degrees  of  heat  are 
called  pyrometers,  and  must  be  formed  either  of  solid  or  gaseous  substances. 
The  former  alone  have  been  hitherto  employed,  though  the  latter,  from  the 
greater  uniformity  with  which  they  expand,  are  better  calculated  for  the  purpose. 
The  action, of  most  pyrometers  depends  on  the  elongation  of  a  metallic  bar  by 
heat;  and  the  difficulty  in  their  construction  consists  in  finding  an  infusible 
metal  of  uniform  expansibility,  and  in  measuring  the  degree  of  expansion  with 
exactness.  The  best  of  these  is  Daniell's  pyrometer,  which,  with  a  little 
practice,  may  be  used  with  facility,  and  appears  susceptible  of  very  great  pre- 
cision. 

['*  It  consists  of  two  parts,  which  may  be  distinguished  as  the  register  and 
the  scale.    The  register  is  a  solid  bar  of  blackrlead  earthenware,  highly  baked. 


% 


HEAT.  29 

In  this  a  hole  is  drilled,  into  which  a  bar  of  any  metal,  six  inches  long-,  may  be 
dropped,  and  which  will  then  rest  upon  its  solid  end.  A  cylindrical  piece  of 
porcelain,  called  the  index,  is  then  placed  upon  the  top  of  the  bar,  and  confined 
in  its  place  by  a  ring  or  strap  of  platinum  passing  round  the  top  of  the  register, 
which  is  partly  cut  away  at  the  top,  and  tightened  by  a  wedge  of  porcelain. 
When  such  an  arrangement  is  exposed  to  a  high  temperature,  it  is  obvious  that 
the  expansion  of  the  metallic  bar  will  force  the  index  forward  to  the  amount  of 
the  excess  of  its  expansion  over  that  of  the  black-lead,  and  that,  when  again 
cooled,  it  will  be  left  at  the  point  of  greatest  elongation.  What  is  now  required, 
is  the  measurement  of  the  distance  which  the  index  has  been  thrust  forward 
from  its  first  position ;  and  this,  though  in  any  case  but  small,  may  be  effected 
with  great  precision  by  means  of  the  scale.] 

["This  is  independent  of  the  register,  and  consists  of  two  rules  of  brass, 
accurately  joined  together  at  a  right  angle  by  their  edges,  and  fitting  square  upon 
two  sides  of  the  black-lead  bar.  At  one  end  of  this  double  rule  a  small  plate 
of  brass  projects  at  a  right  angle,  which  may  be  brought  down  upon  the  shoulder 
of  the  register,  formed  by  the  notch  cut  away  for  the  reception  of  the  index.  A 
moveable  arm  is  attached  upon  this  frame,  turning  at  its  fixed  extremity  upon  a 
centre,  and  at  its  other,  carrying  an  arc  of  a  circle,  whose  radius  is  exactly  five 
inches,  accurately  divided  into  degrees  and  thirds  of  a  degree.  Upon  this  arm, 
at  the  centre  of  the  circle,  another  lighter  arm  is  made  to  turn,  one  end  of 
which  carries  a  nonius  with  it,  which  moves  upon  the  face  of  the  arc,  and  sub- 
divides the  former  graduation  into  minutes  of  a  degree ;  the  other  end  crosses 
the  centre,  and  terminates  in  an  obtuse  steel  point,  turned  inwards  at  a  right 
angle.] 

["  When  an  observation  is  to  be  made,  a  bar  of  platinum,  or  malleable  iron, 
is  placed  in  the  cavity  of  the  register,  the  index  is  to  be  pressed  down  upon  it, 
and  firmly  fixed  in  its  place  by  the  platinum  strap  and  porcelain  wedge.  The» 
scale  is  then  to  be  applied  by  carefully  adjusting  the  brass  rule  to  the  sides  of 
the  register,  and  fixing  it  by  pressing  the  cross  piece  upon  the  shoulder,  and 
placing  the  moveable  arm,  so  that  the  steel  point  of  the  radius  may  drop  into  a 
small  cavity  made  for  its  reception,  and  coinciding  with  the  axis  of  the  metallic 
bar.  The  minute  of  the  degree  must  then  be  noted,  which  the  nonius  indicates 
upon  the  arc.  A  similar  observation  must  be  made  after  the  register  has  been 
exposed  to  the  increased  temperature  which  it  is  designed  to  measure,  and 
again  cooled,  and  it  will  be  found  that  the  nonius  has  been  moved  forward 
a  certain  number  of  degrees  or  minutes.  The  scale  of  this  pyrometer  is 
readily  connected  with  that  of  the  thermometer  by  immersing  the  register  in 
boiling  mercury,  whose  temperature  is  as  constant  as  that  of  boiling  water,  and 
has  been  accurately  determined  by  the  thermometer.  The  amount  of  expan- 
sion for  a  known  number  of  degrees  is  thus  determined,  and  the  value  of  all 
other  expansions  may  be  considered  as  proportional.] 

["  The  melting  point  of  cast  iron  has  been  thus  ascertained  to  be  2786°,  and 
the  highest  temperature  of  a  good  wind  furnace  about  3300°  ;  points  which  were 
estimated  by  Mr.  Wedgwood  at  20577°  and  32277°  respectively.] 

["In  the  accompanying  figures,  1,  represents  the  register;  a  is  the  bar  of 
black-lead  ;  a  a'  the  cavity  for  the  reception  of  the  metal  bar ;  c  c'  is  the  index, 
or  cylindrical  piece  of  porcelain ;  d  the  platinum  band,  with  its  wedge,  e. 

S,  is  the  scale  by  which  the  expansion  is  measured ;  //'  is  the  greater  rule 


ito 


HEAT. 


upon  which  the  smaller,  gj  is  fixed  square.  The  projecting  arm,  h,  is  also  fitted 
square  to  the  ledge,  under  the  platinum  band,  d.  d  is  the  arm  which  carries  the 
graduatecl  arc  of  the  circle  fixed  to  the  rule,  //',  and  moveable  upon  the  centre, 


t.  c  is  the  lighter  bar,  fixed  to  the  first,  and  moving  upon  the  centre,  k.  h  is 
the  nonius  at  one  of  its  extremities,  and  m  the  steel  point  at  the  other."]  (Dan- 
iell's  Introd.  to  Chem.     Phil.) 

The  pyrometer  of  Wedgewood  acts  on  a  different  principle,  being  founded  on 
the  property  which  clay,  a  compound  of  alumnous  earth  and  water,  possesses 
of  gradually  losing  its  water  when  exposed  to  an  increasing  temperature,  and  of 
contracting  as  the  water  is  dissipated.  This  instrument,  however,  is  no  longer 
employed  by  scientific  men,  because  its  indications  cannot  be  relied  on.  Every 
observation  requires  a  separate  piece  of  clay,  and  the  observer  is  never  sure  that 
the  contraction  of  the  second  piece,  from  the  same  heat,  will  be  exactly  similar 
to  that  of  the  first ;  especially  as  it  is  difficult  to  procure  specimens  of  the  earth, 
the  composition  of  which  is  in  every  respect  the  same. 

The  subjoined  table  includes  some  of  the  most  interesting  points  in  the  scale 
of  temperature  which  have  been  determined.    (Bridges'  Graham.) 

— 148°    Fahr.    Greatest  artificial  cold.    Thilorier.* 
— 135         "       Solid  compound  of  alcohol  and  carbonic  acid  melts. 
— 91  "       Greatest  artificial  cold  measured  by  Walker. 

*  [ — 146  Mitchell,  at  which  temperature  alcohol  of  .789,  "assumed  the  appearance  of 
melted  wax — and  sulphuric  ether  is  not  in  the  slightest  degree  altered."     R.  B.] 


HEAT.  31; 

— 58°  Fahr.  Temperature  of  planetary  space.     Fourier. 

— 60  "  Greatest  natural  cold  observed  by  Ross. 

— 56  "  *  Greatest  natural  cold  observed  by  Parry. 

— 47  "  Sulphuric  ether  congeals. 

— 39  "  Melting  point  of  solid  mercury. 

— 7  "  A  mixture  of  equal  parts  of  alcohol  and  water  freezes. 

-j-7  "  A  mixture  of  one  part  of  alcohol  and  three  parts  of  water  freezes. 

-f-20  "  Strong  wine  freezes. 

-f-32  "  Ice  melts. 

-j-60  "  Medium  temperature  of  the  surface  of  the  globe. 

-)-52  "  Mean  temperature  of  England. 

-f9S  "  Heat  of  the  human  blood. 

-j-160  "  Wood-spirit  boils. 

-f-173  "  Alcohol  boils. 

-f212  »  Water  boils. 

-{-442  "  Tin  melts. 

-f6l2  "  Lead  melts. 

-f662  "  Mercury  boils. 

-f-980  "  Red  heat.    Daniell. 

-j-1141  "  Heat  of  a  common  fire.    Do. 

-j-1869  »  Brass  melts.    Do. 

-f-lS73  "  Silver  melts.    Do. 

-j-2786  "  Cast  iron  melts.     Do. 

Though  the  thermometer  is  one  of  the  most  valuable  instruments  of  philo- 
sophical research,  it  must  be  confessed  that  the  sum  of  information  which  it 
conveys  is  very  small.  It  does  indeed  point  out  a  difference  in  the  temperature 
of  two  or  more  substances  with  great  nicety ;  but  it  does  not  indicate  how  much 
heat  any  body  contains.  The  thermometer  gives  the  same  kind  of  information 
which  may  be  discovered,  though  less  accurately,  by  the  feelings ;  it  recognizes 
in  bodies  that  state  alone  which  affects  the  senses  with  an  impression  of  heat  ot 
cold, — the  condition  expressed  by  the  word  temperature.  All  we  learn  by  this 
instrument  is,  whether  the. temperature  of  one  body  is  greater  or  less  than  that 
of  another;  and  if  there  is  a  difference,  it  is  expressed  numerically,  namely,  by 
the  degrees  of  the  thermometer.  But  it  must  be  remembered  that  these  degrees 
are  parts  of  an  arbitrary  scale,  selected  for  convenience,  without  any  reference 
whatever  to  the  actual  quantity  of  heat  present  in  bodies. 

SPECIFIC  HEAT. 

A  little  reflection  will  evince  Ihe  propriety  of  these  remarks.  If  two  glasses 
of  unequal  size  be  filled  with  water  just  taken  from  the  same  spring,  the  ther- 
mometer will  stand  in  both  at  the  same  height,  though  their  quantities  of  heat 
are  certainly  unequal.  This  observation  naturally  suggests  the  inquiry,  whether 
different  kinds  of  substances,  whose  temperatures  as  estimated  by  the  thermo- 
meter are  the  same,  contain  equal  quantities  of  heat, — if,  for  example,  a  pound 
of  iron  contains  as  much  heat  as  a  pound  of  water  or  mercury.  The  foregoing 
remark  shows  that  equality  in  temperature  is  not  necessarily  connected  with 
equality  in  quantity  of  heat;  and  the  inference  has  been  amply  confirmed  by 
experiment.  If  equal  quantities  of  water  are  mixed  together,  one  portion  being 
at  100°  and  the  other  at  50°,  the  temperature  of  the  mixture  will  be  the  arith- 


32  HEAT. 

metical  mean  or  75^;  that  is,  the  25  degrees  lost  by  the  warai  water  will  exactly 
suffice  to  heat  the  cold  water  by  the  same  number  of  degrees.  It  is  hence 
inferred,  that  equal  weights  or  measures  of  water  of  the  same  temperature  con- 
tain equal  quantities  of  heat ;  and  the  same  is  found  to  be  true  of  other  bodies. 
But  if  equal  weights  or  equal  bulks  of  different  substances  are  employed,  the 
result  will  be  different.  Thus,  if  a  pint  of  mercury  at  100^  be  mixed  with  a 
a  pint  of  water  at  40*^,  the  mixture  will  have  a  temperature  of  60°,  so  that  the 
40  degrees  lost  by  the  former,  heated  the  latter  by  20  degrees  only ;  and  when, 
reversing  the  experiment,  the  water  is  at  100°  and  the  mercury  at  40°,  the  mix- 
ture will  be  at  80°,  the  20  degrees  lost  by  the  former  causing  a  rise  of  40  in  the 
latter.  The  fact  is  still  more  strikingly  displayed  by  substituting  equal  weights 
for  measures. 

[For  instance,  on  mixing  a  pound  of  mercury  at  162°,  with  a  pound  of  water 
at  100,  the  temperature  of  the  mixture  will  be  102°.    In  this  case 

The  mercury  by  losing    .....  60" 

raises  the  water  .....  2° 

Again  if  the  water  be  at  162°  and  the  mercury  at  100°,  the  temperature  of 
the  mixture  will  be  160°. 

Here  the  water  by  losing  ....  2" 

raises  the  mercury       .  .  .  .  .  60* 

So  likewise  if  water  at  100°  be  mixed  with  an  equal  weight  of  spermaceti  oil 
at  40°,  the  mixture  will  be  found  at  80°.    In  this  case 

The  water  by  losing        .....  20" 

raises  the  oil    .  .  .  ,  .  .  40" 

Again,  if  the  oil  be  100°  and  the  water  at  40°,  the  temperature  of  the  mixture 
will  be  only  60°. 

Here  the  oil  by  losing     .....  40" 

raises  the  water  .....  20"] 

It  appears  from  these  facts,  that  the  same  quantity  of  heat  imparts  twice  as 
high  a  temperature  to  mercury  as  to  an  equal  volume  of  water;  that  a  similar 
proportion  is  observed  with  respect  to  equal  weights  of  spermaceti  oil  and  water; 
and  that  the  heat  which  gives  2  degrees  to  water  will  raise  an  equal  weight  of 
mercury  by  60  degrees,  being  the  ratio  of  1  to  30.  Hence,  if  equal  quantities 
of  heat  be  added  to  equal  weights  of  water,  spermaceti  oil,  and  mercury,  their 
temperatures  in  relation  to  each  other  will  be  expressed  by  the  numbers  1,  2, 
and  30 ;  or,  what  amounts  to  the  same,  in  order  to  increase  the  temperature  of 
equal  weights  of  those  substances  to  the  same  extent,  the  water  will  require  30 
times  more  heat  than  the  mercury,  and  twice  as  much  as  the  oil.  The  peculiarity 
exemplified  by  these  substances,  and  which  it  would  be  easy  to  illustrate  by 
other  examples,  was  first  noticed  by  Black.  It  is  a  law  admitted  to  be  universal, 
and  may  be  thus  expressed :  that  equal  quantities  of  different  bodies  require 
unequal  quantities  of  heat  to  heat  them  equally.  This  difference  in  bodies  was 
expressed  by  Black  by  the  term  capacity  for  heat,  but  the  term  spccijk  heat  is  now 
generally  preferred. 

The  singular  fact  of  substances  of  equal  temperature  containing  unequal  quan- 
tities of  heat  naturally  excites  speculation  abdut  its  cause,  and  various  attempts 


HEAT.  '  33 

have  been  made  to  account  for  it.  The  explanation  deduced  from  the  views  of 
Black  is  the  following.  He  conceived  that  heat  exists  in  bodies  in  two  oppoeite 
states  :  in  one  it  is  supposed  to  be  in  chemical  combination,  exhibiting  none  of 
its  ordinary  characters,  and  remaining  as  it  were  concealed,  without  evincing  any 
signs  of  its  presence ;  in  the  other,  it  is  free  and  uncombined,  passing  readily 
from  one  substance  to  another,  affecting  the  senses  in  its  passage,  determining 
the  height  of  the  thermometer,  and,  in  a  word,  giving  rise  to  all  the  phenomena 
which  are  attributed  to  this  active  principle. 

Though  it  would  be  easy  to  start  objections  to  this  ingenious  conjecture,  it  has 
the  merit  of  explaining  phenomena  more  satisfactorily  than  any  view  that  has 
been  proposed  in  its  place.  It  is  entirely  consistent  with  analogy.  But  in  admit- 
ting the  plausibility  of  this  explanation,  it  is  proper  to  remember  that  it  is  at 
present  entirely  hypothetical ;  and  that  the  language  suggested  by  an  hypothesis 
should  not  be  unnecessarily  associated  with  the  phenomena  to  which  it  owes  its 
origin.  Accordingly,  the  word  sensible  is  better  than  free  heat,  and  insensible 
preferable  to  combined  or  latent  heat ;  for  by  such  terms  the  fact  is  equally  well 
expressed,  and  philosophical  propriety  strictly  preserved. 

It  is  of  importance  to  know  the  specific  heat  of  bodies.  The  most  convenient 
method  of  discovering  it,  is  by  mixing  different  substances  together  in  the  way 
just  described,  and  observing  the  relative  quantities  of  heat  requisite  for  heating 
them  by  the  same  number  of  degrees. 

This  method  was  first  suggested  by  Black,  and  was  afterwards  practised  to  a 
great  extent  by  Crawford  and  Irvine.*  But  the  same  knowledge  maybe  obtained 
by  reversing  the  process, — by  noting  the  relative  quantities  of  heat  which  bodies 
give  out  in  cooling ;  for  if  water  requires  30  times  more  heat  than  mercury  to 
raise  its  temperature  by  one  or  more  degrees,  it  must  also  lose  30  times  as  much 
in  cooling.  The  calorimeter  of  Lavoisier  and  Laplace  is  founded  on  this  prin- 
ciple. In  this  instrument  the  heat  given  out  by  a  hot  body  in  cooling  is  mea- 
sured by  the  quantity  of  ice  liquefied  by  it.  But  although  the  principle  is 
unexceptionable,  there  are  difficulties  in  the  application  of  it. which  render  the 
calorimeter  an  incorrect  instrument.  It  is,  therefore,  unnecessary  here  to 
describe  it  in  detail. 

[In  the  experiments  of  Dulong  and  Petit,  which  were  conducted  with  great 
exactness,  the  different  substances  were  inclosed  in  a  polished  silver  vessel,  in 
the  centre  of  which  was  the  bulb  of  a  thermometer  to  indicate  the  progress  of 
cooling.  The  silver  vessel  was  placed  in  a  large  reservoir,  exhausted  of  its  air. 
The  time  required  by  equal  weights  of  the  different  substances  to  cool,  through 
the  same  number  of  degrees  in  circumstances  exactly  similar  being  proportioned 
to  the  quantity  of  heat  which  they  gave  out,  indicated  the  comparative  specific 
heats.] 

[In  applying  the  method  of  mixtures  it  is  not  necessary  that  both  the  bodies 
should  be  liquid.  Thus,  if  a  pound  of  pure  copper  at  300°  be  immersed  in  a 
pound  of  water  at  50°,  it  will  yield  its  excess  of  heat  to  the  water,  and  in  time 
both  will  arrive  at  a  common  temperature,  72°.  The  228°  lost  by  the  copper 
having  raised  the  water  22°,  the  specific  heat  of  the  former  will  be  to  that  of 
the  latter  as  22  to  228  ;  that  is,  assuming  the  specific  heat  of  water  as  1*000, 
that  of  copper  will  be  T%^/g  =  0*096.  By  a  skilful  use  of  this  method  Regnault 
has  lately  ascertained  the  specific  heats  of  a  large  number  of  bodies,  elementary 

*  Crawford  on  Animal  Heat,  nnd  Irvine's  Chemical  Essays. 

5 


m 


HEAT. 


and  compound.  The  following  table  includes  some  of  the  more  important  results, 
obMined  by  him  and  other  experimenters  :] 


[Water 
Ether 
Alcohol 
Sulphuric  Acid 
Nitric  Acid 
Sulphur 
Carbon 
Mercury     . 
Arsenic 
Platinum    . 
Silver 
Zinc 

Tellurium  . 
Nickel 
Cobalt 


SPECIFIC  HEATS. 

:  1-000 

Iron   . 

0-520 

Copper 

0-660 

Lead 

0-333 

Gold 

0-442 

Antimony  . 

0-202 

Tin     . 

0-241 

Iodine 

0-033 

Phosphorus 

:  0-081 

Glass 

0-032 

Calomel 

:  0-057 

Common  Salt 

:  0-095 

Nitrate  of  Soda 

:  0-051 

Lime 

0-109 

Magnesia    . 

0-107 

=  0-114 
=  0095 
=  0-031 
=  0-032 
=  0-051 
=  0-056 
=  0-054 
=  0-188 
=  0-177 
=  0041 
=  0-225 
=  0-240 
=  0-20p 
=0-276] 


The  determination  of  the  specific  heat  of  gaseous  substances  is  a  problem  of 
importance,  and  has  occupied  the  attention  of  several  experimenters  of  great 
science  and  practical  skill ;  but  the  inquiry  is  beset  with  so  many  difficulties 
that,  in  spite  of  the  talent  which  has  been  devoted  to  it,  our  best  results  can  be 
viewed  as  approximations  only,  requiring  to  be  corrected  by  future  research. 
Crawford  first  investigated  this  subject,  but  his  results  are  admitted  to  have 
been  erroneous,  and  need  not  here  be  cited.  Lavoisier  and  Laplace,  by  means 
of  the  calorimeter,  obtained  more  accurate  results  ;  but  those  most  to  be  depended 
on  were  obtained  by  Delaroche  and  Berard  by  means  of  a  modification  of  the 
calorimeter,  in  which  they  observed,  not  how  much  ice  was  melted,  but  how  far 
water  was  heated  by  the  hot  body  during  its  cooling.  Their  experiments  were 
made  with  such  skill  as  to  inspire  great  confidence.  They  are  contained  in  the 
following  table ;  the  specific  heat  of  the  gases  being  referred  to  air  as  unity  in 
the  two  first  columns,  and  to  water  in  the  third. 


Under  equal 

Names  of  Substances. 

Volumes  and  con- 

Under equal  Weights. 

. 

stant  Pressure. 

Atmospheric  air    . 

1-0000 

1-0000      .        .        0-2669 

Hydrogen  gas 

0-9033 

12-3400 

32936 

Oxygen  gas   . 

0-9765 

0-8848 

0-2361 

Nitrogen  gas 

1-0000 

1-0318 

0-2754 

Nitrous  oxide  gas 

1-3503 

0-8878 

0-2369 

Olefiantgas  . 

1-5530 

1-5763 

0-4207 

Carbonic  oxide  gas 

1-0340 

1-0805 

0-2884 

Carbonic  Acid  gas 

1-2683 

0-8280 

0-2210 

Water  . 

. 

. 

1-0000 

Aqueous  vapour    . 

• 

• 

0-8470 

Although  objections  have  been  started  to  these  experiments,  and  other  methods 
of  ascertaining  the  specific  heats  of  gases  proposed  by  Haycraft,  Delarive  and 
Marcet,  and  others ;  yet  on  the  whole  we  may  conclude  that,  although  the  spe- 


HEAT.  '  3S 

cific  heats  of  the  gases  are  not  accurately  known,  the  numbers  of  Delaroche  and 
Berard  are  probably  the  best  approximations  hitherto  published. 

[Dulong  had  recourse  to  a  different  and  highly  ingenious  method.  This  con- 
sisted in  ascertaining  the  velocity  of  sound  in  each  gas,  as  measured  by  the 
note  the  same  organ  pipe  gave  in  each.  By  peculiar  mathematical  relations 
connecting  the  specific  heat  with  the  vibratory  motion  of  gases  he  calculated  the 
former.] 

,    The  circumstances  which  merit  particular  notice,  concerning  the  specific  heats 
of  bodies,  may  be  arranged  under  the  eight  following  heads  : — 

1.  Every  substance  has  a  specific  heat  peculiar  to  itself;  whence  it  follows, 
that  a  change  of  composition  will  be  attended  by  a  change  of  specific  heat. 

2.  The  specific  heat  of  a  body  varies  with  its  form.  A  solid  has  a  smaller 
specific  heat  than  the  same  substance  when  in  the  state  of  a  liquid  ;  the  specific 
heat  of  water,  for  instance,  being  *9  in  the  solid  state,  and  U)  in  the  liquid. 
Whether  the  same  weight  of  a  body  has  a  greater  specific  heat  in  the  solid  or 
liquid  form  than  in  that  of  vapour,  is  a  circumstance  not  yet  decided. 

[The  specific  heat  of  bodies  in  the  state  of  vapour  has  only  been  determined 
in  a  few  instances.  That  of  aqueous  vapour  is  0*847,  water  being  1*000.  Thus 
the  specific  heats  of  water,  in  its  three  states  of  solid,  liquid  and  vapour,  are 
•900,  1-000,  0-847.] 

3.  When  a  given  weight  of  any  gas  is  made  to  vary  in  density  and  volume 
while  its  elasticity  is  unchanged,  as  when  air  confined  in  a  tube  over  mercury 
is  heated  and  sufiered  to  expand  without  variation  of  pressure,  the  specific  heat 
is  believed  to  remain  constant. 

4.  Of  the  specific  heat  of  equal  volumes  of  the  same  gas  at  a  varying  density 
and  elasticity,  as  when  air  is  forced  into  a  bottle  with  different  degrees  of  force, 
nothing  certain  has  been  established, 

[By  an  ingenious  contrivance  D'dlton  ascertained  that  aboiit  50°  of  heat  are 
evolved  when  air  is  compressed  to  one  half  of  its  original  bull?,  and  that  on 
the  other  hand  50°  are  absorbed  by  a  corresponding  rarefaction.]  (Manchester 
Mem.,  vol.  v.) 

5.  The  specific  heats  of  equal  weights  of  the  same  gas  vary  as  the  density 
and  elasticity  vary.  Thus,  when  100  measures  of  air  expand  by  diminished 
pressure  to  200  measures,  its  specific  heat  is  increased  ;  and  when  the  same 
quantity  of  air  is  compressed  into  the  space  of  50  measures,  its  specific  heat  is 
diminished.  The  exact  rate  of  increase, is  unknown;  but,  according  to  Dela- 
roche and  Berard,  the  ratio  is  less  rapid  than  the  diminution  in  density  ;  'that  is, 
the  specific  heat  of  any  gas  being  1,  it  is  not  two,  but  between  one  and  two, 
when  its  volume  is  doubled. 

6.  The  specific  heats  of  solids  and  liquids  were  formerly  thought,  especially 
by  Crawford  and  Irvine,  to  be  constant  at  all  temperatures,  so  long  as  they  suf- 
fer no  change  of  form  or  composition.  Dalton,  however,  (Chemical  Philosophy, 
part  i.,  p.  50,)  endeavours  to  show  that  the  specific  heats  of  such  bodies  are 
greater  in  high  than  at  low  temperatures  ;  and  Petit  and  Dulong,  in  the  essay 
already  quoted,  have  proved  it  experimentally  with  respect  to  several  of  them. 

It  is  difficult  to  determine  whether  the  increased  specific  heat  observed  in 
solids  and  liquids  at  high  temperatures  is  owing  to  the  accumulation  of  heat 
within  them,  or  to  their  dilatation.  It  is  ascribed  in  general  to  the  latter,  and  I 
believe  coriectly  ;  because  the  expansion  and  contraction  of  gases  by  change  of 


» 


HEAT. 


pressure,  without  the  aid  of  heat,  is  attended  with  corresponding  changes  of 
specific  heat. 

7.  Change  of  specific  heat  always  occasions  a  change  of  temperature.  Increase 
in  the  former  is  attended  by  diminution  of  the  latter ;  and  decrease  in  the  former, 
by  increase  of  the  latter.  The  ej^lanation  of  these  facts  is  obvious.  In  the 
iirst  case,  a  quantity  of  heat  becomes  insensible,  which  was  previously  in  a  sen- 
sible state;  in  the  second,  heat  is  evolved,  which  was  previously  latent. 

8.  An  important  relation  between  the  specific  heats  of  some  elementary  sub- 
stances and  their  equivalents  was  discovered  by  Dulong  and  Petit,  namely,  that 
the  product  of  the  specific  heat  of  each  element  by  the  weight  of  its  atom  is  a 
constant  quantity.  This  relation,  if  general,  would  be  of  great  interest,  as  lead- 
ing directly  to  the  inference  that  the  atoms  of  elementary  substances  are  asso- 
ciated with  equal  quantities  of  heat,  and  enabling  chemists  to  calculate  either 
the  specific  heats  of  elements  from  their  equivalents,  or  conversely  their  equiva- 
lents from  their  specific  heats.  (An.  de  Ch.  et  Ph.  x.  403.)  The  relation  above 
alluded  to  was  exemplified  by  Dulong  and  Petit  by  a  table  similar  to  the  sub- 
joined. 


Lead 
Tin 
Zinc 

Tellurium 
Copper  . 
Nickel  . 
Iron 

Sulphur   . 
Platinum  . 
Bismuth  . 
Cobalt      . 
Arsenic   . 
Carbon     . 
Iodine 
Phosphorus 
Mercury  . 
Silver 
Gold 


Specific 
Heat. 

Relative  Weights 
of  Atoms. 

Product  of  the  Sp.  Heat 

of  each  element  by  the 

weight  of  its  atom. 

0-0293 

X 

103-  6 

=: 

3-0353 

0-0514 

X 

57-  9 

r= 

2-9760 

0-0927 

X 

32-  3 

= 

2-9942 

00912 

X 

32-  3 

= 

2-9457 

0'0949 

X 

31-  6 

=: 

2-9988 

0-1035 

X 

29-  5 

= 

3-0532 

0-1100 

X 

28 

= 

30800 

0-1880 

X 

16-  1 

= 

3-0268 

0-0355 

X 

98-  8 

= 

3-3098 

0-8288 

X 

71 

= 

2-0448 

01498 

X 

29-  5 

= 

4-4191 

0-OSl 

X 

37-  7 

= 

30537 

0-25 

X 

612 

= 

1-5300 

0-089 

X 

126-  3 

= 

11-2407  , 

0-385 

X 

15-  7 

= 

6-0445 

00330 

X 

202 

= 

6-6660 

0-0557 

X 

108 

== 

6-0156 

0-0298 

X 

199-  2 

= 

5-9361 

It  will  be  observed,  on  inspecting  the  last  column  of  the  table,  that  the  pro- 
duct of  the  specific  heat  into  the  equivalent  is  very  nearly  3  for  the  first  nine 
substances.  Platinum  deviates  visibly  from  the  law  ;  and  bismuth,  cobalt,  and 
iodine,  strikingly.  The  four  last  elements  would  nearly  coincide  with  the  law, 
were  their  respective  equivalents  estimated  at  half  the  numbers  given  in  the 
tables,  as  would  carbon  were  its  equivalent  doubled.  These  coincidences  are 
too  close  and  numerous  to  arise  from  chance,  and  justify  a  belief  in  the  law 
having  a  real  foundation  dependent  on  the  connection  between  heat  and  the 
elementary  particles  of  matter.  The  researches  of  Avogadro  and  Neumann 
give  additional  weight  to  this  opinion  by  tracing  the  same  law  in  many  com- 
pound bodies,  those  compounds  alone  being  compared  together  whose  atomic 


HEAT.  3f 

constitution  is  simHar.     (An.  de  Ch.  et  Ph.  lv.  80,  and  lvii.  113;  and  Peg. 
An.  XXIII.  1.) 

ON  LIQUEFACTION. 

All  bodies  are  solid,  liquid,  or  gaseous ;  and  the  form  th^-  assume  depends 
on  th*e  relative  intensity  of  cohesion  and  repulsion.  Should  the  repulsive  force 
be  comparatively  feeble,  the  particles  will  adhere  so  firmly  together,  that  they 
cannot  move  freely  upon  one  another,  thus  constituting  a  solid.  If  cohesion  is 
so  far  counteracted  by  repulsion,  that  the  particles  move  on  each  other  freely,  a 
liquid  is  formed.*  And  should  the  cohesive  attraction  be  entirely  overcome,  so 
that  the  particles  not  only  move  freely  on  each  other,  but  w^ould,  unless  restrained 
by  external  pressure,  separate  from  one  another  to  an  almost  indefinite  extent, 
an  aeriform  substance  will  be  produced. 

Now  the  property  of  repulsion  is  manifestly  owing  to  heat;  and  as  it  is  easy 
"within  certain  limits  to  increase  or  diminish  the  quantity  of  this  principle  in  any 
substance,  it  follows  that  the  form  of  bodies  may  be  made  to  vary  at  pleasure : 
that  is,  by  heat  sufficiently  intense  every  solid  may  be  converted  into  a  fluid, 
and  every  fluid  into  vapour.  This  inference  is  so  far  justified  by  experience, 
that  it  may  safely  be  considered  as  a  law.  The  converse  ought  also  to  be  true  ; 
and,  accordingly,  several  of  the  gases  have  already  been  condensed  into  liquids 
by  means  of  pressure,  and  liquids  have  been  solidified  by  cold.  The  temperature 
at  which  liquefaction  takes  place  is  called  the  melting  point,  or  point  of  fusion  ; 
and  that  at  which  liquids  solidify,  their  point  of  congelation.  Both  these  points 
are  different  for  different  substances,  but  uniformly  the  same,  under  similar  cir- 
cumstances, in  the  same  body. 

The  most  important  circumstance  relative  to  liquefaction  is  Black's  discovery 
that  a  large  quantity  of  heat  disappears,  or  becomes  insensible  to  the  thermo- 
meter, during  the  process.  If  a  pound  of  water  at  32°  be  mixed  with  a  pound 
of  water  at  172°,  the  temperature  of  the  mixture  will  be  intermediate  between 
them,  or  102°.  But  if  a  pound  of  water  at  172°  be  added  to  a  pound  of  ice  at 
32°,  the  ice  will  quickly  dissolve,  and  on  placing  a  thermometer  in  the  mixture, 
it  will  be  found  to  stand,  not  at  102°,  but  at  32°.  In  this  experiment,  the  pound 
of  hot  water,  which  was  originally  at  172°,  actually  loses  140  degrees  of  heat, 
all  of  which  enters  into  the  ice,  and  causes  its  liquefaction,  but  without  affecting 
its  temperature ;  whence  it  follows  that  a  quantity  of  heat  becomes  insensible 
during  the  melting  of  ice,  sufficient  to  raise  the  temperature  of  an  equal  weight 
of  water  by  140  degrees.  This  explains  the  well-known  fact,  on  which  the 
graduation  of  the  thermometer  depends, — that  the  temperature  of  melting  ice  or 
snow  never  exceeds  32°.  All  the  heat  which  is  added  becomes  insensible,  till 
the  liquefaction  is  complete. 

[Recent  experiments,  made  with  great  care  by  both  Provostaye  and  Regnault, 
have  proved  that  the  number  of  degrees  of  heat  which  becomes  insensible  during 
the  liquefaction  of  ice  is  greater  than  as  above  stated,  being  according  to  the 

*  It  is  an  obvious  objection  to  this  view  that  the  excess  of  either  force  above  its  antago- 
nist w^ould  cause  a  motion  of  the  particles.  Where  the  cohesion  is  the  superior  force  the 
particles  would  be  drawn  nearer,  where  repulsion  is  in  excess  they  would  be  separated 
to  greater  distances.  In  the  quiescent  state  of  the  particles  the  two  forces  must  evidently 
be  in  equilibrium^  and  this  whether  the  mass  be  a  solid  or  a  liquid.    (R.) 


II  JIEAT. 

independent  researches  of  both  observers  143.05.     (Ann.  de  Chem.  et  de  Phys. 
1843.)] 

The  loss  of  sensible  heat  which  attends  liquefaction  seems  essentially  neces- 
sary to  the  change,  and  for  that  reason  is  frequently  called  the  heat  of  fuidiiy. 
The  actual  quantity  of  heat  required  for  this  purpose  varies  with  the  substance, 
as  is  proved  by  the  following  results  obtained  by  Irvine.  The  degrees  indicate 
the  extent  to  which  an  equal  weight  of  each  material  may  be  heated  by  the  heat 
of  fluidity  which  is  proper  to  it. 


Heat  of  Fluidity. 

Heat  of  Fluidity 

Sulphur 

143°6«F. 

Zinc 

493° 

Spermaceti 

145" 

Tin 

500° 

Lead   . 

162° 

Bismuth     . 

550° 

Bees,  wax    . 

175° 

As  so  much  ^eat  disappears  during  liquefaction,  it  follows  that  heat  must  be 
evolved  when  a  liquid  passes  into  a  solid.  This  may  easily  be  proved.  The 
temperature  of  water  in  the  act  of  freezing  remains  at  32^^,  though  exposed  to 
an  atmosphere  in  which  the  thermometer  is  at  zero.  That  the  water  under  such 
circumstances  may  preserve  its  temperature,  heat  must  be  supplied  as  fast  as  it 
is  abstracted ;  and  it  is  obviou%  that  the  only  source  of  supply  is  the  heat  of 
fluidity.  Further,  if  pure  recently  boiled  water  be  cooled  very  slowly,  and  kept 
very  tranquil,  its  temperature  may  be  lowered  to  21°  without  any  ice  being 
formed  ;  but  the  least  motion  causes  it  to  congeal  suddenly,  and  in  doing  so  its 
temperature  rises  to  32°.     (Blagden  in  Phil.  Trans.  1788.) 

The  explanation  which  Black  gave  of  these  phenomena  constitutes  what  is 
called  his  doctrine  of  latent  heat^  which  was  partially  explained  on  a  former 
occasion  (page  33).  He  conceived  that  heat  in  causing  fluidity  loses  its  pro- 
perty of  acting  on  the  thermometer,  in  consequence  of  combining  chemically 
with  the  solid  substance,  and  that  liquefaction  results,  because  the  compound 
so  formed  does  not  possess  that  degree  of  cohesive  attraction  on  which  solidity 
depends.  When  a  liquid  is  cooled  to  a  certain  point,  it  parts  with  its  heat  of 
fluidity,  which  is  set  free  or  becomes  sensible,  and  the  cohesion  natural  to  the 
solid  is  restored.  The  same  mode  of  reasoning  was  applied  by  Black  to  the 
conversion  of  liquids  into  vapours,  a  change  during  which  a  large  quantity  of 
heat  disappears. 

A  different  explanation  of  the  phenomena  was  proposed  by  Irvine.  Observing 
that  a  solid  has  a  smaller  specific  heat  than  the  same  substance  while  liquid,  he 
argued  that  this  circumstance  alone  accounts  for  heat  becoming  insensible  during 
liquefaction.  For  since  the  specific  heat  of  ice  and  water,  or  in 'other  words, 
the  quantity  of  heat  required  to  raise  their  temperature  by  the  same  number  of 
degrees,  was  found  to  be  as  9  to  10,  Irvine  inferred  that  ice  must  contain  one- 
tenth  less  heat  than  water  of  the  same  temperature,  and  that  as  this  difference, 
must  be  supplied  to  the  ice  when  it  is  converted  into  water,  the  change  must 
necessarily  be  accompanied  with  the  disappearance  of  heat.  Irvine  applied  the 
same  argument  to  the  liquefaction  of  all  solids,  and  likewise  to  account  for  the 
heat  which  is  rendered  insensible  during  the  formation  of  vapour. 

Two  objections  may  properly  be  urged  against  the  opinion  of  Irvine.  In  the 
first  place,  no  adequate  reason  is  assigned  for  the  liquefaction.  It  accounts  for 
tlie  disappearance  of  heat  which  accompanies  liquefaction,  but  does  not  explain 


HEAT.  '  H 

•why  the  body  becomes  liquid ;  whereas  the  hypothesis  of  Black  affords  an 
explanation  both  of  the  change  itself,  and  of  the  phenomena  that  attend  it. 
But  the  second  objection  is  still  more  conclusive.  Irvine  argued  on  the  belief 
that  a  liquid  has  in  every  case  a  greater  specific  heat  than  when  solid  ;  and 
though  this  point  has  not  been  demonstrated  in  a  manner  entirely  decisive,  yet 
from  the  experiments  hitherto  made,  it  appears  that  liquids  in  general  have 
greater  specific  heats  than  solids,  and  that  therefore  Irvine's  assumption  is  pro- 
bably correct  in  regard  to  them.  In  like  manner  he  believed  vapours  to  have 
greater  specific  heats  than  the  liquids  that  yield  them  ;  but  from  the  fact  of  most 
gases  having  smaller  specific  heats  than  liquids,  it  is  probable  that  the  specific 
heats  of  elastic  fluids  in  general  are  inferior  to  those  of  th«  liquids  from  which 
they  are  derived.  The  disappearance  of  heat  during  vaporization  is  not  explica- 
ble on  the  views  of  Irvine;  it  is  necessary  to  employ  the  theory  of  Black  to 
account  for  that  change,  and  therefore  the  same  doctrine  should  be  applied  to 
the  analogous  phenomenon  of  liquefaction. 

The  loss  of  sensible  heat  in  liquefection  is  the  basis  of  many  artificial  pro- 
cesses for  producing  cold,  all  of  which  are  founded  on  the  principle  of  liquefying 
solid  substances  without  supplying  heat.  The  heat  of  fluidity  being  then  derived 
from  that  which  had  previously  existed  within  -the  solid  itself  in  a  sensible  state, 
the  temperature  necessarily  falls.  The  degree  of  cold  thus  produced  depends 
upon  the  quantity  of  heat  which  disappears ;  and  this  again  is  dependent  on  the 
quantity  of  solid  matter  liquefied,  and  on  the  rapidity  of  liquefaction. 

[This  depression  of  temperature  is  exhibited  not  only  when  the  solid  becomes 
liquid,  apart  from  other  bodies  as  in  the  case  of  melting  ice,  but  likewise  in 
many  instances  when  it  is  liquefied  by  being  dissolved  in  water,  or  some  other 
menstruum.  Thus  crystallized  glauber  salts,  sal  ammoniac  and  nitre,  while 
dissolving  in  water,  cause  a  considerable  reduction  of  temperature.  It  is  a 
curious  fact  that  a  further  addition  of  water  to  certain  saline  solutions  renders 
them  colder,  thus  seeming  to  indicate  an  increased  degree  of  liquidity.  Con- 
sistently with  this  Person  has  recently  found  that  while  by  dissolving  1  part  of 
common  salt  in  4  parts  of  water,  10  units  of  heat  become  insensible:  by  dis- 
solving the  same  quantity  of  salt  in  50  parts  of  water,  22  such  units  disappear. 
Comptes  Rendus,  1844.] 

The  most  common  method  of  producing  cold  is  by  mixing  together  equal 
parts  of  snow  and  salt.  The  salt  causes  the  snow  to.  melt  by  reason  of  its 
affinity  for  water,  and  the  water  dissolves  the  salt ;  so  that  both  of  them  become 
liquid.  The  cold  thus  generated  is  32  degrees  below  the  temperature  of  freez- 
ing water ;  that  is,  a  thermometer  placed  in  the  mixture  would  stand  at  zero. 
This  is  the  way  originally  proposed  by  Fahrenheit  for  determining  the  com- 
mencement of  his  scale. 

Any  other  substances  which  have  a  strong  afiinity  for  water  may  be  substituted 
for  the  salt ;  and  those  have  the  greatest  effect  in  producing  cold  whose  affinity 
for  that  liquid  is  greatest,  and  which  consequently  produce  the  most  rapid  lique- 
faction. Crystallized  chloride  of  calcium,  proposed  by  Lowitz,  is  by  far  the 
most  convenient  in  practice.  It  may  be  made  by  dissolving  marble  in  hydro- 
chloric acid,  and  concentrating  the  solution  by  evaporation,  till,  upon  letting  a 
drop  of  it  fall  upon  a  cold  saucer,  it  becomes  a  solid  mass.  It  should  then  be 
withdrawn  from  the  fire,  and  when  cold  be  speedily  reduced  to  a  fine  powder. 
From  its  extreme  deliquescence  it  must  be  preserved  in  well-stopped  vessels. 


HEAT. 


The  following  table  by  Mr.  "Walker,  contains  the  best  proportions  for  producing 
intense  cold.     (Phil.  Trans.  1801.) 

FRIGORIFIC  MIXTURES  WITH  SNOW.* 


MIXTURES. 

Parts  by  Weight. 
Sea.  salt          ...         1 
Snow    ....        2 

i 
l< 

>-. 

c 

a 

o 

Thermometer  sinks, 
to  —5° 

Degree  of  cold 
produced. 

Sea- salt         .        •        .        2 

Hydrochlorate  of  Ammonia  1 

,    Snow     ....        5 

to— 12° 

Sea-sait          ...       10 
Hydrochlorate  of  AnAionia  5 
Nitrate  of  Potassa         .        5 
Snow     ....      24 

to  —18° 

Sea- salt          ...        5 
Nitrate  of  Ammonia      .        5 
Snow     ....       12 

to  —25° 

Diluted  Sulphuric  Acidt        2 
Snow     ....         3 

fromf  32°to— 23° 

55  degrees. 

Concentrated  Hydrochloric 

Acid           ...        5 
Snow     ....         8 

fromt32°to— 27° 

59 

Concentrated  Nitrous  Acid    4 
Snow     ....         7 

from  +  32°to— 30" 

62 

Chloride  of  Calcium     .        5 
Snow     ....         4 

from -f- 32°  to — 40° 

72 

Crystallized  Chloride  of 

Calcium     ...        3 
Snow      ....        2 

from-f  32°to— 50° 

82 

Fused  Potassa        .         .        4 
Snow     ....         3 

from-|-32°  to— 51°                   83 

Freezing  mixtures  are  also  made  by  the  rapid  solution  of  salts,  without  the 
use  of  snow  or  ice ;  the  following  table,  by  Walker,  includes  the  most  impor- 
tant of  them.  The  salts  must  be  finely  powdered  and  dry.  (Phil.  Trans.  1795.) 


MIXTURES.             Parts  by  Weight. 
Hydrochlorate  of  Ammonia   5 
Nitrate  of  Potassa          .        5 
Water    ....       16 

Temperature  falls, 
from  1 50°  to  1 10° 

Degree  of  Cold  produced. 
40  degrees. 

Hydrochlorate  of  Ammonia    5 
Nitrate  of  Potassa          .        5 
Sulphate  of  Soda   .         .        8 
Water    .        .         .        .16 

from -{-50°  to  f  4° 

46 

Nitrate  of  Ammonia       .         1 
Water    ....        1 

from  f  50°  tof  4° 

46 

Nitrate  of  Ammonia       .         1 
Carbonate  of  Soda          .         1 
Water    ....         1 

from-|-50°to— 7° 

57 

Sulphate  of  Soda   .         .         3 
Diluted  Nitrous  Acidt    .         2 

from -j- 50°  to  —3° 

53 

Sulphate  of  Soda    .        .        6 
Hydrochlorate  of  Ammonia  4 
Nitrate  of  Potassa           .         2 
Diluted  Nitrous  Acid      .        4 

fromf  50°to— 10° 

60 

*  The  snow  should  be  freshly  fallen,  dry,  and  uncompressed.  If  snow  cannot  be  had, 
finely  pounded  ice  may  be  substituted  for  it. 

t  Made  of  strong  acid,  diluted  with  half  its  weight  of  snow  or  distilled  water. 

t  Composed  of  faming  nitrous  acid  2  parts  in  weight,  and  one  of  water  j  the  mixture 
being  allowed  to  cool  before  being  used. 


HEAT. 


4l 


MIXTURES, 

Parts  by 
Sulphate  of  Soda    . 
Nitrate  of  Ammonia 
Diluted  Nitrous  Acid 

Weight. 
6 
5 
4 

Thermometer 
falls. 

from-|-50°to— 14'' 

Degree  of  cold 
produced. 

64 

Phosphate  of  Soda 
Diluted  Nitrous  Acid 

9 
4 

from-j-50°to— 12° 

62 

Phosphate  of  Soda 
Nitrate  of  Ammonia 
Diluted  Nitrous  Acid 

9 
6 

4 

from  f  50°  to  —21° 

71 

Sulphate  of  Soda    . 
Hydrochloric  Acid 

8 
5 

from -[-50°  to  0° 

50 

Sulphate  of  Soda    . 
Diluted  Sulphuric  Acid* 

5 

4 

from  f  50°  tof  3° 

47 

These  artificial  processes  for  generating  cold  are  much  more  effectual  when 
the  materials  are  previously  cooled  by  immersion  in  other  frigorific  mixtures. 
One  would  at  first  suppose  that  an  unlimited  degree  of  cold  might  be  thus  pro- 
duced ;  but  it  is  found  that  when  the  difference  between  the  mixture  and  the  air 
becomes  very  great,  the  communication  of  heat  from  one  to  the  other  becomes 
so  rapid,  as  to  put  a  limit  to  the  reduction.  The  greatest  cold  produced  by 
Walker  did  not  exceed  100  degrees  below  the  zero  of  Fahrenheit. 

Though  we  shall  probably  never  succeed  in  depriving  any  substance  of  all  its 
heat,  bodies  doubtless  contain  a  certain  definite  quantity  of  this  principle,  and 
various  attempts  have  been  made  to  calculate  its  amount. 

To  be  satisfied  that  such  calculations  cannot  be  trusted,  it  is  suflicient  to 
know  that  the  estimates  made  by  different  chemists  respecting  the  absolute 
quantity  of  heat  in  water  vary  from  900  to  nearly  8000. f 

VAPORIZATION^. 

Aeriform  substances  are  commonly  divided  into  vapours  and  gases.  The  for- 
mer are  characterised  by  their  ready  conversion  into  liquids  or  solids,  either  by 
a  moderate  increase  of  pressure,  the  temperature  at  which  they  were  formed 
remaining  the  same,  or  by  a  moderate  diminution  of  that  temperature,  without 
change  of  pressure.  Gases,  on  the  contrary,  retain  their  elastic  state  more 
obstinately:  they  are  always  gaseous  at  common  temperatures;  and,  with  one 
or  two  exceptions,  cannot  be  made  to  change  their  form,  unless  by  being  sub- 
jected to  much  greater  pressure  than  they  are  naturally  exposed  to.  Several  of 
them,  indeed,  have  hitherto  resisted  every  effort  to  compress  them  into  liquids. 
The  only  difference  between  gases  and  vapours  is  in  the  relative  forces  with 
which  they  resist  condensation. 

Heat  is  the  cause  of  vaporization  as  well  as  of  liquefaction.  A  sufficiently 
intense  heat  would  doubtless  convert  every  liquid  and  solid  into  vapour.  Some 
bodies,  however,  resist  the  strongest  heat  of  our  furnaces  without  vaporizing. 
These  are  said  to  be  fixed  in  the  fire ;  those  which,  under  the  same  circum- 
stances, are  converted  into  vapour,  are  called  volatile. 

The  disposition  of  various  substances  to  yield  vapour  is  very  different;  and 
the  difference  depends  doubtless  on  the  relative  power  of  cohesion  with  which 
they  are  endowed.    Fluids,  in  general,  are  more  easily  vaporized  than  solids,  as 


*  Composed  of  equal  weights  of  strong  acid  and  water,  being  allowed  to  cool  before  use. 
t  Dalton'8  New  System  of  Chemical  Philosophy. 


42  HEAT. 

would  be  expected  from  the  weaker  cohesion  of  the  former.  Some  solids,  such 
as  arsenic  and  sal-ammoniac,  pass  at  once  into  vapour  without  being  liquefied ; 
but  most  of  them  become  liquid  before  assuming  the  elastic  condition. 

Vapours  occupy  more  space  than  the  substances  from  which  they  were  pro- 
duced. Gay  Lussac  found  that  water,  in  passing  from  its  point  of  greatest 
density  into  vapour,  expands  to  1696  times  its  volume,  alcohol  to  659  times,  and 
ether  to  443  times,  each  vapour  being  at  212°  and  under  a  pressure  of  29-92 
inches  of  mercury.  This  shows  that  vapours  differ  in  density.  Watery  vapour 
is  lighter  than  air  at  the  same  temperature  and  pressure  in  the  ratio  of  1000  to 
1604;  or  the  sp.  gr.  of  air  being  1000,  that  of  watery  vapour  is  625.  The 
vapour  of  alcohol,  on  the  contrary,  is  half  as  heavy  again  as  air ;  and  that  of 
ether  is  more  than  twice  and  a  half  as  heavy. 

The  dilatation  of  vapours  by  heat  was  found  by  Gay  Lussac  to  follow  the 
same  law  as  gases ;  that  is,  for  every  degree  of  Fahrenheit,  they  increase  by 
■?5U<h  ^f  *^^  volume  they  occupied  at  32°.*  But  this  law  only  holds  of  vapours 
when  separated  from  the  liquids  that  yield  them.  If  liquid  be  present  heat  not 
only  expands  the  vapour  but  increases  its  volume  by  the  addition  of  a  new  quan- 
tity of  vapour.  In  like  manner,  the  contraction  of  a  vapour  by  cold  will  deviate 
from  the  above  law,  as  soon  as  the  cold  condenses  any  part  of  it  into  liquid. 

Vapours  vary  in  volume  under  varying  pressure  according  to  the  same  law  as 
gases,  provided  always  that  the  gaseous  state  is  preserved.  This  law,  which 
was  discovered  by  Boyle  and  Mariotte,  and  is  more  fully  explained  in  the  sec- 
tion on  atmospheric  air,  merely  expresses  the  fact  that  the  volume  of  gaseous 
substances  at  a  constant  temperature  is  inversely  as  the  pressure  to  which  they 
are  subject. 

Vaporization  is  conveniently  studied  under  two  heads, — Ebullition  and  Evapo- 
ration.  In  the  first,  the  production  of  vapour  is  so  rapid  that  its  escape  gives 
rise  to  a  visible  commotion  in  the  liquid  ;  in  the  second,  it  passes  off  quietly 
and  insensibly. 

EBULLITION. 

The  temperature  at  which  vapour  rises  with  sufficient  freedom  for  causing  the 
phenomena  of  ebullition,  is  called  the  boiling  point.  The  heat  requisite  for  this 
effect  varies  with  the  nature  of  the  fluid. 

[The  following  table  exhibits  the  boiling  point  of  a  number  of  liquids  : 


Boiling  point. 

Boiling  Point. 

Hydrochloric  Ether 

52'' 

Crys.  Chloride  of  Calcium 

302^ 

Sulphuric  Ether 

9Q'> 

Oil  Turpentine        .  '     . 

314° 

Bi  Sulphuret  of  Carbon  . 

116" 

Phosphorus     . 

654° 

Ammonia  (sp.  gr.  0.945) 

140° 

Sulphuric  Acid  (sp.  gr.  1.843)         620° 

Alcohol  (sp.  gr.  0.798)    . 

172" 

Whale  Oil       . 

.        630° 

Water     .... 

212° 

Mercury 

662°] 

Nitric  Acid  (sp.gr.  1.42)         .        248° 

The  boiling  point  of  the  same  liquid  is  constant,  so  long  as  the  necessary 
conditions  are  preserved  ;  but  it  is  liable  to  be  affected  by  several  circumstances. 
The  nature  of  the  vessel  has  some  influence  upon  the  boiling  point.  Thus  Gay 
Lussac  observed  that  pure  water  boils  precisely  at  212°  in  a  metallic  vessel,  and 

*  See  remarks  on  this  subject,  page  24. 


HEAT.  43 

at  '2liP  in  one  of  glass,  owing  apparently  to  its  adhering  to  glass  more  power- 
fully than  to  a  raetal.  It  is  likewise  affected  by  the  presence  of  foreign  parti- 
cles :  when  a  few  iron  filings  are  thrown  into  water  boiling  in  a  glass  vessel, 
its  temperature  quickly  falls  from  214°  to  212°,  and  remains  stationary  at  the 
latter  point. 

[More  recent  observations,  by  Marcet,  have  shown  that  when  the  surface  of 
the  vessel,  whether  of  glass  or  metal,  is  coated  with  sulphur,  shellac,  or  other 
substances  of  the  same  kind,  boiling  takes  place  at  212°.  In  this  case  the  tem- 
perature of  the  water  is  the  same  as  that  of  the  steam.  "Without  such  a  coating 
the  boiling  point  varies 

In  glass  vessels  from  212°.54  to  215°.  6 

In  metallic  vessels  from  212°.27  to  212°.36   (Ann.  de  Chem.) 

In  this  case  the  temperature  of  the  steam  is,  of  course,  less  than  that  of  the 
liquid. 

M.  Magnus  in  his  late  able  investigations  of  the  same  subject,  maintains 
that  the  various  degrees  of  adhesion  of  the  liquid  to  the  surface  of  the  vessel 
causes  these  differences.  When  this  adhesion  is  equal  to  or  exceeds  the  cohe- 
sion of  the  particles  of  the  liquid,  the  particles  more  remote  from  the  surface 
being  held  together  only  by  their  cohesion  will  be  converted  into  steam.  The 
temperature  at  which  this  takes  place  is  the  true  boiling  point ;  but  when  there 
is  no  adhesion  of  the  liquid  to  the  surface,  or  when  this  force  is  less  than  the 
cohesion  of  the  liquid,  then  the  boiling  will  take  place  in  contact  with  the  sur- 
face, because  there  the  restraining  force  is  less,  and  the  boiling  temperature  will 
be  lower  than  if  the  adhesion  were  equal  to  or  greater  than  the  cohesion. 
Hence  glass,  well  washed  with  sulphuric  acid  so  as  to  promote  contact  and 
adhesion,  raises  the  boiling  point  to  221°.     (Ann.  de  Chem.  1844.)] 

But  the  circumstance  which  has  the  greatest  influence  over  the  boiling  point 
of  liquids  is  variation  of  pressure.  All  bodies  upon  the  earth  are  constantly 
exposed  to  considerable  pressure ;  for  the  atmosphere  itself  presses  with  a  force 
equivalent  to  a  weight  of  15  pounds  on  every  square  inch  of  surface.  Liquids 
are  exposed  to  this  pressure  as  well  as  solids,  and  their  tendency  to  take  the 
form  of  vapour  is  very  much  counteracted  by  it.  In  fact,  they  cannot  enter  into 
ebullition  at  all,  till  their  particles  have  acquired  such  elastic  force  as  enables 
them  to  overcome  the  pressure  upon  their  surfaces :  that  is,  till  they  press 
against  the  atmosphere  with  the  same  force  as  the  atmosphere  against  them. 
Now  the  atmospheric  pressure  is  variable,  and  hence  it  follows  that  the  boiling 
point  of  liquids  must  also  vary. 

The  pressure  of  the  atmosphere  is  equal  to  a  weight  of  15  pounds  on  every 
square  inch  of  surface,  when  the  barometer  stands  at  30  inches,  and  then  only 
does  water  boil  at  212°.  If  the  pressure  be  less,  that  is,  if  the  barometer  fall 
below  30  inches,  then  the  boiling  point  of  water  and  every  other  liquid  will  be 
lower  than  usual ;  or  if  the  barometer  rise  above  30  inches,  the  temperature  of 
ebullition  will  be  proportionally  increased.  On  this  account  water  boils  at  a 
lower  temperature  on  the  top  of  a  hill  than  in  the  valley  beneath  it ;  for  as  the 
column  of  air  diminishes  in  length  as  we  ascend,  its  pressure  must  likewise 
suffer  a  proportional  diminution.  The  ratio  between  the  depression  of  the  boil- 
ing point  and  the  diminution  of  the  atmospheric  pressure  is  so  exact,  that  it  has 
been  proposed  as  a  method  for  determining  the  heights  of  mount^ns.    Accord- 


44 


HEAT. 


ing  to  Wollaston  an  elevation  of  530  feet  makes  a  diminution  of  one  degree.* 
(Phil.  Trans,  for  1817.) 

The  influence  of  the  atmosphere  over  the  point  of  ebullition  is  best  shown  by 
removing  its  pressure  altogether.  Robison  found  that  fluids  boil  in  vacuo  at  a 
temperature  140°  lower  than  in  the  open  air.      (Black's  Lectures,  i.  151.) 

Water  cannot  be  heated  under  common  circumstances  beyond  212°,  because 
it  then  acquires  such  expansive  force  as  enables  it  to  overcome  the  atmospheric 
pressure,  and  fly  off  in  the  form  of  vapour.  But  if  subjected  to  sufficient  pres- 
sure, it  may  be  heated  to  any  extent  without  boiling.  This  is  best  done  by 
heating  water  while  confined  in  a  strong  copper  vessel,  called  Papin's  Digester. 
In  this  apparatus,  on  the  application  of  heat,  a  large  quantity  of  vapour  collects 
above  the  water,  and  checks  ebullition  by  the  pressure  which  it  exerts  upon  the 
surface  of  the  liquid.  There  is  no  limit  to  the  degree  to  which  water  may  thus 
be  heated,  provided  the  vessel  is  strong  enough  to  confine  the  vapour;  but  the 
expansive  force  of  steam  under  these  circumstances  is  so  enormous  as  to  over- 
come the  greatest  resistance. 

Robison  (Brewster's  edition  of  his  works,  p.  25)  found  that  the  tension  of 
steam  is  equal  to  two  atmospheres  at  244°,  and  to  three  at  270°.  The  results 
of  Southern's  experiments,  given  in  the  same  volume,  fix  upon  250*3°  as  the 
temperature  of  which  steam  has  the  force  of  two  atmospheres,  on  293*4°  for 
four,  and  343-6°  for  eight  atmospheres. 

This  subject  has  been  examined  by  a  commission  appointed  by  the  Parisian 
Academy  of  Sciences,  and  Dulong  and  Arago  took  a  leading  part  in  the  inquiry. 
The  results,  which  are  given  in  the  following  table,  were  obtained  by  experi- 
ment up  to  a  pressure  of  25  atmospheres,  and  at  higher  pressures  by  calculation. 
(Brande's  Journal,  N.  S.  viii.  191. )f 


Elasticity  of  the 
vapour,  taking 
atmospheric 
press,  as  unity. 

1 

Temperature  ac- 
cording  to 
Fahrenheit. 
212 

Elasticity  of  the 
vapour,  taking 
atmospheric 
press,  as  unity. 
4 

Temperature  ac 
,  cording  to 
Fahrenheit. 
293-72 

li 

233-96 

4i 

300-28 

2 

250-52 

5 

307-5      ' 

U 

263-84 

5i 

314-24 

3 

275-18 

6 

320-36 

Si 

285-08 

6i 

326-26 

*  An  instrument  constructed  for  accurately  noting  the  boiling  temperature  of  water  at 
different  heights,  invented  by  Wollaston,  has  with  some  modifications  been  employed  suc- 
cessfully for  measuring  the  height  of  mountains  in  Virginia  and  Pennsylvania.  Prof.  W. 
and  H.  Rogers,  and  recently  Prof-  Forbes,  of  Edinburgh,  had  made  numerous  accurate 
observations  with  a  somewhat  similar  instrument.  By  comparison  with  barometric  and 
trigonometric  measurements,  it  has  been  found  that  in  Virginia  and  Pennsylvania  one 
degree  of  depression  of  the  boiling  point  corresponds  to  an  elevation  of  548-5  feet.  The 
estimate  of  Prof.  Forbes  for  Edinburgh,  is  almost  precisely  the  same.  Col.  Wright  found 
that  in  the  Andes  one  degree  corresponded  to  about  600  feet. 

Prof.  Forbes  has  inferred  from  his  observations  that  the  depressions  of  the  boiling  point 
are  accurately  proportional  to  the  heights  above  the  earth's  surfkce,  a  law  which  gives 
great  simplicity  to  the  calculation  of  altitudes  from  these  data.    (R.) 

t  For  an  account  of  Regnault's  elaborate  researches  on  the  same  subject,  see  Ann.  de 
Chim.,  1844.    (|L.) 


HEAT. 


46 


Elasticity  of  the 

Elasticity  of  the 

,. 

vapour,  taking 

atmospheric 
press,  as  unity. 
7 

Temperature  ac- 
cording to 
Fahrenheit. 
331-70 

vapour,  taking 
atmospheric 
press,  as  unity. 
19 

Temperature  ac- 
cording to 
Fahrenheit. 
413-78 

7i 

336-86 

20 

418-46 

8 

341-78 

21 

422-96 

9 

350-78 

22 

427-28 

10 

.358-88 

23 

431-42 

11 

366-85 

24 

435-56 

12 

374-00 

25 

439-34 

13 

380-66 

30 

457-16 

14 

386-94 

35 

472.73 

15 

392-86 

40 

486-59 

16 

398-48 

45 

491-14 

17 

403-82 

50 

610-60 

18 

408-92 

The  elasticity  of  steam  is  employed  as  a  moving  power  in  the  steam-engine. 
The  construction  of  this  machine  depends  on  two  properties  of  steam,  namely, 
the  expansive  force  communicated  to  it  by  heat,  and  its  ready  conversion  into 
water  by  cold. 

The  formation  of  vapour  is  attended,  like  liquefaction,  with  loss  of  sensible 
heat.  This  is  proved  by  the  well-known  fact  that  the  temperature  of  steam  is 
precisely  the  same  as  that  of  the  boiling  water  from  which  it  rises;  so  that  all 
the  heat  which  enters  into  the  liquid  is  solely  employed  in  converting  a  portion 
of  it  into  vapour,  without  affecting  the  temperature  of  either,  provided  the  latter 
is  permitted  to  escape  with  freedom.  The  heat,  which  then  becomes  latent,  to 
use  the  language  of  Black,  is  again  set  free  when  the  vapour  is  condensed  into 
water.  The  exact  quantity  of  heat  rendered  insensible  by  vaporization  may 
therefore  be  ascertained  by  condensing  the  vapour  in  cold  water,  and  observing 
the  rise  of  temperature  which  ensues.  From  the  experiments  of  Black  and 
Watt,  conducted  on  this  principle,  steam  of  212°,  in  being  condensed  into  water 
of  212°,  gives  out  as  much  heat  as  would  raise  the  temperature  of  an  equal 
weight  of  water  by  950  degrees,  all  of  which  had  previously  existed  in  the 
vapour  without  being  sensible  to  a  thermometer. 

The  latent  heat  of  steam  and  several  other  vapours  has  been  examined  by 
Dr.  Ure,  whose  results  are  contained  in  the  following  table.  (Phil.  Trans,  for 
1818.) 

[Equal  weights.  Latent  heat. 


Vapour  of  water  at  boiling  point,  .... 
Alcohol,  sp.  gr.  825,  .... 
Ether,  boiling  point,  112%  .'      . 

Petroleum, 

Oil  of  Turpentine,  .... 

Nitric  acid,sp.  gr.  1.494,  boiling  point,  165° 
Liquid  ammonia,  sp.  gr.  0-978, 
Vinegar,  sp.  gr.  1.007        .... 


1000" 
457" 
312-9 
183-8 
183-8 
550 
865-9 
903] 


[When  evaporated  at  temperatures  below  the  boiling  point,  a  liquid  renders 
latent  a  greater  quantity  of  heat  than  when  it  is  converted  into  vapour  at  that 
point.  By  accurate  experiments,  on  the  vaporization  of  water,  it  has  been 
proved  that  the  latent  heat  of  tlie  vapour  when  added  to  the  sensible  heat,  or 


^  HEAT. 

temperature  at  •which  it  is  formed,  always  amounts  to  a  constant  quantity. 
Thus  with  water  evaporating  at 

32°  the  latent  heat  is  1180,  the  sum  being  1212 

100°               «              1112  "          1212 

212°                «              1000  <<          1212 

300                 «'                900  «           1212 

The  same  law  is  believed  to  hold  with  liquids  in  general.] 
The  disappearance  of  heat  that  accompanies  vaporization  was  explained  by 
Black  and  Irvine,  in  the  way  already  mentioned  under  the  head  of  liquefaction ; 
and  as  the  objections  to  the  views  of  Irvine  were  then  stated,  it  is  unnecessary 
to  mention  them  on  the  present  occasion. 

The  variation  of  volume  and  elasticity  in  vapours  is  attended,  as  in  g^ses, 
with  a  change  of  sp.  heat  and  a  consequent  variation  of  temperature  (page  35). 
Thus  when  steam,  highly  heated  and  compressed  in  a  strong  boiler,  is  permitted 
to  escape  by  a  large  aperture,  the  sudden  expansion  is  attended  with  a  great 
loss  of  sensible  heat:  its  temperature  instantly  sinks  so  much,  that  the  hand 
may  be  held  in  the  current  of  vapour  without  inconvenience.  The  same  prin- 
ciple accounts  for  the  fact,  first  ascertained  by  Watt,  that  distillation  at  a  low 
temperature  is  not  attended  with  any  saving  of  fuel.  For  when  water  boils  at 
a  low  temperature  in  a  vacuum,  the  vapour  is  in  a  highly  expanded  state,  and 
contains  more  insensible  heat  than  steam  of  greater  density. 

EVAPORATION. 

Evaporation  as  well  as  ebullition  consists  in  the  formation  of  vapour,  and  the 
only  assignable  difference  between  them  is,  that  the  one  takes  place  quietly,  the 
other  with  the  appearance  of  boiling.  Evaporation  occurs  at  common  tempera- 
tures. This  fact  may  be  proved  by  exposing  water  in  a  shallow  vessel  to  the 
air  for  a  few  days,  when  it  will  gradually  diminish,  and  at  last  disappear  en- 
tirely. Most  fluids,  if  not  all  of  them,  are  susceptible  of  this  gradual  dissipa- 
tion ;  and  it  may  also  be  observed  in  some  solids,  as  for  example  in  camphor. 
Evaporation  is  much  more  rapid  in  some  fluids  than  in  others,  and  it  is  always 
found  that  those  liquids  the  boiling  point  of  which  is  lowest  evaporate  with  the 
greatest  rapidity.  Thus  alcohol,  which  boils  at  a  lower  temperature  than  water, 
evaporates  also  more  freely;  and  ether,  whose  point  of  ebullition  is  yet  lower 
than  that  of  alcohol,  evaporates  with  still  greater  rapidity. 

The  chief  circumstances  that  influence  the  process  of  evaporation  are  extent 
of  surface,  and  the  state  of  the  air  as  to  temperature,  dryness,  stillness,  and 
density. 

1.  Extent  of  surface.  Evaporation  proceeds  only  from  the  surface  of  fluids, 
and  therefore,  cacteris  paribus^  must  depend  upon  the  extent  of  surface  exposed. 

2.'  Temperature.  The  eflfect  of  heat  in  promoting  evaporation  may  easily 
be  shown  by  putting  an  equal  quantity  of  water  into  two  saucers,  one  of  which 
is  placed  in  a  warm,  the  other  in  a  cold  situation.  The  former  will  be  quite 
dry  before  the  latter  has  sufl"ered  appreciable  diminution. 

3.  Slate  of  the  air  as  to  dryness  or  moisture.  When  water  is  covered  by  a 
stratum  of  dry  air,  the  evaporation  is  rapid  even  when  its  temperature  is  low. 
Thus  in  dry  cold  days  in  winter,  the  evaporation  is  exceedingly  rapid  ;  whereas 
it  goes  on  very  tardily,  if  the  atmosphere  contain  much  vapour,  even  though  the 
air  be  very  warm. 


HEAT.  47 

4.  Evaporation  is  far  slower  in  still  air  than  in  a  current,  and  for  an  obvious 
leason.  Tiie  air  immediately  in  contact  with  the  water  soon  becomes  moist, 
and  thus  a  check  is  put  to  evaporation.  But  if  the  air  be  removed  from  the  sur- 
face of  the  water  as  soon  as  it  has|»ecome  charged  with  vapour,  and  its  place 
supplied  with  fresh  dry  air,  then  the  evaporation  continues  without  interruption. 

5.  Pressure  on  the  surface  of  liquids  has  a  remarkable  influence  over  evapo- 
ration. This  is  easily  proved  by  placing  ether  in  the  vacuum  of  an  air-pump, 
when  vapour  rises  so  abundantly  as  to  produce  ebullition. 

[It  was  long"  ago  observed  by  Saussure,  and  others,  that  water  evaporates 
very  slowly  when  placed  on  red  hot  metal,  but  that  as  the  surface  is  allowed 
to  cool,  or  reaching  a  certain  temperature,  much  below  redness,  the  liquid  bursts 
almost  explosively  into  steam.  In  the  former  condition  it  is  easy  to  observe 
that  the  liquid  is  not  in  contact  with  the  heated  surface.  But  when  the  tempe- 
rature falls  to  a  certain  point  the  contact  takes  place,  and  at  the  same  moment 
steam  is  rapidly  formed.  Water  and  other  liquids  placed  in  this  condition  of 
repulsion,  seem  to  have  new  and  peculiar  relations  to  heat.  According  to 
Boutigny's  late  admirable  researches,  the  liquid,  thus  brought  to  what  he  calls 
the  spheroidal  state,  is  endowed  with  the  property  of  perfectly  reflecting  the  heat 
falling  upon  its  surface  from  the  red  hot  metal.  In  proof  of  this  he  found  that 
a  thermometer  plunged  in  water,  in  the  spheroidal  state,  became  stationary  at 
the  temperature  205°-7,  although  the  surrounding  metal  was  at  a  strong  red 
heat.  The  vapour  escaping  from  the  water,  in  this  state,  is  of  very  low  ten- 
sion, but  has  the  temperature  of  the  surrounding  vessel,  thus  differing,  strik- 
ingly, from  the  vapour  produced  by  ordinary  boiling.  The  passage  from  the 
spheroidal  to  the  common  condition,  he  very  plausibly  regards  as  the  cause  of 
the  fulminating  explosions  of  steam  boilers.  Among  the  important  results  of  his 
observations  the  following  are  especially  deserving  notice. 

1.  The  lowest  temperature  at  which  water  can  pass  to  the  spheroidal  state  in 
notable  quantity  is  287°'6. 

2.  Water  in  this  state  evaporates  more  rapidly,  as  the  temperature  of  the 
containing  vessel  is  more  elevated,  but  the  formation  of  vapour  is  greatly  slower 
than  in  the  ordinary  condition.  At  382°  the  spheroidal  liquid  loses  by  evapora- 
tion in  a  given  time  (o/i/y  one  fiftieth  of  what  would  evaporate  by  boiling.) 

3.  Whatever  be  the  temperature  of  the  containing  vessel,  that  of  the  spheroi- 
dal liquid  is  invariable  and  always  below  its  boiling  point,  though  in  a  fixed  ratio 
to  that  point,  being  for  water  205°-7  F.   (Ann.  de  Chim.  1844).  ] 

As  a  large  quantity  of  heat  passes  from  a  sensible  to  an  insensible  state  dur- 
ing the  formation  of  vapour,  it  follows  that  cold  should  be  generated  by  evapo- 
ration. The  fact  may  readily  be  proved  by  letting  a  few  drops  of  ether  evaporate 
from  the  hand,  when  a  strong  sensation  of  cold  will  be  excited  ;  or  if  the  bulb 
of  a  thermometer,  covered  with  lint,  be  moistened  with  ether,  the  production  of 
cold  will  be  marked  by  the  descent  of  the  mercury.  But  to  appreciate  the  de- 
gree of  cold  which  may  be  produced  by  evaporation,  it  is  necessary  to  render  it 
very  rapid  and  abundant  by  artificial  processes ;  and  the  best  means  of  doing  so 
is  by  removing  pressure  from  the  surface  of  volatile  liquids.  Water  placed 
under  the  exhausted  receiver  of  an  air-pump  evaporates  with  great  rapidity,  and 
so  much  cold  is  generated  as  would  freeze  the  water,  did  the  vapour  continue  to 
rise  for  some  time  tvilh  the  same  velocity.  But  the  vapour  itself  soon  fills  the 
vacuum,  and  retards  the  evaporation  by  pressing  upon  the  surface  of  the  water. 
This  difficulty  may  be  avoided  by  putting  under  the  receiver  a  substance,  such 


48  HEAT. 

as  sulphuric  acid,  which  has  the  property  of  absorbing  watery  vapour,  and  con- 
sequently of  removing  it  as  quickly  as  it  is  formed.  Such  is  the  principle  of 
Leslie's  method  for  freezing  water  by  its  own  evaporation.* 

The  action  of  the  cryophorus,  an  ingenio||s  contrivance  of  the  late  Dr.  Wollas- 
ton,  depends  on  the  same  principle.  It  consists  of  two  glass  balls,  perfectly  free 
from  air,  and  joined  together  by  a  tube,  as  here  represented. — One  of  the  balls  con- 
tains a  portion  of  distilled  water, 
while  the  other  parts  of  the  instru- 
ment, which  appear  empty,  are  full 
of  aqueous  vapour,  which  checks  the 
evaporation  from  the  water  by  the  pressure  it  exerts  upon  its  surface.  But  when 
the  empty  ball  is  plunged  into  a  freezing  mixture,  all  the  vapour  within  it  is 
condensed  ;  evaporation  commences  from  the  surface  of  the  water  in  the  other 
ball,  and  it  is  frozen  in  two  or  three  minutes  by  the  cold  thus  produced. 

Liquids  which  evaporate  more  rapidly  than  water,  cause  a  still  greater  reduc- 
tion of  temperature.  The  cold  produced  by  the  evaporation  of  ether  in  the 
vacuum  of  the  air-pump  is  so  intense  as,  under  favourable  circumstances,  to 
freeze  mercury. f 

[According  to  Thilorier,  a  mixture  of  solid  carbonic  acid  and  ether,  by  its 
evaporation  depresses  the  temperature  to  — 148  ;  but  the  most  striking  example 
of  the  cooling  effect  of  evaporation  is  that  furnished  in  the  recent  experiment  of 
Boutigny,  who  by  the  rapid  evaporation  of  liquid  sulphurous  acid  in  a  red  hot 
crucible,  actually  froze  a  portion  of  water  in  the  midst  of  the  heated  mass. — 
Ann.  de  Chim.  1843.] 

Scientific  men  have  differed  concerning  the  cause  of  evaporation.  It  was  once 
supposed  to  be  owing  to  chemical  attraction  between  the  air  and  water,  and  the 
idea  is  at  first  view  plausible,  since  a  certain  degree  of  afl[inity  does  to  all  ap- 
pearance exist  between  them.  But  it  is  nevertheless  impossible  to  attribute 
the  effect  to  this  cause.  For  evaporation  takes  place  equally  in  vacuo  as  in  the 
air ;  nay,  it  is  an  established  fact,  that  the  atmosphere  positively  retards  the 
process,  and  that  one  of  the  best  means  of  accelerating  it  is  by  removing  the 
air  altogether.  The  experiments  of  Dalton  prove  that  heat  is  the  true  and  only 
cause  of  the  formation  of  vapour.  He  finds  that  the  actual  quantity  of  vapour 
which  can  exist  in  any  given  space  is  dependent  solely  upon  the  temperature. 

Dalton  also  found  that  the  tension  or  elasticity  of  vapour  is  always  the  same, 
however  much  the  pressure  may  vary,  so  long  as  the  temperature  remains  con- 
stant, and  there  is  liquid  enough  present  to  preserve  the  state  of  saturation  proper 
to  the  temperature.  This  law  holds  good,  whether  the  vapour  be  pure,  or 
mixed  with  air  or  any  other  gas. 

The  elasticity  of  watery  vapour  at  temperatures  below  212°  was  carefully  ex- 
amined by  Dalton  (Manchester  Memoirs,  vol.  v.) ;  and  his  results,  together 
with  those  since  published  by  lire  (Phil.  Trans.  1818),  are  presented  in  a 
tabular  form  at  the  end  of  the  volume.  They  were  obtained  by  introducing  a 
portion  of  water  into  the  vacuum  of  a  common  barometer,  and  estimating  the 
tension  of  its  vapour  by  the  extent  to  which  it  depressed  the  column  of  mercury 
at  different  temperatures. 
A  knowledge  of  the  influence  of  heat  and  pressure  over  the  volume  of  gaseous 

*  See  art.  Cold,  in  the  Supplement  to  the  Encyclopaedia  Britannica. 

t  See  a  paper  by  the  late  Dr.  Marcet,  in  Nicholson's  Journal,  vol.  xzzir. 


HEAT.  49 

matter  is  elegantly  employed  in  calculating  the  sp.  gr.  of  vapour ;  but  before 
giving  the  mode  of  making  the  calculation,  it  will  be  useful  to  explain  what  is 
meant  by  specific  gravity  or  density.  These  terms  are  generally  used  to  denote 
the  compactness  of  a  substance,  or  the  quantity  of  ponderable  matter  contained 
in  a  body  compared  with  the  space  which  it  occupies.  The  sp.  gr.  of  a  sub- 
stance is  found  by  dividing  its  weight  by  its  volume.  Thus,  if  c?,  nj,  r,  repre- 
sent the  sp.  gr.  weight  and  volume  of  aqueous  vapour,  and  rf',  ly',  t?',  the  sp.  gr. 

xWeightand  volume  of  air,  then  c?=_,  and  d'= — .      Hence,  comparing  these  sp. 

V  v' 

gravities,  d  i  d!  :  :  -  \  —',   \i  the  volumes  are  equal,  then  c?  :  d'  :  :  ly  :  w/ ; 
V       1/ 

and  if  the  weights  are  equal,  did':'.    —  ;  —    Consequently,  the  sp.  gravities 

of  substances  which  have  an  equal  volume  are  directly  as  their  weights ;  and 
when  the  weights  are  equal,  the  sp.  gravities  are  inversely  as  the  volumes.  Ac- 
cordingly, if  we  weigh  an  equal  volume  of  any  number  of  substances,  tempera- 
ture and  pressure  being  the  same  in  all,  the  sp.  gr.  of  each  respectively  will  be 
represented  by  its  weight.  Thus,  Gay  Lussac  ascertained  that  if  a  certain 
volume  of  air  at  212°  and  30  Bar.  weigh  1000  grains,  an  equal  volume  of 
aqueous  vapour,  at  the  same  temperature  and  pressure,  will  weigh  625  grains ; 
and,  therefore,  the  sp.  gr.  of  steam  is  625  compared  to  that  of  air  as  1000. 
Atmospheric  air  is  universally  taken  as  a  term  of  comparison  for  the  sp.  gr.  of 
gaseous  substances,  and  pure  water  for  that  of  liquids  and  solids. 

It  admits  of  inquiry  whether  liquids  of  weak  volatility,  such  as  mercury  and 
oil  of  vitriol,  give  off  any  vapour  at  common  temperatures.  An  opinion  has 
prevailed,  that  evaporation  not  only  takes  place  from  the  surface  of  these  and 
similar  liquids  at  all  times,  but  that  vapour  of  exceedingly  weak  tension  is 
emitted  at  common  temperatures  from  all  substances  however  fixed  in  the  fire, 
even  from  the  earths  and  metals,  when  they  are  either  in  a  vacuum,  or  sur- 
rounded by  gaseous  matter.  It  has  accordingly  been  supposed,  that  the  atmos- 
phere contains  diffused  through  it  minute  quantities  of  the  vapours  of  all  the 
bodies  with  which  it  is  in  contact ;  and  this  idea  has  been  made  the  basis  of  a 
theory  of  the  origin  of  meteorites.  But  this  doctrine  has  been  successfully  com- 
bated by  Faraday,  in  his  essay  On  the  Existence  of  a  Limit  to  Vaporization, 
(Phil.  Trans.  1826).  He  has  there  shown  that  in  many  substances  the  forces 
of  gravity  and  cohesion  are  sufficient  to  overpower  elasticity,  and  that  at  ordi- 
nary temperatures  they  give  off  no  vapour  whatever. 

The  presence  of  vapour  has  a  considerable  influence  over  the  bulk  of  gases ; 
and  as  chemists  often  determine  the  quantity  of  gaseous  substances  by  measure, 
it  is  important  to  estimate  the  increase  of  volume  due  to  the  presence  of  mois- 
ture. The  mode  by  which  a  vapour  acts  is  obvious.  When  two  gases,  which 
do  not  act  chemically  on  each  other,  are  intermingled,  each  retains  the  elasticity 
suited  to  its  volume,  exactly  as  if  the  other  gas  were  absent ;  so  that  the  elas- 
ticity of  the  mixture  is  the  sum  of  the  elastic  forces  of  its  ingredients.  The 
same  remark  applies  to  the  mixture  of  gases  and  vapours.  If  a  few  drops  of 
water  are  added  to  a  portion  of  dry  air,  confined  in  a  glass  tube  over  mercury, 
the  air  will  speedily  become  saturated  with  vapour,  and  must  in  consequence  be 
increased  in  bulk.  For  the  elastic  power  of  the  vapour  being  added  to  that  pre- 
viously exerted  by  the  gas  alone,  the  mixture  will  necessarily  exert  a  stronger 

6 


60  HEAT. 

pressure  upon  the  mercury  that  confines  it,  and  will  therefore  occupy  a  greater 
space.  It  is  equally  clear  that  the  degree  of  augmentation  will  depend  on  the 
temperature ;  for  it  is  the  temperature  alone  which  determines  the  elasticity  of 
the  vapour. 

As  the  elasticity  of  vapour  is  not  at  all  affected  by  mere  admixture  with  gases, 
it  is  easy  to  correct  the  fallacy  to  which  its  presence  give  rise,  by  means  of  the 
data  furnished  by  the  experiments  of  Dalton.  The  formula  for  the  correction  is 
thus  deduced.  Let  n  be  the  bulk  of  dry  air  or  other  gas  exp'ressed  in  the  degrees 
of  a  graduated  tube;  p  the  elasticity  of  the  dry  air,  equal  to  the  atmospheric 
pressure  as  measured  by  a  barometer;  n!  Ihe  bulk  of  the  air  when  saturated  with 
watery  vapour,  and  /  the  elasticity  of  that  vapour  (Biot's  Traite  de  Phys.  i. 
303).  Now,  as  the  elasticity  of  a  gas  for  equal  temperatures  is  inversely  as  its 
volume,  it  follows  that  when  the  dry  air  increases  in  bulk  from  n  to  n',  its  elas- 
ticity will  diminish  in  the  ratio  of  n'  to  n.    Hence  its  elasticity  ceases  to  be 

pn  pn 

=/?,  and  is  expressed  by  — 7  ;  ;?  is  then  =—  -\-f;  that  is,  the  elasticity  of  the 

moist  air,  added  to  the  elasticity  of  the  vapour  present,  is  equal  to  the  pressure 
of  the  atmosphere.     From  this  last  equation  are  deduced  the  following  values  : 

pn -{■  fvf  ^=i  pnf  i  pnssspn' — /n' ,•  and  f»  ^^  — — — —»     One  example  will  suf- 

P 
fice  for  showing  the  use  of  this  formula.     Having  100  measures  of  air  saturated 

with  watery  vapour  at  60°,  the  barometer  standing  at  30  inches,  how  many 

measures  would  the  air  occupy  if  quite  dry  1   fi'=100;   p=30;  /=  0524, 

the  tension  of  watery  vapour  at  60°,  according  to  Dalton's  table.*     Hence 

100  X  (30  —  0  524)      100  X  29746      „„  „^      ....       . 

n   — —^ 1  = =98*26,  which    is   the   answer  re- 

30  30 

quired.' 

The  quantity  of  vapour  present  in  the  atmosphere  is  very  variable,  in  conse- 
quence of  the  continual  change  of  temperature  to  which  the  air  is  subject.  But 
even  when  the  temperature  is  the  same,  the  quantity  of  vapour  is  still  found  to 
vary  ;  for  the  qir  is  not  always  in  a  state  of  saturation.  At  one  time  it  is 
excessively  dry,  at  another  it  is  fully  saturated ;  and  at  other  times  it  varies 
between  these  extremes.  This  variable  condition  of  the  atmosphere  as  to 
saturation  is  ascertained  by  the  hygrometer. 

Hygrometers. — A  great  many  hygrometers  have  been  invented  ;  but  they  may 
all  be  referred  to  three  principles.  The  construction  of  the  first  kind  of  hygro- 
meter is  founded  on  the  property  possessed  by  some  substances  of  expanding  in 
a  humid  atmosphere,  owing  to  a  deposition  of  moisture  within  them ;  and  of 
parting  with  it  again  to  a  dry  air,  and  in  consequence  contracting.  Of  these, 
none  is  better  than  the  human  hair,  which  not  only  elongates  freely  from  imbib- 
ing moisture,  but,  by  reason  of  its  elasticity,  recovers  its  original  length  on  dry- 
ing.    The  hygrometer  of  Saussure  is  made  with  this  material. 

\_The  second  kind  of  hygrometer  depends  upon  the  cooling  effect  of  evaporation. 
The  bulb  of  a  thermometer,  covered  with  a  piece  of  silk  or  linen,  is  exposed  to 
a  current  of  air,  or  is  rapidly  swung  round  until  its  temperature  ceases  to  be 
any  further  depressed.  The  reduction  of  its  temperature  below  that  of  the  sur- 
rounding medium,  as  marked  by  an  adjoining  instrument,  furnishes  the  means 
of  computing  the  quantity  of  moisture  in  the  atmosphere.    When  the  air  is 

*  Manchester  Memoirs,  vol.  v. 


HEAT.  51 

saturated  with  moisture  the  wet  bulb  will  undergo  no  change  of  temperature, 
because  in  that  state  there  is  no  evaporation.  But  where  the  air  is  dry,  or  con- 
tains less  than  a  saturating  amount  of  moisture,  a  greater  or  less  evaporation  will 
take  place,  which,  by  robbing  the  thermometer  of  heat  will  continue  to  reduce 
its  temperature  until  the  loss  from  this  cause  becomes  counterbalanced  by  the 
heat  that  flows  in  from  the  warmer  surrounding  medium.  When  this  takes 
place  the  temperature  of  the  wet  bul6  becomes  stationary. 

This  simple  form  of  the  hygrometer  first  used  by  Sir  John  Leslie,  is  called 
the  Wet-bulb  Hygrometer.  With  the  aid  of  proper  formulae  of  computation  it  is 
capable  of  furnishing  the  most  exact  results.] 

The  third  kind  of  hygrometer  is  on  a  principle  entirely  different  from  the  fore- 
going. When  the  air  is  saturated  with  vapour,  and  any  colder  body  is  brought 
into  contact  with  it,  deposition  of  moisture  immediately  takes  place  on  its  sur- 
face. The  degree  indicated  by  the  thermometer  when  dew  fcegins  to  be  deposited, 
is  called  the  dew-point.  If  the  saturation  be  complete,  the  least  diminution  of 
temperature  is  attended  with  the  formation  of  dew  ;  but  if  the  air  is  dry,  a  bpdy 
must  be  several  degrees  colder  before  moisture  is  deposited  on  its  surface;  and 
indeed  the  drier  the  atmosphere,  the  greater  will  be  the  difference  between  its 
temperature  and  the  dew-point.  Attempts  were  made  to  estimate  the  hygrometric 
state  of  the  air  on  this  principle  by  the  Florentine  Academicians,  but  the  first 
accurate  method  was  introduced  by  Le  Roi,  and  since  adopted  by  Dalton.  It 
consists  simply  in  putting  cold  water  into  a  glass  vessel,  the  outside  of  which  is 
carefully  dried,  and  marking  the  temperature  of  the  liquid  at  which  dew  begins 
to  be  deposited  on  the  glass.  The  water  when  necessary  is  cooled  either  by 
means  of  ice  or  a  freezing  mixture.  A  convenient  form  of  apparatus  is  a  small 
cup  made  of  thin  silver,  nicely  gilt  on  the  outside,  capable  of  holding  about 
half  an  ounce  of  water,  and  fitted  into  a  case  of  turned  wood  lined  with  cloth, 
which  serves  as  a  stand  for  the  cup  during  an  observation.  The  water  is  cooled 
by  successively  adding  a  few  grains  of  a  powder  made  of  equal  parts  of  nitre 
and  sal-ammoniac  intimately  mixed,  stirring  with  the  bulb  of  a  small  thermo- 
meter. As  soon  as  dew  is  deposited,  the  temperature  is  noted ;  and  the  first 
observation  is  corrected  by  waiting  until  the  cup  and  its  contents  grow  warmer, 
and  observing  the  temperature  at  which  the  dew  begins  to  disappear.  The  last 
observation  is  the  most  trustworthy.  This  method,  when  deliberately  performed, 
so  that  the  cup,  the  solution,  and  the  thermometer  should  have  time  to  acquire 
the  same  temperature,  is  susceptible  of  great  precision. 

The  hygrometer  of  Daniell,  described  in  his  Meteorological  Essays,  acts  on 
the  same  principle.  It  consists  of  a  cryophorus,  as  described  at  page  49,  but 
modified  somewhat  in  form,  and  containing  ether  instead  of  water.  Within  one 
of  its  balls  is  fixed  a  delicate  thermometer,  the  bulb  of  which  is  partially 
immersed  in  the  ether  so  as  to  indicate  its  temperature,  and  the  other  ball  is 
covered  with  muslin.  When  the  instrument  is  used  the  muslin' is  moistened 
with  ether,  and  the  cold  produced  by  its  evaporation  condenses  the  vapour  within 
the  cryophorus,  and  causes  the  ether  to  evaporate  rapidly  in  the  other  ball.  The 
cold  thus  generated  chills  the  ether  itself  and  the  ball  containing  it ;  and  in  a 
short  time  its  temperature  descends  so  low,  that  dew  is  deposited  on  the  surface 
of  the  glass.  As  soon  as  this  takes  place,  the  temperature  is  observed  by  the 
thermometer. 

The  same  object  is  attained  in  a  still  easier  way  by  means  of  a  contrivance 
described  by  Jones,  of  London,  (Phil.  Trans.  1826;)  and  soon  after  by  Cold- 


52  HEAT. 

Stream,  of  Leith,  (Phil.  Journ.  ix.  155.)  It  consists  of  a  delicate  mercurial 
thermometer,  the  bulb  of  which  is  made  of  thin  black  glass,  and,  excepting 
about  a  fourth  of  its  surface,  is  covered  with  muslin.  On  moistening  the  mus- 
lin with  ether,  the  temperature  of  the  bulb  and  mercury  falls,  and  the  uncovered 
portion  of  the  bulb  is  soon  rendered  dim  by  the  deposition  of  moisture.  The 
temperature  indicated  at  that  instant  by  the  thermometer  is  the  dew-point. 

It  is  desirable  on  some  occasions,  not  merely  to  know  the  hygrometric  condi- 
tion of  air  or  gases,  but  also  to  deprive  them  entirely  of  their  vapour.  This 
may  be  done  to  a  great  extent  by  exposing  them  to  intense  cold  ;  but  the  method 
now  generally  preferred  is  by  bringing  the  moist  gas  in  contact  with  some  sub- 
stance which  has  a  powerful  chemical  attraction  for  water.  Of  these  none  is 
preferable  to  chloride  of  calcium. 

CONSTITl^ION  OF  GASES  WITH  RESPECT  TO  HEAT. 

From  the  experiments  of  Faraday  on  the  liquefaction  of  gaseous  substances, 
gases  may  be  viewed  as  the  vapours  of  extremely  volatile  liquids.  Most  of 
these  liquids,  however,  are  so  volatile,  that  their  boiling  point,  under  the  atmos- 
pheric pressure,  is  lower  than  any  natural  temperature ;  and  hence  they  are 
always  found  in  the  gaseous  state.  By  subjecting  them  to  great  pressure,  their 
elasticity  is  so  far  counteracted  that  they  become  liquid.  But  even  when  thus 
compressed,  a  very  moderate  heat  is  sufficient  to  make  them  boil ;  and  on  the 
removal  of  pressure  they  resume  the  elastic  form,  most  of  them  with  such  vio- 
lence as  to  cause  a  report  like  an  explosion,  and  others  with  the  appearance  of 
brisk  ebullition.  Intense  cold  is  produced  at  the  same  time,  in  consequence  of 
their  heat  passing  from  a  sensible  to  an  insensible  state. 

The  process  for  liquefying  gases,  as  first  employed  by  Faraday,  consists  in 
exposing  them,  as  they  are  evolved,  to  the  pressure  of  their  own  atmosphere. 
The  materials  for  producing  the  gas  are  put  into  a  strong  glass  tube,  which  is 

afterwards  sealed  hermetically,  and  bent  in  the 
middle,  as  represented  by  the  figure.  The  gas 
is  generated,  if  necessary,  by  the  application  of 
heat;  and  when  the  pressure  becomes  suffi- 
ciently great,  the  liquid  is  formed  and  collects  in  the  free  end  of  the  tube,  which 
is  kept  cool  to  facilitate  the  condensation.  Most  of  these  experiments  are 
attended  with  danger  from  the  bursting  of  the  tubes,  against  which  the  operator 
must  protect  himself  by  the  use  of  a  mask. 

The  pressure  required  to  liquefy  gases  is  very  variable,  as  will  appear  from 
the  following  table  of  the  results  obtained  by  Faraday  : 

Sulphurous  acid  gas  ....  2    atmospheres  at  45° 

Sulphuretted  hydrogen  gas      ...  17  "  60" 

Carbonic  acid  gas 36  "  32* 

Chlorine  gas             4  "  60" 

Nitrous  oxide  gas    .....  50  **  46" 

Cyanogen  gas 3-6  "  45° 

Ammoniacal  gas 6-5  '*  50° 

Muriatic  acid  gas 40  **  60° 

Additional  light  has  been  thrown  on  the  nature  of  gases  by  M.  Thilorier,  who 
has  succeeded  in  obtaining  carbonic  acid  gas  in  a  solid  state  (Ann.  de  Ch.  et 
Ph.  Ix.  431),    It  is  procured  by  directing  a  jet  of  the  liquid  carbonic  acid  into 


HEAT.  53 

a  small  glass  phial,  which  is  rapidly  filled  with  solid  carbonic  acid  in  the  form 
of  a  white  flocculent  powder.  The  solidification  is  evidently  produced  by  the  • 
cold  occasioned  by  the  sudden  transition  of  a  liquid  into  a  gas,  in  which  state 
it  occupies  a  space  400  times  greater  than  its  original  volume.  The  degree 
of  cold  thus  produced  is  estimated  by  Thijorier  at — 148°,  at  which  temperature 
carbonic  acid  appears  to  be  almost  deprived  of  its  elastic  force  ;  fon  the  solid, 
exposed  to  the  ordinary  atmospheric  pressure  and  temperature  evaporates  slowly 
and  quietly,  and  is  gradually  converted  into  carbonic  acid  gas. 

[Recently  M.  Natterer  has  succeeded  in  liquefying  nitrous  oxide  gas  by  com- 
pressing it  with  a  small  iron  pump  in  a  tube  of  wrought  iron,  at  a  pressure  of  50 
atmospheres.  In  this  way  he  obtained  about  half  a  pint  of  a  clear^liquid  of  a 
sweet  taste  occupying  about  4^^th  of  the  volume  of  the  original  gas,  and  which 
could  be  kept  several  hours  exposed  to  the  air.  By  uniting  mechanical  pressure 
with  the  intense  cold  produced  by  Thilorier's  bath  of  solid  carbonic  acid  and 
ether,  under  the  exhausted  receiver,  Faraday  has  very  lately  obtained  many  new 
and  striking  results.     Among  these  the  following  may  be  mentioned  : 

Olejiant  gas  became  a  colourless  transparent  liquid  but  did  not  solidify. 

Hydriodic  add  was  obtained,  both  in  the  solid  and  liquid  states,  the  former 
greatly  resembling  ice. 

Hydrohromic  acid  gave  like  results. 

Sulphuretted  Hydrogen  became  a  white  transparent  crystalline  mass,  resem- 
bling solid  nitrate  of  ammonia  or  camphor. 

Carbonic  acid,  in  passing  from  the  liquid  to  the  solid  state,  without  being  dis- 
persed as  in  Thilorier's  experiment  in  the  form  of  snow,  concretes  into  a  solid, 
transparent  as  crystal.  In  this  condition  its  vapour  exerts  a  pressure  of  only  six 
atmospheres. 

Nitrous  Oxide,  solidified  by  exposing  its  liquid  to  the  cold  .bath,  was  a  beauti- 
ful transparent  crystalline  body,  so  little  volatile  that  in  this  state  the  pressure 
of  its  vapour  did  not  amount  to  one  atmosphere.  The  cold  produced  by  the 
evaporation  of  the  liquefied  gas  is  far  greater  even  than  that  of  the  baths  of  solid 
carbonic  acid  and  ether.  This  bath,  which  instantly  freezes  mercury,  imme- 
diately caused  the  liquid  nitrous  oxide  to  boil  violently. 

Cyanogen  readily  became  solid,  as  previously  shown  by  Bussy. 

Ammonia,  perfectly  pure  and  dry,  was  converted  into  a  transparent,  crystal- 
line, white  substance,  heavier  than  liquid  ammonia,  and  owing  to  its  volatility, 
at  this  temperature,  diffusing  very  little  vapour.     (Ann.  de  Chim.  Jan.  1845.)] 

SOURCES  OF  HEAT. 

[The  sources  of  heat  may  be  reduced  to  six  :  1.  The  sun.  2.  The  interior 
of  the  earth.  3.  Electricity.  4.  Vital  action.  5.  Mechanical  action.  6.  Che- 
mical action.  These,  with  the  exception  of  the  second  and  two  last,  will  be 
more  conveniently  considered  in  other  parts  of  the  work. 

Internal  Heat  of  the  Globe. — ^The  impressions  of  temperature  due  to  the  sun's 
rays,  upon  the  earth's  surface,  are  felt  less  and  less  as  we  descend  to  greater 
depths,  and  at  a  moderate  distance,  varying  with  the  nature  of  the  superficial 
strata,  entirely  disappear.  The  depth  of  the  layer  thus  beyond  the  reach  of  the 
influences  from  above,  and  which  is  called  the  invariable  stratum,  ranges  from 
50  to  100  feet.  Beneath  this  the  temperature  is  seen  to  be  progressively  higher 
as  we  descend,  the  rate  of  its  increase  being  1°  for  from  40  to  50  feet.     Sup- 


54  HEAT. 

posing  the  law  continued,  at  the  depth  of  two  miles,  water  would  be  converted 
Into  steam  ;  at  four  miles,  tin  and  bismuth  would  be  melted  ;  at  five,  lead;  and 
at  thirty  miles  the  temperature  would  be  high  enough  to  melt  iron  and  almost 
all  kinds  of  rocky  material.  We  may  hence  infer  that  the  great  mass  of  our 
globe  is  in  a  state  of  fluidity  from  he^^t,  and  that  its  solid  portion  forms  but  a 
thin  covering  or  crust  around  the  molten  matter  of  the  interior. 

The  chemical  and  mechanical  actions  concerned  in  earthquakes  and  volcanoes, 
have,  with  strong  reason,  been  traced  to  this  cause,  and  form  an  interesting 
branch  of  chemical  and  physical  inquiry,  which,  however,  cannot  properly  find 
a  place  in  this  work.] 

The  mechanical  method  of  exciting  heat  is  by  friction  and  percussion.  When 
parts  of  heavy  machinery  rub  against  one  another,  the  heat  excited,  if  the  parts 
of  contact  are  not  well  greased,  is  sufficient  for  kindling  wood.  The  axle-trees 
of  carriages  have  been  burned  from  this  cause,  and  the  sides  of  ships  are  said  to 
have  taken  fire  by  the  rapid  descent  of  the  cable.  Count  Romford  has  given  an 
interesting  account  of  the  heat  excited  in  boring  cannon,  which  was  so  abundant 
as  10  heat  a  considerable  quantity  of  water  to  its  boiling  point.  It  appeared 
from  his  experiments  that  a  body  never  ceases  to  give  out  heat  by  friction,  how- 
ever long  the  operation  may  be  continued  ;  and  he  inferred  from  this  observation 
that  heat  cannot  be  a  material  substance,  but  is  merely  a  property  of  matter. 
Pictet  observed  that  solids  alone  produce  heat  by  friction,  no  elevation  of  tem- 
perature taking  place  from  the  mere  agitation  of  fluids  with  one  another.  He 
found  that  the  heat  excited  by  friction  is  not  in  proportion  to  the  hardness  and 
elasticity  of  the  bodies  employed.  On  the  contrary,  a  piece  of  brass  rubbed 
with  a  piece  of  cedar  wood  produced  more  heat  than  when  rubbed  with  another 
piece  of  metal ;  and  the  heat  was  still  greater  when  two  pieces  of  wood  were 
employed. 

[^Chemical  action. — Referring  to  a  future  section  for  an  account  of  the  agency 
of  combustion,  as  a  source  of  heat,  we  will  here  restrict  ourselves  to  the  effects 
of  ordinary  chemical  combination  in  developing  heat. 

It  has  long  been  known  that  in  nearly  every  case  of  active  chemical  union, 
between  two  or  more  substances,  a  rise  of  temperature  is  produced.  But,  until 
recently,  no  satisfactory  attempt  has  been  made  to  discover  the  relation  between 
the  amount  of  heat  evolved  and  the  proportion  in  which  the  bodies  combine. 
The  late  researches  of  Hess,  Graham,  ^brea  and  others,  on  this  subject,  have 
disclosed  many  interesting  facts,  which,  although  as  yet  but  partially  reducible 
to  simple  laws,  promise,  when  further  extended,  to  disclose  definite  relations  in 
the  heat  of  combination. 

Thus  Abrea  has  found  that  in  combining  anhydrous  sulphuric  acid  with  suc- 
cessive chemical  equivalents  of  water,  the  quantities  of  heat  successively  evolved 
are  related  nearly  in  the  proportion  of  the  following  series  of  numbers  : 

Equivalents  of  water  1st  2d  3d  4th  6th  6th 

Heat  evolved  1  Jrd  gth         T3th         Tff«h         s^^th 

From  numerous  experiments  on  the  heat  evolved  in  the  combination  of  acids 
with  baftes,  Hess  has  inferred  the  following  law  :  When  a  diluted  acid  combines 
with  a  base  the  amount  of  heat  set  free  by  the  union,  when  added  to  that  libe- 
rated during  the  dilution  of  the  acid  in  the  first  instance,  is  exactly  equal  to  that 
evolved  by  the  combination  of  the  anhydrous  acid  with  the  base;  in  other  words 


LIGHT.  55 


the  aggregate  of  heat  evolved  in  such  cases  is  a  constant  quantity.     With  sul- 
phuric acid  and  ammonia  the  following  were  his  results  : 


Sulphuric  Acid 

First  dilution 
Second  dilution 


With  Ammonia. 

With  Water. 

Sum. 

595-8 

695-8 

518-9 

77-8 

596-7 

480-5 

116-7 

597-2] 

SECTION 

II. 

LIGHT. 

Optics,  from  on-toiiat,  I  see^  is  the  science  which  treats  of  light  and  vision. 
On  the  nature  of  light  two  rival  theories  exist,  the  undulatory  and  corpuscular. 
Prior  to  and  about  the  time  of  Newton's  celebrated  analysis  of  solar  light  in 
1672,  Descartes,  Hooke,  Huygens,  and  others,  had  entertained  the  former;  but 
Newton,  in  adopting  the  latter,  led  to  its  almost  general  reception.  He  con- 
sidered light  to  consist  of  inconceivably  minute  particles,  too  subtile  to  exhibit 
the  common  properties  of  matter,  though  really  material,  which  emanate  from 
luminous  bodies,  such  ^s  the  sun,  the  fixed  stars,  and  incandescent  substances, 
travel  with  immense  velocity,  and  excite  the  sensation  of  light  by  passing  bodily 
through  the  substance  of  the  eye,  and  striking  against  the  expanded  nerve  of 
vision,  the  retina.  This  theory,  with  which  the  language  of  optics  has  become 
identified,  prevailed  with  almost  no  opposition  from  the  time  of  Newton  till 
1801,  when  the  undulatory  theory  was  revived  and  supported  with  great  ability 
by  Young  (Phil.  Trans.).  By  the  researches  of  others,,  the  testimony  in  favour 
of  this  doctrine  gradually  gained  ground,  and  at  present  it  is  all  but  generally 
adopted.  While  some  phenomena,  as  the  absorption  and  refraction  of  light,  are 
even  yet  obscurely  explained  by  either  theory,  others,  especially  the  phenomena 
of  interference  and  polarized  light,  are  wholly  inexplicable  by  the  corpuscular, 
and  receive  a  most  lucid  explanation  by  the  undulatory  theory.  On  this  ground 
the  former  is  considered  untenable,  and  the  latter  alone  suitable  to  the  present 
condition  of  science.  But  to  enter  at  length  into  this  argument  would  be  so 
foreign  to  the  design  of  this  treatise,  that  the  reader  is  referred  to  Pouillet's 
EUmens  de  Physique,  Young's  Essays,  Airy's  Tracts,  2nd  edition,  and  Her- 
schel's  article  on  Light  in  the  Encyclopedia  Metropolitana. 

I  shall  now,  however,  state  the  laws  of  light  in  the  ordinary  language,  which 
is  founded  on  the  corpuscular  theory,  and  analogous  to  that  which  has  been 
employed  in  treating  of  heat. 

Diffusion  of  Light, — Light  emanates  from  every  visible  point  of  a  luminous 
object,  and  is  equally  distributed  on  all  sides  if  not  intercepted,  diverging  like 
radii  drawn  from  the  centre  to  the  circumference  of  a  circle.  Thus,  if  a  single 
luminous  point  were  placed  in  the  centre  of  a  hollow  sphere,  every  point  of  its 
concavity  would  be  illuminated,  and  equal  areas  would  receive  equal  quantities 
of  light.  The  smallest  portion  of  light  which  can  be  separated  from  contiguous 
portion  is  called  a  ray  of  light.     Each  ray,  when  not  interrupted  in  its  course, 


56  LIGHT. 

and  while  it  remains  in  the  same  medium,  moves  in  a  straight  line ;  as  is 
obvious  by  the  appearance  of  shadows  cast  by  the  side  of  a  house,  or  of  a  sun- 
beam admitted  through  a  small  aperture  into  a  dark  room.  Owing  to  these 
modes  of  distribution,  it  follows  that  the  quantity  of  light  which  falls  upon  a 
given  surface  decreases  as  the  square  of  its  distance  from  the  luminous  object 
increases,  the  same  law  which  regulates  the  heating  power  of  a  hot  body. 
(Page  12.) 

The  passage  of  light  is  progressive,  time  being  required  for  its  motion  from 
one  place  to  another.  By  astronomical  observations  it  is  found  that  light  travels 
at  the  rate  of  nearly  195,000  miles  in  a  second  of  time,  and  would  require  about 
eight  minutes  to  pass  from  the  ^un  to  the  earth.  Owing  to  this  prodigious 
velocity,  the  light  caused  by  the  firing  of  a  cannon  or  a  sky-rocket  is  seen  by 
different  spectators  at  the  same  instant,  whatever  may  be  their  respective  dis- 
tances from  the  rocket,  the  time  required  for  light  to  travel  100  or  1000  miles 
being  inappreciable  to  our  senses. 

When  light  falls  upon  any  body,  it  may,  like  radiant  heat  (page  12),  dispose 
of  itself  in  three  different  ways,  being  reflected,  refracted  or  absorbed.  The  phe- 
nomena connected  with  the  two  former  modes  of  distribution  I  shall  proceed  to 
consider  in  succession ;  while  those  of  absorbed  light  will  be  included  under 
the  head  of  Decomposition  of  Light. 

REFLECTION  OF  LIGHT. 

Light  may  be  reflected  by  all  media,  whether  solid,  liquid,  or  gaseous,  when 
it  passes  from  one  medium  into  another  of  a  different  nature  or  density;  but 
there  is  great  difference  in  the  power  of  reflection.  Bright  metallic  surfaces, 
such  as  polished  brass  and  silver,  or  clean  mercury,  reflect  nearly  all  the  rays 
which  fall  upon  them ;  while  those  which  are  dull  and  rough  reflect  but  few. 
The  reflection  of  light,  like  that  of  heat,  takes  place  at  the  surface  of  bodies, 
and  appears  influenced  rather  by  the  condition  of  the  surf^e  than  by  the  nature 
of  the  reflecting  body.  The  direction  of  the  reflected  ray,  whatever  may  be  the 
nature  or  figure  of  the  reflecting  surface,  is  regulated  by  these  two  laws. 

I.  The  incident  and  reflected  rays  always  lie  in  the  same  plane,  which  plane 
is  perpendicular  to  the  reflecting  surface. 

II.  The  incident  and  reflected  rays  always  form  equal  angles  with  the  reflect- 
ing surface ;  or,  what  amounts  to  the  same,  the  angle  of  incidence  is  always 
equal  to  the  angle  of  reflection. 

Hence,  if  the  reflecting  surface  be  a  plane  mirror,  the  direction  of  the  reflected 
ray,  being  known,  gives  us  that  of  the  incident  ray  ;  and  vice  versa. 

These  laws  apply  equally  to  curved  reflecting  surfaces,  whether  convex  or 
concave.  As  a  curve  may  be  viewed  as  a  polygon  with  very  short  sides,  it  fol- 
lows, from  obvious  mathematical  considerations,  that  parallel  rays,  falling  on  a 
convex  mirror,  are  scattered  or  made  to  diverge ;  while  if  they  fall  on  a  concave 
mirror  they  are  concentrated,  or  made  to  converge  into  its  focus.  On  the  same 
principle  it  is  plain  that  divergent  rays,  falling  on  a  convex  surface,  are  rendered 
parallel  by  reflection;  and  that  rays,  diverging  from  the  focus  of  a  concave  mir- 
ror on  its  surface,  are  also  reflected  in  parallel  lines. 

When  the  concave  mirror  is  spherical,  the  parallel  rays  falling  on  it  are  not 
strictly  collected  into  one  point  or  focus;  this  only  happens  when  the  mirror  is 
accurately  parabolic.     Hence,  if  a  luminous  body  be  placed  in  the  focus  of  one 


LIGHT.  57 

parabolic  reflector,  the  rays  which  it  gives  off  are  all  collected  in  the  focus  of  a 
second  parabolic  reflector  placed  opposite  to  the  first. 

On  these  principles  are  constructed  the  reflecting  telescope  and  the  reflecting 
microscope;  but  this  treatise  is  not  the  place  for  a  description  of  these  useful 
instruments. 

REFRACTION  OF  LIGHT. 

Light  traverses  the  same  transparent  medium,  such  as  air,  water,  or  glass,  in 
a  straight  line,  provided  no  reflection  occurs,  knd  there  is  no  change  of  density ; 
but  when  it  passes  from  one  medium  into  another,  or  from  one  part  of  the  same 
medium  into  another  of  a  different  density,  a  change  of  direction  always  ensues 
at  the  plane  of  junction  of  the  media,  ex- 
cept when  the  ray  is  perpendicular  to  that  '^S* 
plane.  For  instance,  let  ab  a'b',  fig.  1,  repre- 
sent a  vertical  section  of  a  vessel  full  of  water,  ^^^  .^^ 
and  pp'  the  perpendicular  to  the  surface  of  the  ^-  '" 
water  at  the  point  c.  Should  a  ray  of  light 
enter  the  water  perpendicularly  to  its  surface, 
as  in  the  line  of  pc,  it  will  continue  on  its 


P 


B' 


course  to  p'  without  deviation;   but  if  it  de-  "^  P^GE : 

scend  obliquely,  as  in  the  direction  of  ic,  it 

will  suffer  a  bend  at  c,  and  proceed  to  e,  instead  of  advancing  along  the  dotted 
line  to  F.  Conversely,  were  a  ray  of  light  to  emanate  from  e  and  emerge  at  c, 
it  would  not  advance  to  e,  but  take  the  direction  of  ci.  By  comparing  the  direc- 
tion of  the  refracted  ray  in  these  two  cases  in  relation  to  the  vertical  pp',  it  will 
be  seen  that  the  ray  approaches  the  perpendicular  in  entering  from  air  into  water, 
and  recedes  from  it  in  passing  out  of  water  into  air.  The  same  remark  applies 
to  the  passage  of  light  from  or  into  air  into  or  out  of  solid  or  liquid  media  in 
general.  "^ 

Bodies  differ  in  their  power  of  refracting  light.  In  general,  the  denser  a 
substance  is,  the  greater  is  the  deviation  which  it  produces.  If  in  fig.  1  sul- 
phuric acid  were  mixed  with  the  water,  the  ray  ic  would  be  refracted  to  some 
point  between  e  and  g;  and  if  a  solid  cake  of  glass  were  substituted  for  that 
liquid,  the  refracted  ray  would  be  bent  down  to  cg.  But  this  is  far  from  uni- 
versal : — ^alcohol,  ether,  and  olive  oil,  which  are  lighter  than  water,  have  a  higher 
refractive  power.  Observation  has  shown  it  to  be  a  law,  to  which  no  exception 
is  yet  known,  that  oils  and  other  highly  inflammable  bodies,  such  as  hydrogen, 
diamond,  phosphorus,  sulphur,  amber,  olive  oil,  and  camphor,  have  a  refractive 
power  which  is  from  two  to  seven  times  greater  than  that  of  incombustible  sub- 
stances of  equal  density.  But  whatever  may  be  the  refractive  power  of  bodies 
in  relation  to  each  other,  refraction  is  always  governed  by  the  two  following 
laws,  discovered  in  1618  by  Snell,  though  usually  ascribed  to  Descartes. 

1.  The  direction  of  the  incident  and  refracted  ray  is  always  in  a  plane  per- 
pendicular to  the  surface  common  to  the  media. 

2.  The  sine  of  the  angle  of  incidence  and  the  sine  of  the  angle  of  refraction 
are  in  a  constant  relation  for  the  same  media. 

The  sine  of  the  angle  of  refraction  being  taken  =  1,  the  sines  of  the  angles 
of  incidence  in  different  substances  may  thus  be  referred  to  a  common  measure 
or  unit  of  comparison.     In  common  flint  glass  the  ratio  is  nearly  as  TG  to  1  ; 


56 


LIGHT. 


in  water,  as  1-336  to  1.  The  numbers  representing  the  sines  of  the  angles  of 
incidence  are  called  the  indices  of  refratiion,  and  indicate  the  degree  of  refrac- 
tive power.  Thus,  the  index  of  refraction  of  flint  glass  is  1'6;  that  of  water, 
1-336  ;  that  of  the  diamond,  2'755. 

Subjoined  is  a  table  of  the  refractive  indices  of  gases,  that  of  a  vacuum  being 
unity. 


Name  of  Gas. 

Ref.  Index. 

Name  of  Gas. 

Ref.  Index 

Oxygen       .        .        .        . 

1-000272 

Carbonic  Oxide  . 

1-000340 

Hydrogen  .        .        .        . 

1-000138 

Carbonic  Acid    . 

1-000449 

Nitrogen    . 

1.000300 

Hydrochloric  Acid     . 

1-000449 

Chlorine     .        .        ,        , 

1-000772 

Ammonia  . 

1-000385 

Protoxide  of  Nitrogen 

1-000503 

Cyanogen  .        . 

1-000834 

Binoxide  of  Nitrogen 

1-000303 

Hydrocyanic  Acid      . 

1000451 

defiant  Gas       .        .        . 

1-000678 

Sulphurous  Acid 

1000665 

Marsh  Gas 

1-000443 

Hydrosulphuric  Acid 

1-000644 

Ether  Vapour     , 

1-001530 

Bisulphuret  of  Carbon  Vapour    1-001500 

In  studying  the  influence  of  curved  media  on  light  on  the  same  principles  as 
have  been  applied  to  reflection  by  curved  mirrors,  it  is  found  that  convex  lenses 
act  like  concave  mirrors,  and  collect  the  refracted  rays  into  a  focus  ;  while  con- 
cave lenses,  like  convex  mirrors,  cause  the  rays  to  diverge.  The  properties  of 
convex  lenses  are,  therefore,  extensively  applied  in  the  construction  of  the  re- 
fracting telescope,  which  is  the  kind  most  commonly  employed,  and  of  the 
refracting  microscope. 

A  convex  lefts  fitted  into  the  wall  of  a  darkened  chamber  constitutes  the 
arrangement  of  a  camera  obscura,  the  inverted  images  of  external  objects  being 
received  on  a  disk  of  paper  or  a  white  board.  In  the  simple  telescope  the  lens 
is  placed  at  the  extremity  of  a  tube  of  suish  length  that  the  image  may  be  formed 
within  the  tube,  and  the  observer  looks  from  the  other  end  at  the  image  formed 
in  the  air.  The  eye  acts  on  the  Same  principle.  Luminous  rays  entering  the 
transparent  parts  of  the  eye  are  refracted  by  the  cornea  and  crystalline  lens,  and 
are  brought  into  a  focus  at  the  bottom  of  the  eye,  an  inverted  image  of  external 
objects  being  formed  upon  the  retina  as  on  the  table  of  a  camera  obscura.  For 
distinct  vision  it  is  necessary  that  this  image  should  be  formed  exactly  on  the 
retina.  Hence,  were  the  eye  an  ordinary  lens,  having  an  invariable  focus,  our 
range  of  vision  would  be  very  narrow ;  an  eye  fitted  for  seeing  at  a  distance 
would  be  useless  for  near  objects ;  and  persons  who  could  see  near  objects 
■would  be  blind  to  remote  ones.  Two  rays  emanating  from  a  distant  point  cannot 
both  fall  upon  so  small  an  object  as  the  eye,  unless  they  are  nearly  parallel ;  for 
if  they  diverged  by  even  a  very  small  angle,  they  would  before  reaching  the 
eye  separate  by  an  interval  exceeding  the  diameter  of  the  cornea.  On  the  con- 
trary, rays  in  rapid  divergence  may  enter  the  eye  provided  the  point  from  which 
they  emanate  be  close  to  it;  and  the  nearer  the  object,  the  more  divergent  the 
rays  which  enter.  When,  therefore,  we  observe  a  distant  landscape,  then  suc- 
cessively notice  nearer  and  nearer  objects,  and  lastly  cast  the  eyes  upon  the 
page  of  a  book  only  six  inches  distant,  we  receive  rays  coming  from  a  multitude 
of  different  objects,  each  set  of  rays  having  its  own  peculiar  divergence,  and 
requiring  a  separate  focus  ;  and  yet,  so  wonderful  is  the  adjusting  power  of  the 
eye,  a  single  minute  suflices  for  distinctly  seeing  all  the  objects  so  beheld, 
without  the  consciousness  of  an  eflfort. 


LIGHT.  59 

The  adjustment  of  the  eye  for  different  distances  appears  to  depend  on  a 
power  of  increasing  or  decreasing  tiie  distance  between  the  posterior  part  of 
the  eye  and  the  lens ;  though  the  mechanism  by  which  this  is  accomplished  is 
unknown.  Some  ascribe  it  to  a  change  in  the  figure  of  the  whole  eye-ball,  pro- 
duced by  the  muscles  which  move  the  eye;  but  Brewster,  I  think  with  better 
reason,  considers  the  position  of  the  lens  to  be  varied  by  the  same  contractile 
tissue  which  determines  the  movements  of  the  iris  and  the  size  of  the  pupil. 
To  this  adjusting  power,  however,  there  is  a  limit.*  The  distance  at  which 
most  persons  see  small  objects  distinctly  is  about  six  inches :  at  shorter  dis- 
tances the  rays  are  so  divergent,  that  their  focal  point  falls  behind  the  retina, 
and  indistinct  vision  is  the  consequence.  Persons  called  long-sighted  are  unable 
to  see  near  objects  distinctly,  owing  to  a  weak  refracting  power  of  the  eye,  due 
to  deficient  convexity  or  density  in  the  humours  of  the  eye.  This  is  the 
infirmity  of  advancing  life,  and  is  remedied  by  convex  glasses,  which  cause 
diverging  rays  to  be  parallel  or  slightly  convergent.  In  short-sighted  persons 
the  refractive  power,  either  from  undue  convexity  or  undue  density  of  the  cornea 
and  lens,  is  so  powerful,  that  all  rays  which  do  not  diverge  rapidly  are  brought 
to  a  focus  before  they  reach  the  retina.  Youth  is  the  period  most  obnoxious  to 
this  imperfection,  and  assistance  is  derived  from  a  concave  glass,  which  causes 
parallel  rays  to  diverge,  and  thereby  counteracts  the  refracting  influence  of 
the  eye. 

Since  the  rays  which  fall  on  a  convex  lens  from  any  object  are  divergent,  and 
are  collected  into  a  focus  behind  the  lens,  it  follows  that  the  image  there  formed 
must  be  inverted,  the  rays  from  the  top  of  the  object  forming  the  lower  part,  in 
point  of  position  of  the  image.  Yet  the  eye  sees  objects  erect.  This  remarkable 
fact  has  not  yet  been  satisfactorily  explained.  It  has  been  supposed  by  some 
that  in  infancy  we  actually  see  objects  inverted,  and  only  discover  that  they  are 
not  so  by  the  correction  derived  from  experience ;  but  this  fallacy  has  been 
fully  corrected  by  observation  on  persons  born  blind,  who  first  obtained  the 
power  of  vision  when  of  an  age  to  describe  what  they  saw. 

Double  Refraction. — If  on  a  piece  of  paper  with  a  black  line  on  its  surface  we 
place  a  rhombohedron  of  Iceland-spar,  and  then  look  at  the  line  through  the 
crystal,  it  will  be  found  that  in  a  certain  position  the  line  appears  single  as 
when  seen  through  water  or  glass ;  but  in  other  positions  of  the  crystal  two 
lines  are  visible  parallel  to  each  other,  and  separated  by  a  distinct  interval.  The 
light  in  passing  through  the  crystal  is  divided  into  two  portions,  one  of  which 
obeys  the  laws  of  refraction  already  explained  (page  52)  ;  whereas  the  other 
portion  proceeds  in  a  wholly  different  direction,  and  hence  gives  the  appearance 
of  two  objects  instead  of  one.  The  former  is  termed  the  ordinary^  the  latter  the 
extraordinary  ray.  This  phenomenon  is  known  by  the  name  of  double  refraction, 
and  has  been  witnessed  in  many  crystallized  substances,  as  in  minerals  and 
artificial  salts. 

Light  transmitted  through  Iceland-spar  or  other  doubly  refracting  substances, 
is  found  to  have  suffered  a  remarkable  change.     In  this  state  it  is  distinguished 

*  A  different  explanation  has  been  very  lately  suggested  by  Prof.  Forbes.  The  lens  being 
composed  of  a  central  nucleus  of  comparatively  solid  matter,  and  of  soft  gelatinous  sub- 
stance  towards  the  margin,  he  conceives  that  by  the  combined  action  of  the  muscles  of  the 
eye  pressing  on  the  outside,  and  communicating  tension  to  the  contents  of  the  globe,  the 
borders  of  the  lens  are  pressed  in  towards  the  axis  and  its  whole  form  is  rendered  more 
nearly  globular.    This  would  of  course  diminish  the  focal  distance.  (Comp.  Rend.,  184'4.)  R. 


i89  LIGHT. 

from  common  light  by  the  cirqumstance,  that  when  it  falls  upon  a  plate  of  glass 
at  an  angle  of  56°  1 1',  it  is  almost  completely  reflected  in  one  position  of  the 
glass,  and  is  hardly  reflected  at  all  in  another:  if  reflected  when  the  plane  of 
reflection  is  vertical,  no  reflection  ensues  when  the  reflecting  plane  is  horizontal, 
the  incident  angle  being  maintained  at  56°  11'.  This  curious  property,  so  dif- 
ferent from  common  light,  has  been  theoretically  ascribed  to  a  kind  of  polarity 
of  such  sort,  that  each  side  of  a  ray  of  light  is  thought  to  have  a  character  dif- 
ferent from  the  two  adjacent  sides  at  right  angles  to  it ;  and  hence  the  origin  of 
the  term  polarized  light,  by  which  this  property  is  distinguished.  Light  is 
polarized  by  reflection  from  many  substances,  such  as  glass,  water,  air,  ebony, 
mother-of-pearl,  and  many  crystallized  substances,  provided  the  light  is  incident 
at  a  certain  angle  peculiar  to  each  surface,  and  which  is  called  the  polarizing 
angle.  Thus,  the  polarizing  angle  for  glass  is  56°  11',  and  for  water  53°  14'; 
that  is  common  light  reflected  by  glass  and  water  at  the  angles  stated  will  be 
polarized. 

The  phenomena  of  double  refraction  and  polarized  light  constitute  a  depart- 
ment of  optics  of  great  and  increasing  interest;  but  it  is  too  remote  from  the 
pursuits  of  a  chemical  student  to  be  treated  of  at  length  in  this  work.  Those 
interested  in  such  studies  will  find  an  excellent  guide  in  Brewster's  Treatise  on 
Optics  in  the  Cabinet  Cyclopedia. 


DECOMPOSITION  OF  LIGHT. 

The  analysis  of  light  may  be  eflfected  either  by  refraction  or  absorption. 
Newton,  who  discovered  the  compound  nature  of  solar  light  eff*ected  its  decom- 
position by  refraction,  employing  a  solid  piece  of  glass  bounded  by  three  plane 
surfaces,  well  known  under  the  ndme  of  the  prism.  His  mode  of  operating 
consisted  in  admitting  a  ray  of  light  ig,  fig.  2,  into  a  dark  chamber  through  a 
window-shutter  def,  and  interposing  the  prism  acb,  so  that  the  ray  should  pass 

Fig.  2. 


Violet. 

Indigo. 

Blue. 

Green. 

Yellow. 

Orange. 

Red. 


obliquely  through  two  surfaces,  and  be  refracted  by  both.  On  receivino-  the 
refracted  ray  upon  a  piece  of  white  paper  lm,  there  appeared,  instead  of  a  spot 
of  white  light,  an  oblong  coloured  surface  composed  of  seven  diff'erent  tints, 
called  the  prismatic  or  solar  spectrum.  On  subjecting  each  of  these  colours  to 
refraction  no  further  separation  was  accomplished  ;  but  on  causing  the  ra)W 
separated  by  one  prism  to  pass  through  a  second  of  the  same  power  and  in  an 
inverted  position  cea,  the  seven  colours  disappeared,  and  a  spot  of  white  light 
appeared  at  h,  in  the  very  position  which   it  would   have  occupied  had   both 


LIGHT.  61 

prisms  been  absent.  From  such  and  similar  experiments  Newton  inferred  that 
white  light  is  a  mixture  of  seven  colorific  rays — red,  orange,  yellow,  green,  blue, 
indigo,  and  violet ;  and  that  the  separation  of  these  primary  or  simple  rays 
depended  on  an  original  difference  of  refrangibility,  violet  being  the  most  refran- 
gible and  red  the  least  so. 

[The  recent  experiments  of  Herschel  have  disclosed  the  existence,  beyond  the 
limit  of  the  violet  space,  of  other  rays  still  more  refrangible,  which  from  their 
colour,  he  proposes  to  call  Lavender  rays.  That  these  are  distinct  from  the 
violet  light,  is  proved  by  their  retaining  their  tint  uilaltered  after  being  concen- 
trated by  a  lens.] 

Though  a  prism  is  the  most  convenient  instrument  for  decomposing  light,  the 
separation  of  the  coloured  rays  is  more  or  less  effected  by  refracting  media  in 
general.  Lenses,  accordingly,  disperse  the  colorific  rays  at  the  same  time  that 
they  refract  them ;  and  this  effect  constitutes  one  of  the  greatest  difficulties  in 
the  construction  of  telescopes,  in  so  much  as  the  separation  or  dispersion^  as  it 
is  termed,  of  these  rays  diminishes  the  distinctness  of  the  image.  The  combi- 
nations by  which  the  defect  is  remedied  are  called  achromatic. 

Newton's  analysis  of  light  led  him  to  explain  the  origin  of  the  colours  of 
natural  objects.  Of  opaque  bodies  those  are  black  which  absorb  all  the  light 
that  falls  upon  them,  and  those  white  which  reflect  it  unchanged  :  the  various 
combinations  of  tints  are  the  consequence  of  certain  rays  being  absorbed,  while 
those  alone  whose  intermixture  produces  the  observed  colour  are  reflected.  The 
same  applies  to  transparent  media,  which  are  colourless  like  pure  water  when 
the  light  passes  through  unchanged,  but  are  coloured  when  some  rays  are  trans- 
mitted and  others  absorbed.  This  tibsorption  of  certain  rays  by  coloured  media, 
such  as  glass  of  different  tints,  affords  another  mode  of  decomposing  light ;  and 
Brewster  has  ingeniously  applied  it  to  analyse  the  seven  colours  which  com- 
pose the  prismatic  spectrum.  He  has  proved  by  such  experiments,  what  has 
been  maintained  before,  that  the  seven  colours  of  the  spectrum  are  occasioned 
not  by  seven,  but  by  three  simple  or  primary  rays;  namely,  the  red,  yellow, 
and  blue.  These  rays  are  concentrated  in  those  parts  of  the  spectrum  where 
each  primary  colour  respectively  appears ;  but  each  spreads  more  or  less  over 
the  whole  spectrum,  the  mixture  of  red  and  yellow  giving  orange,  of  yellow 
and  blue  green,  and  red  with  blue  and  a  little  yellow  causing  the  violet. 

The  prismatic  colours,  according 'to  the  experiments  of  Sir  W.  Herschel, 
differ  in  their  illuminating  power  :  the  orange  illuminates  in  a  higher  degree 
than  the  red,  the  yellow  than  the  orange.  The  maximum  of  illumination  lies  in 
the  brightest  yellow  or  palest  green.  The  green  itself  is  almost  equally  bright 
with  the  yellow;  but  beyond  the  full  deep  green  the  illuminating  power  sensibly 
decreases.  The  blue  is  nearly  equal  to  the  red,  the  indigo  is  inferior  to  the 
blue,  and  the  violet  is  the  lowest  on  the  scale.     (Phil.  Trans.  1800.) 

Calorific  rays  in  Light. — The  solar  rays,  both  direct  and  diffused,  are  capable 
of  exciting  heat.  When  reflected  or  transmitted,  no  such  effect  results  :  the 
concave  reflector  and  burning  glass  remain  cool,  though  intense  heat  is  deve- 
loped at  their  foci ;  and  the  atmosphere  is  not  heated  by  the  solar  rays  to  which 
it  gives  a  passage.  But  opaque  bodies  which  absorb  light  are  invariably  heated 
by  it,  and  the  temperature  is  proportional  to  the  absorbent  power.  Hence,  dark- 
coloured  substances,  which  are  more  absorbent  than  light  ones,  become  hotter 
when  exposed  to  sunshine.  This  is  attested  by  the  general  preference  given  to 
light-coloured  clothing  during  summer.    Hooke,  and  subsequently  Franklin, 


m 


Q^  LIGHT. 

proved  the  fact  by  exposing  pieces  of  cloth  of  the  same  texture  and  size,  but  dif- 
ferent colours,  upon  snow  to  sunshine ;  when  the  snow  under  the  dark  speci- 
mens was  found  to  melt  more  freely  than  under  the  light  ones,  the  effect  being 
nearly  proportional  to  the  depth  of  shade.  Davy  arrived  at  similar  results.  The 
coloured  rays  of  the  spectrum  differ  in  heating  power.  This  is  shown  generally 
by  looking  at  the  sun  through  glass  of  different  colours,  when  it  will  be  found 
that  red  and  yellow  glasses  heat  and  oppress  the  eye  much  more  than  blue  or 
green  ones ;  but  the  fact  was  first  rigidly  demonstrated  by  Sir  W.  Herschel,  by 
placing  the  bulb  of  a  delicate  thermometer  in  the  coloured  spaces  of  the  solar 
spectrum.  He  found  that  it  stood  highest  in  the  red  space,  fell  lower  and 
lower  when  successively  removed  towards  the  violet,  and  was  lowest  in  the 
violet  space.     (Phil.  Trans.  1800.) 

The  foregoing  facts  are  explicable  on  the  suppositions  either  that  light  is  con- 
vertible into  heat  by  absorption,  or  that  heat  is  merely  associated  with  light, 
and  is  absorbed  along  with  it.  Herschel  maintained  the  latter  view,  and 
founded  it  on  his  observation  that,  though  the  red  space  of  the  spectrum  is 
hotter  than  the  other  coloured  spaces,  there  is  a  spot  a  little  beyond  the  red, 
where  little  or  no  light  appears,  where  the  thermometer  is  higher  than  in  the  red 
itself.  He  hence  inferred  that  there  exists  in  the  solar  beam  a  distinct  kind  of 
ray,  which  causes  hea-t  but  not  light ;  and  that  these  rays,  from  being  less 
refrangible  than  the  luminous  ones,  deviate  in  a  smaller  degree  from  their  original 
direction  in  passing  through  the  prism. 

All  succeeding  experimenters  confirm  the  statement  of  Herschel,  that  the 
prismatic  colours  differ  in  heating  power;  but  they  do  not  agree  as  to  the  spot 
where  the  heat  is  greatest.  Englefield,  Davy,  and  others  affirmed  with  Her- 
schel that  it  is  beyond  the  red  ray  ;  while  others,  and  in  particular  Leslie,  con- 
tended that  it  is  in  the  red  itself.  The  observations  of  Seebeck  (Edin.  Journal 
of  Science,  i.  358)  explained  these  contradictory  statements,  by  showing  that 
the  point  of  greatest  heat  varies  with  the  kind  of  prism  which  is  employed  for 
forming  the  spectrum.  When  he  used  a  prism  of  fine  flint-glass,  the  greatest 
heat  was  uniformly  beyond  the  red;  with  a  prism  of  crown-glass,  the  red  itself 
was  the  hottest  part;  and  with  a  prism  externally  of  glass,  but  containing 
water  within,  the  maximum  heat  was  neither  in  the  red  itself,  nor  beyond  it, 
but  in  the  yellow.  These  experiments  have  been  confirmed  by  Melloni,  who 
has  succeeded  with  a  prism  of  rock-salt  in  separating  the  spot  of  maximum  heat 
from  the  coloured  part  of  the  spectrum  by  a  much  greater  interval  than  had  been 
done  previously,  and  dissipating  all  remaining  doubt  as  to  the  existence  in  solar 
light  of  calorific  rays  distinct  from  those  rays  which  produce  colour.  As  in 
simple  radiant  heat  (page  15),  there  exist  in  solar  light  calorific  rays  of  differ- 
ent characters,  some  being  more,  some  less,  refrangible.  The  former  are  pro- 
portionally less  absorbed  by  feebly  diathermanous  media  than  the  latter; 
whereas  good  diathermanous  media  absorb  the  less  refrangible  more  freely  than 
the  more  refrangible  rays.  For  instance,  the  heat  of  the  violet  passes  through 
water  more  readily  than  that  of  the  yellow  space,  that  of  the  yellow  than  the 
red ;  but  in  employing  media  always  rising  in  transcalency,  as  crown-glass, 
flint-glass,  and  rock-salt,  the  obstruction  to  the  least  refrangible  calorific  rays 
continually  decreases.  Hence,  in  successively  taking  prisms  of  rock-salt,  flint- 
glass,  crown-glass,  and  water,  the  spot  of  greatest  heat  will  be  found  first  far 
beyond  the  red,  then  nearer  the  red,  then  in  the  red  itself,  and  lastly  in  the  yel- 
low space  of  the  spectrum.     On  using  a  prism  still  less  transcalent  than  water, 


^ 


LIGHT.  g3 

the  maximum  heat  would  be  found  on  the  violet  side  of  the  yellow  space.  By- 
causing  light,  terrestrial  as  well  as  solar,  to  pass  first  through  water,  and  then 
through  glass  coloured  green  by  oxide  of  copper,  Melloni  so  effectually  absorbed 
all  the  calorific  rays,  that  the  issuing  light  did  not  affect  the  most  delicate  ther- 
moscope.  It  would  hence  follow,  not  merely  that  light  is  associated  with  calo- 
rific rays  quite  distinct  from  the  luminous  rays,  but  that  the  latter  contributes 
nothing  to  the  heat  evolved  ^ring  its  absorption. 

Chemical  rays. — Solar  light  is  capable  of  producing  powerful  chemical 
changes.  One  of  the  most  striking  instances  of  it  is  its  power  of  darkening  the 
white  chloride  of  silver;  an  effect  which  takes  place  slowly  in  the  diffused  light 
of  day,  but  in  the  course  of  two  or  three  minutes  by  exposure  to  sunshine. 
This  effect  was  once  attributed  to  the  influence  of  the  luminous  rays ;  but  Ritter 
and  Wollaston  traced  it  to  the  presence  of  certain  rays  that  excite  neither  heat 
nor  light,  and  which,  from  their  peculiar  agency,  are  termed  chemical  rays.  The 
greatest  chemical  action  is  exerted  just  beyond  or  at  the  verge  of  the  violet  part 
of  the  prismatic  spectrum;  the  spot  next  in  energy  is  the  violet  itself;  and  the 
property  gradually  diminishes  in  advancing  to  the  green,  beyond  which  it  seems 
wholly  wanting.  It  hence  follows  that  the  chemical  rays  are  still  more  refran- 
gible than  the  luminous,  in  consequence  of  which  they  are  dispersed  in  part 
over  the  blue,  indigo,  and  violet,  but  in  the  greatest  quantity  at  the  extreme 
border  of  the  latter. 

The  Daguerreotype,  as  well  as  Mr.  Talbot's  method  of  Photography,  is 
founded  on  the  action  of  the  chemical  rays  on  certain  substances.  The  iodide 
of  silver,  formed  by  exposing  a  plate  of  silver  to  the  vapour  of  iodine,  is  the 
substance  used  in  the  Daguerreotype.  The  chloride,  iodide,  and  bromide  of 
silver,  formed  on  the  surface  of  paper  in  a  thin  and  uniform  layer,  are  the  bases 
of  Talbot's  method.  The  delicacy  and  beauty  of  the  images  produced  in  the 
Daguerreotype,  however,  far  surpasses  anything  that  has  hitherto  been  produced 
on  paper.  For  details  on  this  subject,  the  student  is  referred  to  a  little  treatise 
by  M.  Arago,  which  has  been  translated  into  English. 

Magnetizing  rays. — The  more  refrangible  rays  of  light  were  once  thought  to 
possess  the  property  of  rendering  steel  and  iron  magnetic;  but  since  the  experi- 
ments of  Riess  and  Moser,  this  notion  has  been  abandoned.  (Brewster's  Jour- 
nal, ii.  225.) 

TERRESTRIAL  LIGHT. 

Under  this  head  is  included  all  kinds  of  artificial  light.  The  common  method 
of  obtaining  such  light  is  by  the  combustion  of  inflammable  matter,  which  gives 
out  so  much  heat  that  the  burning  substance  is  rendered  luminous  in  the  act  of 
being  burned.  All  bodies  begin  to  emit  light  when  heat  is  accumulated  within 
them  in  great  quantity  ;  and  the  appearance  of  glowing  or  shining,  which  they 
then  assume,  is  called  incandescence.  The  temperature  at  which  solids  in  gene- 
ral begin  to  shine  in  the  dark  is  between  600°  and  700° ;  but  they  do  not  ap- 
pear luminous  in  broad  daylight  till  they  are  heated  to  about  1000°.  The  colour 
of  incandescent  bodies  varies  with  the  intensity  of  the  heat.  The  first  degree 
of  luminousness  is  an  obscure  red.  As  the  heat  augments,  the  redness  becomes 
more  and  more  vivid,  till  at  last  it  acquires  a  full  red  glow.  If  the  temperature 
still  increase,  the  character  of  the  glow  changes,  and  by  degrees  it  becomes 
white,  shining  with  increasing  brilliancy  as   the  heat  augments.      Liquids  and 


^  LIGHT. 


likewise  become  incandescent  when  strongly  heated :  but  a  very  high 
temperature  is  required  to  render  a  gas  luminous,  more  than  is  sufficient  for 
heating  a  solid  body  even  to  whiteness.  The  different  kinds  of  flame,  as  of  the 
fire,  candles,  and  gas  light,  are  instances  of  incandescent  gaseous  matter. 

Artificial  lights  differ  in  colour,  and  accordingly  exhibit  different  appearances 
when  transmitted  through  a  prism.  The  white  light  of  incandescent  charcoal, 
which  is  the  principal  source  of  the  light  from  candles,  oils,  and  the  illuminating 
gases,  contains  the  three  primary  calorific  rays,  the  red,  yellow,  and  blue.  The 
dazzling  light  emitted  by  lime  intensely  heated,  first  proposed  by  Lieut.  Drum- 
mond  for  the  trigonometrical  survey  (Phil.  Trans.  1830),  and  of  late  so  success- 
fully applied  by  Messrs.  Cooper  and  Carey  for  their  gas  microscope,  gives  the 
prismatic  colours  almost  as  bright  as  in  the  solar  spectrum.  The  light  emitted 
by  iron  feebly  incandescent  consists  principally  of  the  red  rays,  as  does  the  red 
light  obtained  by  means  of  strontia  and  lithia ;  that  from  ignited  boracic  acid  is 
such  a  mixture  of  the  blue  and  yellow  rays  as  constitute  green  ;  and  incandescent 
soda  emits  a  yellow  light  almost  wholly  free  from  the  rays  which  cause  the  red 
and  blue  colours. 

Artificial  light  differs  from  solar  light  in  containing  heat  in  two  states.  It 
contains  simple  radiant  heat  like  that  radiated  from  a  body  not  luminous,  and 
which  may  be  separated  by  transmission  through  a  plate  of  moderately  thick 
glass ;  but  the  light  so  purified  still  heats  any  body  which  absorbs  it,  possess- 
ing calorific  rays  associated  with  its  luminous  rays  like  those  in  solar  light 
(page  61),  and  like  them  susceptible  of  refraction  by  transparent  media.  Thus, 
Daniell  found  that  the  rays  from  incandescent  lime  were  concentrated  by  convex 
lenses,  and  set  fire  to  phosphorus  placed  in  the  focus  (Phil.  Mag.  N.  S.  ii.  59). 
Agreeably  to  the  researches  of  Melloni  (page  8),  artificial  light  contains  dif- 
ferent modifications  of  radiant  heat,  which  not  only  differ  in  refrangibility,  but 
in  transmissibility  through  diathermanous  media. 

The  chemical  agency  of  artificial  light  is  analogous  to  that  from  the  sun.  In 
general  the  former  is  too  feeble  for  producing  any  visible  effect ;  but  light  of 
considerable  intensity,  such  as  that  from  ignited  lime,  darkens  chloride  of  silver, 
and  seems  capable  of  exerting  the  same  chemical  agencies  as  solar  light,  though 
in  a  degree  proportionate  to  its  inferior  brilliancy.  (An.  of  Phil,  xxvii.  451.) 
Light  emanates  from  some  substances  either  at  common  temperatures  or  at  a 
degree  of  heat  disproportioned  to  the  effect,  giving  rise  to  an  appearance  which 
is  called  phosphorescence.  This  is  exemplified  by  a  composition  termed  Canton's 
phosphorus,  made  by  mixing  three  parts  of  calcined  oyster-shells  with  one  of  the 
flowers  of  sulphur,  and  exposing  the  mixture  for  an  hour  to  a  strong  heat  in  a 
covered  crucible.  The  same  property  is  possessed  by  chloride  of  calcium 
(Romberg's  phosphorus),  anhydrous  nitrate  of  lime  (Baldwin's  phosphorus), 
some  carbonates  and  sulphates  of  baryta,  strontia,  and  lime,  the  diamond,  some 
varieties  of  fluor-spar  called  chlornphane,  apatite,  boracic  acid,  bon^x,  sulphate 
of  potassa,  sea-salt,  and  by  many  other  substances.  Scarcely  any  of  these  phos- 
phori  act  unless  they  have  been  previously  exposed  to  light,  though  they  do  not 
always  shine  with  light  of  the  same  colour  as  that  which  excites  the  phospho- 
rescence: for  some,  diffused  daylight  or  even  lamp-light  will  suffice;  while 
others  require  the  direct  solar  light,  or  the  light  of  an  electric  discharge.  Ex- 
posure for  a  few  seconds  to  sunshine  enables  Canton's  phosphorus  to  shine  in 
a  dark  room  for  several  hours  afterwards.  Warmth  increases  the  intensity  of 
light,  or  will  renew  it  after  it  has  ceased; — but  it  diminishes  the  duration. 


LIGHT.  05 

When  the  phosphorescence  has  ceased  it  may  be  restored,  and  in  general  for 
any  number  of  times,  by  renewed  exposure  to  sunshine ;  and  the  same  effect 
'may  be  produced  by  passing  electric  discharges  through  the  phosphorus.  Some 
phosphori,  as  apatite  and  chlorophane,  do  not  shine  until  they  are  gently  heated; 
and  yet  if  exposed  to  a  red  heat,  they  lose  the  property  so  entirely  that  exposure 
to  solar  light  does  not  restore  it.  Pearsall  has  remarked  that  in  these  minerals 
the  phosphorescence,  destroyed  by  heat,  is  restored  by  electric  discharges;  that 
specimens  of  fluor-spar,  not  naturally  phosphorescent,  may  be  rendered  so  by 
electricity ;  and  that  this  agent  exalts  the  energy  of  natural  phosphori  in  a  very 
remarkable  degree.  (R.  Inst.  Journal,  N.  S.  i.)  The  theory  of  these  pheno- 
mena is  obscure.  Chemical  action  is  not  the  cause,  for  these  phosphori  shine 
in  vacuo  or  in  gases  which  do  not  act  chemically  on  them,  and  some  even  under 
water.  It  may  be  presumed  that  light  causes  in  them  a  certain  vibratory  state 
analogous  to  that,  though  in  a  far  lower  degree,  which  exists  in  incandescent 
matter. 

[From  the  recent  experiments  of  Becquerel  and  others,  it  appears  that  the 
rays  of  the  violet  extremity  of  the  spectrum  are  the  real  agents  in  producing 
these  phenomena  of  phosphorescence,  while  the  red  rays  have  the  effect  of  ex- 
tinguishing the  light.  Conceiving  the  rays  which  are  active  in  producing  phos- 
phorescence, to  be  distinct  from  the  so  called  chemical  rays,  although  associated 
with  them  in  the  spectrum,  they  have  been  distinguished  by  Draper  and  others 
by  the  name  of  phosphorogenic  rays.] 

Another  kind  of  phosphorescence  is  observable  in  some  bodies  when  strongly 
heated.  A  piece  of  lime,  for  example,  heated  to  a  degree  which  would  only 
make  other  bodies  red,  emits  a  brilliant  white  light  of  such  intensity  that  the 
eye  cannot  support  its  impression. 

A  third  species  of  phosphorescence  is  observed  in  the  bodies  of  some  animals, 
either  in  the  dead  or  living  state.  Some  marine  animals,  and  particularly  fish, 
possess  it  in  a  remarkable  degree.  It  may  be  witnessed  in  the  body  of  the 
herring,  which  begins  to  phosphoresce  a  day  or  two  after  death,  and  before  any 
visible  sign  of  putrefaction  has  set  in.  Sea-water  is  capable  of  dissolving  the 
luminous  matter ;  and  it  is  probably  from  this  cause  that  the  waters  of  the  ocean 
sometimes  appear  luminous  at  night  when  agitated.  This  appearance  is  also 
ascribed  to  the  presence  of  certain  animalcules,  which,  like  the  glow-worm  of 
this  country,  or  the  fire-fly  of  the  West  Indies,  are  naturally  phosphorescent. 

[It  has  lately  been  inferred  by  Matt-euci,  from  numerous  experiments,  that  the 
phosphorescence  of  the  glow-worm  is  due  to  a  slow  combustion :  carbonic  acid 
being  evolved  in  oxygen,  while  the  animal  continues  luminous.  This  effect  he 
found  to  be  increased  by  heat.  The  phosphorescence  of  the  fire-fly  and  various 
other  animals,  as  well  as  of  decaying  animal  and  vegetable  matter,  is  probably 
owing  to  the  same  cause.] 

Light  sometimes  appears  during  the  process  of  crystallization.  This  is  exem- 
plified by  a  tepid  solution  of  sulphate  of  potassa  in  the  act  of  crystallizing; 
and  it  has  been  likewise  witnessed  under  similar  circumstances  in  a  solution  of 
fluoride  of  sodium  and  nitrate  of  strontia.  Another  instance  of  the  kind  is 
afforded  by  the  sublimation  of  benzoic  acid.  Allied  to  this  phenomenon  is  the 
phosphorescence  which  attends  the  sudden  contraction  of  porous  substances. 
Thus,  on  decomposing  by  heat  the  hydrates  of  zirconia,  peroxide  of  iron,  and 
green  oxide  of  chromium,  the  dissipation  of  the  water  is  followed  by  a  sudden 
increase  of  density  suited  to  the  changed  state  of  the  oxide,  and  a  vivid  glow 

7 


01  LIGHT. 

appears  at  the  same  instant.  The  essential  conditions  are,  that  a  substance 
should  be  naturally  denser  after  decomposition  than  it  was  previously,  and  that 
the  transition  from  one  mechanical  state  to  the  other  should  be  abrupt. 

Instruments  designed  for  measuring  intensities  of  light  are  termed  photometers. 
That  of  Leslie  is  the  only  one  used  to  estimate  the  strength  of  the  sun's  light. 
It  consists  of  his  differential  thermometer,  with  one  ball  made  of  black  glass. 
The  clear  ball  transmits  all  the  light  that  falls  upon  it,  and  therefore  its  tempe- 
rature is  not  affected ;  it  is  all  absorbed,  on  the  contrary,  by  the  black  ball,  and 
by  heating  and  expanding  the  air  within,  causes  the  liquid  to  ascend  in  the 
opposite  stem.  The  whole  instrument  is  covered  with  a  case  of  thin  glass,  the 
object  of  which  is  to  prevent  the  balls  from  being  affected  by  currents  of  cold 
air.  The  action  of  this  photometer  depends  on  the  absorption  of  the  heat  by 
which  light  is  accompanied. 

Leslie  recommended  his  photometer  also  for  determining  the  relative  intensi- 
ties of  artificial  light,  such  as  that  of  candles,  oil,  or  gas.  This  application  of 
it  differs  from  the  foregoing,  because  light  from  terrestrial  sources  contains  calo- 
rific rays  of  different  properties ;  some  being  largely  absorbed  by  glass,  and 
others  freely  transmissible.  The  former,  being  for  the  most  part  arrested  by  the 
outer  glass  case,  will  not  cause  any  great  error ;  but  the  latter  must  give  rise  to 
serious  fallacies  whenever  the  calorific  and  luminous  rays  of  the  two  lights  are 
not  in  the  same  ratio.  This  is  rarely,  if  ever,  the  case  with  lights  which  differ 
in  colour.  Thus,  the  light  emitted  by  burning  cinders  or  red-hot  iron,  even  after 
passing  through  glass,  contains  a  quantity  of  calorific  rays,  which  is  out  of  all 
proportion  to  the  luminous  ones  ;  and,  consequently,  they  may  and  do  produce  a 
greater  effect  on  the  photometer  than  some  lights  whose  illuminating  powers  are 
far  stronger. 

A  photometer  on  a  different  principle  has  been  described  by  Rumford  in  his 
Essays.  It  determines  the  relative  strength  of  lights  by  a  comparison  of  their 
shadows,  and  is  susceptible  of  great  accuracy  when  employed  with  the  required 
care;  but,*  like  the  foregoing,  its  indications  cannot  be  trusted  when  there  is 
much  difference  in  the  colour  of  the  lights.  In  this  case,  the  best  procedure  is, 
to  observe  the  distance  from  each  light  at  which  any  given  object,  as  a  printed 
page,  ceases  to  be  distinctly  visible.  The  illuminating  power  of  the  lights  so 
compared  is  as  the  squares  of  their  distances. 

[An  ingenious  attempt  has  recently  been  made  by  MM.  Fizeau  and  Foucault, 
to  compare  the  intensity  of  solar  radiation  with  that  of  the  charcoal  points  in  the 
voltaic  circuit,  and  that  of  lime  ignited  by  the  oxyhydrogen  blow-pipe.  The 
intensities  were  measured  by  the  time  of  exposure  to  the  light,  necessary  to  ren- 
der the  Daguerre  plate  sensible  to  mercurial  vapour.  The  effects  are  therefore 
proportional,  rather  to  the  chemical  than  the  luminous  rays.  Assuming  the  lime 
light  as  unity,  the  voltaic  light  was  found  to  be  34.3,  and  the  solar  146.  (Ann. 
de  Chim.  July,  1844.)] 

ON  THE  RELATIONS  OF  HEAT  AND  LIGHT. 

Radiant  heat  and  light  have  the  most  intimate  resemblance.  They  are  dis- 
tributed, reflected,  refracted,  absorbed,  transmitted,  polarized,  according  to  laws 
so  exactly  parallel,  as  to  force  on  the  mind  the  conviction  that  their  causes  are 

*  See  an  Essay  on  the  Construction  of  Coal  Gas  Burners,  &c.,  in  the  Edinburgh  Philoso 
phical  Journal,  for  1825. 


ELECTRICITY.  ,  Hf 

likewise  similar.  If  light  be  due  to  ethereal  vibrations,  it  is  difficult  not  to 
assign  a  similar  cause  to  radiant  heat.  The  obstacle  to  adopting  this  view 
arises  from  the  peculiar  relations  of  heat  to  matter  as  connected  with  change  of 
form,  with  specific  heat,  and  with  heat  of  temperature.  The  outline  of  such  an 
undulatory  theory  might  be  thus  stated  : — Heat  may  be  considered  identical  with 
the  universal*ether,  so  that  the  terms  ether  and  matter  of  heat  would  apply  to 
the  same  substance.  Diffused  within  the  pores  of  bodies  this  ether  causes  the 
condition  of  temperature,  and  in  a  state  of  more  intimate  union  it  determines 
their  form.  Conduction  may  be  due  to  a  peculiar  vibration  of  ether,  advancing 
slowly  among  the  molecules  of  matter,  and  modified  by  their  presence, — a  radia- 
tion from  particle  to  particle.  Common  radiation  of  heat  may  be  ascribed,  not 
to  the  ether  itself  being  ejected  from  a  hot  body,  but  to  ethereal  impulses  origi- 
nating in  the  same  manner  as  those  of  light,  but  having  waves  of  different  gTades 
both  of  length  and  intensity.  It  would  not  be  prudent,  however,  at  present,  to 
embody  such  a  theory  with  the  ordinary  doctrines  of  heat,  though  as  a  scientific 
speculation  it  is  a  subject  of  great  and  increasing  interest. 


SECTION  III. 


ELECTRICITY. 


Elementary  Facts. — When  certain  substances,  such  as  amber,  glass,  sealing- 
wax,  sulphur,  are  rubbed  with  dry  silk  or  cloth,  they  are  found  to  have  acquired 
a  property,  not  observable  in  their  ordinary  state,  of  causing  contiguous  light 
bodies  to  move  towards  them ;  or  if  the  substances  so  rubbed  be  light  and  freely 
suspended,  they  will  move  towards  contiguous  bodies.  After  a  while  this  curious 
phenomenon  ceases ;  but  it  may  be  renewed  an  indefinite  number  of  times  by 
friction.  The  principle  thus  called  into  action  is  known  by  the  name  of  elec- 
tricity^ from  the  Greek  word  ^x^x-t^ov,  amber,  because  the  electric  property  was 
first  noticed  in  it.  The  same  term  is  applied  to  the  science  which  treats  of  the 
phenomena  of  electricity. 

When  a  substance  by  friction  or  any  other  means  acquires  the  property  just 
stated,  it  is  said  to  be  electrified^  or  to  be  electrically  excited ,-  and  its  motion 
towards  other  bodies,  or  of  other  bodies  towards  it,  is  ascribed  to  a  force  called 
electric  attraction.  But  its  influence,  on  examination,  will  be  found  to  be  not 
merely  attractive ;  on  the  contrary,  light  substances,  after  touching  the  electrified 
body,  will  be  disposed  to  recede  from  it  just  as  actively  as  they  approached  it 
before  contact.  This  is  termed  electric  repulsion.  By  aid  of  the  electrical 
machine,  electric  attraction  and  repulsion  may  be  displayed  by  a  great  variety 
of  amusing  and  instructive  experiments,  showing  how  readily  an  invisible  power 
is  called  into  operation,  and  how  wonderfully  inert  matter  is  subject  to  its  con- 
trol. But  the  student  may  witness  the^e  effects  quite  satisfactorily  by  very 
simple  apparatus.  Let  him  suspend  a  thread  of  white  sewing  silk  from  the 
back  of  a  chair  so  that  one  end  may  hang  freely,  taking  the  precaution  to  moisten 
that  end  slightly  by  holding  it  between  the  fingers,  while  the  rest  of  the  thread 


68  ELECTRICITY. 

is  carefully  dried  by  the  fire;  and  let  him  then  place  near  the  free  end  a  piece 
of  sealing-wax  previously  rubbed  on  the  sleeve  of  his  coat.  The  silk  will  move 
towards  it ;  but  after  touching  the  excited  wax  two  or  three  times,  it  will  recede 
from  it. 

When  an  electrified  body  touches  another  which  is  not  electrified,  the  electric 
property  is  imparted  by  the  former  to  the  latter.  Thus,  on  touching  the  free  end 
of  the  suspended  silk  thread  with  the  excited  wax,  the  silk  will  itself  be 
excited,  as  shown  by  its  moving  tow^ards  a  book,  a  knife,  or  other  unex- 
cited  object  placed  near  it.  But  although  electricity  is  always  imparted  by 
an  excited  to  an  unexcited  body  by  contact,  the  latter  does  not  always  exhibit 
electric  excitement.  If,  for  example,  the  suspended  silk  be  wetted  along  its 
whole  length,  it  will  be  strongly  attracted  by  the  excited  wax,  but  after  contact 
it  will  not  evince  the  leaSt  sign  of  being  itself  electrified.  Nevertheless,  elec- 
tricity is  communicated  to  the  silk  in  both  cases ;  only  it  is  retained  by  silk 
when  dry,  and  is  lost  as  soon  as  received  by  wet  silk.  Such  observations  led 
to  the  discovery  that  electricity  passes  with  great  ease  over  the  surface  of  some 
substances,  and  with  difficulty  over  that  of  others,  and  hence  to  the  division  of 
bodies  into  conductors  and  non-conductors  of  electricity.  If  electricity  be  imparted 
to  one  end  of  a  conductor,  such  as  a  copper  wire,  the  other  extremity  of  which 
touches  the  ground,  or  is  held  by  a  person  standing  on  the  ground,  the  elec- 
tricity will  pass  along  its  whole  length  and  escape  in  an  instant,  though  the 
wire  were  several  miles  long ;  whereas  excited  glass  and  resin,  which  are  non- 
conductors, may  be  freely  handled  without  losing  any  electricity  except  at  the 
parts^ectually  touched.  To  the  class  of  conductors  belong  the  metals,  charcoal, 
plumbago,  water,  and  aqueous  solutions,  and  substances  generally  which  are 
moist  or  contain  water  in  its  liquid  state,  such  as  animals  and  plants,  and  the 
surface  of  the  earth.  These,  however,  diflfer  in  their  conducting  power :  of  the 
metals,  Harris  found  silver  and  copper  to  be  the  best  conductors ;  and  after 
these  follow  gold,  zinc,  platinum,  iron,  tin,  lead,  antimony,  and  bismuth  (Phil. 
Trans.  1827).  This  order,  as  Forbes  has  remarked,  is  nearly  that  of  their  con- 
ducting powers  for  heat.  Aqueous  solutions  of  acids  and  salts  conduct  much  bet- 
ter than  pure  water.  To  the  list  of  non-conductors  belong  glass,  resins,  sulphur, 
diamond,  dried  wood,  precious  stones,  earth  and  most  rocks  when  quite  dry, 
silk,  hair,  and  wool.  Air  and  gases  in  general  are  non-conductors  if  dry,  but 
act  as  conductors  when  saturated  with  moisture. 

This  knowledge  is  of  continual  application  in  electrical  experiments.  When 
it  is  wished  to  collect  electricity  on  a  metallic  surface,  the  metal  must  be  insu- 
latedj  that  is,  cut  off  from  contact  with  the  earth,  and  with  conductors  touching 
the  ground,  by  means  of  some  non-conductor;  an  object  commonly  eflTec ted 
either  by  supporting  it  on  a  handle  of  glass,  or  by  placing  it  on  a  stool  made 
with  glass  feet.  Another  mode  of  insulating  is  to  suspend  a  substance  by  silk 
threads.  But  such  insulators  must  be  dry  ;  since  they  begin  to  conduct  as  soon 
as  they  grow  damp,  and  conduct  well,  as  in  the  experiment  above  described, 
when  wet.  Again,  electrical  experiments  are  very  apt  to  fail  in  damp  weather, 
because  the  moisture  both  carries  off  electricity  directly,  and  by  being  deposited 
on  the  glass  supports  destroys  the  insulation. 

To  diminish  this  inconvenience  it  i^  usual  to  keep  the  insulators  warm,  and 
to  coat  them  with  a  varnish  made  by  dissolving  the  resin  called  shell-lac  in 
alcohol,  this  resinous  matter  being  much  les.s  prone  to  attract  moisture  from  the 
air  than  glass.    The  same  principles  account  for  an  error  once  prevalent  that  a 


ELECTRICITY.  69 

metal  cannot  be  excited  by  friction  :  if  held  in  the  hand,  indeed,  it  exhibits  no 
sign  of  excitement  when  rubbed,  because  the  electricity  is  carried  off  as  soon  as 
excited  ;  but  if,  while  carefully  insulated,  it  is  rubbed  with  a  dry  cat's  fur,  excite- 
ment readily  ensues. 

On  comparing  the  electric  properties  manifested  by  glass  and  sealing-wax 
when  both  are  rubbed  by  a  woollen  or  silk  cloth,  they  will  be  found  essentially 
different;  hence  it  is  inferred  that  there  are  two  kinds  or  states  of  electricity, 
one  termed  vitreous,  because  developed  on  glass,  and  the  other  resinous  elec- 
tricity, from  being  first  noticed  on  resinous  substances.  These  two  kinds  of 
electricity,  one  or  other  of  which  is  possessed  by  every  electrified  substance, 
are  also  termed  positive  and  negative,  the  terms  vitreous  and  positive  being  used 
synonymously,  as  are  resinous  and  negative  .•  they  are  also  denoted  by  the  signs 
-f-  and  — .  If  two  electrified  substances  are  both  positive  or  -|-  ,  or  both  nega- 
tive or — ,  they  are  invariably  disposed  to  recede  from  each  other,  that  is,  to 
exhibit  electric  repulsion;  but  if  one  be -|- ,  and  the  other  — ,  their  mutual 
action  is  as  constantly  attractive.  The  end  of  a  silk  thread,  after  contact  with 
an  electrified  stick  of  sealing-wax,  is  repelled  by  the  wax,  because  both  are  — ; 
but  a  dry  warm  wine-glass,  if  rubbed  with  cloth  or  silk,  will  be  -|-  ,  and  if  then 
presented  to  the  thread,  attraction  will  ensue.  A  silk  thread  in  a  known  elec- 
tric state,  thus  indicates  the  kind  of  electricity  possessed  by  other  substances  : 
a  convenient  mode  of  doing  this,  is  to  draw  a  thread  of  white  silk  rapidly 
through  a  fold  of  coarse  brown  paper  previously  warmed,  by  which  means  its 
whole  length  will  be  rendered  -f-  . 

When  two  substances  are  rubbed  together  so  as  to  electrify  one  of  them,  the 
other,  if  in  a  state  to  retain  electricity,  will  be  excited  also,  one  being  always  — , 
and  the  other  -f-  .  It  is  easy  to  be  satisfied  of  this  by  very  simple  experiments. 
Rub  a  stick  of  sealing-wax  on  warm  coarse  brown  paper,  and  the  paper  will  be 
found  to  repel  a  positively  excited  thread  of  silk,  while  the  wax  will  attract  it; 
if  a  warm  wine-glass  be  rubbed  on  the  brown  paper,  the  glass  will  be  -f-  ,  as 
shown  by  its  repelling  the  -|-  thread,  while  the  same  thread  will  be  attracted  by 
the  —  paper ;  friction  of  sealing-wax  on  a  silk  riband  renders  the  wax  —  and 
the  riband  -f-  ,  but  with  glass  the  riband  is  — .  If  two  silk  ribands,  one  white 
and  the  other  black,  be  made  quite  warm,  placed  in  contact,  and  then  drawn 
quickly  through  the  closed  fingers,  they  will  be  found  on  separation  to  be  highly 
attractive  to  each  other,  the  white  being  -f-  ,  and  the  black  — .  The  back  of  a 
cat  is  -}-  to  all  substances  with  which  it  has  been  tried,  and  smooth  glass  is  -f- 
to  all  except  the  back  of  a  cat.  Sealing-wax  is  —  to  all  the  substances  just 
enumerated,  but  becomes  -j-  by  friction  with  most  of  the  metals.  The  reader 
will  perceive  from  these  facts  that  the  same  substance  may  acquire  both  kinds 
of  electricity,  becoming  -f  by  friction  with  one  body,  and  —  with  another. 

THEORIES  OF  ELECTRICITY. 

The  nature  of  electricity,  like  that  of  heat,  is  at  present  involved  in  obscurity. 
Both  these  principles,  if  really  material,  are  so  light,  subtile,  and  diffusive,  that 
it  has  hitherto  been  found  impossible  to  recognise  in  them  the  ordinary  charac- 
teristics of  matter ;  and  therefore  electric  phenomena  may  be  referred,  not  to  the 
agency  of  a  specific  substance,  but  to  some  property  or  state  of  common  matter, 
just  as  sound  and  light  are  produced  by  a  vibrating  medium.  But  the  effects  of 
electricity  are  so  similar  to  those  of  a  mechanical  agent — it  appears  so  distinctly 


7^  ELECTRICITY. 

to  emanate  from  substances  which  contain  it  in  excess,  and  rends  asunder  all 
obstacles  in  its  course  so  exactly  like  a  body  in  rapid  motion,  that  the  impres- 
sion of  its  existence  as  a  distinct  material  substance  sut  generis  forces  itself 
irresistibly  on  the  mind.  All  nations,  accordingly,  have  spontaneously  concurred 
in  regarding-  electricity  as  a  material  principle ;  and  scientific  men  give  a  pre- 
ference to  the  same  view,  because  it  offers  an  easy  explanation  of  phenomena, 
and  suggests  a  natural  language  easily  intelligible  to  all. 

Theory  of  two  Electric  Fluids. — ^This  theory,  the  fundamental  facts  of  which 
were  supplied  partly  by  Dufay,  and  partly  by  Symmer,  is  founded  on  the  assumed 
existence  of  two  electric  fluids,  which  Dufay  distinguished  by  the  terras  vitreous 
and  resinous  electricity.  In  order  to  account  for  electric  phenomena  by  this  sup- 
position, the  two  fluids  are  assumed  to  possess  the  following  properties : — ^They 
are  both  equally  subtile  and  elastic,  universally  diffused  and  therefore  present  in 
all  bodies,  possessed  of  the  most  perfect  fluidity,  each  highly  repulsive  to  its 
own  particles,  and  as  highly  attractive  to  those  of  the  opposite  kind,  these 
attractive  and  repulsive  forces  being  exactly  equal  at  the  same  distance,  and 
both  varying  inversely  as  the  square  of  the  distance  varies.  Electric  quiescence 
is  ascribed  to  these  fluids  being  combined  and  neutralized  with  each  other ;  and 
electric  excitation  is  the  consequence  of  either  fluid  being  in  excess.  Their 
combination  is  destroyed  by  several  causes,  of  which  friction  is  one. 

This  theory,  as  commonly  stated,  takes  little  or  no  cognizance  of  any  attrac- 
tion between  the  electric  fluids  and  other  material  substances.  But  it  would  be 
against  all  analogy  to  suppose  no  such  influence  to  exist ;  and  indeed  the  sup- 
position of  an  attractive  force  acting  at  insensible  distances  seems  necessary  to 
account  for  the  impediment  caused  by  non-conductors  to  the  free  movement  of 
the  electric  fluids. 

Theory  of  a  single  Fluid, — The  celebrated  American  philosopher,  Franklin, 
proposed  a  different  theory,  founded  on  the  supposition  of  a  single  electric  fluid, 
the  particles  of  which  are  conceived  to  repel  each  other  with  a  force  diminishing 
as  the  squares  of  the  distance,  and  to  be  attracted  by  matter  in  general  according 
to  the  same  law.  Material  substance  in  its  unelectric  state  is  regarded  as  a 
compound  of  electricity  and  matter,  saturated  and  neutralized  with  each  other. 
It  is  also  an  assumption,  shown  to  be  necessary  by  iEpinus  and  Cavendish, 
that  ponderable  bodies  repel  each  other  with  the  same  force  and  according  to  the 
same  law  as  the  particles  of  electricity.  From  the  nature  of  these  postulates  it 
will  be  easy  to  anticipate  their  application.  Unelectric  bodies  are  such  as  have 
their  natural  quantity  of  electricity,  which  precisely  suffices  to  saturate  and 
neutralize  the  matter  of  which  they  consist.  They  are  then  electrically  indif- 
ferent; because  the  repulsion  exerted  between  the  electricity  and  matter  of  con- 
tiguous bodies  is  exactly  counteracted  by  the  attraction  of  the  electric  fluid  in 
each  for  the  matter  of  the  other.  Electrical  excitement  is  occasioned  either  by 
increase  or  diminution  of  the  natural  quantity  of  electricity.  These  opposite 
states  are  denoted  by  the  algebraic  terms  positive  and  negative ;  the  former  cor- 
responding to  the  vitreous,  the  latter  to  the  resinous  electricity  of  Dufay. 

To  the  theory  of  Franklin  it  is  usually  objected  that  it  involves  an  assumption 
at  variance  with  the  laws  of  gravitation,  namely,  that  of  matter  being  repulsive 
to  itself;  but  this  objection  is  unfounded,  as  the  laws  of  gravitation  have  been 
investigated  for  matter  only  when  in  its  ordinary  state,  and  probably  do  not 
apply  in  cases  of  electric  excitement.  The  .researches  of  Mossotti  on  the  forces 
which  regulate  the  internal  constitution  of  bodies  amply  justify  this  conclusion. 


ELECTRICITY.  7f 

Adopting  with  Franklin  a  single  electric  fluid,  he  has  shown  that  gravitation  is 
perfectly  consistent  with  the  supposition  that  the  molecules  of  matter  are  repul- 
sive to  each  other.  He  has  supported  this  opinion  by  a  mathematical  investiga- 
tion of  the  conditions  of  equilibrium  both  for  the  molecules  of  matter  and  for 
the  electric  fluid.  The  results  at  which  he  arrived  show  that  two  molecules  of 
matter  surrounded  by  their  electric  atmospheres,  are  mutually  attractive  when 
separated  by  a  sensible  distance ; — that  the  attraction  increases  on  the  approach 
of  the  atoms  up  to  a  certain  point,  where  the  attractive  force  attains  its  maxi- 
mum, and  beyond  which  the  molecules  are  mutually  repulsive.  In  this  manner, 
gravitation,  cohesion,  and  the  resistance  of  matter  to  compression,  are  attributed 
to  the  same  forces.  These  views  certainly  aiford  a  happy  explanation  of  the 
molecular  mechanism ;  but  as  they  have  not  yet  been  sufficiently  tested,  I  shall 
retain  the  theory  of  the  two  electricities,  which  was  adopted  in  former  editions, 
substituting  however,  agreeably  to  present  usages,  the  terms  positive  and  nega- 
tive, for  vitreous  and  resinous  electricity. 

CAUSES  OF  ELECTRIC  EXCITEMENT. 

Friction. — This  cause  of  electric  excitement  having  been  already  mentioned, 
it  here  only  remains  to  state  the  usual  modes  of  developing  electricity  by  fric- 
tion. A  supply  of  negative  electricity  is  easily  obtained  by  rubbing  a  stick  of 
sealing-wax,  or  a  glass  tube  covered  with  sealing-wax,  with  silk  or  woollen 
cloth ;  and  positive  electricity  is  freely  developed  when  a  dry  glass  tube  is 
rubbed  with  silk,  brown  paper,  or  flannel,  the  surface  of  which  is  covered  with 
a  little  amalgam.  But  for  obtaining  an  abundant  supply  of  electricity  it  is 
necessary  to  employ  an  electrical  machine,  which  is  a  mechanical  contrivance  for 
exposing  a  large  surface  of  glass  to  continuous  fraction.  As  now  constructed, 
it  is  formed  either  with  a  cylinder  or  plate  of  glass  which  is  made  to  revolve 
upon  an  axis,  and  pressed  during  rotation  by  cushions  or  rubbers  made  of  leather 
stuffed  with  flannel,  and  covered  usually  with  silk.  On  the  rubber  is  spread 
an  amalgam  of  tin  and  zinc,  rendered  adhesive  by  admixture  with  a  small  quan- 
tity of  lard  or  tallow.  To  prepare  the  amalgam,  melt  in  a  Hessian  crucible  one 
ounce  of  tin  and  three  of  zinc,  then  add  two  ounces  of  mercury  heated  to  near 
its  boiling  point,  stir  briskly  with  a  stick  for  a  few  minutes,  and  pour  the  mix- 
ture on  a  clean  dry  stone :  when  cold,  pulverize  and  sift,  and  preserve  the  fine 
powder  in  a  well-corked  dry  phial.  Another  essential  part  of  the  machine  is 
the  prime  conductor,  which  is  an  insulated  conductor,  commonly  made  of  brass, 
placed  in  such  immediate  proximity  to  the  revolving  glass,  that  the  electric 
state  of  the  one  is  instantly  imparted  to  the  other. 

The  electricity  developed  by  the  electrical  machine  is  due  partly  to  friction, 
which  disunites  the  combined  electric  fluids  of  the  glass  and  rubber,  but  princi- 
pally to  the  oxidation  of  the  amalgam.  The  positive  fluid  accumulates  in  the 
glass  and  passes  from  it  to  the  prime  conductor,  while  the  negative  fluid  accu- 
mulates in  the  rubber,  and  its  conductor.  But  to  keep  up  the  supply  of  electri- 
city, the  rubber  must  be  connected  with  the  ground,  so  that  its  —  fluid  may 
escape;  or  if  we  wish  to  obtain  —  electricity  from  the  rubber,  the  prime  con- 
ductor should  communicate  with  the  ground,  that  its  -{-  fluid  may  escape. 

Change  of  temperature. — The  operation  of  this  cause  of  electric  excitement 
was  first  noticed  in  certain  minerals,  such  as  tourmalin  and  boracite,  not  pos- 
sessed of  that  symmetric  arrangement  of  parts  commonly  observed  in  crystals, 


72  ELECTRICITY. 

and  which  are  electrified  by  the  application  of  heat.  But  a  far  more  general 
principle  was  detected  by  Seebeck,  who  found  that  the  electric  equilibrium  is 
disturbed  in  certain  metallic  rods  or  wires  when  one  extremity  has  a  different 
temperature  from  that  of  the  other,  whether  the  difference  be  effected  by  the 
application  of  heat  or  cold.  This  observation  has  been  since  shown  by  Gum- 
ming to  be  true  of  all  metals  (An.  of  Phil.  N.  S.  v.  427) ;  and  the  same  object 
has  been  examined  by  Prideaux  (Phil.  Mag.  and  An.  iii.).  The  experiment  is 
usually  made  by  heating  or  cooling  the  point  of  junction  of  two  metallic  wires, 
which  are  soldered  together;  but  Becquerel  has  proved  that  the  contact  of  dif- 
ferent metals  is  not  essential.     (An.  de  Ch.  et  Ph.  xli.  353.) 

Chemical  action. — Another,  and  perhaps  by  far  the  most  fertile,  source  of 
electricity  is  chemical  action.  This  was  strongly  denied  by  Davy,  in  his 
Bakerian  lecture  for  1826;  but  the  experiments  of  Becquerel,  De  la  Rive,  and 
Pouillet,  afford  decisive  proof  that  chemical  union  and  decomposition  are  both 
attended  with  electrical  excitement.  (An.  de  Ch.  et  Ph.  vol.  35,  36,  37,  38, 
and  39). 

Contact, — Another  reputed  source  of  electricity  is  contact  of  different  sub- 
stances, especially  of  metals;  a  source  originally  suggested  by  Volta,  who 
founded  on  it  a  theory  of  galvanism.  Volta  stated  that  clean  plates  of  zinc  and 
copper,  insulated  by  glass  handles,  became  electric  by  being  made  to  touch 
each  other,  and  then  separated.  When  the  zinc  alone  was  insulated,  it  became 
-f-,  and  when  the  copper  alone  was  insulated,  it  became  — .  But  the  quantity 
of  electricity  thus  developed  is  confessedly  so  small  as  to  require  the  most  deli- 
cate instruments  to  detect  it ;  and  the  experiments  of  De  la  Rive  (An.  de  Ch. 
et  Ph.  xxxix.  297  ;  Ixii.  147,)  and  those  of  Parrot  (ibid.  xlvi.  361),  have  shown, 
in  a  manner  apparently  decisive,  that  the  electricity  developed  in  such  experi- 
ments is  derived  either  from  a  slight  degree  of  chemical  action,  or  from  friction  ; 
and  that  contact  alone,  if  unattended  by  chemical  action  or  by  friction,  produces 
not  the  least  excitement  of  electricity.  I  apprehend,  therefore,  that  the  facts 
adduced  by  Volta  must  be  rejected. 

Charges  of  form. — The  changes  of  form  caused  in  a  substance  by  variations 
of  temperature,  such  as  liquefaction  and  solidification,  the  formation  and  conden- 
sation of  vapour,  constitute  another  reputed  source  of  electricity.  Pouillet^  how- 
ever, questions  this  opinion ;  and  maintains,  that  in  every  case  where  change  of 
form  produces  electric  excitement,  there  is  also  chemical  action.  Thus,  when 
water  evaporates,  the  electricity  is  due  to  the  separation  of  the  water  from  its 
saline  impregnations,  or  to  its  action  on  the  containing  vessel ;  and  pure  water, 
evaporated  in  platinum  vessels,  produces  no  excitement.  He  ascribes  to  the 
separation  of  water  from  saline  matter,  constantly  going  on  at  the  surface  of  the 
earth,  and  to  the  chemical  changes  produced  in  the  growth  of  vegetables,  the 
developement  of  a  great  part  of  the  atmospheric  electricity.  My  own  experi- 
ments have  given  similar  results ;  but  Harris,  with  an  apparatus  of  great  deli- 
cacy, has  detected  electricity  during  the  evaporation  of  pure  water  in  plantinum 
vessels,  although  in  very  small  quantity. 

[Recent  observations  have  shown  that  current^  of  steam,  under  certain  condi- 
tions, may  he  successfully  employed  for  the  generation  of  large  quantities  of 
electricity.  The  accidental  discovery  by  a  workman  in  New  Castle  of  the  elec- 
tricity of  a  steam  boiler,  led  to  a  series  of  experiments,  by  Armstrong  and  others, 
and  subsequently  by  Faraday  ;  showing  that  when  the  steam  boiler  is  insulated 
and  the  steam  allowed  to  escape  by  apertures,  properly  constructed,  the  boiler 


ELECTRICITY.  73 

and  its  appendages  become  strongly  charged  with  electricity.  Faraday  found 
that  while  the  boiler  was  thus  rendered  negative,  the  issuing  steam  was  in  the 
opposite,  or  positive  state,  and  he  inferred  that  the  whole  phenomena  arose  from 
the  rubbing  of  the  condensed  water  against  the  sides  of  the  tube  from  which  the 
steam  was  issuing,  and  was  thus  due  to  a  species  of  friction,  rather  than  to  the 
passage  of  the  water  from  the  liquid  to  the  aeriform  state.  This  discovery  has 
given  rise  to  a  new  and  very  powerful  apparatus  for  accumulating  electricity, 
called  the  hydro-electric  machine.  It  consists  of  a  boiler  supported  on  glass 
pillars,  and  furnished  with  a  long  range  of  jets,  mounted  at  the  end  with  wood. 
Steam  of  high  pressure  is  used,  and  the  electricity  of  the  steam  is  conducted 
into  the  ground  by  a  row  of  metallic  points  placed  in  front  of  the  jets.  From  a 
machine  of  this  kind  sparks  have  been  obtained  twenty  inches  long,  and  the 
electric  supply  is  so  abundant  as  to  charge  a  battery  more  rapidly  than  the  most 
powerful  machine  of  the  ordinary  construction.] 

Proximity  to  an  electrijied  body. — It  is  a  direct  consequence  of  the  attractive 
and  repulsive  powers  ascribed  to  the  electric  fluids,  that  an  unelectrified  con- 
ductor must  be  excited  by  the  vicinity  of  an  electrified  body.  Let  ab,  fig.  l,be 
an  unexcited  conductor,  supported  on  an  insulating  F^o-  ^^ 

glass  rod  hc;  and  let  c,  containing   free   positive    |_^     -p^ ^ 

electricity,  and  similarly  insulated,  be  placed  near    '-^i^ 
it  on  the  side  a.     The  free  positive  electricity  on 
c  will  both  repel  the  positive  fluid  of  ab,  and  attract 
its  negative  fluid,  and  the  result  of  these  concurring    CD 


X 


forces  is  instantly  to  decompose  a  portion  of  the  combined  electricities  of  ab,  the 
free  negative  fluid  approaching  as  close  as  possible  to  c,  and  the  positive  fluid 
receding  from  it.  The  relative  position  of  these  fluids  is  indicated  in  the  figure 
by  the  signs  -f-  and  — ,  the  former  denoting  positive  and  the  latter  negative 
electricity.  The  opposite  ends  of  the  conductor  ab  are  thus  oppositely  electri- 
fied, and  in  an  equal  degree  :  the  excitement  is  found,  as  would  be  anticipated, 
to  be  greatest  at  the  extremities,  and  to  diminish  gradually  towards  the  middle 
line  ah,  which  is  neutral.  The  quantity  of  electricity  thus  set  free  depends  on 
the  extent  to  which  c  is  excited,  and  on  its  distance  from  ab.  If  now  c  be  sud- 
denly withdrawn,  the  opposite  fluids  at  a  and  b  coalesce,  and  the  equilibrium  of 
ab  is  restored.  But  so  long  as  c  retains  iis  position,  a  will  be  negative,  even 
were  it  uninsulated.  The  only  efifect  of  communication  with  the  ground  is  to 
neutralize  the  positive  fluid  at  b  by  supplying  to  it  negative  electricity  from  the 
earth  :  if  after  having  effected  this  by  touching  the  cylinder  for  an  instant  with 
the  finger,  c  be  withdrawn,  ab  is  left  with  an  excess  of  the  negative  fluid. — The 
electricity  thus  developed  by  the  contiguity  of  an  electrified  body  is  said  to'  be 
induced^  or  to  be  excited  by  induction. 

The  student  should  reflect  carefully  on  these  inferences  from  the  theory  of 
electricity,  since  the  applications  of  such  knowledge  are  numerous.  A  few  of 
these  may  now  be  enumerated  : — 

1.  An  electrified  body  attracts  light  objects  near  it,  because  it  induces  in  them 
a  state  opposite  to  itself.  The  attraction  is  most  lively  when  the  light  object  is 
a  conductor,  and  in  contact  with  the  ground,  since  it  then  more  completely 
assumes  an  electric  state  opposed  to  that  of  the  inducing  body.  A  non-con- 
ductor is  very  imperfectly  electrified  by  induction,  because  the  electric  fluids 
cannot  quit  each  other  from  inability  to  move  through  the  non-conductor. 

2.  If  a  stick  of  sealing-wax,  strongly  —  be  presented  to  a  thread  or  pith  ball 


7t  ELECTRICITY. 

which  is  also  negatively,  hut  feebly,  excited,  repulsion  will  ensue  at  a  consider- 
able distance,  followed  by  attraction  when  the  distance  is  small.  This  attrac- 
tion is  due  to  the  strongly  excited  wax  acting  by  induction  on  the  feebly  — 
thread,  thereby  causing  it  to  have  an  excess  of  -f-  electricity. 

3.  The  -|-  electricity  collected  on  the  prime  conductor  of  anelectrical  machine 
is  by  some  ascribed,  not  to  a  transfer  of  that  fluid  from  the  glass  to  the  prime 
conductor,  but  to  a  part  of  the  combined  electricities  of  the  prime  conductor 
being  separated  by  induction,  and  the  —  fluid  being  imparted  to  the  -|-  glass. 
The  same  view  is  applicable  to  any  system  of  conductors  in  contact  with  the 
prime  conductor,  as  also  to  conductors  connected  with  the  rubber.  It  is  difficult 
to  say  which  explanation  is  the  more  correct,  or  whether  both  may  not  be  true. 

4.  On  moving  the  hand  towards  the  prime  conductor  of  an  excited  electrical 
machine,  the  hand  becomes  —  by  induction,  and  the  spark  ultimately  obtained 
restores  the  equilibrium.  In  like  manner  a  negatively  electrified  cloud  renders 
-|-  a  contiguous  tree  or  tower,  and  then  a  stroke  of  lightning  follows  as  a  con- 
sequence of  attraction  between  the  two  accumulated  fluids. 

6.  The  action  of  the  Ley  den  jar  depends  on  the  principle  of  induced  electri- 
city. A  glass  jar  or  bottle  with  a  wide  mouth  is  coated  externally  and  inter- 
nally with  tinfoil,  except  to  within  three  or  four  inches  of  its  summit ;  and  its 
aperture  is  closed  by  dry  wood  or  some  imperfect  conductor,  through  the  centre 
of  which  passes  a  metallic  rod  communicating  with  the  tinfoil  on  the  inside  of 
the  jar.  On  placing  the  metallic  rod  in  contact  with  the  prime  conductor  of  an 
excited  electrical  machine,  while  the  outer  coating  communicates  with  the 
ground,  the  interior  of  the  jar  acquires  a  charge  of  -f-  electricity,  and  the  exterior 
becomes  as  strongly  — .  The  exterior  may  be  handled  without  destroying  the 
charge,  provided  no  communication  be  at  the  same  time  made  with  the  interior. 
But  when  a  conductor  communicates  with  both  surfaces  at  the  same  instant,  the 
two  fluids  rush  together  with  violence,  and  the  equilibrium  is  restored. 
Whether  in  this  and  similar  cases  the  two  fluids  coalesce  entirely  on  the  inter- 
mediate conductor,  or  whether  each  from  its  velocity  may  not  in  part  pass  the 
other,  and  be  projected  to  the  opposite  surface,  is  a  question  on  which  electri- 
cians are  not  agreed. 

The  Leyden  jar  affbrds  the  means  of  passing  through  bodies  a  large  quantity 
of  electricity.  For  not  only  may  jars  of  any  required  size  be  employed,  but  it 
is  easy  so  to  arrange  any  number  of  such  jars,  that  they  shall  all  be  charged 
and  discharged  at  the  same  time,  constituting  what  is  termed  an  electrical  hat- 
iery.  The  arrangement  is  made  by  placing  a  number  of  Leyden  jars  in  a  box 
lined  with  tinfoil,  by  which  means  their  outer  surfaces  have  free  metallic  com- 
munication with  each  other,  and  connecting  their  inner  surfaces  by  wires. 

6.  The  principle  of  induced  electricity  was  ingeniously  applied  by  Volta  in 
Fig.  2.  the  construction  of  the  Condenser,  This  apparatus,  fig.  2,  con- 
sists of  two  brass  plates,  a  and  b,  supported  on  a  common  stand 
D.  One  of  the  plates  b  is  attached  to  the  stand  by  means  of  a 
hinge  c,  so  that,  though  represented  upright,  it  may  be  placed 
horizontally,  and  be  thus  withdrawn  from  the  vicinity  of  the 
plate  A,  the  support  of  which  is  made  of  glass.  On  electrifying 
the  insulated  plate  positively,  the  plate  b,  expressly  placed  close 
to  A,  is  rendered  —  by  induction ;  and,  as  happens  in  the  Leyden 
jar,  the  excitement  of  b  will  be  proportional  to  that  of  a.  The 
—  charge  of  b  tends  to  preserve  the  -|-  charge  of  a,  which  may 


ELECTRICITY. 


7& 


consequently  receive  still  more  electricity  by  contact  with  any  -f-  surface,  withf  ut 
losing  what  it  had  previously  acquired.  Thus  is  electricity  accumulated  or  con- 
densed on  A ;  so  that  a  substance  too  feebly  excited  to  produce  any  appreciable 
effects  of  itself,  may  by  repeated  contact  with  the  insulated  plate  of  a  condenser 
communicate  a  charge  of  considerable  intensity.  The  effect  of  the  accumulation 
is  made  apparent  by  withdrawing  b,  and  bringing  a  in  contact  with  a  delicate 
electrometer.  The  condenser  is  much  employed  in  experiments  of  delicacy,  and 
the  plate  a  is  often  permanently  fixed  on  the  gold  leaf  electrometer. 

7.  The  Eledrophorus  is  another  contrivance  of  Volta's,  which  acts  by  induced 
electricity.  It  consists  essentially  of  two  parts  ;  one  being  a  flat  cake  of  resin, 
made  by  pouring  melted  resin  into  a  shallow  plate  or  circular  dish  of  tinned  iron, 
and  the  other  a  disk  of  brass,  of  rather  smaller  diameter  than  the  resin,  supplied 
with  a  glass  handle.  The  surface  of  the  resin  is  negatively  excited  by  friction 
or  flapping  with  silk  or  flannel,  and  the  brass  disk  is  laid  upon  it.  The  resin 
being  a  non-conductor  retains  its  own  electricity  in  spite  of  the  super-imposed 
brass,  and  decomposes  the  combined  electricities  of  the  latter,  causing  its  under 
surface  to  be  -f-  ,  and  its  upper  — .  On  touching  the  brass  with  the  finger,  its, 
upper  surface  is  neutralized ;  and  on  then  withdrawing  the  brass  plate,  it  is  found 
to  have  an  excess  of  -f-  electricity.  On  replacing  the  brass  as  before,  the  resin, 
having  lost  none  of  its  electricity  in  the  process,  acts  again  upon  the  metallic 
disk  as  on  the  first  occasion,  and  will  continue  so  to  act  for  an  indefinite  number 
of  times.    Kept  in  a  dry  place,  the  electrophoras  will  keep  in  action  for  months. 


INDUCTION  BY  CONTIGUOUS  PARTICLES. 

That  the  excitation  by  induction  of  a  body  at  a  distance  is  effected  from  parti- 
ticle  to  particle  of  the  interposed  substance,  is  beautifully  shown  in  the  results 
obtained  by  Faraday,  concerning  the  influence  of  the  nature  of  the  medium  on  the 


amount  of  inductive  charge  transmitted.  The  instrument, 
Fig.  3,  which  he  has  termed  an  indudomeier,  consists 
of  a  hollow  sphere  of  brass  a  a  b,  and  a  sphere  of 
smaller  size,  h,  also  of  brass,  which  is  placed  exactly 
concentric  with  it.  The  interval  between  these,  o  o, 
may  be  occupied  by  any  substance,  as  air,  or  glass,  or 
sulphur,  and  then  the  central  sphere  being  insulated  from 
the  outer  by  the  shell-lac  column  6,  and  having  been 
excited  from  the  machine,  through  the  ball  and  wire  b, 
the  outer  one  is  uninsulated,  and  the  whole  becomes  a 
Leyden  jar,  in  which  the  material  may  be  varied  at  the 
will  of  the  experimenter.  By  means  of  the  tube  and 
stopcock  /  c?,  the  air  in  o  o,  may  be  removed  and  any 
other  gas  substituted  for  it.  The  outer  sphere  opens  at 
h  in  tvvo,  so  that  melted  sulphur  or  shell-lac,  may  be 
poured  in  to  form  the  inductive  medium. 

When  the  internal  sphere  is  excited  always  to  the 
same  degree,  the  charge  of  the  external  coating  should 
be  the  same,  no  matter  what  might  be  the  nature  of  the 
intervening  substance,  if  the-  action  took  place  simply 
at  a  distance  after  the  manner  of  gravitation.  But  tliis 
is  not  the  case.  With  the  same  internal  charge,  the 
excitation  of  the  external  sphere  was  found  to  be,  that 


Fig.  3. 


f6 


ELECTRICITY. 


Fig.  4. 


ll 


a 


wi^i  air  being  100,  with  shell-lac,  150,  with  flint-glass,  176,  and  with  sulphur, 
224.  In  these  cases,  therefore,  the  molecular  excitation  was  transmitted  in  pro- 
portion to  these  numbers,  which  express,  therefore,  the  degree  of  excitation,  that 
a  common  amount  of  inductive  influence  is  able  to  produce  in  masses  of  these 
bodies.  All  gases,  no  matter  how  different  in  chemical  properties  and  constitu- 
tion, even  though  the  temperature  and  pressure  do  not  remain  the  same,  pos- 
sessed the  same  specific  inductive  capacity  as  air. 

This  principle  is  further  shoAvn  in  an  interesting  manner  by  the  fact,  that  the 
induction  is  not  exercised  only  in  the  straight  line  connecting  the  solid  inducing 
and  induced  bodies,  but  that  at  every  intervening  point  there  is  a  lateral  action 
exercised  by  the  interposed  molecules  of  air  which  may  be 
themselves  considered  centres  of  inductive  force.  Thus, 
Fig.  4,  if  a  cylinder  a  of  shell-lac  be  excited  by  friction  and 
a  brass  hemisphere  A,  placed  on  top  of  it,  the  intensity  of 
.  the  induced  electricity  will  be  found  to  depend  not  merely 
on  the  distance  from  the  excited  source  and  the  nature  of 
the  interposed  material,  but  to  be  more  energetic  in  certain 
positions  in  the  air,  as  when  the  carrier  ball  of  Coulomb's 
torsion  electrometer  was  placed  at  o,  than  when  it  was 
lower  or  higher  at  n  or  /). 

Faraday  has  been  led  by  his  experiments  to  conclude, 
that  the  difference  between  conducting  and  non-conducting 
bodies  is,  that  the  former  assume  with  exceeding  rapidity, 
under  an  inductive  influence,  this  condition  of  molecular 
excitation,  and  hence  appear  to  allow  the  electricity  to  pass, 
actually  and  instantly,  through  their  substance,  whereas  in 
reality  it  is  only  that  the  separation  and  recomposition  of  the  electricities  of  the 
chain  of  molecules  has  been  so  accomplished.  They  lose  also  this  condition  as 
soon  as  the  exciting  cause  has  been  removed,  whereas,  non-conductors,  when 
their  particles  have  acquired  electrical  excitation,  remain  in  that  state  of  tension 
for  a  certain  time.  Thus,  if  the  internal  and  external  coatings  of  a  Leyden  jar 
were  connected  by  a  metallic  wire,  the  inductive  action  should  be  propagated 
immediately  across  it ;  but  the  instant  that  the  source  of  the  excitation  was 
removed,  the  electricities  of  the  two  coatings  should  recombine,  from  the  facility 
with  which  the  molecules  of  the  wire  could  assume  the  inverse  condition.  But 
with  an  interposed  plate  of  glass  the  result  is  different,  the  inductive  action  is 
propagated  equally,  but  more  slowly ;  and  that  it  is  the  particles  of  the  glass 
that  really  produce  the  charge  by  their  excitation,  is  demonstrated  by  the  fact, 
that  the  metallic  coatings  may  be  removed,  and  yet  the  accumulated  electricities 
be  not  disturbed ;  the  tin-foil  serving,  only,  to  discharge  at  the  same  moment 
every  particle  of  the  glass,  as  if  a  wire  had  been  individually  applied  to  each. 
Tliat  the  induction  has  acted  on  the  substance  of  the  glass,  explains  also  the 
peculiarity  of  what  is  called  the  secondary  or  residual  charge.  When  the  parti- 
cles at  the  surface  have  been  discharged,  they  are  acted  on  by  the  deeper  mole- 
cules which  are  still  excited,  and  hence  acquire  a  second  inductive  charge,  and 
with  thick  glass,  and  particularly  with  bodies  which  do  not  insulate  quite  so  well 
as  glass,  there  may  be  even  a  third  or  a  fourth  charge  of  this  kind. 

Conduction  is  therefore  only  the  highest,  most  intense,  and  most  rapid  form  of 
induction;  and  it  appears  from  Faraday's  investigations,  that  the  permanent  exci- 
tation of  an  electrified  body  has  its  origin  also  in  the  inductive  influence  of  the 
bodies  that  are  around.    (Elements  of  Chem.  by  R.  Kane.) 


ELECTRICITY.  77 

ELECTROSCOPES  AND  ELECTROMETERS. 

It  is  very  important,  in  experiments  on  electricity,  to  possess  easy  methods  of 
discovering  when  a  substance  is  electrified,  of  ascertaining  its  intensity  or  the 
degree  to  which  it  is  excited,  and  distinguishing  the  kind  of  excitement.  The 
means  for  effecting  these  objects  are  founded  on  electrical  attraction  and  repul- 
sion, and  the  instruments  employed  for  the  purpose  are  called  Electroscopes  and 
Electrometers ;  the  latter  denoting  the  intensity  of  electricity, — the  former  merely 
indicating  excitement,  and  the  electrical  state  by  which  it  is  produced.  The  term 
"  electrometer,  however,  is  often  indiscriminately  applied  to  all  such  instruments, 
since  the  methods  of  ascertaining  the  kind  of  excitement  give  at  the  same  time 
some  idea  of  its  intensity. 

Gold  Leaf  Electrometer. — Several  simple  electroscopic  methods  have  already 
been  indicated  (page  69).  Small  balls  made  of  the  pith  of  elder  are  used  for  the 
same  purpose.  A  single  pith  ball,  suspended  by  a  cotton  thread,  is  attracted  by 
a  feebly  electrified  substance.  Also,  when  two  pith  balls  are  suspended  from 
the  same  point  by  cotton  threads  of  equal  length,  and  an  electrified  body  is  placed 
near  them,  the  two  balls  are  thrown  by  induction  into  the  same  electric  state,  and 
diverge.  The  gold  leaf  electrometer,  figure  5,  invented  by  Bennett,  acts  -pig.  5. 
upon  the  same  principle,  but  is  far  more  delicate.  It  consists  of  a  glass  a 
cylinder  cemented  below  upon  a  brass  plate  cd,  and  covered  above  by 
a  brass  plate  ab,  pierced  in  its  centre  for  the  insertion  of  a  glass  tube  -^^ 
be,  the  top  of  which  is  closed  by  a  brass  plate  a :  into  this  plate  is 
screwed  a  thick  brass  wire,  which  passes  through  the  glass  tube,  and 
from  the  lower  end  d  of  which  two  slips  of  gold  leaf  are  suspended. 
These  different  parts  are  put  together  while  quite  dry,  all  the  joinings ^^ 
are  secured  by  wax  cement,  and  the  glass  is  covered  by  lac  varnish. 
The  effect  of  these  arrangements  is  to  insulate  the  plate  a  with  its  wire  and  gold 
leaves,  while  the  latter  are  secure  against  being  moved  by  currents  of  air.  The 
approach  of  any  electrified  body,  even  though  feebly  excited,  to  the  plate  a,  is 
immediately  detected  by  the  divergence  of  the  leaves,  as  shown  in  the  figure. 
The  instrument  is  equally  useful  in  indicating  the  kind  of  excitement,  provided 
the  plate  and  leaves  be  permanently  electrified,  which  may  easily  be  done  on  the 
same  principle  as  in  charging  the  metallic  disk  of  an  electrophorus.  If  the  plate 
be  thus  charged  with  -j-  electricity,  the  leaves  diverge,  and  continue  divergent 
for  some  time  if  the  air  be  dry.  In  this  state,  the  approach  of  a  body  charged 
with  -j-  electricity  increases  the  divergence ;  while  the  approach  of  a  body 
charged  with  —  electricity  has  a  contrary  effect. 

Quadrant  Electrometer. — An  instrument  much  used  for  estimating  the  degree 
or  intensity  of  electricity  is  the  quadrant  electrometer,  invented  by  Henley.  This 
instrument,  though  convenient  for  experiments  of  illustration,  is  not  suited  to 
those  of  research,  wherein  the  object  is  to  examine  the  effects  of  substances  feebly 
electrified,  and  ascertain  their  relative  forces  with  accuracy.  Fig.,6. 

Torsion  Electrometer. — This  instrument,  invented  by  Coulomb, 
is  peculiarly  fitted  for  scientific  investigation.     It  consists  of  a 
small  needle  of  gum-lac  c  d,  fig.  6,  suspended  horizontally  by  a 
silk  thread  as  spun  by  the  silkworm,  or  by  a  fine  silver  wire  a  b  ; 
on  the  point  of  the  needle  is  fixed  a  small  gilt  ball  made  of  the  ^te=:= 
pith  of  elder ;  and  the  whole  is  covered  with  a  glass  case  to  pro-     ...,:: 
tect  it  from  moisture  and  currents  of  air.     The  pith  ball,  when    Jt^ 
the  apparatus  is  at  rest,  is  in  contact  with  the  knob  e  of  a  metallic     — 
conductor  fe,  which  passes  through  a  hole  in  the  glass  case,  and  ^^ 


78 


ELECTRICITY. 


is  secured  in  its  place  by  cement ;  but  when  an  excited  body  is  made  to  touch 
the  conductor,  the  pith  ball  in  contact  with  it  is  similarly  excited,  and  recedes 
from  it  to  an  extent  proportional  to  the  degree  of  excitement.  The  needle  con- 
sequently describes  the  arc  of  a  circle,  which  is  measured  on  the  graduated  arc 
A  B,  and  in  its  revolution  twists  the  supporting  thread  more  or  less  according  to 
the  length  of  the  arc  described.  The  torsion  thus  occasioned  calls  into  play  the 
elasticity  of  the  thread, — a  feeble  but  constant  force,  which  opposes  the  move- 
ment of  the  needle,  measures  by  the  extent  to  which  it  is  overcome  by  the  repul- 
sive force  exerted,  and  brings  back  the  needle  to  its  original  position  as  soon  as 
the  electric  equilibrium  is  restored.  It  has  been  proved  that  the  force  wljich 
causes  the  torsion  is  exactly  proportional  to  the  arc  described  by  the  needle. 
,  Balance  Electrometer. — Harris  has  made  a  happy  application  of  the  common 
balance  and  weights  to  estimate  the  mutual  attraction  of  oppositely  electrified 
Fig.  7.  surfaces.    The  apparatus,  figure  4,  consists  of  a  brass  beam 

B  b',  supported  by  a  conductor  c  d  standing  on  a  wooden  frame 
A  a'  ;  rf  is  a  scale  for  holding  weights,  and  e  its  support ;  a,  6, 
are  gilt  cones  made  of  light  wood,  a  being  suspended  by  a 
silver  wire  from  b',  and  h  insulated  by  the  glass  support  a'  ^, 
The  instrument  is  prepared  for  use  by  placing  a  and  d  in  exact 
equipoise ;  the  cone  a  is  suspended  so  that  its  base  shall  be 
opposite  and  parallel  to  the  base  of  the  cone  S,  as  may  be  done 
by  means  of  three  adjusting  screws  in  the  frame  a  a'  ;  and  h 
is  raised  by  help  of  a  graduated  brass  slide  c,  until  the  bases 
of  the  cones  are  just  in  contact.  The  cone  b  is  then  depressed 
to  any  desired  distance,  which  may  be  varied  at  will  during  an 
experiment,  and  it  is  connected  with  the  inner  coating  of  a 
Leyden  jar,  the  outer  coating  of  which  communicates  with  the 
'frame  a  a',  and  along  c  d  b'  with  the  cone  a :  these  cones  may 
thus  be  made  parts  of  a  charged  Leyden  jar,  and  be  oppositely  excited,  as  indi- 
cated by  the  signs  -f-  and  — .  The  attractive  forces  exerted  between  their  bases 
tend  to  draw  down  the  cone  a  into  contact  with  h,  discharging  the  jar ;  but  before 
it  can  do  so,  it  has  to  overcome  the  weight  which  may  be  in  the  scale  d.  By  this 
Fig.  8.  ingenious  contrivance  any  number  of  attractive  forces  are  estimated 
by  a  common  standard,  namely,  the  number  of  grains  which  each 
is  able  to  raise. 

Unit  Jar. — This  is  another  contrivance  by  Harris,  and  is  a  most 
important  addition  to  our  stock  of  electrical  apparatus.  It  is  formed 
of  a  small  inverted  Leyden  jar,  figure  5,  supported  and  insulated 
by  a  slender  glass  rod  ef,  which  is  covered  with  lac  varnish,  and 
fixed  into  a  wooden  frame  a.  The  inner  coating  of  this  jar  is  in 
metallic  contact  with  a  brass  ball  d  and  a  wire  a,  which  wire  com- 
municates with  the  prime  conductor  of  an  active  electrical  machine; 
whereas  the  brass  ball  c  and  wire  h  are  connected  with  its  outer 
coating.  If  the  wire  h  be  held  in  the  hand,  or  otherwise  commu- 
nicate with  the  ground,  the  electrical  machine  being  in  action,  the 
jar  is  charged  in  the  usual  manner,  and  is  discharged  by  a  spark 
passing  between  the  two  brass  balls  c  and  d.  The  interval  may 
be  increased  or  diminished  by  causing  one  of  the  balls  to  be  move- 
able by  means  of  a  slide  or  screw.  It  will  be  readily  conceived 
that  successive  sparks  through  the  same  interval  must  be  caused 
by  equal  quantities  of  electricity ;  and  experiment  shows  this  to  be  the  case,  pro- 


ELECTRICITY.  ^ 

vided  the  apparatus  is  clean  and  dry,  and  the  charges  are  taken  nearly  at  the  same 
time,  that  is,  while  the  air  in  relation  to  temperature,  pressure,  and  moisture,  may 
be  considered  constant.  On  taking  six  successive  sparks  we  employ  six  times 
as  much  electricity  as  for  one  charge,  and  three  times  as  much  as  for  two  charges, 
the  quantity  of  electricity  being  proportional  to  the  number  of  charges.  It  is  on 
this  account  Harris  introduced  the  term  unit  jar.  It  is  used  for  charging  Ley  den 
jars  or  batteries  with  known  proportions  of  electricity. 

Electric  Intensity. — Before  concluding  this  account  of  electrometers,  it  will  be 
useful  to  refer  to  the  kind  of  information  which  they  supply.  From  their  mode 
of  action,  it  is  plain  that  they  indicate  the  degree  of  electric  excitement,  the 
remoteness  from  the  unexcited  state,  a  condition  expressed  by  the  terms  tension 
and  intensity.  If  two  insulated  brass  disks  of  equal  size  be  supplied  with  equal 
quantities  of  free  electricity,  they  will  affect  an  electrometer  equally,  and  there- 
fore their  intensity  or  tension  is  equal ;  but  if  one  of  the  disks  be  larger  than  the 
other,  the  smaller  will  have  the  highest  tension.  In  fact,  one  square  inch  of  the 
smaller  disk  will  possess  more  free  electricity  than  the  larger,  and  that  is  pre- 
cisely the  condition  which  constitutes  differences  of  intensity.  Of  any  number 
of  electrified  substances,,  that  will  have  the  highest  intensity  which  has  the  most 
free  electric  fluid  on  unity  of  surface. 

LAWS  OF  ELECTRICAL  ACCUMULATION. 

1.  The  quantity  of  free  electricity  which  an  insulated  conductor  is  capable  of 
receiving  is  independent  of  its  quantity  of  matter.  Thus,  two  brass  spheres  of 
the  same  size,  one  solid  and  the  other  hollow,  will  take  equal  quantities  of  elec- 
tricity, and  possess  equal  intensities.  The  cause  of  this  is  referable  to  the 
second  law. 

2.  The  free  electricity  of  an  insulated  conductor  is  always  accumulated  on  its 
surface,  where  it  forms  a  layer  or  stratum  enveloping  the  substance  on  every 
side,  and  therefore  possessed  of  the  same  figure.  The  cause  of  free  electricity 
being  disposed  upon  the  surface  of  conductors  is  ascribed  to  the  mutual  repul- 
sion of  its  particles,  which  gives  them  a  tendency  to  recede  as  far  as  possible 
from  each  other,  and  to  be  arrested  at  the  surface  solely  by  some  counteracting 
force,  such  as  the  interposition  of  an  imperfect  conductor. 

3.  The  mode  in  which  electricity  is  distributed  over  the  surface  of  a  conductor 
is  dependent  on  its  figure.  On  a  sphere  it  forms  an  unifdrm  stratum  of  equal 
thickness  all  around,  that  is,  each  part  of  the  surface  has  the  same  quantity  of 
electricity  as  any  other  part  of  equal  size.  But  on  an  ellipsoid  the  stratum  is 
thickest  at  the  extremities  of  the  longer  axis,  and  the  accumulation  at  those 
parts  is  greater  and  greater  as  the  length  of  that  axis  becomes  more  and  more 
predominant.  In  all  conductors  which  are  much  longer  than  broad,  as  in  a  nar- 
row metallic  bar,  as  also  in  those  which  have  elongated  pointed  terminations,  the 
principal  accumulation  is  at  the  ends  and  projecting  points.* 

The  unequal  accumulation  of  electricity  on  conductors  is  a  direct  consequence 
of  the  law  of  electric  repulsion ;  and  Poisson,  assuming  the  truth  of  that  law, 
has  arrived  by  calculation  at  the  very  same  conclusions  which  Coulomb  obtained 
by  experiment.  Those  who  are  prepared  to  follow  such  very  high  mathematical 
inquiries  are  referred  to  Poisson's  original  Essay,  to  the  article  on  Electricity  by 
"Whewell,  in  the  Encyclopedia  Metropolitana,  and  to  a  late  work  on  Electricity 
by  Murphy. 

*  This  has  been  established  experimentally  by  Coulomb. 


80  ELECTRICITY. 

4.  The  electric  fluid  accumulated  at  the  surface  of  conductors  tends  to  escape 
by  the  repulsion  of  its  particles.  Its  pressure  against  the  air,  or  its  effort  to 
escape,  at  any  part,  is  considered  proportional  to  the  square  of  the  quantity  ;  so 
that  if  the  electric  accumulations  at  four  different  parts  of  an  excited  conductor 
are  as  1,  2,  3,  and  4,  the  pressure  against  the  air  at  those  parts  will  be  as  1,  4, 
9,  and  16.  Hence  electricity  passes  off  with  great  rapidity  from  the  ends  or 
projecting  points  of  conductors,  a  result  quite  conformable  to  experience.  But 
the  equilibrium  of  an  excited  conductor  is  perhaps  never  entirely  restored  by 
the  direct  diffusion  of  its  excess  due  to  its  own  repulsion ;  for  the  conductor 
necessarily  tends  to  induce  a  state  opposite  to  itself  in  contiguous  conductors  and 
in  the  circumambient  air,  and  then  the  attraction  of  oppositely  electrified  surfaces 
is  called  into  play. 

5.  Coulomb  proved  experimentally,  by  aid  of  his  torsion  electrometer,  that  the 
repulsion  of  two  similarly  electrified  bodies  varies  inversely  as  the  square  of  their 
distances. 

6.  The  attraction  of  two  oppositely  electrified  bodies  varies  inversely  as  the 
square  of  the  distance  between  them.  Coulomb,  who  verified  this  law  by  experi- 
ment, also  showed  that  the  attractive  force,  the  distance  being  constant,  varies  by 
the  same  law  as  that  for  repulsion  just  stated. 

Harris  has  given  a  beautiful  demonstration  of  these  laws  by  means  of  his 
balance  electrometer  and  unit  jar  (page  78),  the  cones  a  6,  of  figure  4,  being 
connected  respectively  with  the  outer  and  inner  coatings  of  a  large  Leyden  jar. 
On  giving  to  it  a  constant  charge  by  means  of  the  unit  jar,  and  varying  the  dis- 
tance, the  weights  raised,  or  the  attractive  force,  were  found  to  vary  inversely  as 
the  square  of  the  distance  between  the  cones.  On  preserving  the  distance  con- 
stant, giving  a  charge  capable  of  raising  one  grain,  and  then  successively  dou- 
bling, trebling,  and  quadrupling  the  quantity  first  given  to  the  inner  coating,  the 
weights  raised  were  4,  9,  and  16  grains. 

7.  It  may  be  inferred  from  the  law  No.  6,  that  when,  in  two  oppositely  excited 
bodies,  the  whole  quantity  of  electricity  and  the  distance  vary  together  and  at  the 
same  rate,  the  attractive  force  will  be  unchanged.  This  has  been  fully  proved 
by  Harris.  In  fact,  doubling  the  electricity  on  both  cones,  is  to  quadruple  the 
attractive  force  .between  them ;  and  doubling  the  distance  diminishes  the  force  by 
four  times  :  the  force  is  thus  diminished  by  one  cause  as  much  as  it  is  iiicreased 
by  the  other,  and  therefore  continues  unchanged. 

8.  Having  ascertained  the  nature  of  the  influence  exerted  by  the  atmosphere 
over  the  striking  distance  of  a  charged  Leyden  jar,  that  is,  the  interval  through 
which  the  electricity  will  pass,  so  as  to  discharge  it,  by  including  the  balls  con- 
nected with  its  outer  and  inner  coating  within  glass  vessels  susceptible  of  exhaus- 
tion. He  then  found  that  the  resistance  to  the  passage  of  a  charge  varies  as  the 
square  of  the  density  of  the  air.  Agreeably  to  the  same  law,  the  striking  dis- 
tance, when  the  charge  is  constant,  varies  inversely  as  the  density  of  the  air :  a 
charge  which  strikes  through  one  inch  of  air  when  the  barometer  is  at  30  inches, 
will  pass  through  two  inches  in  air  so  rarefied  as  to  support  only  15  inches  of 
mercury,  and  through  four  inches  when  the  mercurial  column  is  7*5  inches. 
Hence  in  a  perfect  vacuum  a  Leyden  jar  ought  to  discharge  itself  through  any 
interval ;  and  in  the  higher  parts  of  the  atmosphere,  where  the  air  is  much  rare- 
fied, two  oppositely-excited  clouds  will  neutralize  each  other,  though  separated 
by  very  great  distances. 

It  is  not  apparent  from  the  preceding  remarks,  whether  the  striking  distance  is 


ELECTRICITY.  8| 

influenced  by  chang-e  of  the  density  or  the  elasticity  of  the  confined  air,  since  in 
rarefying  air  by  the  air-pump,  the  rarefaction  increases,  and  the  elasticity 
decreases  at  the  same  rate.  Harris  has  shown,  contrary  to  what  one  might 
anticipate,  that  the  influential  condition  is  density,  and  not  elasticity.  For  on 
rarefying  air  by  heat  so  as  to  preserve  its  original  elasticity,  the  striking  dis- 
tance was  exactly  the  same  as  in  cold  air  rarefied  to  the  same  degree  by  the 
air-pump ;  and  in  air  first  rarefied  by  the  air-pump,  and  then  heated  until  it  had 
recovered  its  original  elasticity,  its  volume  and  density  being  kept  the  same,  the 
varied  elasticity  had  no  influence  on  the  charge  required  to  pass  through  a 
constant  distance.  From  these  and  similar  experiments  Harris  infers  that  the 
remarkable  conducting  power  known  to  be  possessed  by  hot  air  is  due  to  its 
rarity  alone. — Though  I  have  not  had  occasion  to  repeat  these  experiments  on 
hot  air,  I  have  entire  confidence  in  their  accuracy ;  inasmuch  as,  not  to  mention 
the  known  skill  and  exactness  of  Harris,  I  find  that  the  striking  distance  for  the 
same  charge  is  greater  in  air  than  in  carbonic  acid  g-as,  and  greater  in  hydrogen 
gas  than  in  air,  the  elasticities  being  equal. 

9.  The  continuance  of  an  excited  charge  on  an  insulated  conductor  is  com- 
monly ascribed  to  the  pressure  of  the  air.  An  opposite  opinion,  however,  has 
been  maintained.  Morgan  (Phil.  Trans.  1785),  published  some  experiments  to 
prove  that  a  space  entirely  free  from  air,  such  as  a  Torricellian  vacuum,  is  a 
non-conductor  of  electricity;  and  Cavallo  (Treatise  on  Electricity),  showed 
that  exhaustion  may  be  carried  very  far  within  the  bell-jar  of  an  air-pump 
without  an  electrified  body  placed  under  it  losing  its  charge.  On  repeating 
these  experiments,  at  the  request  of  Harris,  I  obtained  similar  results.  These 
phenomena  appear  to  indicate  the  existence  of  an  adhesive  force  between  the 
particles  of  electricity  and  the  surface  of  bodies,  which  causes  an  obstacle  to 
their  escape. 

10.  Some  elegant  and  most  ingenious  experiments  have  been  made  by  Wheat- 
stone  to  determine  the  velocity  of  electricity  (Phil.  Trans.  1834).  His  principal 
conclusions  are  the  following : — 

1.  The  velocity  of  electricity  along  a  copper  wire  exceeds  that  of  light  throueli 
the  planetary  space.  .,.^^^ 

2.  The  disturbance  of  the  electric  equilibrium  in  a  wire  communicating  at  its 
extremities  with  the  two  coatings  of  a  charged  jar,  travels  with  equal  velocity 
from  the  two  ends  of  the  wire,  and  occurs- latest  in  the  middle  of  the  circuit. 

3.  The  light  of  electricity  of  high  tension  has  a  less  duration  in  passing  as  a 
spark  than  the  millionth  part  of  a  second-.- 

HISTORICAL  NOTICE. 

The  science  of  electricity  is  of  modern  origin.  The  knowledge  of  the  ancients 
was  confined  to  the  fact  that  amber  and  the  lyncurium  (supposed  to  be  tormalin) 
acquired  the  property  of  attracting  light  bodies  by  friction.  It  was  not  known 
that  other  bodies  may  be  similarly  excited  until  the  commencement  of  the  17th 
century,  when  Gilbert  of  Colchester  detected  the  same  property  in  a  variety  of 
other  substances,  and  thereby  laid  the  foundation  of  the  science  of  electricity. 
A  few  additional  facts  were  noticed  during  the  same  century  by  Boyle,  Otto  de 
Guericke,  and  Wall,  and  in  1709  Hawkesbee  published  an  account  of  many 
curious  electrical  experiments  ;  but  no  material  progress  was  made  until  Stephen 
Grey  (Phil.  Trans.  1729  to  1733)  drew  the  distinction  between  conductors  and 

8 


82  GALVANISM. 

non-conductors  of  electricity,  and  illustrated  it  by  new  and  striking  experiments. 
Soon  after,  Dufay  in  France  distinguished  between  the  two  kinds  of  electricity; 
and  in  1759  (Phil.  Trans,  li.  340)  Symmer  added  the  important  fact  that  friction 
developes  both  kinds  of  electricity  at  the  same  time,  an  observation  which  led  to 
the  theory  of  two  electric  fluids  as  now  understood.  These  discoveries,  added 
to  the  confirmation  of  Franklin's  opinion  as  to  the  identity  of  the  cause  of 
lightning  and  electricity,  fixed  the  attention  of  scientific  men  upon  the  new 
study,  and  soon  acquired  for  it  a  high  rank  among  the  sciences. 

For  further  details  respecting  its  origin  and  early  progress  the  reader  may 
consult  the  history  of  electricity  by  Priestley. 


SECTION   IV. 


GALVANISM. 


The  science  of  Galvanism  owes  its  name  and  origin  to  the  experiments  on 
animal  irritability  made  by  Galvani,  Professor  of  Anatomy  at  Bologna,  in  the 
year  1790.  In  the  course  of  the  investigation  he  discovered  the  fact,  that  mus- 
cular contractions  are  excited  in  the  leg  of  a  frog  recently  killed,  when  two 
metals,  such  as  zinc  and  silver,  one  of  which  touches  the  crural  nerve,  and  the 
other  the  muscles  to  which  it  is  distributed,  are  brought  into  contact  with  one 
another.  Galvani  imagined  that  the  phenomena  are  owing  to  electricity  present 
in  the  muscles,  and  that  the  metals  only  serve  the  purpose  of  a  conductor.  He 
conceived  that  the  animal  electricity  originates  in  the  brain,  is  distributed  to 
every  part  of  the  system,  and  resides  particularly  in  the  muscles.  He  was  of 
opinion  that  the  different  parts  of  each  muscular  fibril  are  in  opposite  states  of 
electrical  excitement,  like  the  two  surfaces  of  a  charged  Leyden  phial,  and  that 
contractions  take  place  whenever  the  electric  equilibrium  is  restored.  This  he 
supposed  to  be  effected  during  life  through  the  medium  of  the  nerves,  and  to 
have  been  produced  in  his  experiments  by  the  intervention  of  metallic  con- 
ductors. 

The  views  of  Galvani  had  several  opponents;  one  of  whom,  the  celebrated 
Volta,  Professor  of  Natural  Philosophy  at  Pavia,  succeeded  in  pointing  out 
their  fallacy.  Volta  maintained  that  electric  excitement  is  due  solely  to  the 
metals,  and  that  the  muscular  contractions  are  occasioned  by  the  electricity  thus 
developed  passing  along  the  nerves  and  muscles  of  the  animal.  To  the  experi- 
ments instituted  by  Volta  we  are  indebted  for  the  first  voltaic  apparatus,  which 
has  properly  received  the  name  of  the  voltaic  pile ;  and  to  the  same  distinguished 
philosopher  belongs  the  real  merit  of  laying  the  foundation  of  the  science  of 
Galvanism  (Phil.  Trans.  1800). 

The  identity  of  the  agent  concerned  in  the  pheifomena  of  galvanism  and  of 
the  common  electrical  machine,  is  now  a  matter  of  demonstration.  Voltaic  and 
common  electricity  are  due  to  the  same  force,  excited  by  different  conditions, 
operating  in  general  in  a  different  manner  and  under  different  circumstances. 
The  effects  of  the  latter  are  caused  by  a  comparatively  small  quantity  of  electri- 


GALVANISM.  83 

city  brought  into  a  state  of  insulation,  in  which  state  it  exerts  a  high  intensity, 
as  evinced  by  its  remarkable  attractive  and  repulsive  energies,  and  by  its  power 
to  force  a  passage  through  obstructing  media.  In  galvanism  the  electric  agent 
is  more  intimately  associated  with  other  substances,  is  developed  in  large  quan- 
tity, but  never  attains  a  high  tension,  and  produces  its  peculiar  effects  while 
flowing  along  conductors  in  a  continuous  current. 

VOLTAIC  ARRANGEMENTS  OR  CIRCLES. 

Arrangements  for  exciting  galvanism  are  divided  into  simple  and  compound ; 
the  former  being  voltaic  circles  in  their  most  elementary  form,  and  the  latter  a 
collection  of  simple  circles  acting  together ;  it  will  hence  be  proper  to  com- 
mence the  description  of  them  with  the  most  simple. 

Simple  Voltaic  Circles. — When  a  plate  of  zinc  and  a  plate  of  copper  are 
placed  in  a  vessel  of  water,  and  the  two  metals  are  made  to  touch  each  other, 
either  directly  or  by  the  intervention  of  a  metallic  wire,  galvanism  is  excited. 
The  action  is,  indeed,  very  feeble,  and  not  to  be  detected  by  ordinary  methods  ; 
but  if  a  little  sulphuric  acid  be  added  to  the  water,  numerous  globules  of  hydro- 
gen gas  will  be  evolved  at  the  surface  of  the  copper.  This  phenomenon  con- 
tinues uninterruptedly  while  metallic  contact  between  the  plates  continues,  in 
Avhich  state  the  circuit  is  said  to  be  closed;  but  it  ceases  when  the  circuit  is 
broken,  that  is,  when  metallic  contact  is  interrupted.  The  hydrogen  gas  which 
arises  from  the  copper  plate  results  from  water  decomposed  by  the  electric  cur- 
rent, and  its  ceasing  to  appear  indicates  the  moment  when  the  current  ceases. 
In  this  case  the  voltaic  circle  consists  of  zinc,  copper,  and  interposed  dilute 
acid ;  and  the  circle  gives  rise  to  a  current  only  when  the  two  metals  are  in 
contact.     This  arrangement  is  shown  in  figure  1,  where  y\b.  1. 

metallic  contact  is  readily  made  or  broken  by  means  of 
copper  wires  soldered  to  the  plates.  By  employing  a  gal- 
vanometer (p.  94),  it  is  found  that  a  current  of  -\-  elec- 
tricity continually  circulates  in  the  closed  circuit  from  the 
zinc  through  the  liquid  to  the  copper,  and  from  the  copper  ^ 
along  the  conducting  wires  to  the  zinc,  as  indicated  by  the  ^ 
arrows  in  the  figure.  A  current  of  —  electricity,  agree- 
ably to  the  theory  of  two  electric  fluids,  ought  to  traverse  the  apparatus  in  a 
direction  precisely  reversed  ;  but  for  the  sake  of  simplicity  I  shall  hereafter 
indicate  the  course  of  the  -f-  current  only. 

Two  metals  are  not  absolutely  essential  to  the  formation  of  a  simple  circle. 
A  current  is  obtained  from  one  metal  and  two  liquids,  provided  the  liquids  are 
such  that  a  stronger  chemical  action  takes  place  on  one  side  of  the  metal  than 
on  the  other.  Nay,  a  plate  of  metal,  with  two  portions  of  the  same  liquid,  but 
of  different  strengths,  forms  a  simple  circle ;  and  even  the  same  liquid,  of  but 
one  strength,  if  one  side  of  the  metal  be  more  rapidly  acted  on  by  it  than  the 
other,  will  produce  a  current.  This  may  be  effected,  for  example,  by  having  ore 
side  rough,  the  other  polished. 

An  interesting  kind  of  simple  voltaic  circle  is  afforded  by  commercial  zinc. 
This  metal,  as  sold  in  the  shops,  contains  traces  of  tin  and  lead,  with  rather 
more  than  one  per  cent,  of  iron,  which  is  mechanically  diffused  through  its 
substance  :  on  immersion  in  dilute  sulphuric  acid,  these  small  particles  of  iron 
and  the  adjacent  zinc  form  numerous  voltaic  circles,  transmitting  their  currents 


g4  GALVANISM. 

through  the  acid  which  moistens  them,  and  disengaging  a  large  quantity  of 
hydrogen  gas.  Pure  distilled  zinc  is  very  slowly  acted  on  by  dilute  sulphuric 
acid  of  sp.  gr.  ranging  from  1*068  to  1-215;  but  if  fused  with  about  two  per 
cent,  or  rather  less,  of  iron  filings,  it  is  as  readily  dissolved  as  commercial  zinc. 
Sturgeon  has  remarked  that  commercial  zinc,  with  its  surface  amalgamated, 
which  may  be  done  by  dipping  a  zinc  plate  into  nitric  acid  diluted  with  two  or 
three  parts  of  water,  and  then  rubbing  it  with  mercury,  resists  the  action  of 
dilute  acid  fully  as  well  as  the  purest  zinc.  This  fact,  of  which  Faraday  in  his 
late  researches  has  made  excellent  use,  appears  due  to  the  mercury  bringing  the 
|M|[  surface  of  the  zinc  to  a  state  of  perfect  uniformity,  preventing  those  differences 
between  one  spot  and  another,  which  are  essential  to  the  production  of  minute 
currents  ;  one  part  has  the  same  tendency  to  combine  with  electricity  as  another, 
and  cannot  act  as  a  discharger  to  it  (Faraday). 

While  the  current  formed  by  the  contact  of  two  metals  gives  increased  effect 
to  the  affinity  of  one  of  them  for  some  element  of  the  solution,  the  ability  of 
the  other  metal  to  undergo  the  same  change  is  proportionally  diminished.  Thus, 
when  plates  of  zinc  and  copper  touch  each  other  in  dilute  acid,  the  zinc  oxidizes 
more,  and  the  copper  less,  rapidly  than  without  contact.  This  principle  was 
beautifully  exemplified  by  the  attempt  of  Davy  to  preserve  the  copper  sheathing 
of  ships.  A  sheet  of  copper  immersed  in  sea-water,  or  a  solution  of  chloride 
of  sodium,  in  an  open  vessel,  undergoes  rapid  corrosion ;  and  a  green  powder 
commonly  termed  submuriate  of  copper,  but  which  is  really  an  oxy-chloride,  is 
generated  :  atmospheric  oxygen  dissolved  in  sea-water  unites  both  with  copper 
and  sodium,  the  latter  yields  its  chlorine  to  another  portion  of  copper,  and  the 
oxide  and  chloride  of  copper  unite.  But  if  the  copper  be  in  contact  with  zinc 
or  some  metal  more  electro-positive  than  itself,  the  zinc  undergoes  the  same 
change  as  the  copper  did,  and  the  latter  is  preserved.  Davy  found  that  the 
quantity  of  zinc  required  thus  to  form  an  efficient  voltaic  circle  with  copper  was 
very  small.  A  piece  of  zinc  as  large  as  a  pea,  or  the  head  6f  a  small  round 
nail,  was  found  fully  adequate  to  preserve  40  or  50  square  inches  of  copper;  and 
this  wherever  it  was  placed,  whether  at  the  top,  bottom,  or  middle  of  the  sheet 
of  copper,  or  under  whatever  form  it  was  used.  And  when  the  connection 
between  different  pieces  of  copper  was  completed  by  wires,  or  thin  filaments  of 
the  40th  or  50lh  of  an  inch  in  diameter,  the  effect  was  the  same;  every  side, 
every  surface,  every  particle  of  the  copper  remained  bright,  whilst  the  iron  or 
the  zinc  was  slowly  corroded.  Sheets  of  copper  defended  by  l-40th  to  1- 1000th 
part  of  their  surface  of  zinc,  malleable  and  cast  iron,  were  exposed  during  many 
weeks  to  the  flow  of  the  tide  in  Portsmouth  harbour,  and  their  weight  ascer- 
tained before  and  after  the  experiment.  When  the  metallic  protector  was  from 
l-40th  to  l-150th,  there  was  no  corrosion  nor  decay  of  the  copper ;  with  smaller 
quantities,  such  as  l-200th  to  l-460th,  the  copper  underwent  a  loss  of  weight 
which  was  greater  in  proportion  as  the  protector  was  smaller ;  and  as  a  proof 
of  the  universality  of  the  principle,  it  was  found  that  even  1- 1000th  part  of  cast 
iron  saved  a  certain  proportion  of  the  copper  (Phil.  Trans.  1824). 

Unhappily  for  the  application  of  this  principle  in  practice,  it  is  found  that 
unless  a  certain  degree  of  corrosion  takes  place  in  the  copper,  its  surface 
becomes  foul  from  the  adhesion  of  sea-weeds  and  shell-fish.  The  oxy-chloride 
of  copper,  formed  when  the  sheathing  is  unprotected,  is  probably  injurious  to 
these  plants  and  animals,  and  thus  preserves  the  copper  free  from  foreign  bodies. 

Simple  voltaic  circles  may  be  formed  of  very  various  materials :  but  the  com- 


GALVANISM. 


«$ 


binations  usually  employed  consist  either  of  two  perfect  and  one  imperfect 
conductor  of  electricity,  or  of  one  perfect  and  two  imperfect  conductors.  The 
substances  included  under  the  title  of  perfect  conductors  are  metals  and  char- 
coal, and  the  imperfect  conductors  are  water  and  aqueous  solutions.  It  is  essen- 
tial to  the  operation  of  the  first  kind  of  circle,  that  the  imperfect  conductor  act 
chemically  on  one  of  the  metals ;  and  in  case  of  its  attacking  both,  the  action 
must  be  greater  on  one  metal  than  on  the  other.  It  is  also  found  generally,  if 
not  universally,  that  the  metal  most  oxidized  is  positive  with  respect  to  the  other, 
or  bears  to  it  the  same  relation  as  zinc  to  copper  in  figure  1.  Davy,  in  his 
Bakerian  lecture  for  1826  (Phil.  Trans.),  to  which  the  reader  is  referred,  has 
given  lists  of  different  arrangements  of  both  the  kinds  just  mentioned. 

Faraday  has  shown  that  the  presence  of  water  is  not  essential.  A  battery 
may  be  composed  of  other  liquid  compounds,  such  aS  a  fused  metallic  chloride, 
iodide,  or  fluoride,  provided  it  is  decomposable  by  galvanism,  and  acts  chemi- 
cally on  one  metal  of  the  circle  more  powerfully  than  on  the  other. 

Metallic  bodies  are  not  essential  to  the  production  of  galvanic  phenomena. 
Combinations  have  been  made  with  layers  of  charcoal  and  plumbago,  of  slices 
of  muscle  and  brain,  and  beet-root  and  wood ;  but  the  force  of  these  circles, 
though  accumulated  by  the  union  of  numerous  pairs,  is  extremely  feeble,  and 
they  are  very  rarely  employed  in  practice. 

Of  the  simple  voltaic  circles  described  by  Davy,  the  only  one  used  for  ordinary 
purposes  is  that  composed  of  a  pair  of  zinc  and  copper  plates  excited  by  an  acid 
solution  arranged  as  in  figure  1 .  The  form  and  size  of  the  apparatus  are  exceed- 
ingly various.  Instead  of  actually  immersing  the  plates  in  the  solution,  a  piece 
of  moistened  cloth  may  be  placed  between  them.  Sometimes  the  copper  plate 
is  made  into  a  cup  for  containing  the  liquid,  and  the  zinc  is  fixed  between  its 


Fig.  2. 


two  sides,  as  shown  by  the  accompanying  transverse  vertical 
section,  figure  2  ;  care  being  taken  to  avoid  actual  contact  be- 
tween the  plates,  by  interposing  pieces  of  wood,  cork,  or  other 
imperfect  conductor  of  electricity.     Another  contrivance,  which 
is  much  more  convenient,  because  the  zinc  may  be  removed  at 
will  and  have  its  surface  cleaned,  is  that  represented  by  the 
annexed  woodcut  (fig.  3).     C  is  a  cup  made  with  two  cylinders 
of  sheet  copper,  of  unequal  size,  placed  one  with  the  other,  and 
soldered  together  at  bottom,  so  as  to  leave  an  intermediate  space  a  a  a,  for  con- 
taining the  zinc  cylinder  z  and  the  acid  solution. 
The  small  copper  cups  b  b  are  useful  appendages ; 
for  by  filling  them  with  mercury,  and  inserting 
the  ends  of  a  wire,  the  voltaic  circuit  may  be 
closed  or  broken  with  ease  and  expedition.    This 
apparatus  is  very  serviceable  in  experiments  on 
electro-magnetism. 

Another  kind  of  circle  may  be  formed  by  coil- 
ing a  sheet  of  zinc  and  copper  round  each  other, 
so  that  each  surface  of  the  zinc  may  be  opposed 
to  one  of  copper,  and  separated  from  it  by  a  small  interval.  The  London  Insti- 
tution possesses  a  very  large  apparatus  of  this  sort,  made  under  the  direction  of 
Pepys,  each  plate  of  which  is  60  feet  long  and  two  wide.  The  plates  are  pre- 
vented from  coming  into  actual  contact  by  interposed  ropes  of  horsehair;  and 
the  coil,  when  used,  is  lifted  by  ropes  and  pulleys,  and  let  down  into  a  tub 


86 


GALVANISM. 


}!'i 


containing  dilute  acid.     The  contrivance  of  opposing  one  large  connected  surface 
of  zinc  to  a  similar  surface  of  copper  originated  with  Hare  of  Philadelphia,  who, 
from  its  surprising  power  of  igniting  metals,  gave  it  the  name  of  calori motor. 
Fig.  4.  An  excellent  arrangement  has  been  described  by  Daniell,  of 

which  fig.  4  represents  a  modification  more  simple  and  perhaps 
equally  effective.  It  consists  of  a  cylinder  of  copper,  ab  c  d  ef, 
3  inches  wide  from  a  to  b,  l|  inches  from  c  to  d,  and  four  inches 
from  e  to/,  the  corresponding  heights  being  half  an  inch,  5 
inches,  and  2  inches ;  /  m  n  o,  is  a  collar  of  copper,  which  by  the 
arms  r  r,  s  a,  rests  on  the  top  of  the  cylinder,  and  to  which  a 
membranous  tube  formed  of  the  gullet  of  an  ox  is  tied,  the  mem- 
brane being  longer  than  the  copper  cylinder,  so  as  to  be  baggy 
below  and  nearly  fill  the  space  ef;  upq,  is  a  rod  of  amalgamated 
zinc  resting  on  the  collar  /  m  n  o,  by  means  of  a  piece  of  wood 
r  5,  which  perforates  it ;  m,  t,  are  cups  to  hold  mercury  for  making 
contact.  Between  the  membrane  and  copper  cylinder  is  poured 
a  saturated  solution  of  blue  vitriol,  and  within  the  membrane  dilute  sulphuric 
acid  of  about  sp.  gr.  1*136,  which  is  made  with  1  measure  of  strong  acid  and  8 
of  water.  The  exciting  acid  is  thus  in  contact  with  the  zinc,  but  not  with  the 
copper.  When  this  circle  is  in  action,  the  electric  current  passes  from  the  zinc 
through  the  acid,  membrane,  and  solution  of  blue  vitriol  to  the  copper.  The 
arrangement  is  founded  on  two  important  principles,  established  by  Daniell : — 

1.  However  active  a  circle,  as  made  heretofore,  may  be  when  first  excited,  its 
energy  is  known  rapidly  to  diminish,  and  in  a  few  minutes  to  fall  much  below 
its  original  power.  Daniell  has  traced  the  cause  to  reduction  of  oxide  of  zinc 
by  nascent  hydrogen  at  the  surface  of  the  copper  plate,  whereby  this  metal  be- 
comes coated  with  zinc,  and  is  thus  more  or  less  converted  at  its  surface  into  a 
zinc  plate;  and  as  two  zinc  plates  under  like  conditions  do  not  produce  a  cur- 
rent, of  course  the  action  declines.  In  the  new  circle  this  defect  is  avoided  by 
the  membranous  septum  which  protects  the  copper  plate  from  contact  with  the 
solution  of  zinc;  the  nascent  hydrogen  reduces  oxide  of  copper,  and  a  film  of 
bright  copper  is  deposited  on  the  copper  plate,  thus  constantly  presenting  a  clean 
good  conducting  surface;  while  the  hydrogen  itself,  not  escaping  as  gas,  no 
longer  opposes  an  obstacle,  as  it  does  when  allowed  to  assume  the  gsiseous 
form,  to  the  passage  of  electricity,  from  the  solution  to  the  copper  plate.  To 
supply  the  loss  of  oxide  of  copper,  a  copper  disc,  a,  r,  ar,  b,  studded  with  holes 
like  a  cullender,  is  supplied,  on  which  rest  crystals  of  blue  vitriol,  whereby  the 
solution  is  kept  saturated,  and  its  conducting  power  preserved.  When  the  acid 
within  the  membrane  is  exhausted,  the  membrane  itself  is  removed,  and  fresh 
acid  supplied:  but  to  prevent  the  necessity  of  frequent  renewal,  the  lower  part 
of  the  membrane  is  made  to  act  as  a  reservoir  of  acid. 

2.  The  zinc  of  a  j>air  of  plates  may  be  much  reduced  in  size  without  any  loss 
of  power:  strong  chemical  action  on  a  small  surface  of  zinc,  a  good  conducting 
solution,  and  a  bright  large  surface  of  copper,  are  conditions  by  which  a  pow- 
erful action  is  ensured.  This  is  indicated  by  Davy's  protectors  for  copper 
sheathing  (page  84) ;  but  it  was  not  previously  known  that  the  principle  was 
applicable  to  the  construction  of  voltaic  apparatus.  The  great  merit  of  this  circle 
is  its  constancy:  by  keeping  up  the  supply  of  blue  vi^triol  and  acid,  its  energy 
will  continue  invariable  for  hours,  or  for  an  indefinite  period.  A  similar  appa- 
ratus has  been  described  by  Mullins  (Pliil.  Mag.  &  An.  ix.  122). 


GALVANISM. 


87 


Fig.  5. 


Compound  voltaic  circles. — This  expression  is  applied  to  voltaic  arrangements 
which  consist  of  a  series  of  simple  circles.  The  first  combinations  of  the  kind 
were  described  by  Volta,  and  are  now  well  known  under  the  names  of  voltaic 
pile  and  crown  of  cups.  The  voltaic  pile  is  made  by  placing  pairs  of  zinc  and 
copper,  or  zinc  and  silver  plates,  one  above  the  other,  as  in  figure  5, 
each  pair  being  separated  from  those  adjoining  by  pieces  of  cloth, 
rather  smaller  than  the  plates,  and  moistened  with  a  saturated  solu- 
tion of  salt.  The  relative  position  of  the  metals  in  each  pair  must 
be  the  same  in  the  whole  series ;  that  is,  if  the  zinc  be  placed  below 
the  copper  in  the  first  pair,  the  same  order  should  be  observed  in  all 
the  others.  Without  such  precaution  the  apparatus  would  give  rise 
to  opposite  currents,  which  would  neutralize  each  other  more  or 
less  according  to  their  relative  forces.  The  pile,  which  may  consist 
of  any  convenient  number  of  combinations,  should  be  contained  in 
a  frame  formed  of  glass  pillars,  fixed  into  a  piece  of  thick  dry  wood, 
by  which  it  is  both  supported  and  insulated.  Any  number  of  these  piles  may 
be  made  to  act  in  concert  by  establishing  metallic  communication  between  the 
-f-  extremity  of  each  pile  and  the  —  extremity  of  the  pile  immediately  following. 

The  voltaic  pile  is  now  rarely  employed,  because  we  possess  other  modes  of 
forming  galvanic  combinations  which  are  far  more  powerful  and  convenient.  The 
galvanic  battery  proposed  by  Cruickshank  consists  of  a  trough  of  baked  wood, 
about  30  inches  long,  in  which  are  placed  at  equal  distances  50  pairs  of  zinc  and 
copper  plates  previously  soldered  together,  and  so  arranged  that  the  same  metal 
shall  always  be  on  the  same  side.  Each  pair  is  fixed  in 
a  groove  cut  in  the  sides  and  bottom  of  the  box,  the 
points  of  junction  being  made  water-tight  by  cement.  Thoj 
apparatus  thus  constructed  is  always  ready  for  use,  and 
is  brought  into  action  by  filling  the  cells  left  between  the 
pairs  of  plates  with  some  convenient  solution,  which 
serves  the  same  purpose  as  the  moistened  cloth  in  the 
pile  of  Volta.  By  means  of  the  accompanying  woodcut 
the  mode  in  which  the  plates  are  arranged  will  easily  be 
understood. 

Other  modes  of  combination  are  now  in  use,  which  facilitate  the  employment 
of  the  voltaic  apparatus  and  increase  its  energy.   Most  p.     „ 

of  these  may  be  regarded  as  modifications  of  the  crown 
of  cups.  In  this  apparatus  the  exciting  solution  is 
contained  in  separate  cups  or  glasses,  disposed  circu- 
larly or  in  a  line  ;  each  glass  contains  a  pair  of  plates ; 
and  each  zinc  plate  is  attached  to  the  copper  of  the 
next  pair  by  a  metallic  wire,  as  represented  in  figure  7. 
Instead  of  glasses,  it  is  more  convenient  in  practice  to  employ  a  trough  of  baked 


Fig.  4. 


wood  or  glazed  earthenware,  divided  into  separate  cells 
by  partitions  of  the  same  material ;  and  in  order  that  the 
plates  may  be  immersed  into  and  taken  out  of  the  liquid 
conveniently  and  at  the  same  moment,  they  are  all  at- 
tached to  a  bar  of  dry  wood,  the  necessary  connection 
between  the  zinc  of  one  cell,  and  the  copper  of  the  ad- 
joining one  being  accomplished,  as  in  figure  8,  by  a  slip 
or  wire  of  copper. 
A  material  improvement  in  the  foregoing  apparatus  was 


Fig.  8. 


gB  GALVANISM. 

suggested  by  Wollaston  (Children's  Essay  in  Phil.  Trans.  1815),  who  recom- 
mended that  each  cell  should  contain  one  zinc  and  two  copper  plates,  so  that 
both  surfaces  of  the  former  metal  might  be  opposed  to  one  of  the  latter.  The 
plates  communicate  with  each  other,  and  the  zinc  between  them  with  the  copper 
of  the  adjoining  cell.  An  increase  of  one  half  the  power  is  said  to  be  obtained 
by  this  method. 

The  size  and  number  of  the  plates  may  be  varied  at  pleasure.  It  is  now 
recognized,  however,  that  increasing  the  number  of  plates  beyond  a  very  mode- 
rate limit  gives  for  most  purposes  no  proportionate  increase  of  power  ;  so  that  a 
battery  of  50  or  100  pair  of  plates,  thrown  into  vigorous  action,  will  be  just  as 
effective  as  one  of  far  greater  extent. 

A  very  effective  battery,  which,  I  apprehend,  from  its  constancy  of  action, 
convenience,  cheapness,  and  power,  will  supersede  all  others,  is  made  with 
Daniell's  simple  circles  "(page  86).  Twenty  of  these,  arranged  on  a  wooden 
tray  in  two  rows,  has  an  energy  sufficient  for  the  performance  of  most  experi- 
ments of  demonstration  or  research. 

[An  improvement  lately  introduced  in  the  construction  of  the  battery  cells, 
consists  in  substituting  for  the  membrane,  used  by  Daniell  and  Mullins,  a  dia- 
phragm, or  hollow  cylinder  of  porous  earthenware.  To  obtain  great  power  in  a 
small  compass,  these  arrangements  are  constructed  of  solid  elements  differing  as 
much  as  possible  in  their  chemical  relations.  The  plates  are  brought  as  near 
each  other  as  conveniently  practicable,  and  the  fluids  used  are  such  as  with  great 
exciting  energy  combine  the  highest  conducting  power.  Such  arrangements  are 
called  sustaining  batteries.  The  most  useful  of  these  forms  of  apparatus  at  pre- 
sent used  are  the  following:  .  ),*f  d    i 

[1.  Grove'' s  Battery.  In  this,  probably  thB  most  powerful  voltaic  combination 
that  has  yet  been  made,  the  metals  used  are  zinc  and  platinum,  the  latter  dipping 
into  strong  nitric  acid  contained  in  the  porous  cell,  while  the  zinc  in  the  outer 
vessel  is  exposed  to  the  action  of  dilute  sulphuric  acid.  According  to  the  experi- 
ments of  Jacobi,  an  apparatus  of  this  kind  having  6  square  feet  of  platinum  is 
equal  in  power  to  one  of  the  ordinary  form  in  which  100  square  feet  of  copper 
are  employed.  Instead  of  sheets  of  platinum,  a  cheaper  arrangement  with  plates 
of  platinized  silver  or  iron  may  be  employed.  This  very  efficient  arrangement, 
first  suggested  by  Mr.  Smee,  is  known  under  his  name.] 

[2.  The  Carbon  Battery^  of  Cooper,  Bunson,  and  others.  In  this,  carbon  in 
the  various  forms  of  charcoal,  coke,  anthracite,  and  plumbago,  is  associated  with 
zinc  so  as  to  replace  the  platinum  of  the  preceding  arrangement.  The  material 
of  the  cells  and  the  exciting  liquids  are  the  same.  While  little  inferior  in  energy, 
it  is  greatly  less  expensive  than  the  battery  of  Grove.] 

[3.  The  Iron  Battery.  A  very  active  combination  is  formed  by  connecting 
iron  and  zinc,  in  a  similar  manner ;  the  former  in  contact  with  the  nitric,  the 
latter  with  diluted  sulphuric  acid.  This  is  particularly  powerful,  according  to 
Schoenbein,  when  the  iron  is  previously  brought  into  what  he  calls  the  passive 
state,  in  which  condition  it  is  not  acted  upon  by  nitric  acid  alone.  He  succeeded 
in  forming  a  very  active  arrangement  by  the  combination  of  iron  in  this  state 
with  the  ordinary  iron.] 

[4.  De  la  Rive'^s  apparatus.  This  excellent  electrician  has  recently  shown  that 
a  simple  battery  of  platinum  and  zinc,  in  which  the  nitric  acid  is  replaced  by  a 
peroxide,  and  especially  by  peroxide  of  had,  is  capable,  when  charged  with 
acidulated  or  salt  water,  of  producing  very  energetic  effects.    The  peroxide. 


GALVANISM,  QQ 

reduced  to  a  fine  dry  powder,  is  heated  with  care  in  a  porous  porcelain  vessel, 
and  the  platinum  placed  in  the  middle  of  it  so  as  to  be  completely  surrounded 
by  the  peroxide.  The  external  vessel  containing  the  zinc  plate  is  charged  with 
acidulated  or  salt  water.  A  single  pair  of  this  arrangement  was  found  to  have 
much  greater  activity  in  producing  chemical  effects  than  the  same  pair  when 
excited  by  nitric  and  sulphuric  acid  as  in  Grove's  arrangement.] 

It  must  be  remembered  that  in  a  compound  circle,  the  extreme  plates  at  either 
end,  not  being  in  contact  with  the  exciting  fluid,  are  in  reality  superfluous,  and 
serve  only  as  conductors.  Hence  the  current,  instead  of  flowing  from  the  zinc 
to  the  copper,  seems  to  flow  from  the  copper  to  the  zinc.  But  if  we  abstract  the 
extreme  plates,  which  serve  only  as  conductors,  it  is  then  seen  that  the  direction 
of  the  current  corresponds  to  that  of  the  simple  circle  (see  fig.  5.) 

During  the  action  of  a  simple  circle,  as  of  zinc  and  copper,  excited  by  dilute 
sulphuric  acid,  all  the  hydrogen  developed  in  the  voltaic  process  is  evolved  at 
the  surface  of  the  copper.  This  fact  is  not  apparent  when  common  zinc  plates 
are  used,  owing  to  the  numerous  currents  which  form  on  the  surface  of  the  zinc 
(page  85) ;  but  when  a  plate  of  amalgamated  zinc  and  another  of  platinum  are 
introduced  into  dilute  sulphuric  acid  of  sp.  gr.  1.068,  no  gas  whatever  appears 
until  contact  between  the  plates  is  made,  and  then  hydrogen  gas  rises  solely 
from  the  platinum,  while  zinc  is  tranquilly  dissolved.  On  weighing  the  amal- 
gamated plate  before  and  after  the  action  has  continued  for  half  an  hour  or  an 
hour,  and  collecting  the  hydrogen  gas  evolved  during  that  interval,  the  weight  of 
the  hydrogen  set  free  and  of  zinc  dissolved  will  be  as  1  to  32.3,  being  the  ratio 
of  their  chemical  equivalents.  Faraday,  who  has  proved  this,  has  also  shown 
that  in  a  compound  voltaic  circle,  say  of  10  amalgamated  zinc  plates  and  10  .of 
platinum,  each  of  the  former  during  a  given  period  of  action  loses  exactly  the 
same  weight,  and  from  each  of  the  latter  an  equivalent  quantity  of  hydrogen  gas 
is  evolved.  This  separation  of  one  ingredient  of  the  exciting  solution  at  one 
plate,  while  the  element  previously  combined  with  it  unites  with  the  other  plate, 
seems  essential  to  voltaic  action.  It  is  in  some  way  connected  with  the  passage 
of  the  current  across  the  exciting  liquid.  Oxygen  in  a  free  state  may  by  oxidizing 
zinc  cause  electric  excitement ;  but  the  voltaic  current  is  not  established  unless 
the  oxygen  formed  part  of  a  previous  liquid  compound  in  contact  or  communica- 
tion with  both  the  plates. 

Among  the  different  kinds  of  voltaic  apparatus  is  usually  placed  the  electric 
column  of  De  Luc,  which  is  formed  of  successive  pairs  of  silver  and  zinc,  or 
silver  and  Dutch  metal  leaf,  separated  by  pieces  of  paper,  arranged  as  in  a  voltaic 
pile.  It  is  remarkable  for  its  power  of  exhibiting  attractions  and  repulsions  like 
common  electricity,  but  cannot  produce  chemical  decomposition  or  any  of  the 
effects  most  characteristic  of  a  voltaic  current,  and  is  raxher  an  electrical  than  a 
voltaic  instrument.  It  is  quoted  as  a  proof  of  electric  developement  by  contact, 
since  it  will  continue  in  action  for  years  without  being  cleaned  or  taken  to  pieces. 
True  it  is  that  the  more  oxidable  metal  of  the  column  is  slowly  corroded,  and 
that  no  electricity  is  excited  when  the  paper  is  quite  or  nearly  free  from  hygro- 
metric  moisture,  the  presence  of  which  is  necessary  to  the  oxidation  of  the  zinc 
and  copper ;  but  at  the  same  time  the  quantity  of  electricity  excited  seems  so 
disproportioned  to  the  corrosion,  that  the  one  can  scarcely  be  assigned  as  the 
cause  of  the  other. 


90  GALVANISM. 

[LAWS  OF  THE  ACTION  OF  VOLTAIC  CIRCLES. 

Electricians  distinguish  between  quantity  and  intensity  in  galvanism,  as  in 
ordinary  electricity  (page  79) ;  and  by  most  persons,  as  also  in  this  work,  the 
same  meaning  is  attached  to  them.  The  electric  intensity  of  a  voltaic  circle  is 
most  correctly  estimated  by  the  divergence  which  in  the  broken  circuit  it  causes 
in  a  gold  leaf  or  other  electrometer ;  and  as  the  intensity  is  never  considerable, 
it  is  often  necessary  to  employ  a  condenser.  The  charges  accumulated  on  the 
extreme  plates  of  a  voltaic  circle  cannot  acquire  a  high  tension,  because  the  liquid 
which  separates  them  is  a  good  conductor  for  all  charges  except  such  as  are  of 
a  very  feeble  intensity.  Accordingly,  a  simple  circle  has  necessarily  a  very  feeble 
tension.  The  circle  which  gives  the  highest  tension  is  one  which  excites  elec- 
tricity sufficient  for  duly  charging  the  apparatus,  while  it  opposes  an  obstacle  to 
spontaneous  discharge.  A  battery  of  numerous  small  plates  excited  by  water, 
or  a  weak  saline  or  acid  solution,  fulfils  these  conditions. 

The  quantity  of  electricity  circulating  in  a  voltaic  battery  is  exactly  the  same 
in  all  its  parts.  It  is  found  to  be  exactly  proportional  to  the  magnetic  and  che- 
mical effects  which  it  is  capable  of  producing ;  and  hence  the  quantity  of  elec- 
tricity moving  through  any  closed  circuit  is  readily  estimated  either  by  the 
deflection  which  it  causes  on  a  magnetic  needle,  or  by  its  power  of  chemical 
decomposition.  When  quantity  of  electricity  is  alone  desired,  a  single  pair  of 
plates  is  just  as  useful  as  a  compound  circle. 

The  following  numerical  results  were  obtained  by  Ritchie  by  means  of  a 
magnetic  galvanometer : — 

1.  The  power  of  a  single  pair  of  plates  in  deflecting  the  magnetic  needle  is 
directly  proportional  to  the  surface  of  the  plates  which  is  covered  with  dilute 
acid. 

2.  A  plate  of  zinc  introduced  into  a  rectangular  cup  of  copper,  as  in  figure  2, 
page  85,  deflects  the  needle  twice  as  much  as  when  one  side  of  the  zinc  and  the 
adjacent  surface  of  copper  are  protected  by  a  coating  of  cement  from  the  action 
of  the  acid  solution. 

3.  The  deflection  produced  by  a  pair  of  plates,  in  an  acid  solution  of  Uniform 
strength,  varies  inversely  as  the  square  root  of  the  distance  between  them, — a 
law  previously  established  by  Gumming. 

4.  The  same  law,  as  previously  deduced  by  Gumming  and  Barlow,  applies  to 
variations  in  the  length  of  the  wire  by  which  the  zinc  and  copper  plates  are  con- 
nected. If,  all  other  circumstances  being  uniform,  the  conducting  wire  varies 
from  4  feet  to  1  foot  in  length,  the  deflecting  power  will  vary  in  the  ratio  of  1 
to  2.  Ritchie  has  stated  that  with  short  metallic  wires  the  deflection  varies 
inversely  as  the  square  root  of  the  length  of  the  whole  circuit,  that  is,  of  the  solid 
and  liquid  conductors  taken  together. 

Ritchie  has  also  shown,  agreeably  to  general  observation,  that  the  deflecting 
power  of  a  compound  circle  is  not  increased  by  increasing  the  number  of  its 
plates.  This  is  another  proof  that  the  direct  influence  of  a  number  of  plates  is 
to  increase  the  intensity  and  not  the  quantity  of  electricity  ;  for  the  prevailing 
opinion  that  the  magnetic  needle  takes  no  cognizance  of  intensity  is  fully  borne 
out  by  the  experiments  of  Faraday. 

Though  the  quantity  of  a  compound  decomposed  by  a  battery  is  proportional 
to  the  actual  quantity  of  electricity  which  parses,  yet,  as  a  compound  exposed 


GALVANISM.  91 

to  voltaic  action  is  almost  always  an  imperfect  conductor,  the  quantity  of  elec- 
tricity capable  of  passing  through  it  varies  with  its  intensity.  Hence  chemical 
decomposition  depends  on  the  quantity  and  intensity  together,  and  affords  a  cri- 
terion of  the  increased  tension  of  a  compound  circle  due  to  the  number  of  its 
plates. 

[The  most  extensive  combinations  for  exhibiting  the  effects  of  tension  are  those 
which  have  been  constructed  by  Mr.  Crosse,  and  more  recently  Mr.  Gassiot. 
The  arrangements  used  by  the  latter  consist  of  3520  pairs  of  copper  and  zinc 
cylinders  placed  in  separate  glass  vessels,  which  are  coated  with  black  varnish 
and  well  insulated.  The  phenomena  presented  by  this  apparatus  before  and 
after  the  completion  of  the  circuit,  serve  to  illustrate  the  difference  between  the 
electricity  when  accumulated  at  the  extremities  of  the  battery  and  at  rest,  and 
electricity  in  current ;  in  other  words,  between  what  are  called  the  static  and 
dynamic  conditions.  The  following  are  the  conclusions  he  derived  from  his 
experiments. 

1.  The  elements  constituting  the  voltaic  battery  assume  polar  tension  before 
the  circuit  is  completed,  even  in  a  single  cell ;  this  polar  state  being  shown  to 
exist  by  the  opposite  actions  on  the  electroscope  of  the  two  extremities  of  the 
battery. 

2.  The  tension  thus  produced,  when  heightened  by  a  repetition  of  series,  is 
such  that  a  succession  of  sparks  passes  between  the  polar  extremities  of  the 
battery  before  their  actual  contact. 

3.  These  static  effects  precede  and  are  independent  of  the  completion  of  the 
circuit,  as  well  as  of  any  perceptible  chemical  or  dynamic  action. 

4.  To  produce  these  static  effects  in  the  voltaic  battery  it  is  indispensable  that 
the  elements  be  such  that  they  are  capable  of  combining  by  their  chemical 
affinities ;  and  the  more  those  affinities  are  exalted  the  smaller  is  the  number  of 
parts  composing  the  series  requisite  to  exhibit  the  effects  of  tension.  These 
effects,  therefore,  furnish  direct  evidence  of  the  first  step  towards  chemical  com- 
bination, or  dynamic  action. 

5.  When  the  current  is  established,  either  by  actual  contact  of  the  extremities, 
or  merely  by  their  approximation  so  as  to  admit  of  a  succession  of  sparks,  its 
dynamic  effects  on  the  magnetic  needle  are  the  same  in  both  cases;  each  spark 
producing  a  constant  deflection  of  the  needle.  It  is  hence  inferred  that  the  cur- 
rent, even  when  the  circuit  is  closed,  may  be  regarded  as  a  series  of  discharges 
succeeding  each  other  with  infinite  rapidity. 

G.  When  the  circuit  is  closed  the  dynamic  effects  of  a  chemical  kind,  though 
feeble,  are  precisely  the  same  in  character  as  those  of  the  more  powerful  voltaic 
combinations.     (Gassiot,  Phil.  Trans.)] 

CONDUCTION  OF  GALVANIC  CURRENTS. 

[Great  differences  exist  amongst  bodies  in  their  power  of  conducting  galvanic 
electricity.  The  following  table  exhibits,  according  to  Pouillet's  experiments, 
the  relative  conducting  powers  of  the  various  metals. 


Palladium 

5791 

Bismuth         . 

384 

Silver 

6152 

Brass 

from  900  to  200 

Gold 

3975 

Caststeel 

*«     800  «  500 

Copper 

3838 

Iron 

.        600 

Platinum 

855 

Mercury 

100] 

92-  GALVANISM. 

EFFECTS  OF  GALVANISM. 

The  effects  producible  by  voltaic  combinations  are  conveniently  divisible  into 
the  electrical,  magnetic,  and  chemical  phenomena. 

I.  Electrical  Effects. — These  are  so  called,  as  being  analogous  to  the  effects  of 
ordinary  electricity.  An  active  broken  circuit  produces  the  phenomena  of  elec- 
tric repulsion,  as  already  stated  (p.  89  &  91).  A  Leyden  phial  may  also  be  charged 
by  contact  of  its  inner  coating  with  one  wire  of  the  circle,  while  the  outer  com- 
municates either  with  the  other  wire  or  with  the  ground:  a  full  charge,  though 
of  feeble  intensity,  is  almost  instantly  given.  On  approximating  the  wires  of  an 
active  circle,  a  brilliant  spark  passes  between  them  just  before  contact,  as  well 
as  in  the  act  of  breaking  contact.  When  the  electric  current  is  made  to  pass 
through  the  body  of  an  animal,  as  on  holding  the  conducting  wires  in  the  hands, 
previously  moistened  to  facilitate  conduction,  a  distinct  shock  is  felt,  which  is 
powerful  when  a  battery  of  high  tension  is  employed.  On  sending  the  current 
through  fine  metallic 'wires  or  pieces  of  plumbago  or  compact  charcoal,  these 
conductors  become  intensely  heated,  the  wires  even  of  the  most  refractory  metals 
are  fused,  and  a  vivid  white  light  appears  at  the  charcoal  points,  equal,  if  not 
superior,  in  splendour  to  that  of  phosphorus  burning  in  oxygen  gas ;  a  pheno- 
menon in  no  wise  referable  to  combustion,  as  it  takes  place  in  a  vacuum  or  under 
water.  If  the  electric  current  pass  through  thin  metallic  leaves,  the  metals  burn 
with  vivid  scintillations  : — gold  leaf  emits  a  white  light  tinged  with  blue,  silver 
a  beautiful  emerald  green  light,  copper  a  bluish  white  light  with  red  sparks, 
lead  a  rich  purple,  and  zinc  a  brilliant  white  light  fringed  with  red.  In  burning 
leaves,  fusing  wire,  and  igniting  charcoal,  a  large  quantity  of  electricity  is  the 
only  requisite ;  the  large  battery  of  Children,  though  capable  of  fusing  several 
feet  of  platinum  wire,  had  an  electric  tension  so  feeble,  that  it  did  not  affect  the 
gold  leaves  of  the  electrometer,  gave  a  shock  scarcely  perceptible  even  when  the 
hands  were  moist,  communicated  no  sensible  charge  to  a  Leyden  jar,  and  could 
not  produce  chemical  decomposition.  If  the  quantity  and  intensity  of  the  current 
are  both  great  an  arc  of  light  appears  between  the  charcoal  points  after  contact, 
even  through  an  interval  of  an  inch  or  more. 

The  electrical  effects  of  galvanism  are  so  similar  to  those  of  the  electrical 
machine,  that  it  is  impossible  to  witness  and  compare  both  series  of  phenomena 
without  referring  them  to  the  same  agent.  The  question  of  identity  early  occupied 
the  attention  of  Wollaston,  who  made  some  very  beautiful  and  conclusive  experi- 
ments to  prove  that  not  only  are  the  electrical  effects  of  the  machine  producible  by 
galvanism,  but  that  the  chemical  effects  of  galvanism  may  be  characteristically  pro- 
duced by  a  current  from  an  electrical  machine  (Phil.  Trans.  1801).  The  subject 
has  been  examined  anew  by  Faraday,  who  has  subjected  the  effects  of  electricity 
and  galvanism  to  a  minute  and  critical  comparison :  he  has  obtained  ample  proof 
of  the  decomposing  power  of  an  electric  current  from  an  electrical  machine,  both 
by  repeating  the  experiments  of  Wollaston  and  devising  new  ones  of  his  own. 
He  has  also  completed  the  chain  of  evidence  by  deflecting  a  magnetic  needle  with 
an  electric  current  from  the  machine ;  an  observation,  indeed,  which  had  been 
previously  made  by  Colladon.  These  researches  have  led  to  a  remarkable  contrast 
between  the  quantity  of  electricity  concerned  in  the  production  of  voltaic  and 
ordinary  electrical  phenomena.  Faraday  states  that  the  quantity. of  electric  fluid 
employed  in  decomposing  a  single  grain  of  water  is  equal  to  that  of  a  very  pow- 
erful flash  of  lightning;  and  this  statement,  surprising  as  it  is,  is  supported  by 
such  strong  evidence,  that  it  is  difldcult  to  withhold  assent  to  the  assertion. 


GALVANISM.  -93 

II.  Magnetic  Effects  of  Galvanism. — ^The  power  of  lightning  in  destroying  and 
reversing  the  poles  of  a  magnet,  and  in  communicating  magnetic  properties  to 
pieces  of  iron  which  did  not  previously  possess  them,  was  noticed  at  an  early 
period  of  the  science  of  electricity,  and  led  to  the  supposition  that  similar  effects 
may  be  produced  by  the  common  electrical  and  voltaic  apparatus.  Attempts  were 
accordingly  made  to  communicate  the  magnetic  virtue  by  means  of  electricity  and 
galvanism;  but  no  results  of  importance  were  obtained  till  the  winter  of  1819, 
when  Oersted  of  Copenhagen  made  his  famous  discovery,  which  forms  the  basis 
of  a  new  branch  of  science.     (An.  Phil.  xvi.  273.) 

The  fact  observed  by  Oersted  was,  that  the  metallic  wire  of  a  closed  voltaic 
circle, — and  the  same  is  true  of  charcoal,  saline  fluids,  and  any  conducting 
medium  which  forms  part  of  a  closed  circle, — causes  a  magnetic  needle  placed 
near  it  to  deviate  from  its  natural  position,  and  assume  a  new  one,  the  direction 
of  which  depends  upon  the  relative  position  of  the  needle  and  the  wire.  On 
placing  the  wire  above  the  magnet  and  parallel  to  it,  the  pole  next  the  negative 
end  of  the  battery  always  moves  westward ;  and  when  the  wire  is  placed  under 
the  needle,  the  same  pole  goes  towards  the  east.  If  the  wire  is  on  the  same 
horizontal  plane  with  the  needle,  no  declination  whatever  takes  place ;  but  the 
magnet  shows  a  disposition  to  move  in  a  vertical  direction,  the  pole  next  the 
negative  side  of  the  battery  being  depressed  when  the  wire  is  to  the  west  of  it, 
and  elevated  when  it  is  placed  on  the  east  side. 

When  the  influence  of  the  earth's  magnetism  on  the  needle  which  impedes  its 
free  motion,  is  counteracted  by  another  magnet  placed  near  it,  the  needle  places 
itself  directly  across  the  connecting  wire  ;  so  that  the  real  tendency  of  a  magnet 
is  to  stand  at  right  angles  to  an  electric  current. 

The  communicating  wire  is  also  capable  of  attracting  and  repelling  the  poles 
of  a  magnet.  When  the  connecting  wire  is  held  vertically  near  a  horizontally 
suspended  magnet,  on  the  west  side  of  it,  and  approached  to  the  north  pole, 
attraction  ensues,  till  they  come  very  close,  when  repulsion  follows.  When  the 
wire  is  approached  to  the  south  pole,  similar  effects  ensue,  in  an  inverted  order. 
If  the  wire  be  held  on  the  east  side,  the  effects  are  reversed ;  the  current  in  both 
cases  being  supposed  to  flow  upwards  through  the  wire. 

The  discovery  of  Oersted  was  no  sooner  announced,  than  the  experiments  were 
repeated  and  varied  by  philosophers  in  all  parts  of  Europe,  and,  as  was  to  be 
expected,  new  facts  were  speedily  brought  to  light.  Among  the  most  successful 
of  those  who  early  distinguished  themselves  were  Ampere,  Biot,  and  Arago,  of 
Paris,  and  Davy  and  Faraday  in  this  country.  A  host  of  other  able  men  have 
since  added  their  contributions;  and  their  joint  labours  have  established  an  alto- 
gether new  science,  Electro-Dynamics,  which  has  already  become  one  of  the  most 
important  branches  of  physical  knowledge,  and  still  offers  a  rich  harvest  of  dis- 
covery to  its  cultivators.  Those  who  wish  to  enter  deeply  into  the  study  of  this 
subject  should  consult  the  Recueil  d* Observations  Electro-Dynamiques  by  Ampere, 
Cumming's  Manual  of  Electro-Dynamics,  Murphy's  Treatise  on  Electricity,  and 
the  second  edition  of  Barlow's  Essay  on  Magnetic  Attractions.  A  less  mathe- 
matical, and  therefore  more  generally  intelligible,  treatise  has  been  drawn  up 
with  great  ability  by  Roget,  and  published  as  part  of  the  Library  of  Useful 
Knowledge;  and  a  Popular  Sketch  of  Electro-Magnetism  has  been  given  by 
Watkins  of  Charing-cross.  To  these  works  I  refer  as  supplying  that  detail  of 
the  facts  and  theories  of  electro-dynamics,  which,  as  belonging  more  to  the  pro- 
vince of  physics  than  chemistry,  is  unsuited  to  the  design  of  this  volume. 

The  phenomena  of  electro-dynamics  are  solely  produced  by  electricity  in 


94 


GALVANISM. 


motion.  The  passage  of  electricity  through  solid  or  liquid  conductors  is  essen- 
tial ;  in  fact,  a  magnetic  needle  is  a  galvanoscope,  by  which  means  the  existence 
and  direction  of  an  electric  current  may  be  detected.  In  this  way,  Ampere 
demonstrated  the  fact,  that  electricity  passes  uninterruptedly  through  the  battery 
when  the  circuit  is  closed,  and  not  at  all  in  the  broken  circuit. 

But  a  magnetic  needle  will  not  only  indicate  the  existence  and  direction  of  an 
electric  current :  it  may  even  serve,  by  the  degree  of  deflection,  as  an  exact  mea- 
sure of  its  force.  When  used  for  this  purpose,  under  the  name  of  galvanometer, 
some  peculiar  arrangeinents  are  required  in  order  to  ensure  the  requisite  delicacy 
and  precision.  Experiment  proves  that  a  magnet  is  equally  affected  by  every 
point  of  a  conductor  along  which  an  electric  current  is  passing ;  so  that  a  wire 
transmitting  the  same  current  will  act  with  more  or  less  energy,  according  as  the 
number  of  its  parts  contiguous  to  the  needle  is  made  to  vary.  On  this  principle 
is  constructed  the  Galvanometer  or  Multiplier  of  Schweigger.  A  copper  wire  is 
bent  into  a  rectangular  form  consisting  of  several  coils,  and  in  the  centre  of  the 
rectangle  is  placed  a  delicately  suspended  needle,  as  shown  in  figure  9.  Each 
coil  adds  its  influence  to  that  of  the  others ;  and  as  the  current,  in  its  progress 
along  the  wire,  passes  repeatedly  above  and  below  the  needle  in  opposite  direc- 
tions, their  joint  action  is  the  same.     In  order  to  prevent  the  electricity  from 


Fig.  9. 


passing  laterally  from  one  coil  to  another  in  contact 
with  it,  the  wire  should  be  covered  with  silk.  The 
ends  of  the  wire,  a  and  &,  are  left  free  for  the  pur- 
pose of  communication  with  the  opposite  ends  of 
the  voltaic  circle.  The  needle  ought  to  be  rendered 
astatic,  that  is  the  influence  of  the  earth's  magnetism  ought  to  be  destroyed  by 
placing  another  magnet  above  the  rectangle,  having  its  north  pole  adjacent  to  the 
south  pole  of  the  first.     The  instrument  is  thuS  rendered  extremely  delicate. 

The  mutual  influence  of  a  magnetic  pole  and  a  conducting  wire  changes  with 
the  distance  between  them ;  and  experiment  leads  to  the  conclusion  that  the  attrac- 
tion of  a  magnetic  pole  on  a  single  point  of  a  conductor  varies  as  the  square  of 
the  distance  ;  the  same  well  known  law  which  regulates  the  distribution  of  heat 
and  light,  as  well  as  electricity. 

On  examination,  all  the  phenomena  described  by  Oersted  are  found  to  be  refer- 
able to  a  force  acting  tangentially  on  the  poles  of  a  magnet,  and  in  a  plane  per- 
pendicular to  the  direction  of  the  current. 

The  same  principle  accounts  for  the  rotation  of  a  magnetic  pole  round  a 
current,  discovered  by  Faraday.  Into  the  centre  of  the  bottom 
of  a  cup,  as  in  the  vertical  section,  figure  10,  a  copper  wire 
c  d  was  inserted,  a  cylindrical  magnet  n  s  was  attached  by  a 
thread  to  the  copper  wire  c,  and  the  cup  was  nearly  filled 
with  mercury,  so  that  pole  n  only  of  the  magnet  projected. 
A  conductor  tt  b  was  then  fixed  in  the  mercury  perpendicu- 
larly over  the  wire  c.  On  connecting  the  conducting  wires 
with  the  opposite  ends  of  a  battery,  a  current  was  trans- 
mitted from  one  wire  through  the  mercury  to  the  other.  If 
the  -f-  current  descend,  the  north  pole  of  the  magnet,  if  up- 
permost, will  rotate  round  the  wire  a  b,  passing  from  east 

through  the  south  to  west  like  the  movements  in  the  hands 

rf  "".<—  of  a  watch;  and  if  the  .current  ascend,  the  line  of  rotation 

will  be  It  \.  ,M,i.     Under  similar  circumstances  the  south  pole  would  in  each 
case  rotate  in  the  opposite  direction.  '     ^   ^ 


GALVANISM. 


95 


Fig-  11. 


Fig.  12. 


If  a  magnetic  pole  rotate  round  a  conductor,  a  conductor  will  be" equally  disposed 
to  rotate  round  a  magnetic  pole,  just  as  a  magnet  moves  towards 
iron  or  iron  towards  a  magnet,  according  as  one  or  other  is  free 
to  move.  Accordingly,  on  fixing  a  magnet  vertically  in  the 
middle  of  a  cup  of  mercury,  fig.  11,  and  transmitting  a  cur- 
rent by  the  movable  conductor  a  h  through  the  mercury,  and 
along  a  secoryl  conductor  6?,  fixed  as  before  in  the  bottom  of 
the  cup,  Faftiday  found  that  the  free  extremity  h  of  the  wire 
moved  round  the  .pole  of  the  magnet  in  a  direction  similar 
to  the  last. 

It  is  obvious  that  the  direction  of  rotation  imparted  by  a 
fixed  current  to  the  movable  pole,  will  be  identical  with  that 
which  the  same  pole  tends  to  impart  to  the  same  current. 

A  current  of  voltaic  electricity  not  only  determines  the  ^ 
position  of  a  magnet,  but  renders  steel  permanently  magnetic.  This  was  ob- 
served nearly  at  the  same  time  by  Arago  and  Davy,  who  found  that  when 
needles  are  placed  at  right  angles  to  the  conducting  wire,  permanent  magnetism 
is  communicated ;  and  Davy  also  succeeded  in  producing  this  effect  even  with 
a  shock  of  electricity  from  a  Leyden 
phial.  Arago,  at  the  suggestion  of  Am- 
pere, made  a  voltaic  conductor  into  the 
form  of  a  helix,  into  the  axis  of  which  he 
placed  a  needle,  as  in  figure  12.  As  in 
this  arrangement  the  current  nearly  in 
every  part  of  its  course  is  at  right  angles 
to  the  needle,  and  as  each  coil  adds  its 
effect  to  that  of  the  others,  the  united  ac- 
tion of  the  helix  is  extremely  powerful, 
in  an  instant. 

Though  soft  iron  does  iiot  retain  magnetism,  its  magnetic  properties,  while 
under  the  influence  of  an  electric  current,  are  very  surprising.  A  piece  of  soft 
iron,  about  a  foot  long  and  an  inch  in  diameter,  is  bent  into  the  form  of  a  horse- 
shoe, a  copper  wire  is  twisted  round  the  bar  at  right  angles  to  its  axis,  and  an 
armature  of  soft  iron,  to  which  a  weight  may  be  attached,  is  fitted  to  its  extre- 
mities, as  in  fig.  13.  On  connecting  the 
ends  of  the  wire  with  a  simple  voltaic 
circle,  even  of  small  size,  the  soft  iron 
instantly  becomes  a  powerful  magnet,  and 
will  support  considerable  weights.  In- 
creasing the  number  of  coils  gives  a  great 
increase  of  power;  but  as  the  length  of 
wire  required  for  that  purpose  diminishes 
the  influence  of  the  current  (page  90), 
the  following  arrangement  has  been  suc- 
cessfully adopted.  The  total  length  of 
copper  wire  intended  to  be  used  is  cut 
into  several  portions,  each  of  which, 
covered  with  silk  or  cotton  thread  to 
prevent  lateral  communication,  is  coiled 
separately  on  the  iron.  The  ends  of  all 
the  wires  are  then  collected  into  two  separate  parcels,  and  are  made  to  commu- 


The  needle  was  thus  fully  magnetized 


Fig.  13. 


96  GALVANISM. 

nicate  with  the  same  voltaic  battery,  taking  care  that  the  -j-  current  shall  pass 
along  each  wire  in  the  same  direction.  The  current  is  thus  divided  into  a  num- 
ber of  branches,  and  has  only  a  short  passage  from  one  end  of  the  battery  to  the 
other,  though  it  gives  energy  to  a  multitude  of  coils.  A  combination  of  this 
kind,  connected  with  a  battery  of  five  feet  square,  supported  2063  pounds,  or 
nearly  a  ton  weight. 

In  witnessing  the  influence  of  voltaic  conductors  over  the  directive  property 
of  magnets,  and  in  inducing  magnetism,  it  is  difficult  to  divest  one^  self  of  the 
conviction  that  these  conductors,  while  transmitting  a  current,  are  themselves 
magnetic.  This  belief  was  early  entertained  by  those  who  repeated  the  experi- 
ments of  Oersted,  and  experimental  evidence  of  its  truth  was  speedily  adduced. 
Arago  and  Davy  found  that  a  copper  wire  connecting  the  end  of  a  voltaic  com- 
bination attracted  iron  filings,  but  that  they  instantly  fell  off  as  soon  as  the  cir- 
cuit was  broken ;  and  a  conductor,  when  its  movements  were  not  impeded  by 
friction  or  gravity,  was  proved  by  Ampere  to  be  obedient,  like  an  ordinary  mag- 
net, to  the  magnetic  agency  of  the  earth. 

Since,  therefore,  the  conductors  just  described  may  be  regarded  as  magnets, 
such  magnetized  conductors  ought  mutually  to  repel  or  attract  each  other,  when 
poles  of  the  same  or  a  different  nature  are  adjacent ;  and  as  the  action  of  a  whole 
spiral  or  rectangle  is  merely  the  accumulated  effect  of  its  individual  parts,  it  is 
fair  to  presume  that  each  small  portion  of  a  conductor  has  its  opposite  sides  in  a 
state  of  opposite  polarity,  and  that  two  such  contiguous  portions  should  attract 
or  repel  each  other  on  the  same  principle  as  the  spirals  of  which  they  constitute 
a  part.  Nay,  even  different  parts  of  the  same  conductor  ought  to  be  mutually 
attractive  or  repulsive.  These  inferences  from  the  facts  already  detailed  were 
fully  demonstrated  by  Ampere  soon  after  the  discovery  of  Oersted.  He  proved 
that  two  voltaic  conductors,  or  two  portions  of  the  same  conductor,  attract  each 
other  when  the  currents  have  the  same  direction,  and  are  mutually  repulsive 
when  they  are  traversed  by  opposite  currents  ;  which  is  exactly  what  would  be 
anticipated  from  the  magnetic  influence  of  conductors. 

These  are  a  few  examples  of  the  numerous  facts  experimentally  proved  by 
Ampere  concerning  the  action  of  voltaic  conductors  on  each  other.  It  is  to  this 
branch  of  the  subject  the  term  of  Electro-Dynamics,,  or  the  science  of  electricity 
in  motion,  is  sometimes  restricted,  while  the  mutual  action  of  conductors  and 
magnets  is  called  Electro-Magnetism ;  but  these  two  branches  are  so  entirely 
parts  of  the  same  science,  that  I  have  included  both  under  Ampere's  term  of 
Electro-Dynamics.  Any  one  who  has  studied  the  few  preceding  pages  with 
moderate  care,  cannot  fail  to  trace  a  close  analogy  between  a  helix  traversed  by 
an  electric  current  and  a  magnet.  The  former  is  eflfected  by  other  voltaic  con- 
ductors, by  the  poles  of  a  magnet,  and  by  the  magnetism  of  the  earth,  in  the 
same  manner  as  the  latter.  It  was  this  similarity,  or  rather  identity,  of  action 
which  led  Ampere  to  his  theory  of  magnetism.  He  supposes  that  the  polarity 
of  every  magnet  is  solely  owing  to  the  circulation,  within  its  substance  and  at  its 
surface,  of  electric  currents,  which  continually  pass  around  all  its  particles  in 
planes  perpendicular  to  its  axis.  On  placing  a  magnet  in  its  natural  position  of 
north  and  south,  the  direction  of  its  currents  is  as  follows  :  they  descend  on  the 
east  side,  passing  under  the  magnet  from  east  to  west,  and  ascending  on  the  side 
next  the  west.  In  like  manner  are  currents  supposed  to  circulate  within  the 
earth,  especially  near  its  surface,  passing  from  east  to  west  in  planes  parallel  to 
the  magnetic  equator.  These  terrestrial  currents  cause  all  bodies,  which  are 
freely  suspended,  and  are  possessed  of  electric  currents,  to  place  themselves  in 


GALVANISM.  97 

such  a  position  that  the  current  on  their  under  side  should  flow  in  parallelism, 
and  in  the  same  direction,  with  that  in  the  earth  immediately  beneath.  That  the 
existence  of  such  currents  will  account  for  the  directive  property  of  th6  earth, 
follows  from  the  mutual  action  of  conductors  ;  and  Barlow,  to  render  the  analogy 
still  more  complete,  constructed  a  hollow  sphere  of  wood  in  which  electric  cur- 
rents were  made  to  circulate  in  the  same  direction  as  they  are  thought  to  do  in 
the  earth ;  and  by  placing  an  astatic  needle  on  different  parts  of  its  surface,  he 
found  that  all  the  phenomena  of  terrestrial  magnetism  might  be  imitated.  Obser- 
vation has  even  supplied  a  cause  for  the  existence  of  currents  in  the  earth,  moving 
in  the  direction  which  theory  requires.  The  diurnal  rotation  of  our  planet  on  its 
axis  exposes  its  surface  to  be  heated  in  a  direction  passing  from  east  to  west ; 
and  the  discoveries  which  have  been  made  in  thermo-electricity  (page  72)  suffi- 
ciently prove  the  probability  of  electric  currents  being  established  in  the  conduct- 
ing matter  of  the  earth  by  the  successive  heating  of  its  parts.  In  short,  the 
theory  of  Ampere  connects  the  facts  of  electro-dynamics  with  the  phenomena  of 
terrestrial  magnetism,  and  affords  a  gplendid  instance  of  the  application  of 
mathematical  analysis  to  physical  research. 

Volta-eledric  Induction. — The  developement  of  electricity  by  the  vicinity  of  an 
excited  body,  already  described  under  the  name  of  induced  electricity  (page  73), 
led  Faraday  to  inquire  whether  electricity  in  motion,  as  well  as  that  of  tension 
and  at  rest,  may  not  be  excited  by  induction.  Though  baffled  in  his  early 
attempts,  he  at  last  succeeded  in  laying  open  a  new  branch  of  electro-dynamics, 
which  vies  in  interest  and  importance  with  the  fundamental  discovery  of  Oersted 
(Phil.  Trans.  1831).  A  copper  wire  203  feet  long  was  passed  in  form  of  a  helix 
round  a  large  block  of  wood,  and  an  equal  length  of  a  similar  wire  was  wound 
on  the  same  block  and  in  the  same  direction,  so  that  the  coils  of  each  helix 
should  be  interposed,  but  without  contact,  between  the  coils  of  the  other.  The 
ends  of  one  of  the  helices  were  connected  with  a  galvanometer,  and  the  other 
with  a  strong  galvanic  battery,  with  the  view  of  ascertaining  whether  the  passage 
of  an  electric  current  through  one  helix  would  induce  a  current  in  the  adjoining 
helix.  It  was  found  that  the  galvanometer  needle  indicated  a  current  at  the 
moment  both  of  completing  and  breaking  the  circuit,  but  that  in  the  interval  no 
deflection  took  place ;  and  similarly  the  induced  currents  readily  magnetized  a 
sewing  needle,  while  the  electric  current  along  the  inducing  helix  was  in  the  act 
of  beginning  or  ceasing  to  flow,  but  at  no  other  period.  In  the  former  case  the 
direction  of  the  induced  current  is  opposite  to  that  of  the  inducing  current,  and 
in  the  latter  case  it  is  the  same.  This  phenomenon  is  distinguished  by  Faraday 
under  the  name  of  volta-eledric  induction. 

The  inducing  power  of  a  magnet  greatly  exceeds  that  of  an  electric  current. 
A  ring  of  soft  iron  was  covered  to  nearly  half  its  extent  by  several  helices,  the 
ends  of  which  were  brought  together  so  as  to  constitute  a  compound  helix  ter- 
minating in  the  conductors  a  b,  figure  1 4  ;  and  on  the 
other  half  of  the  ring  were  arranged  similar  helices 
which  communicated  hjcd  with  a  galvanometer.  The 
two  sets  of  helices  were  thus  separated  from  each 
other  by  portions  of  the  ring  M  M',  and  were  pro- 
tected by  cloth  from  direct  contact  with  the  ring  itself. 
At  the  moment  the  wires  a  b  touched  the  ends  of  a  vol- 
taic combination,  the  galvanometer  was  strongly  af- 
fected :  the  needle  then  returned  to  its  former  position  and  remained  there  until 

9 


98  GALVANISM. 

the  voltaic  circuit  was  broken,  when  the  needle  was  again  deflected  as  strongly  as 
before,  but  in  the  opposite  direction.  The  action  was  still  greater  when  both 
compound  helices  were  on  the  same  part  of  the  ring,  the  induction  being 
increased  apparently  by  the  closer  contiguity  of  the  helices.  Other  arrange- 
ments have  been  devised  by  Faraday,  for  producing  similar  results  ;  and  to  the 
action  in  all  these  cases  he  has  given  the  name  of  Magneto-electric  induction. 

The  phenomena  arising  from  magneto-electric  and  volta-electric  induction  are 
manifestly  owing  to  the  same  condition  of  the  induced  wire  :  the  action  on  the 
needle,  though  different  in  force,  is  identical  in  kind.  It  is  equally  clear  that  the 
agent  brought  into  operation  in  the  induced  wire  is  an  electric  current,  or,  to  dis- 
miss the  language  of  theory,  that  the  induced  wire  is  in  the  same  electric  state 
as  the  conducting  wire  in  a  closed  voltaic  circle.  Its  power  in  magnetizing  steel 
and  deflecting  a  magnet  is  sufficient  evidence  of  this  ;  but  Faraday,  by  magneto- 
electric  induction,  succeeded  in  throwing  a  frog's  leg  into  spasms  by  connecting 
it  with  the  induced  wire,  and  by  arming  the  ends  of  that  wire  with  points  of 
charcoal,  and  separating  them  at  the  inst^t  the  galvanic  circuit  of  the  inducing 
wire  was  broken  or  restored,  sparks  of  electricity  were  obtained.  The  mode  in 
which  soft  iron  contributes  to  the  eflfect  is  likewise  obvious.  An  electric  current 
circulating  round  a  bar  of  soft  iron  has  been  shown  to  convert  it  into  a  temporary 
magnet  possessed  of  surprising  power  (page  95) ;  and  it  is  doubtless  to  this 
magnet,  called  into  temporary  existence  by  the  electric  current,  most  of  the 
induced  electricity  is  to  be  ascribed.  Faraday  reduced  this  to  certainty  by  sur- 
rounding a  cylinder  of  soft  iron  with  one  helix  connected  with  the  galvanometer, 
and  converting  the  soft  iron  into  a  temporary  magnet,  not  by  a  voltaic  battery, 
but  by  placing  at  each  end  of  the  cylinder  the  opposite  pole  of  a  magnet.  Dur- 
ing the  act  of  applying  the  magnetic  poles  to  the  iron,  the  galvanometer  needle 
was  deflected ;  and  the  deflection  was  reproduced,  but  in  the  opposite  direction, 
when  the  magnetism  of  the  iron  was  ceasing  by  the  removal  of  the  magnet. 
Similarly,  when  a  helix  was  wound  on  a  hollow  cylinder  of  pasteboard,  and  a  real 
magnet  was  introduced,  the  galvanometer  was  deflected  :  the  needle  then  remained 
quiescent  so  long  as  the  magnet  was  left  in  the  cylinder ;  but  in  the  act  of  its 
removal,  the  needle  was  again  deflected,  though,  as  usual,  in  the  opposite 
direction. 

These  singular  phenomena,  which  establish  such  new  and  intimate  relations 
between  voltaic  and  magnetic  action,  and  supply  additional  evidence  in  favour 
of  Ampere's  beautiful  theory  of  magnetism,  have  led  to  an  experiment  by  which, 
at  first  view,  an  electric  spark  appeared  to  be  derived  from  the  magnet  itself. 
After  Faraday  had  announced  his  experiment,  above  mentioned,  of  obtaining  a 
spark  from  the  induced  wire,  other  attempts  were  made  to  effect  the  same  object 
with  a  magnet,  without  the  aid  of  galvanism.  The  first  person  who  succeeded 
in  this  country  was  Forbes,  who  operated  with  a  powerful  loadstone  (Phil.  Trans. 
Ed.  1832).  A  helix  of  copper  wire  was  formed  round  the  middle  of  a  cylinder 
of  soft  iron,  which  was  of  such  length  that  its  extremities  reached  from  one  pole 
of  the  loadstone  to  the  other.  On  applying  and  withdrawing  the  soft  iron  cylin- 
der to  and  from  the  poles  of  the  loadstone,  magnetism  was  alternately  created 
and  destroyed  within  it.  At  these  periods  of  transition,  electric  currents  were 
induced  in  the  helix  surrounding  the  soft  iron ;  and  when,  at  these  instants, 
metallic  contact  between  the  conducting  wires  of  the  helix  was  broken,  an  elec- 
tric spark  was  visible.  Forbes  succeeded  best  by  connecting  one  wire  with  a  cup 
of  mercury,  and  removing  the  other  wire  from  contact  with  its  surface  at  the 


GALVANISM.  99 

instant  when  an  assistant  withdrew  the  armature  of  soft  iron  from  the  loadstone. 
In  this  experiment,  therefore,  the  electricity  was  obtained  from  the  helix,  and  was 
induced  in  it  by  the  soft  iron  while  in  the  act  of  acquiring  or  losing  magnetism. 
The  same  experiment  was  performed  by  Faraday  with  a  loadstone  belonging  to 
Daniell ;  and  shortly  before  the  experiment  of  Forbes,  Nobili  and  Antinori  suc- 
ceeded with  an  ordinary  steel  magnet.  Pixii  in  Paris  afterwards  performed  this 
experiment  with  great  effect  by  causing  a  strong  horse-shoe  magnet  to  revolve 
upon  an  axis,  its  poles  passing  in  rapid  succession  in  front  of  a  soft  iron  arma- 
ture of  the  same  form ;  and  a  still  better  arrangement  is  to  cause  the  armature  to 
revolve  in  front  of  the  poles  of  a  powerful  magnet,  as  in  the  instrument  fitted  up 
by  Saxton,  and  exhibited  at  the  Adelaide-rooms,  London.  It  produces  brilliant 
sparks,  renders  platinum  wire  red  hot,  and  gives  a  strong  shock.  It  explodes 
gunpowder,  and  also  a  mixture  of  oxygen  and  hydrogen  gases,  and  decomposes 
water  rapidly. 

Intimately  associated  with  magneto-electric  induction,  if  not  referable  to  the 
very  same  origin,  is  the  induction  of  electric  currents  by  movement.  On  intro- 
ducing a  magnet  into  a  hollow  helix  of  copper  wire,  or  other  solid  conductor,  as 
also  on  withdrawing  the  magnet  after  its  introduction,  an  electric  current  was 
momentarily  induced  in  the  wire  ;  and  if,  the  magnet  being  stationary,  the  helix 
were  moved  in  its  vicinity,  an  electric  current  is  likewise  induced.  The  direc- 
tion of  the  movement  is  not  immaterial :  it  is  essential  that  the  plane  in  which 
the  conductor  moves  should  form  an  angle  with  the  axis  of  the  magnet ;  and  the 
most  powerful  currents  were  induced,  when  the  plane  of  motion  was  at  right 
angles  to  that  axis,  and  hence  parallel  to  the  electric  currents  which  Ampere 
supposes  to  exist  in  the  magnet.  With  regard  to  the  direction  of  an  induced 
current,  Faraday's  researches  establish  this  law,  deduced  by  Ritchie :  if  a  wire 
conducting  voltaic  electricity  produce  on  magnets  or  conductors  certain  motions, 
whether  repulsive,  attractive,  or  rotatory,  and  if  the  battery  be  removed,  the  ends 
of  the  wires  brought  into  metallic  contact,  and  the  same  motions  be  produced  by 
mechanical  means,  the  conductor  will  have  the  same  electric  state  induced  in  it 
as  it  had  when  connected  with  the  battery.     (Phil.  Mag.  3rd  series,  iv.  12.) 

Faraday  has  applied  this  principle  in  a  most  happy  manner  to  explain  the  phe- 
nomena of  rotation  discovered  by  Arago.  If  a  plate  of  copper  be  revolved  close 
to  a  magnetic  needle  suspended  so  that  it  may  rotate  in  a  plane  parallel  to  the 
plate,  the  needle  will  rotate  in  the  same  direction ;  and,  reciprocally,  a  rotating 
magnet  tends  to  give  rotation  to  a  contiguous  copper-plate.  The  same  effects 
are  produced  by  the  rotation  not  only  of  all  metals,  but,  according  to  Arago,  of 
all  bodies  whether  solid,  liquid,  or  gaseous.  These  effects,  which  Faraday  has 
principally  examined  in  reference  to  the  rotation  of  metals,  are  entirely  owing  to 
electric  currents  induced  by  the  rotation,  and  flowing  at  right  angles  to  the  direc- 
tion of  motion. 

If  motion  in  the  vicinity  of  a  magnet  induce  an  electric  current,  the  same  effect 
would  be  anticipated  from  the  magnetic  influence  of  the  earth ;  and  this  fact  has 
been  proved  by  Faraday  by  most  decisive  and  interesting  experiments.  When  a 
bar  of  soft  iron  is  held  in  the  position  of  the  dipping  needle,  the  direction  of 
which,  in  regard  to  terrestrial  magnetism,  is  analogous  to  the  axis  of  a  common 
magnet,  it  acquires  magnetic  properties  ;  and  accordingly,  on  introducing  a  soft 
cylinder  into  a  hollow  helix  of  copper  placed  in  the  line  of  the  dip,  a  galvano- 
meter connected  with  the  helix  was  instantly  affected.  But  the  use  of  iron  may 
be  dispensed  with  altogether ;  for  when  a  helix  of  copper  wire  was  simply  moved 


100  GALVANISM. 

at  right  angles  to  the  dipping  needle,  electric  currents  were  induced  by  the  mag- 
netism of  the  earth.  The  form  of  a  helix  is  not  even  necessary :  the  movement 
of  a  piece  of  copper  wire  across  the  line  of  dip  developed  currents  in  the  wire. 
The  same  effect  was  produced  by  the  rotation  of  a  copper  plate  placed  horizon- 
tally so  as  to  be  nearly  at  right  angles  to  the  line  of  dip  ;  and  the  revolution  of 
a  copper  globe  acted  in  the  same  manner.  Faraday  concludes  that  the  rotation 
of  the  earth  on  its  axis  ought  similarly  to  influence  the  conducting  matters  of  its 
surface ;  and  that  electric  currents  should  be  thereby  induced  from  the  equatorial 
regions  to  either  pole.  He  throws  out  the  suggestion  whether  the  aurora  horealis 
and  australis  may  not  be  produced  by  the  returning  currents  passing  from  the 
poles  of  the  earth  into  the  atmosphere. 

III.  Chemical  Effects  of  Galvanism. — ^The  chemical  agency  of  the  voltaic  appa- 
ratus, to  which  chemists  are  indebted  for  a  most  powerful  instrument  of  analysis, 
was  discovered  by  Carlisle  and  Nicholson,  soon  after  the  invention  was  made 
known  in  this  country.  The  substance  first  decomposed  by  it  was  water.  When 
two  gold  or  platinum  wires  are  connected  with  the  opposite  ends  of  a  battery, 
and  their  free  extremities  are  plunged  into  the  same  cup  of  water,  but  without 
touching  each  other,  hydrogen  gas  is  disengaged  at  the  —  and  oxygen  at  the  -f- 
wire.  By  collecting  the  gases  in  separate  tubes  as  they  escape,  they  are  found 
to  be  quite  pure,  and  in  the  exact  ratio  of  two  measures  of  hydrogen  to  one  of 
oxygen.  When  wires  of  a  more  oxidable  metal  are  employed,  the  result  is 
somewhat  different.  The  hydrogen  gas  appears  as  usual  at  the  —  wire ;  but 
the  oxygen,  instead  of  escaping,  combines  with  the  metal,  and  converts  it  into 
an  oxide. 

This  important  discovery  led  many  able  experimenters  to  make  similar  trials. 
Other  compound  bodies,  such  as  acids  and  salts,  were  exposed  to  the  action  of 
galvanism,  and  all  of  them  were  decomposed  without  exception,  one  of  their 
elements  appearing  at  one  side  of  the  battery,  and  the  other  at  its  opposite 
extremity.  An  exact  uniformity  in  the  circumstances  attending  the  decomposi- 
tion was  also  remarked.  Thus,  in  decomposing  water  or  other  compounds,  the 
same  kind  of  body  was  always  disengaged  at  the  same  side  of  the  battery.  The 
raetals,  inflammable  substances  in  general,  the  alkalies,  earth,  and  the  oxides  of 
the  common  metals,  were  found  at  the  —  wire  ;  while  oxygen,  chlorine,  and  the 
acids,  went  over  to  the  -j-  surface. 

In  performing  some  of  these  experiments,  Davy  observed,  that  if  the  conduct- 
ing wires  were  plunged  into  separate  vessels  of  water,  made  to  communicate  by 
some  moist  fibres  of  cotton  or  amianthus,  the  two  gases  were  still  disengaged 
in  their  usual  order,  the  hydrogen  in  one  vessel,  and  the  oxygen  in  the  other, 
just  as  if  the  wires  had  been  immersed  into  the  same  portion  of  that  liquid. 
This  singular  fact,  and  another  of  the  like  kind  observed  by  Hisinger  and  Ber- 
Eelius,  induced  him  to  operate  in  the  same  way  with  other  compounds,  and  thus 
gave  rise  to  his  celebrated  researches  on  the  transfer  of  chemical  substances 
from  one  vessel  to  another  (Phil.  Trans.  1807).  In  these  experiments  two  agate 
cups,  N  and  P,  were  employed,  the  first  communicating  with  the  — ,  the  second 
with  the  -f  wire  of  the  battery,  and  connected  together  by  moistened  amianthus. 
On  putting  a  solution  of  sulphate  of  potassa  or  soda  into  N,  and  distilled  water 
into  P,  the  acid  very  soon  passed  over  to  the  latter,  while  the  liquid  in  the 
former,  which  was  at  first  neutral,  became  distinctly  alkaline.  The  process  was 
reversed  by  placing  the  saline  solution  in  P,«and  the  distilled  water  in  N,  when 
the  alkali  went  over  to  the  —  cup,  leaving  free  acid  in  the  other.    That  the  acid 


GALVANISM.  101 

in  the  first  experiment,  and  the  alkaline  base  in  the  second,  actually  passed  along 
the  amianthus,  was  obvious  ;  for  on  one  occasion,  when  nitrate  of  oxide  of  silver 
was  substituted  for  the  sulphate  of  potassa,  the  amianthus  leading  to  N  was 
coated  with  a  film  of  metal.  A  similar  transfer  was  effected  by  putting  distilled 
water  into  N  and  P,  and  a  saline  solution  in  a  third  cup  placed  between  the 
two  others,  and  connected  with  each  by  moistened  amianthus.  In  a  short  time 
the  acid  of  the  salt  appeared  in  P,  and  the  alkali  in  N.  It  was  in  pursuing 
these  researches  that  Davy  made  his  great  discovery  of  the  decomposition  of  the 
alkalies  and  earths,  which  till  then  had  been  regarded  as  elementary.  (Phil. 
Trans.  1808.) 

Such  is  a  statement  of  the  principal  phenomena  of  electro-chemical  decom- 
position according  to  the  earlier  experiments.  The  facts  then  observed  were 
received  as  established  truths  of  science,  and  passed  current  without  suspicion 
or  scrutiny  till  the  present  time.  But  Faraday,  in  his  revision  of  this  part  of 
the  science,  has  not  only  added  much  new  matter,  but  proved  that  several  points, 
which  were  considered  as  fundamental  maxims,  are  erroneous.  Before  describ- 
ing his  results,  however,  I  will  define  the  new  terms  which  he  has  had  occasion 
to  introduce. — In  order  to  decompose  a  compound,  it  is  necessary  that  it  should 
be  liquid,  and  that  an  electric  current  should  pass  through  it;  an  object  easily 
effected  by  dipping  into  the  liquid  the  ends  of  the  metallic  wires  which  commu- 
nicate with  the  voltaic  circle.  These  extremities  of  the  wires  are  commonly 
termed  poles,  from  a  notion  of  their  exerting  attractive  and  repulsive  energies 
towards  the  elements  of  the  decomposing  liquid,  just  as  the  poles  of  a  magnet 
act  towards  iron ;  and  each  is  further  distinguished  by  the  term  positive  or  nega- 
tive, according  as  it  affects  an  electrometer  with  -{-or  —  electricity.  Now  Fara- 
day contends  that  these  poles  have  not  any  attractive  or  repulsive  energy,  and  act 
simply  as  a  path  or  door  to  the  current :  he  hence  calls  them  electrodes,  from 
ijKsxt^op,  and  o5oj,  a  way.  The  electrodes  are  the  surfaces,  whether  of  air,  water, 
metnl,  or  any  other  substance,  which  serve  to  convey  an  electric  current  into  and 
from  the  liquid  to  be  decomposed.  The  surfaces  of  this  liquid  which  are  in 
Immediate  contact  with  the  electrodes,  and  where  the  elements  make  their 
appearance,  are  termed  anode  and  cathode,  from  am,  upwards,  and  o6oj,  the  way 
in  which  the  sun  rises,  and  xata.,  downwards^  the  way  in  which  the  sun  sets. 
The  anode  is  where  the  -}-  current  is  supposed  to  enter,  and  the  cathode  where 
it  quits,  the  decomposing  liquid,  its  direction,  when  the  electrodes  are  placed 
east  and  west,  corresponding  with  that  of  the  ■\-  current  which  is  thought  to 
circulate  on  the  surface  of  the  earth  (page  dQ).  To  ekctrolyze  a  compound,  is 
to  decompose  it  by  the  direct  action  of  galvanism,  its  name  being  formed  from 
tlUxte,ov  and  >.uco,  to  unloose  or  set  free  ,•  and  an  electrolyte  is  a  compound  which 
may  be  electrolyzed.  The  elements  of  an  electrolyte  are  called  ions,  from  tov, 
going,  neuter  participle  of  the  verb  to  go.  Anions  are  the  ions  which  appear  at 
the  anode,  and  are  usually  termed  the  electro-negative  ingredients  of  a  com- 
pound, such  as  oxygen,  chlorine,  and  acids  ;  and  the  electro-positive  substances, 
hydrogen,  metals,  alkalies,  which  appear  at  the  cathode,  are  cations.  Whatever 
may  be  thought  of  the  necessity  for  some  of  these  terms,  the  words  electrode, 
elec^olyze,  and  electrolyte,  are  peculiarly  appropriate,  and  are  already  in  use. 

The  principal  facts  determined  by  Faraday  may  be  arranged  uncpr  the  follow- 
ing propositions : — 

1.  All  compounds,  contrary  to  what  has  been  hitherto  supposed,  are  not  elec- 
trolytes, that  is,  are  not  directly  decomposable  by  an  electric  current.    But  in 


102  GALVANISM. 

making  this  assertion,  it  is  necessary  to  distinguish  between  primary  and 
secondary  decomposition.  Water  is  an  electrolyte,  its  hydrogen  being  delivered 
up  at  the  —  and  its  oxygen  at  the  -|-  electrode.  A  solution  of  hydrochloric  acid 
is  likewise  an  electrolyte,  being  resolved  into  chlorine  and  hydrogen.  But  nitric 
and  sulphuric  acids  and  ammonia  are  not  electrolytes,  though  the  first  and  last 
are  decomposed  by  secondary  action.  Thus,  on  subjecting  nitric  acid  to  voltaic 
action,  the  water  of  the  solution  is  electrolyzed,  and  its  hydrogen  arriving  at  the 
-j-  electrode,  decomposes  the  nitric  acid,  water  being  there  reproduced  and  nitrous 
acid  formed.  So,  in  a  solution  of  ammonia,  the  oxygen  of  decomposed  water 
unites  at  the  -f-  electrode  with  the  hydrogen  of  the  ammonia,  and  nitrogen  gas 
is  evolved.  Very  numerous  secondary  actions  are  occasioned  in  this  way,  because 
the  disunited  elements  are  presented  in  a  nascent  form,  which  is  peculiarly 
favourable  to  chemical  action ;  and  in  many  instances  the  electrode  itself,  which 
is  commonly  metallic,  is  chemically  attacked.  Thus,  when  chlorine  is  evolved 
against  an  electrode  of  gold,  oxygen  at  one  of  some  easily  oxidable  metal,  as 
copper  or  iron,  or  sulphur  against  a  silver  electrode,  chloride  of  gold,  oxide  of 
copper  or  iron,  and  sulphuret  of  silver,  are  generated.  If  these  changes  are 
caused  by  very  feeble  currents  acting  slowly,  as  for  weeks,  months,  or  years, 
the  new  products  have  opportunity  to  assume  regularly  crystalline  forms.  It  is 
by  such  means  that  Becquerel  has  succeeded  in  procuring  artificial  minerals 
exactly  resembling  those  which  are  found  in  mines  (Traite  d'Electricite) ;  and 
Crosse  has  since  obtained  similar  results  (Phil.  Mag.  and  An.  ix.  229).  Taking 
these  facts  in  conjunction  with  the  researches  of  Fox  on  the  electrical  state  of 
mineral  veins,  there  can  be  no  longer  a  doubt  that  feeble  electric  currents  within 
fissures  of  rocks,  induced  by  terrestrial  magnetism,  by  variations  of  temperature 
at  different  parts  of  the  rock,  or  by  the  different  nature  of  the  walls  of  the 
fissures,  or  of  the  solutions  with  which  they  are  filled,  may  have  been  one  prin- 
cipal source  of  metalliferous  deposits ;  nor  is  it  at  all  unreasonable  or  unphilo- 
sophical  to  suppose  that  the  enormous  mineral  masses  which  now  constitute  our 
metalliferous  veins  may  have  been  the  work  of  such  feeble  currents  acting  during 
hundreds  or  thousands  of  centuries.  Feeble  agencies  operative  for  a  long  period 
are  often  just  as  eflicacious  in  effecting  great  changes  as  powerful  agents  at  work 
during  a  short  period ;  and  Becquerel,  in  opening  this  new  line  of  inquiry,  has 
supplied  a  principle  by  which  the  scientific  geologist  may  explain  many  of  those 
obscure  phenomenon  which  fall  within  his  observation. 

2.  Most  of  the  salts  which  have  been  examined  are  resolvable  into  acid  and 
oxide,  apparently  without  reference  to  their  proportions.  But  in  compounds  of 
two  elements,  the  ratio  of  combination  has  an  influence  which  has  hitherto  been 
wholly  overlooked.  No  two  elements  appear  capable  of  forming  more  than  one 
electrolyte.  Hydrochloric  acid  and  fused  metallic  protochlorides,  such  as  the 
chlorides  of  lead  and  silver,  and  protochloride  of  tin,  are  readily  decomposed ; 
while  bichloride  of  tin  and  other  perchlorides  resist  decomposition.  Substances 
which  consist  of  a  single  equivalent  of  one  element  and  two  or  more  equivalents 
of  some  other  element,  are  not  electrolytes  :  this  is  the  reason  why  sulphuric  and 
nitric  acid  and  ammonia  do  not  yield  primarily  to  voltaic  action.  This  principle 
bids  fair  to  become  very  important  in  determining  which  of  several  compounds 
of  two  elemeiTts  contains  single  equivalents.  Water,  which  is  remarkable  for  its 
easy  decomposition,  may  hence  be  inferred  to  be  a  true  binary  compound. 

3.  It  has  been  ascertained  that  most  of  the  elements  are  /ons,  and  it  is  pro- 
bable that  all  of  them  arc  so;  but  there  are  several  important  elements,  such  as 
nitrogen^  carbon,  phosphorus,  boron,  silicon,  and  aluminium,  which  have  not  yet 


GALVANISM.  103 

been  proved  to  be  ions.  This  arises  from  the  difficulty  of  obtaining  these  elements 
in  compounds  fitted  for  electrolytic  action. 

4.  A  single  ton,  that  is,  one  ion  not  in  combination  with  another,  has  no  ten- 
dency to  pass  to  either  of  the  electrodes,  and  is  quite  indifferent  to  the  passing 
current,  unless  it  be  itself  a  compound  ion,  and  therefore  electrolyzable.  The 
character  of  true  electrolytic  action  consists  in  the  separation  of  ions,  one  passing 
to  one  electrode  and  another  to  the  opposite  electrode,  and  appearing  there  at  the 
same  instant,  unless  the  appearance  of  one  or  both  be  prevented  by  some  second- 
ary action. 

5.  There  is  no  such  thing  as  a  transfer  of  ions  in  the  sense  usually  understood. 
In  order  that  the  elements  of  decomposed  water  should  appear  at  the  opposite 
electrodes,  there  must  be  water  between  the  electrodes ;  and  for  the  similar  sepa- 
ration of  sulphuric  acid  and  soda,  there  must  be  aline  of  particles  of  sulphate  of 
soda  extending  from  one  electrode  to  the  other.  Thus,  if  a  solution  of  sulphate 
of  magnesia  be  covered  with  pure  water,  care  being  taken  to  avoid  all  admixture 
of  particles,  and  the  -f-  metallic  termination  or  pole  touch  the  magnesian  solution 
only,  while  the  —  pole  is  in  contact  with  the  water  only,  a  deposit  of  magnesia 
occurs  just  where  the  pure  water  and  the  magnesian  solution  meet,  and  none 
reaches  the  —  pole.  In  Davy's  experiment,  where  sulphuric  acid  and  soda  ap- 
peared to  quit  each  other,  and  pass  over  separately  into  a  vessel  of  pure  water, 
there  was  certainly  by  capillary  attraction  an  actual  transfer  of  the  salt  before 
decomposition  occurred. 

6.  In  the  foregoing  experiment  a  surface  of  water  acts  as  the  —  electrode, 
clearly  showing  the  contact  of  a  metallic  conductor  with  the  decomposing  liquid 
not  to  be  essential.  Faraday  has  proved  that  even  air  may  serve  as  an  elec- 
trode. A  current  from  the  prime  conductor  of  an  electrical  machine  was  made  to 
pass  from  a  needle's  point  through  air  to  a  pointed  piece  of  litmus  paper  moist- 
ened with  sulphate  of  soda,  and  then  to  issue  from  a  similarly  moistened  point 
of  turmeric  paper.  True  electrolytic  action  took  place,  the  litmus  becoming  red 
and  the  turmeric  paper  brown,  though  both  extremities  of  the  decomposing  solu- 
tion communicated  solely  with  a  stratum  of  air. 

7.  Electro-chemical  decomposition  cannot  occur  unless  an  electric  current  is 
actually  transmitted  through  the  electrolyte;  or,  in  other  terms,  an  electrolyte  is 
always  a  conductor  of  electricity.  Water,  which  conducts  an  electric  current, 
ceases  to  do  so  when  it  passes  into  ice,  and  then  also  resists  decomposition — 
an  observation  equally  true  of  all  electrolytes  on  becoming  solid.  Moreover, 
liquids  which  resist  electro-chemical  decomposition  do  not  permit  the  current  of 
a  voltaic  circle  to  pass.  The  alliance  between  conduction  and  decomposition  is 
so  constant,  that  the  latter  may  be  regarded  as  a  means  by  which  voltaic  currents 
are  transmitted  through  liquid  compounds.  Agreeably  to  this  notion,  solidity 
may  interfere  with  conduction  by  chaining  down  the  elements  of  a  compound, 
and  thereby  preventing  their  transfer  to  the  electrodes.  Improving  the  conduction 
of  a  liquid,  as  by  adding  sulphuric  acid  to  pure  water,  increases  the  decomposing 
power  of  a  voltaic  circle,  the  exciting  fluid  within  the  apparatus  remaining  the 
same;  and  Faraday  has  proved  that  the  quantity  of  a  compound  decomposed  is 
exactly  proportional  to  the  quantity  of  electricity  which  passes,  however  much 
other  circumstances,  such  as  the  size  of  electrodes  and  conducting  wires,  number 
and  size  of  plates,  and  nature  of  exciting  fluid,  may  vary.  Changes  in  these 
conditions  do,  indeed,  influence  the  quantity  of  electricity  transmitted;  but  then 
the  degree  of  chemical  decwnposition  varies  in  the  same  proportion.    The  fore- 


104  GALVANISM. 

going  facts  at  first  led  to  the  opinion  that  the  current  of  a  voltaic  circle  cannot 
pass  through  liquids,  except  those  of  a  metallic  nature,  unless  decomposition 
ensues  at  the  same  time;  but  Faraday  has  noticed  that  when  the  intensity  is  too 
feeble  to  effect  decomposition,  a  small  quantity  of  electricity  maybe  transmitted, 
sufficient  to  be  discovered  by  a  galvanometer.  This  does  not,  however,  essen- 
tially interfere  with  the  law  just  announced. 

8.  Chemical  compounds  differ  in  the  electrical  force  required  for  decomposi- 
tion. A  current  of  very  feeble  tension  suffices  to  decompose  iodide  of  potassium, 
while  a  much  higher  intensity  is  required  for  disuniting  the  elements  of  water. 
The  order  of  easy  decomposition  in  the  annexed  substances  is  as  follows : — 
Solution  of  iodide  of  potassium  ;  fused  chloride  of  silver  ;  fused  protochloride  of 
tin;  fused  chloride  of  lead;  fused  iodide  of  lead  ;  solution  of  hydrochloric  acid; 
and  water  acidulated  with  sulphuric  acid.  By  extending  tables  of  this  kind,  a 
ready  method  will  be  known  for  comparing  the  tension  of  voltaic  circles. 

9.  The  conduction  of  the  electric  currents  within  the  cells  of  a  voltaic  circle 
depends  on  chemical  decomposition  equally  with  that  between  platinum  elec- 
trodes. No  substance  not  an  electrolyte  can  serve  to  excite  a  voltaic  apparatus ; 
and  for  the  passage  of  electricity  from  plate  to  plate  through  the  intervening 
solution,  the  separation  of  substances  previously  combined  in  the  required  ratio 
is  essential.  Neither  free  oxygen  nor  a  solution  of  chlorine  can  excite  a  current, 
though  they  attack  the  zinc  and  develope  electricity;  and  in  a  voltaic  circle  ex- 
cited by  dilute  sulphuiic  acid,  the  electricity  set  in  motion  is  due  to  decomposed 
water  and  oxidized  zinc,  and  not  at  all  to  the  union  of  the  oxide  of  zinc  with 
sulphuric  acid.  The  platinum  electrodes  and  intervening  liquids  may  be  viewed 
as  one  of  the  cells  of  the  circle,  except  that  the  plates  act  merely  as  conductors, 
without  any  oxidation,  the  current  passing  in  virtue  of  the  decomposed  solution. 
In  the  zinc  a«d  copper  cells  the  current  is  urged  on  by  the  appetency  of  the 
zinc  and  oxygen  to  unite;  whereas,  in  passing  between  the  electrodes,  the  elec- 
tricity has  to  surmount  the  mutual  attraction  of  oxygen  and  hydrogen,  or  some 
similar  force,  without  the  assistance  of  any  opposing  affinity.  Hence,  in  experi- 
ments on  decomposition,  the  course  of  the  electricity  should  be  facilitated  by 
employing  large  electrodes  and  wires,  and  placing  them  at  a  short  distance  from 
each  other  in  a  good  conducting  solution. 

The  principles  above  established  show  the  importance  of  exciting  all  the  cells 
of  a  voltaic  circle  with  a  liquid  of  the  same  strength.  The  electricity  circulating 
in  a  voltaic  apparatus  with  the  conducting  wires  in  contact,  is  equal  to  that 
which  the  feeblest  cell  is  able  to  transmit,  any  chemical  action  in  other  cells  more 
than  sufficient  for  exciting  that  quantity  being  wasted. 

[The  important  law  of  definite  electro-chemical  decomposition,  first  demon- 
strated by  Faraday,  has  lately  been  confirmed  and  extended  by  Edmond  Becquerel, 
in  a  series  of  researches  applied  to  a  great  number  of  binary  and  ternary  com- 
pounds.    The  following  is  a  summary  of  conclusions  to  which  he  has  been  led. 

Using  the  term  equivalent  of  electricity^  for  the  amount  of  electricity  necessary 
to  decompose  one  equivalent  of  water,  he  finds, 

1.  That  one  equivalent  of  a  compound  formed  by  the  union  of  an  equivalent 
of  acid,  and  an  equivalent  of  a  base,  always  requires  one  equivalent  of  elec- 
tricity for  its  electro-chemical  decomposition. 

2.  When  an  electrical  current  is  transmitted  through  two  or  more  binary  com- 
pounds, the  decomposition  takes  place  in  such  a  way,  that  for  one  equivalent  of 
electricity  employed,  one  equivalent  of  the  body  which  acts  the  part  of  an  acid, 


*  GALVANISM.  105 

or  electro-negative  element  in  each  compound,  is  disengaged  at  the  positive 
pole. 

As,  from  the  fact  that  an  equivalent  of  electricity  is  required  to  decompose  an 
equivalent  of  any  compound,  we  may  conclude  that  the  electro-positive  and 
electro-negative  elements  of  that  compound,  in  uniting,  would  disengage  the  same 
amount  of  electricity,  he  infers  the  following  laws  : — 

1.  When  one  equivalent  of  a  body,  either  simple  or  compound,  unites  with 
one  or  more  equivalents  of  another,  the  first  playing  the  part  of  an  electro-nega- 
tive element  or  acid,  one  equivalent  of  electricity  is  set  free. 

2.  If  an  equivalent  of  an  electro-negative  body,  such  as  oxygen,  has  already 
entered  into  combination  with  another  body,  which  acts  as  a  base,  and  if  a 
second  equivalent  of  the  former  unites  with  the  compound  thus  produced  to  form 
a  deuto  salt  or  compound  ;  at  the  time  of  this  second  action  another  equivalent  of 
electricity  is  disengaged. 

Thus  the  quantity  of  electricity  set  free  depends  solely  on  the  body  which  acts  the 
part  of  acid  in  the  compound.     (Comp.  Rendus,  Mar.  1844.)] 

THEORIES  OF  GALVANISM  AND  ELECTRO-CHEMICAL  THEORY. 

Of  the  theories  proposed  to  account  for  the  developement  of  electricity  in  voltaic 
combinations,  three  in  particular  have  excited  the  notice  of  philosophers.  The 
first  originated  with  Volta,  who  conceived  that  electricity  is  set  in  motion,  and 
the  supply  kept  up,  solely  by  contact  or  communication  between  the  metals 
(page  82).  He  regarded  the  interposed  solutions  merely  as  conductors,  by  means 
of  which  the  electricity  developed  by  each  pair  of  plates  is  conveyed  from  one 
part  of  the  apparatus  to  the  other.  Thus,  in  the  pile  or  ordinary  battery,  repre- 
sented by  the  following  series : — 


T    zinc  copper       fluid       zinc  copper       fluid       zinc  copper    — 

Volta  considered  that  contact  between  the  metals  occasions  the  zinc  in  each  pair 
to  be-f-,  and  the  corresponding  copper  plate  to  be  — ;  that  the  -{-  zinc  in  each 
pair  except  the  last,  being  separated  by  an  intervening  stratum  of  liquid  from  the 
—  copper  of  the  following  pair,  yields  to  it  its  excess  of  electricity;  and  that  in 
this  way  each  zinc  plate  communicates,  not  only  the  electricity  developed  by  its 
own  contact  with  copper,  but  also  that  which  it  had  received  from  the  pair  of 
plates  immediately  before  it.  Thus,  in  the  three  pairs  of  plates  contained  in 
brackets,  the  second  pair  was  thought  to  receive  electricity  from  the  first  only, 
and  the  third  pair  from  the  first  and  second.  In  batteries  constructed  on  the  prin- 
ciple of  the  crown  of  cups  (fig.  6),  the  electro-motion,  as  Volta  called  it,  is 
ascribed  to  metallic  communication  between  the  zinc  of  one  glass  and  the  copper 
of  the  adjoining  one. 

The  second  is  the  chemical  theory,  proposed  by  Wollaston.  Volta  attached 
little  importance  to  the  chemical  changes  which  never  fail  to  occur  in  every 
voltaic  circle,  whether  simple  or  compound,  considering  them  as  casual  or  unes- 
sential phenomena,  and  therefore  neglected  them  in  the  construction  of  his  theory. 
The  constancy  of  their  occurrence,  however,  soon  attracted  notice.  In  the  earlier 
discussions  on  the  cause  of  spasmodic  movements  in  the  frog  (page  82),Fabroni 
contended,  in  opposition  to  Volta,  that  the  effect  was  not  owing  to  electricity  at 


106  GALVANISM. 

all,  but  to  the  stimulus  of  the  metallic  oxide  formed,  or  of  the  heat  evolved 
during  its  production.  More  extended  researches  soon  proved  the  fallacy  of  this 
doctrine :  but  Fabroni  made  a  most  ingenious  use  of  the  facts  within  his  know- 
ledge, and  paved  the  way  to  the  chemical  theory  of  Wollaston. 

Wollaston,  fully  admitting  electricity  as  the  voltaic  agent,  assigned  chemical 
action  as  the  cause  by  which  it  is  excited.  The  repetition  and  extension  of 
Volta's  experiments  by  the  English  chemists  speedily  delected  the  error  he  had 
committed  in  overlooking  the  chemical  phenomena  which  occur  within  the  pile. 
It  was  observed  that  no  sensible  effects  are  produced  by  a  combination  of  con- 
ductors which  do  not  act  chemically  on  each  other ;  that  the  action  of  the  pile  is 
always  accompanied  by  the  oxidation  of  the  zinc  ;  and  that  the  energy  of  the  pile 
in  general  is  proportional  to  the  activity  with  which  its  plates  are  corroded.  Ob- 
servations of  this  nature  induced  Wollaston  to  conclude  that  the  process  begins 
with  the  oxidation  of  the  zinc, — that  oxidation,  or,  in  other  terms,  chemical 
action,  was  the  primary  cause  of  the  developement  of  electricity, — that  the  fluid 
of  the  circle  served  both  to  oxidize  the  zinc  and  to  conduct  the  electricity  which 
was  excited, — and  that  contact  between  the  plates  served  only  to  conduct  elec- 
tricity, and  thereby  complete  the  circuit. 

The  third  theory  of  the  pile  was  proposed  by  Davy,  and  is  intermediate  be- 
tween the  two  former.  He  adduced  many  experiments  in  support  of  Volta's 
statement,  that  the  electric  equilibrium  is  disturbed  by  the  contact  of  different 
substances,  without  any  chemical  action  taking  place  between  them.  He  ac- 
knowledged, however,  with  Wollaston,  that  the  chemical  changes  contribute  to 
the  general  result ;  and  he  maintained  that,  though  not  the  primary  movers  of 
the  electric  current,  they  are  essential  to  the  continued  and  energetic  action  of 
every  voltaic  circle.  The  electric  excitement  was  begun,  he  thought,  by  metallic 
contact,  and  maintained  by  chemical  action. 

The  progress  of  inquiry  since  these  theories  first  came  into  notice,  has  gradu- 
ally given  more  and  more  support  to  the  views  of  Wollaston,  and  has  at  last,  I 
apprehend,  established  it  to  the  entire  exclusion  of  the  theory  of  Volta.  The 
very  fundamental  position,  that  electricity  is  excitable  as  a  primary  result  by  the 
contact  of  different  substances,  is  warmly  contested,  and,  as  some  think  with 
strong  reason,  has  been  disproved  (page  72) ;  but  admitting,  for  the  sake  of 
argument,  that  a  small  effect,  which  is  all  that  can  now  be  contended  for,  may 
thus  be  produced,  it  is  altogether  insignificant  when  contrasted  with  the  aston- 
ishing phenomena  exhibited  by  a  voltaic  circle.  The  experiments  of  De  la  Rive, 
in  reference  to  this  question,  appear  irreconcilable  with  the  theory  of  Volta  (An. 
de  Ch.  et  Ph.  xxxviii.  225 ;  Ixi.  38 ;  Ixii.  147).  This  ingenious  philosopher 
contends  that  the  direction  of  a  voltaic  current  is  not  determined  by  metallic  con- 
tact, nor  even  by  the  nature  of  the  metals  relatively  to  each  other,  but  by  their 
chemical  relation  to  the  exciting  liquid.  As  the  result  of  his  inquiries,  he  states, 
that  of  two  metals  composing  a  voltaic  circle,  that  one  which  is  most  energeti- 
cally oxidized  will  be  -j-  with  respect  to  the  other.  Thus,  when  tin  and  copper 
are  placed  in  acid  solutions,  the  former,  which  is  most  rapidly  corroded,  gives  a 
-|-  current  through  the  liquid  to  the  copper,  as  the  zinc  does  in  the  circle  in  fig. 
1 ;  but,  if  they  are  put  into  a  solution  of  ammonia,  which  acts  most  on  the  copper, 
the  direction  of  the  current  will  be  reversed.  Copper  is  -f-  in  relation  to  lead  in 
strong  nitric  acid,  which  oxidizes  the  former  most  freely  ;  whereas  in  dilute  nitric 
acid,  by  which  the  lead  is  most  rapidly  dissolved,  the  lead  is  -j-.  Even  two 
plates  of  copper  immersed  in  solutions  of  the  same  acid,  but  of  different  strength, 


fr^^ 


a 


GALVANISM.  107 

will  form  a  voltaic  circle,  the  plate  on  which  chemical  action  is  most  free  causing 
a  current  of  -}-  electricity  to  the  other:  nay,  it  is  possible  to  construct  a  com- 
pound circle  solely  with  zinc  plates  and  one  acid  solution  (page  83,)  provided 
the  same  side  of  each  plate  be  more  rapidly  oxidized  than  the  other. 

The  admirable  researches  of  Faraday  (Phil.  Trans.  1833  &  34),  supply  con- 
clusive evidence  against  the  theory  of  Volta,  proving  metallic  contact  not  to  be 
essential  to  voltaic  action,  inasmuch  as  it  is  procured  characteristically  without 
contact.    A  plate  of  zinc,  a,  fig.  15,  about  8  inches  long  by  -|  an      p.-     ,p. 
inch  wide,  was  cleaned  and  bent  at  a  right  angle ;  and  a  plate  of 
platinum,  of  the  same  width  and  3  inches  long,  was  soldered  to  a  pla-        — ^ 
tinum  wire,  b  s  x,  the  point  of  which,  x,  rested  on  a  piece  of  bibulous      . 
paper  lying  upon  the  zinc,  and  moistened  with  a  solution  of  iodide 
of  potassium.    On  introducing  the  plates  into  a  vessel,  c,  filled  with    -^ 
dilute  sulphuric  and  nitric  acid,  a  -|-  current  instantly  ensued  in    ^ 
the  direction  of  the  arrow,  as  testified  by  the  hydrogen  evolved  at 
the  plate  a,  by  the  decomposed  iodide  of  potassium,  and  by  a  gal- 
vanometer.   We  have  thus  a  simple  circle  of  the  same  construction 
and  action  as  in  figure  1,  except  in  the  absence  of  metallic  con- 
tact. 

The  arrangement  of  figure  15,  however,  though  good  for  establishing  a  prin- 
ciple, is  not  adapted  for  ordinary  practice.  The  moist  paper  at  a?  is  a  much  less 
perfect  conductor  than  a  metal,  and  thus  obstructs  the  passage  of  the  current ; 
nay,  it  does  more,  for  it  tends  to  establish  an  opposite  current.  In  fact,  on  re- 
moving the  dilute  acid  from  c,  and  putting  the  zinc  plate,  a,  in  contact  with  the 
plate  of  platinum,  an  ordinary  simple  circle  would  be  formed,  in  which  a  posi- 
tive current  would  flow  from  the  zinc  at  x  through  the  solution  to  and  along  the 
wire  X  s  b.  This  current,  in  Faraday's  experiment,  was  so  feeble  compared  with 
the  one  excited  by  the  acid  solution,  that  its  influence  was  scarcely  appreciable ; 
but  if  the  opposed  currents  had  been  of  the  same  force,  no  action  would  have 
ensued. 

To  explain  how  chemical  action  excites  electricity,  recourse  is  had  to  the 
electro-chemical  theory,  first  started  by  Davy  in  his  essay  on  Some  Chemical 
Agencies  of  Electricity  (Phil.  Trans.  1807).  The  views  of  Davy,  which  in  some 
form  or  other  have  been  adopted  by  most  persons  who  have  speculated  on  this 
subject,  are  founded  on  the  assumption,  now  rendered  so  much  more  plausible 
than  in  his  day,  that  electrical  and  chemical  attractions  are  owing  to  one  and  the 
same  agent.  He  considered  chemical  substances  to  be  endowed  with  natural 
electric  energies ,-  meaning  thereby  that  a  certain  electric  condition,  either  -f-  or 
— -,  is  natural  to  the  atoms  or  combining  molecules  of  bodies ;  that  chemical 
union  is  the  result  of  electrical  attraction  taking  place  between  oppositely  excited 
atoms,  just  as  masses  of  matter  when  oppositely  excited  are  mutually  attracted  ; 
and  that  ordinary  chemical  decomposition  arises  from  two  combined  atoms  being 
drawn  asunder  by  the  electric  energies  of  other  atoms  more  potent  than  those  by 
which  they  were  united.  Electro-chemical  decomposition  was  at  once  explained 
by  Davy  on  the  same  principles.  He  regarded  the  metallic  terminations  or  poles 
of  a  voltaic  circle  (page  101)  as  two  centres  of  electrical  power,  each  acting 
repulsively  to  particles  in  the  same  electric  state  as  itself,  and  by  attraction  on 
those  which  were  oppositely  excited.  The  necessary  result  was,  that  if  the  elec- 
tric energy  of  the  battery  exceeded  that  by  which  the  elements  of  any  compound 
subject  to  its  action  were  held  together,  decomposition  followed,  and  each  ele- 


108  GALVANISM. 

ment  was  transferred  bodily  to  the  pole  by  which  it  was  attracted,  passing 
through  solutions  not  containing  the  original  compound,  and  refusing  to  unite 
with  substances  for  which  under  other  circumstances  it  would  have  combined. 
Substances  which  appeared  at  the  -j-  pole,  such  as  oxygen,  chlorine,  and  acids, 
were  termed  eleciro-negaiive  substances  ;  and  those  electro-positive  bodies,  which 
were  separated  at  the  —  pole. 

The  views  of  Davy,  both  in  his  original  essay  and  his  subsequent  explanations 
(Phil.  Trans.  1826),  were  so  generally  and  obscurely  expressed,  that  chemists 
have  never  fully  agreed,  as  to  some  points  of  the  doctrine,  about  his  real  mean- 
ing. If  he  meant  that  a  particle  of  free  oxygen  or  free  chlorine  is  in  a  negatively 
excited  state,  then  his  opinion  is  contrary  to  the  fact,  that  neither  of  those  gases 
aflfect  an  electrometer  with  —  or  any  kind  of  electricity,  any  more  than  hydrogen 
gas  or  potassium  alone  exhibit  any  evidence  of  -f-  excitement.  If  sulphur  unites 
with  oxygen  because  it  has  a  -j-  electric  energy,  why  should  it  unite  with 
potassium,  which  confessedly  is  far  more  -f-  than  itself?  The  only  mode  in 
which  such  facts  as  these  seem  reconcilable  with  the  electro-chemical  theory,  is 
to  suppose  all  bodies  in  their  uncombined  state  to  be  electrically  indifferent,  but 
that  they  have  a  natural  appetency  to  assume  one  state  in  preference  to  another. 
Electro-negative  bodies  are  such  as  assume  negative  excitement  under  a  certain 
approximation  to  others  which  at  the  same  time  become  positively  excited,  che- 
mical union  being  the  consequence.  On  this  supposition  it  is  intelligible  that 
sulphur  may  be  in  -|-  relation  to  oxygen,  and  —  to  potassium,  just  as  black 
silk  is  positively  electrified  by  friction  with  sealing-wax,  and  negatively  by  white 
silk.  Accordingly,  Berzelius,  and  others  who  have  since  speculated  on  this 
subject,  have  been  obliged  to  modify  the  theory  as  first  given  by  Davy ;  and  it 
is  viewed  at  present  in  different  ways  by  different  persons.  The  following  is 
what  appears  to  me  most  correctly  to  harmonize  with  the  laws  of  electricity  and 
the  phenomena  to  be  explained : — A  particle  of  zinc  and  a  particle  of  oxygen, 
each  possessed  of  -f-  and  —  electricity,  assume  in  combining  opposite  electric 
conditions,  and  combine,  in  consequence  of  such  assumption,  the  particles  ad- 
hering together  by  virtue  of  their  opposite  states,  just  as  two  oppositely  excited 
pith  balls  are  mutually  attractive.  The  zinc  particle  in  becoming  -[-  gives  off  — 
electricity  to  the  mass  of  zinc  or  other  body  to  which  it  had  belonged ;  and,  in 
like  manner,  the  particle  of  oxygen,  in  becoming  — ,  supplies  -|-  electricity  to 
adjacent  particles  of  oxygen  or  other  adjacent  substances.  Thus  electro-positive 
bodies  in  the  act  of  combining  give  off  —  electricity,  and  electro-negatives  set 
free  -\-  electricity.  In  general,  these  opposite  electricities  instantly  neutralize 
each  other ;  but  under  favourable  circumstances,  as  in  Pouillet's  experiments, 
such  effect  is  prevented.  So,  in  an  experiment  by  De  la  Rive,  of  transmittipg 
dry  chlorine  gas  mixed  with  air  through  an  insulated  copper  tube,  chloride  of 
copper  is  generated :  if  the  gases  pass  onward  in  a  continuous  current,  the  + 
electricity  set  free  by  the  chlorine  is  carried  off  by  the  air,  while  the  tube  is  ren- 
dered negative  by  the  —  electricity  lost  by  those  particlss  of  copper  which  com- 
bine with  the  chlorine. 

Chemical  decomposition  also  excites  electricity ;  and  by  this  theory  it  ought 
to  do  so.  For  a  particle  of  zinc  in  quitting  oxygen  is  -\-j  must  recover  —  elec- 
tricity before  it  can  resume  its  natural  state,  and  in  doing  so  leaves  contiguous 
substances  -f-  ;  and,  similarly  the  —  oxygen  renders  objects  — by  robbing  them 
of  their  -\-  electricity.     Hence,  a  body  in  combining  excites  in  others  an  electric 


GALVANISM.  109 

State  opposite  to  that  which  it  assumes  ;  while  in  the  act  of  decomposition  it  pro- 
duces an  effect  exactly  the  reverse. 

Again,  it  follows  from  the  theory,  that  unless  the  zinc  can  assume  the  -f-  state 
hy  getting  rid  of  —  electricity,  it  cannot  unite  with  oxygen ;  and  that  chemical 
union  will  more  readily  ensue,  the  more  freely  a  connecting  medium  for  carrying 
off  such  —  electricity  is  supplied.  This  is  applicable  to  Davy's  method  of  pre- 
serving copper  in  sea-water  (page  84).  A  piece  of  zinc  in  contact  with  copper 
corrodes  rapidly  by  carrying  off  its  —  electricity ;  while  the  copper  thus  con- 
stantly rendered  — ,  is  prevented  from  assuming  the  -j-  state,  and  hence  loses  its 
power  of  uniting  either  with  oxygen  or  chlorine.  These  principles  readily  apply 
to  a  simple  voltaic  arrangement,  composed  of  zinc,  copper,  and  dilute  acid.  In 
the  broken  circuit,  the  oxidation  of  the  zinc  causes  the  liquid,  which  supplies  the 
oxygen  to  be  -|- ;  while  the  zinc  plate  is  made  —  by  the  electricity  given  off 
by  the  oxidizing  particle  of  zinc.  This  happens  whether  the  copper  plate  is  pre- 
sent or  not.  The  -|-  electricity  diffused  in  the  acid  solution  is  in  part  taken  up 
by  the  copper  plate  which  thereby  becomes  -f-,  and  is  in  part  lost  by  neutralizing 
the  —  electricity  on  the  zinc  plate.  In  the  closed  circuit,  the  —  electricity  on 
the  zinc  escapes  along  the  conducting  wire  to  the  copper  plate;  the  effect  of 
which  is  to  promote  the  oxidation  of  the  zinc  on  the  principle  above  stated,  and 
by  rendering  the  copper  — ,  to  facilitate  the  extraction  of  -f  electricity  from  the 
liquid.  A  current  of  -f-  electricity  thus  circulates  from  the  zinc  through  the 
liquid  to  the  copper,  and  of  —  electricity  in  the  opposite  direction  (page  83). 
The  plate  which  by  chemical  action  with  the  liquid  excites  electricity,  is  called 
the  generating  plate ;  while  the  other  is  the  conducting  plate^  because  it  performs 
the  office  of  a  conductor  merely  :  in  the  common  circle,  zinc  is  the  generating, 
and  copper  the  conducting  plate. 

In  a  compound  circle,  represented  by  three  pairs  of  plates,  as  in  fig.  16,  each 
pair  of  plates,  indicated  by  the  brackets,  sends  a  current  of  -|-  electricity  from 


Fig.  16. 

zinc  copper        fluid      zinc  copper        fluid       zinc  copper 

the  zinc  through  the  liquid  to  the  copper,  rendering  each  copper  plate  -f-,  while 
each  zinc  plate  is  — .  The  first  copper  and  second  zinc  plates,  being  oppositely 
electrified,  neutralize  each  other;  and  the  same  occurs  with  the  second  copper 
and  third  zinc,  as  with  any  number  of  plates  similarly  situated.  The  extreme 
plates  alone  can  evince  an  electric  state,  the  zinc  in  the  broken  circuit  being — , 
and  the  copper  -}- ;  and  if  these  plates  are  connected  by  a  wire,  they,  like  the 
other  zinc  and  copper  plates  of  the  series,  neutralize  each  other,  and  a  continuous 
current  is  established  through  the  whole  battery,  of  -]-  electricity  in  one  direc- 
tion, as  shown  by  the  arrows,  and  of  —  in  the  other.  Thus,  the  quantity  of 
electricity  which  circulates  in  one  part  of  the  closed  battery,  which  is  aptly 
called  a  circle^  is,  contrary  to  the  notion  of  Volta  (page  105),  the  same  in  every 
part  (page  90).  The  influence  of  a  number  of  plates  is  to  augment  the  intensity 
only  (page  87).  This  subject  has  been  ably  discussed  by  De  la  Rive.  (An.  de 
Ch.  et  Ph.  Ixii.  180.) 

Chemists  are  not  agreed  as  to  the  order  of  electric  energy  in  which  the  ele- 
ments should  be  arranged.  The  following  is  that  given  by  Berzelius,  and  may 
be  viewed  as  approximative  rather  than  rigidly  exact : — Sulphur,  nitrogen,  and 
hydrogen  scarcely  occupy  their  true  position  in  the  series.  The  two  former  are 
less  electro-negative  than  chlorine  and  fluorine,  and  hydrogen,  I  conceive,  should 


110  GALVANISM. 

occupy  a  prominent  station  among  the  electro-positive  elements.  All  the  bodies 
in  the  first  series  are  —  with  regard  to  those  in  the  second.  In  the  first  series 
each  element  is  — ,  and  in  the  second  -{-,  to  all  those  which  follow  it. 

1.  Negative  Electrics. — Oxygen,  sulphur,  nitrogen,  chlorine,  iodine,  fluorine, 
phosphorus,  silenium,  arsenic,  chromium,  molybdenum,  tungsten,  boron,  carbon, 
antimony,  tellurium,  columbium,  titanium,  silicon,  osmium,  hydrogen. 

2.  Positive  Electrics. — Potassium,  sodium,  lithium,  barium,  strontium,  calcium, 
magnesium,  glucinium,  yttrium,  aluminium,  zirconium,  manganese,  zinc,  cad- 
mium, iron,  nickel,  cobalt,  cerium,  lead,  tin,  bismuth,  uranium,  copper,  silver, 
mercury,  palladium,  platinum,  rhodium,  iridium,  gold. 

Theory  of  Chemical  Decomposition. — Compounds  aie  decomposed  by  galvan- 
ism, so  far  as  is  known,  only  when  they  are  more  or  less  fluid,  that  state  being 
apparently  necessary  for  giving  mobility  to  the  elements,  which  are  otherwise 
chained  down  to  one  spot  and  prevented  from  separating.  Davy's  opinion,  that 
an  element  is  actually  transferred  beyond  the  place  in  which  the  decomposing 
compound  exists,  is  untenable  after  the  experiments  of  Faraday  (page  103). 

The  facts  adduced  by  the  latter  philosopher  are  inconsistent  with  the  hypo- 
thesis of  Davy,  by  which  he  accounted  for  chemical  decomposition  and  transfer, 
namely,  that  attraction  is  exerted  for  the  elements  of  compounds  by  the  metallic 
conductors  a  h.    The  most  feasible  theory  is  that  of  Grotthus,  of  there  being 
Fig.  17.  successive  decompositions  and  recom positions  in  the  line  of 

particles  lying  between  the  electrodes.  Let  the  upper  part 
of  fig.  17  represent  a  row  of  three  particles  of  water  lying 
X  between  the  electrodes  c  z,  oxygen  being  represented  by  Q , 
and  hydrogen  by  (J) .  A  -f-  current,  in  passing  through  them, 
is  assumed  to  impart  a  kind  of  polar  or  magnetic  virtue  to  the 
particles  of  oxygen  and  hydrogen,  whereby  affinity  is  weakened  or  destroyed  on 
one  side,  and  exalted  on  the  other :  each  particle  of  hydrogen,  for  example, 
loses  its  attraction  for  the  oxygen  on  its  right  side  and  quits  it,  but  acquires  an 
attraction  for  the  oxygen  on  the  left  side  and  combines  with  it.  Three  particles 
of  water  thus  yield,  as  in  the  lower  part  of  fig.  17,  two  other  particles  which 
are  generated  ;  while  the  extreme  particles  of  oxygen  and  hydrogen  are  set  free. 
There  is  thus  no  transfer  from  one  spot  to  another ;  the  oxygen  and  hydrogen 
are  set  free  at  the  place  where  they  pre-existed  ;  and  they  are  evolved  as  gases, 
unless,  by  some  secondary  action,  they  should  unite  with  the  matter  of  the  elec- 
trodes or  with  some  element  of  the  solution. 

The  preceding  theoretical  questions  have  been  discussed  on  the  assumption 
of  electricity,  as  explained  in  the  last  section,  being  an  independent  principle 
susceptible  of  rapid  motion  from  one  body  to  another ;  and  that  the  condition  of 
a  voltaic  conducting  wire  is  similar  to  that  of  a  wire  leading  from  the  ground  to 
the  prime  conductor  of  an  electrical  machine,  or  which  connects  the  inner  and 
outer  surface  of  a  charged  Leyden  phial,  except  that  the  voltaic  current  moves 
slowly,  owing  to  its  lower  tension  and  the  interposed  imperfect  conductor. 
Some  conceive  that  what  is  called  an  electric  current  is  not  an  actual  transfer  of 
anything,  but  a  process  of  induction  among  the  molecules  of  a  conductor  pass- 
ing progressively  along  it.  Others,  denying  independent  materiality  to  electri- 
city, may  ascribe  it  to  a  wave  of  vibrating  matter,  just  as  the  phenomena  of 
optics  are  explained  by  the  undulatory  theory.  But  whatever  theory  of  the  nature 
of  electricity  may  be  adopted,  it  seems  necessary,  after  the  experiments  of  Fara- 
day on  the  identity  of  voltaic  and  common  electricity,  that  the  nature  of  an  elec- 
tric and  yoltaic  current  is  essentially  the  same. 


0O0O  ®o 

-* CSX 

O0  OCD 


PART   II. 


INORGANIC  CHEMISTRY. 


PRELIMINARY  REMARKS. 


In  teaching  a  science  such  as  chemistry,  the  details  of  which  are  numerous 
and  complicated,  it  would  be  injudicious  to  follow  the  order  of  discovery,  and 
proceed  from  individual  facts  to  the  conclusions  which  have  been  deduced  from 
them.  An  opposite  course  is  indispensable.  It  is  necessary  to  discuss  general 
principles  in  the  first  instance,  in  order  to  aid  the  beginner  in  remembering  insu- 
lated facts,  and  in  comprehending  the  explanations  connected  with  them.  The 
second  part  of  this  work  will  therefore  commence  with  an  explanation  of  the 
leading  doctrines  of  the  science.  One  inconvenience,  indeed,  arises  from  this 
method.  It  is  often  necessary,  by  way  of  illustration,  to  refer  to  facts  of  which 
the  beginner  is  ignorant;  and  hence  on  some  occasions  more  knowledge  will 
be  required  for  understanding  a  subject  fully,  than  the  reader  may  have  at  his 
command.  But  these  instances  will,  it  is  hoped,  be  rarely  met  with ;  and  when 
they  do  occur,  the  reader  is  advised  to  quit  the  point  of  difficulty,  and  return  to 
the  study  of  it  when  he  shall  have  acquired  more  extensive  knowledge  of  the 
details. 

To  the  chemical  history  of  each  substance  its  chief  physical  characters  will 
be  added.  A  knowledge  of  these  properties  is  not  only  advantageous  in  assist- 
ing the  chemist  to  distinguish  one  body  from  another,  but  in  many  instances  it 
is  applied  to  uses  still  more  important.  The  character  called  specific  gravity, 
the  meaning  of  which  was  explained  at  page  49,  is  of  so  much  importance  that 
the  mode  of  determining  it  will  be  mentioned  in  this  place.  The  process  con- 
sists in  weighing  a  body  carefully,  and  then  determining  the  weight  of  an  equal 
bulk  of  water,  the  latter  being  regarded  as  unity.  If,  for  example,  a  portion  of 
water  weigh  nine  grains,  and  the  same  bulk  of  another  body  20  grains,  its  sp. 
gr.  is  determined  by  this  formula ; — as  9 :  20  :  :  1  (assumed  as  the  sp.  gr.  of 
water)  to  the  fourth  proportional  2*2222 ;  so  that  the  sp.  gr.  of  any  substance  is 
found  by  dividing  its  weight  by  the  weight  of  an  equal  volume  of  water.  It  is 
easy  to  discover  the  weight  of  equal  bulks  of  water  and  any  other  liquid  by 
filling  a  small  bottle  of  known  weight  with  each  successively,  and  weighing 
them.^     The  method  of  obtaining  the  necessary  data  in  case  of  a  solid  is  some- 

*  Bottles  are  prepared  for  this  purpose  by  the  philosophical  instrument  makers. 


112  PRELIMINARY  REMARKS. 

what  different.  The  body  is  first  weighed  in  air,  is  next  suspended  in  water  by- 
means  of  a  hair  attached  to  the  scale  of  the  balance,  and  is  then  weighed  again. 
The  difference  between  the  two  weights  "gives  the  weight  of  a  quantity  of  water 
equal  to  the  bulk  of  the  solid.  This  rule  is  founded  on  the  hydrostatic  law, 
that  a  solid  body,  immersed  in  any  liquid,  not  only  weighs  less  than  it  does  in 
air,  but  the  difference  corresponds  exactly  to  the  weight  of  liquid  which  it  dis- 
places ;  and  it  is  obvious  that  the  liquid  so  displaced  is  exactly  of  the  same 
dimensions  as  the  solid.  Another  method  is  by  the  use  of  the  bottle  recom- 
mended for  taking  the  sp.  gr.  of  liquids.  After  weighing  the  bottle  filled  with 
water,  a  known  weight  of  the  solid  is  put  into  it,  which  of  course  displaces  a 
quantity  of  water  precisely  equal  to  its  own  volume.  The  exact  weight  of  the 
displaced  water  is  found  by  weighing  the  bottle  again,  after  its  outer  surface  is 
made  perfectly  dry. 

The  determination  of  the  sp.  gr.  of  gaseous  substances  is  an  operation  of 
much  greater  delicacy.  From  the  extreme  lightness  of  gases,  it  would  be  incon- 
venient to  compare  them  with  an  equal  bulk  of  water,  and  therefore  atmospheric 
air  is  taken  as  the  standard  of  comparison.  The  first  step  of  the  process  is  to 
ascertain  the  weight  of  a  given  volume  of  air.  This  is  done  by  weighing  a 
very  light  glass  flask,  furnished  with  a  good  stopcock,  while  full  of  air ;  and 
then  weighing  it  a  second  time,  after  the  air  has  been  withdrawn  by  means  of 
the  air-pump.  The  difference  between  the  two  weights  gives  the  information 
required.  According  to  the  observation  of  Prout,  100  cubic  inches  of  pure  and 
dry  atmospheric  air,  at  the  temperature  of  60°  and  when  the  barometer  stands 
at  30  inches,  weigh  31-0117  grains.  By  a  similar  method  the  weight  of  any 
other  gas  may  be  determined,  and  its  sp.  gr.  be  inferred  accordingly.  For 
instance,  suppose  100  cubic  inches  of  oxygen  gas  are  found  to  weigh  34*109 
grains,  its  sp.  gr.  will  be  thus  deduced  ;  as  31'0117 :  34*109  :  :  1  (the  sp.  gr.  of 
air) :  1*1025,  the  sp.  gr.  of  oxygen. 

There  are  four  circumsta»c€s  to  which  particular  attention  must  be  paid  in  tak- 
ing the  specific  gravity  of  gases  : — 

1.  The  gas  should  be  perfectly  pure,  otherwise  the  result  cannot  be  accurate. 

2.  Due  regard  must  be  had  to  its  hygrometic  condition.  If  it  is  saturated 
with  moisture,  the  necessary  correction  may  be  made  by  the  formula  of  page 
50  ;  or  it  may  be  dried  by  the  use  of  substances  which  have  a  powerful  attrac- 
tion for  moisture,  such  as  chloride  of  calcium,  quicklime,  or  fused  potassa. 

3.  As  the  bulk  of  gaseous  substances,  owing  to  their  elasticity  and  compres- 
sibility, is  dependent  on  the  pressure  to  which  they  are  exposed,  no  two  obser- 
vations admit  of  comparison,  unless  made  under  the  same  elevation  of  the 
barometer.  It  is  always  understood,  in  taking  the  sp.  gr.  of  a  gas,  that  the 
barometer  must  stand  at  30  inches,  by  which  means  the  operator  is  certain  that 
each  gas  is  subject  to  equal  degrees  of  compression.  An  elevation  of  thirty 
inches  is  called  the  standard  height;  and  if  the  mercurial  column  be  not  of  that 
length  at  the  time  of  performing  the  experiment,  the  error  arising  from  this 
cause  must  be  corrected  by  calculation.  It  has  been  established  by  experiment 
that  the  bulk  of  gases  is  inversely  as  the  pressure  to  which  they  are  subject. 
Thus,  100  measures  of  air,  under  the  pressure  of  30  inches  of  mercury,  will 
dilate  to  200  measures,  if  the  pressure  be  diminished  by  one  half;  and  will  be 
compressed  to  50  measures,  when  the  pressure  is  double,  or  equal  to  a  mercurial 
column  of  GO  inches.  The  correction  for  the  effect  of  pressure  may  therefore 
be  made  by  the  rule  of  three,  as  will  appear  by  an  example.     If  a  certain  por- 


PRELIMINARY  REMARKS.  113 

tion  of  gas  occupy  the  space  of  100  measures  at  29  inches  of  the  barometer,  its 
bulk  at  30  inches  may  be  obtained  by  the  following  proportion ;  as  30 :  29  :  : 
100 :  96-66. 

It  is  understood  that  the  temperature  of  the  mercurial  column  is  constant :  if 
not  so,  correction  must  be  made  for  the  change  in  the  volume  of  the  mercury 
produced  by  change  of  temperature,  on  the  principle  laid  down  at  page  22. 

4.  For  a  similar  reason  the  temperature  should  always  be  the  same.  The 
standard  or  mean  temperature  is  60° ;  and  if  the  gas  be  admitted  into  the 
weighing-flask  when  the  thermometer  is  above  or  below  that  point,  the  formula 
of  page  24  should  be  employed  for  making  the  necessary  correction. 

Chemical  Nomenclature. — The  first  attempt  to  form  a  systematic  chemical 
nomenclature  was  by  Lavoisier,  Berthollet,  Guyton  de  Morveau,  and  Fourcroy, 
soon  after  the  discovery  of  oxygen  gas.  To  avoid  an  undue  use  of  new  terms, 
the  known  elements  and  the  more  familiar  compound  bodies  were  allowed  to 
retain  the  names  which  usage  had  assigned  to  them.  The  newly-discovered 
elements  were  named  from  some  striking  property.  Thus,  oxygen,  from  o|i'j 
acid,  and  yiwasw  to  generate,  was  so  called  from  a  belief  that  it  is  the  universal 
cause  of  acidity ;  and  the  term  hydrogen,  from  iSw^  water,  and  ysi/mstr,  was 
applied  to  the  inflammable  element  of  water.  The  compounds  into  which  oxy- 
gen enters  were  termed  acids  or  oxides,  according  as  they  do  or  do  not  possess 
acidity.  The  name  of  an  acid  was  derived  from  the  substance  acidified  by  the 
oxygen,  to  which  was  added  the  termination  in  ic.  Thus  sulphurtc  and  carbon/c 
acids  signified  compounds  of  sulphur  and  carbon  with  oxygen.  Should  sulphur 
or  any  other  body  form  two  acids,  the  name  of  that  containing  least  oxygen  was 
made  to  terminate  in  ows,  as  sulphurous  acid.  The  termination  in  uret  was 
applied  to  compounds  of  the  simple  non-metallic  substances  with  each  other, 
with  a  metal,  or  with  a  metallic  oxide  :  thus,  sulphured  and  carhuret  of  iron 
signify  compounds  of  sulphur  and  carbon  with  iron.  The  general  term  salt 
comprehended  compounds  of  acids  with  alkaline  bases,  and  the  names  of  the 
salts  were  so  contrived  as  to  indicate  the  substances  contained  in  them.  If  the 
acid  contain  a  maximum  of  oxygen,  the  name  of  the  salt  terminated  in  ate ;  if 
a  minimum,  the  termination  in  ite  was  used  :  thus,  sulpha/e  and  phospha/fe  of 
potassa  are  salts  of  sulphuric  and  phosphoric  acids;  while  the  terms  sulphide 
and  pho*sphi7e  of  potassa  denote  salts  of  that  alkaly  with  sulphurous  and  phos- 
phorous acids. 

These  instances  suffice  to  exhibit  the  principles  by  which  the  framers  of  the 
nomenclature  were  guided.  Their  object  was  to  apply  similar  names  to  similar 
things,  and  so  to  construct  those  names  as  to  indicate  the  nature  or  composition 
of  the  bodies  to  which  they  were  attached.  The  same  views  have  been  acted  on 
by  succeeding  chemists,  who,  with  this  intention,  have  availed  themselves  of 
the  laws  of  definite  combination.  The  more  essential  parts  of  this  method,  as 
adopted  in  these  elements,  are  the  following : — The  names  of  newly-discovered 
elements  are  selected  from  some  obvious  property :  thus,  chlorine  and  iodine 
were  so  called  from  their  colour.  The  termination  of  a  name  is  rendered  similar 
to  those  of  nearly  allied  substances  :  thus,  iodine,  and  flourine  received  that  ter- 
mination from  their  analogy  to  chlorine ;  the  compounds  of  chlorine,  iodine, 
bromine,  and  flourine,  from  their  relations  to  oxygen,  are  termed  chlorides,  iod- 
ides,  &c. ;  and  the  compounds  of  selenium,  and  other  similar  inflammables,  are 
called  seleniurets,  from  their  analogy  to  sulphwre^s  and  phosphi^re^s.  The  names 
of  metals,  except  some,  as  iron  and  tin,  whose  names  have  been  sanctioned  by 

10 


114  PRELIMINARY  REMARKS. 

usage,  terminate  in  wm,  as  potassium  and  titanium.  The  names  of  alkaline 
bases,  when  expressed  by  one  word,  terminate  in  a,  as  potassa  and  morphia. 
When  one  substance  forms  with  oxygen  three  or  more  acids,  a  Greek  preposi- 
tion is  usually  prefixed  to  indicate  the  relative  quantity  of  oxygen :  thus,  hypo- 
nitrous  acid  cotitaLjas  less  oxygen  than  the  nitrous  :  hypermXrows  would  apply  to 
an  acid  w^ith  more  oxygen  than  the  nitrous  ;  and  Ay^osulphurtc  acid  indicates  an 
acid  with  less  oxygen  than  the  sulphuric,  and  more  than  the  sulphurous.  Per 
is  sometimes  prefixed  with  the  same  intention  as  hyper:  thus,  joerchloric  acid 
contains  more  oxygen  than  the  chloric.  Different  oxides  of  the  same  metal  are 
distinguished  by  derivates  from  the  Greek  or  Latin.  An  oxide  consisting  of  an 
equivalent  of  each  element  is  denoted  either  by  the  term  oxide  without  any  aifix, 
or  by  jwo/oxide  (Tt^wfoj,  first)  ;  the  highest  grade  is  the  j?eroxide ;  and  the  inter- 
mediate grades  are  distinguished  by  Latin  numerals  expressing  the  number  of 
equivalents  of  oxygen  combined  with  one  equivalent  of  the  metal,  such  as  bin- 
oxide,  /eroxide,  &c.  Sesqui,  one  and  a  half,  is  used  to  indicate  the  relation  of 
1  to  1 5,  or  2  to  3,  as  in  the  Sesquioxide  of  iron  or  cobalt.  The  Greek  nume- 
rals dis,  iris,  ietrahis,  are  prefixed  in  like  manner  to  denote  oxides  formed  with 
one  equivalent  of  oxygen,  and  two,  three,  or  more  equivalents  of  a  metal.  More 
complex  ratios,  such  as  3  eq.  of  a  metal  to  4  eq.  of  oxygen,  are  denoted  by  a 
fraction,  ^,  placed  before  the  name  of  the  oxide. 

The  same  system  is  extended  not  merely  to  the  union  of  elements  generally 
with  each  other,  but  to  compounds  of  a  more  complex  nature,  such  as  the  saTts. 
To  a  salt  formed  of  an  equivalent  of  the  acid  and  alkali,  its  generic  name  with- 
out other  addition  is  applied ;  but  if  two  or  more  equivalents  of  the  acid  are 
attached  to  one  eq.  of  the  base,  or  two  or  more  equivalents  of  the  base  to  one  eq. 
of  the  acid,  a  numeral  is  prefixed  so  as  to  indicate  its  composition.  The  two 
salts  of  sulphuric  acid  and  potassa  are  called  sulphate  and  itsulphate ;  the  first 
containing  an  eq.  of  the  acid  and  alkali,  and  the  latter  one  eq.  of  the  alkali  to 
two  of  the  acid.  The  three  salts  of  oxalic  acid  and  potassa  are  termed  the 
oxalate,  imoxalate,  and  juacfroxalate  of  potassa ;  because  one  eq.  of  the  alkali 
is  united  with  one  eq.  of  acid  in  the  first  salt,  with  two  in  the  second,  and  with 
three  in  the  third.  In  the  chromate  and  bichromate  of  oxide  of  lead,  one  eq.  of 
the  acid  is  united  with  1  eq.  of  oxide  in  the  former,  and  with  two  in  the  latter. 
The  term  salt  has  of  late  received  considerable  extension,  being  now  applied  to 
compounds  analogous  to  common  salts  in  constitution,  though  not  formed  of  an 
acid  and  alkali.  The  grounds  on  which  this  has  been  done,  and  the  nomencla- 
ture introduced  in  consequence,  are  explained  in  the  section  of  the  salts. — In 
speaking  of  salts  of  metallic  oxides,  many  chemists  are  in  the  practice,  for  the 
sake  of  brevity,  of  mentioning  the  name  of  the  metals  only.  Thus,  in  the 
expressions  sulphates  if  silver  and  ledd,  the  oxide  of  silver,  and  oscide  of  lead, 
are  to  be  understood.  The  present  comprehensive  sense  in  which  the  word  salt 
is  used  begins  to  render  this  practice  objectionable. 

The  generic  part  of  the  name  of  a  compound  is  usually  formed  from  that 
ingredient  which  is  considered  the  most  highly  electro-negative.  Thus,  to  com- 
pounds of  oxygen  and  chlorine,  chlorine  and  iodine,  iodine  and  sulphur,  sulphur 
and  potassium,  in  which  the  first  of  each  pair  is  the  electro-negative  element, 
the  correct  appellations  are  oxides  of  chlorine,  chloride  of  iodine,  iodide  of  sul- 
phur, sulphuret  of  potassium ;  and  not  chloride  of  oxygen,  iodide  of  chlorine, 
sulphuret  of  iodine,  and  potassiuret  of  sulphur.  This  practice  is  invariably 
observed  in  this  treatise. 


AFFINITY.      .  115 

Convenient  and  philosophical  as  this  nomenclature  may  at  first  appear,  its 
principles  are  now  felt  to  be  far  from  coextensive  with  the  science.  It  much 
needs  extension  and  modification.  To  many  of  the  complex  compounds  known 
to  chemists  it  is  impracticable  to  apply  convenient  names  correctly  expressive  of 
their  constitution ;  and  this  has  led  to  the  use  of  those  symbolic  characters 
which  have  become  general  among  chemists,  and  which  are  essential  to  the  / 
present  state  of  chemistry.  The  mode  of  employing  such  notation  will  be' 
explained  in  the  second  section  of  this  part. 


SECTION  I. 


AFFINITY. 


All  chemical  phenomena  are  owing  to  Affinity  or  Chemical  Attraction.  It  is 
the  basis  on  which  the  science  of  chemistry  is  founded.  It  is,  as  it  were,  the 
instrument  which  the  chemist  employs  in  all  his  operations,  and  hence  it  forms 
the  first  and  leading  object  of  his  study. 

Affinity  is  exerted  between  the  minutest  particles  of  different  kinds  of  matter, 
causing  them  to  combine  so  as  to  form  new  bodies  endowed  with  new  properties. 
It  acts  only  at  insensible  distances  ;  in  other  words,  apparent  contact,  or  the 
closest  proximity,  is  necessary  to  its  action.  Everything  which  prevents  such 
contiguity  is  an  obstacle  to  combination  ;  and  any  force  which  increases  the  dis- 
tance between  particles  already  combined,  tends  to  separate  them  permanently 
from  each  other.  In  the  former  case,  they  do  not  come  within  the  sphere  of 
their  mutual  attraction ;  in  the  latter,  they  are  removed  out  of  it.  It  follows, 
therefore,  that  though  affinity  is  regarded  as  a  specific  power  distinct  from  the 
other  forces  which  act  on  matter,  its  action  may  be  promoted,  modified,  or  coun- 
teracted by  them ;  and  consequently,  in  studying  the  phenomena  produced  by 
affinity,  it  is  necessary  to  inquire  into  the  conditions  that  influence  its  operation. 

The  most  simple  instance  of  the  exercise  of  chemical  attraction  is  afforded 
by  the  admixture  of  two  substances.  Water  and  sulphuric  acid,  or  water  and 
alcohol,  combine  readily.  On  the  contrary,  water  shows  little  disposition  to 
unite  with  ether,  and  still  less  with  oil ;  for,  however  intimately  their  particles 
may  be  mixed  together,  they  are  no  sooner  left  at  rest  than  the  ether  separates 
almost  entirely  from  the  water,  and  a  total  separation  takes  place  between  that 
fluid  and  the  oil.  Sugar  dissolves  very  sparingly  in  alcohol,  but  to  any  extent 
in  water ;  while  camphor  is  dissolved  in  a  yery  small  degree  by  water,  and 
abundantly  by  alcohol.  It  appears,  from  these  examples,  that  chemical  attrac- 
tion is  exerted  between  different  bodies  with  different  degrees  of  force.  There 
is  sometimes  no  proof  of  its  existence  at  all ;  between  some  substances  it  acts 
very  feebly,  and  between  others  with  great  energy. 

Simple  combination  of  two  substances  is  a  common  occurrence  ;  of  which  the 
solution  of  salts  in  water,  the  combustion  of  phosphorus  in  oxygen  gas,  and  the 
neutralization  of  a  pure  alkali  by  an  acid,  are  instances.  But  the  phenomena 
are  often  more  complex.  The  formation  of  a  new  compound  is  often  attended 
by  the  destruction  of  a  pre-existing  one ;  as  when  some  third  body  acts  on  a 


116  AFFINITY. 

compound,  for  one  element  of  which  it  has  a  greater  affinity  than  they  have  for 
one  another.  Thus,  oil  has  an  affinity  for  the  volatile  alkali,  ammonia,  and  will 
unite  with  it,  forming  a  soapy  substance  called  a  liniment.  But  the  ammonia 
has  a  still  greater  attraction  for  sulphuric  acid  ;  and  hence,  if  the  acid  be  added 
to  the  liniment,  the  alkali  will  quit  the  oil,  and  unite  by  preference  with  the  acid. 
If  a  solution  of  camphor  in  alcohol  be  poured  into  water,  the  camphor  will  be 
set  free  because  the  alcohol  combines  with  the  water.  Sulphuric  acid,  in  like 
manner,  separates  baryta  from  nitric  acid.  Combination  and  decomposition 
occur  in  each  of  these  cases; — combination  of  sulphuric  acid  with  ammonia,  of 
water  with  alcohol,  of  baryta  with  sulphuric  acid  ; — decomposition  of  the  com- 
pounds formed  of  oil  and  ammonia,  of  alcohol  and  camphor,  of  nitric  acid  and 
baryta.  These  are  examples  of  what  Bergmann  called  single  elective  affinity  ; — 
elective,  because  a  substance  manifests,  as  it  were,  a  choice  for  one  of  two  others, 
uniting  with  it  by  preference,  and  to  the  exclusion  of  the  other.  Many  of  the 
decompositions  that  occur  in  chemistry  are  instances  of  single  elective  affinity. 

The  order  in  which  these  decompositions  take  place  has  been  expressed  in 
tables ;  of  which  the  following,  drawn  up  by  Geoffrey,  is  an  example  : — 

Sulphuric  acid. 

Baryta, 

Strontia, 

Potassa, 

Soda, 

Lime, 

Ammonia, 

Magnesia. 

This  table  signifies,  first,  that  sulphuric  acid  has  an  affinity  for  the  sub- 
stances placed  below  the  horizontal  line,  and  may  unite  separately  with  each  ; 
and,  secondly,  that  the  bases  of  the  salts  so  formed  will  be  separated  from  the 
acid  by  adding  any  of  the  alkalies  or  earths  which  stand  above  it  in  the  column. 
Thus,  ammonia  will  separate  magnesia,  lime  ammonia,  and  potassa  lime;  but 
none  can  withdraw  baryta  from  sulphuric  acid,  nor  can  ammonia  or  magnesia 
decompose  sulphate  of  lime,  though  strontia  or  baryta  will  do  so.  Bergmann 
conceived  that  these  decompositions  are  solely  determined  by  chemical  attraction, 
and  that  consequently  the  order  of  decomposition  represents  the  comparative 
forces  of  affinity ;  and  this  view,  from  the  simple  and  natural  explanation  it 
affords  of  the  phenomenon,  was  for  a  time  very  generally  adopted.  But  Berg- 
mann was  in  error.  It  does  not  necessarily  follow,  because  lime  separates 
ammonia  from  sulphuric  acid,  that  the  lime  has  a  greater  attraction  for  the  acid 
than  the  volatile  alkali.  Other  causes  are  in  operation  which  modify  the  action 
of  affinity  to  such  a  degree,  that  it  is  impossible  to  discover  how  much  of  the 
effect  is  owing  to  that  power.  It  is  conceivable  that  ammonia  may  in  reality 
have  a  stronger  affection  for  sulphuric  acid  than  lime,  and  yet  that  the  latter, 
from  the  great  influence  of  disturbing  causes,  may  succeed  in  decomposing  sul- 
phate of  ammonia. 

The  propriety  of  the  foregoing  remark  will  appear  from  the  following  exam- 
ple : — When  a  stream  of  hydrogen  gas  is  passed  over  oxide  of  iron  heated  to 
redness,  the  oxide  is  reduced  to  the  metallic  state,  and  water  is  generated.  On 
the  contrary,  when  watery  vapour  is  brought  into  contact  with  red -hot  metallic 
iron,  the  oxygen  of  the  water  quits  the  hydrogen  and  combines  with  the  iron. 
It  follows  from  the  result  of  the  first  experiment,  according  to  Bergmann,  that 


AFFINITY.  1^ 

hydrogen  has  a  stronger  attraction  than  iron  for  oxygen ;  and  from  that  of  the 
second,  that  iron  has  a  greater  affinity  for  oxygen  than  hydrogen.  But  these 
inferences  are  incompatible  with  each  other.  The  affinity  of  oxygen  for  the  two 
elements,  hydrogen  and  iron,  must  either  be  equal  or  unequal.  If  equal,  the 
result  of  both  experiments  was  determined  by  modifying  circumstances  ;  since 
neither  of  these  substances  ought  on  this  supposition  to  take  oxygen  from  the 
other.  But  if  the  forces  are  unequal,  the  decomposition  in  one  of  the  experi- 
ments must  have  been  determined  by  extraneous  causes,  in  direct  opposition  to 
the  tendency  of  affinity. 

The  fallacy  of  Bergmann's  opinion  was  detected  by  Berthollet.  He  first 
showed  that  the  relative  forces  of  chemical  attraction  cannot  always  be  deter- 
mined by  observing  the  order  in  which  substances  separate  each  other  when  in 
combination,  and  that  the  tables  of  Geoffrey  are  merely  tables  of  decomposition, 
not  of  affinity.  He  likewise  traced  all  the  various  circumstances  that  modify 
the  action  of  affinity,  and  gave  a  consistent  explanation  of  the  mode  in  which 
they  operate.  Berthollet  went  even  a  step  further.  He  denied  the  existence  of 
elective  affinity  as  an  invariable  force,  capable  of  effecting  the  perfect  separation 
of  one  body  from  another,  and  maintained  that  all  the  instances  of  complete 
decomposition  attributed  to  elective  affinity  are  in  reality  determined  by  one  or 
more  of  the  collateral  circumstances'  that  influence  its  operation.  But  here  this 
acute  philosopher  went  too  far.  Bergmann  erred  in  supposing  the  result  of 
chemical  action  to  be  in  every  case  owing  to  elective  affinity ;  but  Berthollet 
ran  into  the  opposite  extreme  in  declaring  that  the  effects  formerly  ascribed  to 
that  power  are  never  produced  by  it.  That  chemical  attraction  is  exerted 
between  bodies  with  different  degrees  of  energy,  is,  I  apprehend,  indisputable. 
Water  has  a  much  greater  affinity  for  hydrochloric  acid  and  ammoniacal  gases 
than  carbonic  and  hydrosulphuric  acids,  and  for  these  than  for  oxygen  and 
hydrogen.  The  attraction  of  lead  for  oxygen  is  greater  than  that  of  silver  for 
the  same  substance.  The  disposition  of  gold  and  silver  to  combine  with  mer- 
cury is  greater  than  the  attraction  of  platinum  and  iron  for  that  fluid.  As  these 
differences  cannot  be  accounted  for  by  the  operation  of  any  modifying  causes,  we 
must  admit  a  difference  in  the  force  of  affinity  in  producing  combination.  It  is 
equally  clear  that  in  some  instances  the  separation  of  bodies  from  one  another 
can  only  be  explained  on  the  same  principle.  No  one,  I  conceive,  will  contend 
that  the  decomposition  of  hydriodic  acid  by  chlorine,  or  of  hydrosulphuric  acid 
by  iodine,  is  determined  by  the  concurrence  of  any  modifying  circumstances. 

Affinity  is  the  cause  of  changes  still  more  complicated  than  those  which  have 
just  been  considered.  In  a  case  of  single  elective  affinity,  three  substances  only 
are  present,  and  two  affinities  are  in  play.  But  it  frequently  happens  that  two 
compounds  are  mixed  together,  and  four  different  affinities  brought  into  action. 
The  changes  that  may  or  do  occur  under  these  circumstances  may  be  studied  by 
aid  of  a  diagram.  Thus,  in  mixing  together  a  solution  of  carbonate  of  ammonia 
and  nitrate  of  lime,  their  mutual  action  may  be  represented  in  the  following 
manner : — 

Carbonic  acid  Ammonia 


Nitric  acid  Lime. 


118  AFFINITY. 

Each  of  the  acids  has  an  attraction  for  both  bases,  and  hence  it  is  possible 
either  that  the  two  salts  should  continue  as  they  were,  or  that  an  interchange 
of  principles  should  ensue,  giving  rise  to  two  new  compounds, — carbonate  of 
lime  and  nitrate  of  ammonia.  According  to  the  views  of  Bergmann,  the  result 
is  solely  dependent  on  the  comparative  strength  of  affinities.  If  the  affinity  of 
carbonic  acid  for  ammonia,  and  of  nitric  acid  for  lime,  exceed  that  of  carbonic 
acid  for  lime,  added  to  that  of  nitric  acid  for  ammonia,  then  will  the  two  salts 
experience  no  change  whatever ;  but  if  the  latter  affinities  preponderate,  then,  as 
does  actually  happen  in  the  present  example,  both  the  original  salts  will  be  de- 
composed, and  two  new  ones  generated.  Two  decompositions  and  two  combi- 
nations take  place,  being  an  instance  of  what  is  called  double  elective  affinity, 
Kirwan  applied  the  terms  quiescent  and  divellent  to  denote  the  tendency  of  the 
opposing  affinities, — the  action  of  the  former  being  to  prevent  a  change,  the  latter 
to  produce  it. 

The  doctrine  of  double  elective  affinity  was  assailed  by  Berthollet  on  the  same 
ground  and  with  the  same  success  as  in  the  case  of  single  elective  attraction.  He 
succeeded  in  proving  that  the  effect  cannot  always  be  ascribed  to  the  sole  influ- 
ence of  affinity.  For,  to  take  the  example  already  adduced,  if  carbonate  of 
ammonia  decompose  nitrate  of  lime  by  the  mere  force  of  a  superior  attraction,  it 
is  manifest  that  carbonate  of  lime  ought  never  to  decompose  nitrate  of  ammonia. 
But  if  these  two  salts  are  mixed  in  a  dry  state  and  exposed  to  heat,  double  de- 
composition^'does  take  place,  carbonate  of  ammonia  and  nitrate  of  lime  being 
formed ;  and  therefore,  if  the  change  in  the  first  example  was  produced  by  che- 
mical attraction  alone,  that  in  the  second  must  have  occurred  in  direct  opposition 
to  that  power.  It  does  not  follow,  however,  because  the  result  is  sometimes 
determined  by  modifying  conditions,  that  it  must  always  be  so.  I  apprehend 
that  the  decomposition  of  the  solid  cyanuret  of  mercury  by  h)^drosulphuric  acid 
gas,  which  takes  place  even  at  a  low  temperature,  cannot  be  ascribed  to  any 
other  cause  than  a  preponderance  of  the  divellent  over  the  quiescent  affinities. 

ON  THE  CHANGES  THAT  ACCOMPANY  CHEMICAL  ACTION. 

The  leading  circumstance  that  characterises  chemical  action  is  the  loss  of  pro- 
perties experienced  by  the  combining  substances,  and  the  acquisition  of  new 
ones  by  the  product  of  their  combination.  The  change  of  property  is  sometimes 
inconsiderable.  In  a  solution  of  sugar  or  salt  in  water,  and  in  mixtures  of  water 
with  alcohol  or  sulphuric  acid,  the  compound  retains  so  much  of  the  character 
of  its  constituents,  that  there  is  no  difficulty  in  recognising  their  presence.  But 
more  generally  the  properties  of  one  or  both  of  the  combining  bodies  disappear 
entirely.  One  would  not  suppose  from  its  appearance,  that  water  is  a  compound 
body  ;  much  less  that  it  is  composed  of  two  gases,  oxygen  and  hydrogen,  neither 
of  which,  when  uncombined,  has  ever  been  compressed  into  a  liquid.  Hydrogen 
is  one  of  the  most  inflammable  substances  in  nature,  and  yet  water  cannot  be  set 
on  fire:  oxygen,  on  the  contrary,  enables  bodies  to  bum  with  great  bril- 
liancy, and  yet  water  extinguishes  combustion.  The  alkalies  and  earths  were 
regarded  as  simple  till  Davy  proved  them  to  be  compound ;  and  certainly  they 
evince  no  sign  whatever  of  containing  oxygen  and  a  metal.  Numerous  exam- 
ples of  a  similar  kind  are  afforded  by  the  mutual  action  of  acids  and  alkalies. 
Sulphuric  acid  and  potassa,  for  example,  are  highly  caustic.  The  former  is  in- 
tensely sour,  reddens  the  blue  colour  of  vegetables,  and  has  a  strong  affinity  for 
alkaline  substances ;  the  latter  has  a  pungent  taste,  converts  the  blue  colour  of 


AFFINITY.  119 

vegetables  to  green,  and  combines  readily  with  acids.  On  adding  these  princi- 
ples cautiously  to  each  other,  a  compound  results  called  a  neutral  salt,  which 
does  not  in  anji  way  affect  the  colouring  matter  of  plants,  and  in  which  the  other 
distinguishing  features  of  the  acid  and  alkali  can  no  longer  be  perceived.  They 
appear  to  have  destroyed  the  properties  of  each  other,  and  are  hence  said  to  neu- 
tralize  one  another. 

The  other  phenomena  that  accompany  chemical  action  are  changes  of  density, 
temperature,  form,  and  colour. 

1.  Change  of  density.  It  is  observed  that  two  bodies  rarely  occupy,  after 
combination,  the  same  space  which  they  possessed  separately.  In  general  their 
bulk  is  diminished,  so  that  the  sp.  gr.  of  the  new  body  is  greater  than  the  mean 
of  its  components.  Thus  a  mixture  of  100  measures  of  water  and  an  equal 
quantity  of  sulphuric  acid  does  not  occupy  the  space  of  200  measures,  but  con- 
siderably less.  A  similar  contraction  frequently  attends  the  combination  of 
solids.  Gases  often  experience  a  remarkable  condensation  when  they  unite. 
The  elements  of  olefiant  gas,  for  instance,  would  expand  to  four  times  the  bulk 
of  that  compound,  if  they  were  suddenly  to  become  free,  and  assume  the  g'aseous 
form.  But  the  rule  is  not  without  exception.  The  reverse  happens  in  some 
metallic  compounds ;  and  there  are  examples  of  combination  between  gases  with- 
out any  change  of  bulk. 

2.  A  change  of  temperature  generally  accompanies  chemical  action.  Heat  is 
evolved  either  when  there  is  a  diminution  in  the  bulk  of  the  combining  sub- 
stances without  change  of  form,  or  when  a  gas  is  condensed  into  a  liquid,  or  a 
liquid  becomes  solid.  The  heat  caused  by  mixing  sulphuric  acid  with  water  is 
an  instance  of  the  former;  and  the  common  process  of  slaking  lime,  during  which 
water  loses  its  liquid  form  in  combining  with  that  earth,  is  an  example  of  the 
latter.  The  rise  of  temperature  in  these  cases  is  obviously  referable  to  diminished 
sp.  heat  in  the  new  compound  ;  but  intense  heat  sometimes  accompanies  chemi- 
cal action  under  circumstances  in  which  an  explanation  founded  on  a  change  of 
sp.  heat  is  inadmissible.  At  present  it  is  enough  to  have  stated  the  fact;  its 
theory  will  be  discussed  under  the  subject  of  combustion.  The  production  of 
cold  seldom  or  never  takes  place  during  combination,  except  when  heat  is  ren- 
dered insensible  by  the  conversion  of  a  solid  into  a  liquid,  or  a  liquid  into  a  gas. 
All  the  frigorific  mixtures  act  in  this  way. 

3.-  The  changes  cf  form  that  attend  chemical  action  are  exceedingly  various. 
The  combination  of  gases  may  give  rise  to  a  liquid  or  a  solid  ;  solids  sometimes 
become  liquid,  and  liquids  solid.  Several  familiar  chemical  phenomena,  such  as 
detonation,  eifervescence,  and  precipitation,  are  owing  to  these  changes.  The 
sudden  evolution  of  a  large  quantity  of  gaseous  matter  causes  an  explosion,  as 
when  gunpowder  detonates.  The  slower  disengagement  of  gas  produces  effer- 
vescence, as  when  marble  is  put  into  hydrochloric  acid.  A  precipitate  is  owing 
to  the  formation  of  a  new  body  which  happens  to  be  insoluble  in  the  liquid  in 
which  its  elements  were  dissolved. 

4.  Change  of  colour  frequently  attends  chemical  action.  No  uniform  relation 
ha*  been  traced  between  the  colour  of  a  compound  and  that  of  its  elements. 
Iodine,  whose  vapour  is  of  a  violet  hue,  forms  a  beautiful  red  compound  with 
mercury,  and  a  yellow  one  with  lead.  The  black  oxide  of  copper  generally  gives 
rise  to  green  and  blue  coloured  salts;  while  the  salts  of  the  oxide  of  lead,  which 
is  itself  yellow,  are  for  the  most  part  colourless.    The  colour  of  precipitates  is  a 


130  AFFINITY. 

very  important  study,  as  it  supplies  a  character  by  which  most  substances  may 
be  distinguished. 

# 
ON  THE  CIRCUMSTANCES  THAT  MODIFY  AND  INFLUENCE  THE  OPERATION 
!•  OF  AFFINITY. 

Of  the  conditions  which  are  capable  of  promoting  or  counteracting  the  ten- 
dency of  chemical  attraction,  the  following  are  the  most  important :  cohesion, 
elasticity,  quantity  of  matter,  gravity,  and  contact  with  other  bodies.  To  these 
may  be  added  the  agency  of  the  imponderables. 

Cohesion, — The  first  obvious  effect  of  cohesion  is  to  oppose  affinity,  by  im- 
peding or  preventing  that  mutual  penetration  and  close  proximity  of  the  particles 
of  different  bodies,  which  is  essential  to  the  successful  exercise  of  their  attrac- 
tion. Bodies  seldom  act  chemically  in  their  solid  state;  their  molecules  do  not 
come  within  the  sphere  of  attraction,  and  therefore  combination  cannot  take 
place,  although  their  affinity  may  in  fact  be  considerable.  Liquidity,  on  the  con- 
trary, favours  chemical  action ;  it  permits  the  closest  possible  approximation, 
while  the  cohesive  power  is  comparatively  so  trifling  as  to  oppose  no  appreciable 
barrier  to  affinity. 

Cohesion  may  be  diminished  in  two  ways, — by  mechanical  division,  or  by 
the  application  of  heat.  The  former  aids  by  increasing  the  extent  of  surface  ; 
but  it  is  not  of  itself  in  general  sufficient,  because  the  particles,  however  minute, 
etill  retain  that  degree  of  cohesion  which  constitutes  solidity.  Heat  acts  with 
greater  effect,  and  never  fails  in  promoting  combination,  whenever  the  cohesive 
power  is  a  barrier  to  it.  Its  intensity  should  always  be  so  regulated  as  to  pro- 
duce liquefaction.  The  fluidity  of  one  of  the  substances  frequently  suffices  for 
effecting  chemical  union,  as  is  proved  by  the  facility  with  which  water  dissolves 
many  salts  and  other  solid  bodies.  But  the  cohesive  force  is  still  in  operation  ; 
for  a  solid  is  commonly  dissolved  in  greater  quantity  when  its  cohesion  is 
diminished  by  heat.  The  reduction  of  both  substances  to  the  liquid  state  is  the 
best  method  for  ensuring  chemical  action.  The  slight  degree  of  cohesion  pos- 
sessed by  liquids  does  not  appear  to  cause  any  impediment  to  combination;  for 
they  commonly  act  as  energetically  on  each  other  at  low  temperatures,  or  at  a 
temperature  just  sufficient  to  cause  perfect  liquefaction,  as  when  their  cohesive 
power  is  still  further  diminished.  It  seems  fair  to  infer,  therefore,  that  very  little, 
if  any,  affinity  exists  between  two  bodies  which  do  not  combine  when  they  are 
intimately  mixed  in  a  liquid  state. 

The  phenomena  of  crystallization  are  owing  to  the  ascendency  of  cohesion 
over  affinity.  When  a  large  quantity  of  salt  has  been  dissolved  in  water  by  the 
aid  of  heat,  part  of  the  saline  matter  generally  separates  as  the  solution  cools, 
because  the  cohesive  power  of  the  salt  then  becomes  comparatively  too  powerful 
for  chemical  attraction.  Its  particles  begin  to  cohere  together,  and  are  deposited 
in  crystals,  the  process  of  crystallization  continuing  till  it  is  arrested  by  the 
affinity  of  the  liquid.  A  similar  change  happens  when  a  solution  made  in  the 
cold  is  gradually  evaporated.  The  cohesion  of  the  saline  particles  is  no  longer 
counteracted  by  the  affmity  of  the  liquid,  and  the  salt  therefore  assumes  the  solid 
form. 

Cohesion  plays  a  still  more  important  part.  It  sometimes  determines  the 
result  of  chemical  action,  probably  even  in  opposition  to  affinity.    Thus,  on 


AFFINITY.  121 

mixing  together  a  solution  of  two  acids  and  one  alkali,  of  which  two  salts  may 
be  formed,  one  soluble  and  the  other  insoluble,  the  alkali  will  unite  with  that 
acid  with  which  it  forms  the  insoluble  compound,  to  the  total  exclusion  of  the 
other.  This  is  one  of  the  modifying  circumstances  employed  by  Berthollet  to 
account  for  the  phenomena  of  single  elective  attraction,  and  is  certainly  applica- 
ble to  many  of  the  instances  to  be  found  in  the  tables  of  affinity.  When,  for 
example,  hydrochloric  acid,  sulphuric  acid,  and  baryta  are  mixed  together,  sul- 
phate of  baryta  is  formed  in  consequence  of  its  insolubility.  Lime,  which  yields 
an  insoluble  salt  with  carbonic  acid,  separates  that  acid  from  ammonia,  potassa, 
and  soda,  with  all  of  which  it  makes  soluble  compounds. 

A  similar  explanation  may  be  given  of  many  cases  of  double  elective  attrac- 
tion. On  mixing  together  in  solution  four  substances,  a,  b,  c,  d,  of  which  it  is 
possible  to  form  four  compounds,  ab  and  cd,  or  ac  and  bd,  that  compound  will 
certainly  be  produced  which  happens  to  be  insoluble.  Thus,  sulphuric  acid, 
soda,  nitric  acid,  and  baryta  may  give  rise  either  to  sulphate  of  soda  and  nitrate 
of  baryta,  or  to  sulphate  of  baryta  and  nitrate  of  soda;  but  the  first  two  salts 
cannot  exist  together  in  the  same  liquid,  because  the  insoluble  sulphate  of  baryta 
is  instantly  generated,  and  its  formation  necessarily  causes  the  nitric  acid  to 
combine  with  the  soda.  In  like  manner  a  solution  of  nitrate  of  lime  is  decom- 
posed by  carbonate  of  ammonia,  in  consequence  of  the  insolubility  of  carbonate 
of  lime. 

To  comprehend  the  manner  in  which  cohesion  acts  in  these  instances,  it  is 
necessary  to  consider  what  takes  place  when  in  the  same  liquid  two  or  more 
compounds  are  brought  together,  which  do  not  give  rise  to  an  insoluble  sub- 
stance. Thus,  on  mixing  solutions  of  sulphate  of  potassa  and  nitrate  of  soda, 
no  precipitate  ensues  ;  because  the  salts  capable  of  being  formed  by  double 
decomposition,  sulphate  of  soda  and  nitrate  of  potassa,  are  likewise  soluble.  In 
this  case  it  is  possible  either  that  each  acid  may  be  confined  to  one  base,  so  as 
to  constitute  two  neutral  salts ;  or  that  each  acid  may  be  divided  between  both 
bases,  yielding  four  neutral  salts.  It  is  difficult  to  decide  this  point  in  an  une- 
quivocal manner :  but,  judging  from  many  chemical  phenomena,  there  can,  I 
apprehend,  be  no  doubt  that  the  arrangement  last  mentioned  is  the  most  frequent, 
and  is  probably  universal  whenever  the  relative  forces  of  affinity  are  not  very 
unequal.  When  two  acids  and  two  bases  meet  together  in  neutralizing  propor- 
tion, it  may  therefore  be  inferred,  that  each  acid  unites  with  both  the  bases  in  a 
manner  regulated  by  their  respective  forces  of  affinity,  and  that  four  salts  are 
contained  in  solution.  In  like  manner,  the  presence  of  three  acids  and  three 
bases  will  give  rise  to  nine  salts ;  and  w4ien  four  of  each  are  present,  sixteen  salts 
will  be  produced.  This  view  affords  the  most  plausible  theory  of  the  constitu- 
tion of  mineral  waters,  and  of  the  products  which  they  yield  by  evaporation. 

The  influence  of  insolubility  in  determining  the  result  of  chemical  action  may 
be  readily  explained  on  this  principle.  If  nitric  acid,  sulphuric  acid,  and  baryta 
are  mixed  together  in  solution,  the  base  may  be  conceived  to  be  at  first  divided  be- 
tween the  two  acids,  the  nitrate  and  sulphate  of  baryta  to  be  generated.  The  latter, 
being  insoluble,  is  instantly  removed  beyond  the  influence  of  the  nitric  acid,  so 
that  for  an  instant  nitrate  of  baryta  and  free  sulphuric  acid  remain  in  the  liquid: 
but  as  the  base  left  in  solution  is  again  divided  between  the  two  acids,  a  fresh 
quantity  of  the  insoluble  sulphate  is  generated ;  and  this  process  of  partition 
continues,  until  either  the  baryta  or  the  sulphuric  acid  is  withdrawn  from  the 


122  AFFINITY. 

solution.  Similar  changes  ensue  when  nitrate  of  baryta  and  sulphate  of  soda 
are  mixed. 

The  separation  of  salts  by  crystallization  from  mineral  waters  or  other  saline 
mixtures  is  explicable  by  a  similar  mode  of  reasoning.  Thus,  on  mixing  nitrate 
of  potassa  and  sulphate  of  soda,  four  salts,  according  to  this  view,  are  gene- 
rated,— namely,  the  sulphates  of  soda  and  potassa,  and  the  nitrates  of  those 
bases  ;  and  if  the  solution  be  allowed  to  evaporate  gradually,  a  point  at  length 
arrives  when  the  least  soluble  of  these  salts,  the  sulphate  of  potassa,  will  be 
disposed  to  crystallize.  As  soon  as  some  of  its  crystals  are  deposited,  and  thus 
withdrawn  from  the  influence  of  the  other  salts,  the  constituents  of  these  undergo 
a  new  arrangement,  whereby  an  additional  quantity  of  sulphate  of  potassa  is 
generated  ;  and  this  process  continues  until  the  greater  part  of  the  sulphuric  acid 
and  potassa  has  combined,  and  the  compound  is  removed  by  crystallization.  If 
the  difference  in  solubility  is  considerable,  the  separation  of  salts  may  be  often 
rendered  very  complete  by  this  method. 

The  efflorescence  of  a  salt  is  sometimes  attended  with  a  similar  result.  If 
carbonate  of  soda  and  chloride  of  calcium  are  mingled  together  in  solution,  the 
insoluble  carbonate  of  lime  subsides.  But  if  carbonate  of  lime  and  sea-salt  are 
mixed  in  the  solid  state,  and  a  certain  degree  of  moisture  is  present,  carbonate 
of  soda  and  chloride  of  calcium  are  slowly  generated  ;  and  since  the  former,  as 
soon  as  it  is  formed,  separates  itself  from  the  mixture  by  efflorescence,  its  pro- 
duction continues  progressively.  The  efflorescence  of  carbonate  of  soda,  which 
is  sometimes  seen  on  old  walls,  or  which  in  some  countries  is  found  on  the  soil, 
appears  to  have  originated  in  this  manner. 

Elasticity. — From  the  obstacle  which  cohesion  puts  in  the  way  of  affinity,  the 
gaseous  state,  in  which  the  cohesive  power  is  wholly  wanting,  might  be  ex- 
pected to  be  peculiarly  favourable  to  chemical  action.  The  reverse,  however, 
is  the  fact.  '  Bodies  evince  little  disposition  to  unite  when  presented  to  each 
other  in  the  elastic  form.  Combination  does  indeed  sometimes  take  place,  in 
consequence  of  a  very  energetic  attraction ;  but  examples  of  an  opposite  kind  are 
much  more  common.  Oxygen  and  hydrogen  gases,  and  chlorine  and  hydrogen, 
though  their  mutual  affinity  is  very  powerful,  may  be  preserved  together  for  any 
length  of  time  without  combining.  This  want  of  action  seems  to  arise  from  the 
distance  between  the  particles  preventing  that  close  approximation  which  is  so 
necessary  to  the  successful  exercise  of  affinity.  Hence  many  gases  cannot  be 
made  to  unite  directly,  which  nevertheless  combine  readily  while  in  their 
nascent  state ;  that  is,  while  in  the  act  of  assuming  the  gaseous  form  by  the  de- 
composition of  some  of  their  solid  or  flbid  combinations. 

Elasticity  operates  likewise  as  a  decomposing  agent.  If  two  gases,  the  recipro- 
cal attraction  of  which  is  feeble,  suffer  considerable  condensation  when  they 
unite,  the  compound  will  be  decomposed  by  very  slight  causes.  Chloride  of 
nitrogen,  which  is  an  oil-like  liquid,  composed  of  the  two  gases  chlorine  and 
nitrogen,  affords  an  apt  illustration  of  this  principle,  being  distinguished  for  its 
remarkable  facility  of  decomposition.  Slight  elevation  of  temperature,  by  in- 
creasing the  natural  elasticity  of  the  two  gases,  or  contact  of  substances  which 
have  an  affinity  for  either  of  thpm,  produces  immediate  explosion. 

Many  familiar  phenomena  of  decomposition  are  owing  to  elasticity.  All  com- 
pounds that  contain  a  volatile  and  a  fixed  principle  are  liable  to  he  decomposed 
by  a  high  temperature.  The  expansion  oacasioned  by  heat  removes  the  elements 


AFFINITY.  123 

of  the  compound  to  a  greater  distance  from  each  other,  and  thus,  by  diminishing 
the  force  of  chemical  attraction,  favours  the  tendency  of  the  volatile  principle  to 
assume  the  form  which  is  natural  to  it.  The  evaporation  of  water  from  a  solu- 
tion of  salt  is  an  instance  of  this  kind. 

Many  solid  substances  which  contain  water  in  a  state  of  intimate  combination 
part  with  it  in  a  strong  heat,  in  consequence  of  the  volatile  nature  of  Jhat  liquid. 
The  separation  of  oxygen  from  some  metals,  by  heat  alone,  is  explicable  on  the 
same  principle. 

~  From  these  and  some  preceding  remarks,  it  appears  that  the  influence  of  heat 
over  affinity  is  variable ;  for  at  one  time  it  promotes  chemical  union,  and  opposes 
it  at  another.  Its  action,  however,  is  always  consistent.  Whenever  the  cohesive 
power  is  an  obstacle  to  combination,  heat  favours  affinity  either  by  diminishing 
the  cohesion  of  a  solid,  or  converting  it  into  a  liquid.  As  the  cause  of  the 
gaseous  state,  on  the  contrary,  it  keeps  at  a  distance  particles  which  would  other- 
wise unite ;  or,  by  producing  expansion  it  tends  to  separate  from  one  another 
substances  which  are  already  combined.  There  is  one  effect  of  heat  which 
seems  somewhat  anomalous  ;  namely,  the  combination  which  ensues  in  gaseous 
explosive  mixtures  on  the  approach  of  flame.  The  explanation  given  by  Bet- 
thollet  is  probably  correct, — that  the  sudden  dilatation  of  the  gases  in  the  imme- 
diate vicinity  of  the  flame  acts  as  a  violent  compressing  power  to  the  contiguous 
portions,  and  thus  brings  them  within  the  sphere  of  their  attraction. 

Some  of  the  decompositions,  which  were  attributed  by  Bergmann  to  the  sole 
influence  of  elective  affinity,  may  be  ascribed  to  elasticity.  If  three  substances 
are  mixed  together,  two  of  which  can  form  a  compound  which  is  less  volatile 
than  the  third,  the  last  will,  in  general,  be  completely  driven  off  by  the  applica- 
tion of  heat.  The  decomposition  of  the  salts  of  ammonia  by  the  pure  alkalies  or 
alkaline  earths  may  be  adduced  as  an  example;  and,  for  a  like  reason,  all  the 
carbonates  are  decomposed  by  nitric  acid,  and  all  the  nitrates  by  sulphuric  acid. 
This  explanation  applies  equally  well  to  some  cases  of  double  decomposition. 
It  explains,  for  instance,  why  dry  carbonate  of  lime  will  decompose  nitrate  of 
ammonia  by  the  aid  of  heat ;  for  carbonate  of  ammonia  is  more  volatile  than  the 
nitrate  either  of  ammonia  or  lime. 

The  influence  of  elasticity  in  determining  the  result  of  chemical  action  in 
these  instances  seems  owing  to  the  same  cause  which  enables  insolubility  to  be 
productive  of  similar  effects.  Thus,  on  mixing  nitrate  of  ammonia  with  lime, 
the  acid  is  divided  between  the  two  bases  ;  some  ammonia  becomes  free,  which, 
in  consequence  of  its  elasticity,  is  entirely  expelled  by  a  gentle  heat.  The  acid 
of  the  remaining  nitrate  of  ammonia  is  again  divided  between  the  two  bases  ; 
and  if  a  sufficient  quantity  of  lime  is  present,  the  ammoniacal  salt  will  be  com- 
pletely decomposed.  In  like  manner,  the  decomposition  of  potassa  may  be 
effected  by  iron,  though  the  affinity  of  this  metal  for  oxygen  seems  much  infe- 
rior to  that  of  potassium  for  oxygen.  If  potassa  in  the  fused  state  be  brought 
in  contact  with  metallic  iron  at  a  white  heat,  the  oxygen  is  divided  between  the 
two  metals,  and  a  portion  of  potassium  set  at  liberty.  But  as  potassium  is 
volatile  at  a  white  heat,  it  is  expelled  at  the  instant  of  reduction  ;  and  thus,  by 
its  influence  being  withdrawn,  an  opportunity  is  given  for  the  decomposition  of 
an  additional  quantity  of  potassa. 

Quantity  of  Matter. — The  influence  of  quantity  of  matter  over  affinity  is  uni- 
versally admitted.  If  one  body,  a,  unites  with  another,  b,  in  several  propor- 
tions, that  compound  will  be  most  difficult  of  decomposition  which  contains  the 


124  AFFINITY. 

smallest  quantity  of  b.  Of  the  three  oxides  of  lead,  for  instance,  the  peroxide 
parts  most  easily  with  its  oxygen  by  the  action  of  heat ;  a  higher  temperature  is 
required  to  decompose  the  red  oxide  ;  and  the  protoxide  will  bear  the  strongest 
heat  of  our  furnaces  without  losing  a  particle  of  its  oxygen. 

The  influence  of  quantity  over  chemical  attraction  may  be  further  illustrated 
by  the  phenomena  of  solution.  When  equal  weights  of  a  soluble  salt  are  added 
in  succession  to  a  given  quantity  of  water,  which  is  capable  of  dissolving  almost 
the  whole  of  the  salt  employed,  the  first  portion  of  the  salt  will  disappear  more 
readily  than  the  second,  the  second  than  the  third,  the  third  than  the  fourth,  and 
so  on.  The  affinity  of  the  water  for  the  saline  substance  diminishes  with  each 
addition,  till  at  last  it  is  so  weakened  as  to  be  unable  to  overcome  the  cohesion 
of  the  salt.     The  process  then  ceases,  and  a  saturated  solution  results. 

Quantity  of  matter  is  employed  advantageously  in  many  chemical  operations. 
If  a  chemist  wishes  to  displace  a  metallic  oxide  from  an  acid  by  the  superior 
affinity  of  potassa  for  the  latter,  he  frequently  uses  rather  more  of  the  alkali 
than  is  sufficient  for  neutralizing  the  acid.  He  employs  an  excess  of  the  alkali, 
in  order  the  more  effectually  to  bring  every  particle  of  the  substance  to  be  decom- 
posed in  contact  with  the  decomposing  agent. 

But  Berthollet  has  attributed  much  greater  influence  to  quantity  of  matter. 
It  was  the  basis  of  his  doctrine,  developed  in  the  Staiique  Chimique,  that  bodies 
cannot  be  wholly  separated  from  each  other  by  the  affinity  of  a  third  substance 
for  one  element  of  a  compound  ;  and  to  explain  why  a  superior  chemical  attrac- 
tion does  not  produce  the  effect  which  might  be  expected  from  it,  he  contended 
that  quantity  of  matter  compensates  for  a  weaker  affinity.  From  the  co-opera- 
tion of  several  disturbing  causes,  Berthollet  perceived  that  the  force  of  affinity 
cannot  be  estimated  with  certainty  by  observing  the  order  of  decomposition  ;  and 
he  therefore  had  recourse  to  another  method.  He  supposed  the  affinity  of  dif- 
ferent acids  for  the  same  alkali  to  be  in  the  inverse  ratio  of  the  ponderable 
quantity  of  each  which  is  necessary  for  neutralizing  equal  quantities  of  the 
alkali.  Thus,  if  two  parts  of  one  acid,  a,  and  one  part  of  another  acid,  b,  are 
required  to  neutralize  equal  quantities  of  the  alkali,  c,  it  was  inferred  that  the 
affinity  of  b  for  c  was  twice  as  great  as  that  of  a.  He  conceived,  further,  that 
as  two  parts  of  a  produce  the  same  neutralizing  effect  as  one  part  of  b,  the 
attraction  exerted  by  any  alkali  towards  two  parts  of  a  ought  to  be  precisely 
the  same  as  for  the  one  part  of  b  ;  and  he  hence  concluded  that  there  is  no  rea- 
son why  the  alkali  should  prefer  the  small  quantity  of  one  to  the  large  quantity 
of  the  other.  On  this  he  founded  the  principle  that  quantity  of  matter  compen- 
sates for  force  of  attraction. 

Berthollet  has  here  obviously  confounded  two  things,  namely,  force  of  attrac- 
tion and  neutralizing  power,  which  are  really  distinct.  The  relative  weights  of 
hydrochloric  and  sulphuric  acids  required  to  neutralize  an  equal  quantity  of  any 
alkali,  or,  in  other  words,  their  capacities  of  saturation,  are  as  36*4  to  40,  a  ratio 
which  remains  constant  with  respect  to  all  other  alkalies.  The  affinity  of  these 
acids,  according  to  Berthollet's  rule,  will  be  expressed  by  the  inverse  ratio  of 
these  numbers.  But  in  taking  this  estimate,  we  have  to  make  three  assump- 
tions, each  of  which  is  disputable.  There  is  no  proof,  in  the  first  place,  that 
hydrochloric  acid  has  a  greater  affinity  for  an  alkali,  such  as  potassa,  than  sul- 
phuric acid.  Such  an  inference  would  be  directly  opposed  to  the  general  opinion 
founded  on  the  order  of  decomposition  ;>  and  though  that  order,  as  we  have 
shown,  is  by  no  means  a  satisfactory  test  of  the  strength  of  affinity,  it  would  be 


AFFINITY.  125 

improper  to  adopt  an  opposite  conclusion  without  having  good  reasons  for  so 
doing.  Secondly,  were  it  established  that  hydrochloric  acid  has  the  greater 
affinity,  it  does  not  follow  that  the  attraction  of  those  acids  for  potassa  is  in  the 
inverse  ratio  of  36-4  to  40.  And,  thirdly,  supposing  this  point  settled,  it  is 
very  improbable  that  the  ratio  of  their  affinities  for  one  alkali  will  apply  to  all 
others ;  analogy  would  lead  us  to  anticipate  the  reverse.  Independently  of  these 
objections,  Dulong  has  found  that  the  principle  of  Berthollet  is  not  in  accord 
with  the  results  of  experiment. 

^Gravity. — The  influence  of  gravity  is  perceptible  when  it  is  wished  to  make 
two  substances  unite,  the  densities  of  which  are  different.  In  a  case  of  simple 
solution,  a  larger  quantity  of  saline  matter  is  found  at  the  bottom  than  at  the  top 
of  the  liquid,  unless  the  solution  shall  have  been  well  mixed  subsequently  to  its 
formation.  In  making  an  alloy  of  two  metals  which  differ  in  density,  a  larger 
quantity  of  the  heavier  metal  will  be  found  at  the  lower  than  in  the  upper  part 
of  the  compound,  unless  great  care  be  taken  to  counteract  the  tendency  of  gravity 
by  agitation.  This  force  obviously  acts,  like  the  cohesive  power,  in  preventing 
a  sufficient  degree  of  approximation. 

Contact  with  other  bodies. — The  influence  of  contact  of  different  substances  in 
modifying  affinity  is  observable  either  in  the  increased  or  diminished  energy  of 
chemical  action.  The  former  is  always  the  result  of  a  galvanic  current,  and  has 
been  treated  of  elsewhere :  the  latter  is  produced  by  the  interposition  of  an 
indifferent  body  by  which  others  are  removed  out  of  the  sphere  of  their  mutual 
action.  Thus,  on  immersing  a  fragment  of  pure  zinc  into  dilute  sulphuric  acid 
the  chemical  action  is  no  sooner  commenced  than  it  is  checked  by  the  hydrogen 
which  is  liberated  ;  this  is  effected  by  the  minute  globules  of  the  gas  collecting 
upon  the  surface  of  the  zinc,  and  adhering  firmly  to  it,  preventing  the  zinc  and 
dilute  acid  from  coming  into  that  close  contact  which  is  essential  to  chemical 
action.  Some  means  must  therefore  be  used  to  remove  this  intervening  film 
of  hydrogen,  if  a  continuous  action  be  desired :  this  is  effected  when  the  com- 
mon zinc  of  commerce  is  used  by  the  minute  portions  of  other  metals  present 
in  it  as  impurities,  by  which  small  but  numerous  galvanic  currents  are  excited, 
and  by  their  action*the  hydrogen  is  collected  and  makes  its  escape  as  globules 
of  gas. 

Imponderables. — The  influence  which  heat  exerts  over  chemical  phenomena, 
and  the  modes  in  which  it  operates,  have  been  already  discussed.  The  chemical 
agency  of  galvanism  has  also  been  described.  The  effects  of  light  will  be  most 
conveniently  stated  in  other  parts  of  the  work.  Electricity  is  frequently  em- 
ployed to  produce  the  combination  of  gases  with  one  another,  and  in  some 
instances  to  separate  them.  It  appears  to  act  by  the  heat  which  it  occasions, 
and  therefore  on  the  same  principle  as  flame. 

On  the  measure  of  affinity.— -As  the  foregoing  observations  prove  that  the 
order  of  decomposition  is  not  always  a  satisfactory  measure  of  affinity,  it  becomes 
a  question  whether  there  are  any  means  of  determining  the  comparative  forces  of 
chemical  attraction.  When  no  disturbing  causes  operate,  the  phenomena  of 
decomposition  afford  a  sure  criterion;  but  when  the  conclusions  obtained  in  this 
way  are  doubtful,  assistance  may  be  frequently  derived  from  other  sources.  The 
sarest  indications  are  procured  by  observing  the  tendency  of  different  substances 
to  unite  with  the  same  body  under  the  same  circumstances,  and  subsequently 
marking  the  comparative  facility  of  decomposition  when  the  compounds  so 
formed  are  exposed  to  the  same  decomposing  agent.    Thus,  on  exposing  silver. 


]26  ON  THE  LAWS  OF  COMBINATION. 

lead,  and  iron,  to  air  and  moisture,  the  iron  soon  rusts,  the  lead  is  oxidized  in 
a  slight  degree  only,  and  the  silver  resists  oxidation  altogether.  Iron  is  hence 
inferred  to  have  the  greatest  aflBnity  for  oxygen,  lead  next,  and  silver  the  least. 
This  conclusion  is  supported  by  concurring  observations  of  a  like  nature,  and 
confirmed  by  the  circumstances  under  which  the  oxides  of  those  metals  part 
with  their  oxygen.  Oxide  of  silver  is  reduced  by  heat  alone ;  and  oxide  of 
lead  is  decomposed  by  charcoal  at  a  lower  temperature  than  oxide  of  iron. 

It  is  inferred  from  the  action  of  heat  on  the  carbonate  of  potassa,  baryta,  lime, 
and  oxide  of  lead,  that  potassa  has  a  stronger  attraction  for  carbonic  acid  than 
baryta,  baryta  than  lime,  and  lime  than  oxide  of  lead.  The  affinity  of  different 
substances  for  water  may  be  determined  in  a  similar  manner. 

Of  all  chemical  substances,  our  knowledge  of  the  relative  degrees  of  attrac- 
tion of  acids  and  alkalies  for  each  other  is  the  most  uncertain.  Their  mutual 
action  is  aifected  by  so  many  circumstances,  that  it  is  in  most  cases  impossible, 
with  certainty,  to  refer  any  effect  to  its  real  cause.  The  only  methods  that  have 
been  hitherto  devised  for  remedying  this  defect  are  those  of  Berthollet  and  Kir- 
wan.  Both  are  founded  on  the  capacities  of  saturation,  and  the  objections  which 
have  been  urged  to  the  rule  suggested  by  the  former  philosopher  apply  equally 
to  that  proposed  by  the  latter.  But  this  uncertainty  is  of  no  great  consequence 
in  practice.  We  know  perfectly  the  order  of  decomposition,  whatever  may  be 
the  actual  forces  by  which  it  is  effected. 


SECTION  11. 


ON  THE  PROPORTIONS  IN  WHICH  BODIES  UNITE,  AND  ON  THE  LAWS  OF 

COMBINATION.  ,^ 

\ 
The  study  of  the  proportions  in  which  bodies  unite  naturally  resolves  itself 
into  two  parts.    The  first  includes  compounds  whose  elements  appear  to  unite  in 
a  great  many  proportions ;  the  second  comprehends  those,  the  elements  of  which 
combine  in  a  few  proportions  only. 

I.  The  compounds  contained  in  the  first  division  are  of  two  kinds.  In  one, 
combination  takes  place  unlimiiedly  in  all  proportions  ;  in  the  other,  it  occurs  in 
every  proportion  within  a  certain  limit.  The  union  of  water  with  alcohol  and 
the  liquid  acids,  such  as  the  sulphuric,  hydrochloric,  and  nitric,  affords  instances 
of  the  first  mode  of  combination ;  the  solutions  of  salts  in  water  are  examples 
of  the  second.  One  drop  of  sulphuric  acid  may  be  diffused  through  a  gallon  of 
water,  or  a  drop  of  water  through  a  gallon  of  the  acid  ;  or  they  may  be  mixed 
together  in  any  intermediate  proportions ;  and  nevertheless  in  each  case  they  *^ 
appear  to  unite  perfectly  with  each  other.  A  hundred  grains  of  water,  on  the 
contrary,  will  dissolve  any  quantity  of  sea-salt  which  does  not  exceed  forty 
grains.  Its  solvent  power  then  ceases,  because  the  cohesion  of  the  solid  becomes 
comparatively  too  powerful  for  the  force  of  affinity.  The  limit  to  combination 
is  in  such  instances  owing  to  the  cohesive  power ;  and  but  for  the  obstacle 


ON  THE  LAWS  OF  COMBINATION.  127 

which  it  occasions,  the  salt  would  most  probably  unite  with  water  in  every 
proportion. 

All  substances  that  unite  in  many  proportions,  give  rise  to  compounds  which 
have  this  common  character,  that  their  elements  are  united  by  a  feeble  affinity, 
and  preserve,  when  combined,  more  or  less  of  the  properties  which  they  possess 
in  a  separate  state.  In  a  scientific  point  of  view,  these  combinations  are  of  a 
minor  importance;  but  they  are  exceedingly  useful  as  instruments  of  research. 
They  enable  the  chemist  to  present  bodies  to  each  other,  under  circumstances 
peculiarly  favourable  for  acting  with  effect :  the  liquid  form  is  thus  communi- 
cated to  them ;  while  the  affinity  of  the  solvent  or  menstruum,  which  holds 
them  in  solution,  is  not  sufficiently  powerful  to  interfere  with  their  mutual 
attraction. 

II.  The  most  interesting  series  of  compounds  is  produced  by  substances  which 
unite  in  a  few  proportions  only ;  and  which,  in  combining,  lose  more  or  less 
completely  the  properties  that  distinguished  them  when  separate.  Of  these 
bodies,  some  form  but  one  combination.  Thus  there  is  only  one  compound  of 
boron  and  oxygen,  and  of  chlorine  and  hydrogen.  Others  combine  in  two  pro- 
portions. For  example,  two  compounds  are  formed  by  mercury  and  oxygen,  and 
by  hydrogen  and  oxygen.  Other  bodies  again  unite  in  three,  four,  five,  or  even 
six  proportions,  which  is  the  greatest  number  of  compounds  that  any  two  sub- 
stances are  known  to  produce,  except  perhaps  carbon  and  hydrogen,  and  those 
which  belong  to  the  first  division. 

The  combination  of  substances  that  unite  in  a  few  proportions  only,  is  regu- 
lated by  the  three  following  remarkable  laws  :  — 

First  Law  of  Cbmhination.  The  composition  of  bodies  is  fixed  and  invariable.  A 
compound  substance,  so  long  as  it  retains  its  characteristic  properties,  always 
consists  of  the  same  elements  united  together  in  the  same  proportion.  Sulphuric 
acid,  for  example,  is  always  composed  of  sulphur  and  oxygen  in  the  ratio  of  16 
parts  of  the  former  to  24  of  the  latter :  no  other  elements  can  form  it,  nor  can  it 
be  produced  by  its  own  elements  in  any  other  proportion.  Water,  in  like  man- 
ner, is  formed  of  I  part  of  hydrogen  and  8  of  oxygen ;  and  were  these  elements . 
to  unite  in  any  other  ratio,  some  new  compound,  diflferent  from  water,  would  be 
the  product.  The  same  observation  applies  to  all  other  substances,  however 
complicated,  and  at  whatever  period  they  were  produced.  Thus  sulphate  of 
baryta,  whether  formed  ages  ago  by  the  hand  of  nature,  or  quite  recently  by  the 
operations  of  the  chemist,  is  always  composed  of  40  parts  of  sulphuric  acid  and 
76*7  of  baryta.  This  law,  in  fact,  is  universal  and  permanent.  Its  importance 
is  equally  manifest :  it  is  the  essential  basis  of  chemistry,  without  which  the 
science  itself  could  have  no  existence. 

Two  views  have  been  proposed  by  way  of  accounting  for  this  law.  The  ex- 
planation now  universally  given  is  confined  to  a  mere  statement,  that  substances 
are  disposed  to  combine  in  those  proportions  to  which  they  are  so  strictly  limited, 
in  preference  to  any  others ;  it  is  regarded  as  an  ultimate  fact,  because  the  phe- 
nomena are  explicable  on  no  other  known  principle.  A  different  doctrine  was 
advanced  by  Berthollet,  in  his  Statique  Chimique,  published  in  1803.  Having 
observed  the  influence  of  cohesion  and  elasticity  in  modifying  the  action  of 
affinity  as  already  described,  he  thought  he  could  trace  the  operations  of  the  same 
causes  in  producing  the  effect  at  present  under  consideration.  As  the  solubility 
of  a  salt  and  of  a  gas  in  water  is  limited,  in  the  former  by  cohesion,  in  the  latter 
by  elasticity,  he  conceived  that  the  same  forces  would  account  for  the  unchange- 


128  ON  THE  LAWS  OF  COMBINATION. 

able  composition  of  certain  compounds.  He  maintained  that  within  certain 
limits  bodies  have  a  tendency  to  unite  in  every  proportion ;  and  that  combination 
is  never  definite  and  invariable,  except  when  rendered  so  by  the  operation  of 
modifying  causes,  such  as  cohesion,  insolubility,  elasticity,  quantity  of  matter, 
and  the  like.  Thus,  according  to  Berthollet,  sulphate  of  baryta  is  composed  of 
40  parts  of  sulphuric  acid  and  76*7  of  baryta,  not  because  those  substances  are 
disposed  to  unite  in  that  ratio  rather  than  in  another,  but  because  the  compound 
so  constituted  happens  to  have  great  cohesive  power. 

These  opinions  were  ably  and  successfully  combated  by  Proust  in  several 
papers  published  in  the  Journal  de  Phisique,  wherein  he  proved  that  the  metals 
are  disposed  to  combine  with  oxygen  and  with  sulphur  only  in  one  or  two  pro- 
portions, which  are  definite  and  invariable  ;  and  a  controversy  ensued  remarkable 
for  the  moderation  with  which  it  was  conducted  on  both  sides.  The  question  is 
now  no  longer  at  issue.  The  great  variety  of  facts,  similar  to  those  observed  by 
Proust,  which  have  since  been  established,  has  proved  beyond  a  doubt  that  the 
leading  principle  of  Berthollet  is  erroneous.  The  tendency  of  bodies  to  unite  in 
definite  proportions  only,  is  indeed  so  great  as  to  excite  a  suspicion  that  all  sub- 
stances combine  in  this  way ;  and  that  the  exceptions  thought  to  be  afl'orded  by 
the  phenomena  of  solution  are  rather  apparent  than  real ;  for  it  is  conceivable 
that  the  apparent  variety  of  proportion,  noticed  in  such  cases,  may  arise  from  the 
mixture  or  combination  of  a  few  definite  compounds  with  each  other. 

2.  Second  Law  of  Combination,  The  relative  quantities  in  which  bodies  unite, 
may  be  expressed  by  proportional  numbers.  Thus,  8  parts  of  oxygen  united  with 
1  part  of  hydrogen,  16  of  sulphur,  35*4  of  chlorine,  37*6  of  selenium,  and  108 
parts  of  silver.  Such  are  the  quantities  of  these  five  bodies  which  are  disposed 
to  unite  with  8  parts  of  oxygen ;  and  it  is  found  that  when  they  combine  with 
one  another,  they  unite  either  in  the  proportions  expressed  by  those  numbers,  or 
in  multiples  of  them  according  to  the  third  law  of  combination.  Hydrosulphuric 
acid,  for  instance,  is  composed  of  1  part  of  hydrogen  and  16  of  sulphur,  and 
bisulphuret  of  hydrogen  of  1  part  of  hydrogen  to  32  of  sulphur;  35*4  of  chlorine 
unite  with  1  of  hydrogen,  16  of  sulphur,  and  108  of  silver;  and  39*6  parts  of 
selenium  with  1  of  hydrogen,  and  16  of  sulphur. 

From  the  occurrence  of  such  proportional  numbers  has  arisen  the  use  of  cer- 
tain terms,  as  Proportion,  Combining  Proportion,  Proportional,  and  Chemical 
Equivalent,  or  Equivalent,  to  express  them.  The  latter  term,  introduced  by 
Wollaston,  and  which  is  employed  in  this  treatise,  was  suggested  by  the  cir- 
cumstance that  the  combining  proportion  of  one  body  is,  as  it  were,  equivalent 
to  that  of  another  body,  and  may  be  substituted  for  it  in  combination.  Among 
the  tables  at  the  end  of  the  volume  will  be  found  one  of  the  equivalents  of  ele- 
mentary substances. 

This  law  is  not  confined  to  elementary  substances,  since  compound  bodies 
have  their  combining  proportions  or  equivalents,  which  may  likewise  be  ex- 
pressed in  numbers.  Thus,  since  water  is  composed  of  1  eq.  or  8  parts  of  oxy- 
gen, and  1  eq.  or  1  of  hydrogen,  its  combining  proportion  or  equivalent  is  9. 
The  equivalent  of  sulphuric  acid  is  40,  because  it  is  a  compound  of  one  eq.  or 
16  parts  of  sulphur,  and  three  eq.  or  24  parts  of  oxygen;  and  in  like  manner, 
the  eq.  of  hydrochloric  acid  is  36*4,  because  it  is  a  compound  of  one  eq.  or  35*4 
parts  of  chlorine,  and  one  eq.  or  1  part  of  hydrogen.  The  equivalent  number  of 
potassium  is  39,  and  as  thatquantity  combines  with  8  of  oxygeii  to  form  potassa, 
the  equivalent  of  the  latter  is  39  -f-  8  =47.     Now  when  these  compounds  unite, 


ON  THE  LAWS  OF  COMBINATION.  129 

one  equivalent  of  the  one  combines  with  one,  two,  three,  or  more  equivalents  of 
the  other,  precisely  as  the  simple  substances  do.  Hydrate  of  potassa,  for  exam- 
ple, is  constituted  of  47  parts  of  potassa  and  9  of  water,  and  its  equivalent  is 
consequently  47  -j-  9,  or  56.  Sulphate  of  potassa  is  composed  of  40  sulphuric 
acid  -f-  47  potassa ;  and  the  nitrate  of  that  alkali  of  54  nitric  acid  +  47  of 
potassa.  The  equivalent  of  the  former  salt  is  therefore  87,  and  of  the  latter  101. 
The  composition  of  the  salts  affords  a  very  instructive  illustration  of  this  sub- 
ject ;  and  to  exemplify  it  still  further,  a  list  of  the  equivalents  of  a  few  acids  and 
alkaline  bases  is  annexed  : — 


Hydrofluoric  Acid 

19-7 

Lithia 

14 

Phosphoric  Acid 

35-7 

Magnesia 

20-7 

Hydrochloric 

36-4 

Lime 

.  28-5 

Sulphuric  Acid 

40-1 

Soda 

31-3 

Nitric  Acid 

64-15 

Potasaa 

[  47-15 

Arsenic  Acid 

57-7 

Strontia 

51-8 

Selenic  Acid 

63-6 

Baryta 

76-7 

The  alkalies  here  are  shown  to  differ  widely  in  neutralizing  power;  for  the 
equivalent  of  each  base  expresses  the  quantity  required  to  neutralize  an  equiva- 
lent of  each  of  the  acids.  Thus  14  of  lithia,  31*3  of  soda,  and  76*7  of  baryta, 
combine  with  64*15  of  nitric  acid,  forming  the  neutral  nitrates  of  lithia,  soda,  and 
baryta.  The  same  fact  is  obvious  with  respect  to  the  acids;  for  40*1  of  sul- 
phuric, 54'15  of  nitric,  and  63.6  of  selenic  acid  unite  with  76-7  of  baryta,  form- 
ing a  neutral  sulphate,  nitrate  and  selenate  of  baryta. 

These  circumstances  afford  a  ready  explanation  of  a  curious  fact,  first  noticed 
by  the  Saxon  chemist  Wenzel ;  namely,  that  when  two  neutral  salts  mutually 
decompose  each  other,  the  resulting  compounds  are  likewise  neutral.  The  cause 
of  this  fact  is  now  obvious.  If  71*3  parts  of  neutral  sulphate  of  soda  are  mixed 
with  130'7  of  nitrate  of  baryta,  the  76*7  parts  of  baryta  unite  with  40  of  sul- 
phuric acid,  and  the  54  parts  of  nitric  acid  of  the  nitrate  combine  with  the  31*3 
of  soda  of  the  sulphate,  not  a  particle  of  acid  or  alkali  remaining  in  an  uncom- 
bined  condition. 

Sulphate  of  Soda.  Nitrate  of  Baryta. 

Sulphuric  acid  40  54        Nitric  acid. 

Soda  31-3  76-7     Baryta. 

71-3  1307 

It  matters  not  whether  more  or  less  than  71'3  parts  of  sulphate  of  soda  are 
added ;  for  if  more,  a  small  quantity  of  sulphate  of  soda  will  remain  in  solution ; 
if  less,  nitrate  of  baryta  will  be  in  excess;  but  in  either  case  the  neutrality  will 
be  unaffected. 

3.  Third  Law  of  Combination.  When  one  body,  a,  unites  with  another  body,  b, 
in  two  or  more  proportions^  the  quantities  of  the  latter,  united  with  the  same  quantity 
of  the  former,  bear  to  each  other  a  very  simple  ratio.  The  progress  of  chemical 
research,  in  discovering  new  compounds  and  ascertaining  their  exact  composition, 
has  shown  that  these  ratios  of  b  may  be  represented  by  one  or  other  of  the  two 
following  series : — 

1st  Series,    a  unites  with  1,  2,  3,  4,  5,  &c.  of  b. 

2d  Series,    a  unites  with  1,  1^,  2,  2i,  &c.  of  b. 

11 


130  ON  THE  LAWS  OF  COMBINATION. 

The  first  series  is  exemplified  by  the  subjoined  compounds. 


Water  is  composed  of 
Binoxide  of  Hydrogen 

Hydrogen  1 
Do.          1 

Oxygen  8> 
Do.  16^ 

1 
2 

Carbonic  Oxide 
Carbonic  Acid 

Carbon        6 
Do.          9 

Do.    8i 
Do.  16 

2 

Nitrous  Oxide 
Nitric  Oxide 
Hyponitrous  Acid 
Nitrous  Acid 
Nitric  Acid 

Nitrogen  14-15    . 
Do.        1415    . 
Do.        14-15     . 
Do.        14-15     . 
Do.        14-15     . 

Do.     8^ 
Do.  16 
Do.  24  > 
Do.  32  ! 
Do.  40J 

1 
2 
3 
4 
5 

sts  of  Iron 
.    Do. 

28 
28 

Oxygen 

^1} 

1 

u 

.    Manganese 
.     Do. 
.    Do. 

27-7 
27-7 
27-7 

Do. 
Do. 
Do. 

.11 
16) 

1 
u 

2 

.    Arsenic 
.    Do. 

37-7 
37-7 

Do. 
Do. 

11} 

u 

2^ 

.    Phosphorus 
.     Do. 
.    Do. 

15-7 
15-7 
15-7 

Do. 
Do. 
Do. 

12^ 

20) 

u 

2i 

In  all  these  compounds  the  ratio  of  the  oxygen  are  expressed  by  whole  numbers. 
In  water  the  hydrogen  is  combined  with  half  as  much  oxygen  as  in  the  binoxide 
of  hydrogen,  so  that  the  ratio  is  as  1  to  2.  The  same  relation  holds  in  carbonic 
oxide  and  carbonic  acid.  The  oxygen  in  the  compounds  of  nitrogen  and  oxygen 
is  in  the  ratio  of  1,  2,  3,  4,  and  5.  In  like  manner  the  ratio  of  sulphur  in  the 
two  sulphurets  of  mercury,  and  that  of  chlorine  in  the  two  chlorides  of  mercury, 
is  as  1  to  2.  So,  in  bicarbonate  of  potassa,  the  alkali  is  united  with  twice  as 
much  carbonic  acid  as  in  the  carbonate ;  and  the  acid  of  the  three  oxalates  of 
potassa  is  in  the  ratio  of  1,  2,  and  4. 

The  following  compounds  exemplify  the  second  series : — 

Protoxide  of  Iron  cons 

Peroxide 

Protoxide  of  Manganese 

Sesqui-oxide 

Bin-oxide 

Arsenious  Acid 

Arsenic  Acid 

Hypophosphorous  Acid 

Phosphorus  Acid 

Phosphoric  Acid 

Both  of  these  series,  which  together  constitute  the  Third  Law  of  Combination, 
result  naturally  from  the  operation  of  the  second  law.  The  first  series  arises 
from  one  equivalent  of  a  body  uniting  with  1,  2,  3,  or  more  equivalents  of  an- 
other body.  The  second  series  is  a  consequence  of  two  equivalents  of  one  sub- 
stance combining  with  3,  5,  or  more  equivalents  of  another.  Thus,  if  two  equiva- 
lents of  phosphorus  unite  both  3  and  with  5  equivalents  of  oxygen,  we  obtain 
the  ratio  of  1|  to  2^  ,  and  should  one  equivalent  of  iron  combine  with  one  of 
oxygen,  and  another  compound  be  formed  of  two  equivalents  of  iron  to  three  of 
oxygen,  then  the  oxygen  united  with  the  same  weight  of  iron  would  have  the 
ratio,  as  in  the  table  of  1  to  l^.  The  compounds  of  manganese  and  phosphorus 
with  oxygen  afford  examples  of  the  same  nature.  Still  more  complex  arrange- 
ments will  be  readily  conceived,  such  as  3  equivalents  of  one  substance  to  4,  5, 
or  more  of  another.  But  it  is  remarkable  that  combinations  of  this  kind  are 
very  rare ;  and  even  their  existence,  though  theoretically  possible,  has  not  been 
decidedly  established.  Even  some  of  the  compounds  which  are  usually  included 
in  the  second  series  belong  properly  to  the  first.  The  red  oxide  of  lead,  for  in- 
stance, appears  in  its  chemical  relations  not  so  much  as  a  direct  compound  of 
lead  and  oxygen,  but  as  a  kind  of  salt  formed  by  the  union  of  the  binoxide  of 
lead  with  the  protoxide  of  the  same  metal.  On  this  supposition  the  two  other 
oxides  belong  to  the  first  series. 

The  merit  of  establishing  the  first  law  of  combination  seems  due  to  Wenzel, 


ON  THE  LAWS  Of'  COMBINATION.  131 

a  Saxon  chemist ;  and  the  second  law  is  deducible  from  his  experiments  on  the 
composition  of  the  salts.  His  work,  entitled  Lehre  der  VerwandhcJiaft,  was  pub- 
lished in  1777.  Bergmann  and  Richter,  a  few  years  after,  confirmed  the  obser- 
vations of  Wenzel,  though  without  adding  materially  in  the  way  of  generaliza- 
tion. Higginsin  1789  speculated  on  the  atomic  constitution  of  compound  bodies 
in  a  manner  which,  if  pursued,  would  have  led  to  the  discovery  of  Dalton.  It 
is  to  the  latter,  science  is  indebted  for  deducing  from  the  scattered  facts  which 
had  been  previously  collected,  a  theory  of  chemical  union,  embracing  the  whole 
science,  and  giving  it  a  consistency  and  form  which  before  his  time  it  had  never 
possessed.  In  his  hands  the  second  law  of  combination  first  attained  its  full 
generality ;  but  the  discovery,  which  is  more  peculiarly  his  own,  is  that  part  of 
the  third  law  of  combination  which  is  contained  in  the  first  of  the  two  series 
above  mentioned.  The  first  public  announcement  of  his  views  appears  to  have 
been  made  to  the  Philosophical  Society  of  Manchester  in  1803 ;  and  in  1808 
they  were  explained  in  his  New  System  of  Chemical  Philosophy.  In  the  same^ 
year  Wollaston  and  Thomson  gave  their  evidence  in  support  of  the  new  doctrine, 
and  other  chemists  have  followed  in  the  same  path  of  inquiry.  But  of  all  who 
have  successfully  laboured  in  establishing  the  laws  of  combination,  the  most 
splendid  contribution  is  that  of  the  celebrated  Berzelius.  Struck  with  the 
perusal  of  the  works  of  Richter,  he  commenced  in  1807  an  investigation  into  the 
Laws  of  Definite  Proportion. ,  Since  that  period  his  labours  in  this  important 
field  have  been  incessant,  and  every  department  of  the  science  has  been  enriched 
by  his  skill  and  indefatigable  industry.  Whether  we  look  to  pneumatic  chemistry, 
to  the  chemical  history  of  the  metals  and  of  the  salts,  or  to  the  composition  of 
minerals,  we  are  alike  indebted  to  Berzelius.  In  all  he  has  traced  the  laws  of 
definite  proportion,  and  by  a  multitude  of  exact  analyses  given  to  the  laws  of 
combination  that  certainty  which  accumulated  facts  can  alone  convey. 

The  utility  of  being  acquainted  with  these  important  laws  is  manifest. 
Through  their  aid,  and  by  remembering  the  equivalents  of  a  few  elementary 
substances,  the  composition  of  an  extensive  range  of  compound  bodies  may  be 
calculated  with  facility.  Thus  by  knowing  that  6  is  the  eq.  of  carbon  and  8  of 
oxygen  it  is  easy  to  recollect  the  composition  of  carbonic  oxide  and  carbonic 
acid  ;  the  first  consisting  of  ^6  parts  of  carbon  -j-  8  of  oxygen,  and  the  second  of 
6  carbon  -j-  16  of  oxygen.  The  eq.  of  potassium  is  39  ;  and  potassa,  its  protox- 
ide, is  composed  of  39  of  potassium  -f-  8  of  oxygen.  From  these  few  data,  the 
composition  of  carbonate  and  bi-carbonate  of  potassa  are  given  ;  the  former  being 
composed  of  22  parts  of  carbonic  acid  -f  47  potassa,  and  the  latter  of  44  car- 
bonic acid  -|-  47  potassa.  This  method  acts  as  an  artificial  memory,  the  advan- 
tage of  which,  compared  with  the  former  practice  of  stating  the  composition  in 
100  parts,  will  be  manifest  by  inspecting  the  following  quantities  and  attempting 
to  recollect  them. 


Carbonic  Oxide. 

Carbonic  Acid. 

Carbon               42-86 

.        27-27 

Oxygen               57-14 

72-73 

Carbonate  of  Potassa. 

Bi-carbonate  of  Potassa. 

Carbonic  acid    31-43 

.        47-83 

Potassa               68-57 

52-17 

From  the  same  data,  calculations,  which  would  otherwise  be  difficult  or  tedious, 
may  be  made  rapidly  and  with  ease,  without  reference  to  books,  and  frequently 


132  ON  THE  LAWS  OF  COMBINATION. 

by  a  simple  mental  process.  The  exact  quantities  of  substances  required  to  pro- 
duce a  given  effect  may  be  determined  with  certainty,  thus  affording  information 
which  is  often  necessary  to  the  success  of  chemical  processes,  and  of  great 
consequence  both  in  the  practice  of  the  chemical  arts,  and  the  operations  of 
pharmacy. 

The  same  knowledge  affords  a  good  test  to  tbe  analyst  by  which  he  may  judge 
of  the  accuracy  of  his  result,  and  even  sometimes  correct  an  analysis  which  he 
has  not  the  means  of  performing  with  rigid  precision.  Thus  a  powerful  argu- 
ment for  the  accuracy  of  an  analysis  is  derived  from  the  correspondence  of  its 
result  with  the  laws  of  chemical  nnion.  On  the  contrary,  if  it  form  an  exception 
to  them,  we  are  authorized  to  regard  it  as  doubtful ;  and  may  hence  be  led  to 
detect  an  error,  the  existence  of  which  might  not  otherwise  have  been  suspected. 
If  an  oxidized  body  be  found  to  contain  one  equivalent  of  the  combustible  with 
7*99  of  oxygen,  it  is  fair  to  infer  that  8,  or  one  equivalent  of  oxygen,  would 
have  been  the  result,  had  the  analysis  been  perfect. 

The  composition  of  a  substance  may  sometimes  be  determined  by  a  calcula- 
tion, founded  on  the  laws  of  chemical  union,  before  an  analysis  of  it  has  been 
accomplished.  When  the  new  alkali  lithia  was  first  discovered,  chemists  did 
not  possess  it  in  sufficient  quantity  for  determining  its  constitution  analytically. 
But  the  neutral  sulphates  of  the  alkalies  and  alkaline  earths  are  known  to  be 
composed  of  one  equivalent  of  each  constituent^  and  the  oxides  to  contain  one 
eq.  of  oxygen.  If  it  be  found,  therefore,  by  analysis,  th^t  neutral  sulphate  of 
lithia  is  composed  of  40  parts  of  sulphuric  acid  and  14  of  lythia,  it  may  be 
inferred,  since  40  is  one  eq.  of  the  acid,  that  14  is  the  eq.  for  lithia;  and  that 
this  oxide  is  formed  of  8  parts  of  oxygen  and  6  of  lithium. 

The  method  of  determining  equivalent  numbers  will  be  anticipated  from  what 
has  already  been  said.  The  commencement  is  made  by  carefully  analyzing  a 
definite  compound  of  two  simple  substances  which  possess  an  extensive  range  of 
affinity.  Thus  water,  a  compound  of  oxygen  and  hydrogen,  is  found  to  contain 
8  parts  of  the  former  to  1  of  the  latter ;  and  if  it  be  assumed  that  water  consists 
of  1  eq.  of  oxygen  and  1  of  hydrogen,  the  relative  weights  of  these  equivalents 
will  be  as  8  to  1.  The  chemist  then  selects  for  analysis  such  compounds  as  he 
believes  to  contain  1  eq.  of  each  element,  in  which  either  oxygen  or  hydrogen, 
but  not  both,  is  present.  Carbonic  oxide  and  hydro-sulphuric  acid  are  suited  to 
his  purpose  :  as  the  former  consists  of  8  parts  of  oxygen  and  6  of  carbon,  and 
the  latter  of  1  part  of  hydrogen  and  16  of  sulphur,  the  equivalent  of  carbon  is 
inferred  to  be  6,  and  that  of  sulphur  16.  The  equivalent  of  all  the  other  ele- 
ments may  be  determined  in  a  similar  manner.  ^ 

In  researches  on  chemical  equivalents  there  are  two  kinds  of  difficulty,  one 
involved  in  the  processes  for  ascertaining  the  exact  composition  of  compounds, 
and  the  other  in  the  selection  of  the  compounds  which  contain  single  equivalents. 
Important  general  precautions  in  the  experimental  part  of  the  subject  are  the 
following : — 1,  to  exert  scrupulous  care  about  the  purity  of  materials  ;  2,  to  select 
methods  which  consist  of  a  few  simple  operations  only ;  3,  to  repeat  experiments, 
and  with  materials  prepared  at  different  times  ;  4,  to  arrive  at  the  same  conclusion 
by  two  or  more  processes  independent  of  each  other.  In  the  selection  of  com- 
pounds of  single  equivalents  there  are  several  circumstances  calculated  to  direct 
the  judgment : — 

1.  If  two  substances  combine  in  several  proportions,  the  law  of  multiples 
usually  effects  the  electro-negative  element  of  a  compound.    Thus,  in  the  5 


ON  THE  LAWS  OF  COMBINATION.  133 

compounds  of  nitrogen  and  oxygen,  in  which  oxygen  is  the  —  element,  14  parts 
of  nitrogen  are  united  with  8,  16,  24,  32,  and  40  parts  of  oxygen;  whereas, 
taking  the  quantity  of  oxygen  as  constant,  8  parts  of  oxygen  are  united  with  14, 
7,  4*66,  3*5,  and  2'8  parts  of  nitrogen,  in  which  the  simple  ratio  of  the  first 
series  does  not  exist.  This  circumstance  induces  the  chemist  always  to  search 
among  the  oxides  of  the  same  element  for  the  lowest  grade  of  oxidation,  and  in 
most  cases  to  consider  it  as  a  compound  of  single  equivalent.  In  some  instances, 
however,  the  second  degree  of  oxidation  is  formed  of  single  equivalents,  while 
the  lowest  oxide  consists  of  2  eq.  of  the  -\-  element  and  one  of  oxygen.  Such 
compounds  are  called  dioxides  (page  114)  and  sometimes  suboxides. 

2.  Metallic  oxides,  distinguished  for  strong  alkalinity,  or  for  acting  as  strong 
alkaline  bases,  are  always  protoxides.  Dioxides  rarely  unite  definitely  with 
acids,  and  are  remarkable  for  their  ready  conversion  into  protoxides  with  separa- 
tion of  metal.  If  the  same  metal  yield  several  oxides,  the  protoxide  is  the 
strongest  base ;  the  highest  grade  of  oxidation  is  frequently  an  acid,  and  the 
intermediate  oxides  are  in  general  little  distinguished  either  for  alkalinity  or 
acidity.  Protoxides  usually  resist  decomposition  more  obstinately  than  other 
oxides. 

3.  When  a  metal  forms  two  oxides,  the  oxygen  of  which  is  in  a  ratio  of  1  to 
1^,  the  first  is  usually  the  protoxide,  and  the  second  a  compound  of  2  eq.  of  tlie 
metal  to  three  of  oxygen.     The  oxides  of  iron  and  nickel  are  examples. 

4.  If  two  compounds  resemble  each  other  in  their  modes  of  combination,  it  is 
a  strong  presumption  that  their  constitution  is  similar.  Alumina  and  the  per- 
oxide of  iron  are  remarkably  allied  in  their  chemical  relations ;  and  hence  it  is 
inferred,  since  the  latter  consists  of  2  eq.  of  iron  and  3  eq.  of  oxygen,  that  the 
former,  whose  composition  would  otherwise  be  very  doubtful,  is  composed  of  2 
eq.  of  aluminium  and  3  eq.  of  oxygen. 

5.  Mitscherlich  has  found,  as  is  more  fully  stated  in  the  article  on  crystalliza- 
tion, that  certain  compounds  which  resemble  each  other  in  composition  and  in 
their  modes  of  combining,  are  likewise  disposed  in  crystallizing  to  affect  the 
same  form.  Hence  it  is  a  strong  presumption  that  compounds  which  are  analo- 
gous both  in  their  crystalline  figure  and  modes  of  combining,  are  also  similar  in 
their  composition.  In  the  oxide  and  acid  of  chromium  the  oxygen  is  in  the  ratio 
1  to  2,  and  hence  it  was  at  first  supposed  that  1  eq.  of  chromium  was  united  in 
the  oxide  with  1  eq.  and  in  the  acid  with  2  eq.  of  oxygen.  But  the  chromates 
resemble  the  sulphates  in  form  and  modes  of  combining,  and  the*oxide  of  chro- 
mium bears  the  same  analogy  to  alumina  and  peroxide  of  iron.  The  inference 
is,  that  oxide  of  chromium  consists  of  2  eq.  of  chromium  and  3  eq.  of  oxygen, 
and  chromic  acid  of  1  eq.  of  chromium  and  3  eq.  of  oXygen. 

6.  Another  guide  in  these  inquiries  is  derived  from  the  relation  traced  by 
Dulong  and  Petit  between  the  equivalents  of  a  body  and  its  sp.  heat.  The  coin- 
cidences pointed  out  at  page  36  are  sufficiently  numerous  to  show  an  interesting 
relation  which  is  sometimes  useful  in  selecting  between  doubtful  numbers ;  but 
the  instances  of  failure  are  at  present  too  frequent  to  admit  of  this  principle  being 
used  except  with  much  caution. 

7.  The  ready  decomposition  by  galvanism,  observed  by  Faraday,  of  compounds 
which  consist  of  single  equivalents,  and  the  resistance  to  the  same  agent  of  many 
others  not  so  constituted,  promises  to  become  an  indication  of  great  value  in 
determining  eq.  numbers.  The  facts  as  yet  known  respecting  it  will  be  found  in 
the  section  on  galvanism. 


184 


ON  THE  LAWS  OF  COMBINATION. 


8.  Great  light  is  often  thrown  on  the  chemical  constitution  of  a  compound  by 
a  knowledge  of  the  volumes  of  the  substances  of  which  it  is  composed.  This 
subject,  however,  will  be  discussed  in  an  after  part  of  this  section. 

Since  the  equivalents  merely  express  the  relative  quantities  of  diflferent  sub- 
stances which  combine  together,  it  is  in  itself  immaterial  what  figures  are 
employed  to  express  them.  The  only  essential  point  is,  that  the  relation  should 
be  strictly  observed.  Thus,  the  eq.  of  hydrogen  maybe  assumed  as  10;  but 
then  oxygen  must  be  80,  carbon  60,  and  sulphur  160.  We  may  call  hydrogen 
100  or  1000;  or,  if  it  were  desirable  to  perplex  the  subject  as  much  as  possible, 
some  high  uneven  number  might  be  selected,  provided  the  due  relation  between 
the  different  numbers  were  faithfully  preserved.  But  such  a  practice  would 
destroy  the  advantage  above  ascribed  to  the  use  of  equivalents ;  and  it  is  the 
object  of  every  one  to  employ  such  as  are  simple,  that  their  relation  may  be  per- 
ceived by  mere  inspection.  Thomson  makes  oxygen  1,  so  that  hydrogen  is 
eight  times  less  than  unity,  or  0*125,  carbon  0*75,  and  sulphur  2.  Wollaston, 
in  his  scale  of  chemical  equivalents,  estimated  oxygen  at  10 ;  and  hence  hydro- 
gen is  1*25,  carbon  7*5  and  so  on.  According  to  Berzelius,  oxygen  is  100.  And 
lastly,  several  other  chemists,  such  as  Dalton,  Davy,  Henry,  and  others,  selected 
hydrogen  as  their  unit ;  and  therefore  the  eq.  of  oxygen  is  8.  One  of  these 
series  may  easily  be  reduced  to  either  of  the  others  by  an  obvious  and  simple 
calculation.  The  numbers  adopted  in  this  work  refer  to  hydrogen  as  unity,  and 
are  given  in  the  subjoined  table.* 


CHEMICAL  EQUIVALENTS  OF  ELEMENTARY  SUBSTANCES. 

Elements. 

Equivalents. 

Elements. 

Equivalents. 

Elements. 

Equivalents. 

Alluminium 

13.7 

Gold 

199.2 

jPotassium 

39.15 

Antimony 

64.6 

Hydrogen 

1 

Rhodium 

52.2 

Arsenic 

37.7 

Iodine 

126.3 

jSelenium 

39.6 

Barium 

68.7 

llridium 

98.8 

iSilicium 

7.5 

Bismuth 

71 

llron 

28 

Silver 

108 

Boron 

10.9 

,Lead 

103.6 

jSodium 

23.3 

Bromine 

78.4 

Lithium 

10 

Strontium 

43.8 

Cadmium 

55.8 

Magnesium 

12.7 

Sulphur 

16.1 

Calcium 

20.5 

Manganese 

27.7 

Tellurium 

32.3 

Carbon 

6.12 

Mercury 

202 

Thorium 

59.6 

Cerium 

46 

iMolybdenum 

47.7 

Tin 

57.9 

Chlorine 

35.42 

Nickel 

29.5 

TiUnium 

24.3 

Chromium 

.       28 

Nitrogen 

14.15 

Tungsten 

99.7 

Cobalt 

29.5 

Osmium 

99.7 

Vanadium 

68.5 

Columbium 

185 

Oxygen 

8 

Uranium 

217 

Copper 

31.6 

Palladium 

53.3 

Yttrium 

32.2 

Fluorine 

18.68 

Phosphorus 

15.7 

Zinc 

32.3 

Glucinium 

17.7 

|Platinum 

98.8 

Zirconium 

33.7 

The  preceding  table  is  constructed  principally  from  the  published  tables  of 
Berzelius,  and  partly  from  facts  supplied  by  my  own  researches.  The  hypothesis 
that  all  equivalent  numbers  are  simple  multiples  of  the  equivalent  of  hydrogen, 
has  been  elsewhere  shown  to  be  untenable.  (Phil.  Trans.  1833,  Part  ii.  page 
523.)  Whenever  the  experimental  quantity  is  nearly  a  whole  number,  the  last 
may  for  many  purposes  be  used  as  a  sufficient  approximation;  and,  accordingly, 
for  such  elements  as  carbon,  sulphur,  nitrogen,  and  potassium,  which  are  often 
referred  to  in  the  way  of  illustration,  I  have  generally  adopted  round  numbers,  as 

*  For  a  Tull  table  of  equivalents,  expressed  on  both  the  oxygen  and  hydrogen  scales, 
refer  to  Appendix.    (R.) 


ON  THE  LAWS  OF  COMBINATION.  135 

being  shorter  and  more  easily  remembered  than  fractions.  But  on  all  occasions 
where  exact  calculations  are  concerned,  the  numbers  given  in  the  table  should 
be  employed.* 

The  useful  instrument  known  by  the  name  of  the  Scale  of  Chemical  Equiva- 
lents^ was  originally  devised  by  Dr.  Wollaston,  and  is  a  table  of  equivalents  com- 
prehending all  those  substances  which  are  most  frequently  employed  by  chemists 
in  the  laboratory ;  and  it  only  differs  from  other  tabular  arrangements  of  the  same 
kind,  in  the  numbers  being  attached  to  a  slWing  rule,  which  is  divided  according 
to  the  principle  of  that  of  Gunter.  From  the  mathematical  construction  of  the 
scale,  it  not  only  serves  the  same  purpose  as  other  tables  of  equivalents,  but  in 
many  instances  supersedes  the  necessity  of  calculation.  Thus,  by  inspecting  the 
common  table  of  equivalents,  we  learn  that  87  parts,  or  one  equivalent,  of  sul- 
phate of  potassa,  contain  40  parts  of  sulphuric  acid  and  47  of  potassa ;  but 
recourse  must  be  had  to  calculation,  when  it  is  wished  to  determine  the  quantity 
of  acid  or  alkali  in  any  other  quantity  of  the  salt.  This  knowledge,  on  the  con- 
trary, is  obtained  directly  by  means  of  the  scale  of  chemical  equivalents.  For 
example,  on  pushing  up  the  slide  until  100  marked  upon  it  is  in  a  line  with  the 
name  sulphate  of  potassa  on  the  fixed  part  of  the  scale,  the  numbers  opposite  to 
the  terms  sulphuric  acid  and  potassa  will  give  the  precise  quantity  of  each  con- 
tained in  100  parts  of  the  compound.  In  the  original  scale  of  Wollaston,  for  a 
particular  account  of  which  I  may  refer  to  the  Philosophical  Transactions  for 
1814,  oxygen  is  taken  as  the  standard  of  comparison ;  but  hydrogen  may  be 
selected  for  that  purpose  with  equal  propriety,  and  scales  of  this  kind  have  been 
prepared  for  sale  by  Reid  of  Edinburgh.  A  very  complete  scale  of  equivalents 
has  been  drawn  up  by  Prideaux  of  Plymouth.  (Phil.  Mag,  and  Annals,  viii.  430.) 

ON  THE  ATOMIC  THEORY. 

The  brief  sketch  which  has  been  given  of  the  laws  of  combination  will,  I 
trust,  set  in  its  true  light  the  importance  of  that  department  of  chemical  science. 
It  is  founded  on  experiment  alone,  and  the  laws  which  have  been  stated  are  the 
mere  expression  of  fact.  It  is  not  necessarily  connected  with  any  speculation, 
and  may  be  kept  wholly  free  from  it.  The  notion  that  the  laws  of  combination 
involve  something  uncertain  or  hypothetical,  is  a  fallacy  easily  referable  to  its 
source.  It  was  impossible  to  reflect  on  the  regularity  and  constancy  with  which 
bodies  obey  these  laws,  without  speculating  about  the  cause  of  that  regularity ; 
and,  consequently,  the  facts  themselves  were  no  sooner  noticed,  than  an  attempt 
was  made  to  explain  them.  Accordingly,  when  Dalton  published  his  discovery 
of  those  laws,  he  at  once  incorporated  the  description  of  them  with  his  notion  of 
their  physical  cause,  and  even  expressed  the  former  in  language  suggested  by 
the  latter.  Since  that  period,  though  several  British  chemists  of  eminence,  and 
in  particular  Wollaston  and  Davy,  recommended  and  practised  an  opposite  course, 
both  subjects  have  been  too  commonly  comprised  under  the  name  of  atomic 
theory ;  hence  it  has  often  happened  that  beginners  have  rejected  the  whole  as 
hypothetical,  because  they  could  not  satisfactorily  distinguish  those  parts  which 
are  founded  on  fact  from  those  which  are  conjectural.  All  such  perplexity  would 
have  been  avoided,  and  this  department  of  the  science  have  been  far  better  under- 

*  The  recent  researches  of  Dumas,  Erdmann  and  Marchand,  on  the  equivalents  of  oxy- 
gen, hydrogen,  carbon,  and  lime,  have  revived  the  hypothesis  alluded  to  in  the  text.  The 
numbers  in  the  table  are,  therefore,  to  be  regarded  as  still  open  to  revision.    (R.) 


136  ON  THE  LAWS  OF  COMBINATION. 

stood,  and  its  value  more  justly  appreciated,  had  the  discussion  concerning  the 
atomic  constitution  of  bodies  been  always  kept  distinct  from  that  of  the  phe- 
nomena which  it  is  intended  to  explain.  When  employed  in  this  limited  sense, 
the  atomic  theory  may  be  discussed  in  a  few  words. 

Two  opposite  opinions  have  long  existed  concerning  the  ultimate  elements  of 
matter.  It  is  supposed,  according  to  one  party,  that  every  particle  of  matter, 
however  small,  may  be  divided  into  smaller  portions,  provided  our  instruments 
and  organs  were  adapted  to  the  op^tion.  Their  opponents  contend,  on  the 
other  hand,  that  matter  is  composed  of  certain  ultimate  particles  of  molecules, 
which  by  their  nature  are  indivisible,  and  are  hence  termed  atoms  (from  a  not, 
and  tifjLVHv  to  cut).  These  opposite  opinions  have  from  time  to  time  been  keenly 
contested,  and  with  variable  success,  according  to  the  acuteness  and  ingenuity 
of  their  respective  champions.  But  it  was  at  last  perceived  that  no  positive 
data  existed  capable  of  deciding  the  question,  and  its  interest  therefore  gradually 
declined.  The  progress  of  modem  chemistry  has  revived  attention  to  this  con- 
troversy, by  affording  a  far  stronger  argument  in  favour  of  the  atomic  constitu- 
tion of  matter  than  was  ever  advanced  before,  and  one  which  is  almost  irresistible. 
For  the  assumption  that  all  bodies  consist  of  ultimate  atoms,  the  weight  of  which 
differs  in  different  kinds  of  matter,  supplies  a  luminous  explanation  of  the  laws 
of  chemical  union,  which  do  not  appear  explicable  on  any  other  supposition. 

According  to  the  atomic  theory,  every  compound  is  formed  of  the  atoms  of  its 
constituents.  An  atom  of  A  may  unite  with  1,  2,  3,  or  more  atoms  of  B.  Thus, 
supposing  water  to  be  composed  of  1  atom  of  hydrogen  and  1  atom  of  oxygen, 
binoxide  of  hydrogen  will  consist  of  1  atom  of  hydrogen  and  2  atoms  of  oxygen. 
If  carbonic  oxide  is  formed  of  1  atom  of  carbon  and  1  atom  of  oxygen,  car- 
bonic acid  will  consist  of  1  atom  of  carbon  and  2  atoms  of  oxygen.  If,  in  the 
compounds  of  nitrogen  and  oxygen,  enumerated  at  page  130,  the  first  or  pro- 
toxide consist  of  1  atom  of  nitrogen  and  1  atom  of  oxygen,  the  four  others  will 
be  regarded  as  compounds  of  1  atom  of  nitrogen  to  2,  3,  4,  and  5  atoms  of 
oxygen.  From  these  instances  it  will  appear  that  the  law  of  multiple  propor- 
tion is  a  necessary  consequence  of  the  atomic  theory.  There  is  also  no  apparent 
reason  why  2  or  more  atoms  of  1  substance  may  not  combine  with  2,  3,  4,  5,  or 
more  atoms  of  another ;  but,  on  the  contrary,  these  arrangements  are  necessary 
in  explanation  of  the  not  unfrequent  occurrence  of  half  equivalents,  as  formerly 
stated.  (Page  130.)  Such  combinations  will  also  account  for  the  complicated 
proportion  noticed  in  certain  compounds,  especially  in  many  of  those  belonging 
to  the  animal  and  vegetable  kingdoms. 

In  consequence  of  the  satisfactory  explanation  which  the  laws  of  chemical 
union  receive  by  means  of  the  atomic  theory,  it  has  become  customary  to  em- 
ploy the  term  atom  in  the  same  sense  as  combining  proportion  or  equivalent. 
For  example,  instead  of  describing  water  as  a  compound  of  1  eq.  of  oxygen  and 
1  eq.  of  hydrogen,  it  is  said  to  consist  of  1  atom  of  each  element.  In  like  man- 
ner sulphate  of  potassa  is  said  to  be  form'ed  of  I  atom  of  sulphuric  acid  and  1 
atom  of  potassa,  the  word  in  this  case  denoting  as  it  were  a  compound  atom, 
that  is,  the  smallest  integral  particle  of  the  acid  or  alkali ;  a  particle  which  does 
not  admit  of  being  divided,  except  by  the  separation  of  its  elementary  or  consti- 
tuent atoms.  The  numbers  expressing  the  proportions  in  which  bodies  unite 
must  likewise  indicate,  consistently  with  this  view,  the  relative  weights  of  atoms ; 
and  accordingly  these  numbers  are  often  called  atomic  weights.  Thus,  as  water 
is  composed  of  8  parts  of  oxygen  and  1  of  hydrogen,  it  follows,  on  the  supposition 


ON  THE  LAWS  OF  COMBINATION.  137 

of  water  consisting  of  I  atom  of  each  element,  that  an  atom  of  oxygen  must  be 
8  times  heavier  than  an  atom  of  hydrogen.  If  carbonic  oxide  be  formed  of  an 
atom  of  carbon  and  an  atom  of  oxygen,  the  relative  weights  of  their  atoms  are  as 
6  to  8  ;  and  in  short  the  chemical  equivalents  of  all  bodies  may  be  considered  as 
expressing  the  relative  weights  of  their  atoms. 

The  foregoing  argument  in  favour  of  the  atomic  constitution  of  matter  becomes 
much  stronger  when  we  trace  the  intimate  connection  which  subsists  among 
many  substances,  between  their  crystalline  form  and  chemical  composition.  This 
subject,  however,  now  known  under  the -name  of  {somorphisniy  will  be  more  con- 
veniently discussed  under  the  head  of  crystallization. 

Dalton  supposes  the  atoms  of  bodies  to  be  spherical ;  and  he  has  invented 
certain  symbols  to  represent  the  mode  in  which  he  conceives  they  may  combine 
together,  as  illustrated  by  this  following  figures  : — 

0  Hydrogen.  O  Oxygen. 

Q  Nitrogen.  #  Carbon. 

BINARY   COMPOUNDS. 

O0  Water. 

0#  Carbonic  oxide. 

TERNARY    COMPOUNDS. 

OOO  Binoxide  of  hydrogen. 
00#  Carbonic  acid. 
&c.  &c.  &c. 

All  substances  containing  only  2  atoms  he  called  binary  compounds,  those 
composed  of  3  atoms  ternary  compounds,  of  4  quaternary,  and  so  on. 

There  are  several  questions  relative  to  the  nature  of  atoms,  most  of  which  will 
perhaps  never  be  decided.  Of  this  nature  are  the  questions  which  relate  to  the 
actual  form,  size,  and  weight  of  atoms,  and  to  the  circumstances  in  which  they 
mutually  differ.  All  that  we  know  with  any  certainty  is,  that  their  weights  do 
differ,  and  by  exact  analysis  the  relations  between  them  may  be  determined. 
Peculiar  views  of  the  constitution  of  matter  are  held  by  Ampere,  whose  opinions 
are  always  acute  and  philosophical.  He  not  only  believes  dissimilar  atoms,  as 
of  oxygen  and  hydrogen,  to  be  capable  of  uniting,  but  that  2  or  more  atoms  of 
the  same  kind  have  a  power  of  mutual  attraction  whereby  they  are  arranged  in 
groups  of  definite  figure,  which  he  calls  molecules.  These  molecules,  more  or 
less  intimately  bound  together  by  cohesion,  give  rise  to  the  different  states  of 
bodies,  the  solid,  liquid,  and  gaseous.  Thus,  oxygen  gas  is  conceived  not  an 
assemblage  of  self-repulsive  atoms  of  oxygen,  but  of  molecules,  each  of  which  is 
a  polyhedral  solid  made  up  of  a  constant  number  of  atoms  and  repulsive  to  neigh- 
bouring molecules.  In  like  manner  he  conceives  the  ultimate  particles  of  com- 
pounds, as  water  and  potassa,  to  be  arranged  in  groups  so  as  to  constitute 
molecules.  Similar  views  are  maintaineid  by  Prout  in  his  Bridgewater  Treatise. 
This  doctrine  receives  strong  support  from  some  phenomena  of  gaseous  combina- 
tion, and  from  the  complex  nature  of  organic  compounds. 

It  is  but  justice  to  the  memory  of  Higgins,  to  state  that  he  first  made  use  of 
the  atomic  hypothesis  in  chemical  reasonings.  In  his  "  Comparative  View  of 
the  Phlogistic  and  Antiphlogistic  Theories,"  published  in  the  year  1789,  he  ob- 
serves (pages  36  and  37)  that  "  in  volatile  vitriolic  acid  a  single  ultimate  particle 
of  sulphur  is  intimately  united  only  to  a  single  particle  of  dephlogisticated  air ; 


138  ON  THE  LAWS  OF  COMBINATION. 

and  that,  in  perfect  vitriolic  acid,  every  single  particle  of  sulphur  is  united  to  2 
of  dephlogisticated  air,  being  the  quantity  necessary  to  saturation;"  and  he  rea- 
sons in  the  same  way  concerning  the  constitution  of  water  and  the  compounds  of 
nitrogen  and  oxygen.  These  remarks  of  Higgins  do  not  appear  to  have  had  the 
slightest  connection  with  the  subsequent  views  of  Dalton,  who  seems  to  have 
never  seen  the  work  of  Higgins  till  after  he  had  given  an  account  of  his  own 
doctrine.  The  observations  of  Higgins,  though  highly  creditable  to  his  sagacity, 
do  not  affect  Dalton's  merit  as  an  original  observer.  They  were  made,  moreover, 
in  so  casual  a  manner,  as  not  only  not  to  have  attracted  the  notice  of  his  contempo- 
raries, but  to  prove  that  Higgins  himself  attached  no  particular  interest  to  them. 
Dalton's  chief  merit  consists  in  having  formed  a  complete  theory  of  chemical 
union,  and  in  the  discovery  of  an  essential  and  most  important  part  of  the  doc- 
trine, a  merit  which  is  solely  and  indisputably  his ;  but  in  which  he  would  have 
been  anticipated  by  Higgins,  had  that  chemist  perceived  the  importance  of  his 
own  opinions. 

To  the  student  who  may  desire  a  more  ample  account  of  the  doctrine  of  atoms 
than  the  nature  and  limits  of  this  volume  admit  of  being  given  here,  I  may  recom- 
mend a  small  work  by  Daubeny  on  the  atomic  theory,  which  in  other  respects 
will  be  found  well  worthy  of  perusal. 

ON  THE  THEORY  OF  VOLUMES. 

Soon  after  the  publication  of  the  New  System  of  Chemical  Philosophy  in  1808, 
in  which  work  Dalton  explained  his  views  of  the  atomic  constitution  of  bodies, 
Gay-Lussac  published  in  the  Memoiresd'Arcueil  on  the  "  Combination  of  Gaseous 
Substances  with  one  another."  He  there  proved  that  gases  unite  together  by 
volume  in  very  simple  proportions,  which  he  exemplified  by  the  ratios  in  which 
the  following  gases  unite : — 

100  Hydrogen  ,       to       .  60  Oxygen. 

100  Ammoniacal  .        .        .  100  Hydrochloric  acid  gas. 

100        do.  .        .        .  100  Fluoboric  acid  gas. 

100        do.  ...  200  do. 

100        do.  ,        .        .  100  Carbonic  acid  gas. 

100        do.  ...  200  do. 

Various  other  examples  were  quoted,  both  from  his  own  experiments  and  from 
those  of  others,  all  demonstrating  the  same  fact.  Thus  ammonia  was  found  by 
A.  Berthollet  to  consist  of  100  volumes  of  nitrogen  gas  and  300  volumes  of 
hydrogen ;  sulphuric  acid  contains  100  volumes  of  sulphurous  acid  and  60  vol- 
umes of  oxygen :  and  carbonic  acid  is  formed  by  burning  a  mixture  of  50  volumes 
of  oxygen  and  100  volumes  of  carbonic  oxide. 

From  these  and  other  instances  Gay-Lussac  established  the  fact,  that  gaseous 
substances  unite  in  the  simple  ratio  of  1  to  1,  I  to  2,  1  to  3,  &c. ;  and  this  ori- 
ginal observation  has  been  confirmed  by  such  a  multiplicity  of  experiments,  that 
it  may  be  regarded  as  one  of  the  best  established  laws  in  chemistry.  Nor  does 
it  apply  to  gases  merely,  but  to  vapours  also.  For  example,  hydrosulphuric, 
sulphurous,  and  hydriodic  acid  gases  are  composed  of 

600  vol    hydrogen  gas  and  100  vol.  vapour  of  sulphur. 
600  oxygen  lOO         .        .         sulphur. 

100  hydrogen  100         .        .         iodine. 


ON  THE  LAWS  OF  COMBINATION. 


139 


Another  remarkable  fact  established  by  Gay-Lussac  in  the  same  'essay  is,  that 
the  volumes  of  compound  gases  and  vapours  always  bear  a  very  simple  ratio  to 
the  volumes  of  their  elements.  This  will  appear  from  the  following  table,  in 
which  all  the  substances  are. supposed  to  be  in  the  gaseous  state : — 

Volumes  of  resulting  compounds, 

eld  200  Ammonia. 

.  100  Water. 

.  100  Protoxide  of  Nitrogen, 

.  600  Hydrosulphuric  acid. 

.  600  Sulphurous  acid. 

.  200  Hydrochloric  acid. 

.  200  Hydriodic  acid. 

.  200  Hydrobromic  acid. 

.  200  Hydrocyanic  acid. 

.  200  Binoxide  of  Nitrogen. 

The  law  of  multiples  (page  130)  is  equally  demonstrable  by  means  of  com- 
bining or  eq.  volumes  as  by  combining  or  eq.  weights.  The  annexed  tabular 
view  will  justify  this  statement : — 


Volumes 

of  Elements. 

100  Nitrogen        -i" 

300  Hydrogen 

60  Oxygen          -f- 

100  Hydrogen 

50  Oxygen           -Jr 

100  Nitrogen 

100  Sulphur          -f 

600  Hydrogen 

100  Sulphur          -|- 

600  Oxygen 

100  Chlorine        -f- 

100  Hydrogen 

100  Iodine            -j- 

100  Hydrogen 

100  Bromine        -f 

100  Hydrogen 

100  Cyanogen      -f 

100  Hydrogen 

100  Oxygen         -f 

100  Nitrogen 

Volumes  of  Elements. 

Resulting  Compound 

100  Nitrogen 

+ 

60  Oxygen 

yield 

Protoxide  of  Nitrogen. 

100      do. 

+ 

100 

do. 

Binoxide  of  Nitrogen. 

100      do. 

+ 

150 

do. 

Hyponitrous  acid. 

100      do. 

+ 

200 

do. 

Nitrous  acid. 

100      do. 

t 

250 

do. 

Nitric  acid. 

100  Hydrogen 

+ 

50 

do. 

Water. 

100      do. 

t 

100 

do. 

Binoxide  of  Hydrogen. 

100  Carbon  Vapour -f- 

50 

do. 

Carbonic  oxide. 

100      do. 

+ 

100 

do. 

Carbonic  acid. 

It  thus  appears  that  the  laws  of  combination  may  equally  well  be  deduced  from 
the  volumes  or  from  the  weights  of  the  combining  substances,  and  that  the  compo- 
sition of  gaseous  bodies  may  be  expressed  as  well  by  measure  as  weight.  In  the 
subjoined  table  is  a  comparative  view  of  equivalent  weights  and  volumes,  to  which 
is  added  the  respective  sp.  gravities  in  relation  both  to  air  and  hydrogen  :  the  facts 
respecting  the  vapours  are  drawn  from  an  essay  by  Mitscherlich.  (An.  de  Ch.  et 
Ph.  Iv.  5.)  In  constructing  the  table  100  volumes  of  hydrogen  are  assumed  as  the 
unit  to  which  the  eq.  vol.  of  other  substances  are  compared,  and  as  the  volume  oc- 
cupied by  a  weight  of  hydrogen  represented  by  its  equivalent.  The  eq.  vol.  of  other 
substances,  considered  as  gases,  are  in  like  manner  the  volumes  corresponding 
to  their  equivalents  taken  as  weights.  In  all  substances,  whose  sp.  gr.  and 
equivalents  are  the  same  compared  to  the  sp.  gr.  and  eq.  of  hydrogen  as  unity, 
the  eq.  vol.  is  100.  If  the  sp.  gr.  is  smaller  than  its  equivalent,  as  in  mercury, 
this  must  arise  from  its  eq.  vol.  being  proportionally  greater  than  the  eq.  vol. 
of  hydrogen :  and  if  the  sp.  gr.  is  greater  than  its  equivalent,  as  in  oxygen  or 
sulphur,  the  eq.  vol.  is  proportionally  smaller  than  the  eq.  vol.  of  hydrogen.  A 
simple  rule  of  three,  therefore,  enables  the  eq.  vol.  to  be  calculated.  Thus  the 
eq.  vol.  of  mercury  is  f  Jf  X  100  =  200 ;  that  of  oxygen  j%  X 100  =  50  ;  and 
that  of  sulphur  is  -gl-'lg  X  100  =  16.66,  agreeably  to  the  numbers  which  will  be 
found  in  the  table. 


140 


ON  THE  LAWS  OF  COMBINATION. 


Gas  and  Vapours. 

Specific 

Gravities. 

Chemical  Equivalenlsl 

Air  as  1. 

Hydrogen  as  1. 

By  Vol. 

By  Weight. 

Hydrogen           .... 

0-0690 

1-00 

100 

1-00 

Nitrogen 

, 

0-9727 

14-12 

100 

14-15 

Chlorine 

2-4700 

35-84 

100 

35-42 

Carbon  (hypothetical) 

0-4215 

6-12 

100 

6-12 

Iodine 

8-7011 

126-30 

100 

126-30 

Bromine 

5-3930 

78-40 

100 

78-40 

Water                 .            , 

0-6202 

9-00 

100 

9-00 

Alcohol 

16012 

23-24 

100 

23-25 

Sulphuric  Ether 

2-5822 

37-50 

100 

37-50 

Light  Carburetted  Hydrogen 

0-^595 

8-12 

100 

8-12 

Olefiant  Gas 

0-9810 

14-24 

100 

14-24 

Carbonic  Oxide 

0-9727 

14-12 

100 

1412 

Carbonic  Acid 

1-5239 

22-12 

100 

22-12 

Protoxide  of  Nitrogen 

1-5239 

2212 

100 

22-15 

Sulphurous  Acid 

•      2-2105 

32-10 

100 

32-10 

Sulphuric  Acid  (anhydrous) 

2-7617 

40-10 

100 

40-10 

Cyanogen           .            .            , 

1-8157 

26-35 

100 

26-35 

Hydrosulphuric  Acid 

M770 

17-10 

100 

17-10 

Binoxide  of  Nitrogen 

1-0377 

15-06 

200 

30-15 

Mercury 

6-9690 

101-00 

200 

202-00 

Ammonia 

0-5898 

8-56 

200 

17-15 

Hydrochloric  Acid 

1-2695 

18-42 

200 

36-42 

Hydriodic  Acid 

4-3850 

63-63 

200 

127-26 

Hydrobromic  Acid              . 

2-7310 

39-71 

200 

79  40 

Hydrocyanic  Acid 

0.9423 

13-67 

200 

27-35 

Arsenuretted  Hydrogen      . 

2-6950 

39-20 

200 

78-20 

Sesquichloride  of  Arsenic 

6-2950 

91-36 

200 

181-66 

Sesquiodide  of  Arsenic 

15-6400 

227-00 

200 

454-28 

Protochloride  of  Mercury 

8-2040 

119-00 

200 

237-42 

Bichloride  of  Mercury 

9-4390 

137-00 

200 

272-84 

Bromide  of  Mercury     . 

9-6650 

140-26 

200 

280-40 

Bibromide  of  Mercury        , 

12-3620 

179-40 

200 

358-80 

Biniodide  of  Mercury 

15-6700 

227-40 

200 

454-52 

Oxygen 

1-1025 

1600 

50 

8-00 

Arsenious  Acid             , 

13-6695 

198-4 

50 

99-40 

Phosphorus 

4-3273 

62-8 

25 

15-70 

Arsenic 

10-3620 

150-8 

25 

37-7 

Sulphur 

6-6480 

96-48 

16.66 

16-10 

Bisulphuret  of  Mercury            ,        ^ , 

5-3840 

78-10 

33.33 

234-18 

The  observations  which  more  immediately  flow  from  the  facts  in  the  pre- 
ceding table  are  these  i-r-- 

1.  The  combining  or  eq.  volumes  of  substances,  both  elementary  and  com- 
pound, are  either  equal  or  have  the  simple  ratio  of  1  to  1,  I  to  2,  1  to  3,  &c. 
The  same  simplicity  rarely  exists  among  the  equivalent  weights. 

2.  On  comparing  the  third  and  fifth  columns,  the  corresponding  numbers  for 
the  first  18  substances  will  be  found  nearly  or  quite  identical.  As  those  sub- 
stances have  the  same  uniting  volume  as  hydrogen,  which  is  the  assumed  unit 
of  comparison,  and  as  the  sp.  gravities  are  merely  the  weights  of  equal  volumes, 
the  numbers  of  the  third  column,  were  they  quite  exact,  must  coincide  with  those 
in  the  fifth :  their  want  of  identity  indicates  errors  of  observation. 

3.  The  identity  in  the  eq.  volumes  of  the  elementary  gases,  hydrogen,  nitrogen, 
and  chlorine,  led  to  the  notion  that  the  eq.  volumes  of  most  other  elements,  such 
as  carbon,  sulphur,  and  phosphorus,  might  also  be  identical.  Assuming  that 
identity,  the  sp.  gravity  which  those  elements  ought  to  have  when  gaseous,  may 
easily  be  calculated.  Thus,  taking  I,  6*12,  and  16*1  as  the  equivalents  of  hydro- 
gen, carbon,  and  sulphur,  then  will  their  sp.  gravities  in  the  gaseous  state,  eq. 
volumes  being  supposed  equal,  be  in  the  ratio  of  1,  6-12,  and  15-1.  This  method, 


ON  THE  LAWS  OF  COMBINATION.  141 

by  "which  the  hypothetical  sp.  gravity  of  carbon,  as  stated  in  the  table,  was  ob- 
tained, was  first  indicated  by  Dr.  Prout.  (An.  of  Phil.  vi.  321.)  But  though 
such  hypothetical  numbers  may  sometimes  be  used  for  the  convenience  of  ex- 
pressing the  relation  of  uniting  substances  by  measure,  recent  facts  show  how 
dangerous  it  would  be  to  confide  in  them ;  for  by  the  table  it  appears  that  the  eq. 
volume  of  sulphurous  vapour  is  one  sixth  of  that  of  hydrogen,  which  renders  the 
sp.  gravity  of  the  vapour  of  sulphur  six  times  greater  than  the  hypothetical 
number.  Similar  deviation  is  observable  in  phosphorus,  arsenic,  and  mercury. 
In  these  cases,  the  real  sp.  gravity  of  a  vapour  is  as  much  greater  or  less  than 
the  hypothetical  as  its  eq.  volume  is  less  or  greater  than  that  of  hydrogen. 

4.  The  identity  in  the  eq.  volumes  of  hydrogen,  nitrogen,  and  chlorine,  sug- 
gested the  idea  that  the  atoms  of  all  the  elements  are  of  the  same  magnitude ; 
and  this,  coupled  with  the  supposition  that  the  self-repulsive  energy  of  these 
atoms  is  equal,  led  to  the  opinion  that  equal  volumes  of  the  elements  in  the 
gaseous  state  must  contain  an  equal  number  of  atoms.  This  hypothesis,  recom- 
mended by  its  simplicity,  and  supported  by  the  fact  that  the  volumes  of  gaseous 
substances  vary  according  to  the  same  law  by  varying  temperature  and  pressure, 
was  accordingly  employed  as  a  mode  of  determining  the  relative  weights  of 
atoms.  As  water  consists  of  50  measures  of  oxygen  and  100  of  hydrogen  gas, 
it  was  infeired  to  be  a  compound  of  one  atom  of  oxygen  and  two  atoms  of 
hydrogen ;  and  consequently,  taking  8  as  the  weight  of  an  atom  of  oxygen,  the 
weight  of  one  atom  of  hydrogen  is  J-  instead  of  1,  as  in  the  table ;  or  taking 
hydrogen  as  1,  the  atom  of  oxygen  is  16.  On  the  same  principle  may  the  num- 
bers which  in  the  table  represent  the  eq.  weights  of  chlorine,  bromine,  iodine, 
and  nitrogen,  which  have  the  same  eq.  volumes  as  hydrogen,  be  considered  as 
the  weights  of  two  equivalents.  The  equivalents  adopted  by  Davy  in  his  Ele- 
ments of  Chemical  Philosophy,  as  well  as  those  of  Berzelius,  which  are  now  in 
general  use  on  the  Continent,  were  framed  in  accordance  with  these  views :  this 
the  British  chemist  requires  to  bear  in  mind,  since  the  same  numbers  which 
Berzelius  uses  for  2  eq.  of  hydrogen,  nitrogen,  chlorine,  bromine,  and  iodine, 
he  considers  as  one  equivalent.  But  the  opinion  of  Davy  and  Berzelius  must 
now  either  be  abandoned,  or  maintained  on  other  principles,  since  the  late 
researches  of  Dumas  and  Mitscherlich  have  shown  experimentally  that  eq. 
volumes  of  the  elementary  gases  and  vapours  do  not  contain  the  same  number 
of  atoms. 

5.  The  facts  contained  in  the  last  and  preceding  tables  supply  material  for 
calculating  the  sp.  gravity  of  compound  gases,  by  which  means  the  accuracy  of 
other  conclusions  respecting  their  composition  may  be  verified.  Thus  analysis 
proves  that  ammoniacal  gas  is  composed  of  100  volumes  of  i^itrogen  and  300  of 
hydrogen  gases,  condensed  into  the  space  of  200  volumes  :  if  so,  its  sp.  gravity 
will  be 

0-9727  t  3  X  0-069^  M797^o.53gg 


The  near  agreement  of  this  calculated  number  with  that  found  by  weighing  the 
gas  itself,  proves  that  ammonia  has  really  the  constitution  above  assigned  to  it, 
and  gives  great  probability  that  the  sp.  gravity  of  nitrogen  and  hydrogen  gases 
is  nearly  correct. 
Again,  hydrochloric  acid  gas  consists  of  100  volumes  of  hydrogen  and  100  of 


142  ON  THE  LAWS  OF  COMBINATION. 

chlorine  gases  united  without  any  change  of  bulk.     Hence  its  sp.  gravity  ought 
to  be 

2 

Hydrocyanic  acid  vapour  is  formed  of  100  volumes  of  hydrogen  and  100  of 
cyanogen  gases  united  without  change  of  volume ;  and  therefore  its  sp.  gravity 
should  be 

.     18157 10-069^(,9,,3 

Considering  olefiant  gas  as  a  compound  of  200  volumes  of  hydrogen  gas  and 
200  of  the  vapour  of  carbon  condensed  into  100,  its  sp.  gravity  will  be  (2  x 
0-069  t  2  X  0-4215)  =  (0'1380  +  0-8430)  =  0-9810. 

Aqueous  vapour  is  composed  of  100  volumes  of  hydrogen  and  50  of  oxygen 
gases  condensed  into  the  space  of  100  volumes ;  and  therefore  its  sp,  gravity 
ought  to  be  0-069  +  0*5512  (half  the  sp.  gr.  of  oxygen)  =  0-6202. 

Protoxide  of  nitrogen  is  formed  of  100  volumes  of  nitrogen  and  50  of  oxygen 
gases  condensed  into  100  volumes,  and  hence  its  sp.  gravity  should  be  0-9727 
+  0-5512  =  1-5239. 

Assuming  carbonic  oxide  to  be  a  compound  of  100  volumes  of  carbon  vapour 
and  50  of  oxygen  gas  contracted  in  uniting  into  100  volumes,  ite  sp.  gravity 
should  be  0-4215  +  0-5512  =  0-9727. 

As  the  different  sp.  gravities  thus  calculated  are  very  nearly  those  found  by 
direct  experiment,  there  is  a  strong  presumption  that  the  elements  of  the  calcu- 
lations are  correct. 

The  principle  of  these  calculations  is  sufficiently  obvious.  The  sp.  gravities 
represent  the  weights  of  equal  volumes  of  the  gases ;  taking  100  as  the  stand- 
ard volume  of  which  the  sp.  gravity  of  each  gas  denotes  the  weight,  then  50 
volumes  of  a  gas  may  be  indicated  by  half,  25  volumes  by  a  fourth,  and  16-66 
by  a  sixth  of  its  sp.  gravity.  Thus  hydrosulphuric  acid  is  a  compound  of  100 
volumes  of  hydrogen  gas,  and  16-66  (-g^)  of  the  vapour  of  sulphur  condensed 
it  to  100  volumes,  and  therefore  its  sp.  gravity  is 

0-069  -f-  51^=  0-069  -f-  11080=  1-1770. 


Sulphurous  acid  consists  of  100  volumes  of  oxygen  gas  and  16-66  of  the  vapour 
of  sulphur  condensed  into  100  volumes;  and  hence  its  sp.  gravity  is 

1-1026  +  5:^--  1.1025  -|-  M0«0  =  2-2106. 

In  these  two  gases  the  volume  is  the  same  as  the  hydrogen  or  oxygen  which 
they  contain,  and  therefore  their  sp.  gravities  are  the  sum  of  the  weights  of 
their  elements.  The  same  applies  to  water,  protoxide  of  nitrogen,  and  carbonic 
oxide.  In  olefiant  gas  400  volumes  are  condensed  into  100,  and  therefore  its 
sp.  gravity  is  the  sum  of  the  sp.  gravities  of  its  elements.  Hydrochloric  acid 
gas  occupies  the  same  space  as  its  elements,  and  therefore  its  sp.  gravity  is 


ON  THE  LAWS  OF  COMBINATION.  143 

found  by  taking  the  mean  of  their  sp.  gravities.  The  same  remark  applies  to 
hydrocyanic  acid.  In  ammonia  400  volumes  are  condensed  into  200,  and  therefore 
the  sum  of  the  sp.  gravities  is  halved. 

As  vapours  are  easily  condensed  by  cold,  and  in  many  cases  exist  as  such  only 
at  high  temperatures,  their  sp.  gravities  may  often  be  obtained  by  calculation 
more  accurately  than  by  experiment.  Thus  it  is  easier  accurately  to  ascertain 
the  sp.  gravity  of  hydrogen  and  hydrosulphuric  acid  gases  than  of  the  vapour 
of  sulphur  ;  and  therefore  as  soon  as  experiment  has  shown  that  the  sp.  gravity 
of  that  vapour  is  somewhere  about  6"6480,  then  the  precise  number  may  be  cal- 
culated. For  as  100  volumes  of  hydrosulphuric  acid  gas  contain  100  of  hydro- 
gen gas,  the  sp.  gravity  of  the  latter  deducted  from  that  of  the  former  (1*177 
—  0*069),  gives  1*108  as  the  weight  of  combined  sulphur.  If  the  eq.  volume 
of  sulphur  were  100,  then  must  1*108  be  its  sp.  gravity;  but  as  the  number 
found  experimentally  is  nearly  six  times  1*108,  the  inference  is  that  the  real  sp. 
gravity  is  6  X  1'108  =  6*648,  and  that  its  eq.  volume  is  six  times  less  than  100, 
or  16*66.  The  only  assumption  here  is,  that  if  the  eq.  volume  of  the  vapour  is 
not  100,  it  must  be  some  multiple  or  submultiple  of  it  by  a  whole  number,  con- 
sistently with  the  theory  of  volumes.  In  the  construction  of  the  preceding  table 
I  have  given  the  sp.  gravities  of  vapours  calculated  on  these  principles  rather 
than  the  precise  numbers  given  by  experiment. 

6.  The  volume  of  a  compound  gas  in  reference  to  the  volumes  of  its  compo- 
nents is  determined  by  one  of  the  following  rules : — 

1.  One  volume  of  gas  united  with  one  volume,  yield  two  volumes  of  the  com- 
pound. 

2.  The  volume  of  the  compound  gas  often  has  the  volume  of  that  gas  which 
enters  most  largely  into  it  by  volume. 

3.  The  volume  of  the  compound  gas  is  equal  to  the  sum  of  the  volumes  of 
its  components  divided  generally  by  2,  but  sometimes  by  4  or  8. 

4.  In  a  few  cases  the  sum  of  the  component  volumes  must  be  divided  by  3. 

[ON  THE  RELATIVE  VOLUMES  IN  WHICH  SOLIDS  AND  LIQUIDS  RESPECT- 
IVELY  COMBINE. 

[The  recent  researches  of  Schroder,  Amraermuller,  and  Kopp,  have  brought 
to  light  several  interesting  facts  in  regard  to  the  proportion,  by  volume,  in  which 
solids  and  liquids  respectively  combine,  indicating  laws  of  combination,  in  refer- 
ence to  the  volumes  of  the  solid  and  liquid  ingredients,  analogous  in  some 
respects  to  those  already  described,  as  applicable  to  the  union  of  the  gases.  A 
few  of  the  more  prominent  of  these  results  are  deserving  of  mention  here,  as 
well  from  their  intrinsic  interest  as  from  the  light  they  seem  destined  to  shed  on 
various  important  points  of  chemical  theory. 

[As  the  chemical  equivalents  or  atomic  weighty  of  bodies  represent  the  pro- 
portion hy  weights  in  which  they  enter  into  combinl[tion,  so  these  numbers  when 
divided  by  the  specific  gravities  of  the  respective  bodies  to  which  they  refer,  will 
represent  the  proportional  volumes  in  which  they  unite.  The  numbers  thus  result- 
ing from  the  division  of  the  equivalents,  or  atomic  weights,  by  the  specific  gra- 
vities are  called  the  equivalent,  or  atomic  volumes.  Thus  the  atomic  weight  of 
silver  being  108*3,  and  its  sp.  gravity  105,  we  have  the  equivalent  volume  of 

108 
«7i;er  =  -— =  10*40.      In  like  manner  the  atomic  weight  of  potassium  being 


144 


ON  THE  LAWS  OF  COMBINATION. 


39*3   and   its    sp.    gravity  0*865,  we   have  the   equivalent  volume  of  potas- 
39*3 

The  following  table  includes  the  equivalent  volumes  of  a  number  of  the  sim- 
ple bodies,  reduced  to  the  hydrogen  scale.* 

TABLE  OF  EQUIVALENT  VOLUMES. 


Elements. 

Eq.  Vol. 

Elements. 

Eq.  Vol. 

Carbon 

2-87 

Iron 

3-52 

Sulphur 

8-00 

Cobalt 

3-52 

Phosphorus 

8-08 

Copper 

3-52 

Chlorine 

12-80 

Manganese 

3-52 

Bromine 

12-80 

Nickel 

3-52 

Iodine 

12-80 

Iridium 

4-56 

Chromium 

5-52 

Osmium 

4-56 

Molybdenum 

5-52 

Palladium 

4-56 

Tungsten 

5-52 

Platinum 

4-56 

Silver 

10.40 

Rhodium 

4-56 

Gold 

5-20 

Titanium 

4-56 

Sodium 

23-31 

Zinc 

4-64 

Potassium 

46-64 

Lead 

9-12 

From  this  table  we  see  that  the  chlorine,  chromium,  iron,  and  iridium  groups, 
have  respectively  the  eq.  volumes  12*80,  5*52,  3-52,  and  4*56,  while  the  eq. 
volumes  of  potassium  and  silver,  are  respectively  double  those  of  sodium  and 
gold. 

[The  numbers  in  the  above  table  are  called  by  Kopp  the  primative  atomic  or 
equivalent  volumes,  to  distinguish  them  from  those  which  the  same  elements 
must,  in  many  cases,  be  inferred  to  possess  while  they  are  actually  in  the 
state  of  combination.  The  latter  often  differ  from  the  former,  although  related 
to  them  by  some  simple  arithmetical  rule,  applicable  to  all  the  individuals  of  a 
particular  group  of  compounds.  The  most  important  law,  deduced  from  a  com- 
parison of  equivalent  volumes,  is  the  following : — 

The  equivalent  volumes  of  homorphous  bodies  are  equal,  or  in  some  very  simple 
ratio  to  each  other. 

This  law,  partially  illustrated  in  the  above  table,  has  been  shown  by  Kopp  to 
be  true  of  a  large  number  of  compound  isomorphous  bodies,  among  which  are 
the  following : — 

1. 

Ajuraina. 

Sesquioxide  of  Iron. 
Seaquioxide  of  Chromium. 

t  *■ 

Carbonate  oRZinc. 

"  Magnesia. 

«<  Iron. 

"  Manganese. 

"  Lime. 

Dolomite. 


*  The  corresponding  numbers  in  Kopp's  and  Schroder'i  tables  are  calculated  according 
to  the  scale  in  which  the  eq.  of  oxygen  is  reckoned  100. 


ON  THE  LAWS  OF  COMBINATION.  145 

3. 
Double  Sulphate  of  Potassa  and  Ammonia. 
«  "  "  Alumina. 

**  **  **  Sesquioxide  of  Iron. 

**  "  **  Sesquioxide  of  Chromium. 

4. 
Sulphate  of  Zinc. 

'*  Magnesia, 

"  Nickel. 

[Where  a  gas,  as  oxygen  or  hydrogen,  enters  into  the  composition  of  a  solid 
compound,  it  is  obvious  that  we  cannot  compute  its  equivalent  volume,  as  part 
of  the  compound,  from  its  equivalent  weight,  and  its  sp.  gravity  in  the  gaseous 
condition,  its  sp.  gravity  in  the  solid  form,  being  requisite  for  this  purpose.  In 
such  cases  the  equivalent  volume  of  the  gaseous  element  is  inferred  from  a  com- 
parison of  the  equivalent  volume  of  the  compound  and  the  non-gaseous  ingre- 
dient.    Thus 

Equivalent  volume  of  Protoxide  of  Lead,  or  Ph  0  =  11-68 )  ^rr. a  e^c 

Do.  do.    of  Lead,  or  Ph     =   912j  ^'"•— ^■^^• 

In  the  protoxide  of  lead,  therefore,  the  eq.  volume  of  the  oxygen  is,  in  this 
way,  inferred  to  be  2*56. 

It  will  readily  appear,  however,  that  this  result  is  only  correct  upon  the  sup- 
position that  the  lead  exists  in  this  compound  in  its  primitive  equivalent  volume 
(9*12).  Were  it  condensed  to  one  half,  or  in  any  other  way  changed,  the  eq. 
vol.  of  the  oxygen  thus  deduced  would  differ  from  the  above.  It  is,  however, 
an  interesting  fact  that  we  obtain  the  same  eq.  vol.  for  the  combined  oxygen  in 
a  large  number  of  analogous  oxides,  by  adopting  the  same  hypothesis  in  regard  to 
eq.  volumes  of  the  other  metals.     Thus  ^ 

Equivalent  volume  of  Protoxide  Zinc,  or  Zn  0  =  7-20)  ^./r        „  kc 
Do.  do.    of  Zinc,  or  Zn     =4-64}  ^^"- —  ^*^''- 

Equivalent  volume  of  Protoxide  of  Cadmium,  or  Cd  0=9-04)  ^..^ 

Do.  do.    of  Cadmium,  or  Cd     =6-48^  ^^"' ==^'^^- 

Equivalent  volume  of  Protoxide  of  Copper,  or  Cu  0  =  6-08)  ^.q.       „  ^^ 
Do.  do.    of  Copper,  or  Cu     =  3-625  ■^^"•  =  ^"^^' 

Applying  the  same  mode  of  calculation  to  the  binoxides  and  sesquioxides,  and 
still  assitming  the  primitive  equivalent  volume  of  the  metal  to  be  retained  by  it 
while  combined,  we  obtain  in  a  large  number  of  cases  the  same  value  as  above, 
for  the  equivalent  volume  of  the  oxygen.     Thus 

Equivalent  volume  of  Binoxide  of  Lead,  or  PhOa  =  14-24)  ;.  ,„       o    ^  o  kp 
Do.  do.     of  Lead,  or  Ph      =    9.12J  ^"^^  —  ^  X -^'O^- 

Equivalent  volume  of  Sesquioxide  of  Lead,  or  PhoOa  =  25-92)  _  ^o       o  vx  o  kc 
Do,  do.     of  Lead,  or  Ph       =   9.i2p'68  =  3  X  2-&b. 

Equivalent  volume  of  Sesquioxide  of  Iron,  or  Fe^Oa  =  14-72)  „  r,Q       o  vx  o  kc 
Do.  do.    of  Iron,  or  Fe       =   7.04J  ^•6^  =  ^  X  2-5b. 

[It  is  therefore  a  reasonable  presumption  from  these  facts,  that  the  equivalent 
volume  of  the  oxygen,  as  it  exists  in  the  various  oxides  referred  to,  is  invariable, 
and  is  represented,  according  to  the  hydrogen  scale,  by  2-56.  There  is,  how- 
ever, a  second  class  of  oxides,  such  as  the  sesquioxide  of  chromium,  (Cr  O3)  in 
which  the  eq.  vol.  of  the  oxygen,  as  inferred  by  a  similar  process,  is  one  half, 
and  a  third  class,  including  the  binoxide  of  copper  (CujO),  in  which  it  is  twice 

12 


146  ON  THE  LAWS  OF  COMBINATION. 

as  great  as  that  above  given.  Neither  of  these  latter  groups  is  as  large  as  that 
first  referred  to.  They,  however,  serve  to  indicate  a  law  of  dilatation  and  conden- 
sation on  the  part  of  the  solid  oxygen  entering  into  these  various  compounds,  of 
remarkable  simplicity,  the  several  combining  volumes  having  the  relation  of  the 
numbers  1,  2,  4.] 

[Applying  similar  reasonings  aijd  calculations  to  the  salts,  we  find  that  in  the 
nitrates  the  (NOg),*  associated  with  the  metallic  base,  has  an  invariable  equiva- 
lent volume  =  28-64    Thus 

m 
Equivalent  volume  of  Nitrate  of  Lead,  or  Pb  N06  =  37-76)  no  ca 

Do.           do.    of  Lead,  or                    Pb         =r' 9-12^  — '^^'^^' 
Equivalent  volume  of  Nitrate  of  Silver,  or  Ag  N06  =  39.04)  no  />. 

Do.  do.    of  Silver,  or  Ag         =  10-405  ~*'^*'*'^" 

In  the  sulphates  we  find  the  eq.  vol.  of  the  SO4  combined  with  the  metal,  to 
have  two  diiFerent  values.  For  one  class  of  the  sulphates  the  eq.  vol.  of  SO^  is 
18*88.  Sulphate  of  copper,  Cu  SO^,  is  an  example  of  this  class.  For  the  other 
the  eq.  vol.  is  14*88.  Sulphate  of  lead,  Pb  SO4,  illustrates  this.  These  two 
numbers  are  very  nearly  in  the  ratio  of  4  to  5.] 

[According  to  the  researches  of  Kopp,  the  equivalent  volume  of  a  compound  is 
very  rarely  equal  to  the  sum  of  the  primitive  equivalent  volumes  of  its  elements. 
Hence  the  eq.  volumes  in  which  these  elements  exist  in  the  compound  are  to  be 
sought  for  by  comparisons,  such  as  those  above  given  of  the  various  compounds 
of  analogous  character.  It  will  be  seen,  from  the  preceding  results,  that  the 
changes  of  equivalent  volume,  due  to  the  diflferent  combinations  into  which  a 
given  element  enters,  is,  like  the  condensation  or  expansion  in  gaseous  combi- 
nation, governed  by  certain  numerical  laws  peculiar  to  each  group  of  compounds, 
although,  according  to  Kopp,  these  condensations  and  rarefactions  of  the  solid 
volumes,  are  not  expressed  by  the  same  simple  ratios,  as  in  the  case  of  the  gas«s. 
This  very  interesting  inquiry  has,  as  yet,  been  too  little  advanced  to  furnish,  in 
a  positive  form,  any  more  general  results  than  those  above  indicated ;  but  there 
is  good  reason  to  hope  for  new  and  important  generalizations  in  its  further  prose- 
cution.   (Pogg.  Ann.  xlvii.)] 

CHEMICAL  SYMBOLS. 

The  impracticability  in  many  cases  of  contriving  convenient  names,  expres- 
sive of  the  constitution  of  chemical  compounds,  especially  of  minerals,  suggested 
the  employment  of  symbols  as  an  abbreviated  mode  of  denoting  the  composition 
of  bodies.  It  was  thought  that  the  names  of  elementary  substances,  instead  of 
being  written  at  full  length,  might  often  be  more  conveniently  indicated  by  the 
first  letter  of  their  names;  and  that  the  combination  of  elements  with  each  other 
might  be  expressed  by  placing  together,  in  some  way  to  be  agreed  on,  the  letters 
which  represent  them.  The  advantage  of  such  a  symbolic  language  was  felt 
so  strongly  by  Berzelius,  that  he  some  years  ago  contrived  a  set  of  symbols, 
which  he  has  since  used  extensively  in  his  writings  ;  and  other  eminent  chemists 
as  well  as  mineralogists,  believing  symbols  to  be  useful,  adopted  those  which 
Berzelius  had  proposed.  The  consequence  is,  that  symbolic  expressions,  called 
chemical  formulas^  are  now  so  much  resorted  to,  and  are  so  identified  with  the 
language  of  chemistry,  that  essays  of  great  value  are  in  a  measure  as  sealed  books 

*  See  general  remarks  on  salts  in  a  subsequent  part  of  the  work. 


ON  THE  LAWS  OF  COMBINATION. 


147 


to  those  who  cannot  read  symbols.  It  is  therefore  important  that  the  chemical 
student,  whatever  he  may  think  of  the  value  of  symbols,  should  not  be  unac- 
quainted with  them.  Fortunately,  the  labour  of  a  few  minutes  will  enable  him 
to  understand  the  subject.  The  following  table  includes  the  symbols  of  all  the 
elementary  substances  according  to  Berzelius. 


Elements. 

Symb. 

1           Elements. 

Symb. 

1           Elements. 

Symb. 

Alluminium 

Al 

Gold  (Aurum) 

Au 

iPlatinum     . 

PI 

Antimony  (Stibium) 

Sb 

Hydrogen 

H 

!  Potassium  (Kalium) 

K 

Arsenic 

As 

Iodine 

I 

Rhodium     .. 

R 

Barium 

Ba 

Iridium 

Ir 

Selenium 

Se 

Bismuth 

Bi 

Iron  (ferrum) 

Fe 

Silicon 

Si 

Boron    . 

B      • 

Lantanum 

Ln 

Silver  (Afgentum) 

Ag 

Bromine 

Br 

Lead  (Plumbum)     . 

P% 

1  Sodium  (Natrium)   . 

Na 

Cadmium 

Cd 

Lithium 

L 

Strontium 

Sr 

Calcium 

Ca 

Magnesium 

Mg" 

Sulphur 

S 

Carbon 

C 

Manganese 

Mn   * 

Tellurium 

Te 

Cerium 

Ce 

Mercury     (Hydrargy- 

Thorium     . 

Th 

Chlorine 

CI 

rum) 

Hg 

Tin  (Stannum)  . 

Sn 

Chromium 

Cr 

Molybdenum 

Mo 

Titanium 

Ti   . 

Cobalt 

Co 

Nickel 

Ni 

Tungsten  (Wolfram) 

W 

Columbium      (Tanta- 

Nitrogen 

N 

Vanadium 

V 

lum)  . 

Ta 

Osmium 

Os 

Uranium, 

U' 

Copper  (Cuprum)     . 

Cu 

Oxygen 
Palladium 

0 

Yttrium 

Y 

Fluorine 

F 

Pd 

Ziric 

Zn 

Glucinium  . 

G 

!  Phosphorus 

P 

1  Zirconium 

Zr      1 

For  the  sake  of  uniformity,  and  to  prevent  confusion,  it  is  much  to  be  wished 
that  these  symbols,  being  now  generally  known,  should  be  rigorously  adhered 
to.  Berzelius  has  properly  selected  them  from  Latin  names,  as  being  known  to 
all  civilized  nations ;  and  when  the  names  of  twp  or  more  elements  begin  with  the 
same  letter,  the  distinction  is  made  by  means  of  an  additional  letter. 

The  foregoing  symbols  are  intended  to  represent  the  chemical  eq.  of  the  ele- 
ments. Thus,  the  letters  H,  I,  and  Ba,  stand  for  one  eq.  of  hydrogen,  iodine, 
and  barium ;  and  2  H,  3  H,  and  4  H,  for  2,  3,  and  4  eq.  of  hydrogen.  Two  eq. 
of  an  element  ar6  often  denoted  by  placing  a  dash  through  or  under  its  symbol : 
for  instance,  H  or  H  means  2  H,  and  P  or  P  signifies  2  P.  Certain  compounds 
are  often,  for  the  sake  of  brevity,  denoted  by  single  symbols  in  the  same  manner 
as  the  elements :  thus  an  eq.  of  water,  ammonia,  and  cyanogen,  is  sometimes 
expressed  by  Aq,  Am,  and  Cy ;  but  in  general  the  formulae  for  compound  bodies 
are  so  contrived  as  to  indicate  the  elements  they  contain,  and  the  mode  in  which 
they  are  united.  This  may  be  done  in  several  ways  ;  but  that  which  first  sug- 
gests itself  is,  to  connect  together  the  symbols  by  the  same  signs  as  are  used  in 
Algebra.  Thus  the  formulae  K  +  O,  Ca  +0,  Ba  -f-  O,  Mn  -f-  0,  Fe  f  O, 
2  Fe  +  3  0,  3  H  +  N,  2  H  t  .2  C,  C  +  2  0,  N  t  5  O,  S  +  3  O,  and  H  +  CI, 
denote  single  eq.  of  potassa,  lime,  baryta,  protoxide  of  manganese,  protoxide  of 
iron,  peroxide  of  iron,  ammonia,  olefiant  gas,  carbonic  acid,  nityic  acid,  sulphuric 
acid,  and  hydrochloric  acid.  The  formula  C  -|-  N  -f  6  O  indicates  the' elements 
which  are  contained  in  an  eq.  of  nitrate  of  potassa :  in  order  to  express  further 
that  the  potassium  is  combined  with  only  1  eq.  of  oxygen,  the  remaining  oxygen 
with  the  nitrogen,  and  the  potassa  with  nitric  acid,  the  symbols  are  placed  thus, 
(K  "h  O)  -f-  (N  -j-  5  0,)  the  brackets  containing  the  symbols  of  those  elements 
which  are  supposed  to  be  united.  A  number  placed  on  the  outside  of  a  bracket 
multiplies  the  compound  within  it:  thus  (K  -f-  0)  -|-  (S  -|-  3  0)  is  sulphate  of 
potassa,  and  (K  -|-  O)  -{-  2  (S  +  8  0)  is  the  bisulphate.    All  the  elements  con- 


148  '  ON  THE  LAWS  OF  COMBINATION. 

tained  in  a  compound  are  thus  visibly  represented,  and  the  chemist  is  abler^dily 
to  trace  all  possible  modes  of  combination,  and  to  select  that  which  is  most  in 
harmony  with  the  facts  and  principles  of  his  science.  He  may,  and  often  does, 
thereby  detect  relations  which  might  otherwise  have  escaped  notice. 

Another  advantage  attributable  to  such  formulae  is,  that  they  facilitate  the  com- 
prehension of  chemical  changes.  If  hydrosulphuric  acid  acts  upon  the  protoxide 
of  lead,  it  is  easy  to  say  that  the  sulphur  combines  with  the  lead  and  the  hydro- 
gen with  the  oxygen;  but  the  exact  adaptation  of  the  quantities  for  mutual  inter- 
change appears  to  me  more  clearly  shown  by  symbols  than  by  a  description  or 
a  diagram,  both  of  which  are  apt  to  produce  confusion  where  the  change  to  be 
explained  is  complex.  In  the  simple  instance  alluded  to,  H  -f-  S  reacts  on 
Pb  -|-  0,  and  the  products  ar^Pb  -fS  and  H  -|-  O.  When  hydrosulphuric  acid 
acts  on  bicyanuret  of  mercury,  the  result  is  bisulphuret  of  mercury  and  hydro- 
cyanic acid :  the  substances  which  interchange  elements  are  2  (H  -|-  S)  and 
Hg  -|-  2  Cy  ;  and  the  products  are  Hg  -f  2  S,  and  2  (H  -f-  Cy).  In  more  com- 
plicated changes  the  advantage  of  chemical  formulae  is  still  more  manifest,  ex- 
aAiples  of  which  kind  will  be  found  in  the  section  on  cyanogen,  and  in  other 
parts  of  this  volume. 

Useful  as  the  algebraic  chemical  formulae  are  for  the  purposes  of  studying 
chemical  changes,  they  are  sometimes  found  inconveniently  long  where  the  object 
is  merely  to  express  the  composition  of  bodies,  and  accordingly  Berzelius  has 
introduced  several  abbreviations.    For  instance,  he  indicates  degrees  of  oxidation 

by  dots  placed  over  the  symbol,  writing,  K,  C,  N,  instead  of  K  -f-  O,  C  -f-  20, 
N  -|-  50,  for  potassa,  carbonic  acid,  and  nitric  acid.    In  like  manner  he  denotes 

compounds  of  sulphur  by  commas,  writing  K,  Hg,  H  instead  of  K  -f-  S, 
Hg  -f-  2  S,  H  -[-  S,  for  sulphuret  of  potassium,  bisulphuret  of  mercury,  and 
hydrosulphuric  acid.    When  the  ratio  is  that  of  2  to  3  he  employs  the  symbol 

for  two  eq.  above  stated  :  thus  Fe,  5,  ^,  is  used  instead  of  2  Fe  -j-  30,  2P  -j-  50, 
2 As  -f-  50,  for  an  equivalent  of  peroxide  of  iron,  phosphoric  acid,  and  arsenic 

»»     > » « 
acid  ;  and  similarly  we  have  ^,  ^,  instead  of  2  As  -f-  3  S,  2  As  -f  5  S  for  the 

sesquisulphuret  and  persulphuret  of  arsenic.  These  last  formulae  are  sometimes 
used  to  indicate  two  eq.  instead  of  one  ;  but  as,  agreeably  to  the  atomic  theory, 
the  smallest  possible  particle  of  peroxide  of  iron  consists  of  2  atoms  of  iron  and 
3  of  oxygen,  the  formula  2  Fe  -f-  3  O  ought  to  stand  for  1  eq.  only. 

Berzelius  often  dispenses  with  the  sign,  -|-,  and  writes  combined  elements 
side  by  side,  the  sign  of  addition  being  understood  instead  of  expressed.     Thus 

he  uses  HO,  KO,  FeS,  Ca  C,  Ba  N,  K  S  +  Ni  S,  instead  of  H  +  O,  K  f  O, 

Fe  t  S,  da  t  C,  Ba  +  N,  (K  f  §,)  +  (Ni  -f  S),  for  water,  potassa',  sul- 
phuret of  iron,  carbonate  of  lime,  nitrate  of  baryta,  and  the  double  sulphate  of 
potassa  and  oxide  of  nickel.  Two  or  more  equivalents  of  one  constituent  of  a 
compound  are  denoted  by  numbers  placed  in  the  same  position  as  the  indices  of 

powers  in  algebra :  thus  NH^,  NC^,  Fe«^  H^,  is  the  abbreviation  of  N  f  3H, 

N  -|-  2C,  2F£,  -\-  3H  for  ammonia,  cyanogen,  and  sesquihydrate  of  iron,  a  com- 
pound of  2  eq.  of  peroxide  of  iron  and  3  of  water.  A  number  used  before 
symbols,  like  coefficients  in  algebra,  multiplies  all  the  following  symbols  not 

separated  from  it  by  a  f  sign.    Thus  in  8  Ca  Si  +  K  Si^  +  16  aq.  (which  is 


ON  THE  LAWS  OF  COMBINATION.  149 

the  formula  for  the  mineral  called  apophyllite)  the  8  denotes  8  eq.  of  Ca  Si,  or 
silicate  of  lime,  which  are  united  with  1  eq.  of  bisilicate  of  potassa,  and  16  of 
water. 

Berzelius  also  expresses  the  vegetable  and  animal  acids  by  the  first  letter  of 
their  name,  with  a  dash  over  it.  Thus  Tj  A",  C",  F,  G",  F,  are  the  symbols  for 
tartaric,  acetic,  citric,  benzoic,  gallic,  and  formic  acids. 

Several  objections,  some  of  which  are  of  great  weight,  have  been  made  to 
this  system  of  symbols,  and  various  modifications  have  been  proposed  by  dif- 
ferent authors.  Among  these,  that  which  has  been  adopted  by  Liebig  and  Pog- 
gendorff  in  their  chemical  dictionary,  combine  more  successfully  than  any  other 
the  requisite  clearness,  brevity,  and  generality,  and  will  be  used  in  this  work. 
The  following  are  the  principles  of  this  method.  T^he  numbers  which  are  written 
before  a  symbol  affect  all  that  follow  as  far  as  the  first  full  stop  or  sign  of  addi- 
tion ;  while  those  which  are  written  a  little  below  and  to  the  right  hand,  multiply 
only  the  symbol  to  which  they  are  attached.  Two  symbols  placed  side  by  side 
are  understood  to  be  combined  together;  thus  HO  signifies  water;  KO  potassa, 
&c.  When  two  compounds  are  separated  only  by  a  comma,  they  are  also  to  be 
considered  as  combined.  Thus  KO,HO  is  the  symbol  of  hydrate  of  potash ; 
K0,S03  that  of  sulphate  of  potash.  When  two  salts  or  other  complex  com- 
pounds are  combined,  the  -j-  sign  is  used ;  thus  KOjSOg  -\-  H0,S03  represents 
bisulphate  of  potash,  a  compound  of  sulphate  of  potash  with  hydrated  sulphuric 
acid.  In  this  system  of  notation,  no  dots  are  employed,  nor  is  any  abbreviation 
used  to  express  two  equivalents.  For  example,  alumina,  which  Berzelius  abbre- 
viates thus,  Al^  is  represented  by  AI2O3,  which  is  equally  short,  more  easily 
written  and  printed,  and  which  moreover  has  this  advantage,  that  there  is  only 
one  symbol  used  for  each  element ;  while  the  composition  of  allied  compounds 
admits  of  a  more  ready  comparison.  If,  f(tr  example,  it  is  wished  to  show  the 
analogy  between  the  oxides  and  chlorides  of  phosphorus,  this  is  at  once  done  by 
writing  their  formulae  according  to  the  method  of  Liebig  and  Poggendorff. 

P2O3  P2O5  P2CI3  P2CI5 

Whereas  if  dots  are  employed  for  oxygen,  the  analogy  is  far  from  being  so 
obvious : — 

P  P  PCl^  PCI' 

unless  chlorine  be,  like  oxygen,  expressed  in  two  ways  ;  which,  however,  would 
embarrass  the  learner  unnecessarily.  By  comparing  the  symbol  for  apophyllite, 
according  to  Berzelius,  above  given,  with  that  for  the  same  mineral,  accoiding 
to  Liebig  and  Poggendorff,  8  (CaO,Si03)  f  KO,2Si03  +  16  aq.,  it  will  be  seen 
that  the  latter  is  at  least  equally  clear,  and  from  the  absence  of  dots,  far  less 
liable  to  error  in  printing  or  in  reading.  In  the  first  limb  of  the  above  formula 
it  is  to  be  observed  that  the  figure  8  multiplies  all  contained  within  the  parenthe- 
sis.    In  like  manner,  crystallised  alum  is  represented,  according  to  Berzelius,  by 

KS  -f-  Al  S3  -|-  24H;  and,  on  the  method  here  preferred,  by  K0,S03  +  Al^Og, 
3SO3  -\-  24HO.  For  the  reasons  above  mentioned,  the  method  of  Liebig  and 
Poggendorff  will  be  uniformly  employed  hereafter ;  but  I  have  thought  it  right 
to  explain  that  of  Berzelius,  that  where  it  is  met  with  it  may  be  understood. 


150  OXYGEN. 

ISOMERIC  BODIES.  • 

It  was  formerly  thought  that  the  same  elements  united  in  the  same  ratio  must 
always  give  rise  to  the  same  compound ;  but  within  these  few  years  several 
examples  have  been  discovered  of  two  or  even  more  substances  containing  the 
same  elements  in  the  same  ratio,  and  yet  exhibiting  chemical  properties  distinct 
from  each  other.  For  Buch  compounds  Berzelius  has  suggested  the  general 
appellation  of  isomeric,  from  taoj  equal,  and  fxt^o^  part,  expressive  of  equality  in 
the  ingredients.  Interesting  instances  of  this  kind  are  the  two  cyanic  acids, 
which  consist  of  cyanogen  and  oxygen  in  the  same  ratio,  and  have  the  same 
equivalent,  yet  differ  widely  in  their  chemical  properties  ;  and  a  similar  example 
is  afforded  by  the  tartaric  an^)aratartaric  acids.  Para  from  rta^a  near  to,  is  pre- 
fixed in  order  to  mark  the  relation  to  tartaric  acid,  a  principle  of  nomenclature 
which  is  extended  to  other  cases. 

Unexpected  as  was  the  discovery  of  isomerism,  it  is  quite  consistent  with  our 
theories  of  chemical  union,  insomuch  as  the  same  elements  may  be  grouped  or 
combined  in  different  ways,  and  thereby  give  rise  to  compounds  essentially 
distinct.  Thus  the  elements  of  sulphate  of  potassa  may  perhaps  be  united 
indiscriminately  with  each  other,  as  expressed  by  the  formula  KSO^;  or 
they  may  form  KO  -|-  SO3 ;  or  KS  +  O4 ;  or  KOj  +  SO2 ;  and  other  com- 
binations might  be  made.  The  second  of  these  is  thought  to  be  the  real  one ; 
but  no  one  can  say  that  the  others  are  impracticable.  Again,  the  elements  of 
peroxide  of  tin,  Sn  and  20,  may  either  form  SnOj,  or  SnO  -j-  O ;  and  those  of 
the  peroxide  of  iron,  2Fe  and  30,  may  either  be  FejOg,  or  FeO  +  FeOj,  not  to 
mention  other  possible  combinations.  The  elements  of  alcohol  are  4C,  GH, 
and  20,  which  may  be  united  indiscriminately  as  H^Cfig,  HgC^  -|-  20,  HgC^O 
-j-  HO,  or  H4C4  +  2H0,  besides  others. 

Some  bodies  consist  of  the  same  elements  in  the  same  ratio,  and  yet  differ  in 
their  equivalents.  A  marked  example  is  supplied  by  defiant  gas  and  etherine, 
the  former  of  which  contains  200  volumes  of  carbon  vapour  and  200  of  hydrogen 
gas  condensed  into  100  volumes,  and  the  latter  of  400  volumes  of  carbon  vapour 
and  400  of  hydrogen  gas,  united  so  as  to  yield  100  volumes  of  etherine.  The 
equivalent  of  olefiant  gas  is  14*24,  and  that  of  etherine  28*48,  or  exactly  double. 
A  similar  case  will  be  found  in  the  description  of  cyanuric  acid.  The  nature  of 
these  compounds  is  at  once  detected  by  their  equivalents  being  unlike,  and  by 
the  volume  which  they  occupy  as  gases  compared  with  the  volumes  of  the  ele- 
ments of  which  they  consist.  Isomeric  bodies  of  this  kind  are  obviously  much 
less  intimately  allied  than  those  above  described. 


SECTION   III, 


OXYGEN. 


History. — Discovered  by  Priestley  in  1774,  and  by  Scheele  a  year  or  two  after, 
without  previous  knowledge  of  Priestley's  discovery.  It  was  termed  Dephlogis- 
Heated  air  by  Priestley,  Empyreal  air  by  Scheele,  and  Vital  air  by  Condorcet. 


OXYGEN.  15  X 

The  name  it  now  bears,  derived  from  the  Greek  words  oluj  acid  and  yiwauv  to 
generate,  was  proposed  by  Lavoisier,  who  considered  it  the  sole  cause  of  acidity. 
Preparation. — From  several  sources,  the  peroxides  of  manganese,  lead,  and 
mercury,  nitre,  and  chlorate  of  potassa,  yield  it  in  large  quantities  when  they 
are  exposed  to  a  red  heat.  The  substances  commonly  employed  for  the  purpose 
are  peroxide  of  manganese  and  chlorate  of  potassa.  It  may  be  procured  from 
the  former  in  two  ways ;  either  by  heating  it  to  redness  in  a  gun-barrel,  or  in  a 
-retort  of  iron  or  earthenware ;  or  by  putting  it  in  fine  powder  into  a  flask  with 
about  an  equal  weight  of  concentrated  sulphuric  acid,  and  heating  the  mixture 
by  means  of  a  lamp.  To  understand  the  theory  of  these  processes,  it  is  neces- 
sary to  bear  in  mind  the  composition  of  the  three  following  oxides  of  manganese: — 

Manganese.  Oxygen. 

Protoxide  .  27-7  or  1  equiv.  -|-    8  .  =  35'7 

/  Sesquioxi^e        .  27-7  -j-  12  .  =  39-7 

Peroxide  .  27-7  \k  .  =  43-7 

On  applying  a  red  heat  to  the  last,  it  parts  with  half  an  equivalent  of  oxygen, 
and  is  converted  into  the  sesquioxide.  Every  437  grains  of  the  peroxide  will 
therefore  lose,  if  quite  pure,  4  grains  of  oxygen,  or  nearly  12  cubic  inches;  and 
one  ounce  will  yield  about  128  cubic  inches  of  gas.  [If  more  strongly  heated 
it  loses  uniformly  one  third  of  its  oxygen.  That  is  three  equivalents  of  the  per- 
oxide yield  two  equivalents  of  oxygen,  and  is  thereby  converted  into  the  red 
oxide,  a  compound  of  the  first  two  oxides.  The  change  is  expressed  in  sym- 
bols thus :  SMnOi  =  20  &  Mn304  or  MnO  ■\-  Mn^O^.  Every  43*7  grains, 
therefore,  of  the  peroxide,  will  lose  about  5|rd  grains  of  oxygen  or  16  cubic 
inches.  Hence  one  pound  will  yield  about  700  grains,  or  nearly  2000  cubic 
inches  of  gas.]  With  sulphuric  acid  the  peroxide  loses  a  whole  eq.  of  oxygen, 
and  is  converted  into  the  protoxide,  which  unites  with  the  acid,  forming  a  sul- 
phate of  the  protoxide  of  manganese.  Every  43'7  grains  of  peroxide  yields  8 
grains  of  oxygen  and  35*7  of  protoxide,  which  by  uniting  with  one  eq.  (40)  of 
the  acid,  forms  75*7  of  the  sulphate.  The  first  of  these  processes  is  the  most 
convenient  in  practice. 

The  gas  obtained  from  peroxide  of  manganese,  though  hardly  ever  quite  pure, 
owing  to  the  presence  of  iron,  carbonate  of  lime,  and  other  earthy  substances,  is 
sufficiently  good  for  ordinary  purposes.  It  yields  a  gas  of  better  quality,  if  pre- 
viously freed  from  carbonate  of  lime  by  dilute  hydrochloric  or  nitric  acid  ;  but 
when  oxygen  of  great  purity  is  required,  it  is  better  to  obtain  it  from  chlorate  of 
potassa.  For  this  purpose,  the  salt  should  be  put  into  a  retort  of  green  glass, 
or  of  white  glass  made  without  lead,  and  be  heated  nearly  to  redness.  It  first 
becomes  liquid,  though  quite  free  from  water,  and  then,  on  increase  of  heat,  is 
wholly  resolved  into  pure  oxygen  gas,  which  escapes  with  effervescence,  and 
into  a  white  compound,  called  chloride  of  potassium,  which  is  left  in  the  retort. 
The  composition  of  the  chloric  acid  and  potassa  which  constitute  the  salt  is 
stated  below : — 

Chlorine  .  35'42  or  1  eq.  Potassium  .        39- 15  or  1  eq. 

Oxygen  .  40       or  5  eq.  Oxygen  .  8       or  1  eq. 

Chloric  acid     .  75-42  or  1  eq.  Potassa  .        47-15  or  1  eq. 

Hence  the  oxygen  which  passes  over  from  the  retort,  is  derived  partly  from 


152  OXYGEN. 

the  potassa  and  partly  from  the  chloric  acid  ;  while  chlorine  and  potassium  enter 
into  combination.  Thus  are  122*57  grains  of  the  chlorate  resolved  into  74*57 
grains  of  chloride  of  potassium,  and  48  grains,  or  about  161  cubic  inches  of 
pure  oxygen.  The  following  equation  briefly  and  clearly  explains  the  change, 
KO  t  C10g==KCl  t  Ofi.* 

Properties. — Colourless,  tasteless,  inodorous  ;  feeble  refractor  of  light ;  non- 
conductor of  electricity ;  heavier  than  atmospheric  air,  sp.  gr.  being  estimated 
at  1*1026  by  Dulong  and  Berzelius,  so  that  100  cubic  inches  weigh  at  60°  and 
30'  Bar.  34*193  grains.  It  is  always  gaseous  when  not  combined  with  other 
ponderable  matter;  though  even  in  its  simplest  form  it  is  associated,  like  other 
elementary  principles,  with  the  agents  productive  of  heat,  light,  and  electricity. 
Like  all  gases  it  emits  a  str«ng  heat  when  suddenly  compressed :  light  also 
appears ;  but  this  is  solely  due  to  its  chemical  action  on  the  oil  with  which  the 
compressing  tube  is  lubricated.  It  is  the  most  perfect  —  electric,  always  appear- 
ing at  the  -f  electrode  when  Jlny  of  its  compounds  are  electrolized  ;  is  sparingly 
absorbed  by  water,  which  dissolves  only  3  or  4  per  cent,  of  the  gas  ;  is  neither 
acid  nor  alkaline,  as  it  does  not  change  the  colour  of  blue  flowers,  nor  evince  a 
disposition  to  unite  directly  either  with  acids  or  alkalies.  It  has  a  very  powerful 
attraction  for  most  simple  substances  ;  and  there  is  not  one  of  them,  except 
perhaps  the  highly-negative  fluorine,  with  which  it  may  not  be  made  to  combine. 
The  act  of  combining  with  oxygen  is  called  oxidation^  and  bodies  which  have 
united  with  it  are  said  to  be  oxidized.  The  compounds  so  formed  are  divided 
by  chemists  into  acids  and  oxides.  The  former  division  includes  those  com- 
pounds which  possess  the  general  properties  of  acids ;  and  the  latter  compre- 
hends those  which  not  only  do  not  possess  that  character,  but  of  which  many 
are  highly  alkaline,  and  yield  salts  by  uniting  with  acids.  The  phenomena  of 
oxidation  are  variable.  It  is  sometimes  produced  with  great  rapidity,  and  with 
evolution  of  heat  and  light.  Ordinary  combustion,  for  instance,  is  nothing  more 
than  rapid  oxidation ;  and  all  inflammable  or  combustible  substances  derive 
their  power  of  burning  in  the  open  air  from  their  afl^nity  for  oxygen.  On  other 
occasions  it  takes  place  slowly,  and  without  any  appearance  either  of  heat  or 
light,  as  in  the  rusting  of  iron  by  moist  air.  Different  as  these  processes  may 
appear,  oxidation  is  the  result  of  both ;  and  both  depend  on  the  same  circum- 
stance, namely,  the  presence  of  oxygen  in  the  atmosphere. 

All  substances  that  are  capable  of  burning  in  the  open  air,  bum  with  far 
greater  brilliancy  in  oxygen  gas.  A  piece  of  wood,  on  which  the  least  spark  of 
light  is  visible,  bursts  into  flame  the  moment  it  is  put  into  a  jar  of  oxygen  j 
lighted  charcoal  emits  beautiful  scintillations;  and  phosphorus  burns  with  so 
powerful  and  dazzling  a  light  that  the  eye  cannot  bear  its  impression.  Even 
iron  and  steel,  which  are  not  commonly  ranked  among  the  inflammables,  undergo 
rapid  combustion  in  oxygen  gas. 

The  changes  that  accompany  these  phenomena  are  no  less  remarkable  than  the 
phenomena  themselves.  When  a  lighted  taper  is  put  into  a  vessel  of  oxygen 
gas,  it  burns  for  a  while  with  increased  splendour ;  but  the  size  of  the  flame  soon 
begins  to  diminish,  and  if  the  mouth  of  the  jar  be  closed,  the  light  will  in  a 

*  If  the  chlorate  of  potassa  be  previously  mixed  with  about  l*10th  of  its  weight  of  per- 
oxide of  manganese,  it  yields  its  oxygen  at  a  lower  temperature  than  when  alone,  and  with 
uniform  rapidity  throughout  the  whole  process.'  According  to  Balmain  the  peroxide  of 
manganese  remains  undecomposed.    (R.) 


OXYGEN.  153 

short  time  disappear  entirely.  The  gas  has  now  lost  its  characteristic  pro- 
perty; for  a  second  lighted  taper,  immersed  in  it,  is  instantly  extinguished. 
This  result  is  general.  The  burning  of  one  body  in  a  given  portion  of  oxygen 
unfits  it  more  or  less  completely  for  supporting  the  combustion  of  another;  and 
the  reason  is  manifest.  Combustion  is  produced  by  the  combination  of  inflam- 
mable matter  with  oxygen.  The  quantity  of  free  oxygen,  therefore,  diminishes 
daring  the  process,  and  is  at  length  nearly  or  quite  exhausted.  The  burning  of 
all  bodies,  however  inflammable,  must  then  cease,  because  the  presence  of  oxy- 
gen is  necessary  to  its  continuance.  For  this  reason  oxygen  gas  is  called  a  sup- 
porter of  combustion.  Oxygen  often  loses  its  gaseous  form  as  well  as  its  other 
properties.  If  phosphorus  or  iron  be  burned  in  a  jar  of  pure  oxygen  over 
water  or  mercury,  the  disappearance  of  the  gas  becomes  obvious  by  the  ascent 
of  the  liquid,  which  is  forced  up  by  the  pressure  of  the  atmosphere,  and  fills 
the  vessel.  Sometimes,  on  the  contrary,  the  oxygen  gas  suffers  diminution  of 
volume  only,  or  it  may  even  undergo  no  change  of  bulk  at  all,  as  is  exemplified 
by  the  combustion  of  the  diamond. 

The  changes  experienced  by  the  burning  body  are  equally  striking.  While 
the  oxygen  loses  its  power  of  supporting  combustion,  the  inflammable  substance 
lays  aside  its  combustibility.  It  is  then  an  oxidized  body,  and  cannot  be  made 
to  burn  even  by  aid  of  the  purest  oxygen  gas.  It  has  also  increased  in  weight. 
It  is  an  error  to  suppose  that  bodies  lose  any  thing  while  they  burn.  The  mate- 
rials of  our  fires  and  candles  do  indeed  disappear,  but  they  are  not  destroyed. 
Although  they  fly  off"  in  the  gaseous  form,  and  are  commonly  lost  to  us,  it  is  not 
difficult  to  collect  and  preserve  all  the  products  of  combustion.  When  this  is 
done  with  the  required  care,  the  combustible  matter  is  always  found  to  weigh 
more  after  than  before  combustion ;  and  the  increase  in  weight  is  exactly  equal 
to  the  quantity  of  oxygen  which  has  disappeared  during  the  process. 

Oxygen  gas  is  necessary  to  respiration.  No  animal  can  live  in  an  atmosphere 
which  does  not  contain  a  certain  portion  of  uncombined  oxygen  ;  for  an  animal 
soon  dies  if  put  into  a  portion  of  air  from  which  the  oxygen  has  been  previously 
removed  by  a  burning  body.  Oxygen  disappears  during  respiration.  If  a  bird 
be  confined  in  a  limited  quantity  of  atmospheric  air,  it  will  at  first  feel  no  incon- 
venience ;  but  as  a  portion  of  oxygen  is  withdrawn  at  each  inspiration,  its  quan- 
tity diminishes  rapidly,  so  that  respiration  soon  becomes  laborious,  and  in  a 
short  time  ceases  altogether.  Should  another  bird  be  then  introduced  into  the 
same  air,  it  will  die  in  the  course  of  a  few  seconds  ;  or  if  a  lighted  candle  be 
immersed  in  it,  its  flame  will  be  extinguished.  Respiration  and  combustion  have 
therefore  the  same  effect.  An  animal  cannot  live  in  an  atmosphere  which  is 
unable  to  support  combustion ;  nor,  in  general,  can  a  candle  burn  in  air  which 
contains  too  little  oxygen  for  respiration. 

It  is  singular  that,  though  oxygen,  as  a  constituent  of  the  atmosphere,  is 
necessary  to  respiration,  in  a  state  of  purity  it  is  deleterious.  When  an  animal, 
as  a  rabbit  for  example,  breathes  pure  oxygen  gas,  no  inconvenience  is  at  first 
perceived ;  but  after  the  interval  of  an  hour  or  more  the  circulation  and  respira- 
tion become  very  rapid,  and  the  system  in  general  is  highly  excited.  Symp- 
toms of  debility  subsequently  ensue,  followed  by  insensibility  ;  and  death  occurs 
in  six,  ten,  or  twelve  hours.  On  examination  after  death,  the  blood  is  found 
highly  florid  in  every  part  of  the  body,  and  the  heart  acts  strongly  even  after  the 
breathing  has  ceased.  For  these  experiments  we  are  indebted  to  Broughton. 
Its  eq,  t5  =  8 ;  eq.  vol  =  50 ;  symb,  0. 


154  OXYGEN. 

**• 

THEORY  OF  COMBUSTION. 

The  only  phenomena  of  combustion  noticed  by  an  ordinary  observer,  are  the 
destruction  of  the  burning  body,  and  the  developement  of  heat  and  light;  but  it 
has  been  demonstrated  that  in  addition  to  these  circumstances,  oxygen  gas  inva- 
riably disappears,  and  a  new  compound  consisting  of  oxygen  and  the  combus- 
tible is  generated.  The  term  combustion,  therefore,  in  its  common  signification, 
implies  the  rapid  union  of  oxygen  gas  and  combustible  matter,  accompanied 
with  heat  and  light.  As  the  evolution  of  heat  and  light  is  dependent  on  chemi- 
cal action,  the  same  phenomena  may  be  expected  in  other  chemical  processes  ; 
and  accordingly  heat  and  light  are  frequently  emitted  quite  independently  of 
oxygen.  Thus  phosphorus  takes  fire,  and  a  taper  burns  for  a  short  time,  in  a 
vessel  of  chlorine ;  and  several  of  the  common  metals,  such  as  copper,  antimony, 
and  arsenic,  in  a  state  of  fine  division,  become  red  hot  when  introduced  into  a 
jar  of  that  gas.  Potassium  takes  fire  in  cyanogen  gas  ;  and  copper  leaf  or  iron 
wire,  ff  moderately  heated,  undergoes  the  same  change  in  the  vapour  of  sulphur. 
A  mixture  of  iron  filings  and  sulphur,  when  heated  so  as  to  bring  the  latter  into 
perfect  fusion,  emits  intense  heat  and  light  at  the  instant  of  combination ;  and  a 
like  effect,  though  in  a  far  less  degree,  is  produced  by  the  action  of  concentrated 
sulphuric  acid  on  pure  magnesia.  Most  of  these  and  similar  examples,  espe- 
cially when  one  of  the  combining  substances  is  gaseous,  are  frequently  included 
under  the  idea  of  combustion;  and  they  certainly  belong  to  the  same  class  of 
phenomena.  In  the  subsequent  observations,  however,  I  shall  employ  the  term 
in  its  ordinary  sense;  but  the  remarks  concerning  increase  of  temperature, 
whether  with  or  without  light,  apply  equally  to  all  cases  where  heat  is  developed 
as  a  result  of  chemical  action.* 

For  many  years  prior  to  the  discovery  of  oxygen  gas,  the  phenomena  of  com- 
bustion were  explained  on  the  Stahlian  or  phlogistic  hypothesis.  All  combus- 
tible bodies,  according  to  Stahl,  contain  a  certain  principle  which  he  called  phlo- 
giston^  to  the  presence  of  which  he  ascribed  their  combustibility.  He  supposed 
that  when  a  body  burns,  phlogiston  escapes  from  it ;  and  that  when  the  body 
has  lost  phlogiston,  it  ceases  to  be  combustible,  and  is  then  a  dephlogisticated 
or  incombustible  substance.  A  metallic  oxide  was  consequently  regarded  as  a 
simple  substance,  and  the  metal  itself  as  a  compound  of  its  oxide  with  phlogiston. 
The  heat  and  light  which  accompany  combustion,  were  attributed  to  the  rapidity 
with  which  phlogiston  is  evolved  during  the  process. 

The  discovery  of  oxygen  proved  fatal  to  the  Stahlian  doctrine.  Lavoisier  had 
the  honour  of  overthrowing  it,  and  of  substituting  in  its  place  the  antiphlogistic 
theory.  The  basis  of  his  doctrine  has  already  been  stated, — that  combustion  and 
oxidation  in  general  consist  in  the  combination  of  combustible  matter  with  oxy- 
gen. This  fact  he  established  beyond  a  doubt.  On  burning  phosphorus  in  a  jar 
of  oxygen,  he  observed  that  a  considerable  quantity  of  the  gas  disappeared,  that 
the  phosphorus  gained  materially  in  weight,  and  that  the  increase  of  the  latter 
exactly  corresponded  to  the  loss  of  the  former.  An  iron  wire  was  burnt  in  a 
similar  manner,  and  the  weight  of  the  oxidized  iron  was  found  equal  to  that  of 
the  wire  originally  employed,  added  to  the  quantity  of  oxygen  which  had  disap- 
peared. That  the  oxygen  is  really  present  in  the  oxidized  body  he  proved  by  a 
very  decisive  experiment.     Some  liquid  mercury  was  confined  in  a  vessel  of 

*  In  its  comprehensive  sense,  the  term  comhustion  is  applied  by  chemists  to  all  cases  of 
chemical  combination  accompanied  by  the  evolution  of  heat  and  light.    (R.) 


OXYGEN.  155 

oxygen  gas,  and  exposed  to  a  temperature  sujQGicient  for  causing  its  oxidation. 
The  oxide  of  mercury,  so  produced,  was  put  into  a  small  retort  and  heated  to 
redness,  when  it  was  reconverted  into  oxygen  and  fluid  mercury,  the  quantity  of 
the  oxygen  being  exactly  equal  to  that  which  had  combined  with  the  mercury  in 
the  first  part  of  the  operation. 

To  account  for  the  production  of  heat  and  light  during  combustion,  Lavoisier 
had  recourse  to  Black's  Theory  of  latent  heat.     Heat  is  always  evolved  when  a 
substance,  without  change  of  form,  passes  from  a  rarer  into  a  denser  state,  and 
also  when  a  gas  becomes  liquid  or  solid,  or  a  liquid  solidifies  ;  because  a  quan- 
tity of  heat  previously  combined,  or  latent,  within  it,  is  then  set  free.     Now  this 
is  precisely  what  happens  in  many  instances  of  combustion.     Thus  water  is 
formed  by  the  burning  of  hydrogen,  in  which  case  two  gases  give  rise  to  a  liquid; 
and  in  forming  phosphoric  acid  with  phosphorus,  or  in  oxidizing  metals,  oxygeiu 
is  condensed  into  a  solid.    When  the  product  of  combustion  is  gaseous,  as  in  tKe^ 
burning  of  charcoal,  the  evolution  of  heat  is  ascribed  to  the  circumstance  that  the    v 
oxidized  body  contains  a  smaller  quantity  of  combined  heat,  or  has  a  smaller  sp.      ' 
heat,  than  the  substances  by  which  it  is  produce^. 

This  is  the  weak  point  of  Lavoisier's  theory.  Chemical  action  is  very  often 
accompanied  by  increase  of  temperature,  and  the  heat  evolved  during  combustion 
is  only  a  particular  instance  of  it.  Any  theory,  therefore,  by  which  it  is  proposed 
to  account  for  the  production  of  heat  in  some  cases,  ought  to  be  applicable  to  all. 
When  combustion,  or  any  other  chemical  action,  is  followed  by  considerable 
condensation,  in  consequence  of  which  the  new  bcfdy  contains  less  insensible  heat 
than  its  elements  did  before  combination,  it  is  obvious  that  heat  will,  in  that  case, 
be  disengaged.  But  if  this  were  the  sole  cause  of  the  phenomenon,  a  rise  of 
temperature  should  always  be  preceded  by  a  corresponding  diminution  of  sp. 
heat,  and  the  extent  of  the  former  ought  to  be  in  a  constant  ratio  with  the  degree 
of  the  latter.  Now  Petit  and  Dulong  infer  from  their  researches  on  this  subject 
(Aii.  de  Ch.  et  Ph.  x.),  that  the  degree  of  heat  developed  during  combination, 
bears  no  relation  to  the  sp.  heat  of  the  combining  substances ;  and  that  in  the 
majority  of  cases,  the  evolution  of  heat  is  not  attended  by  any  diminution  in  the 
sp.  heat  of  the  compound.  It  is  a  well-known  fact,  that  increase  of  temperature 
frequently  attends  chemical  action,  though  the  products  contain  much  more  in- 
sensible heat  than  the  substances  from  which  they  were  formed.  This  happens 
remarkably  in  the  explosion  of  gunpowder,  which  is  attended  by  intense  heat ; 
and  yet  its  materials,  in  passing  from  the  solid  to  the  gaseous  state,  expand  to 
at  least  250  times  their  volume,  and  consequently  render  latent  a  large  quantity 
of  heat. 

These  circumstances  leave  no  doubt  that  the  evolution  of  heat  during  chemical 
action  is  owing  to  some  cause  quite  unconnected  with  that  assigned  by  Lavoisier; 
and  if  this  cause  operates  so  powerfully  in  some  cases,  it  is  fair  to  infer  that  part 
of  the  effect  must  be  owing  to  it  on  those  occasions,  when  the  phenomena  appear 
to  depend  on  change  of  sp.  heat  alone.  A  new  theory  is  therefore  required  to 
account  for  the  chemical  production  of  heat.  But  it  is  easier  to  perceive  the 
fallacies  of  one  doctrine,  than  to  substitute  another  which  shall  be  faultless ;  and 
it  appears  to  me  that  chemists  must,  for  the  present,  be  satisfied  with  the  simple 
statement,  that  energetic  chemical  action  does  of  itself  give  rise  to  increase  of 
temperature.  Bemelius,  in  adopting  the  electro-chemical  theory,  regards  the 
heat  of  combination  as  an  electrical  phenomenon,  believing  it  to  arise  from  the 
oppositely  electrical  substances  neutralizing  one  another,  in  the  same  manner  as 


1^  HYDROGEN. 

the  electric  equilibrium  is  restored  during  the  discharge  of  a  Leyden  jar.  Elec- 
trical action  certainly  appears  to  be  an  essential  part  of  every  chemical  change, 
and  it  is  probable  that  the  heat  developed  during  the  latter  may  be  due  to  the 
former ;  but  this  part  of  science  is  as  yet  too  imperfect  for  indicating  the  precise 
mode  by  which  the  effect  is  produced. 

The  heat  emitted  during  combustion  varies  with  the  nature  of  the  material. 
The  effect  of  the  combustible  gases  in  raising  the  temperature  of  water,  accord- 
ing to  the  experiments  of  Dalton,  is  shown  in  the  following  table. — (Chemical 
Philosophy,  ii.  309.) 

Hydrogen,  in  burning,  raises  an  equal  volume  of  water  .  .  5°  F. 

Carbonic  oxide  ........       4^ 

Light  carburetted  hydrogen        ......  18 

defiant  gas  ........      27 

Coal  gas,  varies  with  the  quality  of  the  gas  from  .  .  10  to  16 

Oil  gas,  varies  also  with  the  quality  of  the  gas  from  .  .        12  to  20 

Dalton  further  states  that  generally  the  combustible  gases  give  out  heat  nearly 
in  proportion  to  the  oxygen  which  they  consume. 

Despretz  has  given  a  notice  of  some  experiments  on  the  heat  developed  in 
combustion  (An.  de  Ch.  et  Ph.  xxxvii.  180).  The  substances  burned  were  hy- 
drogen, carbon,  phosphorus,  and  several  metals ;  and  so  much  of  each  was  em- 
ployed as  to  require  the  same  quantity  of  oxygen.  When  the  combustion  of 
hydrogen  gas  produced  2578  degrees  of  heat,  carbon  gave  out  2967,  and  iron 
5325.  Phosphorus,  zinc,  and  tin,  emit  quantities  of  heat  very  nearly  the  same 
as  iron.  Hence  it  follows  that,  for  equal  quantities  of  oxygen,  hydrogen  in 
burning  evolves  less  heat  than  most  other  substances.  These  results  do  not  accord 
with  those  of  Dalton. 


SECTION  IV. 


HYDROGEN. 


Hht. — First  correctly  described  in  1766  by  Cavendish  (Phil.  Trans.  Ivi.  144), 
under  the  name  of  inflammable  air.  It  had  been  previously  confounded  with 
other  combustible  gases,  and  it  was  by  some  called  phlogiston^  from  the  notion 
that  it  is  the  matter  of  heat.  Its  present  name  is  derived  from  i-Sw^  water,  and 
yswasiv  to  generate. 

Prep. — Commonly  in  two  ways.  The  first  consists  in  passing  the  vapour  of 
water  over  metallic  iron  heated  to  redness.  This  is  done  by  putting  iron  wire 
into  a  gun-barrel  open  at  both  ends,  to  one  of  which  is  attached  a  retort  contain- 
ing pure  water,  and  to  the  other  a  bent  tube.  The  gun-barrel  is  placed  in  a  fur- 
nace, and  when  it  has  acquired  a  full  red  heat,  the  water  in  the  retort  is  made  to 
boil  briskly.  The  gas,  which  is  copiously  disengaged  as  soon  as  the  steam 
comes  in  contact  with  the  glowing  iron,  passes  along  the  bent  tube,  and  may  be 


HYDROGEN.  I57  , 

'f. 
collected  in  convenient  vessels,  by  dipping  the  free  extremity  of  the  tube  into  the  ^ 
water  of  a  pneumatic  trough.  The  second  and  more  convenient  method  consists  in 
putting  pieces  of  iron  or  zinc  into  dilute  sulphuric  acid,  formed  of  one  part  of  strong 
acid  and  four  or  five  of  water.  Zinc  is  generally  preferred.  The  hydrogen  ob- 
tained in  these  processes  is  not  absolutely  pure.  The  gas  evolved  during  the 
solution  of  iron  has  an  offensive  odour,  ascribed  by  Berzelius  to  the  presence  of 
a  volatile  oil,  which  may  be  almost  entirely  removed  by  transmitting  the  gas 
through  alcohol.  The  oil  appears  to  arise  from  some  compound  being  formed 
between  hydrogen  and  the  carbon  which  is  always  contained  even  in  the  purest 
kinds  of  common  iron ;  and  it  is  probable  that  a  little  carburetted  hydrogen  gas 
is  generated  at  the  same  time.  The  zinc  of  commerce  contains  sulphur,  and 
almost  always  traces  of  charcoal,  in  consequence  of  which  it  is  contaminated  with 
hydro-sulphuric  acid,  fend  probably  with  the  same  impurities,  though  in  a  less 
degree,  as  are  derived  from  iron.  A  little  metallic  zinc  is  also  contained  in  it, 
apparently  in  combination  with  hydrogen.  All  these  impurities,  carburetted 
hydrogen  excepted,  may  be  removed  by  passing  the  hydrogen  through  a  solution 
of  pure  potassa.  To  obtain  hydrogen  of  great  purity  distilled  zinc  should  be 
employed. 

Prop. — Colourless,  inodorous,  tasteless;  always  gaseous  when  uncombined; 
a  powerful  refractor  of  light;  the  lightest  body  in  nature;  and  hence  the  best 
material  for  filling  balloons.  From  its  extreme  lightness,  it  is  difficult  to  ascer- 
tain its  sp.  gr.  by  weighing,  because  the  presence  of  minute  quantities  of  com- 
mon air  or  watery  vapour  occasions  considerable  error.  By  the  table  of  sp. 
gravities  (page  140)  it  appears  that  hydrogen  gas  is  just  16  times  lighter  than 
oxygen,  an  inference  derived  from  the  composition  of  water  to  be  shortly  stated  : 
hence  100  C.  I.  60°  and  30  Bar.  should  weigh  J^  x  34-193  =  2-1371  grains, 
and  its  sp.  gr.  should  be  0*06896. 

It  is  neither  acid  nor  alkaline.  Water  dissolves  only  Ij  per  cent,  of  its 
volume.  It  cannot  support  respiration  :  death  ensues  from  deprivation  of  oxygen 
rather  than  from  any  noxious  quality  of  the  hydrogen,  since  an  atmosphere  com- 
posed of  a  due  proportion  of  oxygen  and  hydrogen  gases  may  be  respired  without 
inconvenience.  Nor  is  it  a  supporter  of  combustion ;  for  when  a  lighted  candle, 
fixed  on  wire,  is  passed  up  into  an  inverted  jar  full  of  hydrogen  gas,  the  light 
instantly  disappears. 

Hydrogen  gas  is  inflammable  in  an  eminent  degree,  though,  like  other  CTom- 
bustibles,  it  requires  the  aid  of  a  supporter  of  combustion,  burning  only  where 
it  is  in  contact  with  the  air.  Its  combustion,  when  conducted  in  this  manner, 
goes  on  tranquilly,  and  is  attended  with  a  yellowish  blue  flame  and  a  very  feeble 
light.  The  phenomena  are  different  when  the  hydrogen  is  previously  mixed  with 
a  due  quantity  of  air.  The  approach  of  flame  not  only  sets  fire  to  the  gas  near 
it,  but  the  whole  is  kindled  at  the  same  instant;  and  a  flash  of  light  passes 
through  the  mixture,  followed  by  a  violent  explosion.  The  best  proportion  for 
the  experiment  is  two  measures  of  hydrogen  to  five  or  six  of  air.  The  explosion 
is  far  more  violent  when  pure  oxygen  is  used  instead  of  atmospheric  air,  parti- 
cularly when  the  gases  are  mixed  together  in  the  ratio  of  one  measure  of  oxygen 
to  two  of  hydrogen. 

Oxygen  and  hydrogen  gases  cannot  combine  at  ordinary  temperatures,  and 
may,  therefore,  be  kept  in  a  state  of  mixture  without  even  gradual  combination 
taking  place  between  them.  Hydrogen  may  be  set  on  fire,  when  in  contact  with 
air  or  oxygen  gas,  by  flame,  by  a  solid  body  heated  to  bright  redness,  and  by 


158  HYDROGEN. 

the  electric  spark.  If  a  jet  of  hydrogen  gas  be  thrown  upon  recently  prepared 
spongy  platinum,  this  metal  almost  instantly  becomes  red  hot,  and  then  sets  fire 
to  the  gas,  a  discovery  which  was  made  in  the  year  1824,  by  Professor  Doebe- 
reiner,  of  Jena.  The  power  of  flame  and  electricity  in  causing  a  iwixture  of 
hydrogen  with  air  or  oxygen  gas  to  explode,  is  limited.  Mr.  Cavendish  found 
that  flame  occasions  a  very  feeble  explosion  when  the  hydrogen  is  mixed  with 
nine  times  its  bulk  of  air  ;  and  that  a  mixture  of  four  measures  of  hydrogen  with 
one  of  air  does  not  explode  at  all.  An  explosive  mixture  formed  of  two  measures 
of  hydrogen  and  one  of  oxygen  gas,  explodes  from  all  the  causes  above  enume- 
rated. Biot  found  that  sudden  and  violent  compression  likewise  causes  an  ex- 
plosion, apparently  from  the  heat  emitted  during  the  operation;  for  an  equal 
degree  of  condensation,  slowly  produced,  has  not  the  same  effect.  The  electric 
spark  ceases  to  cause  detonation  when  the  explosive  mi^xture  is  diluted  with 
twelve  times  its  volume  of  air,  fourteen  of  oxygen,  or  nine  of  hydrogen ;  or 
when  it  is  expanded  to  sixteen  times  its  bulk  by  diminished  pressure.  Spongy 
platinum  acts  just  as  rapidly  as  flame  or  the  electric  spark  in  producing  explo- 
sion, provided  the  gases  are  quite  pure,  and  mixed  in  the  exact  ratio  of  two  to 
one.*  Mr.  Faraday  finds  that  platinum  foil,  if  perfectly  clean,  produces  gradual, 
though  rather  rapid  combination  of  the  gases,  often  followed  by  explosion.  (Phil. 
Trans.  1834.) 

When  the  action  of  heat,  the  electric  spark,  and  spongy  platinum  no  longer 
cause  explosion,  a  silent  and  gradual  combination  between  the  gases  may  still 
be  occasioned  by  them.  Sir  H.  Davy  observed  that  oxygen  and  hydrogen 
gases  unite  slowly  with  one  another,  when  they  are  exposed  to  a  temperature 
above  the  boiling  point  of  mercury,  and  below  that  at  which  glass  begins  to 
appear  luminous  in  the  dark.  An  explosive  mixture,  diluted  with  airto  too 
great  a  degree  to  explode  by  electricity,  is  made  to  unite  silently  by  a  succes- 
sion of  electric  sparks.  Spongy  platinum  causes  them  to  unite  slowly,  though 
mixed  with  one  hundred  times  their  bulk  of  oxygen  gas. 

A  large  quantity  of  heat  is  evolved  during  the  combustion  of  hydrogen  gas. 
Lavoisier  concludes,  from  experiments  made  with  his  calorimeter,  (Elements, 
vol.  i.),  that  one  pound  of  hydrogen  occasions  as  much  heat  in  burning  as  is 
suflScient  to  melt  295*6  pounds  of  ice.  Dr.  Dal  ton  fixes  the  quuntity  of  ice  at 
320  pounds,  and  Dr.  Crawford  at  480.  The  most  intense  heat  that  can  be  pro- 
duced, is  caused  by  the  combustion  of  hydrogen  in  oxygen  gas.  Dr.  Hare,  of 
Philadelphia,  who  first  burned  hydrogen  for  this  purpose,  collected  the  gases  in 
separate  gas-holders,  from  which  a  stream  was  made  to  issue  through  tubes  com- 
municating with  each  other,  just  before  their  termination.  At  this  point,  the  jet 
of  the  mixed  gases  was  inflamed.  The  effect  of  the  combustion,  though  very 
great,  is  materially  increased  by  forcing  the  two  gases,  in  due  proportion,  into  a 
strong  metallic  vessel,  by  means  of  a  condensing  syringe,  and  setting  fire  to  a 
jet  of  the  mixture  as  it  issues.  An  apparatus  of  this  kind,  now  known  by  the 
name  of  the  oxy-hydrogen  blow-pipe,  was  contrived  by  Mr.  Newman,  and  em- 
ployed by  the  late  Professor  Clarke  in  his  experiments  on  the  fusion  of  refrac- 

*  For  a  variety  of  facts  respecting  the  causes  which  prevent  the  action  of  flame,  electri- 
city, and  platinum  in  producing  detonation,  the  reader  may  consult  the  Essay  of  M.  Grotthus 
in  the  Ann.  de  Chimie,  vol.  xxxii. ;  Sir  H.  Davy's  work  on  Flame  ;  Dr.  Henry's  Essay  in  the 
Philosophical  Transactions  for  1S24 ;  and  a  paper  by  myself  in  the  Edinburgh  Philosophical 
Journal  for  the  same  year. 


HYDROGEN.  159    ' 

tory  substances.  On  opening  a  stop-cock  which  confines  the  compressed  gases, 
a  jet  of  the  explosive  mixture  issues  with  force  through  a  small  blowpipe  tube, 
at  the  extremity  of  which  it  is  kindled.  In  this  state,  however,  the  apparatus 
should  never  be  used  ;  for  as  the  reservoir  is  itself  full  of  an  explosive  mixture, 
there  is  great  danger  of  the  flame  running  back  along  the  tube,  and  setting  fire 
to  the  whole  gas  at  once.  To  prevent  the  occurrence  of  such  an  accident,  which 
would  most  probably  prove  fatal  to  the  operator.  Professor  Gumming  proposed 
that  the  gas,  as  it  issues  from  the  reservoir,  should  be  made  to  pass  through  a 
cylinder  full  of  oil  or  water  before  reaching  the  point  at  which  it  is  to  burn ;  and 
Dr.  WoUaston  suggested  the  additional  precaution  of  fixing  successive  layers  of 
fine  wire  gauze  within  the  exit  tube,  each  of  which  would  be  capable  of  inter- 
cepting the  communication  of  flame.  A  modification  of  this  apparatus  has  been 
devised  by  Mr.  Gurney ;  but  both  his  and  Newman's  are  rendered  unnecessary 
by  the  safety-tube  lately  proposed  by  Mr.  Hemming.  It  consists  of  a  brass 
cylinder,  about  6  inches  long,  and  3-4ths  of  an»inch  wide,  filled  with  very  fine 
brass  wire,  in  length  equal  to  that  of  the  tube.  A  pointed  rod  of  metal,  l-8th  of  an 
inch  thick,  is  then  forcibly  inserted  through  thd  centre  of  the  bundle  of  wires  in 
the  tube,  so  as  to  wedge  them  tightly  together.  The  interstices  between  the  wires 
thus  constitute  very  fine  metallic  tubes,  the  conducting  power  of  which  is  so 
great  as  entirely  to  intercept  the  passage  of  flame.  The  mixed  gases  are  supplied 
from  a  common  bladder.  (Phil.  Mag.  3d  S.  i.  82.)  A  very  intense  heat  may 
be  safely  and  easily  procured  by  passing  a  jet  of  oxygen  gas  through  the  flame 
of  a  spirit  lamp,  as  proposed  by  the  late  Dr.  Marcet.  An  elegant  improvement 
on  this  principle  has  been  devised  by  Mr.  Daniell,  by  fixing  a  jet  for  conveying 
oxygen  within  another  jet  for  hydrogen  or  coal  gas,  so  that  a  current  of  oxygen 
may  be  introduced  into  the  middle  of  the  flame.  (Phil.  Mag.  ii.  57.  3d  Series.) 
The  heat  from  this  apparatus  is  quite  sufficient  for  most  purposes ;  and  it  may  be 
still  further  increased  by  causing  the  gases  to  pass  separately  through  heated  tubes, 
in  order  that  they  may  have  a  temperature  of  400°  or  500°  on  issuing  from  the 
jets. — On  this  principle  is  founded  the  patent  of  Mr.  Dunlop,  of  the  Carroi^  Iron 
Works,  for  increasing  the  temperature  of  blast  furnaces  :  the  air  which  supports 
the  combustion  is  previously  heated  by  transmission  through  iron  tubes  kept  at 
a  low  red  heat,  whereby  the  power  of  the  furnaces  is  surprisingly  increased,  and 
a  great  saving  in  fuel  and  time  is  accomplished. 
Its  eq.  is  =  1 ;  eq.  vol.  =  100  ;  Symb.  H.     Gompounds  with  oxygen : — 

By  Weight.  By  Volume. 

Hydrogen.        Oxygen.      Equiv.  Hyd.      Oxy. 

Water  (Protoxide  of  Hydrogen)        1  or  1  eq.  -f    8  or  1  eq.  =   9  100  50 

Peroxide  of  Hydrogen  1  or  1  eq.  -j-  16  or  2  eq.  =  17  100        100 

Water. — ^First  proved  by  Gavendish  to  be  the  sole  product  of  the  combustion 
of  hydrogen  gas.  He  demonstrated  it  by  burning  oxygen  and  hydrogen  gases 
in  a  dry  glass  vessel,  when  a  quantity  of  pure  water  was  generated,  exactly  equal 
in  weight  to  that  of  the  gases  which  had  disappeared.  This  experiment,  which 
is  the  synthetic  proof  of  the  composition  of  water,  was  afterwards  made  on  a 
much  larger  scale  in  Paris  by  Vauquelin,  Fourcroy,  and  Seguin.  Lavoisier  first 
demonstrated  its  nature  analytically,  by  passing  a  known  quantity  of  watery 
vapour  over  metallic  iron  heated  to  redness  in  a  glass  tube.  Hydrogen  gas  was 
disengaged,  the  metal  in  the  tube  was  oxidized,  and  the  weight  of  the  former, 


160  HYDROGEN. 

added  to  the  increase  which  the  iron  had  experienced  from  combining  with  oxy 
gen,  exactly  corresponded  to  the  quantity  of  water  decomposed. 

Its  composition  by  volume  was  demonstrated  very  satisfactorily  by  Nicholson 
and  Carlisle:  by  resolving  water  into  its  elements  by  galvanism,  and  collecting 
them  in  separate  vessels,  they  obtained  precisely  two  measures  of  hydrogen  and 
one  of  oxygen, — a  result  which  has  been  fully  confirmed  by  subsequent  experi- 
menters. The  same  fact  was  proved  synthetically  by  Gay-Lussac  and  Humboldt, 
in  their  Essay  on  Eudiometry,  published  in  the  Journal  de  Physique  for  1805. 
They  found  that  when  a  mixture  of  oxygen  and  hydrogen  is  inflamed  by  the 
electric  spark,  those  gases  always  unite  in  the  exact  ratio  of  one  to  two,  whatever 
may  be  their  relative  quantity  in  the  mixture.  "When  one  measure  of  oxygen  is 
mixed  with  three  of  hydrogen,  one  measure  of  hydrogen  remains  after  the  explo- 
sion ;  and  a  mixture  of  two  measures  of  oxygen  and  two  of  hydrogen  leaves  one 
measure  of  oxygen.  When  one  volume  of  oxygen  is  mixed  with  two  of  hydro- 
gen, both  gases,  if  quite  pure,  disappear  entirely  on  the  electric  spark  being 
passed  through  them.  The  composition  of  water  by  weight  was  determined  with 
great  care  by  Berzelius  and  Dulong;  and  we  cannot  hesitate,  considering  the 
known  dexterity  of  the  operators,  and  the  principle  on  which  their  method  of 
analysis  was  founded,  to  regard  their  result  as  a  nearer  approximation  to  the  truth 
than  that  of  any  of  their  predecessors.  They  state,  as  a  mean  of  three  careful 
experiments  (Ann.  de  Ch.  et  Ph.  xv.),  that  100  parts  of  pure  water  consist  of 
ll'l  of  hydrogen,  and  88*9  oxygen,  which  is  the  ratio  of  1  to  8*009,  very  nearly 
that  of  1  to  8  above  stated. 

The  processes  for  procuring  a  supply  of  hydrogen  gas  will  now  be  intelligible. 
The  first  is  the  method  by  which  Lavoisier  made  the  analysis  of  water.  It  is 
founded  on  the  fact  that  iron  at  a  red  heat  decomposes  water,  the  oxygen  of  that 
liquid  uniting  with  the  metal,  and  the  hydrogen  gas  being  set  free.  That  the 
hydrogen  which  is  evolved  when  zinc  or  iron  is  put  into  dilute  sulphuric  acid 
must  be  derived  from  the  same  source,  is  obvious  from  the  consideration,  that  of 
the  three  substances,  iron,  sulphuric  acid,  and  water,  the  last  is  the  only  one 
which  contains  hydrogen.  The  product  of  the  operation,  besides  hydrogen,  is 
sulphate  of  the  protoxide  of  iron,  if  iron  is  used,  or  of  the  oxide  of  zinc,  when 
zinc  is  employed,  according  to  the  following  equation ;  HO  -f-  SO3  -|-  Fe,=  FeO 
-f-  SO3  -f-  H.  The  knowledge  of  the  combining  proportions  of  these  substances 
will  readily  give  the  exact  quantity  of  each  product.    These  numbers  are — 

Water  (8  oxy.  -|-  1  hyd.) 9 

Sulphuric  acid  .  .  .  .  .  .  .40-1 

Iron  ........  28 

Protoxide  of  Iron  (28  iron  -j-  8  oxygen)  .  .  .  .36 

Sulphate  of  the  protoxide  of  iron  (40-1  -f- 36).      .  .  .  76-1 

Hence  for  every  9  grains  of  water  which  are  decomposed,  1  grain  of  hydrogen 
will  be  set  free ;  8  grains  of  oxygen  will  unite  with  28  grains  of  iron,  forming 
36  of  the  protoxide  of  iron;  and  the  36  grains  of  protoxide  will  combine  with 
40-1  grains  of  sulphuric  acid,  yielding  76*1  of  sulphate  of  the  protoxide  of  iron. 
A  similar  calculation  maybe  employed  when  zinc  is  used,  merely  by  substituting 
the  equivalent  of  zinc  (32*5)  for  that  of  iron. — According  to  Mr.  Cavendish,  an 
ounce  of  zinc  yields  676  cubic  inches,  and  an  equal  quantity  of  iron  783  cubic 
inches  of  hydrogen  gas. 


HYDROGEN.  161 

The  action  of  dilute  sulphuric  acid  on  metallic  zinc  affords  an  instance  of  what 
was  once  called  Disposing  Jlffmity.  Zmc  decomposes  pure  water  at  common 
temperatures  with  extreme  slowness  ;  but  as  soon  as  sulphuric  acid  is  added, 
decomposition  of  the  water  takes  place  rapidly,  though  the  acid  merely  unites 
with  oxide  of  zinc.  The  former  explanation  was,  that  the  affinity  of  the  acid  for 
oxide  of  zinc  disposed  the  metal  to  unite  with  oxygen,  and  thus  enabled  it  to 
decompose  water;  that  is,  the  oxide  of  zinc  was  supposed  to  produce  an  effect 
previous  to  its  existence.  The  obscurity  of  this  explanation  arises  from  regard- 
ing changes  as  consecutive,  which  are  in  reality  simultaneous.  There  is  no 
succession  in  the  process  ;  the  oxide  of  zinc  is  not  formed  previously  to  its  com- 
bination with  the  acid,  but  at  the  same  instant.  There  is,  as  it  were,  but  one 
chemical  change,  which  consists  in  the  combination  at  one  and  the  same  moment 
of  zinc  with  oxygen,  and  of  oxide  of  zinc  with  the  acid;  and  this  change  occurs 
because  these  two  affinities,  acting  together,  overcome  the  attraction  of  oxygen 
and  hydrogen  for  one  another.* 

Frop, — Transparent,  colourless,  inodorous,  tasteless;  powerful  refractor  of 
light;  imperfect  conductor  of  heat  and  electricity;  very  incompressible,  its  abso- 
lute diminution  for  a  pressure  of  one  atmosphere  being  only  51*3  millionths  of 
its  volume.  (An.  de  Ch.  et  Ph.  xxxvi.  140.)  Its  changes  of  form  under  vary- 
ing temperatures  have  been  already  stated  in  the  section  on  heat.  Its  sp.  gr.  is 
1,  being  the  unit  to  which  the  sp.  gr.  of  all  solids  and  liquids  is  referred  as  a 
convenient  term  of  comparison.  One  cubic  inch,  at  63°  and  30  Bar.,  weighs 
252-458  grains.  It  is  815  times  heavier  than  atmospheric  air.  The  sp.  gr.  of 
aqueous  vapour  is  0*6202,  and  100  C.  I.  (containing  100  hydrogen  and  50  oxy- 
gen), at  212°  and  30  Bar.,  weigh  14*96  grains;  sp.  gr.  of  ice  is  0*92. 

Owing  partly  to  the  extensive  range  of  its  own  affinity,  and  partly  to  the  nature 
of  its  elements,  water  is  a  chemical  agent  of  great  power.  Of  this,  the  prepa- 
ration of  hydrogen  gas  is  an  example;  and  indeed  there  are  few  complex  changes, 
where  oxygen  and  hydrogen  are  present,  which  do  not  give  rise  either  to  the 
production  or  decomposition  of  water.  But,  independently  of  the  elements  of 
which  it  is  composed,  it  combines  directly  with  many  bodies.  Sometimes  it  is 
contained  in  a  variable  ratio,  as  in  ordinary  solution  ;  in  other  compounds  it  is 
present  in  a  fixed  definite  proportion,  as  is  exemplified  by  its  union  with  several 
of  the  acids,  the  alkalies,  and  all  salts  that  contain  water  of  crystallization. 
These  combinations  are  termed  hydrates.  Thus,  concentrated  sulphuric  acid  is  a 
compound  of  one  eq.  of  the  real  acid  and  one  eq.  of  water ;  and  its  proper  name 
is  hydrous  sulphuric  acid,,  or  hydrate  of  sulphuric  acid.  The  prefix  hydro  has  been 
sometimes  used  to  signify  the  presence  of  water  in  definite  proportion ;  but  it  is 
advisable,  to  prevent  mistakes,  to  limit  its  employment  to  the  compounds  of 
hydrogen. 

[Of  late  the  investigations  of  chemists  have  shown  that  in  relation  to  chemical 
compounds  water  performs  at  least  4  functions.  1st.  That  of  a  feeble  acid  when 
in  combination  with  a  base  to  which  the  term  hydrate  is  more  properly  restricted. 
2d.  In  combination  with  acids  acting  as  a  base  forming  basic  water,,  as  in  the 

*  Most  chemists  now  regard  this  case  as  simply  one  oi' substitution,  in  which  the  hydrogen 
of  that  portion  of  water  which  is  intimately  combined  with  the  acid,  is  replaced  by  a  metallic 
body,  performing  the  same  function.  HO,  SO3  becoming,  by  the  substitution  of  zinc  for  the 
hydrogen  ZnO,  SO3.  The  large  quantity  of  water  present  is  useful  to  dissolve  the  sulphate 
of  zinc  as  it  is  formed.     (R.) 

13 


162  HYDROGEN. 

so  called  hydrated  acids.  3d.  In  a  neutral  state,  as  a  necessary  constituent  of 
certain  neutral  salts,  and  mutually  replaceable  in  such  salts  by  another  neutral 
salt,  and  called  saline  or  constitutional  water.  4.  In  feeble  union  with  neu- 
tral salts,  and  easily  expelled  by  heat,  the  salt  thereby  losing  its  crystalline 
form  and  falling  into  powder;  in  this  state  called  water  of  crystallization.  For 
a  full  exposition  of  this  subject  see  chapter  on  salts.] 

The  purest  water  which  can  be  found  as  a  natural  product,  is  procured  by 
melting  freshly  fallen  snow,  or  by  receiving  rain  in  clean  vessels  at  a  distance 
from  houses.  But  this  water  is  not  absolutely  pure ;  for  if  placed  under  the  ex- 
hausted receiver  of  an  air-pump,  or  boiled  briskly  for  a  few  minutes,  bubbles  of 
gas  escape  from  it.  The  air  obtained  in  this  way  from  snow  water  is  much 
richer  than  atmespheric  air  in  oxygen  gas.  According  to  Gay-Lussac  and  Hum- 
boldt it  contains  34"8  per  cent,  of  oxygen,  and  the  air  separated  by  ebullition 
from  rain  water  contains  32  per  cent.  All  water  which  has  once  fallen  on  the 
ground  becomes  impregnated  with  more  or  less  earthy  or  saline  matters,  and  can 
be  separated  from  them  only  by  distillation.  The  distilled  water,  thus  obtained, 
and  preserved  in  clean  well-stopped  bottles,  is  absolutely  pure.  Recently  boiled 
water  has  the  property  of  absorbing  a  portion  of  all  gases,  when  its  surface  is  in 
contact  with  them  ;  and  the  absorption  is  promoted  by  brisk  agitation.  The  fol- 
lowing table,  from  Henry's  chemistry,  shows  the  absorbability  of  different  gases 
by  water,  deprived  of  all  its  air  by  ebullition. 

100  C.  I.  water,  at  60°  and  30  Bar.,  absorb  of 


Dalton  and  Henry. 

Saussure 

Sulphuretted  hydrogen 

100  C.  I. 

253 

Carbonic  acid 

.      100 

106 

Nitrous  oxide 

100 

76 

defiant  gas 

12-5 

15.3 

Oxygen 

3-7 

6-5 

Carbonic  oxide 

1-56 

6-2 

Nitrogen 

1-56 

4-1 

Hydrogen 

1-56 

4-6 

The  estimate  of  Saussure  is  in  general  too  high.  That  of  Dalton  and  Henry 
for  nitrous  oxide,  according  to  the  experiments  of  Davy,  is  considerably  beyond 
the  truth. 

Its  eq.  is  =9;  eq.  vol.  100;  symb.  H  -[-  0,  or  HO,  or  H,  or  aq.  from  aqua. 

Peroxide  or  Binoxide. — Discovered  by  Thenard  in  1818.  Its  preparation  is 
founded  on  the  fact  that  there  are  two  oxides  of  barium,  the  peroxide  and  pro- 
toxide, the  former  of  which  is  converted  into  the  protoxide  by  the  action  of  acids. 
When  this  process  is  conducted  with  the  necessary  precautions,  the  oxygen 
which  is  set  free,  instead  of  escaping  in  the  form  of  gas,  unites  with  the  hydro- 
gen of  the  water,  and  brings  it  to  a  maximum  of  oxidation.  For  a  full  detail  of 
all  the  minutiae  of  the  process,  the  reader  may  consult  the  original  memoir  of 
Thenard  ;*  the  general  directions  are  the  following: — To  six  or  seven  ounces  of 
water  add  so  much  pure  concentrated  hydrochloric  acid  as  is  sufficient  to  dissolve 
230  grains  of  baryta;  and  after  having  placed  the  mixed  fluids  in  a  glass  vessel 
surrounded  with  ice,  add  in  successive  portions  185  grains  of  peroxide  of  barium 

*  In  the  An.  de  Chim.  et  de  Phys.  vol.  viii.  ix.  x.  and  1.;  Annals  of  Philosophy,  vol.  xiii. 
and  xiv. ;  and  M.  Thenard's  Traite  de  Chimie. 


HYDROGEN.  163 

rednced  to  powder,  and  stir  with  a  glass  rod  after  each  addition.  When  the  solu- 
tion, which  takes  place  without  effervescence,  is  complete,  sulphuric  acid  is 
added  in  sufficient  quantity  for  precipitating  the  whole  of  the  baryta  in  the  form 
of  an  insoluble  sulphate,  leaving  the  hydrochloric  acid  in  solution.  Another  por- 
tion of  peroxide  of  barium,  amounting  to  185  grains,  is  then  put  into  the  liquid  : 
the  free  hydrochloric  acid  instantly  acts  upon  it,  and  as  soon  as  it  is  dissolved, 
the  baryta  is  again  separated  as  a  sulphate  by  the  addition  of  sulphuric  acid. 
The  solution  is  then  filtered,  in  order  to  separate  the  insoluble  sulphate  of  baryta  ; 
and  fresh  quantities  of  peroxide  of  barium  are  added  in  succession,  till  about  three 
ounces  have  been  employed.  The  liquid  then  contains  from  25  to  30  times  its 
volume  of  oxygen  gas.  The  hydrochloric  acid  which  has  served  to  decompose 
the  peroxide  of  barium  during  the  whole  process,  is  now  removed  by  the  cautious 
addition  of  sulphate  of  oxide  of  silver,  and  tHfe  sulphuric  acid  afrerwards  sepa- 
rated by  solid  baryta. 

[M.  Pelouse  proposes  a  much  easier  process  for  the  preparation  of  this 
compound.  This  consists  in  substituting  hydrofluoric  acid  or  fluosilicic  acid  for 
hydrochloric  to  decompose  the  peroxide  of  barium.  By  this  means  the  baryta 
is  deposited  as  an  insoluble  fluoride  of  barium,  and  the  peroxide  of  hydrogen 
remains  dissolved  in  the  water.  The  change  is  thus  simply  expressed. 
HF  t  Ba02  =  BaF  +  HO,.] 

Peroxide  of  hydrogen,  as  thus  prepared,  is  still  diluted  with  a  considerable 
quantity  of  M'ater.  To  separate  the  latter,  the  mixed  liquids  are  placed,  with  a 
vessel  of  strong  sulphuric  acid,  under  the  exhausted  receiver  of  an  air-pump.  As 
the  water  evaporates,  the  density  of  the  residue  increases,  till  at  last  it  acquires 
the  sp.  gr.  of  1*452.  The  concentration  cannot  be  pushed  further;  for  if  kept 
under  the  receiver  after  reaching  this  point,  the  peroxide  itself  gradually  but 
slowly  volatilizes  without  change. 

Prop. — A  colourless,  transparent  liquid,  inodorous,  and  of  a  metallic  taste ; 
volatilizes  in  vacuo  less  rapidly  than  water;  retains  its  liquid  form  at  all  degrees 
of  cold  to  which  it  has  been  exposed  ;  at  59°  is  resolved  into  oxygen  and  water, 
and  hence  should  be  always  kept  in  glass  tubes  surrounded  by  ice.  It  inter- 
mixes with  water  in  all  proportions  ;  bleaches  litmus  and  turmeric  paper,  whitens 
the  skin  and  tongue,  causing  to  both  a  pricking  sensation,  and  thickens  the 
saliva.  The  most  remarkable  of  its  properties  is  its  facility  of  decomposition. 
Diffused  daylight  does  not  seem  to  exert  any  influence  over  it,  and  even  the 
direct  solar  rays  act  upon  it  tardily.  It  effervesces  from  escape  of  oxygen  at  59°, 
and  the  sudden  application  of  a  higher  temperature,  as  that  of  212°,  gives  rise  to 
such  rapid  evolution  of  gas  as  to  cause  an  explosion.  Water,  apparently  by  com- 
bining with  the  peroxide,  renders  it  more  permanent ;  but  no  degree  of  dilution 
can  enable  it  to  bear  the  heat  of  boiling  water,  at  which  temperature  it  is  entirely 
decomposed.  All  the  metals  except  iron,  tin,  antimony,  and  tellurium,  have  a 
tendency  to  decompose  it,  converting  it  into  oxygen  and  water.  A  state  of 
minute  mechanical  division  is  essential  for  producing  rapid  decomposition.  If 
the  metal  is  in  mass,  and  the  peroxide  diluted  with  water,  the  action  is  slow. 
The  metals  which  have  a  strong  affinity  for  oxygen  are  oxidized  at  the  same 
time,  such  as  potassium,  sodium,  arsenic,  molybdenum,  manganese,  zinc,  tung- 
sten, and  chromium,  while  others,  such  as  gold,  silver,  platinum,  iridium, 
osmium,  rhodium,  palladium,  and  mercury,  retain  the  metallic  state. 

It  is  decomposed  at  common  temperatures  by  many  of  the  metallic  oxides. 
That  some  protoxides  should  have  this  effect,  would  be  anticipated  in  conse- 


164  HYDROGEN. 

quence  of  their  tendency  to  pass  into  a  higher  state  of  oxidation.  The  protoxides 
of  iron,  manganese,  tin,  cobalt,  and  others,  act  on  this  principle,  and  are  really 
converted  into  peroxides.  The  peroxides  of  barium,  strontium,  and  calcium  may 
likewise  be  formed  by  the  action  of  peroxide  of  hydrogen  on  baryta,  strontia,  and 
lime.  But  it  is  a  singular  fact,  of  which  no  satisfactory  explanation  has  been 
given,  that  some  oxides  decompose  it  without  passing  into  a  higher  degree  of 
oxidation.  The  peroxides  of  lead,  mercury,  gold,  platinum,  manganese,  and 
cobalt,  possess  this  property  in  the  greatest  perfection,  acting  on  peroxide  of 
hydrogen,  when  concentrated,  with  surprising  energy.  The  decomposition  is 
complete  and  instantaneous ;  oxygen  gas  is  evolved  so  rapidly  as  to  produce  a 
kind  of  explosion ;  and  such  intense  temperature  is  excited,  that  the  glass  tube 
in  which  the  experiment  is  conducted  becomes  red-hot.  The  reaction  is  very 
great  even  when  the  peroxide  of  hydrogen  is  diluted  with  water.  Oxide  of  silver 
occasions  very  perceptible  effervescence  when  put  into  water  which  contains  only 
l-60th  of  its  bulk  of  oxygen.  All  the  metallic  oxides,  which  are  decomposed  by 
a  red  heat,  such  as  those  of  gold,  platinum,  silver,  and  mercury,  are  reduced  to 
the  metallic  state  when  they  act  upon  peroxide  of  hydrogen.  This  effect  cannot 
be  altogether  ascribed  to  heat  disengaged  during  the  action ;  for  oxide  of  silver 
suffers  reduction  when  put  into  a  very  dilute  solution  of  the  peroxide,  although 
the  decomposition  is  not  then  attended  by  an  appreciable  rise  of  temperature. 

While  the  tendency  of  metals  and  metallic  oxides  is  to  decompose  the  perox- 
ide of  hydrogen,  acids  have  the  property  of  rendering  it  more  stable.     In  proof  of 
this,  let  a  portion  of  that  liquid,  somewhat  diluted  with  water,  be  heated  till  it 
begins  to  effervesce  from  the  escape  of  oxygen  gas ;  let  some  strong  acid,  as  the 
nitric,  sulphuric,  or  hydrochloric,  be  then  dropped  into  it,  and  the  effervescence 
will  cease  on  the  instant.     When  a  little  finely  divided  gold  is  put  into  a  weak 
solution  of  peroxide  of  hydrogen,  containing  only  10,  20,  or  30  times  its  bulk  of 
oxygen,  brisk  effervescence  ensues ;  but  on  letting  one  drop  of  sulphuric  acid 
fall  into  it,  effervescence  ceases  instantly ;  it  is  reproduced  by  the  addition  of 
potassa,  and  is  again  arrested  by  adding  a  second  portion  of  acid.     The  only 
acids  that  do  not  possess  this  property  are  those  that  have  a  low  degree  of  acid- 
ity, as  carbonic  and  boracic  acids  ;  or  those  which  suffer  a  chemical  change  when 
mixed  with  peroxide  of  hydrogen,  such  as  hydriodic,  hydrosulphuric,  and  sul- 
phurous acids.     Acids  appear  to  increase  the  stability  of  the  peroxide  in  the  same 
way  as  water  does,  namely,  by  combining  chemically  with  it.  Several  compounds 
of  tliis  kind  were  formed  by  Thenard,  before  he  was  aware  of  the  existence  of  the 
peroxide  of  hydrogen.     They  were  made  by  dissolving  peroxide  of  barium  in 
some  dilute  acid,  such  as  the  nitric,  and  then  precipitating  the  baryta  by  sul- 
phuric acid.     As  nitric  acid  was  supposed  under  these  circumstances  to  combine 
with  an  additional  quantity  of  oxygen,  Thenard  applied  the  term  oxygenized  nitric 
acid  to  the  resulting  compound,  and  described  several   other  new  acids  under  a 
similar  title.     But  the  subsequent  discovery  of  peroxide  of  hydrogen  put  the 
nature  of  the  oxygenized  acids  in  a  clearer  light ;  for  their  properties  are  easily 
explicable  on  the  supposition  that  they  are  composed,  not  of  acids  and  oxygen 
gas,  but  of  acids  united  with  peroxide  of  hydrogen. 

Peroxide  of  hydrogen  was  analysed  by  diluting  a  known  weight  of  it  with 
water,  and  then  decomposing  it  by  boiling  the  solution. 

7/8  eg.  is  =  17 ;  symb.  H  -\-  20,  or  flO^,  or  H. 


NITROGEN.  165 


SECTION  V. 


NITROGEN. 


Hist. — First  noticed  by  Rutherford  of  Edinburgh  in  1772.  Discovered  to  be 
a  constituent  of  the  atmosphere  by  Lavoisier  in  1775,  and  by  Scheele  about  the 
same  time.  It  was  termed  azote,  (a  privative,  and  ^«>;  /?Je,)  by  Lavoisier,  from 
its  inability  to  support  respiration.  The  name  of  nitrogen  is  derived  from  its 
being  an  element  of  nitric  acid. 

Prep. — 1 .  By  burning  a  piece  of  phosphorus  in  a  jar  full  of  air  inverted  over 
water.  The  strong  affinity  of  phosphorus  for  oxygen  enables  it  !o  burn  till  the 
whole  of  that  gas  is  consumed.  The  product  of  the  combustion,  metaphosphoric 
acid,  is  at  first  diffused  through  the  residue  in  the  form  of  a  white  cloud ;  but  as 
this  substance  is  rapidly  absorbed  by  water,  it  disappears  entirely  in  the  course 
of  half  an  hour.  The  residual  gas  is  nitrogen,  containing  a  small  quantity  of  car- 
bonic acid  and  vapour  of  phosphorus,  both  of  which  maybe  removed  by  agitating 
it  briskly  with  a  solution  of  pure  potassa.  Several  other  substances  may  be  em- 
ployed for  withdrawing  oxygen  from  atmospheric  air.  A  solution  of  protosul- 
phate  of  iron,  charged  with  binoxide  of  nitrogen,  absorbs  the  oxygen  in  the  space 
of  a  few  minutes.  A  stick  of  phosphorus  produces  the  same  effect  in  twenty- 
four  hours,  if  exposed  to  a  temperature  of  60°.  A  solution  of  sulphuret  of  potas- 
sium or  calcium  acts  in  a  similar  manner ;  and  a  mixture  of  equal  parts  of  iron 
filings  and  sulphur,  made  into  a  paste  with  water,  may  be  employed  with  the 
same  intention.  Both  these  processes,  however,  are  inconvenient  from  their 
slowness. — 2.  By  exposing  a  mixture  of  fresh  muscle  and  nitric  acid  of  sp.  gr. 
1*20  to  a  moderate  temperature.  Effervescence  then  takes  place,  and  a  large 
quantity  of  gaseous  matter  is  evolved,  which  is  nitrogen  mixed  with  a  little  car- 
bonic acid.  The  latter  must  be  removed  by  agitation  with  lime  water ;  but  the, 
residue  still  retains  a  peculiar  odour,  indicative  of  the  presence  of  some  volatile 
principle  which  cannot  be  wholly  separated  from  it.  The  theory  of  this  process 
is  somewhat  complex,  and  will  be  considered  more  conveniently  in  a  subsequent^ 
part  of  the  work.  3.  By  transmitting  chlorine  gas  through  a  solution  of  ammo- 
nia, when  that  alkali  yields  its  hydrogen  to  the  chlorine,  and  its  nitrogen  is 
evolved. 

Prop. — Colourless,  tasteless,  inodorous ;  always  gaseous  when  uncombined; 
sp.  gr.  0-9722,  so  that  100  C.I.  weigh  30.166  grains ;  no  action  on  the  blue  colour 
of  plants ;  water  dissolves  1  ^  per  cent.  It  is  distinguished  from  other  gases  more 
by  negative  characters  than  by  any  striking  quality.  It  is  not  a  supporter  of 
combustion;  but,  on  the  contrary,  extinguishes  all  burning  bodies  that  are  im- 
mersed in  it.  No  animal  can  live  in  it ;  but  yet  it  exerts  no  injurious  action  either 
on  the  lungs  or  on  the  system  at  large,  the  privation  of  oxygen  gas  being  the 
sole  cause  of  death.  It  is  not  inflammable  like  hydrogen;  though,  under  favour- 
able circumstances,  it  may  be  made  to  unite  with  oxygen. 


166  NITROGEN. 

Considerable  doubt  exists  as  to  the  nature  of  nitrogen.  Though  ranked  among  ' 
the  simple  non-metallic  bodies,  some  circumstances  have  led  to  the  suspicion 
that  it  is  compound  ;  and  this  opinion  has  been  warmly  advocated  by  Davy  and|fl 
Berzelius.  The  chief  argument  in  favour  of  this  view  is  drawn  from  the  pheno- 
mena that  attend  the  formation  of  what  is  called  the  ammoniacal  amalgam.  From 
the  metallic  appearance  of  this  substance,  it  was  supposed  to  be  a  compound  of 
mercury  and  a  metal ;  and  as  one  method  of  forming  it  is  by  the  action  of 
galvanism  on  a  salt  of  ammonia,  in  contact  with  a  globule  of  mercury,  it  follows 
that  the  metal,  if  present  at  all,  must  have  been  supplied  by  the  ammonia.  Now 
ammonia  is  composed  of  hydrogen  and  nitrogen  ;  and  as  the  former,  from  its  small 
sp.  gravity,  can  hardly  be  supposed  to  contain  a  metal,  it  was  inferred  that  it 
must  be  present  in  the  latter.  Unfortunately  for  this  argument,  the  supposed 
metal  cannot  be  obtained  in  a  separate  state.  The  amalgam  no  sooner  ceases  to 
be  under  galvanic  influence  than  its  elements  begin  to  separate  spontaneously, 
and  in  a  few  minutes  decomposition  is  complete,  the  sole  products  being  ammo- 
nia, hydrogen,  and  puremercury.  Davy  accounted  for  this  change  on  the  suppo- 
sition that  water  is  decomposed ;  that  its  oxygen  reproduces  nitrogen  by  uniting 
with  the  supposed  metal ;  and  that  one  part  of  its  hydrogen  forms  ammonia  by 
uniting  with  the  nitrogen,  while  the  remainder  escapes  in  the  form  of  gas.  But 
Gay-Lussac  and  Thenard  (Recherches  Physico-Chimiques,  vol.  i.)  declare  that 
the  amalgam  resolves  itself  into  mercury,  ammonia,  and  hydrogen,  even  though 
perfectly  free  from  moisture ;  and  they  infer  from  their  experiments  that  it  is 
composed  of  those  three  substances  combined  directly  with  each  other.  It  hence 
appears  that  the  examination  of  the  ammoniacal  amalgam  affords  no  proof  of  the 
compound  nature  of  nitrogen;  nor  was  D  a  vy's' attempt  to  decompose  that  gas  by 
aid  of  potassium,  intensely  heated  by  a  galvanic  current,  attended  with  better 
success. 

Its  eq.is  14-15  ;  eq.  vol.  =  100  ;  symb.  N. 

The  compounds  of  nitrogen  treated   of  in  this  section  are  the   following, 
exclusive  of  atmospheric  air,  which  is  regarded  as  a  mechanical  mixture  : — 

By  volume.  By  weight. 

Nit.        Oxy.        Nit.      Oxy.    Equiv.  Formulae. 


Nitrous  oxide 

100    . 

.      60 

14-15 -|-    8  =  22-15 

Nf    0 

Nitric  oxide 

100    , 

.     100 

14-15 -j-  16  =  30-15 

N  t20 

Hyponitrous  acid 

100     . 

,     150 

14- 16  -j-  24  =  38- 15 

N-h  30 

Nitrous  acid 

100 

.    200 

14-15-1-  32  =  46-15 

N-f  40 

Nitric  acid 

100     . 

,    250 

14-15-1- 40  =  45-15 

N-h50 

ON  THE  ATMOSPHERE. 

The  earth  is  everywhere  surrounded  by  a  mass  of  gaseous  matter  called  the 
atmosphere,  which  is  preserved  at  its  surface  by  the  force  of  gravity,  and  revolves 
together  with  it  around  the  sun.  It  is  colourless  and  invisible,  excites  neither 
taste  nor  smell  when  pure,  and  is  not  sensible  to  the  touch  unless  when  it  is  in 
motion.  It  possesses  the  physical  properties  of  elastic  fluids  in  a  high  degree. 
Its  sp.  gr.  is  imity,  being  the  standard  with  which  the  density  of  all  gaseous 
substances  are  compared.  At  30  Bar.  and  32°  it  is  7G9-4  times  lighter  than 
water,  and  10462  than  mercury ;  or  at  62°,  815  times  lighter  than  water,  and 
nearly  11065  times  lighter  than  mercury.    The  knowledge  of  its  exact  weight  is 


NITROGEN.'  167 

an  essential  element  in  many  j)hysical  and   chemical  researches,  and  has  been 
determined  with  very  great  care  by  Prout,  who  finds  that  100  C.  I.  of  pure  and 
^dry  atmospheric  air,  at  60°  and  30  Bar.  weigh  31"0117  grains. 

The  pressure  of  the  atmosphere  was  first  noticed  early  in  the  17th  century  by 
Galileo,  and  was  afterwards  demonstrated  by  his  pupil  Torricelli,  to  whom 
science  is  indebted  for  the  invention  of  the  barometer.  Its  pressure  at  the  level 
of  the  sea  is  equal  to  a  weight  of  about  15  pounds  on  every  square  inch  of  sur- 
face, and  is  capable  of  supporting  a  column  of  water  34  feet  high,  and  one  of 
mercury  of  30  inches ;  that  is,  a  column  of  mercury  of  one  inch  square  and  30 
inches  long  has  the  same  weight  (nearly  15  pounds)  as  a  column  of  water  of 
equal  base  and  34  feet  long,  and  as  a  column  of  air  of  equal  base  reaching 
from  the  level  of  the  sea  to  the  extreme  limit  of  the  atmosphere.  By  the  use 
of  the  barometer  it  was  discovered  that  the  atmospheric  pressure  is  variable.  It 
varies  according  to  the  elevation  above  the  level  of  the  sea,  and  on  this  principle 
the  height  of  mountains  is  estimated.  Supposing  the  density  of  the  atmosphere 
to  be  uniform,  a  fall  of  one  inch  in  the  barometer  would  correspond  to  11065 
inches,  or  922  feet  of  air;  but  in  order  to  make  the  calculation  with  accuracy, 
allowance  must  be  made  for  the  increasing  rarity  of  the  air,  and  for  various  other 
circumstances  which  are  detailed  in  works  on  meteorology.  (Daniel's  Meteoro- 
logical Essays,  2nd  edit.  376.)  From  causes  at  present  not  understood,  the 
pressure  varies  likewise  at  the  same  place.  On  this  depends  the  indications  of 
the  barometer  as  a  weather-glass ;  for  observation  has  fully  proved,  that  the 
weather  is  commonly  fair  and  calm  when  the  barometer  is  high,  and  usually  wet 
and  stormy  when  the  mercury  falls. 

Atmospheric  air  is  highly  compressible  and  elastic,  so  that  its  particles  admit 
of  being  approximated  to  a  great  extent  by  compression,  and  expand  to  an 
extreme  degree  of  rarity,  when  the  tendency  of  its  particles  to  separate  is  not 
restrained  by  external  force.  The  volume  of  air  and  all  other  gaseous  fluids,  so 
long  as  they  retain  the  elastic  state,  is  inversely  as  the  pressure  to  which  they  are 
exposed.  Thus  a  portion  of  air  which  occupies  100  measures  when  compressed 
by  a  force  of  one  pound,  will  be  diminished  to  50  measures  when  the  pressure 
is  doubled,  and  will  expand  to  200  measures  when  the  compression  is  equal  to 
half  a  pound.  This  law  was  first  demonstrated  in  1662  by  the  celebrated  Boyle, 
and  a  second  demonstration  of  it  was  given  some  years  afterwards  by  the  French 
philosopher  Mariotte,  apparently  without  being  aware  that  the  discovery  had 
been  previously  made  in  England.  It  is  hence  frequently  called  the  law  of 
Mariotte.  Till  lately  it  had  not  been  verified  for  very  great  pressures ;  but  from 
the  experiments  of  Oersted  in  1825,  who  extended  his  observations  to  air  com- 
pressed by  a  force  equal  to  110  atmospheres,  it  maybe  inferred  to  be  quite 
general,  except  when  the  gaseous  matter  assumes  the  liquid  form.  (Ed.  Journal 
of  Science,  iv.  224.)  Gases  vary  from  this  law  when  they  approach  the  point 
at  which  they  assume  the  liquid  form.  At  what  pressure  air  becomes  liquid  is 
uncertain,  since  all  attempts  to  condense  it  have  hitherto  been  unsuccessful. 

The  extreme  compressibility  and  elasticity  of  the  air  accounts  for  the  facility 
with  which  it  is  set  in  motion,  and  the  velocity  with  which  it  is  capable  of  mov- 
ing. It  is  subject  to  the  laws  which  characterize  elastic  fluids  in  general.  It 
presses,  therefore,  equally  on  every  side ;  and  when  some  parts  of  it  become 
lighter  than  the  surrounding  portions,  the  denser  particles  rush  rapidly  into  their 
place  and  force  the  more  rarefied  ones  to  ascend.    The  motion  of  air  gives  rise 


mg  NITROGEN. 

to  varfou 8  familiar  phenomena.    A  stream  or  current   of  air  is  wind,  and  an 
undulating  vibration  excites  the  sensation  of  sound. 

The  atmosphere  is  not  of  equal  density  at  all  its  parts.  This  is  obvious,  from  jk,- 
the  consideration  that  those  portions  which  are  next  the  earth  sustain  the  whole 
pressure  of  the  atmosphere,  while  the  higher  strata  bear  only  a  part.  The 
atmospheric  column  diminishes  in  length  as  the  distance  from  the  earth's  sur- 
face increases;  and,  consequently,  the  greater  the  elevation,  the  lighter  must  be 
the  air.  It  is  not  known  to  what  height  the  atmosphere  extends.  From  calcu- 
lations founded  on  the  phenomena  of  refraction,  its  height  is  supposed  to  be 
about  45  miles;  and  Wollaston  estimated,  from  the  law  of  expansion  of  gases, 
that  it  must  extend  to  at  least  40  miles  with  properties  unimpaired  by  rarefac- 
tion. In  speculating  on  its  extent  beyond  that  distance,  it  becomes  a  question 
whether  the  atmosphere  is  or  is  not  limited  to  the  earth.  This  subject  was  dis- 
cussed with  his  usual  sagacity  by  Wollaston  in  an  Essay  on  the  Finite  Extent 
of  the  Atmosphere  (Phil.  Trans.  1822).  Supposing  the  atmosphere  unlimited, 
it  should  pervade  all  space,"  and  accumulate  about  the  sun,  moon,  and  planets, 
forming  aroun(f  each  an  atmosphere,  the  density  of  which  would  depend  on  their 
respective  forces  of  attraction.  Now  Wollaston  inferred  from  astronomicai 
observations  made  by  himself  and  Kater,  that  there  is  no  solar  atmosphere ;  and 
the  observations  of  other  astronomers  appear  to  justify  the  same  inference  with 
respect  to  the  planet  Jupiter.  If  the  accuracy  of  these  conclusions  be  admitted, 
it  follows  that  our  atmosphere  is  confined  to  the  earth  ;  and  it  may  next  be  asked, 
by  what  means  is  its  extent  limited  ]  Wollaston  accounted  for  it  by  supposing 
the  air,  after  attaining  a  certain  degree  of  rarefaction,  to  possess  such  feeble 
elasticity,  that  the  tendency  of  its  particles  to  separate  further  from  each  other 
is  counteracted  by  gravity.  The  unknown  height  at  which  this  equilibrium 
between  the  two  forces  of  elasticity  and  gravitation  takes  place,  is  the  extreme 
limit  of  the  atmosphere.  The  loss  of  elasticity  may  be  ascribed  to  two  power- 
ful and  concurring  causes  ;  namely,  to  the  distance  between  the  particles  of  air 
when  highly  rarefied,  and  to  the  extreme  cold  which  prevails  in  the  higher  strata 
of  the  atmosphere. 

The  temperature  of  the  atmosphere  varies  with  its  elevation.  Gaseous  fluids 
permit  radiant  matter  to  pass  freely  through  them  without  any  absorption,  and 
therefore  without  their  temperature  being  influenced  by  its  passage.  The  atmos- 
phere is  not  heated  by  transmitting  the  rays  of  the  sun,  but  receives  its  heat 
solely  from  the  earth,  and  chiefly  by  actual  contact;  so  that  its  temperature 
becomes  progressively  lower,  as  the  distance  from  the  general  mass  of  the  earth 
increases.  Another  circumstance  which  contributes  to  the  same  eflfect,  is  the 
increasing  tenuity  of  the  atmosphere;  for  the  temperature  of  rarefied  air  is  less 
raised  by  a  given  quantity  of  heat,  than  that  of  the  same  portion  of  air  when 
compressed,  owing  to  its  sp.  heat  being  greater  in  the  former  state  than  in  the 
latter.  From  the  joint  influence  of  both  these  causes  it  is  found  that,  in  ascend- 
ing into  the  atmosphere,  the  temperature  diminishes  at  the  rate  of  one  degree 
for  about  every  352  feet.  The  rate  of  decrease  is  probably  much  slower  at  con- 
siderable distances  from  the  earth  ;  but  still  there  is  no  reason  to  doubt  that  the 
temperature  continues  to  decrease  with  the  increasing  elevation.  There  must 
consequently,  in  every  latitude,  be  a  point  where  the  thermometer  never  rises 
above  32°,  and  where  ice  is  never  liquefied.  This  point  varies  with  the  latitude, 
being  highest  within  the  tropics,  and  descending  gradually  as  we  advance  towards 


NITROGEN. 


169 


the  poles.  The  following  table,  from  the  Supplement  to  the  Encyclopedia  Bri- 
tannica,  page  190,  article  Climate,  shows  the  point  of  perpetual  ice  correspond- 
ing to  different  latitudes  : — 


English  feet 

Latitude. 

English  feet 

in  height. 

in  height. 

15,207 

45°        .        .        . 

7,671 

15,095 

60°        .        .        . 

6,334 

14,764 

55°        .        .        . 

5,034 

14,220 

60°        .        .        . 

3,818 

13,478 

65°        .        .        . 

2,722 

12,557 

70° 

1,778 

11,484 

75°        .        .        . 

1,016 

10,287 

80°        .        .        . 

457 

9,001 

85°        .        .        . 

117 

r  elements  of 

the  ancient  philosophers,  an 

d  their  opi- 

Latitude. 

0° 

5° 
10° 
15» 
20° 
25° 
30° 
35° 
40° 


nion  of  its  nature  prevailed  generally,  till  its  accuracy  was  rendered  questionable 
by  the  experiments  of  Boyle,  Hooke,  and  Mayow.  The  discovery  of  oxygen 
gas  in  1774  paved  the  way  to  the  knowledge  of  its  real  composition,  which  was 
discovered  about  the  same  time  by  Scheele  and  Lavoisier.  The  former  exposed 
some  atmospheric  air  to  a  solution  of  sulphuret  of  potassium,  which  gradually 
absorbed  the  whole  of  the  oxygen.  Lavoisier  effected  the  same  object  by  the 
combustion  of  iron  wire  and  phosphorus. 

The  earlier  analyses  of  the  air  did  not  agree  very  well  with  each  other.  Ac- 
cording to  the  researches  of  Lavoisier,  it  is  composed  of  27  measures  of  oxygen 
and  73  of  nitrogen.  The  analysis  of  Scheele  gave  a  somewhat  higher  proportion 
of  oxygen.  Priestley  found  that  the  quantity  of  oxygen  varies  from  20  to  25  per 
cent. ;  and  Cavendish  estimated  it  only  at  20.  These  discrepancies  must  have 
arisen  from  imperfections  in  the  mode  of  analysis ;  for  the  proportion  of  oxygen 
has  been  found  by  subsequent  experiments  to  be  almost,  if  not  exactly,  that 
which  was  stated  by  Cavendish.  The  results  of  Scheele  and  Priestley  are  clearly 
referable  to  this  cause.  It  is  now  known  that  the  processes  they  employed  cannot 
be  relied  on,  unless  certain  precautions  are  taken  of  which  these  chemists  were 
ignorant.  Recently  boiled  water  absorbs  nitrogen  ;  and  consequently,  if  sul- 
phuret of  potassium  be  dissolved  in  that  liquid  by  the  aid  of  heat,  the  solution, 
when  agitated  with  air,  takes  up  a  portion  of  nitrogen,  and  thereby  renders  the 
apparent  absorption  of  oxygen  too  great.  This  inconvenience  may  be  avoided  by 
dissolving  the  sulphuret  in  cold  unboiled  water.  Binoxide  of  nitrogen,  employed 
by  Priestley,  removes  all  the  oxygen  in  the  course  of  a  few  seconds ;  but  for 
reasons  which  will  soon  be  mentioned,  its  indications  are  apt  to  be  fallacious. 
The  combustion  of  phosphorus,  as  well  as  the  gradual  oxidation  of  that  substance, 
acts  in  a  very  uniform  manner,  and  removes  the  whole  of  the  oxygen  completely. 
The  residual  nitrogen  contains  a  little  of  the  vapour  of  phosphorus,  which  in- 
creases the  bulk  of  that  gas  by  l-40th,  for  which  an  allowance  must  be  made  in 
estimating  the  real  quantity  of  nitrogen. 

Since  chemists  have  learned  the  precautions  to  be  taken  in  the  analysis  of  the 
air,  a  close  correspondence  has  been  observed  in  the  results  of  their  experiments 
upon  It.  The  researches  of  Davy,  Dalton,  Gay-Lussac,  Thomson,  and  others, 
leave  no  doubt  that  100  measures  of  pure  atmospheric  air  consist  of  20  or  21 
volumes  of  oxygen,  and  80  or  79  of  nitrogen.     The  most  approved  mode  of 


170  NITROGEN, 

analysis  consists  in  mixing  with  the  air  a  quantity  of  hydrogen  sufficient  to  con- 
vert all  the  oxygen  present  into  water,  and  kindling  the  mixture  by  the  electric 
spark.  The  combination  may  also  be  effected  without  detonation  by  means  of 
spongy  platinum.  Water  is  formed,  and  is  condensed;  and  since  that  liquid  is 
composed  of  one  volume  of  oxygen  and  two  of  hydrogen,  one-third  of  the  dimi- 
nution must  give  the  exact  quantity  of  oxygen.  This  process  is  so  easy  of  exe- 
cution, and  so  uniform  in  its  indications,  that  it  is  now  employed  nearly  to  the 
total  exclusion  of  all  others. 

Such  is  the  constitution  of  pure  atmospheric  air.  But  the  atmosphere  is  never 
absolutely  pure ;  for  it  always  contains  a  certain  variable  quantity  of  carbonic 
acid  and  watery  vapour,  besides  the  odoriferous  matter  of  flowers  and  other  vola- 
tile substances,  which  are  also  frequently  present.  Saussure  found  carbonic  acid 
in  air  collected  at  the  top  of  Mont  Blanc  ;  and  it  exists  at  all  altitudes  which  have 
been  hitherto  attained.  Saussure,  in  a  recent  essay,  states  the  proportion  of  this 
gas  to  vary  at  the  same  place  within  short  intervals  of  time.  It  is  greater  in 
summer  than  in  winter ;  and  from  observations  made  during  spring,  summer, 
and  autumn,  in  the  open  fields,  and  in  calm  weather,  its  proportion  is  inferred  to 
be  always  greater  at  night  than  in  the  day,  and  to  be  more  abundant  in  gloomy 
than  in  bright  weather.  A  very  moist  state  of  the  ground,  as  after  much  rain, 
diminishes  the  quantity  of  carbonic  acid,  apparently  by  direct  absorption.  It  is 
rather  more  abundant  in  elevated  situations,  as  on  the  summits  of  high  moun- 
tains, than  in  the  plains:  but  its  quantity  is  there  nearly  the  same  in  day  and 
night,  in  wet  and  dry  weather,  because  the  higher  strata  of  the  air  are  less  influ- 
enced by  vegetation,  and  the  state  of  the  soil.  Saussure  thinks  also  that  a  highly 
electrical  state  of  the  atmosphere  tends  to  diminish  the  quantity  of  carbonic 
acid.  He  found  that  10,000  parts  of  air  contain  4*9  of  carbonic  acid  as  a  mean, 
6*2  as  a  maximum,  and  3*7  as  a  minimum.  (An.  de  Ch.  et  Ph.  xxxviii.  411. 
xliv.  5.) 

The  chief  chemical  properties  of  the  atmosphere  are  owing  to  the  presence  of 
oxygen  gas.  Air  from  which  this  principle  has  been  withdrawn  is  nearly  inert. 
It  can  no  longer  support  respiration  and  combustion,  and  metals  are  not  oxidized 
by  being  heated  in  it.  Most  of  the  spontaneous  changes  which  mineral  and 
dead  organized  matters  undergo,  are  owing  to  the  powerful  affinities  of  oxygen. 
The  uses  of  the  nitrogen  are  in  a  great  measure  unknown.  It  was  supposed  to 
act  as  a  mere  diluent  to  the  oxygen ;  but  it  most  probably  serves  some  useful 
purpose  in  the  economy  of  animals,  the  exact  nature  of  which  has  not  been  dis- 
covered. 

The  knowledge  of  the  composition  of  the  air,  and  of  the  importance  of  oxygen 
to  the  life  of  animals,  naturally  gave  rise  to  the  notion  that  the  healthiness  of  the 
air,  at  different  times,  and  in  different  places,  depends  on  the  relative  quantity  of 
this  gas.  It  was  therefore  supposed  that  the  purity  of  the  atmosphere,  or  its 
fitness  for  communicating  health  and  vigour,  might  be  discovered  by  determining 
the  proportion  of  the  oxygen  ;  and  hence  the  origin  of  the  term  Eudiometer,  which 
was  applied  to  the  apparatus  for  analyzing  the  air.  But  this  opinion,  though  at 
first  supported  by  the  discordant  results  of  the  earlier  analysts,  was  soon  proved  to 
be  fallacious.  On  the  contrary,  the  composition  of  air  is  not  only  constant  in  the 
same  place,  but  is  the  same  in  all  regions  of  the  earth,  and  at  all  altitudes.  Air 
collected  at  the  summit  of  the  highest  mountains,  such  as  Mont  Blanc  and  Chim- 
borazo,  contains  the  same  proportion  of  oxygen  as  that  of  the  lowest  valleys. 
The  air  of  Egypt  was  found  by  Berthollet  to  be  similar  to  that  of  France.    The 


NITROGEN.  171 

air  which  Gay-Lussac  broug-ht  from  an  altitude  of  21,735  feet  above  the  earth,  had 
the  same  composition  as  that  collected  at  a  short  distance  from  its  surface.  Even 
the  miasms  of  marshes,  and  the  effluvia  of  infected  places,  owe  their  noxious 
qualities  to  some  principle  of  too  subtile  a  nature  to  be  detected  by  chemical 
means,  and  not  to  a  deficiency  of  oxygen.  Seguin  examined  the  infectious  atmo- 
sphere of  an  hospital,  the  odour  of  which  was  almost  intolerable,  and  could  dis- 
cover no  appreciable  deficiency  of  oxygen,  or  other  peculiarity  of  composition. 
-  The  question  has  been  much  discussed,  whether  the  oxygen  and  nitrogen  gases 
of  the  atmosphere  are  simply  intermixed,  or  chemically  combined  with  each  other. 
Appearances  are  at  first  view  greatly  in  favour  of  the  latter  opinion.  Oxygen 
and  nitrogen  gases  differ  in  density,  and  therefore  it  might  be  expected,  were 
they  merely  mixed  together,  that  the  oxygen  as  the  heavier  gas  ought,  in  obedi- 
ence to  the  force  of  gravity,  to  collect  in  the  lower  regions  of  the  air ;  while  the 
nitrogen  should  have  a  tendency  to  occupy  the  higher.  But  this  has  nowhere 
been  observed.  If  air  be  confined  in  a  long  tube  preserved  at  perfect  rest,  its 
upper  part  will  contain  just  as  much  oxygen  as  the  lower,  even  after  an  interval 
of  many  months  ;  nay,  if  the  lower  part  of  it  be  filled  with  oxygen,  and  the  upper 
with  nitrogen,  these  gases  will  be  found  in  the  course  of  a  few  hours  to  have 
mixed  intimately  with  one  another.  The  constituents  of  the  air  are,  also,  in  the 
exact  proportion  for  combining.  By  measure  they  are  nearly  in  the  simple  ratio 
of  1  to  4,  which  agrees  with  the  law  of  combination  by  volume ;  and  by  weight 
they  are  as  8  to  28,  which  corresponds  to  1  eq.  of  oxygen  and  2  of  nitrogen. 

Strong  as  are  these  arguments  in  favour  of  the  chemical  theory,  it  is  never- 
theless liable  to  objections  which  appear  insuperable.  The  atmosphere  possesses 
all  the  characters  that  should  arise  from  a  mechanical  mixture.  There  is  not,  as 
in  all  other  cases  of  chemical  union,  any  change  in  the  bulk,  form,  or  other  quali- 
ties of  its  elements.  The  nitrogen  manifests  no  attraction  for  the  oxygen.  All 
bodies  which  have  an  affinity  for  oxygen  abstract  it  from  the  atmosphere  with  as 
much  facility  as  if  the  nitrogen  were  absent  altogether.  Even  water  effects  this 
separation  ;  for  the  air  which  is  expelled  from  rain  water  by  ebullition,  contains 
more  than  21  per  cent,  of  oxygen.  When  oxygen  and  nitrogen  gases  are  mixed 
together  in  the  ratio  of  1  to  4,  the  mixture  occupies  precisely  5  volumes,  and  has 
every  property  of  pure  atmospheric  air.  The  refractive  power  of  the  atmosphere 
is  precisely  such  as  a  mixture  of  oxygen  and  nitrogen  gases  ought  to  possess ; 
and  different  from  what  would  be  expected  were  its  elements  chemically  united. 
(Edinburgh  Journal  of  Science,  iv.  211.) 

Since  the  elements  of  the  air  cannot  be  regarded  as  in  a  state  of  actual  combi- 
nation, it  is  necessary  to  account  for  the  steadiness  of  their  proportion  on  some 
other  principle.  It  has  been  conceived  that  the  affinity  of  oxygen  and  nitrogen 
for  one  another,  though  insufficient  to  cause  their  combination  when  mixed  toge- 
ther at  ordinary  temperatures,  might  still  operate  in  such  a  manner  as  to  prevent 
their  separation ;  that  a  certain  degree  of  attraction  is  even  then  exerted  between 
them,  which  is  able  to  counteract  the  tendency  of  gravity.  An  opinion  of  this 
kind  was  advanced  by  Berthollet,  in  his  Statique  Chhnique,  and  defended  by 
Murray.  This  doctrine,  however,  is  not  satisfactory.  It  is  conceivable  that 
oxygen  and  nitrogen  may  attract  each  other  in  the  way  supposed  :  and  it  may  be 
admitted  that  this  supposition  explains  why  these  two  gases  continue  in  a  state 
of  perfect  mixture.  But  still  the  explanation  is  unsatisfactory  ;  and  for  the  fol- 
lowing reason : — Dalton  took  two  cylindrical  vessels,  one  of  which  was  filled 
with  carbonic  acid,  the  other  with  hydrogen  gas  ;  the  latter  was  placed  perpen- 


172  NITROGEN. 

dicularly  over  the  other,  and  a  communication  was  established  between  them. 
In  the  course  of  a  few  hours  hydrogen  was  detected  in  the  lower  vessel,  and 
carbonic  acid  gas  in  the  upper.  If  the  upper  vessel  be  filled  with  oxygen,  nitro- 
gen, or  any  other  gas,  the  same  phenomena  will  ensue :  the  gases  will  be  found, 
after  a  short  interval,  to  be  in  a  state  of  mixture,  and  will  at  last  be  distributed 
equally  through  both  vessels.  Now  this  result  cannot  be  ascribed  to  the  action 
of  affinity.  Carbonic  acid  cannot  be  made  to  unite  either  with  hydrogen,  oxygen, 
or  nitrogen ;  and  therefore,  it  is  gratuitous  to  assert  that  it  has  an  affinity  for 
them.  Some  other  power  must  be  in  operation,  capable  of  producing  the  mixture 
of  gases  with  each  other,  independently  of  chemical  attraction  ;  and  if  this  power 
can  cause  carbonic  acid  to  ascend  through  a  gas  which  is  twenty-two  times  lighter 
than  itself,  it  will  surely  explain  why  oxygen  and  nitrogen  gases,  the  densities 
of  which  differ  so  little,  should  be  intermingled  in  the  atmosphere. 

The  explanation  which  Dalton  has  given  of  these  phenomena  is  founded  on  the 
assumption,  that  the  particles  of  one  gas,  though  highly  repulsive  to  each  other, 
do  not  repel  those  of  a  different  kind.  Hence  one  gas  should  act  as  a  vacuum 
with  respect  to  another ;  and  if  a  vessel  full  of  carbonic  acid  communicate  with 
another  of  hydrogen,  the  particles  of  each  gas  should  insinuate  themselves  be- 
tween the  particles  of  the  other,  till  they  are  equally  diffused  through  both  ves- 
sels. The  particles  of  the  carbonic  acid  do  not  indeed  fill  the  space  occupied  by 
the  hydrogen  with  the  same  velocity  as  if  it  were  a  real  vacuum,  because  the 
particles  of  the  hydrogen  afford  a  mechanical  impediment  to  their  progress.  The 
ultimate  effect,  however,  is  the  same  as  if  the  vessel  of  hydrogen  had  been  a 
vacuum.     (Manchester  Memoirs,  voL  v.) 

Though  it  would  not  be  difficult  to  find  objections  to  this  hypothesis,  it  has 
tlie  merit  of  being  applicable  to  every  possible  case ;  which  cannot,  I  conceive, 
be  admitted  of  the  other.  It  accounts  not  only  for  the  mixture  of  gases,  but  for 
the  equable  diffusion  of  vapours  through  gases,  and  through  each  other.  This 
view  receives  support  from  Graham's  experiments  on  the  diffusion  of  gases. 
(Phil.  Trans.  Edin.  1831.)  When  a  gas  is  contained  in  a  glass  bell  jar  which 
has  a  crack  or  fissure  in  its  sides,  or  communicates  with  the  air  by  a  narrow  aper- 
ture, or  is  contained  in  a  porous  vessel,  the  gas  gradually  diffuses  itself  into  the 
air,  and  air  into  the  gas,  each  passing  through  the  chink  or  other  small  opening 
at  the  same  time,  but  in  opposite  directions.  On  ascertaining  after  an  interval 
how  much  gas  has  escaped  from,  and  how  much  air  entered  into,  the  vessel,  it 
will  be  found  that  the  respective  quantities  depend  on  the  relative  sp.  gravities ; 
and  the  same  principle  of  intermixture  equally  applies  when  the  apertures  of  cpm- 
munication  are  large,  as  when  they  are  small.  Each  gas  has  a  diffusiveness 
peculiar  to  itself,  and  which  is  greater  as  its  sp.  gr.  is  less.  Graham  determined 
the  rate  of  diffusion  for  different  gases  by  means  of  what  he  calls  a  diffusion  iuhe^ 
which  is  simply  a  graduated  tube  closed  at  one  end  by  plaster  of  Paris,  a  sub- 
stance, when  moderately  dry,  possessed  of  the  requisite  porosity.  He  has  been 
led  by  direct  experiment  to  the  following  conclusion, — that  "the  diffusion  or 
spontaneous  intermixture  of  two  gases  in  contact,  is  effected  by  an  interchange  in 
position  of  indefinitely  small  volumes  of  the  gases,  which  volumes  are  not  neces- 
sarily of  equal  magnitude,  being,  in  the  case  of  each  gas,  inversely  proportional 
to  the  square  root  of  the  density  of  that  gas."  The  relative  diffusivenes  of  each 
gas  may  hence  be  represented  by  the  reciprocal  of  the  square  root  of  its  sp.  gr. 
Thus,  the  sp.  gr.  of  air  being  1,  its  diffusiveness  is  1  also ;  that  of  hydrogen  is 


NITROGEN.  173 

1  1  1         ' 

=  3-807 ;  that  of  oxygen    = =  0-9524  ; 


v/0-069       0-2627  ^1-102       1-05 

1 
and  that  of  nitrogen        0-972  =  1-014  : 
v/ 
so  that  the  relative  power  of  diffusion  of  air,  hydrogen,  oxygen,  and  nitrogen,  is 
indicated  by  the  numbers,  1,  3-807,  0-9524  and  1-014.     In  gases  which  are  very 
sparingly  soluble  in  water,  and  hence  not  condensable  by  the  moisture  of  the 
plaster  of  Paris,  the  results  of  experiment  coincide  so  exactly  with  the  law,  that 
Graham  suggests  its  application  to  determine  the  sp.  gr.  of  gases.     Thus  if  g 
denote  the  diffusiveness  of  a  gas,  as  found  by  careful  experiment,  and  d  its  sp. 
gr. ;  then  since,  by  the  law  of  diffusion, 

1  1 

g  = we  have  d  =  — 

s/d,  gK 

It  is  obvious  that  these  phenomena  cannot  be  referred  to  any  chemical  princi- 
ple, but  are  dependent  on  the  mechanical  constitution  of  gases.  It  has  been 
lately  shown  in  a  very  clever  paper  by  T.  Thomson  of  Clitheroe  (Phil.  Mag.  3rd 
Series,  iv.  321),  that  the  law  of  gaseous  diffusion  is  included  under  Dalton's  hy- 
pothesis, that  one  gas  is  as  a  vacuum  with  respect  to  another.  For  it  is  a  law 
deduced  from  the  physical  properties  of  gaseous  bodies,  that  the  velocities  of 
gases  flowing  under  like  circumstances  into  a  vacuum  are  inversely  as  ihe  square 
roots  of  their  sp.  gravities,  which  is  precisely  the  same  law  that  regulates  their 
flow  into  each  other. 

There  is  still  one  circumstance  for  consideration  respecting  the  atmosphere. 
Since  oxygen  is  necessary  to  combustion,  to  the  respiration  of  animals,  and  to 
various  other  natural  operations,  by  all  of  which  that  gas  is  withdrawn  from  the 
air,  it  is  obvious  that  its  quantity  would  gradually  diminish,  unless  the  tendency 
of  those  causes  were  counteracted  by  some  compensating  process.  To  all  appear- 
ance there  does  exist  some  source  of  compensation ;  for  chemists  have  not  hith- 
erto noticed  any  change  in  the  constitution  of  the  atmosphere.  The  only  source 
by  which  oxygen  is  known  to  be  supplied,  is  the  action  of  growing  vegetables. 
A  healthy  plant  absorbs  carbonic  acid  during  the  day,  appropriates  the  carbona- 
ceous part  of  that  gas  to  its  own  wants,  and  evolves  the  oxygen  with  which  it 
was  combined.  During  the  night,  indeed,  an  opposite  effect  is  produced.  Oxy- 
gen gas  then  disappears,  and  carbonic  acid  is  eliminated;  but  it  follows  from  the 
experiments  of  Priestley,  Davy,  and  Daubeny,  that  plants  during  24  hours  yield 
more  oxygen  than  they  consume.  Whether  living  vegetables  make  a  full  com- 
pensation for  the  oxygen  removed  from  the  air  by  the  processes  above  mentioned, 
is  uncertain.  From  the  great  extent  of  the  atmosphere,  and  the  continual  agita- 
tion to  which  its  different  parts  are  subject  by  the  action  of  winds,  the  effects  of 
any  deteriorating  process  would  be  very  gradual,  and  a  change  in  the  proportion 
of  its  elements  could  be  perceived  only  by  observations  made  at  very  distant  in- 
tervals. 

Besides  oxygen,  nitrogen,  carbonic  acid,  and  traces  of  volatile  organic  sub- 
stances, air,  as  already  stated,  always  contains  a  greater  or  less  amount  of  the 
vapour  of  Water.  The  methods  and  instruments  employed  for  determining  its 
quantity  have  been  described  in  the  article  Evaporation.  As  these  instruments 
are  termed  hygrometers,  the  moisture  of  the  atmosphere  is  often  called  hygro- 


;I5^|  NITROGEN. 

metric ;  and  solid  substances  which  absorb  it  are  said  to  contain  hygrometric 
water. 

PROTOXIDE  OF  NITROGEN. 

Hist. — Dephlogisticated  air  of  Priestley,  its  discoverer;  and  the  nitrous  oxide  of 
Davy,  who  studied  it  minutely.     (Researches  on  the  Nitrous  Oxide,  1800.) 

Prep. — It  may  be  formed  by  exposing  nitric  oxide  for  some  days  to  the  action 
of  iron  filings,  or  other  substances  which  have  a  strong  affinity  for  oxygen,  when 
the  nitric  oxide  loses  one  half  of  its  oxygen,  and  is  converted  into  the  protoxide ; 
but  the  most  convenient  method  is  by  nitrate  of  ammonia.  This  salt  is  prepared 
by  neutralizing  with  carbonate  of  ammonia  pure  nitric  acid  diluted  with  about 
three  parts  of  water,  and  concentrating  by  evaporation  until  a  drop  of  the  liquid 
let  fall  on  a  cold  plate  becomes  a  firm  mass,  adding  a  little  ammonia  towards  the 
close  to  ensure  neutrality.  The  salt  after  cooling  is  broken  to  pieces,  introduced 
into  a  retort,  and  heated  by  a  lamp  or  pan  of  charcoal :  at  first,  below  400°,  fusion 
ensues ;  and  as  the  heat  rises  to  480°  or  500°,  rapid  decomposition  sets  in,  which 
continues  until  all  the  salt  disappears.  If  a  white  cloud  appears  within  the  retort, 
due  to  some  of  the  salt  subliming  undecomposed,  the  heat  should  be  checked. 

The  sole  products  of  this  operation,  when  carefully  conducted,  are  water  and 
protoxide  of  nitrogen.  The  nature  of  the  change  will  be  readily  understood  by 
comparing  the  composition  of  nitrate  of  ammonia'with  that  of  the  products  derived 
from  it.    These,  in  round  numbers,  are  as  follows : — 

Nitric  Acid.  Ammonia.  j*  Water.  Prot.  of  Nitrogen. 

Nitrogen  14  or  1  eq.    Nitrogen  14  or  1  eq.    |    Hyd.    3  or  3  eq.  Nit.  l3  or  2  eq. 

Oxygen    40  or  5  eq.    Hydrogen  3  or  3  eq.    [    Oxy.  24  or  3  eq.  Oxy.  lBor2eq. 

64  17  I  27  44 

The  same  expressed  in  symbols  is 

NH3  +  N06  =  3HOt2NO. 

It  thus  appears  that  the  hydrogen  in  the  ammonia  takes  so  much  oxygen  as 
is  sufficient  for  forming  water,  and  the  residual  oxygen  converts  the  nitrogen  both 
of  the  nitric  acid  and  of  the  ammonia  into  protoxide  of  nitrogen:  71  grains  of  the 
salt  will  thus  yield  44  grains  of  protoxide  of  nitrogen  and  27  of  water. 

Prop, — Colourless,  slightly  agreeable  odour,  and  sweetish  taste ;  commonly 
gaseous,  but  at  45°  and  under  a  pressure  of  50  atmospheres  it  is  liquid ;  [under 
the  same  pressure,  this  liquid  exposed  to  the  intense  cold  of  Thilorier's  bath  of 
solid  carbonic  acid  and  ether,  becomes  a  transparent  crystalline  solid  (page  53.)] 
sp.  gr.  of  the  gas  =  1*5241,  and  100  C.  I.  weigh  47*22  grains;  no  action  on  test 
paper.  Recently  boiled  water  at  60°  dissolves  nearly  its  own  volume  of  the  gas, 
and  yields  it  unchanged  by  boiling :  hence  it  cannot  be  preserved  over  cold  water, 
and  may  by  it  be  separated  from  gases  which  are  insoluble  in  water.  It  is  a  sup- 
porter of  combustion.  Most  substances  burn  in  it  with  far  greater  energy  than 
in  the  atmosphere.  When  a  recently  extinguished  candle  with  a  very  red  wick 
is  introduced  into  it,  the  flame  is  instantly  restored.  Phosphorus,  if  previously 
kindled,  bums  in  it  with  great  brilliancy.  Sulphur,  when  burning  feebly,  is  ex- 
tinguished by  it ;  but  if  immersed  while  the  combustion  is  lively,  the  size  of  the 
flame  is  considerably  increased.  With  an  equal  bulk  of  hydrogen  it  forms  a 
mixture  which  explodes  violently  by  the-  electric  spark  or  by  flame.  In  all  these 
cases  the  product  of  combustion  is  the  same  as  when  oxygen  gas  or  atmospheric 


NITROGEN.  175 

air  is  used.  The  protoxide  is  decomposed  ;  the  combustible  matter  unites  with 
its  oxygen,  and  the  nitrogen  is  set  free.  It  suffers  decomposition  when  a  succes- 
sion of  electric  sparks  is  passed  through  it,  and  a  similar  effect  is  caused  by 
conducting  it  through  a  porcelain  tube  heated  to  incandescence.  It  is  resolved, 
in  both  instances,  into  nitrogen,  oxygen,  and  nitrous  acid. 

Davy  discovered  that  it  may  be  taken  into  the  lungs  with  safety,  and  that  it 
supports  respiration  for  a  few  minutes.  He  breathed  9  quarts  of  it,  contained 
in  a  silk  bag,  for  three  minutes,  and  12  quarts  for  rather  more  than  four ;  but 
no  quantity  could  enable  him  to  bear  the  privation  of  atmospheric  air  for  a  longer 
period.  Its  action  on  the  system,  when  inspired,  is  very  remarkable.  A  few 
deep  inspirations  are  followed  by  most  agreeable  feelings  of  excitement,  similar 
to  the  earlier  stages  of  intoxication.  This  is  shown  by  a  strong  propensity  to 
laughter,  by  a  rapid  flow  of  vivid  ideas,  and  an  usual  disposition  to  muscular 
exertion.  These  feelings,  however,  soon  subside  ;  and  the  person  returns  to  his 
usual  state  without  experiencing  the  langour  or  depression  which  so  universally 
follows  intoxication  from  spirituous  liquors.  Its  effects,  however,  on  different 
persons,  are  various  ;  and  in  individuals  of  a  plethoric  habit  it  sometimes  pro- 
duces giddiness,  headache,  and  other  disagreeable  symptoms. 

When  100  measures  of  it  are  mixed  with  100  of  hydrogen  and  fired  by  elec- 
tricity, 100  of  nitrogen  gas  remain,  and  the  sole  other  product  is  water.  As  100 
of  hydrogen  unite  with  50  of  oxygen,  it  follows  that  100  measures  of  the  pro- 
toxide contain  100  of  nitrogen  and  50  of  oxygen  gases.  This  result,  obtained 
by  Davy,  has  been  confirmed  by  Henry,  who  analyzed  it  by  means  of  carbonic 
oxide  gas  (An.  Phil.  N.  S,  viii,  299).     Now, 

100  cubic  inches  of  nitrogen  gas  weigh       .  .  .  30-166  grains 

50  do.  oxygen  .  .  .  .  17-054 


These  numbers  added  together  amount  to  .  ,  47*220 

which  must  be  the  weight  of  100  C,  I.  of  the  protoxide.  Its  composition  by 
weight  is  determined  by  the  same  data,  being  17-054  oxygen  to  30-1 G6  nitrogen, 
or  8  to  14  nearly,  as  already  stated.     Its  eq.  is  =  22*15  ;   eq,  vol.  =  100 ;  symh, 

N  +  0,  NO.  or  N, 

BINOXIDE  OF  NITROGEN. 

Hist. — Discovered  by  Hales,  but  first  carefully  studied  by  Priestley,  under  the 
name  of  nitrous  gas.     It  is  also  called  nitric  oxide  and  deutoxide  of  nitrogen. 

Prep. — Preferably  by  the  action  of  nitric  acid,  of  sp.  gr.  1*2,  on  metallic  cop- 
per. Brisk  effervescence  takes  place  without  the  aid  of  heat,  and  the  gas  may 
be  collected  over  water  or  mercury.  The  copper  gradually  disappears  during  the 
process ;  the  liquid  -acquires  a  beautiful  blue  colour,  and  yields  on  evaporation 
a  salt  which  is  composed  of  nitric  acid  and  oxide  of  copper.  The  chemical 
changes  that  occur  are  the  following  : — One  portion  of  nitric  acid  suffers  decora- 
position  :  part  of  its  oxygen  oxidizes  the  copper;  while  another  part  is  retained 
by  the  nitrogen  of  the  nitric  acid,  forming  binoxide  of  nitrogen.  The  oxide  of 
copper  attaches  itself  to  some  undecomposed  nitric  acid,  and  forms  the  blue 
nitrate.     Many  other  metals  are  oxidized  by  nitric  acid,  with  disengagement  of 


176  NITROGEN. 

a  similar  compound  ;  but  none,  mercury  excepted,  yields  so  pure  a  gas  as  cop- 
per.    The  following  equation  expresses  the  reaction  : — 

Cu3  -f-  4  N  05=  3  (Cu  0.  N  O5)  f  N  O2. 

Prop. — Gaseous,  not  hitherto  condensed  into  a  liquid  ;  colourless,  tasteless, 
and  inodorous;  excites  violent  spasm  of  the  glottis  when  an  attempt  is  made  to 
inhale  it ;  sp.  gr.  =  1-0377,  and  100  C.  I.  weigh  32-137  grains.  Water  at  60° 
.dissolves  about  1 1  per  cent.  It  has  no  action  on  test  paper  ;  but  if  any  free 
oxygen  is  present,  it  produces  dense,  suffocating,  acid  vapours  of  a  red  or  orange 
colour,  called  nitrous  acid  vapours^  which  are  freely  absorbed  by  water,  and  render 
it  acid.  This  character  distinguishes  it  from  all  other  gases,  and  is  a  good  test 
of  the  presence  of  free  oxygen.  In  some  cases  it  supports  combustion  :  burning 
sulphur  and  a  lighted  candle  are  extinguished  by  it ;  but  charcoal  and  phos- 
phorus, when  in  vivid  combustion,  burn  in  it  with  increased  brilliancy.  The 
product  of  the  combustion  is  carbonic  acid  in  the  former  case,  and  metaphos- 
phoric  acid  in  the  latter,  nitrogen  being  separated  in  both  instances.  With  an 
equal  bulk  of  hydrogen  it  forms  a  mixture  which  cannot  be  made  to  explode, 
but  which  is  kindled  by  contact  with  a  lighted  candle,  and  burns  rapidly  with  a 
greenish  white  flame,  water  and  pure  nitrogen  gas  being  the  sole  products.  The 
action  of  freshly  ignited  spongy  platinum  on  a  mixture  of  hydrogen  and  bin- 
oxide  of  nitrogen  gases  leads  to  the  slow  production  of  water  and  ammonia. 

It  is  partially  resolved  into  its  elements  by  being  passed  through  red-hot  tubes, 
and  a  succession  of  electric  spaiks  has  a  similar  effect.  It  is  converted  into 
protoxide  of  nitrogen  by  substances  which  have  a  strong  affinity  for  oxygen,  such 
as  moist  iron  filings,  and  a  solution  of  sulphuret  of  potassium.  Davy  ascer- 
tained its  composition  by  the  combustion  of  charcoal  (Elements  of  Chemical 
Philosophy,  p.  200).  Two  volumes  of  the  binoxide  yielded  one  volume  of 
nitrogen,  and  about  one  of  carbonic  acid ;  whence  it  was  inferred  to  consist  of 
equal  measures  of  oxygen  and  nitrogen  gases  united  without  any  condensation. 
Gay  Lussac  (Memoires  d'Arcueil)  proved  that  this  proportion  is  rigidly  exact. 
He  decomposed  100  measures  of  the  gas,  by  heating  potassium  in  it;  when  50 
measures  of  pure  nitrogen  were  left,  and  the  potassa  formed  corresponded  to  50 
measures  of  oxygen.  The  same  fact  has  been  lately  proved  by  Henry  (An.  of 
Phil.  N.  S.  viii.  299).     Hence,  as 

60  cubic  inches  of  oxygon  gas  weigh  .  .  '  17054  grains 

50  do.  nitrogen  ....  15*083 


100  cubic  inches  of  the  binoxide  must  weigh  .  .  32- 137 

From  the  invariable  formation  of  red-coloured  acid  vapours,  whenever  binoxide 
of  nitrogen  and  oxygen  are  mixed  together,  these  gases  detect  the  presence  of 
each  other  with  great  certainty  :  and  since  the  product  is  wholly  absorbed  by 
water,  either  of  them  may  be  entirely  removed  from  any  gaseous  mixture  by 
adding  a  sufficient  quantity  of  the  other.  Priestley,  who  first  observed  this 
fact,  supposed  that  combination  takes  place  between  them  in  one  proportion 
only;  and  inferring  on  this  supposition,  that  a  given  absorption  must  always 
indicate  the  same  quantity  of  oxygen,  he  was  led  to  employ  binoxide  of  nitrogen 
in  Eudiometry.  But  in  this  opinion  he  was  mistaken.  The  discordant  results 
obtained  by  his  method  soon  excited  suspicion  of  their  accuracy ;  and  the  source 


NITROGEN.  177 

of  error  has  since  been  discovered  by  the  researches  of  Dalton  and  Gay-Lussac. 
It  appears  from  the  experiments  of  Gay-Lussac,  and  his  results  do  not  differ 
material ly^rom  those  of  Dalton,  that  for  100  measures  of  oxygen,  400  of  the 
binoxide  may  be  absorbed  as  a  maximum,  and  133  as  a  minimum;  and  that 
between  these  extremes,  the  quantity  of  the  binoxide  corresponding  to  100  of 
oxygen  is  exceedingly  variable.  It  does  not  follow  from  this,  that  oxygen  and 
binoxide  of  nitrogen  unite  in  every  proportion  within  these  limits.  The  true 
explanation  is,  that  the  mixture  of  these  gases  may  give  rise  to  three  compounds, 
— hyponitrous,  nitrous,  and  nitric  acids;  and  that  either  may  be  formed  almost, 
if  not  entirely,  to  the  exclusion  of  the  others,  if  certain  precautions  are  adopted. 
But  in  the  usual  mode  of  operating,  two  if  not  all  are  generated  at  the  same 
time,  and  in  a  proportion  to  each  other  which  is  by  no  means  uniform.  The 
circumstances  that  influence  the  degree  of  absorption,  when  a  mixture  of  oxygen 
and  binoxide  of  nitrogen  is  made  over  water,  are  the  following: — 1.  The  diame- 
ter of  the  tube ;  2.  The  rapidity  with  which  the  mixture  is  made ;  3.  The  rela- 
tive proportion  of  the  two  gases ;  4.  The  time  allowed  to  elapse  after  mixing 
them  ;  5.  Agitation  of  the  tube  ;  and  lastly.  The  opposite  conditions  of  adding 
the  oxygen  to  the  binoxide,  or  the  binoxide  to  the  oxygen. 

The  binoxide  may,  notwithstanding,  be  usefully  employed  in  Eudiometry. 
Dalton  operates  (An.  of  Phil.  x.  38,  and  Henry's  Elements)  by  mixing  the  gases 
in  a  graduated  tube  about  A  an  inch  wide  over  water,  and  waiting,  without  agi- 
tating the  mixture,  till  decrease  of  volume  is  at  an  end,  which  usually  occurs  in 
less  than  6  or  10  minutes.  Every  27  measures  which  have  disappeared,  indi- 
cate 10  of  oxygen.  A  large  excess  of  the  binoxide  should  be  avoided  ;  and  if 
the  gas  under  examination  contain  more  than  20  per  cent,  of  oxygen,  it  should 
be  previously  diluted  with  nitrogen.  Gay-Lussac  advises  that  100  measures  of 
the  gas  under  examination  should  be  introduced  into  a  very  wide  tube  or  jar,  and 
that  an  equal  volume  of  the  binoxide  should  then  be  added  (Mem.  d'Arcueil.  ii. 
247).  The  red  vapours,  which  are  instantly  produced,  disappear  very  quickly  ; 
and  the  absorption,  after  half  a  minute,  or  a  minute  at  the  most,  may  be  regarded 
as  complete.  The  residue  is  then  transferred  into  a  graduated  tube  and  mea- 
sured. One-fourth  of  the  loss  is  oxygen. — Results  very  near  the  truth  may  be 
obtained  by  both  methods. 

If  a  current  of  the  binoxide  be  conducted  into  a  solution  of  protosulphate  of 
iron,  the  gas  is  absorbed  in  large  quantity,  and  the  solution  acquires  a  deep 
olive-brown  colour,  which  appears  almost  black  when  fully  saturated.  This  solu- 
tion absorbs  oxygen  with  facility.  But  it  cannot  be  safely  employed  in  Eudi- 
ometry ;  because  the  absorption  of  oxygen  is  accompanied,  or  at  least  very  soon 
followed,  by  evolution  of  gas  from  the  liquid  itself.  The  binoxide  is  combined 
with  the  sulphate  in  the  ratio  of  1  eq.  of  the  former  to  4  eq.  of  the  latter ;  and 
the  gas  may  be  recovered  by  exposure  to  a  vacuum,  the  original  salt  being  left 
unchanged  (Peligot  in  An.  de  Ch.  et  Ph.  liv.  17).  On  applying  heat,  part  of 
the  gas  is  evolved  and  part  decomposed  :  the  protoxide  of  iron  takes  oxygen 
both  from  the  binoxide  and  from  water,  forming  peroxide  of  iron ;  while  the 
hydrogen  of  the  decomposed  water,  and  nitrogen  of  the  binoxide  combine 
together,  and  generate  ammonia.  Nitric  acid  is  formed  when  the  solution  is 
exposed  to  the  air  or  oxygen  gas,  but  not  otherwise  (Davy).  When  a  mixture 
of  binoxide  of  nitrogen  and  sulphurous  acid  are  brought  into  contact  with  a 
solution  of  potassa  or  ammonia,  both  gases  are  absorbed,  and  a  peculiar  acid  is 
generated,  which  has  been  called  by  Pelouze,  its  discover,  nitrusulphuric  add. 

14 


178  NITROGEN. 

It  is  composed  of  1  eq.  of  nitrogen,  1  of  sulphur,  and  4  of  oxygen,  200  volumes 
of  binoxide  of  nitrogen  combining  with  100  of  sulphurous  acid.  The  nitro- 
sulphates  are  very  prone  to  decomposition,  a  sulphate  being  formed  with  the 
evolution  of  protoxide  of  nitrogen :  this  ensues  by  the  mere  contact  of  certain 
substances,  which  do  not  themselves  undergo  any  change,  such  as  spongy  pla- 
tinum, silver  and  its  oxide,  charcoal  powder,  peroxide  of  manganese,  and  solu- 
tions of  corrosive  sublimate,  lunar  caustic,  and  the  sulphates  of  the  oxides  of 
zinc,  copper,  and  iron.  The  same  effect  is  produced  by  an  acid,  as  when  an 
attempt  is  made  to  procure  nitrosulphuric  acid  in  a  separate  state,  even  the  car- 
bonic acid  of  the  atmosphere  being  capable  of  causing  the  decomposition.  The 
crystals  of  the  nitiosulphates  of  potash  and  ammonia  may  be  preserved  in  well- 
stopped  bottles  at  ordinary  temperatures ;  the  solutions,  on  the  contrary,  are  not 
stable  above  the  freezing  point,  but  the  stability  is  much  increased  by  an  excess 
of  alkali.  On  this  is  founded  the  best  mode  of  preparing  the  nitrosulphates, 
which  consists  in  transmitting  binoxide  of  nitrogen  through  a  strong  solution  of 
sulphite  of  ammonia  or  potash  with  an  excess  of  alkali,  when  the  corresponding 
nitrosulphate  separates  in  colourless  prismatic  .or  acicular  crystals.  The  dry 
crystals  decompose  at  a  moderate  heat,  namely,  at  230°  for  the  ammoniacal  salt, 
and  266°  for  that  of  potash,  the  former  giving  rise  to  a  slight  explosion  owing 
to  the  rapid  evolution  of  protoxide  of  nitrogen.  The  decomposition  of  the 
nitrosulphate  of  potassa  by  heat  is  particularly  interesting,  from  its  forming  sul- 
phite of  potassa  and  binoxide  of  nitrogen  instead  of  sulphate  of  potassa  and 
the  protoxide,  as  occurs  in  every  other  instance.     (Lieb.  Ann.  xv.  240.) 

It  is  singular  that  both  binoxide  and  protoxide  of  nitrogen,  notwithstanding 
the  absence  of  acidity,  are  capable  of  forming  compounds  of  considerable  per- 
manence with  the  pure  alkalies.  The  circumstances  which  give  rise  to  the  for- 
mation of  these  compounds  will  be  stated  in  the  description  of  nitre. 

Its  eq.  is  =  30-15 ;  eq.  vol.  =  200 ;  symb.  N  +  20,  NO2,  or  N. 

HYPONITROUS  ACID. 

Hist,  and  Prep. — «First  prepared  by  Gay-Lussac,  who  showed  that  on  adding 
binoxide  of  nitrogen  in  excess  to  oxygen  gas,  confined  in  a  glass  tube  over 
mercury,  the  absorption  is  always  uniform,  provided  a  strong  solution  of  pure 
potassa  is  put  into  the  tube  before  mixing  the  two  gases  :  50  measures  of  oxygen 
gas  combine  under  these  circumstances  with  200  of  the  binoxide,  forming  an 
acid  which  unites  with  the  potassa.  As  the  binoxide  contains  half  its  volume 
of  oxygen  gas,  the  new  acid  must  be  composed  of  100  measures  of  nitrogen  and 
150  of  oxygen,  as  already  stated.  It  is  generated  when  the  binoxide  is  kept  for 
a  considerable  time,  say  three  months,  in  a  glass  tube  over  mercury,  with  a 
strong  solution  of  pure  potassa,  when  the  binoxide  is  resolved  into  hyponitrous 
acid,  which  unites  with  the  alkali,  while  protoxide  of  nitrogen  remains  in  the 
tube ;  and  Dulong  formed  it  by  mixing  200  measures  of  binoxide  of  nitrogen 
with  50  of  oxygen  gas,  both  quite  dry,  and  exposing  the  resulting  orange  fumes 
to  intense  cold,  which  condensed  it  into  a  liquid.  It  is  the  nitrmis  acid  of  Ber- 
zelius  and  other  Continental  chemists. 

Prop. — At  0°  it  is  a  colourless  liquid,  and  green  at  common  temperatures.  It 
is  so  volatile,  that  in  open  vessels  the  green  fluid  wholly  and  rapidly  passes  off 
in  the  form  of  an  orange  vapour,  which  is  said  by  Mitscherlich  to  have  a  density 


NITROGEN.  179 

of  1*72.  On  admixture  with  water  it  is  converted  into  nitric  acid  and  binoxide 
of  nitrogen,  thus  3NO3  =  NO5  -f-  2NO2,  the  latter  escaping  with  effervescence ; 
but  when  much  nitric  acid  is  present,  the  hyponitrous  is  changed  into  nitrous 
acid,  the  presence  of  which  imparts  several  shades  of  colour,  orange,  yellow, 
green,  and  blue,  according  as  its  quantity  is  more  or  less  predominant.  One  eq. 
of  hyponitrous  and  one  of  nitric  acid  yield  two  eq.  of  nitrous  acid  : — Thus  NO3 
and  NO5  obviously  contain  the  elements  for  forming  2NO4. 

Hyponitrous  acid  does  not  unite  directly  with  alkalies,  being  then  resolved 
principally  into  nitric  acid  and  binoxide  of  nitrogen ;  but  the  hyponitrites  of  the 
alkalies  and  alkaline  earths  may  be  obtained  by  heating  the  corresponding 
nitrates  to  a  gentle  red  heat ;  and  the  hyponitrite  of  the  oxide  of  lead  is  formed 
by  boiling  a  solution  of  the  nitrate  of  that  oxide  with  metallic  lead. 

Hyponitrous  acid  forms  with  water  and  sulphuric  acid  a  crystalline  compound, 
which  is  formed  in  large  quantity  during  the  manufacture  of  sulphuric  acid,  and 
the  production  of  which  is  an  essential  part  of  that  process.  It  is  generated 
whenever  moist  sulphurous  acid  gas  and  nitrous  acid  vapour  are  intermixed, 
being  instantly  deposited  in  the  form  of  white  acicular  crystals;  and  Gay-Lussac 
discovered  that  it  may  also  be  made  by  the  direct  action  of  anhydrous,  nitrous 
and  strong  sulphuric  acid.  The  first  attempt  to  determine  its  composition  ana- 
lytically was  by  Henry,  who  found  it  to  consist  of  1  eq.  of  hyponitrous  acid,  5 
of  sulphuric  acid,  and  5  of  water.  (Ann.  of  Phil,  xxvii.  367.)  G.  De  Claubry 
has  lately  repeated  the  analysis  of  the  same  compound  in  a  state  of  more  per- 
fect dryness,  and  by  what  he  considers  a  better  method  ;  and  he  gives  as  its  con- 
stituents 2  eq.  of  hyponitrous  acid,  4  of  water,  and  5  of  sulphuric  acid.  (An. 
de  Ch.  et  Ph.  xlv.  284.)  The  theory  of  its  production  has  been  very  carefully 
studied  by  De  Claubry.  It  appears  that  when  moist  sulphurous  and  nitrous 
acids  react  on  each  other,  the  former  is  converted  into  sulphuric  and  the  latter 
into  hyponitrous  acid,  the  oxygen  lost  by  one  being  gained  by  the  other,  NO4  -\- 
SO4  =  NO3  -j-  SO3.  A  little  nitrogen  gas  is  always  disengaged  at  the  same  time, 
which  can  only  arise  from  a  small  portion  of  nitrous  acid  losing  the  whole  of  its 
oxygen.  The  action  of  sulphuric  on  nitrous  acid  is  diiSerent :  in  this  case  the 
nitrous  acid  is  resolved  into  nitric  and  hyponitrous  acids,  2N04=:  NO5  -f  NO3, 
the  latter  uniting  with  sulphuric  acid  and  most  of  its  water  to  produce  the  crys- 
talline solid,  while  the  remainder  of  the  water  unites  with  the  nitric  acid.  When 
the  crystalline  matter  is  put  into  water,  the  hyponitrous  is  resolved  into  nitrous 
acid  and  binoxide  of  nitrogen,  both  of  which  escape  with  effervescence,  2NO3 
=  NO4  -f  NO2.  If  much  water  is  present,  more  or  less  of  the  nitrous  acid  is 
converted  into  nitric  acid  and  the  binoxide.  Similar  changes  ensue  when  the 
crystals  are  exposed  to  the  air,  humidity  being  rapidly  absorbed.  This  subject 
has  also  been  examined  by  Bussy  with  similar  results.* 

Its  eq.  IS  =  38-15 ;  symb.  N  -|-  30,  NO3,  or  N. 

NITROUS  ACID. 

Prep. — It  is  always  formed  when  binoxide  of  nitrogen  and  oxygen  gases  are 
intermixed.    Davy  showed,  by  making  the  mixture  in  a  dry  glass  vessel  pre- 

*  From  recent  observations  it  would  appear  that  the  production  of  the  crystalUne  com- 
pound, mentioned  in  the  text,  is  not  indispensable  in  the  process  of  the  manufacture  of 
sulphuric  acid,  and  that  it  is  not  a  constant  attendant  upon  that  process.  See  Sulphuric 
Acid.— (R.) 


•^s... 


180  NITROGEN. 

viously  exhausted,  that  nitrous  acid  vapour  is  formed  by  the  action  of  200  mea- 
sures of  the  binoxide  on  100  of  oxygen  gas;  and  hence,  as  200  of  the  binoxide 
contains  100  of  nitrogen  and  100  of  oxygen,  nitrous  acid  was  inferred  to  consist 
of  100  measures  of  nitrogen  united  with  200  of  oxygen  gas  (page  166).  This 
inference  has  been  confirmed  by  the  researches  of  Gay-Lussac  and  Dulong  (An. 
de  Ch.  et  Ph.  i.  and  ii.),  the  former  of  whom  also  proved  that  its  elements  con- 
tract to  l-3rd  of  their  volume,  or  in  other  words,  100  measures  of  nitrous  acid 
vapour  contain  100  of  nitrogen  acid  gas  and  200  of  oxygen.  The  specific  gravity ' 
of  this  vapour  ought  to  be  3*1777,  formed  of  0*9727  the  sp.  gr.  of  nitrogen  -j- 
2 '2050,  twice  the  sp.  gr.  of  oxygen.  It  is  best  prepared  by  heating  to  redness 
in  an  earthen  retort  the  nitrate  of  oxide  of  lead,  carefully  dried  ;  when  nitric  acid 
is  resolved  into  nitrous  acid  and  oxygen,  and  on  receiving  the  products  in  a  dry 
tube,  surrounded  by  a  mixture  of  ice  and  salt,  the  former  is  condensed.  The 
following  equation  represents  the  decomposition : — 

PbO,  NOg  =  PbO  t  0  +  NO, 

Prop. — An  anhydrous  liquid  of  sp.  gr.  1*451,  and  orange  colour  at  60°,  yellow 
at  32°,  and  almost  colourless  at  0°  ;  acid,  pungent,  and  powerfully  corrosive ; 
and  imparts  a  yellow  stain  lo  the  skin.  It  is  very  volatile,  boiling  at  82°  :  in  a 
stopped  bottle  it  preserves  its  liquid  form  at  60°  ;  but  when  exposed  to  the 
atmosphere  it  is  rapidly  dissipated  in  orange  red  fumes,  which  when  once  mixed 
with  air  or  other  gases  require  intense  cold  for  condensation. 

Nitrous  acid  vapour  is  characterized  by  its  orange  red  colour,  acid  reaction, 
and  by  being  absorbed  by  water  with  disengagement  of  binoxide  of  nitrogen  and 
formation  of  nitric  acid.  It  is  quite  irrespirable,  exciting  great  irritation  and 
spasm  of  the  glottis,  even  when  moderately  diluted  with  air.  A  taper  burns  in 
it  with  considerable  brilliancy.  It  extinguishes  burning  sulphur ;  but  the  com- 
bustion of  phosphorus  continues  in  it  with  great  vividness. 

Nitrous  acid  is  a  powerful  oxidizing  agent,  readily  giving  oxygen  to  the  more 
oxidable  metals,  and  to  most  substances  which  have  a  strong  affinity  for  it.  The 
acid  is  decomposed  at  the  same  time,  being  commonly  changed  into  binoxide  of 
nitrogen,  though  sometimes  the  protoxide  and  even  pure  nitrogen  gases  are 
evolved.  When  transmitted  through  a  red-hot  porcelain  tube,  it  suffers  decom- 
position, and  a  mixture  of  oxygen  and  hydrogen  gases  is  obtained. 

When  nitrous  acid  is  mixed  with  a  considerable  quantity  of  water,  it  is  in- 
stantly resolved  into  nitric  acid,  which  unites  with  the  water,  and  binoxide  of 
nitrogen  which  escapes  with  effervescence.  Three  eq.  of  nitrous  acid  yield  two 
eq.  of  nitric  acid  and  one  of  the  binoxide;  for  3NO,  =  2N05  +  NO2.  When  a 
rather  small  quantity  of  water  is  used,  the  evolved  binoxide,  at  first  considerable, 
becomes  less  and  less  as  successive  quantities  of  nitrous  acid  are  added,  till  at 
last  the  evolution  of  gas  ceases  altogether.  The  colour  of  the  solution  varies 
remarkably  during  the  process  :  from  being  colourless  the  liquid  acquires  a  blue 
tint,  then  passes  into  bluish  green,  green,  yellow,  and  lastly  orange.  These  dif- 
ferent solutions  contain  different  relative  quantities  of  nitric  acid,  nitrous  acid, 
and  water,  on  which  circumstance  the  varying  shades  of  colour  depend.  Nitric 
and  nitrous  acids  are  disposed  to  unite  with  each  other,  and  the  influence  of  this 
attraction  enables  nitrous  acid  to  sustain  admixture  with  water  without  decompo- 
sition. Strong  nitric  acid  will  unite  with  a  considerable  quantity  of  nitrous  acid, 
and  thereby  acquires  an  orange  red  tint.  In  a  weaker  nitric  acid  the  water  de- 
composes part  of  the  nitrous  acid,  and  the  colour  of  the  solution  is  orange  or 


NITROGEN.  181 

yellow.  As  the  strength  of  the  nitric  acid  becomes  weaker  and  weaker,  the 
quantity  of  nitrous  acid  which  it  can  protect  from  decomposition  becomes  less  and 
less,  and  the  colour  of  the  solution  varies  from  yellow  to  green  and  blue,  and  is 
at  length  colourless.  These  changes  may  be  witnessed,  not  only  by  adding 
successive  quantities  of  nitrous  acid  to  water,  and  thereby  at  length  producing  a 
strong  nitric  acid,  but  commencing  with  the  latter,  saturating  it  with  nitrous  acid, 
and  then  successively  diluting  with  water. 

When  nitrous  acid  is  mixed  with  a  very  small  quantity  of  water,  no  binoxide 
of  nitrogen  is  disengaged,  but  the  liquid  becomes  green,  like  the  colour  of 
hyponitrous  acid.  I  have  repeatedly  obtained  a  similar  liquid  in  preparing  nitrous 
acid  from  nitrate  of  oxide  of  lead,  when  the  materials  were  not  adequately  dried  ; 
and  that  green  liquid,  when  allowed  to  dissipate  in  the  air,  leaves  some  nitric 
acid  behind.  From  these  facts  it  seems  probable  that  in  the  decomposition  of 
nitrous  acid  by  water,  the  first  change  is  the  conversion  of  nitrous  into  nitric  and 
hyponitrous  acids,  which  last  is  subsequently  changed,  when  the  required  quan- 
tity of  water  is  present,  into  nitric  acid  and  binoxide  of  nitrogen.  It  may  thus 
well  happen  that  hyponitrous  acid  contributes  to  produce  the  varying  colours 
above  described. 

Some  chemists  consider  nitrous  acid  as  a  compound  of  nitric  and  hyponitrous 
acids,  rather  than  of  nitrogen  and  oxygen.  In  fact,  on  adding  nitrous  acid  to  an 
alkaline  solution,  we  obtain  a  nitrate  and  hyponitrite  ;  a  circumstance  which  has 
given  rise  to  the  notion  that  nitrous  acid  cannot  act  as  a  distinct  acid. 

Its  eg.  is  46*15 ;  eq,  vol,  =  100 ;  symb.  N  -|-  40,  NO^,  or  N. 

NITRIC  ACID.  1 

Hist. — If  a  succession  of  electric  sparks  be  passed  through  a  mixture  of  oxy- 
gen and  nitrogen  gases  confined  in  a  glass  tube  over  mercury,  a  little  water  being 
present,  the  volume  of  the  gases  will  gradually  diminish,  and  the  water  after  a 
time  will  be  found  to  have  acquired  acid  properties.  On  neutralizing  the  solution 
with  potassa,  or  what  is  better,  by  putting  a  solution  of  that  alkali  instead  of 
water  into  the  tube  at  the  beginning  of  the  experiment,  a  salt  is  obtained  which 
possesses  all  the  properties  of  nitrate  of  potassa.  This  experiment  was  per- 
formed in  1785  by  Cavendish,  who  inferred  from  it  that  nitric  acid  is  composed 
of  oxygen  and  nitrogen,  though  the  acid  itself,  under  the  name  of  spirit  of  nitre, 
had  been  long  previously  known.  The  best  proportion  of  the  gases  was  found  to 
be  seven  of  oxygen  to  three  of  nitrogen ;  but  as  some  nitrous  acid  is  always 
formed  during  the  process,  the  exact  composition  of  nitric  acid  cannot  in  this 
way  be  accurately  determined. 

Nitric  acid  may  be  formed  much  more  conveniently  by  adding  binoxide  of 
nitrogen  slowly  over  water  to  an  excess  of  oxygen  gas.  Gay-Lussac  proved  that 
nitric  acid  may  in  this  manner  be  obtained  quite  free  from  nitrous  or  hyponitrous 
acid  ;  and  that  it  is  composed  of  100  measures  of  nitrogen  and  250  of  oxygen,  a 
result  fully  confirmed  by  Davy,  Henry,  Berzelius,  and  others. 

Nitric  acid  cannot  exist  in  an  insulated  state.  Binoxide  of  nitrogen  and  oxy- 
gen gases  never  form  nitric  acid  if  mixed  together  when  quite  dry ;  and  nitrods 
acid  vapour  may  be  kept  in  contact  with  oxygen  gas  without  change,  provided 
no  water  is  present.  The  most  simple  form  under  which  chemists  have  hitherto 
procured  nitric  acid  is  in  solution  with  water ;  a  liquid  which,  in  its  concentrated 


i^  NITROGEN. 

State,  is  the  nitric  acid  of  the  pharmacopoeia.  By  manufacturers  it  is  better  known 
by  the  name  of  aqua  fortis. 

The  nitric  acid  of  commerce  is  procured  by  decomposing  some  salt  of  nitric 
acid  by  means  of  oil  of  vitriol,  and  common  nitre,  as  the  cheapest  of  the  nitrates, 
is  employed  for  the  pui-pose.  This  salt,  previously  vv^ell  dried,  is  put  into  a  glass 
retort,  and  a  quantity  of  the  strongest  oil  of  vitriol  is  poured  upon  it.  On  apply- 
ing heat,  ebullition  ensues,  owing  to  the  escape  of  nitric  acid  vapours,  which 
must  be  collected  in  a  receiver  kept  cold  by  moist  cloths.  The  heat  should  be 
steadily  increased  during  the  operation,  and  continued  as  long  as  any  acid 
vapours  come  over. 

Chemists  differ  as  to  the  best  proportions  for  forming  nitric  acid.  The  London 
College  recommends  equal  weights  of  nitre  and  oil  of  vitriol ;  and  the  Edinburgh 
and  Dublin  colleges  employ  three  parts  of  nitre  to  two  of  the  acid.  In  the  pro- 
cess of  the  London  College  the  alkali  of  the  nitre  is  left  as  a  bisulphate  in  the 
retort;  since  .one  eq.  of  nitre  (54  nitric  acid  and  47  potassa)  is  100,  and  the 
nearly  equal  number  98  corresponds  to  2  eq.  of  oil  of  vitriol,  which  contain  2 
eq.  of  anhydrous  sulphuric  acid  and  3  eq.  of  water.  During  the  distillation  the 
nitric  acid  passes  over  along  with  1  eq.  of  water,  and  1  eq.  of  water  is  retained 
by  the  bisulphate  of  potassa.     The  reaction  may  be  tlius  expressed  : — 

KO,  NO5  +  2  (HO,  SO3)  =  HO,  NO5  f  (KO,  HO,  2SO3). 

The  presence  of  water  is  essential :  nitric  acid  of  1*50  consists  of  real  or  anhy- 
drous acid  and  water  in  the  ratio  of  1  eq.  of  each,  and  unless  water  in  at  least 
this  proportion  be  supplied,  a  proportional  quantity  of  nitric  acid  is  resolved,  at 
the  moment  of  quitting  the  potassa,  into  oxygeii  and  nitrous  acid  (Phillips,  in 
Phil.  Mag.  ii.  430).  If  the  mixture  be  introduced  into  the  retort  without  soiling 
its  neck,  and  the  heat  be  cautiously  raised,  the  product  will  be  quite  free  from 
sulphuric  acid  ;  and  therefore  the  second  distillation  from  nitre,  recommended  in 
the  pharmacopoeia,  is  superfluous. 

The  proportions  of  the  Edinburgh  and  Dublin  Colleges  are  such,  that  the 
residual  salt  is  a  mixture  of  sulphate  and  bisulphate  of  potassa.  The  acid  of  the 
nitre  does  not  receive  from  the  oil  of  vitriol  the  requisite  quantity  of  water,  and 
hence  part  of  it  is  decomposed,  yielding  towards  the  close  of  the  operation  an 
abundant  supply  of  nitrous  acid  fumes.  If  the  receiver  be  kept  cool,  nearly  all 
these  vapours  are  condensed,,  and  the  product  is  a  mixture  of  nitric  and  nitrous 
acids,  of  a  deep  orange  red  colour,  (the  nitroso  nitric  acid  of  Berzelius)  very 
strong  and  fuming,  and  of  a  greater  sp.  gr.  though  proportionally  less  in  quantity, 
than  that  obtained  by  the  foregoing  process.  The  sp.  gr.  of  the  pale  acid  is 
1*500  ;  while  that  of  the  red  acid  is  1*520,  or  by  previously  drying  the  nitre  and 
boiling  the  sulphuric  acid,  Hope  states  that  it  may  be  made  so  high  as  1*54. 

Some  manufacturers  decompose  nitre  with  half  its  weight  of  sulphuric  acid, 
thus  employing  the  ingredients  in  the  proportion  of  1  eq.  of  each.  In  this  case 
about  half  of  the  nitric  acid  is  decomposed,  and  considerable  loss  sustained,  un- 
less the  requisite  quantity  of  water  is  previously  mixed  with  the  sulphuric  acid, 
or  water  be  placed  in  the  receiver  to  condense  the  nitrous  acid.  Some  of  the 
nitre  is  likewise  apt  to  escape  decomposition;  and  the  residue,  consisting  of 
neutral  sulphate,  which  is  much  less  soluble  than  the  bisulphate,  is  removed 
from  the  retort  with  difficulty. 

In  none  of  the  preceding  processes,  not  even  in  the  first,  is  the  product  quite 


NITROGEN.  iy3 

colourless  :  for  at  the  commencement  and  close  of  the  operation,  nitrous  acid 
fumes  are  disengaged,  which  communicate  a  straw  yellow  or  an  orange  red  tint, 
according  to  their  quantity.  If  a  very  pale  acid  is  required,  two  receivers  should 
be  used,  one  for  condensing  the  colourless  vapours  of  nitric  acid,  and  another  for 
the  coloured  products.  The  coloured  acid  is  called  nitrous  acid  by  the  College  ; 
but  it  is  in  reality  a  mixture  or  compound  of  nitric  and  nitrous  acids,  similar  to 
what  may  be  obtained  by  mixing  anhydrous  nitrous  with  colourless  nitric  acid. 
It  is  easy  to  convert  the  common  mixed  acid  of  the  College  into  colourless  nitric 
acid,  by  exposing  the  former  to  a  gentle  heat  for  some  time,  when  all  the  nitrous 
acid  will  be  expelled.  But  this  process  is  rarely  necessary,  as  the  coloured  acid 
may  be  substituted  in  most  cases  for  that  which  is  colourless.  AVhere  an  acid 
of  great  strength  is  required,  the  former  is  even  preferable. 

Nitric  acid  frequently  contains  portions  of  sulphuric  and  hyrochloric  acid.  The 
former  is  derived  from  the  acid  which  is  used  in  the  process,  and  the  latter  from 
sea-salt  which  is  frequently  mixed  with  nitre.  These  impurities  may  be  detected 
by  adding  a  few  drops  of  a  solution  of  chloride  of  barium  and  oxide  of  silver  to 
separate  portions  of  nitric  acid,  diluted  with  three  or  four  parts  of  distilled  water. 
If  chloride  of  barium  cause  a  cloudiness  or  precipitate,  sulphuric  acid  must  be 
present ;  if  a  similar  effect  be  produced  by  nitrate  of  oxide  of  silver,  the  presence 
of  hydrochloric  acid  may  be  inferred.  Nitric  acid  is  purified  from  sulphuric  acid 
by  redistilling  it  from  a  small  quantity  of  nitrate  of  potassa,  with  the  alkali  of 
which  the  sulphuric  acid  unites,  and  remains  in  the  retort.  To  separate  hydro- 
chloric acid,  it  is  necessary  to  drop  a  solution  of  nitrate  of  oxide  of  silver  into 
the  nitric  acid  as  long  as  a  precipitate  is  formed,  and  draw  off  the  pure  acid  by 
distillation. 

Prop. — A  strong,  highly  corrosive  acid ;  in  its  purest  and  most  concentrated 
state  a  colourless  liquid,  of  sp.  gr.  1*50  or  1*510,  chemically  combined  with 
water,  from  which  it  cannot  be  separated  without  decomposition,  or  by  uniting 
with  some  other  body.  An  acid  of  sp.  gr.  1*50  contains  25  per  cent,  of  water, 
according  to  the  experiments  of  Phillips,  and  20*3  per  cent,  according  to  those  of 
Ure.*  Nitric  acid  of  this  strength  emits  dense,  white,  suffocating  vapours  when 
exposed  to  the  atmosphere.  It  attracts  watery  vapour  from  the  air,  whereby  its 
density  is  diminished.  A  rise  of  temperature  is  occasioned  by  mixing  it  with  a 
certain  quantity  of  water.  "When  58  measures  of  nitric  acid  of  sp.  gr.  1*5  are 
suddenly  mixed  with  42  of  water,  the  temperature  rises  from  60°  to  140°  ;  and 
the  mixture,  on  cooling  to  60°,  occupies  the  space  of  92*65  measures  instead  of 
100.  From  its  strong  affinity  for  water,  it  occasions  snow  to  liquefy  with  great 
rapidity ;  and  if  the  mixture  is  made  in  due  proportion,  intense  cold  will  be  gen- 
erated. (Page  40.)  It  boils  at  187°,  and  may  be  distilled  without  suffering 
material  change.  An  acid  of  lower  density  than  1*42  becomes  stronger  by  being 
heated ;  because  the  water  evaporates  more  rapidly  than  the  acid.  An  acid,  on 
the  contrary,  which  is  stronger  than  1*42  is  weakened  by  the  application  of  heat. 
It  may  be  frozen  by  cold  :  the  point  of  congelation  varies  with  the  strength  of 
the  acid.  The  strongest  acid  freezes  at  about  50°  below  zero.  When  diluted 
with  half  its  weight  in  water,  it  becomes  solid  at  — 1  ^° ;  but  a  little  more  water 
lowers  its  freezing  point  to  — 45°.  It  acts  powerfully  on  oxidable  substances, 
and  is  hence  much  employed  by  chemists  for  bringing  bodies  to  their  maximum 
of  oxidation.     Nearly  all  the  metals  are  oxidized  by  it ;  and  some  of  them,  such 

*  See  his  Table  in  the  Appendix,  showing  the  strength  of  diluted  acid  of  different  densities. 


184  NITROGEN. 

as  tin,  copper,  and  mercury,  are  attacked  with  great  violence.  If  flung  on  burning 
charcoal,  it  increases  the  brilliancy  of  its  combustion  in  a  high  degree.  Sulphur 
and  phosphorus  are  converted  into  acids  by  its  action.  All  vegetable  substances 
are  decomposed  by  it.  In  general  the  oxygen  of  the  nitric  acid  enters  into  direct 
combination  with  the  hydrogen  and  carbon  of  those  compounds,  forming  water 
with  the  former,  and  carbonic  acid  with  the  latter.  This  happens  remarkably  in 
those  compounds  in  which  hydrogen  and  carbon  are  predominant,  as  in  alcohol 
and  the  oils.  It  effects  the  decomposition  of  animal  matters  also.  The  cuticle 
and  nails  receive  a  permanent  yellow  stain  when  touched  with  it ;  and  if  applied 
to  the  skin  in  sufficient  quantity  it  acts  as  a  powerful  cautery,  destroying  the 
organization  of  the  part  entirely. 

When  oxidation  is  effected  through  the  medium  of  nitric  acid,  the  acid  itself 
is  commonly  converted  into  binoxide  of  nitrogen.  This  gas  is  sometimes  given 
off  nearly  quite  pure ;  but  in  general  some  nitrous  acid,  protoxide  of  nitrogen,  or 
pure  nitrogen,  are  evolved  at  the  same  time.  The  escape  of  nitrous  acid  in  these 
cases  seems  owing,  according  to  some  late  observations  of  Phillips,  not  so  much 
to  its  direct  formation,  as  to  the  binoxide  at  first  formed  acting  on  the  nitric  acid 
of  the  solution.  Direct  solar  light  deoxidizes  nitric  acid,  resolving  a  portion  of 
it  into  oxygen  and  nitrous  acid.  The  former  escapes  as  gas  ;  the  latter  is  absorbed 
by  the  nitric  acid,  and  converts  it  into  the  mixed  nitrous  acid  of  the  shops.  When 
the  vapour  of  nitric  acid  is  transmitted  through  red-hot  porcelain  tubes,  it  suffers 
complete  decomposition,  and  a  ihixture  of  oxygen  and  nitrogen  gases  is  the  pro- 
duct. 

Nitric  acid  may  also  be  deoxidized  by  transmitting  a  current  of  binoxide  of 
nitrogen  through  it.  That  gas,  by  taking  oxygen  from  the  nitric,  is  converted 
into  nitrous  acid  ;  and  a  portion  of  nitric  acid,  by  losing  oxygen,  passes  into  the 
same  compound.  The  nitrous  acid,  thus  derived  from  two  sources,  gives  a  colour 
to  the  nitric  acid,  the  depth  and  kind  of  which  depend  on  the  strength  of  the 
acid.  On  saturating  with  binoxide  of  nitrogen  four  separate  portions  of  nitric 
acid  of  sp.  gr.  1*15,  1*35,  1*40,  and  1*50,  the  colour  will  be  blue  in  the  first, 
green  in  the  second,  yellow  in  the  third,  and  brownish  red  in  the  fourth ;  and 
acid  of  1'05  is  not  coloured  at  all.  Pfiillips  found  that  acid  of  density  1'497  ac- 
quired a  density  1*541,  that  is,  was  made  stronger,  by  saturation  with  the  binox- 
ide ;  but  those  acids  which  become  green  are  much  weakened,  because  nitrous 
acid  vapour  is  mechanically  carried  off  by  those  portions  of  binoxide  which  pass 
unabsorbed  through  the  liquid. 

Tests. — All  the  salts  of  nitric  acid  are  soluble  in  water,  and  therefore  it  is  im- 
possible to  precipitate  that  acid  by  any  reagent.  The  presence  of  nitric  acid, 
when  uncombined,  is  readily  detected  by  its  strong  action  on  copper  and  mer- 
cury, emitting  ruddy  fumes  of  nitrous  acid,  and  by  its  forming  with  potassa  a 
neutral  salt,  which  crystallizes  in  prisms,  and  has  all  the  properties  of  nitre. 
Gold  leaf  is  a  still  more  delicate  test.  When  hydrochloric  acid  is  added  to  the 
solution  of  a  nitrate,  chlorine  is  disengaged,  and  the  liquid  hence  acquires  the 
property  of  dissolving  gold  leaf;  but  as  the  action  of  hydrochloric  acid  on  the 
salts  of  chloric,  bromic,  iodic,  and  selenic  acids  likewise  yields  a  solution  capable 
of  dissolving  gold,  no  inference  can  be  drawn  from  the  experiment,  unless  the 
absence  of  these  acids  shall  have  been  previously  demonstrated.  Another  cha- 
racter which  may  be  useful  is  to  mix  the  supposed  nitric  acid  or  nitrate  with 
dilute  sulphuric  acid  in  a  tube,  add  a  few  fragments  of  pure  zinc,  and  set  fire  to 
the  hydrogen  as  it  issues :  if  nitric  acid  be  present,  the  flame  of  the  hydrogen 


CARBON.  185 

will  have  a  greenish  white  tint,  due  to  admixture  with  binoxide  of  nitrogen.  This 
test  occurred  to  my  assistant,  Mr.  Balmain ;  and  Mr.  Maitland  at  the  same  time 
proposed  alcohol  instead  of  zinc  with  the  same  intention.  A  very  delicate  test 
has  been  proposed  by  O'Shaughnessy,  founded  on  the  orange  red  followed  by  a 
yellow  colour,  which  nitric  acid  communicates  to  morphia.  The  supposed  nitrate 
is  heated  in  a  test  tube  with  a  drop  of  sulphuric  acid,  and  then  a  crystal  of  mor- 
phia is  added.  (Lancet,  1829-30.)  It  is  advisable  to  try  the  process  in  a  sepa- 
rate tube  with  the  sulphuric  acid  alone,  in  order  to  prove  the  absence  of  .nitric 
acid.  But  the  most  delicate  test  is  the  following,  proposed  by  Derbanius  de 
Richemont : — The  suspected  substance  is  mixed  with  pure  sulphuric  acid  in  a 
tube,  and  gently  warmed,  and  a  solution  of  green  vitriol  cautiously  added.  At 
the  line  of  junction  of  the  two  liquids,  the  dark  colour  produced  by  the  action  of 
nitric  acid  on  the  protosulphate  of  iron  is  distinctly  seen,  even  when  only  35  J^^j 
of  nitric  acid  is  present.* 


SECTION  VI. 


CARBON. 


Hist,  and  Prep. — It  occurs  pure  and  crystallized  in  forms  of  the  octohedral 
system  in  the  diamond,  a  mineral  of  unknown  origin,  but  probably  derived  from 
the  slow  decomposition  of  vegetable  matter.  It  is  sometimes  a  constituent  of  the 
rocks  in  the  form  of  small  tabular  crystals  called  graphite,  and  in  larger  masses 
mixed  with  iron,  as  plumbago  with  which  pencils  are  made,  and  in  anthracite 
mixed  with  earth  and  metallic  sulphurets.  It  is  the  essential  principle  of  the 
different  varieties  of  charcoal — the  black  mass  left  when  most  vegetable  and  ani- 
mal matters  are  heated  to  redness  in  close  vessels,  and  which  contains  any  fixed 
principles  originally  present  in  its  source.  Common  charcoal  is  made  from  wood 
and  contains  about  l-50th  of  its  weight  of  alkaline  and  earthy  salts,  which  con- 
stitute the  ashes  when  wood-charcoal  is  burned.  Coke  is  the  charcoal  from  coal, 
ivory  black  or  animal  charcoal  is  that  from  bones,  lamp-black  from  resin.  Very 
pure  varieties  of  charcoal  may  be  formed  from  spirit  of  wine,  turpentine,  sugar, 
and  starch. 

Prop. — Carbon,  as  it  exists  in  the  diamond,  is  the  hardest  substance  in  nature; 
sp.  gr.  3'52;  it  crystallizes  in  the  regular  system  in  forms  which  are  frequently 
hemihedral,  and  are  characterized  by  a  perfect  cleavage  parallel  to  the  faces  of 
the  octohedron ;  beautifully  transparent  and  a  powerful  refractor  of  light ;  a  non- 
conductor of  heat  and  electricity.  It  is  very  unchangeable,  resists  the  action  of 
acids  and  alkalies,  and  bears  the  most  intense  heat  in  close  vessels  without  fusing 
or  undergoing  any  perceptible  change.  Heated  to  redness  in  the  open  air,  it  is 
entirely  consumed.  Newton  first  suspected  it  to  be  combustible  from  its  great 
refracting  power,  a  conjecture  which  was  rendered  probable  by  the  experiments 

*  The  bleaching  effect  which  it  exercises  upon  a  boiling  solution  of  the  sulphate  of  Indig(^ 
is  another  good  test;  provided,  all  traces  of  chlorine  are  absent. — (R.) 


186 


CARBON. 


of  the  Florentine  academicians  in  1694.  Lavoisier  first  proved  it  to  contain  car- 
bon by  throwing  the  sun's  rays,  concentrated  by  a  powerful  lens,  upon  a  diamond 
contained  in  a  vessel  of  oxygen  gas.  The  diamond  was  consumed  entirely,  oxy- 
gen disappeared,  and  carbonic  acid  w^as  generated.  It  has  since  been  demonstrated 
by  the  researches  of  Guyton-Morveau,  Smithson  Tennant,  Allen  and  Pepys,  and 
Davy,  that  carbonic  acid  is  the  product  of  its  combustion.  Guyton-Morveau  in- 
ferred from  his  experiments  that  the  diamond  is  pure  carbon,  and  that  charcoal 
is  an  oxide  of  carbon.  Tennant  burned  diamonds  by  heating  them  with  nitre  in 
a  gold  tube ;  and  comparing  his  own  results  with  those  of  Lavoisier  on  the  com- 
bustion of  charcoal,  he  concluded  that  equal  weights  of  diamond  and  pure  char- 
coal, in  combining  with  oxygen,  yield  precisely  equal  quantities  of  carbonic  acid. 
He  was  thus  induced  to  adopt  the  opinion,  that  charcoal  and  the  diamond  are 
chemically  the  same  substance ;  and  that  the  difference  in  their  physical  character 
is  solely  dependent  on  a  difference  of  aggregation.*  This  conclusion  was  con- 
firmed by  the  experiments  of  Allen  and  Pepysf ,  and  Davy:|:,  who  compared  the 
product  of  the  combustion  of  the  diamond  with  that  derived  from  different  kinds 
of  charcoal.  The  latter  chemist  did  indeed  observe  the  production  of  a  minute 
quantity  of  water  during  the  combustion  of  the  purest  charcoal,  indicative  of  a 
trace  of  hydrogen:  but  its  quantity  is  so  small,  that  it  cannot  be  regarded  as  a 
necessary  constituent.  It  proves  only  that  a  trace  of  hydrogen  is  retained  by 
charcoal  with  such  force,  that  it  cannot  be  expelled  by  the  temperature  of  ignition. 

Charcoal,  as  obtained  from  wood,  is  hard  and  brittle,  conducts  heat  very 
slowly,  but  is  a  good  conductor  of  electricity;  quite  insoluble  in  water,  is 
attacked  with  difficulty  by  nitric  acid,  and  is  little  affected  by  any  of  the  other 
acids,  or  by  the  alkalies.  It  undergoes  little  change  from  exposure  to  air  and 
moisture,  being  less  injured  under  these  circumstances  than  wood.  It  is  exceed- 
ingly refractory  in  the  fire,  if  excluded  from  the  air,  supporting  the  most  intense 
heat  which  chemists  are  able  to  produce  without  change. 

It  possesses  the  property  of  absorbing  a  large  quantity  of  air  or  other  gases  at 
common  temperatures,  and  of  yielding  the  greater  part  of  them  again  when  it  is 
heated.  It  appears  from  the  researches  of  Saussure,  that  different  gases  are 
absorbed  by  it  in  different  proportions.  His  experiments  were  performed  by 
plunging  a  piece  of  red-hot  charcoal  under  mercury,  and  introducing  it  when 
cool  into  the  gas  to  be  absorbed.  He  found  that  charcoal  prepared  from  box- 
wood absorbs,  during  the  space  of  24  or  36  hours,  of 


Ammoniacal  gas 

, 

90  times  its  volume. 

Muriatic  acid 

. 

85 

Sulphurous  acid 

. 

65 

Sulphuretted  hydrogen 

81  (Dr.  C.  Henry.) 

Nitrous  oxide 

40 

Carbonic  acid 

35 

defiant  gas 

35 

Carbonic  oxide 

9-42 

Oxygen 

9-25 

Nitrogen 

7-5 

Hydrogen 

1-75 

The  absorbing  power  of  charcoal,  with  respect  to  gases,  cannot  be  attributed 
to  chemical  action ;  for  the  quantity  of  jeach  gas  which  is  absorbed  bears  no  rela- 


*  Phil.  Trans.  1797. 


t  Ibid.  1807. 


t  Ibid.  1814. 


CARBON.  18t 

tion  whatever  to  its  affinity  for  charcoal.  The  effect  is  in  reality  owing  to  the 
peculiar  porous  texture  of  that  suhstance,  which  enables  it,  in  com!hon  with 
most  spongy  bodies,  to  absorb  more  or  less  of  ail  gases,  vapours,  and  liquids 
with  which  it  is  in  contact.  This  property  is  most  remarkable  in  charcoal  pre- 
pared from  wood,  especially  in  the  compact  varieties  of  it,  the  pores  of  which 
are  numerous  and  small.  It  is  materially  diminished  by  reducing  the  charcoal 
to  powder ;  and  in  plumbago,  which  has  not  the  requisite  degree  of  porosity,  it 
is-wanting  altogether. 

The  porous  texture  of  charcoal  accounts  for  the  general  fact  of  absorption 
only ;  its  power  of  absorbing  more  of  one  gas  than  of  another,  must  be  explained 
on  a  different  principle.  This  effect,  though  modified  to  all  appearance  by  the 
influence  of  chemical  attraction,  seems  to  depend  chiefly  on  the  natural  elasticity 
of  the  gases.  Those  which  possess  such  a  great  degree  of  elasticity  as  to  have 
hitherto  resisted  all  attempts  to  condense  them  into  liquids,  are  absorbed  in  the 
smallest  proportion ;  while  those  that  admit  of  being  converted  into  liquids  by 
compression,  are  absorbed  more  freely.  For  this  reason,  charcoal  absorbs 
vapours  more  easily  than  gases,  and  liquids  than  either. 

Allen  and  Pepys  determined  experimentally  the  increase  in  weight  experienced 
by  different  kinds  of  charcoal,  recently  ignited,  after  a  week's  exposure  to  the 
atmosphere.  The  charcoal  from  fir  gained  13  per  cent. ;  that  from  lignum  viiae, 
9*6  ;  that  from  box,  14  ;  from  beech,  16*3;  from  oak,  16*5 ;  and  from  mahogany, 
18.  The  absorption  is  most  rapid  during  the  first  24  hours.  The  substance 
absorbed  is  both  water  and  atmospheric  air,  which  the  charcoal  retains  with  such 
force,  that  it  cannot  be  completely  separated  from  them  without  exposure  to  a 
red  heat.  Vogel  has  observed  that  charcoal  absorbs  oxygen  in  a  much  greater 
proportion  from  the  air  than  nitrogen.  Thus,  when  recently  ignited  charcoal, 
cooled  under  mercury,  was  put  into  a  jar  of  atmospheric  air,  the  residue  contained 
only  8  per  cent,  of  oxygen  gas ;  and  if  red-hot  charcoal  be  plunged  into  water, 
and  then  introduced  into  a  vessel  of  air,  the  oxygen  disappears  almost  entirely. 
It  is  said  that  pure  nitrogen  may  be  obtained  in  this  way.  (Schweigger's  Jour- 
nal, iv.) 

Charcoal  likewise  absorbs  the  odoriferous  and  colouring  principles  of  most 
animal  and  vegetable  substances.  When  coloured  infusions  of  this  kind  are 
digested  with  a  due  quantity  of  charcoal,  a  solution  is  obtained,  which  is  nearly 
if  not  quite  colourless.  Tainted  flesh  may  be  deprived  of  its  odour  by  this 
means,  and  foul  water  be  purified  by  filtration  through  charcoal.  The  substance 
commonly  employed  to  decolorize  fluids  is  animal  charcoal  reduced  to  a  fine 
powder.  It  loses  the  property  of  absorbing  colouring  matters  by  use,  but  reco- 
vers it  by  being  heated  to  redness. 

Charcoal  is  highly  combustible.  When  strongly  heated  in  the  open  air,  it 
takes  fire,  and  burns  slowly.  In  oxygen  gas,  its  combustion  is  lively,  and 
accompanied  with  the  emission  of  sparks.  In  both  cases  it  is  consumed  without 
flame,  smoke,  or  residue,  if  quite  pure ;  and  carbonic  acid  gas  is  the  product  of 
its  combustion. 

i       Its  eq.  is  =  6*12 ;  its  vapour  (theoretical,  p.  140)  has  a  sp.  gr.  =  0'4215,  and 

i  eq,  vol.  =  100,  and  100  C.  I.  weigh  13-153  grains. 

The  composition  of  the  compounds  of  carbon  described  in  this  section  is  as 

!  follows : — 


Carbon. 

Oxygen. 

Equiv. 

Formulae. 

Carbonic  Oxide 

6-12  or  1  eq. 

+ 

8  or  1  eq. 

=     14-12 

CfOorCO. 

Carbonic  Acid 

6-12  or  1  eq. 

+ 

16  or  2  eq. 

=    22-12 

C  f  20  or  C02. 

1S8  CARBON. 

Carbonic  oxide  gas  is  theoretically  considered  as  a  compound  of  100  measures 
of  the  v^our  of  carbon  and  50  of  oxygen  condensed  into  100  measures ;  and 
carbonic  acid  gas,  of  100  measures  of  the  vapour  of  carbon  and  100  of  oxygen 

condensed  into  100  measures. 

< 

CARBONIC  ACID. 

Hist. — Discovered  by  Black  in  1757,  and  described  by  him  in  his  inauguraK 
dissertation  on  magnesia  under  the  name  of  Jixed  air.  He  observed  the  exist- 
ence of  this  gas  in  common  limestone  and  magnesia,  and  found  that  it  may  be 
expelled  from  these  substances  by  the  action  of  heat  or  acids.  He  also  remarked 
that  the  same  gas  is  formed  during  respiration,  fermentation,  and  combustion. 
Its  composition  was  first  demonstrated  synthetically  by  Lavoisier,  who  burned 
carbon  in  oxygen  gas,  and  obtained  carbonic  acid  as  the  product.  The  same 
experiment  has  been  repeated  by  Davy,  Allen  and  Pepys,  and  others,  with  the 
result  that  in  the  combustion  of  diamond  or  other  pure  carbonaceous  matter  the 
oxygen  undergoes  no  change  of  volume,  or  in  other  words,  that  carbonic  acid 
gas  contains  its  own  volume  of  oxygen  :  hence  the  difference  of  the  sp.  gravi- 
ties of  carbonic  acid  and  oxygen  gases  (1*524  — 1*1025),  or  0*4215,  gives  the 
exact  ratio  of  the  quantities  of  carbon  and  oxygen  combined,  being  0*4215  to 
1*1025,  or  6*12  to  16.  Smithson  Tennant  illustrated  its  nature  analytically  by 
passing  the  vapour  of  phosphorus  over  chalk,  or  carbonate  of  lime,  heated  to 
redness  in  a  glass  tube.  The  phosphorus  took  oxygen  from  the  carbonic  acid, 
charcoal  in  the  form  of  a  light  black  powder  was  deposited,  and  the  phosphoric 
acid,  which  was  formed,  united  with  the  lime. 

Prep. — Conveniently  by  the  action  of  hydrochloric  acid,  diluted  with  two  or 
three  times  its  weight  of  water,  on  fragments  of  marble,  when  carbonic  acid  gas 
escapes  with  effervescence,  and  chloride  of  calcium  is  left  in  solution. 

Prop. — Commonly  a  colourless  gas  of  a  pungent  odour  and  acidulous  taste, 
condensable  at  32°  by  a  pressure  of  36  atmospheres  into  a  liquid,  which  con- 
geals by  the  cold  produced  by  its  own  evaporation,  estimated  at  —  148°,  and  at 
that  temperature  is  solid  under  the  atmospheric  pressure,  being,  until  recently, 
the  first  instance  of  a  solidified  gas  (page  53).  The  sp.  gr.  of  the  gas  is  1*524, 
and  100  C.  I.  at  60°  and  30  Bar.  weigh  47*262  grains ;  the  sp.  gr.  of  the  liquid 
at  32°  is  0*83  ;  it  dilates  remarkably  from  heat,  its  expansion  being  upwards  of 
four  times  that  of  air,  20  volumes  of  the  liquid  at  32°  occupying  29  volumes  at 
86°,  and  its  sp.  gr.  varies  from  0*9  to  0*6  as  the  temperature  rises  from  —  4°  to 
+  86°.  When  heated  from  32°  to  86°  its  elasticity  rises  from  36  to  73  atmos- 
pheres, being  0*68  atmospheres  for  each  degree.  It  is  insoluble  in  water  and  fat 
oils,  but  soluble  in  all  proportions  in  ether,  alcohol,  naphtha,  oil  of  turpentine, 
and  bisulphuret  of  carbon.  The  evaporation  of  its  ethereal  solution  causes  an 
intense  degree  of  cold,  by  which  large  quantities  of  mercury  may  be  frozen. 
(Thilorier  in  Ann.  de  Ch.  et  Ph.  Ix.  427.) 

Carbonic  acid  gas  extinguishes  burning  substances  of  all  kinds,  and  the  com- 
bustion does  not  cease  from  the  want  of  oxygen  only.  It  exerts  a  positive 
influence  in  checking  combustion,  as  appears  from  the  fact,  that  a  candle  cannot 
bum  in  a  gaseous  mixture  composed  of  four  measures  of  atmospheric  air,  and 
one  of  carbonic  aid. 

It  is  not  better  qualified  to  support  the  respiration  of  animals ;  for  its  pre- 
sence, even  in  moderate  proportion,  is  soon  fatal.  An  animal  cannot  live  in  air 
which  contains  sufficient  carbonic  acid  for  extinguishing  a  lighted  candle ;  and 


CARBON.  IQC) 

hence  the  practical  rule  of  letting  down  a  burning  taper  into  old  wells  or  pits 
before  any  one  ventures  to  descend.  If  the  light  is  extinguished,  the  air  is  cer- 
tainly impure ;  and  there  is  generally  thought  to  be  no  danger,  if  the  candle 
continues  to  burn.  But  some  instances  have  been  known  of  the  atmosphere 
being  sufficiently  loaded  with  carbonic  acid  to  produce  insensibility,  and  yet  not 
so  impure  as  to  extinguish  a  burning  candle.  (Christison  on  Poisons,  2nd  ed. 
707.)  When  an  attempt  is  made  to  inspire  pure  carbonic  acid,  violent  spasm 
of  the  glottis  takes  place,  which  prevents  the  gas  from  entering  the  lungs.  If 
it  be  so  much  dilated  with  air  as  to  admit  of  its  passing  the  glottis,  it  then  acts 
as  a  narcotic  poison  on  the  system.  It  is  this  gas  which  has  often  proved 
destructive  to  persons  sleeping  in  a  confined  room  with  a  pan  of  burning  charcoal. 
It  is  quite  incombustible,  and  cannot  be  made  to  unite  with  an  additional  por- 
tion of  oxygen.    It  is  a  compound,  therefore,  in  which  carbon  is  in  its  highest^ 

degree  of  oxidation,  ~" • 

Lime  water  becomes  turbid  when  brought  into  contact  with  carbonic  acid. 
The  lime  unites  with  the  gas,  forming  carbonate  of  lime,  which,  from  its  insolu- 
bility in  water,  at  first  renders  the  solution  milky,  and  afterwards  forms  a  white 
flaky  precipitate.  Hence  lime  water  is  not  only  a  valuable  test  of  the  presence 
of  carbonic  acid,  but  is  frequently  used  to  withdraw  it  altogether  from  any 
gaseous  mixture  that  contains  it. 

Recently  boiled  water  dissolves  its  own  volume  of  carbonic  acid  gas  at  60° 
and  30  Bar. ;  but  it  will  tai^e  up  much  more  if  the  pressure  be  increased.  The 
quantity  of  the  gas  absorbed  is  in  exact  ratio  with  the  compressing  force ;  that 
is,  water  dissolves  twice  its  volume  when  the  pressure  is  doubled,  and  three 
times  its  volume  when  the  pressure  is  trebled.  A  saturated  solution  may  be 
made  by  transmitting  a  stream  of  the  gas  through  a  vessel  of  cold  water  during 
the  space  of  half  an  hour,  or  still  better  by  the  use  of  a  Woulfe's  bottle  or  Nooth's 
apparatus,  so  as  to  aid  the  absorption  by  pressure.  Water  and  other  liquids, 
which  have  been  charged  with  carbonic  acid  under  great  pressure,  lose  the 
greater  part  of  the  gas  when  the  pressure  is  removed.  The  effervescence  which 
takes  place  on  opening  a  bottle  of  ginger  beer,  cider,  or  brisk  champaigne,  is 
owing  to  the  escape  of  carbonic  acid  gas.  Water,  if  fully  saturated  with  car- 
bonic acid  gas,  sparkles  when  it  is  poured  from  one  vessel  into  another.  The 
solution  has  an  agreeably  acidulous  taste,  and  gives  to  litmus  paper  a  red  stain, 
which  is  lost  on  exposure  to  the  air.  On  the  addition  of  lime  water  to  it,  a 
cloudiness  is  produced,  which  at  first  disappears,  because  the  carbonate  of  lime 
is  soluble  in  excess  of  carbonic  acid ;  but  a  permanent  precipitate  ensues  when 
the  free  acid  is  neutralized  by  an  additional  quantity  of  lime  water.  The  water 
which  contains  carbonic  acid  in  solution  is  wholly  deprived  of  the  gas  by  boil- 
ing. Removal  of  pressure  from  its  surface  by  means  of  the  air-pump  has  a 
similar  effect. 

The  agreeable  pungency  of  beer,  porter,  and  ale,  is  in  a  great  measure  owing 
to  the  presence  of  carbonic  acid  ;  by  the  loss  of  which,  on  exposure  to  the  air, 
IHhey  become  stale.  All  kinds  of  spring  and  well  water  contain  carbonic  acid 
absorbed  from  the  atmosphere,  and  to  which  they  are  partly  indebted  for  their 
pleasant  flavour.  Boiled  water  has  an  insipid  taste  from  the  absence  of  carbonic 
acid. 

Carbonic  acid  is  always  present  in  the  atmosphere,  even  at  the  summit  of  the 
highest  mountains,  or  at  a  distance  of  several  thousand  feet  above  the  ground. 
Its  presence  may  be  demonstrated  by  exposing  lime  water  in  an  open  vessel  to 


190  CARBON. 

the  air,  when  its  surface  will  soon  be  covered  with  a  pellicle,  which  is  carbonate 
of  lime.  The  origin  of  the  carbonic  acid  is  obvious.  Besides  being  formed 
abundantly  by  the  combustion  of  all  substances  which  contain  carbon,  the  respi- 
ration of  animals  is  a  fruitful  source  of  it,  as  may  be  proved  by  breathing  for  a 
few  minutes  into  lime  water ;  and  it  is  also  generated  in  all  the  spontaneous  ^ 
changes  to  which  dead  animal  and  vegetable  matters  are  subject.  The  carbonic 
acid  proceeding  from  such  sources  is  commonly  diffused  equably  through  the 
air ;  but  when  any  of  these  processes  occur  in  low  confined  situations,  as  at  the 
bottom  of  old  wells,  the  gas  is  then  apt  to  accumulate  there,  and  form  an  atmos- 
phere called  cholte.  damp,  which  is  fatal  to  any  animals  that  are  placed  in  it. 
These  accumulations  happily  never  take  place,  except  when  there  is  some  local 
origin  for  the  carbonic  acid  ;  as,  for  example,  when  it  is  generated  by  fermenta- 
tive processes  going  on  at  the  surface  of  the  ground,  or  when  it  issues  directly 
from  the  earth,  as  happens  at  the  Grotto  del  Cane  in  Italy,  and  at  Pyrmont  in 
Westphalia.  There  is  no  real  foundation  for  the  opinion  that  caibonic  acid  can 
separate  itself  from  the  great  mass  of  the  atmosphere,  and  accumulate  in  a  low 
situation  merely  by  the  force  of  gravity.  Such  a  supposition  is  contrary  to  the 
well-known  tendency  of  gases  to  diffuse  themselves  equally  through  each  other. 
It  is  also  contradicted  by  observation ;  for  many  deep  pits,  which  are  free  from 
putrefying  organic  remains,  though  otherwise  favourably  situated  for  such  accu- 
mulations, contain  pure  atmospheric  air. 

Though  carbonic  acid  is  the  product  of  many  natural  operations,  chemists  have 
not  hitherto  noticed  any  increase  in  the  quantity  contained  in  the  atmosphere. 
The  only  known  process  which  tends  to  prevent  increase  in  its  proportion,  is 
that  of  vegetation.  Growing  plants  purify  the  air  by  withdrawing  carbonic  acid, 
and  yielding  an  equal  volume  of  pure  oxygen  in  return ;  but  whether  a  full 
compensation  is  produced  by  this  cause  has  not  yet  been  satisfactorily  deter- 
mined. 

Carbonic  acid  is  contained  in  the  earth.  Many  mineral  springs,  such  as  those 
of  Tunbridge,  Pyrmont,  and  Carlsbad,  are  highly  charged  with  it.  In  combi- 
nation with  lime  it  forms  extensive  masses  of  rock,  which  geologists  have  found 
to  occur  in  all  countries,  and  in  every  formation. 

Carbonic  acid  unites  with  alkaline  substances,  and  the  salts  so  constituted  are 
called  carbonates.  Its  acid  properties  are  feeble,  so  that  it  is  unable  to  neutralize 
completely  the  alkaline  properties  of  potassa,  soda,  and  lithia.  For  the  same 
reason,  all  the  carbonates,  without  exception,  are  decomposed  by  the  hydrochloric 
and  all  the  stronger  acids ;  when  carbonic  acid  is  displaced,  and  escapes  in  the 
form  of  gas. 

Its  eg.  is  22'12;  eg.  vol.  =  100 ;  si/mb.  C  -\-  20,  COj,  or  C. 


CARBONIC  OXIDE  GAS. 


Hist. — Priestley  discovered  it  by  igniting  chalk  in  a  gun-barrel,  and  afterwari 
obtained  it  by  heating  a  mixture  of  chalk  and  iron  filings.     He  supposed  it  to 
be  hydrogen  mixed  with  carbonic  acid.      Its  real  nature  was  pointed  out  by 
Cruickshank  (Nicholson's  Journal,  4to  ed.  v.),  and  about  the  same  time  b; 
Clement  and  Desormes  (An.  de  Chimie,  xxxix.). 

Prep. — 1.  By  transmitting  carbonic  acid  gas  over  red-hot  fragments  of  chai 
coal  contained  in  a  tube  of  iron  or  porcelain.  2.  By  igniting  alkaline  or  earth; 
carbonates  with  iron  filings,  charcoal,  or  some  deoxidizing  substance.     3.  B 


i 


CARBON.  191 

heating  binoxalate  of  potassa  with  five  or  six  times  its  weight  of  strong  oil  of 
vitriol  in  a  retort.  Effervescence  soon  ensues,  owing  to  the  escape  of  gas  con- 
sisting of  equal  measures  of  carbonic  acid  and  carbonic  oxide  gases ;  and  on 
absorbing  the  former  by  an  alkaline  solution,  the  latter  is  left  in  a  state  of  per- 
fect purity.  To  comprehend  the  theory  of  the  process  it  is  necessary  to  premise, 
that  oxalic  acid  is  a  compound  of  equal  measures  of  carbonic  acid  and  c^bonic 
oxide,  or  at  least  its  elements  are  in  the  proportion  to  form  these  gases ;  and  that 
it  cannot  exist  unless  in  combination  with  water  or  some  other  substance.  Now 
the  sulphuric  acid  unites  both  with  the  potassa  and  water  of  the  binoxalate,  and 
the  oxalic  acid  being  thus  set  free,  is  instantly  decomposed.  Oxalic  acid  may 
be  substituted  in  this  process  for  binoxalate  of  potassa.  The  following  equa- 
tion represents  the  reaction  ; — 

KO,  HO,  2C203t2S03=KO,  HO,  2SO3+2CO+2CO2. 

[4.  By  heating,  in  the  same  manner,  one  part  of  finely  powdered  ferrocyanide 
of  potassium  along  with  ten  parts  of  oil  of  vitriol.  The  salt  is  entirely  decom- 
posed, and  yields  an  abundant  supply  of  pure  carbonic  oxide.     (Fownes.*)] 

Prop. — A  colourless,  inodorous  gas;  sp.  gr.  =  0*9727,  and  100  C.  I.  at  60° 
and  30  Bar.  weigh  30*207  grains ;  has  neither  acid  nor  alkaline  properties ;  is 
sparingly  dissolved  by  water,  and  does  not  render  lime  water  turbid.  It  is 
inflammable.  When  a  lighted  taper  is  plunged  into  it,  the  taper  is  extinguished ; 
but  the  gas  itself  is  set  on  fire,  and  burns  calmly  at  its  surface  with  a  lambent 
blue  flame.  The  sole  product  of  its  combustion,  when  the  gas  is  quite  pure,  is 
carbonic  acid ;  a  fact  which  proves  that  it  does  not  contain  any  hydrogen.  It 
cannot  support  respiration.  It  acts  injuriously  on  the  system;  for  if  diluted  with 
air,  and  taken  into  the  lungs,  it  very  soon  occasions  headache  and  other  unplea- 
sant feelings ;  and  when  breathed  pure,  it  almost  instantly  causes  profound 
coma. 

A  mixture  of  carbonic  oxide  and  oxygen  gases  may  be  made  to  explode  by 
flame,  by  a  red-hot  solid  body,  or  by  the  electric  spark.  If  mixed  together  in 
the  ratio  of  100  measures  of  carbonic  oxide  and  rather  more  than  50  of  oxygen, 
and  the  mixture  is  inflamed  in  Volta's  Eudiometer  by  electricity  so  as  to  collect 
the  product  of  the  combustion,  the  whole  of  the  carbonic  oxide,  together  with  50 
measures  of  oxygen,  disappears,  and  100  measures  of  carbonic  acid  gas  occupy 
their  place.  From  this  fact,  first  ascertained  by  Berthollet,  and  since  confirmed 
by  subsequent  observation,  it  follows  that  carbonic  oxide  contains  half  as  much 
oxygen,  and  as  much  carbon,  as  carbonic  acid.  Accordingly  its  density  should 
be  0*4215  (sp.  gr.  of  carbon  vapour)  -j-  0*5512  (half  the  sp.  gr.  of  oxygen  gas) 
=  0*9727,  which  is  the  number  found  experimentally  by  Dulong  and  Berzelius. 
■'  The  two  first  processes  mentioned  for  generating  carbonic  oxide  will  now  be 
intelligible.  The  principle  of  the  methods  is  to  bring  carbonic  acid  at  a  red  heat 
in  contact  with  some  substance  which  has  a  strong  affinity  for  oxygen.  This 
condition  is  fulfilled  by  igniting  chalk,  or  any  carbonate  which,  can  bear  a  red 
heat  without  decomposition,  such  as  the  carbonates  of  baryta,  strontia,  soda, 
potassa,  or  lithia,  with  half  its  weight  of  iron  filings  or  charcoal.  The  carbonate 
t|  is  reduced  to  the  caustic  state,  and  its  carbonic  acid  is  converted  into  carbonic 
oxide  by  yielding  oxygen  to  the  iron  or  charcoal.  When  the  former  is  used, 
oxide  of  iron  is  the  product ;  when  charcoal  is  employed,  the  charcoal  itself  is 

*  Memoirs  Chem.  Soc.  Lond.,  i.  p.  215. 

t 


192  SULPHUR. 

oxidized,  and  yields  carbonic  oxide.  Tliis  gas  may  likewise  be  generated  by 
heating  to  redness  a  mixture  of  almost  any  metallic  oxide  with  one-sixlh  of  its 
weight  of  charcoal  powder.  The  oxides  of  zinc,  iron,  or  copper,  are  the  cheapest 
and  most  convenient.  In  all  these  processes  it  is  essential  that  the  ingredients 
be  quite  free  from  moisture  and  hydrogen,  otherwise  some  carburetted  hydrogen 
gas  would  be  generated.  The  product  should  always  be  washed  with  lime 
water  to  separate  it  from  carbonic  acid. 

Henry  has  ascertained  that  when  a  succession  of  electric  sparks  is  passed 
through  carbonic  acid  confined  over  mercury,  a  portion  of  that  gas  is  converted 
into  carbonic  oxide  and  oxygen.  When  a  mixture  of  hydrogen  and  carbonic  acid 
gases  is  electrified,  a  portion  of  the  latter  yields  one  half  of  its  oxygen  to  the 
former ;  water  is  generated,  and  carbonic  oxide  produced.  On  electrifying  a  mix- 
ture of  equal  measures  of  carbonic  oxide  and  protoxide  of  nitrogen,  both  gases  are 
decomposed  without  change  of  volume,  and  the  residue  consists  of  equal  mea- 
sures of^^arbonic  acid  and  nitrogen  gases.  The  carbonic  oxide  should  be  in  very 
slight  excess,  in  order  to  ensure  the  success  of  the  experiment.  On  this  fact  is 
founded  Henry's  method  of  analyzing  protoxide  of  nitrogen,  and  testing  its 
purity,  as  will  be  more  particularly  mentioned  in  the  fourth  part  of  the  work. 

[Carbonic  oxide  combines  also  with  chlorine  and  several  other  elementary 
bodies,  and  forms  compounds  in  which  it  appears  to  act  the  part  of  an  element, 
and  is  on  this  account  viewed  as  the  radical  of  a  series  of  bodies,  which  will  be 
treated  of  in  the  third  part  of  this  work  under  the  head  of  compound  or  organic 
radicals.] 

Us  eq.  is  14'12 ;  eq.  vol,  =  100 ;  symb.  C  +  0,  CO,  or  C. 


SECTION  VII. 


SULPHUR. 


d 


Hist. — It  occurs  as  a  mineral  production  in  some  parts  of  the  earth,  particu- 
larly in  the  neighbourhood  of  volcanoes,  as  in  Italy  and  Sicily.  It  is  commonly 
found  in  a  massive  state ;  but  it  is  sometimes  met  with  crystallized  in  the  form 
of  a  right  rhombjc  octohedron.  It  exists  much  more  abundantly  in  combination 
with  several  metals,  such  as  silver,  copper,  antimony,  lead,  and  iron.  It  is  pro- 
cured in  a  large  quantity  by  exposing  iron  pyrites  to  a  red  heat  in  close  vessels. 

Prop. — A  nearly  tasteless,  brittle  solid ;  colour  greenish  yellow  ;  odour  when 
rubbed  peculiar;  sp.  gr.  1*99  ;  non-conductor  of  electricity  and  heat.  Its  point 
of  fusion  is  232° ;  between  232°  and  280°  it  possesses  the  highest  degree  of 
fluidity,  is  then  of  aii  amber  colour,  and  if  cast  into  cylindrical  moulds,  forms  the 
common  roll  sulphur  of  commerce.  It  begins  to  thicken  near  320°,  and  acquires 
a  reddish  tint ;  and  at  temperatures  between  428°  and  482°,  it  is  so  tenacious  tha^ 
the  vessel  may  be  inverted  without  causing  it  to  change  its  place.  From  482^H 
to  its  boiling  point  it  again  becomes  liquid,  but  never  to  the  same  extent  as  when 
at  248°.  When  heated  to  at  least  428°,  and  then  poured  into  water,  it  becomes 
a  ductile  mass,  which  may  be  used  for  taking  the  impression  of  seals. 


SULPHUR.  -  193 

Fused  sulphur  has  a  tendency  to  crystallize  in  cooling.  A  crystalline  arrange- 
ment is  perceptible  in  the  centre  of  common  roll  sulphur ;  and  by  good  manage- 
ment regular  crystals  may  be  obtained.  For  this  purpose  several  pounds  of 
sulphur  should  be  melted  in  an  earthen  crucible ;  and  when  partially  cooled,  thG 
outer  solid  crust  should  be  pierced,  and  the  crucible  quickly  inverted,  so  that  the 
inner  and  as  yet  fluid  parts  may  gradually  flow  out.  On  breaking  the  solid  mass, 
when  quite  cold,  crystals  of  sulphur  will  be  found  in  its  interior. 

Sulphur  is  very  volatile.  It  begins  to  rise  slowly  in  vapour,  even  before  it  is 
completely  fused.  At  550°  or  600°  it  volatilizes  rapidly,  and  condenses  again 
unchanged  in  close  vessels.  Common  sulphur  is  purified  by  this  process;  and 
if  the  sublimation  be  conducted  slowly,  the  sulphur  collects  in  the  receiver  in 
the  form  of  detached  crystalline  grains,  called  flowers  of  sulphur.  In  this  state, 
however,  it  is  not  quite  pure,  for  the  oxygen  of  the  air  within  the  apparatus  com- 
bines with  a  portion  of  sulphur  during  the  process,  and  forms  sulphurous  acid. 
The  acid  may  be  removed  by  washing  the  flowers  repeatedly  with  water. 

The  sp.  gr.  of  sulphur  vapour  was  found  by  Dumas  to  lie  between  6*51 
and  6-617,  and  by  Mitscherlich  6-9  (An.  de  Ch.  et  Ph.  Iv.  8.)  :  its  sp.  gr.  by 
calculation  (page  140)  is  6*648.  Hence,  could  the  vapour  continue  as  such  at 
60°  and  30  Bar.,  100  cubic  inches  should  weigh  206*17  grains. 

Sulphur  is  insoluble  in  water.  It  dissolves  readily  in  boiling  oil  of  turpen- 
tine. The  solution  has  a  reddish  brown  colour  like  melted  sulphur,  and  if  fully 
saturated  deposits  numerous  small  crystals  in  cooling.  Its  best  solvent  is  liquid 
bisulphuret  of  carbon.  It  is  also  soluble  in  alcohol,  if  both  substances  are 
brought  together  in  the  form  of  vapour.  The  sulphur  is  precipitated  from  the 
solution  by  the  addition  of  water. 

Sulphur,  like  charcoal,  retains  a  portion  of  hydrogen  so  obstinately  that  it 
cannot  be  wholly  freed  from  it  either  by  fusion  or  sublimation.  Davy  detected 
its  presence  by  exposing  sulphur  to  the  strong  heat  of  a  powerful  galvanic  bat- 
tery, when  some  hydrosulphuric  acid  gas  was  disengaged.  The  hydrogen,  from 
its  minute  quantity,  can  only  be  regarded  in  the  light  of-  an  accidental  impurity, 
and  as  in  no  wise  essential  to  the  nature  of  sulphur. 

When  sulphur  is  heated  in  the  open  air  to  300°  or  a  little  higher,  it  kindles 
spontaneously,  and  burns  with  a  faint  blue  light.  In  oxygen  gas  its  combustion 
is  far  more  vivid ;  the  flame  is  much  larger,  and  of  a  bluish  white  colour.  Sul- 
phurous acid  is  the  product  in  both  instances  ; — no  sulphuric  acid  is  formed  even 
in  oxygen  gas  unless  moisture  be  present. 

Crystals  of  native  sulphur,  which  have  been  formed  by  the  condensation  of 
sulphurous  vapour,  as  well  as  those  which  are  deposited  from  a  solution  of  sul- 
phur in  any  menstruum,  possess  forms  which  are  either  identical,  or  connected 
by  being  referable  to  the  same  crystalline  axes.  Such,  on  the  contrary,  as  are 
produced  by  the  cooling  of  fused  sulphur  in  the  manner  above  described,  belong 
to  a  different  system  of  crystallization.  The  condition  determining  the  form  is 
temperature :  if  the  crystal  be  formed  below  232°,  it  belongs  to  the  right  prismatic 
system ;  if  at  that  point,  to  the  oblique  prismatic.  This  is  proved  by  the  influ- 
ence of  temperature  on  a  crystal  of  either  system  :  a  crystal  of  fusion  when  first 
formed  is  perfectly  clear  and  transparent,  but  kept  at  common  temperatures,  it 
soon  becomes  opaque,  and  presents  the  appearance  of  the  roll  sulphur  of  com- 
merce :  the  same  change  occurs  when  a  native  crystal  is  placed  in  a  solution  of 
a  salt  which  boils  at  232°.  The  opacity  is  in  both  cases  produced  by  a  new 
arrangement  of  the  particles  of  sulphur,  by  which,  without  any  change  in  the 

15 


194  SULPHUR. 

exterior  form,  the  internal  structure  of  the  crystal  is  altered  to  conespond  to  the 
crystallization  peculiar  to  the  temperature. 

The  eq.  of  sulphur  is  16'1 ;  eq.  vol.  16*66;  symh.  S, 

The  compounds  of  sulphur  described  in  this  section  are  composed  as  fol- 


Sulphur,  Oxygen.        Equiv.  FormulaB. 

Sulphurous  acid  161  or  1  eq.  -f  16  or  2  eq.  =  321  S  -^  20  or  SOj 

Sulphuric  acid  16-1  or  1  eq.  -f"  24  or  3  eq.  =  40-1  S  -f"  30  or  SO3 

Hyposulphurous  acid       322  or  2  eq.  -f  16  or  2  eq.  =  48-2  2S  -f"  20  or  S2O2 

Hyposulphuric  acid         32-2  or  2  eq.  -j-  40  or  5  eq.  =  72-2  2S  -[-  50  or  S A- 

l;'?L7phuricacid    }    48.3or3eq.t40or5eq.  =  88-3    38  +  50  or  S3O5. 
Hy"fu?pTuHc  acid  }      ^^'^  -  ^  ^<^'  +  ^^  -  ^  ^^•=  ^^^'^    '^  +  ^^  -  «*«- 

Taking  16*56  as  the  eq.  vol.  of  the  vapour  of  sulphur,  the  weight  of  which  is 
represented  by  1*108  (page  140),  these  compounds,  by  measure,  are  thus  consti- 
tuted : — 


Sulp.      Oxy. 

Cond.  into.               Densities. 

Sulphurous  acid 

16-66  t  100 

100            1-108  -j-  M025  =  2-2105 

Sulphuric  acid 

16-66  t  160 

100            M08t  1-6537  =  276i7 

Hyposulphurous  acid 

33-33  4-  100 

unknown. 

Hyposulphuric  acid 

33-33  t  250 

unknown. 

ffffi 


SULPHUROUS  ACID. 


Hist,  and  Prep. — Discovered  as  a  gas  by  Priestley.  It  is  the  sole  product  of 
the  combustion  of  sulphur  in  air  or  dry  oxygen  gas,  and  is  freely  evolved,  mixed 
with  carbonic  acid,  when  chips  of  wood,  straw,  cork,  oil,  or  most  other  organic  mat- 
ters are  heated  in  strong  sulphuric  acid,  which  yields  oxygen  to  the  carbon  and 
hydrogen  of  those  substances,  and  is  thereby  converted  into  sulphurous  acid. 
Nearly  all  the  metals,  with  the  aid  of  heat,  have  a  similar  effect :  one  portion  of 
the  acid  yields  oxygen  to  the  metal,  and  is  thus  reduced  to  sulphurous  acid ; 
while  the  metallic  oxide,  at  the  moment  of  its  formation,  unites  with  sulphuric 
acid.    A  very  pure  gas  may  thus  be  obtained  by  means  of  copper  or  mercury. 

Prop. — Commonly  gaseous,  colourless,  of  a  pungent  suffocating  odour,  being 
that  emitted  by  burning  sulphur ;  taste,  acid,  sp.  gr.  2*2105,  and  100  C.  I.  at 
60°  and  30  Bar.  weigh  68-691  grains;  it  is  liquid  at  45°  under  the  pressure  of 
two  atmospheres,  and  at  0°  under  that  of  one  atmosphere.  The  gas  extinguishes 
all  burning  bodies  which  are  immersed  into  it,  and  is  not  inflammable.  It  does 
not  support  respiration,  but  causes  violent  irritation  and  spasm  of  the  glottis ; 
and  even  when  diluted  with  air,  it  excites  cough  when  inspired,  and  causes  a 
peculiar  uneasiness  about  the  chest.  Water  at  60°  and  30  Bar.  dissolves  33 
times  its  volume,  the  solution  having  the  peculiar  odour  of  the  gas,  and  yielding 
it  unchanged  by  ebullition.  It  has  considerable  bleaching  properties  ;  at  first  it 
reddens  litmus  paper,  and  then  slowly  bleaches  it:  but  most  vegetable  colours, 
as  of  the  rose  and  violet,  are  speedily  removed  by  it  without  being  first  reddened. 
The  colouring  principle  is  not  destroyed,  but  may  be  restored  by  a  stronger  aci 
or  by  an  alkali. 

Davy  proved  that  sulphurous  acid  gas  contains  exactly  its  own  volume  of  0x3 


SULPHUR.  195 

gen  (Elements,  p.  273),  and  consequently  the  difference  in  the  weights  or  sp.  gr. 
.  of  these  gases  (2-2105  —  1.1025  =  I'lOS)  gives  the  weight  of  sulphur  combined 
with  oxygen.  The  sulphur  and  oxygen  are  thus  found  to  be  in  the  ratio  of 
M08  to  1-1025,  or  16*1  to  16. 

Liquid  sulphurous  acid  is  easily  obtained  by  transmitting  the  dry  pure  gas 
through  a  glass  tube  surrounded  by  a  freazing  mixture  of  snow  and  salt.  Its  sp. 
gr.  is  1-45  ;  it  boils  at  14°,  and  from  the  rapidity  of  its  evaporation  causes  intense 
cold  ;  it  conducts  electricity  (Kemp).  When  exposed  to  cold  in  the  moist  state, 
a  crystalline  solid  is  formed,  which  contains  20  per  cent,  of  water,  and  probably 
consists  of  one  eq.  of  the  acid  to  14  eq.  of  water. 

Though  sulphurous  acid  cannot  be  made  to  burn  by  the  approach  of  flame,  it 
has  a  very  strong  attraction  for  oxygen,  uniting  with  it  under  favourable  circum- 
stances, and  forming  sulphuric  acid.  The  presence  of  moisture  is  essential  to 
this  change.  A  mixture  of  sulphurous  acid  and  oxygen  gases,  if  quite  dry,  may 
be  preserved  over  mercury  for  any  length  of  time  without  chemical  action  ;  but 
if  a  little  water  be  admitted,  the  sulphurous  acid  gradually  unites  with  oxygen, 
and  sulphuric  acid  is  generated.  Many  of  the  chemical  properties  of  sulphurous 
acid  are  owing  to  its  afiinity  for  oxygen.  The  solutions  of  metals  which  have  a 
weak  affinity  for  oxygen,  such  as  gold,  platinum,  and  mercury,  are  completely 
decomposed  by  it,  those  substances  being  precipitated  in  the  metallic  form. 
Nitric  acid  converts  it  instantly  into  sulphuric  acid  by  yielding  some  of  its  oxy- 
gen. Peroxide  of  manganese  causes  a  similar  change,  and  is  itself  converted 
into  protoxide  of  manganese,  which  unites  with  the  resulting  sulphuric  acid. 

Sulphurous  acid  gas  may  be  passed  through  red-hot  tubes  without  decomposi- 
tion. Several  substances  which  have  a  strong  affinity  for  oxygen,  such  as 
hydrogen,  carbon,  and  potassium,  decompose  it  at  the  temperature  of  ignition. 

Sulphurous  acid  combines  with  metallic  oxides,  and  forms  salts  which  are 
called  sulphites,  which  are  decomposed  by  sulphuric  acid,  and  then  emit  the  cha- 
racteristic odour  of  sulphurous  acid. 

Its  eq.  is  32-1 ;  eq,  vol,  =  100 ;  symh,  S  +  20,  SO2,  or  S. 

SULPHURIC  ACID. 

Hist  and  Prep. — Sulphuric  acid,  or  oil  of  vitriol  as  it  is  often  called,  was 
discovered  by  Basil  Valentine  towards  the  close  of  the  15th  century.  It  is  pro- 
cured for  the  purposes  of  commerce  by  two  methods.  One  of  these  has  been 
long  pursued  in  the  manufactory  at  Nordhausen  in  Germany,  and  consists  in 
decomposing  sulphate  of  oxide  of  iron  (green  vitriol)  by  heat.  This  salt  con- 
tains 6  eq.  of  water  of  crystallization ;  and  when  strongly  dried  by  the  fire,  it 
crumbles  down  into  a  white  powder,  which,  according  to  Thomson,  contains  1 
eq.  of  water.  On  exposing  this  dried  protosulphate  to  a  red  heat,  its  acid  is 
wholly  expelled,  the  greater  part  passing  over  unchanged  into  the  receiver,  in 
combination  with  the  water  of  the  salt.  Part  of  the  acid,  however,  is  resolved 
by  the  strong  heat  employed  in  the  distillation  into  sulphurous  acid  and  oxygen. 
The  former  escapes  as  gas  throughout  the  whole  process  ;  the  latter  only  in  the 
middle  and  latter  stages,  since,  in  the  beginning  of  the  distillation,  it  unites  with 
the  protoxide  of  iron.     Peroxide  of  iron  is  the  sole  residue. 

The  acid,  as  procured  by  this  process,  is  a  dense,  oily  liquid  of  a  brownish 
tint.  It  emits  copious  white  vapours  on  exposure  to  the  air,  and  is  hence  called 
fuming  sulphuric  acid.    Its  sp.  gr.  is  1*896  or  1-90.     According  to  Thomson  it 


196  SULPHUR. 

consists  of  80  parts  or  2  eq.  of  anhydrous  acid,  and  9  parts  or  1  eq.  of  water. 
On  putting  this  acid  into  a  glass  retort,  to  which  a  receiver  surrounded  by  snow 
is  securely  adapted,  and  heating  it  gently,  a  transparent  colourless  vapour  passes 
over,  which  condenses  into  a  white  crystalline  solid.  This  substance  is  pure 
anhydrous  sulphuric  acid.  It  is  tough  and  elastic  ;  liquefies  at  66°  and  boils  at 
a  temperature  between  104°  and  122°,  forming,  if  no  moisture  is  present,  a  trans- 
parent vapour.  Exposed  to  the  air,  it  unites  with  watery  vapour,  and  flies  oif  in 
the  form  of  dense  white  fumes.  [It  has  so  strong  an  affinity  for  water  that  when 
dropped  into  that  liquid  it  hisses  like  a  hot  iron,  from  the  violence  of  the  combi- 
nation. It  has  no  acid  action  on  litmus  or  vegetable  blues,  unless  moisture  is 
present.  When  intensely  heated  it  is  resolved  into  sulphurous  acid  and  oxygen.] 
The  residue  of  the  distillation  is  no  longer  fuming,  and  is  in  every  respect  simi- 
lar to  the  common  acid  of  commerce. 

The  other  process  for  forming  sulphuric  acid,  which  is  practised  in  Britain  and 
inmost  parts  of  the  Continent,  is  by  burning  sulphur  previously  mixed  with  one- 
eighth  of  its  weight  of  nitrate  of  potassa.  The  mixture  is  burned  in  a  furnace 
so  contrived  that  the  current  of  air,  which  supports  the  combustion,  conducts  the 
gaseous  products  into  a  large  leaden  chamber,  the  bottom  of  which  is  covered  to 
the  depth  of  several  inches  with  water.  The  nitric  acid  yields  oxygen  to  a  por- 
tion of  sulphur,  and  converts  it  into  sulphuric  acid,  which  combines  with  the 
potassa  of  the  nitre ;  while  the  greater  part  of  the  sulphur  forms  sulphurous 
acid  by  uniting  with  the  oxygen  of  the  air.  The  nitric  acid,  in  losing  oxygen,  is 
converted,  partly  perhaps  into  nitrous  acid,  but  chiefly  into  binoxide  of  nitrogen, 
which,  by  mixing  with  air  at  the  moment  of  its  separation,  gives  rise  to  the  red 
nitrous  acid  vapours.  The  gaseous  substances,  present  in  the  leaden  chamber, 
are  therefore  sulphurous  and  nitrous  acids,  atmospheric  air,  and  watery  vapour. 
The  explanation  of  the  mode  in  which  these  substances  react  on  each  other,  so 
as  to  form  sulphuric  acid,  was  suggested  by  the  experiments  of  Clement  and 
Desormes  (An.  de  Ch.  lix.),  and  Davy  (Elements,  p.  276).  When  dry  sulphur- 
ous acid  gas  and  nitrous  acid  vapour  are  mixed  together  in  a  glass  vessel  quite 
free  from  moisture,  no  change  ensues ;  but  if  a  few  drops  of  water  be  added,  in 
order  to  fill  the  space  with  aqueous  vapour,  the  white  crystalline  compound, 
described  at  page  179,  is  immediately  produced.  Clement  and  Desormes  believed 
it  to  consist  of  sulphuric  acid,  binoxide  of  nitrogen,  and  water;  and  Davy,  of 
sulphurous  acid,  nitrous  acid,  and  water.  But  the  observation  that  the  same 
compound  may  be  made  with  sulphuric  and  anhydrous  nitrous  acids,  and  that 
when  decomposed  by  water  both  nitrous  acid  and  binoxide  of  nitrogen  are  dis- 
engaged, led  Gay-Lussac  to  the  opinion  which  now  seems  to  be  fully  substan- 
tiated by  experiment.  A  consistent  account  may,  therefore,  be  given  of  what 
really  takes  place  within  the  leaden  chambers. — The  mutual  reaction  of  humidity, 
sulphurous  acid,  and  nitrous  acid,  gives  rise  to  the  crystalline  compound  of  sul- 
phuric acid,  hyponitrous  acid,  and  water;  and  when  this  solid  falls  into  the  water 
of  the  chamber,  it  is  instantly  decomposed,  sulphuric  acid  is  dissolved,  and 
nitrous  acid  and  binoxide  of  nitrogen  escape  with  effervescence.  The  nitrous 
acid  thus  set  free,  as  well  as  that  reproduced  by  the  binoxide  uniting  with  the 
oxygen  of  the  atmosphere,  is  again  intermixed  with  sulphurous  acid  and  humi- 
dity, and  thus  gives  rise  to  a  second  portion  of  the  crystalline  solid,  which 
undergoes  the  same  change  as  the  first.  A  certain  portion  of  nitric  acid  is 
usually  formed  by  the  action  of  water  on  the  nitrous  acid ;  but  the  presence  of 
sulphuric  acid  in  that  water  tends  to  prevent  the  free  decomposition  of  nitrous 


J 


SULPHUR.  197 

acid  which  pure  water  produces.  Nay,  when  the  water  hecomes  pretty  strongly 
acid,  the  nitric  acid  at  first  generated  is  reduced,  by  absorbed  sulphurous  acid, 
into  the  hyponitrous,  which  unites  with  sulphuric  acid,  and  remains  even  after 
concentration ;  it  is  the  cause  of  the  evolution  of  binoxide  of  nitrogen  which 
usually  ensues  when  common  oil  of  vitriol  is  diluted,  the  hyponitrous  acid  being 
then  decomposed  by  the  water  (Dana).  When  the  water  of  the  chamber  is  suf- 
ficiently charged  with  acid,  it  is  drawn  off,  and  concentrated  by  evaporation.  It 
hence  appears  that  the  oxygen,  by  which  the  sulphurous  is  converted  into  sul- 
phuric acid,  is  in  reality  supplied  by  the  air;  that  the  combination  is  effected, 
not  directly,  but  through  the  medium  of  nitrous  acid ;  and  that  a  small  quantity 
of  nitrous  acid  is  sufficient  for  the  production  of  a  large  quantity  of  sulphuric 
acid.  The  decomposition  of  the  crystalline  solid  by  water  seems  owing  to  the 
strong  affinity  of  that  liquid  for  sulphuric  acid. 

[An  improvement  has  recently  been  made  in  the  chamber  process  for  the  manu- 
facture of  sulphuric  acid,  by  which  a  larger  product  is  obtained  than  by  the  old 
mode  of  burning  a  mixture  of  sulphur  and  nitrate  of  potassa.  The  method 
generally  adopted  at  present  is  that  of  passing  sulphurous  acid  and  nitric  acid 
vapours  along  with  steam,  simultaneously  into  the  leaden  chamber.  The  sul- 
phurous acid  is  formed  by  the  combustion  of  sulphur,  in  a  properly  constructed 
furnace,  on  the  floor  of  which  there  is  a  tripod  supporting  an  iron  capsule  con- 
taining the  materials  for  nitric  acid,  viz :  oil  of  vitriol  and  nitrate  of  potassa. 
The  heat  from  the  combustion  of  the  sulphur,  evolves  the  nitric  acid  vapours, 
which  together  with  the  sulphurous  acid  are  carried  by  a  tube  into  the  chamber, 
where  these  acid  vapours  meet  with  the  steam  from  a  small  steam  boiler,  which 
is  admitted  near  the  same  point.  According  to  the  foregoing  theory  the  changes 
in  the  chamber  are  to  be  looked  upon  as  the  same,  for  the  nitric  acid  vapour  is 
equivalent  to  nitric  oxide  or  nitrous  acid,  as  the  immediate  effect  of  the  sulphur- 
ous acid  is  to  reduce  the  nitric  acid  to  a  lower  degree  of  oxidation.] 

[In  a  recent  memoir  by  M.  Peligot,  it  is  shown  that  the  conversion  of  the 
sulphurous  acid  into  sulphuric  is  the  consequence  of  a  decomposition  of  nitric 
acid,  and  that  the  action  of  the  white  crystalline  compound  above  referred  to, 
has  no  concern  in  the  chamber  process  when  in  regular  operation.  This  com- 
pound is  then  not  formed.  The  process  is  conceived  to  be  as  follows : — The 
sulphurous  acid  is  oxidized  directly  at  the  expense  of  the  nitric  acid  which  thus 
becomes  nitrous  acid ;  water,  however,  decomposes  the  latter  into  nitric  and 
hyponitrous  acids ;  the  latter  is  again  decomposed  by  contact  with  a  large  quan- 
tity of  water  into  nitric  acid  and  nitric  oxide,  which,  in  the  presence  of  atmos- 
pheric air,  yields  nitrous  acid ;  which  is  again  resolved  into  nitric  and  hyponitrous 
acids,  &c. 

The  nature  of  these  successive  reactions  is  clearly  expressed  by  the  following 
equations : 

NO3,  Aq.  -f  SO2  =  SO3,  Aq.  -|-  N04 

2NO4  -f-  Aq.  =  NO3  -|-  NO5 

3NO3  +  Aq.  =  2NO2  -|-  NO5 

NO2  4-20  =  NO4,  &c. 

The  nitric  acid  is  thus  constantly  regenerated,  and  the  sulphurous  acid  acts 
upon  this  exclusively,  and  in  a  peculiar  manner  to  deprive  it  of  one  equivalent 
of  oxygen.     (Ann.  de  Chim.  et  de  Phys.  Ixi.  p.  263.)] 

Besides  hyponitrous  acid,  as  above  stated,  it  contains  potassa,  and  the  oxide 


( 


198  SULPHUR. 

of  lead  and  sometimes  iron,  the  first  derived  from  the  nitre  employed  in  making 
it,  and  the  two  latter  from  the  leaden  chamber.  To  separate  them,  the  acid 
should  be  distilled  from  a  glass  or  platinum  retort :  the  former  may  be  safely 
used  by  putting  into  it  some  fragments  of  platinum  leaf,  which  cause  the  acid  to 
boil  freely  on  applying  heat,  without  danger  of  breaking  the  vessel.  Arsenious 
acid,  derived  from  arsenic  in  Ihe  sulphur  used  in  the  manufacture,  has  been 
lately  detected  in  most  of  the  oil  of  vitriol  made  in  Germany ;  and  from  that 
source  arsenic  is  introduced  into  preparations  for  which  such  acid  is  employed, 
as  into  phosphorus  and  hydrochloric  acid.  The  arsenic  is  discovered  by  diluting 
with  water  and  transmitting  through  the  solution  hydrosulphuric  acid  gas,  which 
causes  orpiment  to  be  formed.  The  oil  of  vitriol  maybe  purified  from  arsenious 
acid  by  adding  a  little  hydrated  peroxide  of  iron  before  distilling. 

Prop. — As  obtained  by  the  second  process,  pure  sulphuric  acid  is  a  dense, 
colourless,  oily  fluid,  which  boils  at  620°  F.,  and  has  a  sp.  gr.  in  its  most  con- 
centrated form,  of  1*847  or  a  little  higher,  never  exceeding  1*850.  [It  consists 
of  40  parts  or  1  eq.  anhydrous  acid  and  9  parts  or  1  eq.  water,  (HO,  SO3.)] 
Mitseherlich  found  the  density  of  its  vapour  to  be  3.  It  is  one  of  the  strongest 
acids  with  which  chemists  are  acquainted,  and  when  undiluted  is  powerfully  cor- 
rosive. It  decomposes  all  animal  and  vegetable  substances  by  the  aid  of  heat, 
causing  deposition  of  charcoal  and  formation  of  water.  It  has  a  strong  sour 
taste,  and  reddens  litmus  paper,  even  though  greatly  diluted.  It  unites  with 
alkaline  substances,  and  separates  all  other  acids  more  or  less  completely  from 
their  combinations  with  the  alkalies. 

In  a  very  concentrated  state  it  dissolves  small  quantities  of  sulphur,  and 
acquires  a  blue,  green,  or  brown  tint.  Tellurium  and  selenium  are  also  spar- 
ingly dissolved,  the  former  causing  a  crimson,  and  the  latter  a  green  colour.  By 
dilution  with  water,  these  substances  subside  unchanged  ;  but  if  heat  is  applied, 
they  are  oxidized  at  the  expense  of  the  acid,  and  sulphurous  acid  gas  is  disen- 
gaged. Charcoal  also  appears  soluble  to  a  small  extent  in  sulphuric  acid,  com- 
municating at  first  a  pink,  and  then  a  dark  reddish  brown  tint. 

It  has  a  very  great  affinity  for  water,  and  the  combination  takes  place  with,  pro- 
duction of  intense  heat.  When  four  parts  by  weight  of  the  acid  are  suddenly 
mixed  with  one  of  water,  the  temperature  of  the  mixture  rises,  according  to  Ure, 
to  300°.  By  its  attraction  for  water  it  causes  the  sudden  liquefaction  of  snow  ; 
and  if  mixed  with  it  in  due  proportion  (p.  40),  intense  cold  is  generated.  It 
absorbs  watery  vapour  with  avidity  from  the  air,  and  on  this  account  is  employed 
in  the  process  for  freezing  water  by  its  own  evaporation.  Its  action  in  destroy- 
ing the  texture  of  the  skin,  and  in  decomposing  animal  and  vegetable  substances 
in  general,  seems  dependent  on  its  affinity  for  water. 

To  ascertain  the  quantity  of  real  acid  present  in  liquid  acid  of  djflerent  strengths, 
dilute  a  known  weight  of  the  acid  moderately  with  water,  and,  while  warm,  add 
pure  anhydrous  carbonate  of  soda,  until  the  solution  is  exactly  neutral.  Every 
53*3  parts  of  carbonate  of  soda,  required  to  produce  this  effect,  correspond  to  40*lH 
parts  of  real  sulphuric  acid.  If  minute  precision  is  not  desired,  the  strength  off 
the  acid  may  be  estimated  by  its  sp.  gr.  according  to  the.  table  of  Ure  inserted  in 
the  Appendix. 

Sulphuric  acid  of  commerce  freezes  at  —  15°,  yielding,  often,  six  sided  tabu- 
lar crystals.     Diluted  with  water  so  as  to  have  a  sp.  gr.  of  1*78,  it  congeals  even^ 
above  32°,  and  remains  in  the  solid  state,  according  to  Keir,  till  the  temperature^ 
rises  to  45°.    [This  is  a  second  hydrate,  containing  2  eq.  of  water  and  1  eq.  of 


SULPHUR.  1^ 

acid.  The  dilute  acid  when  evaporated  at  a  temperature  not  above  400°,  loses 
water  and  is  reduced  to  the  same  hydrate.  At  a  higher  heat,  this  second  eq.  of 
water  is  expelled;  but  the  first  can  only  be  removed  by  the  substitution  of  a  stronger 
base.  A  third  hydrate  is  believed  to  be  formed,  having  the  sp.  gr.  of  1*63,  con- 
taining 3  equivalents  of  water,  when  a  dilute  acid  is  evaporated  in  vacuo  at  the 
temperature  of  212°. — Including  the  Nordhausen  acid,  there  are  then  four  defi- 
nite hydrates  of  sulphuric  acid,  represented  by  the  following  formulae : — 

Nordhausen  acid,  .....        HO,  2  SO^ 

Oil  of  Vitriol,  (sp.  gr.  1-850)        .....  HO,     SOj 

Acidofsp.gr.  1-78, HO,      SO3  +       HO 

Acidofsp.gr.  1-63 HO,     803  +  2  HO] 

When  mixed  with  rather  more  than  its  weight  of  water,  its  freezing  point  is  low- 
ered to  —  36°.  .1 

The  composition  of  sulphuric  acid  as  before  given  is  founded  on  the  observa^ 
tion  of  Gay-Lussac,  that  when  the  vapour  of  sulphuric  acid  is  passed  through  a 
small  porcelain  tube  heated  to  redness,  it  is  resolved  into  two  measures  of  sul- 
phurous acid  gas  and  one  of  oxygen.  Berzelius  has  confirmed  this  conclusion 
by  directly  converting  a  known  weight  of  sulphur  into  sulphuric  acid. 

Chemists  possess  an  unerring-  test  of  the  presence  of  sulphuric  acid.     If  a 
solution  of  chloride  of  barium  is  added  to  a  liquid  containing  sulphuric  acid,  it  , 
causes  a  white  precipitate,  sulphate  of  baryta,  which  is  characterized  by  its  in- 
solubility in  acids  and  alkalies. 

Sulphuric  acid  does  not  occur  free  in  nature,  except  occasionally  in  the  neigh- 
bourhood of  volcanoes.  In  combination,  particularly  with  lime  and  baryta,  it  is 
very  abundant. 

Hydmsulphurous  Acid. — It  may  be  formed  either  by  digesting  sulphur  in  a  so- 
lution of  any  sulphite,  or  by  transmitting  a  current  of  sulphurous  acid  into  a  so- 
lution of  sulphuret  of  calcium  or  strontium.  In  the  former  case,  the  sulphurous 
acid  takes  up  an  additional  quantity  of  sulphur,  and  a  salt  of  hyposulphurous  acid 
is  obtained ;  and  in  the  latter,  the  sulphurous  acid  gives  part  of  its  oxygen  to  the 
metal,  and  its  remaining  oxygen  unites  with  sulphur.  Three  equivalents  of  sul- 
phurous acid  and  two  of  sulphuret  of  calcium  contain  the  elements  for  forming 
two  eq.  of  hyposulphite  of  lime,  one  eq.  of  sulphur  being  deposited.  A  conve- 
nient solution  for  this  purpose  is  made  by  boiling  3  parts  of  slaked  lime  and  one 
of  sulphur  with  20  parts  of  water  for  one  hour,  and  decanting  the  clear  liquid 
from  the  undissolved  portions ;  but  when  this  solution  is  used,  the  deposite  of  ~j^ 
sulphur  is  abundant.  Herschel  states  that  hydrosul£lmrausji.cid  may  be  formed -4(5^* 
by  the  action  of  sulphurous  acid  on  iron  filings ;  but  the  nature  of  the  change  Is 
not  well  understood. 

The  salts  of  hyposulphurous  acid  were  first  described  by  Gay-Lussac  (An.  de 
Ch.  Ixxxv.)  under  the  name  of  Sulphuretted  Sulphites,  Thomson  in  his  System 
of  Chemistry  suggested  that  the  acid  of  these  salts  might  be  regarded  as  a  com- 
pound of  one  equivalent  of  sulphur  and  one  of  oxygen,  and  proposed  for  it  the 
name  of  hyposulphurous  acid;  and  the  subsequent  researches  of  Herschel  (Phil. 
Journal,  i.  8  and  396)  accorded  so  entirely  with  this  opinion,  that  it  was  univer- 
sally adopted.  But  it  appears  from  the  experiments  of  Rose,  that  though  the 
ratio  of  its  elements  is  as  16  to  8,  the  equivalent  of  the  acid,  or  the  quantity  re- 
quired to  neutralize  one  eq.  of  an  alkali,  is  not  24,  but  48 ;  and  hence  that  its 


2#0  SULPHUR. 

smallest  molecule  must  be  formed  of  2  atoms  of  sulphur  united  with  2  atoms  of 
oxygen  (Pog.  Ann.  xxi.  431.) 

Prop. — It  cannot  exist  permanently  in  a  free  state.  On  decomposing  a  hypo- 
sulphite by  any  stronger  acid,  such  as  the  sulphuric  or  hydrochloric,  the  hypo- 
sulphurous  acid,  at  the  moment  of  quitting  the  base,  resolves  itself  into  sulphurous 
acid  and  sulphur.  Herschel  succeeded  in  obtaining  free  hyposulphurous  acid, 
by  adding  a  slight  excess  of  sulphuric  acid  to  a  dilute  solution  of  hyposulphite 
of  strontia ;  but  its  decomposition  very  soon  took  place,  even  at  common  temper- 
atures, and  was  instantly  effected  by  heat.  Most  of  the  hyposulphites  are  soluble 
in  water,  and  have  a  bitter  taste.  The  solution  precipitates  the  nitrates  of  the 
oxides  of  silver  and  mercury  black,  as  sulphuret  of  the  metals ;  and  salts  of  baryta 
and  oxide  of  lead  are  thrown  down  as  white  insoluble  hyposulphites  of  those 
bases.  That  of  baryta  is  soluble  without  decomposition  in  water  acidulated  with 
hydrochloric  acid.  The  solution  of  all  the  neutral  hyposulphites  has  the  peculiar 
property  of  dissolving  recently  precipitated  chloride  of  silver  in  large  quantity, 
and  forming  with  it  a  liquid  of  an  exceedingly  sweet  taste.  Its  eq.  is  48*2  ;  sym. 
2S  +  20  or  Sg  Oj. 

Hyposulphuric  acid. — It  was  discovered  in  1819  by  Welter  and  Gay-Lussac 
(An.  de  Ch.  et  Ph.  x.),  and  is  formed  by  transmitting  a  current  of  sulphurous 
acid  gas  through  water  containing  peroxide  of  manganese  in  fine  powder ;  when 
by  a  new  arrangement  of  their  elements, 

2  eq.  Sulp.  acid  and  1  eq.  Perox.  Mang.  ;2  1  eq«  Protox.  Mang.  &  1  eq.  Hyposulp.  acid, 
2S02  Mn02     •?,        MnO  S2O5 

hyposulphate  of  protoxide  of  manganese  remaining  in  solution.  During  the  action 
heat  is  freely  evolved,  and  in  consequence  sulphuric  acid  is  also  generated ;  but 
if  the  peroxide  of  manganese  be  pure  and  the  materials  kept  cool,  the  formation 
of  sulphuric  acid  is  almost  completely  prevented.  To  the  liquid,  after  filtration, 
a  solution  of  pure  baryta  or  sulphuret  of  barium  in  slight  excess  is  added,  whereby 
the  manganese  is  thrown  down  as  an  oxide  or  sulphuret,  sulphuric  acid  as  sul- 
phate of  baryta,  and  a  solution  of  hyposulphate  of  baryta  is  obtained  :  the  excess 
of  baryta  is  got  rid  of  by  a  free  current  of  carbonic  acid  gas,  and  then  heating  the 
solution.  The  hyposulphate  of  baryta  crystallizes  by  evaporation,  and  on  de- 
composing a  solution  of  that  salt  by  a  quantity  of  sulphuric  acid  exactly  sufiicient 
for  precipitating  the  baryta,  the  hyposulphuric  acid  is  left  in  solution. 

Prop. — ^Taste  sour  ;  distinct  acid  reaction ;  neutralizes  alkalies ;  inodorous,  and 
thus  distinguished  from  sulphurous  acid ;  forms  soluble  salts  with  baryta,  stron- 
tia, lime,  and  oxide  of  lead,  by  which  it  is  distinguished  from  sulphuric  acid.  It 
cannot  be  obtained  free  from  water.  Its  solution,  if  confined  with  a  vessel  of 
sulphuric  acid  under  the  exhausted  receiver  of  an  air-pump,  may  be  concentrated 
till  it  has  a  density  of  1*347;  but  if  an  attempt  is  made  to  condense  it  still  fur- 
ther, the  acid  is  decomposed,  sulphurous  acid  gas  escapes,  and  sulphuric  acid 
remains  in  solution.  A  similar  change  is  still  more  readily  produced  if  the  eva- 
poration is  conducted  by  heat. 

Welter  and  Gay-Lussac  analyzed  hyposulphuric  acid  by  exposing  neutral  hy- 
posulphate of  baryta  to  heat.  At  a  temperature  a  little  above  212°  this  salt 
suffers  complete  decomposition ;  sulphurous  acid  gas  is  disengaged,  and  neutral 
sulphate  of  baryta  is  obtained.  It  was  thus  ascertained  that  72  grains  of  hypo- 
sulphuric acid  yield  32  grains  of  sulphurous,  and  40  of  sulphuric  acid ;  from  which 


PHOSPHORUS.  201 

it  is  inferred  that  hyposulphuric  acid  is  composed  either  of  an  equivalent  of  each 
of  those  acids  combined  with  each  other,  or  of  2  eq.  of  sulphur  and  5  of  oxygen. 
Its  eq,  is  72-2 ;  sym.  2S  +  50  or  Sj  O5. 

ISulphureiied  Hyposulphuric  Acid. — A  salt  containing  this  new  acid  was  acci- 
dentally discovered  by  M.  Langlois  in  the  preparation  of  hyposulphite  of  potassa. 
It  is  prepared  by  digesting  the  bisulphate  of  potassa  along  with  sulphur  and  water 
without  boiling.  The  salt  thus  formed  crystallizes  easily,  and  is  resolved  by  heat 
-into  sulphurous  acid,  sulphur  and  sulphate  of  potassa.  Perchloric  acid  removes 
the  potassa,  and  the  new  acid  is  thereby  isolated.  The  acid  solution  slowly  de- 
composes, and  when  heated  yields  sulphurous  acid,  sulphur  and  sulphuric  acid; 
S3  O5  =  80^;  S  and  SO3.— //s  eq.  is  88-3 ;  sym.  S3  O5.  (Ann.  Chim.  de  Phys. 
3,  sec  iv.  p.  77.)] 

[Bisulphuretted  Hyposulphuric  Acid. — Discovered  by  M.  Fordos  and  Gellis. 
When  iodine  is  dissolved  in  a  solution  of  the  hyposulphite  of  baryta,  the  clear 
solution  which  is  obtained  is  found  to  contain  both  iodide  of  barium,  and  the 
baryta  salt  of  this  new  acid.  The  former  is  dissolved  by  alcohol,  and  the  latter 
is  left  pure.  The  baryta  is  removed  by  the  cautious  addition  of  dilute  sulphuric 
acid,  and  the  new  acid  is  obtained  dissolved  in  water.  It  resembles  the  two 
preceding  acids  in  being  exceedingly  prone  to  change,  and  like  the  last,  is  resolved 
by  heat  into  the  same  substances,  but  the  quantity  of  sulphur  separated  is  exactly 
twice  as  great;  S4  O3  =  SO2,  Sg  &  SO3. — Its  eq.  is  104*4;  sym,  SO4  O3.  (Ann. 
Chim.  de  Phys.  iv.  p.  454.)] 


SECTION  VIII. 


PHOSPHORUS. 


Hist,  and  Prep. — Phosphorus  (^Mfpo^o^,  from  ^^^^  light  and  ^i^siv  to  carry),  so 
called  from  its  property  of  shining  in  the  dark,  was  discovered  about  the  year 
1669  by  Brandt,  an  alchemist  of  Hamburgh.  It  was  originally  prepared  from 
urine  ;  but  Scheele,  after  Gahn's  discovery  of  bones  containing  phosphate  of  lime, 
extracted  it  from  that  source.  The  bones  are  first  ignited  in  an  open  fire  till  they 
become  white,  so  as  to  destroy  their  animal  matter,  and  burn  away  the  charcoal 
derived  from  it,  in  which  state  they  contain  nearly  4-5ths  of  phosphate  of  lime. 
They  are  then  reduced  to  a  fine  powder,  and  digested  for  a  day  or  two  with  half 
their  weight  of  strong  sulphuric  acid,  with  the  addition  of  so  much  water  as  will 
give  the  consistence  of  a  thin  paste.  Decomposition  of  the  phosphate  of  lime  is 
thus  effected,  and  two  new  salts  formed,  the  sparingly  soluble  sulphate  and  a 
soluble  superphosphate  of  lime.  The  latter  is  dissolved  in  warm  water,  and  the 
solution,  after  being  separated  by  filtration  from  the  sulphate  of  lime,  is  evapo- 
rated to  the  consistence  of  syrup,  mixed  with  a  fourth  of  its  weight  of  powdered 
charcoal,  and  strongly  heated  in  an  earthen  retort  well  luted  with  clay.  The 
beak  of  the  retort  is  put  into  water,  in  which  the  phosphorus,  as  its  vapour 


202  PHOSPHORUS. 

passes  over,  is  condensed.  When  first  obtained  it  is  usually  of  a  reddish  brown 
colour,  owing  to  the  presence  of  phosphuret  of  carbon  formed  during  the  process. 
It  may  be  purified  by  fusion  in  hot  water,  and  being  pressed  while  liquid  through 
chamois  leather,  or  by  a  second  distillation. 

In  this  process  the  oxygen  of  that  part  of  the  phosphoric  acid  which  constitutes 
superphosphate,  unites  with  charcoal,  giving  rise  to  carbonic  acid  and  carbonic 
oxide  gases ;  and  phosphate  of  lime  in  the  state  of  bone  earth,  together  with  re- 
dundant charcoal,  remains  in  the  retort.  The  lime  acts  an  important  part  in 
fixing  the  phosphoric  acid,  which  if  not  so  combined  would  distil  over  before  the 
heat  was  high  enough  for  its  decomposition.  In  extracting  phosphorus  from 
urine,  the  phosphoric  acid  should  be  thrown  down  by  acetate  of  the  oxide  of  lead, 
and  the  insoluble  salt  converted  by  the  action  of  sulphuric  acid  into  the  super- 
phosphate, which  is  decomposed  by  charcoal  as  in  the  former  process. 

Prop. — When  pure,  transparent,  and  almost  colourless.  At  common  tempera- 
tures it  is  a  soft  solid  of  sp.  gr.  1*77;  is  easily  cut  with  a  knife,  and  the  cut  sur- 
face has  a  waxy  lustre :  at  108°  it  fuses,  and  at  550°  is  converted  into  vapour, 
which,  according  to  Dumas,  has  a  sp.  gr.  of  4*355.  It  is  soluble  by  the  aid  of 
heat  in  naphtha,  in  fixed  and  volatile  oils,  in  the  chloride  of  sulphur,  sulphuret  of 
carbon,  and  sulphuret  of  phosphorus.  On  its  cooling  from  solution  in  the  latter, 
Mitscherlich  obtained  it  in  regular  dodecahedral  crystals.  By  the  fusion  and 
slow  cooling  of  a  large  quantity  of  phosphorus,  M.  Frantween  has  obtained  very 
fine  crystals  of  an  octohedral  form,  and  as  large  as  a  cherry-stone.  Thenard  has 
remarked  that  when  phosphorus  is  fused  at  150°,  and  suddenly  cooled  by  being 
plunged  into  cold  water,  it  appears  black ;  but  by  fusion  and  slow  cooling  it 
recovers  its  original  aspect. 

It  is  exceedingly  inflammable.  Exposed  to  the  air  at  common  temperatures, 
it  undergoes  slow  combustion,  emits  a  white  vapour  of  a  peculiar  alliaceous 
odour,  appears  distinctly  luminous  in  the  dark,  and  is  gradually  consumed.  On 
this  account,  phosphorus  should  always  be  kept  under  water.  The  disappear- 
ance of  oxygen  which  accompanies  these  changes  is  shown  by  putting  a  stick 
of  phosphorus  in  a  jar  full  of  air,  inverted  over  water.  The  volume  of  the  gas 
gradually  diminishes ;  and  if  the  temperature  of  the  air  is  at  60°,  the  whole  of 
the  oxygen  will  be  withdrawn  in  the  course  of  12  or  24  hours.  The  residue  is 
nitrofen  gas,  containing  about  l-40th  of  its  bulk  of  the  vapour  of  phosphorus. 
It  is  remarkable  that  the  slow  combustion  of  phosphorus  does  not  take  place  in 
pure  oxygen,  unless  its  temperature  be  about  80°.  But  if  the  oxygen  be  diluted 
with  nitrogen,  hydrogen,  or  carbonic  acid  gases,  the  oxidation  occurs  at  60° ; 
and  it  takes  place  at  temperatures  still  lower  in  a  vessel  of  pure  oxygen,  rarefied 
by  diminished  pressure.  Mr.  Graham  finds  that  the  presence  of  certain  gaseous 
substances,  evert  in  minute  quantity,  has  a  remarkable  effect  in  preventing  the 
slow  combustion  of  phosphorus :  thus  at  66°  it  is  entirely  prevented  by  the  pre- 
sence, (Quart.  Jour,  of  Science,  N.  S.  vi.  83.) 

Volumes  of  air. 
of  1  volume  of  olefiant  gas  in  ...  450 

1    ditto    of  vapour  of  sulphuric  ether  in  -  150    . 

1     ditto    of  vapour  of  naphtha  in  -  -  1820 

1    ditto    of  vapour  of  oil  of  turpentine  in  .  4444 

and  by  an  equally  slight  impregnation  of  the  vapour  of  the  other  essential 


PHOSPHORUS.  203 

Their  influence  is  not  confined  to  low  temperatures.      Phosphorus  becomes 
faintly  luminous  in  the  dark,  in  mixtures  of 

1  volume  of  air  and  1  volume  of  olefiant  gas  at  -  -  200°  F. 

1        .        ^       and  1     ditto    of  vapour  of  ether  at  -  215° 

111        .        .        and  1     ditto    of  vapour  of  naphtha  at  -  170° 

156        .        -        and  1    ditto    of  vapour  of  turpentine  at  186° 

It  may  be  sublimed  at  its  boiling  temperature,  in  air  containing  a  considerable 
proportion  of  the  vapour  of  oil  of  turpentine,  without  diminishing  the  quantity 
of  oxygen  present,  provided  the  heat  be  gradually  and  uniformly  applied.  Mr. 
Graham  has  also  remarked,  that  the  oxidation  of  phosphorus  in  the  air  is  pro- 
moted by  the  presence  of  hydrochloric  acid  gas. 

A  very  slight  degree  of  heat  is  sufficient  to  inflame  phosphorus  in  the  open 
air.  Gentle  pressure  between  the  fingers,  friction,  or  a  temperature  not  much 
above  its  point  of  fusion,  kindles  it  readily.  It  burns  rapidly  even  in  the  air, 
emitting  a  splendid  white  light,  and  causing  intense  heat.  Its  combustion  is 
far  more  rapid  in  oxygen  gas,  and  the  light  proportionally  more  vivid. 

When  phosphorus  is  kept  for  a  long  time  under  water,  especially  if  exposed 
to  light,  its  surface  acquires  a  thin  coating  of  white  matter,  which  some  have 
described  as  an  oxide,  and  others  as  a  hydrate  of  phosphorus.  It  seems,  accord- 
ing to  Rose,  to  be  neither  an  oxide  nor  a  hydrate,  but  phosphorus  in  a  peculiar 
mechanical  state,  which  deprives  it  of  its  usual  action  upon  light,  and  renders  it 
opaque.     (Pog.  Annalen,  xxvii.  565.) 

Repeated  researches  by  Berzelius  have  shown  that  the  oxygen  in  phosphorus 
and  phosphoric  acids  is  in  the  ratio  of  3  to  5,  a  result  conformable  to  experiments 
on  the  same  subject  by  Dulong,  and  admitted  by  most  chemists.  It  is  hence 
inferred  that  the  smallest  molecule  of  phosphoric  acid  contains  5  atoms  of  oxygen. 
Also  Berzelius  finds  that  31*4  parts  of  phosphorus  require  40  of  oxygen  for  form- 
ing phosphoric  acid :  if  this  acid  consist  of  one  atom  of  phosphorus  and  five 
atoms  of  oxygen,  31*4  will  represent  one  atom  of  phosphorus;  or  if  the  acid  con- 
tain two  atoms  to  five,  the  atom  of  phosphorus  will  be  half  31*4  or  15.7.  It  is 
doubtful  which  view  is  preferable,  and  I  therefore  continue  to  use  the  latter. 

Its  equivalent  is  therefore  15*7 ;  eq.  vol.  =  25  ;  symb.  P. 

The  compounds  of  phosphorus  described  in  this  section  are  the  following  :— 

Phosp.  Oxy.        Equiv.  Formulae. 

Oxide  of  Phosphorus       47-1  or  3  eq.  -f    8  or  1  eq.  =  55-1  3P  -f-    O  or  P3O 

Hypophosphorous  acid    31-4  or  2  eq.  -|-    8  or  1  eq.  =  39-4  2P  -f-    0  or  PjO 

Phosphorous  acid  31-4  o  2  eq.  -f"  24  or  3  eq.  =  55-4  2P  -f  30  or  P2O3 

Phosphoric  acid  -% 

Pyrophosphoric  acid    C  31.4  ^^  2  eq.  -f-  40  or  5  eq.  =  71-4  2P  -|-  50  or  P2O5 
Metaphosphoric  acid  j 

COMPOUNDS  OF  OXYGEN  AND  PHOSPHORUS. 

Oxide. — When  a  jet  of  oxygen  gas  is  thrown  upon  phosphorus  while  in  fusion 
under  hot  water,  combustion  ensues,  phosphoric  acid  is  formed,  and  a  number  of 
red  particles  collect,  which  have  been  examined  by  M.  Pelouze,  who  has  shown 
them  to  be  an  oxide  of  phosphorus.  The  red  matter  left  when  phosphorus  is 
burned,  is  probably  of  the  same  nature. 

This,  the  only  known  oxide  of  phosphorus,  is  of  a  red  colour,  without  taste  or 
odour,  and  is  insoluble  in  water,  ether,  alcohol,  and  oil.    It  is  permanent  in  the 


PHOSPHORUS. 

air,  even  at  662°  F.,  but  takes  fire  at  a  low  red  heat.  Heated  to  redness  in  a 
tube,  phosphorus  is  expelled,  and  metaphosphoric  acid  remains.  It  takes  fire  in 
chlorine  gas,  and  is  rapidly  oxidized  by  nitric  acid.  It  does  not  appear  to  pos- 
sess any  alkaline  character.  (An.  de  Ch.  et  Ph.  1.  83.)  Its  equivalent  is  55*1 ; 
symb.  3P  -\-  O,  or  P3O. 

Hypophosphorous  Acid. — ^This  acid  was  discovered  in  1816  by  Dulong.  (An. 
de  Ch.  et  Ph.  ii.)  When  water  acts  upon  the  phosphuret  of  barium  the  elements 
of  both  enter  into  a  new  arrangement,  giving  rise  to  phosphuretted  hydrogen, 
phosphoric  acid,  hypophosphorous  acid,  and  baryta.  The  former  escapes  in  the 
form  of  gas,  and  the  two  latter  combine  with  the  baryta.  Hypophosphite  of 
baryta,  being  soluble,  dissolves  in  the  water,  and  may  consequently  be  separated 
by  filtration  from  the  phosphate  of  baryta,  which  is  insoluble.  On  adding  a  suf- 
ficient quantity  of  sulphuric  acid  for  precipitating  the  baryta,  hypophosphorous 
acid  is  obtained  in  a  free  state,  and  on  evaporating  the  solution,  a  viscid  liquid 
remains,  highly  acid  and  even  crystallizable,  which  is  a  hydrate  of  hypophospho- 
roxis  acid.  When  exposed  to  heat  in  close  vessels,  it  undergoes  the  same  kind 
of  change  as  hydrated  phosphorous  acid. 

Prop. — It  is  a  powerful  deoxidizing  agent.  It  unites  with  alkaline  bases ; 
and  it  is  remarkable  that  all  its  salts  are  soluble  in  water.  The  hypophosphites 
of  potassa,  soda,  and  ammonia,  dissolve  in  every  proportion  in  rectified  alcohol ; 
and  hypophosphite  of  potassa  is  even  more  deliquescent  than  chloride  of  calcium. 
They  are  all  decomposed  by  heat,  and  yield  the  same  products  as  the  acid 
itself.  They  are  conveniently  prepared  by  precipitating  hypophosphite  of  baryta, 
strontia,  or  lime,  with  the  alkaline  carbonates ;  or  by  directly  neutralizing  these 
carbonates  with  hypophosphorous  acid.  The  hypophosphite  of  baryta,  strontia, 
and  lime,  are  formed  by  boiling  these  earths  in  the  caustic  state  in  water  together 
with  fragments  of  phosphorus.  The  same  change  occurs  as  during  the  action 
of  water  on  phosphuret  of  barium.  The  composition  of  this  acid,  as  stated  at 
page  203,  is  on  the  authority  of  Rose.     (Poggen.  Annalen,  ix.  367.)    Its  eq.  is 

39-4 ;  symb.  2P  +  O,  P,  or  PgO. 

Phosphorous  Mid. — Prep. — When  phosphorus  is  burned  in  air  highly  rarefied, 
imperfect  oxidation  ensues,  and  metaphosphoric  and  phosphorous  acids  are  gene- 
rated, the  latter  being  obtained  in  the  form  of  a  white  volatile  powder.  It  may  be 
procured  more  conveniently  by  subliming  phosphorus  through  powdered  bichlo- 
ride of  mercury  contained  in  a  glass  tube;  when  a  limpid  liquid  comes  over, 
which  is  a  compound  of  chlorine  and  phosphorus.  (Davy's  Elements,  p.  288.) 
This  substance  and  water  mutually  decompose  each  other :  the  hydrogen  of 
water  unites  with  the  chlorine,  and  forms  hydrochloric  acid  ;  while  the  oxygen 
attaches  itself  to  the  phosphorus,  and  thus  phosphorous  acid  is  produced.  The 
solution  is  then  evaporated  to  the  consistence  of  syrup  to  expel  the  hydrochloric 
acid ;  and  the  residue,  which  is  hydrate  of  phosphorous  acid,  becomes  a  crystal- 
line solid  on  cooling.  It  is  also  generated  during  the  slow  oxidation  of  phos- 
phorus in  atmospheric  air.  The  product  attracts  moisture  from  the  air,  and  forms 
an  oil-like  liquid.  Dulong  thinks  that  a  distinct  acid  is  produced  in  this  case, 
which  he  calls  phosphatic  acid,-  but  the  opinion  of  Davy,  that  it  is  merely  a  mix- 
ture of  phosphoric  and  phosphorous  acids,  is,  in  my  opinion,  perfectly  correct. 

Prop. — When  obtained  by  the  first  process,  it  is  anhydrous.  Heated  in  the 
open  air,  it  takes  fire  and  forms  metaphosphoric  acid ;  but  in  close  vessels  it  is 
resolved  into  metaphosphoric  acid  and  phosphorus.    The  action  of  the  hydrate 


PHOSPHORUS.  205 

under  the  latter  circumstances  is  different,  owing  to  the  reaction  of  the  elements 
of  the  water  and  acid,  by  which  metaphosphoric  acid  and  a  gaseoQS  compound 
of  phosphorus  and  hydrogen  are  produced.  The  nature  of  this  gas  will  be  more 
particularly  noticed  in  the  section  on  phosphureted  hydrogen.  It  dissolves 
readily  in  water,  has  a  sour  taste,  and  smells  somewhat  like  garlic.  It  unites 
with  alkalies,  and  forms  salts  which  are  termed  phosphites.  The  solution  of 
phosphorous  acid  absorbs  oxygen  slowly  from  air,  and  is  converted  into  phos- 
phoric acid.  From  its  tendency  to  unite  with  an  additional  quantity  of  oxygen, 
it  is  a  powerful  deoxidizing  agent ;  and  hence,  like  sulphurous  acid,  precipitates 
mercury,  silver,  platinum,  and  gold,  from  their  saline  combinations  in  the 
metallic  form.     Nitric  acid  converts  it  into  phosphoric  acid. 

Its  eq.  is  55-4 ;  symb.  2P  +  30,  P,  or  P2O3. 

Phosphoric  Acid. — Hist. — It  was  shown  in  the  year  1827  by  Dr.  Clark,  now 
Professor  of  Chemistry  in  Aberdeen,  that  under  the  term  phosphoric  acid  had 
previously  been  confounded  two  distinct  acids,  one  of  which  he  proposed  to  dis- 
tinguish by  the  name  pyrophosphoric  acid  (from  hv^  fire),  to  indicate  that  it  is 
phosphoric  acid  modified  by  heat ;  and  very  lately  Mr.  Graham  has  described 
another  modification  of  phosphoric  acid,  to  which  he  has  given  the  provisional 
name  of  metaphosphoric  (from  jUffa  together  with),  implying  phosphoric  acid  and 
something  besides ;  but  this  name  is  rather  unfortunate,  since  it  is  applied  to  the 
only  one  of  the  three  modifications  which  can  be  obtained  free  from  water.  Per- 
haps paraphosphoric  (from  yta^a  near  to)  would  be  more  appropriate.  These 
three  acids  contain  phosphorus  and  oxygen  in  the  same  ratio,  and  have  the  same 
equivalent,  so  that  they  may  be  considered  as  isomeric  bodies  (page  150) ;  but 
that  difference  in  the  arrangement  of  their  elements  on  which  their  peculiarities 
may  be  presumed  to  depend  is  very  slight,  since  they  are  easily  convertible  into 
each  other.  Mr.  Graham,  indeed,  supposes  the  difference  to  arise  solely  from  a 
disposition  to  unite  in  different  proportions  with  water  and  alkaline  bases  ;  but 
this  view  scarcely  suffices  as  an  explanation,  because  it  does  not  account  for  the 
peculiar  disposition  which  causes  their  distinctive  characters.  (Phil.  Trans.  1833, 
Part,  ii.,  and  Phil.  Mag.  3rd  Series,  iv.  401.) 

Prep. — Phosphoric  acid  has  hitherto  been  obtained  only  in  combination  with 
water  or  some  alkaline  base.  One  of  the  best  modes  for  procuring  it,  is  to  oxi- 
dize phosphorus  by  strong  nitric  acid ;  but  in  this  process  care  is  necessary,  as 
the  action  is  sometimes  very  violent,  and  the  escape  of  binoxide  of  nitrogen  gas 
ungovernably  rapid.  It  is  safely  conducted  by  adding  fragments  of  phosphorus, 
or  the  so-called  phosphatic  acid,  to  strong  nitric  acid  contained  in  a  platinum 
crucible  partially  closed  by  its  cover.  Gentle  heat  is  applied  so  as  to  commence, 
and,  when  necessary,  to  maintain  moderate  effervescence  ;  and  when  one  portion 
of  phosphorus  disappears,  another  is  added,  till  the  whole  of  the  nitric  acid  is 
exhausted.  The  solution  is  then  evaporated  to  dryness,  and  exposed  to  a  red 
heat  to  expel  the  last  traces  of  nitric  acid.  This  should  always  be  done  in  ves- 
sels of  platinum,  since  phosphoric  acid  acts  chemically  upon  those  of  glass  or 
porcelain,  and  is  thereby  rendered  impure.  In  this  case,  as  in  some  other 
instances  of  the  oxidation  of  combustibles  by  nitric  acid,  water  is  decomposed  ;. 
and  while  its  oxygen  unites  with  phosphorus,  its  hydrogen  combines  with  nitro- 
gen of  the  nitric  acid.  A  portion  of  ammonia,  thus  generated,  is  expelled  by 
heat  in  the  last  part  of  the  process. 

Phosphoric  acid  may  be  prepared  at  a  much  cheaper  rate  from  bones.  For  this 


206  PHOSPHORUS. 

purpose,  superphosphate  of  lime,  obtained  in  the  way  already  described,  should 
be  boiled  for  a  few  minutes  with  excess  of  carbonate  of  ammonia.  The  lime  is 
thus  precipitated  as  a  phosphate,  and  the  solution  contains  phosphate,  together 
with  a  little  sulphate,  of  ammonia.  The  liquid,  after  filtration,  is  evaporated  to 
dryness,  and  then  ignited  in  a  platinum  crucible,  by  which  means  the  ammonia 
and  sulphuric  acid  are  expelled. 

In  both  the  foregoing  processes  phosphoric  acid  exists  only  in  solution ;  for 
on  heating  to  redness,  in  order  to  expel  ammonia  in  the  one  case,  and  nitric  acid 
in  the  other,  metaphosphoric  acid  is  generated.  To  reproduce  the  phosphoric 
acid,  the  residue  in  the  crucible  requires  to  be  dissolved  in  water  and  boiled  for 
a  few  minutes. 

Prop, — Phosphoric  acid  is  colourless,  intensely  sour  to  the  raste,  reddens  lit- 
mus strongly,  and  neutralizes  alkalies ;  but  it  does  not  destroy  the  texture  of  the 
skin,  like  sulphuric  and  nitric  acids.  Its  solution  may  be  evaporated  at  a  tem- 
perature of  300°  without  decomposition,  and  when  thus  concentrated  it  assumes 
a  dark  colour,  is  as  thick  as  treacle  when  cold,  and  consists  of  71 '4  parts  or  1  eq. 
of  phosphoric  acid  and  27  parts  or  3  eq.  of  water.  Mr.  Graham  obtained  this 
hydrate  in  thin  crystalline  plates,  which  were  extremely  deliquescent,  by  keeping 
it  for  seven  days  in  vacuo  along  with  sulphuric  acid.  On  heating  this  hydrate 
for  several  days  to  415°,  it  lost  nearly  two-thirds  of  an  equivalent  of  water,  and 
then  principally  consisted  of  pyrophosphoric  acid  with  two  equivalents  of  water.. 
At  a  still  higher  temperature  metaphosphoric  acid  began  to  be  formed :  and  at  a 
red  heat  the  conversion  was  complete.  But  after  ignition  it  still  contains  water, 
amounting,  according  to  Rose,  to  9*44  per  cent.,  which  is  more  than  an  equiva- 
lent of  water  to  one  of  metaphosphoric  acid. 

Phosphoric  acid  is  remarkable  for  its  tendency  to  unite  with  alkaline  bases,  in 
such  proportions  that  the  oxygen  of  the  base  and  of  the  acid  is  as  3  to  5 ;  or,  in 
other  words,  it  is  prone  to  form  subsalts,  in  which  one  equivalent  of  acid  is  com- 
bined with  three  equivalents  of  base.  It  manifests  the  same  character  in  regard 
to  water,  and  ceases  to  be  phosphoric  acid  unless  three  equivalents  of  water  to 
one  of  acid  are  present :  it  even  appears  that  the  water  acts  the  part  of  a  base, 
hence  called  basic  water,  and  that  the  aqueous  solution  is  not  a  mere  solution  of 
phosphoric  acid,  but  of  triphosphate  of  water,  a  sort  of  salt  composed  of  one 
equivalent  of  acid  and  three  equivalents  of  water.  Part  of  this  basic  water  enters 
along  with  soda  into  the  constitution  of  two  of  the  phosphates  of  soda,  the  water 
and  soda  together  forming  the  three  equivalents  of  base  required  by  one  equiva- 
lent of  the  acid.  This  point  will  be  more  fully  described  in  the  history  of  the 
phosphates. 

When  phosphoric  acid  is  neutralized  by  ammonia  and  mixed  with  nitrate  of 
oxide  of  silver,  the  yellow  phosphate  of  that  oxide  subsides ;  a  character  by 
which  it  is  distinguished  from  pyrophosphoric  and  metaphosphoric  acids,  as  well 
as  from  all  other  acids  except  the  arsenious.  A  certain  test  between  phosphoric 
and  arsenious  acids  is,  that  the  former  is  neither  changed  in  colour  nor  precipi- 
tated when  a  stream  of  sulphuretted  hydrogen  gas  is  transmitted  through  it ;  while 
the  latter,  with  the  required  precautions,  first  acquires  a  yellow  tint,  and  then 
yields  a  yellow  precipitate. 

Its  eq.  is  71*4  ;  symh.  2P  -j-  50,  P,  or  P3O5 :  but  as  it  cannot  exist  uncom- 
bined,  it  is  best  denoted  by  X3.  P2O5,  where  X  represents  an  equivalent  of  water 
or  any  base. 


i 


PHOSPHORUS.  207 

Pyrophosphoric  Acid. — ^This  acid  is  formed  by  exposing  concentrated  phos- 
phoric acid  for  some  time  to  a  heat  of  415°.  Its  general  characters  resemble 
phosphoric  acid ;  but  when  neutralized  by  ammonia  and  mixed  with  nitrate  of 
oxide  of  silver  it  yields  a  snow-white  granular  precipitate,  pyrophosphate  of  that 
oxide,  by  which  it  is  distinguished  from  phosphoric  and  metaphosphoric  acids. 
In  solution  with  cold  water  pyrophosphoric  acid  passes  gradually,  and  at  a  boil- 
ing temperature  rapidly,  into  phosphoric  acid.  Its  salts,  while  neutral,  are  very 
permanent ;  but  when  boiled  with  either  of  the  stronger  acids  in  water,  they  are 
quickly  converted  more  or  less  completely  into  phosphates. 

Pyrophosphoric  acid  is  remarkable  for  its  tendency  to  unite  with  two  equiva- 
lents of  a  base.  Its  aqueous  solution  probably  contains  a  dipyrophosphate  of 
water,  that  is,  1  eq.  of  the  acid  with  2  eq.  of  water,  expressed  by  2H0  -\-  Pg  O5, 
or  2H0.  P2O5.  This  basic  water  is  readily  displaced  by  2  eq.  of  stronger  bases, 
such  as  soda  ;  or  if  1  eq.  only  of  soda  be  added,  then  the  soda  and  water  together 
make  up  the  two  eq.  of  base,  the  formula  of  the  salt  being  NaO,  HO.  PaOg. 
The  readiest  mode  of  obtaining  a  pyrophosphate  is  to  heat  phosphoric  with  any 
fixed  base  in  the  ratio  of  one  to  two  of  their  equivalents.  This  was  done  by 
Dr.  Clark  in  the  experiments  by  which  he  established  the  existence  of  pyro- 
phosphoric acid.  (Brewster's  Journal,  vii.  298.)  Phosphate  of  soda  is  a  com- 
pound of  1  eq.  phosphoric  acid,  2  eq.  soda,  1  eq.  basic  water,  and  24  eq.  water 
of  crystallization,  its  formula  being  2NaO,  HO.  P^  O5  -j-  24HO :  on  drying  this 
salt  its  water  of  crystallization  is  expelled,  there  remains  2NaO,  HO.  Pg  O5, 
which  is  still  a  phosphate,  but  on  heating  to  redness  the  basic  water  is  expelled, 
and  2Na.  P^  O5,  pyrophosphate  of  soda,  remains.  By  being  forced  to  unite  with 
2  eq.  of  base,  the  acid  acquires  a  disposition  to  do  so  on  all  occasions. 

Its  eq.  is  71*4:  symb.  Xj.  P2  O5,  X  being  used  as  above. 

Iletaphosphoric  Acid. — ^This  acid  is  obtained  by  burning  phosphorus  in  dry  air 
or  oxygen  gas,  or  heating  to  redness  a  concentrated  solution  of  phosphoric  or 
pyrophosphoric  acids.  By  the  former  method  the  acid  is  a  white  solid,  and  anhy- 
drous ;  in  the  latter  it  is  a  hydrate,  or  probably  a  metaphosphate  of  water,  com- 
posed of  1  eq.  acid  and  1  eq.  of  wa^er,  its  formula  being  HO.  Pg  O5.  The  water 
in  this  compound  cannot  be  expelled  by  fire,  since  on  attempting  to  do  so  by  a 
violent  heat,  the  whole  is  sublimed.  In  an  open  crucible  it  volatilizes  at  a  tem- 
perature by  no  means  high. 

The  peculiarity  of  this  acid  is  to  combine  with  one  equivalent  of  a  base.  On 
exposing  the  anhydrous  acid  to  the  air  it  rapidly  deliquesces,  and  at  the  same 
time  acquires  its  basic  water,  which  can  only  be  replaced  by  an  equivalent  quan- 
tity of  soda  or  some  other  alkaline  base.  The  water  is  also  driven  off  by  fusion 
with  siliceous  or  aluminous  substances  with  which  the  acid  unites  and  forms 
very  fusible  compounds.  The  pure  hydrated  acid  is  of  itself  very  fusible,  and 
on  cooling  concretes  into  a  transparent  brittle  solid,  being  known  under  the  name 
of  glacial  phosphoric  acid,  which  is  highly  deliquescent,  and  can  hence  only  be 
preserved  in  its  glassy  state  in  bottles  carefully  closed. 

The  metaphosphoric  resembles  pyrophosphoric  acid  in  the  facility  with  which 
its  aqueous  solution  passes  into  phosphoric  acid.  On  the  contrary,  both  of  the 
other  acids  are  converted  into  metaphosphates  when  heated  to  redness  in  contact 
with  no  more  than  one  equivalent  of  certain  fixed  bases,  such  as  potassa  and 
soda.  Tliis  acid  when  free  occasions  precipitates  in  solutions  of  the  salts  of 
baryta,  and  most  of  the  earths  and  metallic  oxides,  and  forms  an  insoluble  com- 
pound with  albumen.    The  metaphosphate  of  baryta  and  oxide  of  silver  both  fall 


208  BORON. 

in  gelatinous  flakes  of  a  ^ey  colour.     Its  eg.  is  71*4;  si/mh,  Pj  O5,  or  X, 

n  an  admirable  paper  on  the  constitution  of  the  organic  acids,  Liebig  has 
hown,  that,  if  we  adopt  the  view  first  suggested  by  Davy,  and  afterwards  by 
Dulong,  namely,  that  the  hydrated  acids,  as  well  as  the  hydracids,  are  all  com- 
pounds of  hydrogen,  we  can  easily  understand  how  the  three  forms  of  phosphoric 
acid  differ  from  each  other.  On  this  view,  just  as  hydrochloric  acid  is  H,C1, 
hydrated  sulphuric  acid  is  H,S04.  In  like  manner  metaphosphoric  acid  is  H, 
^2^6 ;  pyrophosphoric  acid  is  H2,P207,  and  common  phosphoric  acid  is  H3,P208. 
They  are  thus  distinct  compounds,  as  is  evident  from  the  differences  among  their 
salts.  When  the  hydrogen  in  them  is  replaced,  equivalent  for  equivalent,  by  a 
^  metal,  a  salt  is  formed ;  and  we  thus  see  how  the  salts  of  metaphosphoric  acid 
contain  1  eq.  of  metal,  those  of  pyrophosphoric  acid  2  eq.,  and  those  of  common 
phosphoric  acid  3  eq.  of  metal.  The  first  is  a  monobasic  acid,  the  second  a 
bibasic,  and  the  third  a  tribasic  acid.  The  memoir  of  Liebig  just  referred  to 
(Ann.  der  Pharm.  vol.  xxvi.)  has  placed  beyond  question  the  existence  of  poly- 
basic  acids ;  that  is,  acids  which  combine  with  more  than  one  equivalent  of 
base  to  form  neutral  salts.    This  subject  will  be  more  fully  discussed  hereafter. 


SECTION   IX. 


BORON. 


Hist,  and  Prep. — Sin  H.  Davy  discovered  the  existence  of  Boron  in  1807  by 
exposing  boracic  acid  to  the  action  of  a  powerful  galvanic  battery;  but  he  did 
not  obtain  a  sufiicient  supply  of  it  for  determining  its  properties.  Gay-Lussac  and 
Thenard*  procured  it  in  greater  quantity  in  1808  by  heating  boracic  acid  with 
potassium.  The  boracic  acid  is  by  this  means  deprived  of  its  oxygen,  and  boron 
is  set  free.  The  easiest  and  most  economical  method  of  preparing  this  substance, 
according  to  Berzelius,  is  to  decompose  borofluoride  of  potassium  or  sodium  by 
means  of  potassium.     (Annals  of  Philosophy,  xxvi.  128.) 

Prop. — It  is  a  dark  olive-coloured  substance,  which  has  neither  taste  nor 
smell,  and  is  a  non-conductor  of  electricity.  It  is  insoluble  in  water,  alcohol, 
ether,  and  oils.  It  does  not  decompose  water  whether  hot  or  cold.  It  bears 
intense  heat  in  close  vessels,  without  fusing  or  undergoing  any  other  change 
except  a  slight  increase  of  density.  Its  sp,  gr.  is  about  twice  as  great  as  that  of 
water.  It  may  be  exposed  to  the  atmosphere  at  common  temperatures  without 
change ;  but  if  heated  to  600°,  it  suddenly  takes  fire,  oxygen  gas  disappears, 
and  boracic  acid  is  generated.  It  is  very  difficult  to  oxidize  all  the  boron  by 
burning,  becr.use  the  boracic  acid  fuses  at  the  moment  of  being  formed,  and  by 
glazing  the  surface  of  the  unburned  boron  protects  it  from  oxidation.  It  also 
passes  into  boracic  acid  when  heated  with  liitric  acid,  or  with  any  substance 
that  yields  oxygen  with  facility. 

*  Recherches  Pbysico-Chimiques.  toI.  i. 


BORON.  ^  209 

According  to  the  experiments  of  Davy  and  Berzelius,  boron  in  burning  unites 
with  68  per  cent,  of  oxygen ;  and  the  latter,  from  the  composition  of  borax,  esti- 
mates the  oxygen  in  boracic  atid  at  68*8  per  cent.  In  this,  as  in  some  other 
cases,  where  a  combustible  unites  with  oxygen  in  one  proportion  only,  it  is  diffi- 
cult with  any  certainty  to  assign  the  true  atomic  constitution  of  the  compound. 
Boracic  acid  may  be  a  compound  of  boron  and  oxygen  in  the  ratio  of  1  atom  to 
1  atom,  in  that  of  1  to  2  as  supposed  by  Thomson,  or  of  1  to  3.  When  dry 
boracic  acid  is  heated  with  charcoal  in  chlorine  gas,  it  is  decomposed,  and  two 
volumes  of  chloride  of  boron  and  three  of  carbonic  oxide  gas  are  produced.  The 
latter  contains  Ij  volumes  of  oxygen,  and  the  former  has  been  proved  by  Dumas 
to  be  composed  of  3  volumes  of  chlorine  united  with  1  volume  of  the  vapour  of 
boron,  the  density  of  which  is  estimated  at  '751,  its  eq.  vol.  being  100.  From 
this  it  may  be  deduced  that  the  constitution  of  boracic  acid  is  BO3,  which  has 
also  been  recently  adopted  by  Berzelius  (Pog.  An.  xxiv.  561.)  Hence  its  eq.  is 
10-9  ;  eq.  vol.  =  100 ;  syinb.  B. 

Boracic  Acid. — Hist,  and  Prep. — ^This  is  the  only  known  compound  of  boron 
and  oxygen.  As  a  natural  product  it  is  found  in  the  hot  springs  of  Lipari,  in 
those  of  Sasso  in  the  Florentine  territory,  and  in  considerable  quantities  in  the 
hot  volcanic  lagoons  of  Tuscany,  whence  a  large  supply  is  at  present  obtained. 
It  is  a  constituent  of  several  minerals,  among  which  the  datolite  and  boracite 
may  in  particular  be  mentioned.  It  also  occurs  abundantly  under  the  form  of 
impure  borax  or  tinkal,  a  native  compound  of  boracic  acid  and  soda.  It  is  pre- 
pared for  chemical  purposes  by  adding  sulphuric  acid  to  a  solution  of  purified 
borax  in  about  four  times  its  weight  of  boilinf  water,  till  the  liquid  acquires  a 
distinct  acid  reaction.  The  sulphuric  acid  unites  with  the  soda ;  and  the  boracic 
acid  is  deposited,  when  the  solution  cools,  in  a  confused  group  of  shining  scaly 
crystals.  It  is  then  thmwn  on  a  filter,  washed  with  cold  water  to  separate  the 
adhering  sulphate  of  so§a  and  sulphuric  acid,  and  still  further  purified  by  solu- 
tion in  boiling  water  and  re-crystallization.  But  even  after  this  treatment  it  is 
apt  to  retain  a  little  sulphuric  acid  ;  on  this  account,  when  required  to  be  abso- 
lutely pure,  it  should  be  fused  in  a  platinum  crucible,  and  once  more  dissolved 
in  hot  water  and  crystallized. 

Prop. — In  the  crystallized  state  it  is  a  hydrate,  which  contains  43*62  percent, 
of  water,  being  a  ratio  of  34*9  parts  or  1  eq.  of  the  anhydrous  acid  to  27  parts  or 
3  eq.  of  water.  Its  formula  is  therefore  BO3-I-3HO.  This  hydrate  dissolves  in 
25*7  times  its  weight  of  water  at  60°,  and  in  three  times  at  212^^.  Boilinff 
alcohol  dissolves  it  freely,  and  the  solution,  when  set  on  fire,  burns  with  a  beau- 
tiful green  flame ;  a  test  which  affords  the  surest  indication  of  the  presence  of 
boracic  acid.  Its  sp.  gr.  is  1*479.  It  has  no  odour,  and  its  taste  is  rather  bitter 
than  acid.  It  reddens  litmus  paper  feebly,  and  effervesces  with  alkaline  car- 
bonates. Faraday  has  noticed  that  it  renders  turmeric  paper  brown  like  the  alka- 
lies. From  the  weakness  of  the  acid  properties  of  boracic  acid,  all  the  borates, 
when  in  solution,  are  decomposed  by  the  stronger  acids ;  and  the  neutral  borates 
of  potash  and  soda  are  deprived  of  half  their  base  by  carbonic  acid,  at  common 
temperatures. 

When  hydrous  boracic  acid  is  exposed  to  a  gradually  increasing  heat  in  a  pla- 
tinum crucible,  its  water  of  crystallization  is  wholly  expelled,  and  a  fused  mass 
remains  which  bears  a  white  heat  without  being  sublimed.  On  cooling,  it  forms 
a  hard,  colourless,  transparent  glass,  which  is  anhydrous  boracic  acid.  If  the 
water  of  crystallization  be  driven  off  by  the  sudden  application  of  a  strong  heat, 

16 


210  #  SILICON. 

a  large  quantity  of  boracic  acid  is  carried  away  during  the  rapid  escape  of  watery 
vapour.  The  same  happens,  though  in  a  less  degree,  when  a  solution  of  boracic 
acid  in  water  is  boiled  briskly.  Vitrified  boracic  acid  should  be  preserved  in 
well-stopped  vessels  ;  for  if  exposed  to  the  air  it  absorbs  water,  and  gradually 
loses  its  transparency.  Its  sp.  gravity  is  1-803.  It  is  exceedingly  fusible,  and 
communicates  this  property  to  the  substances  with  which  it  unites.  For  this 
reason  borax  is  often  used  us  a  flux. 

Its  eq,  is  34'9  ;  symh,  BfSO,  B,  or  BO3. 


SECTION  X. 


SILICON. 


Hist. — ^That  silicic  acid  or  silica  is  composed  of  a  combustible  body  united 
with  oxygen,  was  demonstrated  by  Davy;  for  on  bringing  the  vapour  of  potas- 
sium in  contact  with  pure  silicic  acid  heated  to  whiteness,  a  silicate  of  potassa 
resulted,  through  which  was  diffused  the  inflammable  base  of  silicic  acid  in  the 
form  of  black  particles  like  plumlfego.  To  this  substance,  on  the  supposition  of 
its  being  a  metal,  the  term  silidum  was  applied.  But  though  this  view  has 
been  adopted  by  most  chemists,  so  little  was  known  with  certainty  concerning 
the  real  nature  of  the  base  of  silica,  that  Thomson  inclii^d  to  the  opinion  of  its 
being  a  non-metallic  body,  and  accordingly  associated  itiln  his  system  of  chem- 
istry with  carbon  and  boron  under  the  name  of  silicon.  The  recent  researches  of 
Beizelius  appear  almost  decisive  of  this  question.  A  substance  which  has  not 
the  metallic  lustre,  and  is  a  non-conductor  of  elfectricity,  cannot  be  regarded  as 
a  metal. 

Prep. — ^Pure  silicon  was  first  procured  by  Berzelius  in  the  year  1824  by  the 
action  of  potassium  on  fluosilicic  acid  gas,  but  it  is  more  conveniently  prepared 
from  the  double  fluoride  of  silicon  and  potassium  or  sodium,  previously  dried  by 
a  temperature  near  that  of  redness.  When  this  compound  is  heated  in  a  glass 
tube  with  potassium,  the  latter  unites  with  fluorine,  and  silicon  is  separated. 
The  heat  of  a  spirit-lamp  is  sufiicient  for  the  purpose,  and  the  decomposition 
takes  place,  accompanied  with  feeble  detonation,  before  the  mixture  becomes 
red-hot.  When  the  mass  is  cold,  the  soluble  parts  are  removed  by  the  action  of 
water  ;  the  first  portions  of  which  produce  disengagement  of  hydrogen  gas,  owing 
to  the  presence  of  some  silicuret  of  potassium.  The  silicon  thus  procured  is 
chemically  united  with  a  little  hydrogen,  and  at  a  red  heat  burns  vividly  in 
oxygen  gas.  In  order  to  render  it  quite  pure,  it  should  be  first  heated  to  redness, 
and  then  digested  in  dilute  hydrofluoric  acid  to  dissolve  adherent  particles  of 
silicic  acid.     (An.  of  Phil.  xxvi.  116.) 

Prop. — Silicon,  obtained  in  this  manner,  has  a  dark  nut-brown  colour,  without 
the  least  trace  of  metallic  lustre.  It  is  a  non-conductor  of  electricity.  It  is 
incombustible  in  air  and  in  oxygen  gas ;  and  may  be  exposed  to  the  flame  of 
the  blowpipe  without  fusing  or  undergoing  any  other  change.    It  is  neither  dis- 


SILICON.  21 X 

solved  nor  oxidized  by  the  sulphuric,  nitric,  hydrochloric,  or  hydrofluoric  acids ; 
but  a  mixture  of  the  nitric  and  hydrofluoric  acids  dissolves  it  readily  even  in  the 
cold. 

It  is  not  changed  by  ignition  with  chlorate  of  potassa.  In  nitre  it  does  not 
deflagrate  until  the  temperature  is  raised  so  high  that  the  acid  is  decomposed ; 
and  then  the  oxidation  is  effected  by  the  affinity  of  the  disengaged  alkali  for  sili- 
cic acid  co-operating  with  the  attraction  of  oxygen  for  silicon.  For  a  similar 
reason  it  burns  vividly  when  brought  into  contact  with  carbonate  of  potassa  or 
soda,  and  the  combustion  ensues  at  a  temperature  considerably  below  that  of  red- 
ness. It  explodes  in  consequence  of  a  copious  evolution  of  hydrogen  gas,  when 
it  is  dropped  upon  the  fused  hydrate  of  potassa,  soda,  or  baryta. 

Berzelius  ascertained,  by  oxidizing  a  known  weight  of  silicon,  that  100  parts 
of  silicic  acid  are  composed  of  48*4  of  silicon  and  51*6  of  oxygen.  Now,  if  silicic 
acid,  as  Thomson  supposes,  be  composed  of  single  atoms  of  its  elements,  then 
the  equivalent  of  silicon  will  be  7*5 ;  but  if,  as  Berzelius  believes,  the  smallest 
molecule  of  that  acid  contain  3  atoms  of  oxygen  united  with  1  atom  of  silicium, 
the  equivalent  of  silicium  would  be  22*5.  The  latter  view  is  supported  by  very 
strong  analogies.     Its  equivalent  is  therefore  22*5 ;  symh»  Si. 

Silicic  Acid. — Hist,  and  Prep. — This  compound,  known  also  by  the  names  of 
silica  and  siliceous  earth,  exists  abundantly  in  nature.  It  enters  into  the  compo- 
sition of  most  of  the  earthy  minerals ;  and  under  the  name  of  quartz  rock,  forms 
independent  mountainous  masses.  It  is  the  chief  ingredient  of  sandstones,  flint, 
calcedony,  rock  crystal,  and  other  analagous  substances.  It  may  indeed  be  pro- 
cured, of  sufficient  purity  for  most  purposes,  by  igniting  transparent  specimens 
of  rock  crystal,  throwing  them  while  red-hot  into  water,  and  then  reducing  them 
to  powder. 

Prop. — Pure  silicic  acid,  in  this  state,  is  a  light  white  powder,  which  feels 
rough  and  dry  when  rubbed  between  the  fingers  ;  is  both  insipid  and  inodorous ; 
the  sp.  gr.  is  2*69.  It  is  fixed  in  the  fire,  and  very  infusible ;  but  fuses  before 
the  oxy-hydrogen  blowpipe  with  greater  facility  than  lime  or  magnesia.  It  is 
quite  insoluble  in  water ;  but  Berzelius  has  shown,  that  if  presented  to  water 
while  in  the  nascent  state,  it  is  dissolved  in  large  quantity.  On  evaporating  the 
solution  gently,  a  bulky  gelatinous  hydrate  separates,  which  is  partially  decom- 
posed by  a  very  moderate  temperature,  but  does  not  part  with  all  its  water  except 
at  a  red  heat. 

Silicic  acid  has  no  action  on  test  paper ;  but  in  all  its  chemical  relations  it 
manifests  the  properties  of  an  acid,  and  displaces  carbonic  acid  by  the  aid  of  heat 
from  the  alkalies.  Its  combinations  with  the  fixed  alkalies  are  effected  by  mix- 
ing pure  sand  with  carbonate  of  potassa  or  soda,  and  heating  the  mixture  to  red- 
ness. During  the  process,  carbonic  acid  is  expelled,  and  a  silicate  of  the  alkali 
is  generated.  The  nature  of  the  product  depends  upon  the  proportions  which  are 
employed.  On  igniting  one  part  of  silicic  acid  with  three  of  carbonate  of  potassa, 
a  vitreous  mass  is  formed,  which  is  deliquescent,  and  may  be  dissolved  com- 
pletely in  water.  This  solution,  which  was  formerly  called  liquor  silicum,  has 
an  alkaline  reaction,  and  absorbs  carbonic  acid  on  exposure  to  the  atmosphere,  by 
which  it  is  partially  decomposed.  Concentrated  acids  precipitate  the  silicic  acid 
as  a  gelatinous  hydrate ;  but  if  a  considerable  quantity  of  water  is  present,  and 
the  acid  is  added  gradually,  the  alkali  may  be  perfectly  neutralized  without  any 
separation  of  silicic  acid.    When  a  solution  of  this  kind  is  evaporated  to  dryness, 


212  SELENIUM. 

the  silicic  acid  is  rendered  quite  insoluble,  and  may  thus  be  obtained  in  a  pure 
form. 

But  if  the  proportion  of  silicic  acid  and  alkali  be  reversed,  a  transparent  brittle 
compound  results,  which  is  insoluble  in  water,  is  attacked  by  none  of  the  acids 
excepting  the  hydrofluoric,  and  possesses  the  well-known  properties  of  glass. 
Every  kind  of  ordinary  glass  is  a  silicate,  and  all  its  varieties  are  owing  to  differ- 
ences in  the  proportion  of  the  constituents,  to  the  nature  of  the  alkali,  or  to  the 
presence  of  foreign  matters.  Thus,  green  bottle  glass  is  made  of  impure  mate-  . 
rials,  such  as  river  sand,  which  contains  iron,  and  the  most  common  kind  of  kelp 
or  pearl-ashes.  Crown  glass  for  windows  is  made  of  a  purer  alkali,  and  sand 
which  is  free  from  iron.  Plate  glass,  for  looking-glasses,  is  composed  of  sand 
and  alkali  in  their  purest  state ;  and  in  the  formation  of  flint-glass,  besides  these 
pure  ingredients,  a  considerable  quantity  of  litharge  or  red  lead  is  employed.  A 
small  portion  of  peroxide  of  manganese  is  also  used,  in  order  to  oxidize  carbona- 
ceous matters  contained  in  the  materials  of  the  glass ;  and  nitre  is  sometimes 
added  with  the  same  intention.  Ordinary  flint-glass,  according  to  Faraday,  con- 
tains 51*93  per  cent,  of  silicic  acid,  33"28  of  oxide  of  lead,  and  13*77  of  potassa; 
proportions  which  correspond  to  1  eq.  of  potassa,  1  eq.  of  oxide  of  lead,  and 
nearly  4  eq.  of  silicic  acid.  Flint-glass,  accordingly,  is  a  double  salt,  consisting 
chiefly  of  bisilicate  of  potassa,  and  bisilicate  of  oxide  of  lead. 

//«  eq.  ia  46*5 ;  symh.  Si  +  30,  Si,  or  SO  . 


SECTION  XI. 


SELENIUM. 


Hist,  and  Prep. — ^This  substance  was  discovered  in  1818  by  Berzelius,  who 
called  it  selenium,  from  ScX^i'iy  ihe  Moon,  suggested  by  its  having  at  first  been 
mistaken  for  the  metal  tellurium.  (An.  de  Ch.  et  Ph.  ix.  160,  and  An.  of  Phil, 
xiii.  401.)  It  has  hitherto  been  obtained  in  very  small  quantity,  and  occurs  for 
the  most  part  in  combination  with  some  varieties  of  iron  pyrites.  Stromeyer  has 
also  detected  it,  as  a  sulphuret  of  selenium,  among  the  volcanic  products  of  the 
Lipari  isles.  It  is  found  likewise  at  Clausthal  in  the  Hartz,  combined,  according 
to  Stromeyer  and  Rose,  with  several  metals,  such  as  lead,  cobalt,  silver,  mercury, 
and  copper.  Berzelius  found  it  in  the  sulphur  obtained  by  sublimation  from  the 
iron  pyrites  of  Fahlun.  In  a  manufactory  of  sulphuric  acid,  at  which  this  sul- 
phur was  employed,  it  was  observed  that  a  reddish-coloured  matter  always  col- 
lected at  the  bottom  of  the  leaden  chamber;  and  on  burning  this  substance,  Ber- 
zelius perceived  a  strong  and  peculiar  odour,  similar  to  that  of  decayed  horse- 
radish, which  induced  him  to  submit  it  to  a  careful  examination,  and  thus  led  to 
the  discovery  of  selenium.  For  the  extraction  of  selenium  from  the  native  sul- 
phuret, Magnus  proposes  to  mix  it  with  eight  times  its  weight  of  peroxide  of 
manganese,  and  to  expose  the  mixture  "to  a  low  red  heat  in  a  glass  retort,  the 


SELENIUM.  213 

beak  of  which  dips  into  water.  The  sulphur,  oxidized  at  the  expense  of  the 
manganese,  escapes  in  the  form  of  sulphurous  acid ;  while  the  selenium  either 
sublimes  as  such  or  in  the  state  of  selenious  acid.  Should  any  of  the  latter  be 
carried  over  into  the  water,  it  would  there  be  reduced  by  the  sulphurous  acid. 

Prop. — Selenium  in  many  of  its  physical  and  chemical  properties,  is  closely 
allied  to  sulphur.  At  common  temperatures,  is  a  brittle  opaque  solid  body,  with- 
out taste  or  odour.  It  has  a  metallic  lustre  and  the  aspect  of  lead,  when  in  mass; 
but  it  is  of  a  deep  red  colour  when  reduced  to  powder.  Its  sp.  gr.  is  between 
4*3  and  4'32.  At  212°  it  softens,  and  is  then  so  tenacious,  that  it  may  be  drawn 
out  into  fine  threads  which  are  transparent,  and  appear  red  by  transmitted  light. 
It  becomes  quite  fluid  at  a  temperature  somewhat  above  that  of  boiling  water.  It 
boils  at  about  650°,  forming  a  vapour  which  has  a  deep  yellow  colour,  but  is  free 
from  odour.  It  may  be  sublimed  in  close  vessels  without  change,  and  condenses 
again  into  dark  globules  of  a  metallic  lustre,  or  as  a  cinnabar-red  powder,  accord- 
ing as  the  space  in  which  it  collects  is  small  or  large.  Berzelius  at  first  regarded 
it  as  a  metal ;  but  since  it  is  an  imperfect  conductor  of  heat  and  electricity,  it 
more  properly  belongs  to  the  class  of  the  simple  non-metallic  bodies. 

Selenium  is  insoluble  in  water.  It  suffers  no  change  from  mere  exposure  to 
the  atmosphere ;  but  if  heated  in  the  open  air,  it  combines  readily  with  oxygen, 
and  two  compounds,  oxide  of  selenium  and  selenious  acid  are  generated.  If  ex- 
posed to  the  oxidizing  part  of  the  blowpipe  flame,  it  tinges  the  flame  with  a  light 
blue  colour,  and  exhales  a  strong  odour  like  that  of  decayed  horse-radish,  so 
strong  that  l-50th  of  a  grain  is  said  to  be  suflicient  to  scent  the  air  of  a  large 
apartment.  By  this  character  the  presence  of  selenium,  whether  alone  or  in  com- 
bination, may  always  be  detected. 

Berzelius  has  shown  that  selenic  acid  is  composed  of  24  parts  of  oxygen  and 
39*6  of  selenium.  This  substance,  also,  has  three  grades  of  oxidation,  the  oxy- 
gen in  the  two  last  of  which  is  in  the  ratio  of  2  and  3 ;  and  the  highest  grade, 
selenic  acid,  has  in  all  its  chemical  relations  a  singularly  close  analogy  to  sul- 
phuric acid.  From  these  facts  it  is  inferred  that  selenic  acid  is  composed  of  I 
atom  of  selenium  and  3  atoms  of  oxygen.     Its  eq.  is  39*6 ;  si/mb.  Se. 

The  compounds  of  selenium  described  in  this  section  are  the  following : — 

Selenium.  Oxygen.      Equiv.  Formulae. 

Oxide  of  Selenium  (probably)      39-6  or  1  eq.  -f-    8  or  1  eq.  =  47-6  SeO. 

Selenious  Acid  .  .    396  -f"  1^  or  2  eq.  =  55-6  SeOz. 

Selenic  Acid        .  .  39-6  -f  24  or  3  eq.  =  63-6  SeOa. 

Oxide  of  Selenium. — ^This  compound  is  formed  in  greatest  abundance  by  heating 
selenium  in  a  limited  quantity  of  atmospheric  aijr,  and  by  washing  the  product  to 
separate  selenious  acid,  which  is  generated  at  the  same  time.  It  is  a  colourless 
gas,  which  is  very  sparingly  soluble  in  water,  and  does  not  possess  any  acid 
properties.  It  is  the  cause  of  the  peculiar  odour  which  is  emitted  during  the  oxi- 
dation of  selenium. 

Selenious  Acid. — This  acid  is  most  conveniently  prepared  by  digesting  selenium 
in  nitric  or  nitro-hydrochloric  acid  till  it  is  completely  dissolved.  On  evaporat- 
ing the  solution  to  dryness,  a  white  residue  is  left,  which  is  selenious  acid.  By 
increase  of  temperature,  the  acid  itself  sublimes,  and  condenses  again  unchanged 
into  long  four-sided  needles.  [It  is  also  obtained  by  passing  a  current  of  oxygen 
over  selenium  strongly  heated  in  a  glass  tube,  the  selenium  takes  fire,  and  burns 
with  a  bluish  green  flame  at  the  point  and  edges,  while  selenious  acid  is  con' 


3|4  SELENIUM. 

densed  in  the  cooler  parts  of  the  tube.]  It  attracts  moisture  from  the  air,  whereby 
it  supers  imperfect  liquefaction.  It  dissolves  in  alcohol  and  water.  It  has  dis- 
tinct acid  properties,  and  its  salts  are  called  selenites, 

Selenious  acid  is  readily  decomposed  by  all  substances  which  have  a  strong 
affinity  for  oxygen,  such  as  sulphurous  and  phosphorous  acids.  When  sulphurous 
acid,  or  an  alkaline  sulphite,  is  added  to  a  solution  of  selenious  acid,  a  red-co- 
loured powder,  pure  selenium,  is  thrown  down,  and  the  sulphurous  is  converted 
into  sulphuric  acid.  Hydrosulphuric  acid  also  decomposes  it ;  and  an  orange- 
yellow-precipitate  subsides,  which  is  a  sulphuret  of  selenium. 

Selenic  Acid. — Hist, — ^The  preceding  compound,  discovered  by  Berzelius,  was 
till  lately  the  only  known  acid  of  selenium,  and  has  been  described  in  elementary 
works  under  the  name  of  selenic  acid ;  but  the  recent  discovery  of  another  acid 
of  selenium  containing  more  oxygen  than  the  other,  has  rendered  necessary  a 
change  of  nomenclature.  The  existence  of  selenic  acid  was  first  noticed  by  M. 
Nitzsch,  assistant  of  Mitscherlich,  and  its  properties  have  been  examined  and 
described  by  the  Professor  himself.     (Edin.  Journal  of  Science,  viii.  294.) 

Prep. — ^This  acid  is  prepared  by  fusing  nitrate  of  potassa  or  soda  with  sele- 
nium, a  metallic  seleniuret,  or  with  selenious  acid  or  any  of  its  salts.  Seleniuret 
of  lead,  as  the  most  common  ore  of  selenium,  wull  generally  be  employed ;  but 
it  is  very  difficult  to  obtain  pure  selenic  acid  by  its  means,  because  it  is  com- 
monly associated  with  metallic  sulphurets.  The  ore  is  first  treated  with  hydro- 
chloric acid  to  remove  any  carbonate  that  may  be  present ;  and  the  insoluble  part, 
which  is  about  a  third  of  the  mass,  is  mixed  with  its  own  weight  of  nitrate  of 
soda,  and  thrown  by  successive  portions  into  a  red-hot  crucible.  The  lead  is 
thus  oxidized,  and  the  selenium  converted  into  selenic  acid,  which  unites  with 
soda.  The  fused  mass  is  then  acted  on  by  hot  water,  which  dissolves  only  sele- 
niate  of  soda,  together  with  nitrate  and  nitrite  of  soda ;  while  the  insoluble  mat- 
ter, when  well  washed,  is  quite  free  from  selenium.  The  solution  is  next  made 
to  boil  briskly,  when  anhydrous  seleniate  of  soda  is  deposited  ;  while,  on  cooling, 
nitrate  of  soda  crystallizes.  On  renewing  the  ebullition  and  subsequent  cooling, 
fresh  portions  of  seleniate  and  nitrate  are  procured ;  and  these  successive  opera- 
tions are  repeated,  until  the  former  salt  is  entirely  separated.  This  process  is 
founded  on  the  fact,  that  seleniate  of  soda,  like  the  sulphate  of  the  same  base,  is 
more  soluble  in  water  of  about  90°  than  at  higher  or  lower  temperatures.  The 
nitrite  of  soda,  formed  during  the  fusion,  is  purposely  reconverted  into  nitrate  by 
digestion  with  nitric  acid. 

The  seleniate  of  soda  thus  procured  always  contains  a  little  sulphuric  acid, 
derived  from  the  metallic  sulphurets  of  the  ore ;  and  it  is  not  possible  to  sepa- 
rate this  acid  by  crystallization. .  All  attempts  to  separate  it  by  means  of  baryta 
were  likewise  fruitless ;  and  the  only  method  of  effecting  this  object  is  by  reduc- 
ing the  selenic  acid  into  selenium.  This  is  done  by  heating  a  mixture  of  sele- 
niate of  soda  with  hydrochlorate  of  ammonia,  when  the  sodium  unites  with 
chlorine,  all  the  hydrogen  with  oxygen,  and  selenium  and  nitrogen  are  set  free. 
This  change  will  be  more  readily  followed  when  stated  in  symbols ; — thus 

NaO,  SeOa,  NH3  and  HCl,  yield  N,  Se,  4H0  and  NaCI. 

The  selenium  which  sublimes  is  quite  free  from  sulphur.  It  is  then  converted 
by  nitric  acid  into  selenious  acid,  which 'should  be  neutralized  with  soda,  and 
fused  with  nitre  or  nitrate  of  soda.    The  pure  seleniate  of  soda,  separated  from 


CHLORINE.  215 

the  nitrate  according  to  the  foregoing  process,  is  subsequently  dissolved  in  water, 
and  obtained  in  crystals  by  spontaneous  evaporation. 

To  procure  the  acid  in  a  free  state,  seleniate  of  soda  is  decomposed  by  nitrate 
of  oxide  of  lead.  The  seleniate  of  that  oxide,  which  is  as  insoluble  as  the  sul- 
phate, after  being  well  washed,  is  exposed  to  a  current  of  hydrosulphuric  acid 
gas,  which  precipitates  all  the  lead  as  a  sulphuret,  but  does  not  decompose  the 
selenic  acid.  The  excess  of  the  gas  is  driven  off  by  heat,  and  pure  selenic  acid 
remains  diluted  with  water.  The  absence  of  fixed  substances  may  be  proved  by 
its  being  volatilized  by  heat  without  residue;  and  if  free  from  sulphuric  acid,  it 
gives  no  precipitate  with  chloride  of  barium  after  being  boiled  with  hydrochloric 
acid.  Any  nitric  acid  which  may  be  present  is  expelled  by  concentrating  the 
solution  by  means  of  heat. 

Prop. — It  is  a  colourless  liquid,  which  may  be  heatsd  to  536°  without  appre- 
ciable decomposition ;  but  above  that  point  decomposition  commences,  and  it 
becomes  rapid  at  554°,  giving  rise  to  disengagement  of  oxygen  and  selenious 
acid.  When  concentrated  by  a  temperature  of  329°,  its  sp.  gr.  is  2*524  ;  at  512° 
it  is  2*60,  and  at  545°  it  is  2*625,  but  a  little  selenious  acid  is  then  present. 
When  procured  by  the  process  above  described,  selenic  acid  always  contains 
water,  but  it  is  very  difficult  to  ascertain  its  precise  proportion.  Some  acid, 
which  had  been  heated  higher  than  536°,  contained,  subtracting  the  quantity  of 
selenious  acid  present,  15*75  per  cent,  of  water,  which  approximates  to  the  ratio 
of  one  equivalent  of  water  and  one  of  the  acid.  It  is  certain  that  selenic  acid  is 
decomposed  by  heat  before  parting  with  all  the  water  which  it  contains. 

Selenic  acid  has  a  powerful  affinity  for  water,  and  emits  as  much  heat  in  uniting 
with  it  as  sulphuric  acid  does.  Like  this  acid  it  is  not  decomposed  by  hydro- 
sulphuric  acid,  and  hence  this  gas  may  be  employed  for  decomposing  seleniate 
of  the  oxides  of  lead  or  copper.  With  hydrochloric  acid  the  change  is  peculiar ; 
for  on  boiling  the  mixture  mutual  decomposition  ensues,  water  and  selenious  acid 
are  formed,  and  chlorine  is  set  free ;  so  that  the  solution,  like  aqua  regia,  is  capa- 
ble of  dissolving  gold  and  platinum.  Selenic  acid  dissolves  zinc  and  iron  with 
disengagement  of  hydrogen  gas,  and  copper  with  formation  of  selenious  acid. 
It  dissolves  gold  also,  but  not  platinum.  Sulphurous  acid  has  no  action  on 
selenic  acid,  whereas  selenious  acid  is  easily  reduced  by  it.  Consequently,  when 
it  is  wished  to  precipitate  selenium  from  selenic  acid,  it  must  be  boiled  with 
hydrochloric  acid  before  sulphurous  acid  is  added. 

Mitscherlich  has  observed,  that  selenic  and  sulphuric  acids  are  not  only  analo- 
gous in  composition  and  in  many  of  their  properties,  but  that  the  similarity  runs 
through  their  compounds  with  alkaline  substances,  their  salts  resembling  each 
other  in  chemical  properties,  constitution,  and  form. 


SECTION  XII. 


CHLORINE. 


Hist  — TitE  discovery  of  chlorine  was  made  in  the  year  1774  by  Scheele,  while 
investigating  the  nature  of  manganese,  and  he  described  it  under  the  name  of 
dephhgisficated  marine  acid.     The  French  chemists  called  it  oxygenized  muriatic 


216  CHLORINE. 

acid,  a  term  which  was  afterwards  contracted  to  oxy-muriatic  acid,  from  an  opi- 
nion proposed  by  Berthollet  that  it  is  a  compound  of  muriatic  acid  and  oxygen. 
In  1809  Gay-Lussac  and  Thenard  published  an  abstract  of  some  experiments 
upon  this  substance,  which  subsequently  appeared  at  len^h  in  their  Recherches 
Physico-Chimiques,  wherein  they  stated  that  oxy-muriatic  acid  might  be  regarded 
as  a  simple  body,  though  they  gave  the  preference  to  the  doctrine  advanced  by 
Berthollet.  Davy  engaged  in  the  inquiry  about  the  same  time ;  and  after  having 
exposed  oxy-muriatic  acid  to  the  most  powerful  decomposing  agents  which  che- 
mists possess,  without  being  able  to  effect  its  decomposition,  he  communicated 
to  the  Royal  Society  an  essay,  in  which  he  denied  its  compound  nature;  and  he 
maintained  that,  according  to  the  true  logic  of  chemistry,  it  is  entitled  to  rank 
with  simple  bodies.  This  view,  which  is  commonly  termed  the  new  theory  of 
cJdorine,  though  strongly  objected  to  at  the  time  it  was  first  proposed,  is  now 
universally  received  by  chemists.  The  grounds  of  preference  will  hereafter  be 
briefly  stated. 

Prep. — Chlorine  gas  is  obtained  by  the  action  of  hydrochloric  acid  on  peroxide 
of  manganese.  The  most  convenient  method  of  preparing  it  is  by  mixing  con- 
centrated hydrochloric  acid,  contained  in  a  glass  flask,  with  half  its  weight  of 
finely  powdered  peroxide  of  manganese.  Effervescence,  owing  to  the  escape  of 
chlorine,  takes  place  even  in  the  cold ;  but  the  gas  is  evolved  much  more  freely 
by  the  application  of  a  moderate  heat.  It  should  be  collected  by  displacement 
of  air  in  dry  bottles.  Tlie  tube  conducting  the  gas  reaches  to  the  bottom  of  the 
bottle,  where  the  chlorine,  being  heavier  than  air,  accumulates,  and  displaces  it. 
When  the  bottle  is  full,  which  is  known  by  the  colour  of  the  gas  appearing  at 
the  mouth  of  the  bottle,  it  is  stopped  with  a  greased  stopper,  and  another  bottle 
put  in  its  place.  As  some  hydrochloric  acid  gas  commonly  passes  over  with  it, 
the  chlorine  should  not  be  considered  quite  pure,  till  after  being  transmitted 
through  water. 

The  theory  of  this  process  will  be  readily  understood  by  first  viewing  the  ele- 
ments which  act  on  each  other,  namely,— 

Manganege       .        27*7  or  1  eq.    Mn  Chlorine        .        7084  or  2  eq.       2C1 

Oxygen  .        16  2  eg.    2  0  Hydrogen      . or  2  eg.       2H 

Perox.  of  Mang]       437  or  1  eq.    Mn  -f-  20    Hydrochl.  acid      72-84  or  2  eq.  2  (H  -f-  CI) ;« 

and  then  inspecting  the  products  derived  from  them,  namely, 

Manganese        .        27-7  Hydrogen    2  . 

^,,  '  -_  ^_  '       *      , -Chlorine  35-42  or  1  eg. 

Chlorine  .         35-42  Oxygen       16  ^ 

Chloride  of  Mang.    63*  12  Water        18". 

In  symbols, 

^  MnOj  and  2HC1  yield  MnCl,  2H0,  and  CI. 

The  affinities  which  determine  these  changes  are  the  mutual  attraction  of  oxygen 
and  hydrogen,  and  of  chlorine  and  manganese. 

When  it  is  an  object  to  prepare  chlorine  at  the  cheapest  rate,  as  for  the  pur- 
poses of  manufacture,  the  preceding  process  is  modified  in  the  following  manner. 
Three  parts  of  sea-salt  are  intimately  mixed  with  one  of  peroxide  of  manganese, 
and  to  this  mixture  two  parts  of  sulphuric  acid,  diluted  with  an  equal  weight  of 
water,  are  added.  By  the  action  of  sulpliuric  acid  on  sea-salt,  hydrochloric  acid 
is  disengaged,  wliich  reacts,  as  in  the  former  case,  upon  the  peroxide  of  man- 


CHLORINE.  217 

ganese ;  so  that,  instead  of  adding  hydrochloric  acid  directly  to  the  manganese, 
the  materials  for  forming  it  are  employed.  In  this  process,  however,  the  sul- 
phates of  soda  and  protoxide  of  manganese  are  generated,  instead  of  chloride  of 
manganese.  Thus  the  materials  which  act  on  each  other  are  Mn02,  NaCl,  and 
2SO3 ;  and  the  products  MnO.  SO3,  NaO.  SO3,  and  CI. 

Prop. — Chlorine  (from  x'><^^°^  green)  is  a  yellowish-green  coloured  gas,  which 
has  an  astringent  taste,  and  a  disagreeable  odour.  It  is  one  of  the  most  suffo- 
cating of  the  gases,  exciting  spasm  and  great  irritation  of  the  glottis,  even  when 
considerably  diluted  with  air.  When  strongly  and  suddenly  compressed,  it 
emits  both  heat  and  light,  the  latter  being  solely  due,  as  in  the  case  of  air  and 
oxygen,  to  the  chlorine  acting  chemically  on  the  oil  with  which  the  compress- 
ing apparatus  is  lubricated  (An.  de  Ch.  et  Ph.  xliv.  181).  According  to  Davy, 
100  cubic  inches  of  dry  chlorine  at  30  B.  and  60°  F.  weigh  between  76  and  77 
grains.  Gay-Lussac  and  Thenard  found  the  density  of  pure  and  dry  chlorine  to 
be  2*47,  which  gives  76*599  grains  as  the  weight  of  100  cubic  inches  at  60°  F. 
and  30  B.  Under  the  pressure  of  about  four  atmospheres  it  is  a  limpid  liquid 
of  a  bright  yellow  colour,  which  does  not  freeze  at  the  temperature  of  zero, 
and  which  assumes  the  gaseous  form  with  the  appearance  of  ebullition  when  the 
pressure  is  removed.  Kemp  finds  that  this  liquid  is  a  non-conductor  of  elec- 
tricity. 

Cold  recently  boiled  water,  at  the  common  pressure,  absorbs  twice  its  volume 
of  chlorine,  and  yields  it  again  when  heated.  The  solution,  which  is  made  by 
transmitting  a  current  of  chlorine  gas  through  cold  water,  bas  the  colour,  taste, 
and  most  of  the  other  properties  of  the  gas  itself.  When  moist  chlorine  gas  is 
exposed  to  a  cold  of  32°,  yellow  crystals  are  formed,  which  consist  of  water 
and  chlorine  in  definite  proportions.  They  are  composed,  according  to  Faraday, 
of  35*42  parts  or  1  eq.  of  chlorine,  and  90  parts  or  10  eq.  of  water.  It  expe- 
riences no  chemical  change  from  the  action  of  the  imponderables.  Thus  it  is 
not  affected  chemically  by  intense  heat,  by  strong  shocks  of  electricity,  or  by 
a  powerful  galvanic  battery.  Davy  exposed  it  also  to  the  action  of  charcoal 
heated  to  whiteness  by  galvanic  electricity,  without  separating  oxygen  from  it, 
or  in  any  way  affecting  its  nature.  Light  does  not  act  on  dry  chlorine  ;  but  if 
\yater  be  present,  the  chlorine  decomposes  that  liquid,  unites  with  the  hydrogen 
to  form  hydrochloric  acid,  and  oxygen  gas  is  set  at  liberty.  This  change  takes 
place  quickly  in  sunshine,  more  slowly  in  diffused  daylight,  and  not  at  all  when 
light  is  wholly  excluded.  Hence  the  necessity  of  keeping  moist  chlorine  gas, 
or  its  solution,  in  a  dark  place. 

Chlorine  unites  with  some  substances  with  evolution  of  heat  and  light,  and 
is  hence  termed  a  suporter  of  combustion.  On  plunging  a  lighted  taper  into 
chlorine  gas,  it  burns  for  a  short  time  with  a  small  red  flame,  and  emits  a  large 
quantity  of  smoke.  Phosphorus  takes  fire  in  it  spontaneously  and  burns  with 
a  pale  white  light.  Several  of  the  metals,  such  as  tin,  copper,  arsenic,  anti- 
mony, and  zinc,  when  introduced  into  chlorine  in  the  state  of  powder  or  in  fine 
leaves,  are  suddenly  inflamed.  In  all  these  cases  the  combustible  substances 
unite  with  chlorine. 

Chlorine  has  a  very  powerful  attraction  foj  hydrogen;  and  many  of  the  che- 
mical phenomena  to  which  it  gives  rise  are  owing  to  this  property.  A  striking 
example  is  its  power  of  decomposing  water  by  the  action  of  light,  or  at  a  red- 
heat;  the  same  effect  is  produced  on  most  compound  substances,  of  which  hy- 
drogen is  an  element.     For  the  same  reason,  when  chlorine,  water,  and  some 


218  CHLORINE. 

other  body  which  has  a  strong  affinity  for  oxygen,  are  presented  to  one  another, 
water  is  usually  resolved  into  its  elements,  its  hydrogen  attaching  itself  to  the 
chlorine,  and  its  oxygen  to  the  other  body.  Thus  chlorine  is,  indirectly,  one  of 
the  most  powerful  oxydizing  agents  which  we  possess. 

When  any  compound  of  chlorine  and  an  inflammable  is  exposed  to  the  influ- 
ence of  galvanism,  the  inflammable  body  goes  over  to  the  — ,  and  chlorine  to 
the  -f-  pole  of  the  battery.  This  establishes  a  close  analogy  between  oxygen 
and  chlorine,  both  of  them  being  supporters  of  combustion,  and  both  negative 
electrics. 

Though  formerly  called  an  acid,  it  possesses  no  acid  properties.  It  has  not 
a  sour  taste,  does  not  redden  the  blue  colour  of  plants,  and  shows  comparatively 
21ttle  disposition  to  unite  with  alkalies.  Its  strong  affinity  for  the  metals  is  suf- 
/  ficient  to  prove  that  it  is  not  an  acid  ;  for  chemists  are  not  acquainted  with  any 
V instance  of  an  acid  combining  directly  in  definite  proportion  with  a  metal.  Its 
action  on  the  pure  alkalies  leads  to  complicated  changes,  which  will  be  consi- 
dered while  speaking  of  the  oxides  of  chlorine. 

One  of  the  most  important  properties  of  chlorine  is  its  bleaching  power.  All 
animal  and  vegetable  colours  are  speedily  removed  by  chlorine;  and  when  the 
colour  is  once  discharged,  it  can  never  be  restored.  Davy  proved  that  chlorine 
cannot  bleach  unless  water  is  present.  Thus  dry  litmus  paper  suffers  no  change 
in  dry  chlorine ;  but  when  water  is  admitted,  the  colour  speedily  disappears. 
It  is  well  known  also  that  hydrochloric  acid  is  always  generated  when  chlorine 
bleaches.  From  these  facts  it  is  inferred  that  water  is  decomposed  during  the 
process ;  that  its  hydrogen  unites  with  chlorine,  and  that  decomposition  of  the 
colouring  matter  is  occasioned  by  the  oxygen  which  is  liberated.  The  bleaching 
property  of  binoxide  of  hydrogen  and  of  chromic  and  permanganic  acids,  of  which 
oxygen  is  certainly  the  decolorizing  principle,  leaves  little  doubt  of  the  accuracy 
of  the  foregoing  explanation. 

Chlorine  is  useful,  likewise,  for  the  purposes  of  fumigation.  The  experience 
of  Guyton-Morveau  is  sufficient  evidence  of  its  power  in  destroying  the  volatile 
principles  given  oflf  by  putrefying  animal  matter;  it  probably  acts  in  a  similar 
way  on  contagious  eflHuvia.  A  peculiar  compound,  formed  by  the  action  of  chlo- 
rine on  soda,  has  been  lately  introduced  for  this  purpose  by  Labaraque. 

Chlorine  is  in  general  easily  recognized  by  its  colour  and  odour.  Chemically 
it  may  be  detected  by  its  bleaching  properly,  added  to  the  circumstance  that  a 
solution  of  nitrate  of  oxide  of  silver  occasions  in  it  a  dense  white  precipitate  (a 
compound  of  chlorine  and  metallic  silver),  which  becomes  dark  on  exposure  to 
light,  is  insoluble  in  acids,  and  dissolves  completely  in  pure  ammonia.  The 
whole  of  the  chlorine,  however,  is  not  thrown  down ;  for  the  oxygen  of  the 
oxide  of  silver  unites  with  a  portion  of  the  chlorine,  and  converts  it  into  chloric 
acid. 

Those  compounds  of  chlorine  which  are  not  acid,  are  termed  chlorides  or  chlo' 
rurets.  The  former  expression,  from  the  analogy  between  chlorine  and  oxygen, 
is  perhaps  the  more  appropriate. 

Berzelius  inferred  the  equivalent  of  chlorine  from  the  oxygen  lost  by  chlorate 
of  potassa  when  decomposed  by  heat,  and  the  quantity  of  chlorine  found  in  the 
residual  chloride  of  potassium.  I 'investigated  the  same  subject  by  examining 
into  the  composition  of  the  nitrate  of  the  oxide  and  chloride  of  silver,  of  the  pro- 
toxide and  chloride  of  lead,  and  of  the  peroxide  and  chlorides  of  mercury. 
These  researches  concur  in  showing  36,  the  eq.  of  chlorine  commonly  adopted 


CHLORINE. 


219 


in  this  country,  to  be  erroneous.  The  number  inferred  from  the  sp.  gr.  of  chlo- 
rine and  hydrogen  gases  is  35'84 ;  but,  unfortunately,  the  densities  of  these  gases 
are  not  known  with  the  precision  required  for  an  application  of  this  nature. 

Its  eq.  is  35'42 ;  eq.  vol.  =  100  ;  symh.  CI. 

The  composition  of  the  compounds  described  in  this  section  is  as  follows  : — 

Hydrochloric  Acid 

Hypochlorous  Acid 

Chlorous  Acid 

Chloric  Acid 

Perchloric  Acid 

Quadrochloride  of 
Nitrogen 

Protochloride   of 
Carbon 

Dichloride  of  Car- 
bon 

Perchloride  of  Car- 
bon 

Dichloride  of  Sul- 
phur 

Bichloride  of  Sul- 
phur 

Sesquichloride   of 
Phosphorus 

Perchloride      of 

Phosphorus 
Chlorocarbonic 

Acid  Gas 
Terchloride      of 

Boron 
Terchloride  of  Sili- 
con 

Hydrochloric,,  Chlorohydricj  or  Muriatic  Acid. — Hist,  and  Prep. — A  concen- 
trated aqueous  solution  of  this  acid  has  been  long  known  under  the  names  of 
spirit  of  salt,  and  of  marine  or  muriatic  acid  ;  but  in  its  purer  form  of  gas  it  was 
discovered  in  1772  by  Piiestley.  It  may  be  conveniently  prepared  by  putting 
an  ounce  of  strong  hydrochloric  acid  solution  into  a  glass  flask,  and  heating  it  by 
means  of  a  lamp  till  the  liquid  boils,  when  the  gas  is  freely  evolved,  and  may 
be  collected  over  mercury.  Another  method  of  prep-aring  it  is  by  the  action  of 
concentrated  sulphuric  acid  on  an  equal  weight  of  sea-salt.  Brisk  effervescence 
ensues  at  the  moment  of  making  the  mixture,  and  on  the  application  of  heat  a 
large  quantity  of  hydrochloric  acid  gas  is  disengaged.  In  the  former  process, 
hydrochloric  acid  previously  dissolved  in  water  is  simply  expelled  from  the  solu- 
tion by  heat.  The  explanation  of  the  latter  process  is  more  complicated.  Sea- 
salt  was  formerly  supposed  to  be  a  compound  of  hydrochloric  acid  and  soda ; 
and,  on  this  supposition,  the  soda  was  believed  merely  to  quit  the  hydrochloric 
and  unite  with  sulphuric  acid.  But  the  researches  of  Gay-Lussac,  Thenard,  and 
Davy,  proved  that  it  consists  of  chlorine  and  sodium  combined  in  the  ratio  of 
their  equivalents.  The  nature  of  its  action  with  sulphuric  acid  will  be  under- 
stood by  comparing  the  elements  concerned  in  the  change  before  and  after  it  has 
occurred : — 


Chlorine. 
35-42 
35  42 
35.42 
35-42 
35-42 

1  eq.  -j-  Hydrogen 
-f-  Oxygen 

-  -  Ditto 

-  -  Ditto 
-j-  Ditto 

1 

8 
32 
40 
66 

Equiv. 
1  eq.  =   36-42 
1  eq.  =    43-42 
4eq.=    67-42 
5eq.=    75-42 
7eq.=   91.42 

Formulae. 
HCl. 
Clo. 

C104. 

ClOs. 
CIO7. 

141-68 

4  eq.  -j-  Nitrogen 

14-15 

1  eq.  =  155-83 

NCI4. 

35-42 

1  eq.  -\-  Carbon 

6-12 

1  eq.=   41-54 

CCl. 

35-42 

1  eq.  -j-  Ditto 

12-24 

2eq.=   47-66 

C2C1. 

106-26 

3  eq.  -f-  Carbon 

12-24 

2  eq.  =  118-50 

C2C13. 

35-42 

1  eq.  -\-  Sulphur 

32-2 

2eq.=   67-62 

SCI. 

70 

2  eq.  -f-  Ditto 

16-1 

1  eq.=   86-1 

SC12. 

106-26 

3  eq.  -|-  Phospho. 

31-4 

1  eq,  ==  137-66 

P2C13. 

175 

5  eq.  -f-  Ditto 

31-4 

1  eq.  ==  206-4 

P2C15. 

35-42 

1  eq.  -j-  Carb.  ox. 

14-12 

1  eq.  =   49-54 

Co  -f-  CI. 

106-26 

3  eq.  -\-  Boron 

10-9 

1  eq.==  117-16 

BCig. 

106-26 

3  eq.  -f-  Silicon 

22-5 

1  eq.  =  128-76 

Sicls. 

Hydrous  Sulp.  Acid. 

Chloride  of  Sodium. 

Real  Acid           4M 

Chlorine        35-42 

Water        i^^^'  U 

Sodium          23-3 

or  in  symbols, 

SO3,  HO  +  NaCl  = 

Sulph.  of  Soda. 
Acid  40-1 

(Sod.  23-3) 
iOxy.    8    \ 


Soda 


Hydrochloric  Acid. 
Chlorine        35.42 

Hydrogen        1 


SO3,  NaO  +  HCl. 


220  CHLORINE. 

Thus  it  appears  that  single  equivalents  of  water,  sulphuric  acid,  and  chloride 
of  sodium,  yield  sulphate  of  soda  and  hydrochloric  acid.  The  water  of  the  sul- 
phuric acid  is  essential ;  so  much  so,  indeed,  that  chloride  of  sodium  is  not 
decomposed  at  all  by  anhydrous  sulphuric  acid. 

Hydrochloric  acid  may  be  generated  by  the  direct  union  of  its  elements.  When 
equal  measures  of  chlorine  and  hydrogen  are  mixed  together,  and  an  electric 
spark  is  passed  through  the  mixture,  instantaneous  combination  takes  place,  heat 
and  light  are  emitted,  and  hydrochloric  acid  is  generated.  A  similar  effect  is 
produced  by  flame,  by  a  red-hot  body-  and  by  spongy  platinum.  Light  also 
causes  them  to  unite.  A  mixture  of  the  two  gases  may  be  preserved  without 
change  in  a  dark  place ;  but  if  exposed  to  the  diffused  light  of  day,  gradual 
combination  ensues,  which  is  completed  in  the  course  of  24  hours.  The  direct 
solar  rays  produce,  like  flame  and  electricity,  sudden  inflammation  of  the  whole 
mixture,  accompanied  with  explosion;  and,  according  to  Brande,  the  vivid  light 
emitted  by  charcoal  intensely  heated  by  galvanic  electricity  acts  in  a  similar 
manner. 

This  acid  is  most  commonly  used  in  the  form  of  a  concentrated  aqueous  solu- 
tion, which  is  made  by  transmitting  a  current  of  the  gas  into  water  as  long  as 
any  of  it  is  absorbed.  All  the  Pharmacopoeias  give  directions  for  conducting  the 
process.  That  adopted  by  the  Edinburgh  College  is  practically  good.  The 
proportions  they  recommend  are  equal  weights  of  sea-salt,  water,  and  sulphuric 
acid,  more  acid  being  purposely  employed  than  is  sufficient  to  form  a  neutral 
sulphate  with  the  soda,  so  that  the  more  perfect  decomposition  of  the  sea-salt 
may  be  insured.  The  acid,  to  prevent  too  violeflt  effervescence  at  first,  is  mixed 
with  one-third  of  the  water ;  and  when  the  mixture  has  cooled,  it  is  poured  upon 
the  salt  previously  introduced  into  a  glass  retort.  The  distillation  is  continued 
to  dryness ;  and  the  gas,  as,  it  escapes,  is  conducted  into  the  remainder  of  the 
water.  The  theory  of  the  process  has  been  already  explained.  The  residue  is 
a  mixture  of  sulphate  and  bisulphate  of  soda.  The  sp.  gr.  of  the  acid  solution 
obtained  by  this  process  is  1*170. 

Prop. — It  is  a  colourless  gas,  has  a  pungent  odour  and  an  acid  taste.  Under 
a  pressure  of  40  atmospheres,  and  at  the  temperature  of  50°,  it  is  liquid.  Sp.  gr. 
1*2695.  It  is  quite  irrespirable,  exciting  violent  spasm  of  the  glottis;  but  when 
diluted  with  air,  it  is  far  less  irritating  than  chlorine.  All  burning  bodies  are 
extinguished  by  it,  nor  is  the  gas  itself  inflammable. 

It  is  not  chemically  changed  by  mere  heat.  It  is  readily  decomposed  by  gal- 
vanism, hydrogen  appearing  at  the  — ,  and  chlorine  at  the  -f-  pole.  It  is  also 
decomposed  by  ordinary  electricity.  The  decomposition,  however,  is  incom- 
plete ;  for  though  one  electric  spark  resolves  a  portion  of  the  gas  into  its  ele- 
ments, the  next  shock  in  a  great  measure  effects  their  reunion.  It  is  not  affected 
by  oxygen  under  common  circumstances;  but  if  a  mixture  of  oxygen  and 
hydrochloric  acid  gases  is  electrified,  the  oxygen  unites  with  the  hydrogen  of 
the  acid  to  form  water,  and  chlorine  is  set  at  liberty.  For  this  and  the  pre- 
ceding fact  we  are  indebted  to  the  researches  of  Henry. 

One  of  the  most  striking  properties  of  hydrochloric  acid  gas  is  its  powerful 
attraction  for  water.  A  dense  white  cloud  appears  whenever  it  escapes  into  the 
air,  owing  to  its  combining  with  the  aqueous  vapour  of  the  atmosphere.  A 
piece  of  ice  put  into  a  jar  full  of  the  gas  confined  over  mercury  liquefies  on  the 
instant,  and  the  whole  of  the  gas  disappears  in  the  course  of  a  few  seconds.  On 
opening  a  long  wide  jar  of  hydrochloric  acid  gas  under  water,  the  absorption  of 


CHLORINE. 


^i 


the  gas  takes  place  so  instantaneously,  that  the  water  is  forced  up  into  the  jar 
with  the  same  violence  as  into  a  vacuum.  Considerable  increase  of  temperature 
takes  place  during  the  absorption,  and  therefore  the  apparatus  should  be  kept 
cool  by  ice.  Davy  states  (Elements,  p.  252)  that  water  at  the  temperature  of  40° 
absorbs  480  times  its  volume  of  the  gas,  and  that  the  solution  has  a  sp.  gr.  of 
1*2109.  Thomson  finds  that  one  cubic  inch  of  water  at  69°  absorbs  418  cubic 
inches  of  gas,  and  occupies  the  space  of  1*34  cubic  inch.  The  solution  has  a 
sp.  gr.  of  1'1958,  and  one  cubic  inch  of  it  contains  311.04  cubic  inches  of  hydro- 
chloric acid.  gas.  The  quantity  of  real  acid  contained  in  solutions  of  diflferent 
densities  may  be  determined  by  ascertaining  the  quantity  of  pure  marble  dis- 
solved by  a  given  weight  of  each.  Every  50'6  grains  of  marble  correspond  to 
36*42  of  real  acid.  The  following  table,  from  Thomson's  *' Principles  of  Che- 
mistry," is  constructed  according  to  this  rule.  The  first  and  second  columns 
show  the  atomic  constitution  of  each  acid. 


Table  exhihiti 

ng  the  Specific 

Gravity  of  Muriatic  acid 

of  determinate  strengths. 

Atoms  of 

Atoms  of 

Real  Acid  in  100  of  the 

Specific 

Atoms  of 

Atoms  of 

Real  Acid  in  100  of  tbe 

.  Specific 

Acid. 

Water. 

liquid. 

Gravity. 

Acid. 

Water. 

liquid. 

Gnvity. 

6 

40-559 

1-203 

14 

22-700 

1-1060 

7 

37-000 

1-179 

15 

21-512 

1-1008 

8 

33-945 

M62 

16 

20-442 

1-0960 

9 

31-346 

M49 

17 

19-474 

1-0902 

10 

29-134 

1-139 

18 

18;jyj 

1-0860 

11 

27-206 

1-1285 

19 

17-790 

1-0820 

12 

25-517 

1-1197 

20 

17051 

1-0780 

13 

24-026 

1-1127 

Hydrochloric  acid  of  commerce  has  a  yellow  colour,  and  is  always  impure. 
Its  usual  impurities  are  nitric  acid,  sulphuric  acid,  oxide  of  iron,  and  occasionally 
sulphurous  acid.  The  latter,  according  to  Girardin,  may  be  detected  by  the  addi- 
tion of  some  crystals  of  the  protochloride  of  tin,  which  decomposes  the  sulphurous 
acid  and  precipitates  a  brown  powder  containing  sulphur  in  combination  with 
tin.  The  presence  of  nitric  acid  may  be  inferred  if  the  hydrochloric  acid  has  the 
property  of  dissolving  gold  leaf.  Iron  may  be  detected  by  ferrocyanide  of  potas- 
sium, and  sulphuric  acid  by  chloride  of  barium,  the  suspected  hydrochloric  acid 
being  previously  diluted  with  three  or  four  parts  of  water.  The  presence  of 
nitric  acid  is  provided  against,  by  igniting  the  sea-salt,  as  recommended  by  the 
Edinburgh  College,  in  order  to  decompose  any  nitre  which  it  may  contain.  The 
other  impurities  may  be  avoided  by  employing  Woulfe's  Apparatus.  A  few 
drachms  of  water  are  put  into  the  first  bottle  to  retain  the  chloride  of  iron  and 
sulphuric  acid  which  pass  over,  and  the  hydrochloric  acid  gas  is  condensed  in 
the  second. 

A  strong  solution  of  pure  hydrochloric  acid  is  a  colourless  liquid,  which 
emits  white  vapours  when  exposed  to  the  air,  is  intensely  sour,  reddens 
,  litmus  paper  strongly,  and  neutralizes  alkalies.  It  combines  with  water  in  every 
proportion,  and  causes  increase  of  temperature  when  mixed  with  it,  though  in  a 
much  less  degree  tjian  sulphuric  acid.  It  freezes  at  60°  F. ;  and  boils  at  110°, 
or  a  little  higher,  giving  off  pure  hydrochloric  acid  gas  in  large  quantity. 

[The  strongest  acid  which  can  be  easily  procured,  as  represented  in  the  table, 
contains  6  atoms  of  water.  When  this  liquid  is  evaporated  in  the  open  air,  it  aban- 
dons a  quantity  of  acid  gas,  and  according  to  Graham  becomes  a  compound 


222  CHLORINE.  , 

containing  12  atoms  of  water.  Dal  ton  found  that  when  the  concentrated  acid 
was  heated  in  a  retort,  its  boiling  point  gradually  rose  to  230°,  at  which  tem- 
perature the  residual  acid  distilled  over  unchanged,  and  had  a  sp.  gr.  of  1*094. 
This  acid  Dr.  Clark  found  to  contain  16*4  atoms  of  water  to  1  of  acid.] 

Hydrochloric  acid  is  decomposed  by  substances  which  yield  oxygen  readily. 
Thus  several  peroxides,  such  as  those  of  manganese,  cobalt,  and  lead,  effect  its 
decomposition.  Chloric,  iodic,  bromic,  nitric,  and  selenic  acids  act  on  the  same 
principle.  A  mixture  of  nitric  and  hydrochloric  acids,  in  the  ratio  of  one  mea- 
sure of  the  former  to  two  of  the  latter,  has  long  been  known  under  the  name  of 
Aqua  regia,  as  a  solvent  for  gold  and  platinum.  When  these  acids  are  mixed 
together,  the  solution  instantly  becomes  yellow;  and  on  heating  the  mixture,  pure 
chlorine  is  evolved,  and  the  colour  of  the  solution  deepens.  On  continuing  the 
heat,  chlorine  and  nitrous  acid  vapours  are  disengaged.  At  length  the  evolution 
of  chlorine  ceases,  and  the  residual  liquid  is  found  to  be  a  solution  of  hydro- 
chloric and  nitrous  acids,  which  is  incapable  of  dissolving  gold.  The  explana- 
tion of  these  facts  is,  that  nitric  and  hydrochloric  acids  decompose  one  another, 
giving  rise  to  the  production  of  water  and  nitrous  acid,  and  the  separation  of 
chlorine;  while  hydrochloric  and  nitrous  acids  may  be  heated  together  without 
mutual  decomposition.  It  is  hence  inferred  that  the  power  of  nitro-hydrochloric 
acid  in  dissolving  gold  is  owing  to  the  chlorine  which  is  liberated.  (Davy  in 
the  Quarterly  Journal,  vol.  i.) 

Hydrochloric  acid  is  distinguished  by  its  odour,  volatility,  and  strong  acid 
properties.  With  nitrate  of  oxide  of  silver  it  yields  the  same  precipitate  as  chlo- 
rine ;  but  no  chloric  acid  is  generated,  because  the  oxygen  of  the  oxide  of  silver 
unites  with  the  hydrogen  of  the  hydrochloric  acid,  and  the  chlorine  in  conse- 
quence is  entirely  precipitated.  Notwithstanding  that  nitrate  of  oxide  of  silver 
yields  the  same  precipitate  with  chlorine  and  hydrochloric  acid,  there  is  no  dif- 
ficulty in  distinguishing  between  them,  for  the  bleaching  property  of  the  former 
is  a  sure  ground  of  distinction. 

The  composition  of  hydrochloric  acid  has  been  determined  by  Davy,  and  Gay- 
Lussac  and  Thenard.  Their  experiments  concur  in  proving  that  chlorine  and 
hydrogen  unite  in  equal  volumes,  and  that  the  hydrochloric  acid,  which  is  the 
sole  and  constant  product,  occupies  the  same  space  as  the  gases  from  which  it 
is  formed.  From  these  facts  the  composition  of  hydrochloric  acid  is  easily  in- 
ferred.   For,  as 

Grains. 
60  cubic  inches  of  Chloride  weigh            ....        38-299 
60    "        "       of  Hydrogen 10699 

100  C.  I.  of  Hydrochloric  acid  gas  must  weigh        .        .        39-3689 

'These  numbers  are  in  the  ratio  of  1  to  35*84,  being  nearly  that  of  single  eq. 
of  hydrogen  and  chlorine.  Hence  its  eq.  is  36*42 ;  eq.  vol.  =  100 ;  symb.  H  -f  01, 
or  HCl. 

COMPOUNDS  OF  CHLORINE  AND  OXYGEN. 

The  leading  character  of  these  compounds  is  derived  from  the  circumstance 
that  chlorine  and  oxygen,  the  attraction  of  which  for  most  elementary  substances 
is  so  energetic,  have  but  a  feeble  affinity  for  each  other.    These  principles,  con- 


CHLORINE.  223 

sequently,  are  never  met  with  in  nature  in  a  state  of  combination.     Indeed,  they 
cannot  be  made  to  combine  directly ;  and  when  they  do  unite,  very  slight  causes 
effect  their  separation.     Chemists  have  long  beendoubtful  astojthe  exact  num-      ^^^ 
ber  of  the  compounds  of  chlorine  and  hydrogen"    The  recent  labours  of  Balard  ' 

and  Martens  have  established  the  existence  of  four,  all  of  which  they  have 
shown  to  possess  acid  properties.  Their  names  and  constitutions  are  given  in 
the  subjoined  table. 

By  weight.  By  volume. 


Chi. 

Oxy. 

Chi. 

Oxy, 

Hypochlorous  acid 

35-42     . 

,    .      8 

2    . 

.     1 

Chlorous  acid 

35-42    . 

,    .    32 

2    . 

.    4 

Chloric  acid 

35-42     . 

.    .    40 

.        2     . 

.    5 

Perchloric  acid     . 

35-42     . 

,    .    56 

.        2    . 

.    7 

According  to  the  practice  of  most  British  chemists,  two  volumes  of  chlorine, 
as  also  two  volumes  of  hydrogen  and  of  nitrogen,  are  considered  as  respectively 
corresponding  to  one  equivalent  or  one  atom  ;  whereas  one  volume  of  oxygen 
corresponds  to  one  equivalent.  Berzelius,  with  many  continental  chemists,  con- 
sidering the  atoms  of  all  elements  to  possess  the  same  volume,  regard  the  four 
preceding  compounds  as  composed  of  2  atoms  or  2  eqs.  of  chlorine  combined 
with  1,  4,  5,  and  7  atoms  or  eqs.  of  oxygen. 

Hypochlorous  Acid. — Hist,  and  Prep. — Davy,  in  1811,  discovered  a  gaseous 
compound,  which  was  described  by  him  in  the  Philosophical  Transactions  of  the 
same  year  under  the  name  of  Euchlorine.  This  gas,  which  until  recently  has 
been  considered  to  be  the  protoxide  of  chlorine,  is  made  by  the  action  of  hydro- 
chloric acid  on  the  chlorate  of  potassa ;  and  its  production  is  explicable  by  the 
fact,  that  hydrochloric  and  chloric  acids  mutually  decompose  each  other.  When 
hydrochloric  acid  and  chlorate  of  potassa  are  mixed  together,  more  or  less  of  the 
potassa  is  separated  by  the  hydrochloric  from  the  chloric  acid,  and  the  latter 
being  set  at  liberty,  reacts  on  free  hydrochloric  acid.  The  result  depends  upon 
the  relative  quantities  of  the  materials.  If  hydrochloric  acid  be  in  excess,  the 
chloric  acid  undergoes  complete  decomposition.  For  each  eq.  of  chloric  acid,  5 
eq.  of  hydrochloric  acid  are  decomposed  :  the  5  eq.  of  oxygen  contained  in  the 
former,  unite  with  the  hydrogen  of  the  latter,  producing  5  eq.  of  water;  while 
the  chlorine  of  both  acids  is  disengaged.  If,  on  the  contrary,  chlorate  of  potassa 
be  in  excess,  the  chloric  acid  is  deprived  of  part  of  its  oxygen  only;  the  products 
are  water  and  the  euchlorine  of  Davy.  The  chloric  and  hydrochloric  acids  react 
on  each  other  in  the  ratio  of  1  eq.  to  2,  or  what  is  the  same  thing,  in  that  of  4 
eq.  to  8  eq. ;  thus 

4CIO5  +  8HC1  =  8H0  +  12C10. 

The  gas  thus  obtained,  though  containing  chlorine  and  fxygen  in  the  ratio  of 
atom  to  atom,  is  not,  as  was  supposed  by  Davy,  a  distinct  compound,  but  is  a 
mixture  of  chlorine  and  chlorous  acid.  For  this  fact,  which  has  long  been  sus- 
pected, we  are  indebted  to  the  researches  of  Soubeiran.  On  transmitting  a  stream 
of  euchlorine  through  a  tube  nearly  full  of  calomel,  the  free  chlorine  is  readily 
absorbed  ;   on  subsequently  exploding  the  purified  gas,  he  obtained  one  volume 


224  CHLORINE. 

of  chlorine  to  two  volumes  of  oxygen,  being  the  exact  composition  of  chlorous 
acid.    The  product  of  the  last  decomposition  is  therefore 

3CIO4  +  9C1,  and  not  12C10. 

The  experiments  of  Soubeiran  have  been  confirmed  by  the  discoveries  of  Balard. 

If  a  stream  of  chlorine  gas  be  passed  into  a  solution  of  the  pure  alkalies,  or 

be  allowed  to  act  upon  the  alkaline  e^frths  in  the  form  of  hydrates,  a  bleaching 

substance  is  procured  which  has  been  commonly  viewed  as  a  direct  compound 

(oj  chlorine  and  an  alkaline  base.  It  consists,  however,  according  to  Balard,  of 
a  mixture  of  a  metallic  chloride  and  the  hypochlorite  of  the  alkali  employed 
([An.  de  Ch.  et  Ph.  Ivii.  225).  The  process  recommended  for  obtaining  the  pure 
acid  is  to  pour  into  bottles  filled  with  chlorine  gas  peroxide  of  mercury  in  fine 
powder,  and  mixed  with  twice  its  weight  of  distilled  water:  by  brisk  agitation 
the  chlorine  is  rapidly  and  completely  absorbed,  if  a  slight  excess  of  the  perox- 
ide be  used.  By  this  process  one  portion  of  the  peroxide  of  mercury,  Hg  0^,  is 
decomposed,  both  its  constituents  combining  with  chlorine,  the  mercury  forming 
corrosive  sublimate,  Hg  Clj,  and  the  oxygen  hypochlorous  acid.  The  latter 
remains  in  solution  in  the  water;  while  the  former,  by  combining  with  undecom- 
posed  peroxide  of  mercury,  forms  the  sparingly  soluble  oxychloride  of  mercury, 
which  is  separated  by  filtration.  The  hypochlorous  acid  being  volatile,  is  ob- 
tained in  a  pure  but  diluted  state  by  distillation.  The  temperature  which  is  used 
for  this  purpose  should  be  kept  considerably  below  212°,  as  the  hypochlorous 
acid  decomposes  rapidly  at  that  heat :  the  process  is,  therefore,  best  performed 
under  reduced  pressure.  A  more  concentrated  solution  of  the  acid  is  obtained  by 
submitting  the  first  products  to  a  second  distillation. 

Prop. — As  thus  obtained,  hypochlorous  acid  is  a  transparent  liquid  of  a  slightly 
yellow  colour  when  concentrated.  Its  odour  is  strong  and  penetrating,  and  dif- 
ferent though  somewhat  similar  to  chlorine.  Its  action  on  the  skin  is  exceed- 
ingly active,  the  eflfect  being  similar  to  but  greater  than  that  produced  by  nitric 
acid.  It  is  a  highly  bleaching  compound.  In  a  concentrated  state  it  is  very 
unstable,  a  slow  decomposition  taking  place  at  common  temperatures,  by  which 
chlorine  is  evolved  and  chloric  acid  produced.  This  change  is  promoted  by 
light,  and  is  effected  almost  instantly  by  exposure  for  a  few  moments  to  the 
direct  rays  of  the  sun.  It  is  also  decomposed  by  agitation  with  angular  bodies ; 
and  on  throwing  into  the  acid  a  portion  of  pounded  glass,  a  brisk  eflfervescence 
is  observed  from  the  escape  of  chlorine. 

It  is  one  of  the  most  powerful  oxidizing  agents.  Its  action  in  this  respect, 
however,  is  various,  and  is  principally  observed  in  relation  to  the  simple  non- 
metallic  elements.  Thus  sulphur  and  phosphorus  are  readily  brought  to  their 
highest  state  of  oxidation,  and  even  selenium  is  converted  into  selenic  acid,  an 
effect  which  the  nitric  acid  cannot  accomplish.  Iodine  and  bromine  are  also  in- 
stantly changed  into  iodic  and  bromic  acids.  Its  action  on  the  more  perfect  metals, 
on  the  contrary,  is  slight:  iron  and  silver,  however,  are  remarkable  exceptions  to 
this  rule  ;  for  when  either  of  them  is  brought  in  a  finely  divided  state  in  contact 
with  hypochlorous  acid,  the  latter  suffers  instantaneous  decomposition.  When  iron 
is  used,  it  is  oxidized  at  the  expense  of  the  acid,  and  chlorine  is  evolved  ;  with 
silver  the  oxygen  escapes,  and  the  chlorine  unites  exclusively  with  the  metal. 
The  decomposition  of  hypochlorous  acid  may  also  be  produced  by  metallic  mer- 
cjiry,  but  the  decomposition  is  unattended  by  the  evolution  of  either  gas.     Both 


J 


CHLORINE.  225 

the  chloride  and  oxide  of  mercury  are  produced,  and  instantly  unite  to  form  than 
oxychloride.  -^ 

Balard  has  also  succeeded  in  obtaining  hypochlorous  acid  in  the  gaseous  form. 
A  small  quantity  of  a  concentrated  solution  is  introduced  into  a  bell  jar  over 
mercury,  and  fragments  of  dry  nitrate  of  lime  are  successively  added.  The 
nitrate  of  lime  being  highly  deliquescent,  unites  with  the  water,  and  the  acid 
gas  escapes  with  effervescence  :  the  presence  of  the  saline  solution  is  essential, 
as  it  prevents  the  decomposition  of  the  gas  by  the  mercury. 

[M.  Pelouse  has  found  that  when  chlorine,  and  the  common  crystallized  red 
oxide  of  mercury,  both  quite  dry,  are  presented  to  each  other,  the  reaction  is 
such  as  not  to  form  hypochlorous  acid,  but  simply  chloride  of  mercury,  with  the 
liberation  of  free  oxygen  gas.  When,  however,  the  oxide  used  is  prepared  by 
precipitation,  and  subsequent  exposure  to  a  temperature  of  about  550°  F.  this 
acid  is  readily  produced.  By  passing  over  the  oxide  so  prepared,  and  placed  in  a 
glass  tube,  a  gentle  current  of  dry  chloride  gas  an  active  reaction  ensues,  chloride 
of  mercury  is  formed,  which  remains  in  the  tube,  and  hypochlorous  acid  gas  is 
evolved,  which  may  be  collected,  by  displacement,  from  the  open  end  of  the 
tube,  so  bent  as  to  reach  to  the  bottom  of  a  dry  flask,  or  bottle.  By  exposure  to 
the  cold  arising  from  a  mixture  of  ice  and  snow,  the  hypochlorous  acid  gas  con- 
denses as  a  deep  red  liquid,  which  is  slowly  dissolved  by  water,  and  readily 
decomposed  by  heat,  often  with  explosive  violence.  (Ann.  de  Ch.  et  Ph.  3rd 
88.  p.  179.)  ] 

The  gas  is  of  a  yellowish  green  colour,  and  is  very  similar  to  chlorine  in  ap- 
pearance. It  unites  rapidly  with  water,  which  absorbs  at  least  100  times  its  own 
volume  of  gas.  It  detonates  by  a  slight  increase  of  temperature ;  and  though 
less  explosive  than  the  chlorous  acid,  there  is  a  probability  of  an  accident  in 
transferring  it  from  one  vessel  to  another.  The  results  of  explosion  are  oxygen 
and  chlorine;  and  Balard  found  that  100  measures  produced  100  of  chlorine  and 
50  of  oxygen.     From  these  data  its  sp.  gr.  is  3-0212;  its  eq.  43*42;  eq.  vo2.= 

100;  s^mb.  CI  +  O,  CI  or  CIO. 

Chlorous  Acid. — Hist,  and  Prep, — ^This  compound  was  discovered  by  Davy  in 
1815  (Phil.  Trans.),  and  soon  after  by  Count  Stadion  of  Vienna.  It  is  formed 
by  the  action  of  sulphuric  acid  on  chlorate  of  potassa.  A  quantity  of  this  salt, 
not  exceeding  50  or  60  grains,  is  reduced  to  powder,  and  made  into  a  paste  by 
the  addition  of  strong  sulphuric  acid.  The  mixture,  which  acquires  a  deep  yel- 
low colour,  is  placed  in  a  glass  retort,  and  heated  by  warm  water,  the  tempera- 
ture of  which  is  kept  under  212°  F.  A  bright  yellowish  green  gas  of  a  richer 
colour  than  chlorine  is  disengaged,  which  has  an  aromatic  odour  without  any 
smell  of  chlorine,  is  absorbed  rapidly  by  water,  to  which  it  communicates  its 
tint.  This  gas,  which  has  long  been  described  as  the  peroxide  of  chlorine,  must 
now  be  called  chlorous  acid,  as  it  has  been  shown  to  possess  acid  properties, 
and  to  form  definite  compounds  with  the  alkaline  bases. 

The  chemical  changes  which  take  place  in  the  process  are  explained  in  the 
following  manner.  The  sulphuric  acid  decomposes  some  of  the  cHlorate  of 
potassa,  and  sets  chloric  acid  at  liberty.  The  chloric  acid,  at  the  moment  of 
separation,  resolves  itself  into  peroxide  of  chlorine  and  oxygen ;  the  last  of 
which,  instead  of  escaping  as  free  oxygen  gas,  goes  over  to  the  acid  of  some 
undecomposed  chloride  of  potassa,  and  converts  it  into  perchloric  acid.  The 
products  are  bisulphate  and  perchlorate  of  potassa,  and  chlorous  acid.     It  is 

17 


226  CHLORINE. 

I     V 

.  most  probable,  from  the  data  contained  in  the  preceding  table,  that  every  3  eq. 

'  of  chloride  acid  yield  1  eq.  of  perchloric  acid  and  2  eq.  of  chlorous  acid. 

/^  Pr^. — Chlorous  acid  unites  readily  with  the  alkalies  and  alkaline  earths, 
forming  salts  which  are  more  stable  than  those  of  the  hypochlorous  acid.  They 
are  produced  by  transmitting  the  gas  into  the  alkaline  solutions,  which  may 
thus  be  rendered  perfectly  neutral  (Martens,  An.  de  Ch.  et  Ph.  Ixi.  293.)  All 
the  salts  hitherto  examined  are  soluble  in  water,  and  are  possessed,  like  the  acid 
itself,  of  bleaching  properties.  The  neutral  salts  pass  readily  into  a  metallic 
chloride  and  chlorate  of  the  base,  particularly  such  as  the  chlorite  of  potassa, 
.  which  form  a  sparingly  soluble  chlorate.  This  change  does  not  so  readily  ensue 
when  alkali  is  in  excess.  The  proportion  in  which  the  chloride  and  chlorate 
are  produced  indicate  that  6  eq.  of  chlorite  are  decomposed,  by  which  1  eq.  of 
metallic  chloride  and  5  eq.  of  chlorate  are  produced ;  thus  6K0  CIO4  yields 
KCl  and  5  KO  ClOg.  The  solution  of  the  pure  acid  gradually  yields  chloric 
acid  and  chlorine.  It  is  a  powerful  oxidizing  agent,  and  in  this  respect  is  very 
similar  to  the  hypochlorous  acid.  It  causes  a  precipitate  with  nitrate  of  silver  ; 
but  it  is  best  recognized  by  the  evolution  of  chlorous  acid  gas  on  the  addition  of 
an  acid  to  its  salts. 

Phosphorus  takes  fire  when  introduced  into  the  gas,  and  occasions  an  explo- 
sion. It  explodes  violently  when  heated  to  a  temperature  of  212°,  emits  a 
strong  light,  and  undergoes  a  greater  expansion  than  protoxide  of  chlorine.  Ac- 
cording to  Davy,  whose  result  is  confirmed  by  Gay-Lussac,  40  measures  of  the 
gas  occupy  after  explosion  the  space  of  60  measures ;  and  of  these,  20  are 
chlorine  and  40  oxygen.  The  peroxide  is  therefore  composed  of  36"42  parts,  or 
1  eq.  of  chlorine,  united  with  32  or  4  eq.  of  oxygen;  and  its  sp.  gr.  must  be 
23-375. 

Its  tq.  is  67-42  ;  eq.  vol.  =  100;  symb.  CI  +  40,  CI,  or  ClO^. 

Chloric  Acid. — Prep. — If  a  current  of  chlorine  gas  be  transmitted  into  a  strong 
solution  of  pure  potassa,  a  portion  of  the  alkali  is  decomposed,  and  chloride  of 
potassium  and  hypochlorite  of  potassa  are  generated.  On  bringing  the  solution 
to  the  boiling  point,  the  latter  salt  is  decomposed.  The  changes  which  occur 
are  complicated,  and  give  rise  to  the  evolution  of  oxy'gen,  and  the  formation  of 
chlorate  of  potassa  and  chloride  of  potassium.  According  to  the  experiments  of 
Morin  and  Soubeiran,  which  accord  entirely  with  the  observations  of  Balard,  9 
eq.  of  hypochlorite  of  potassa  produce  1  eq.  of  chlorate  of  potassa,  8  eq.  of  chlo- 
ride of  potassium,  and  12  eq.  of  oxygen;  or  thus, 

9(K0f  CIO)  yield  (KO+Clos),  8KC1,  and  120. 

Hence  for  every  eq.  of  chlorate,  17  eq.  of  chloride  are  formed. 

When  to  a  dilute  solution  of  chlorate  of  baryta  a  quantity  of  weak  sulphuric 
acid,  exactly  sufficient  for  combining  with  the  baryta,  is  added,  the  insoluble 
sulphate  of  baryta  subsides,  and  pure  chloric  acid  remains  in  the  liquid.  This 
acid,  the  existence  of  which  was  originally  observed  by  Mr.  Chenevix,  was  first 
obt||ned*ln  a  separate  state  by  Gay-Lussac.  , 

Prop. — Chloric  acid  reddens  vegetable  blue  colours,  has  a  sour  taste,  and  forms 
neutral  salts,  called  chlorates  (formerly  hyperoxy muriates,)  with  alkaline  bases. 
It  possesses  no  bleaching  properties,  a  circumstance  by  which  it  is  distinguished 
from  chlorine,  hypochlorous,  and  chlorous  acids.  It  gives  no  precipitate  in  solu- 
tion of  nitrate  of  oxide  of  silver,  and  hence  cannot  be  mistaken  for  hydrochloric 


CHLORINE.  227 

acid.  Its  solution  may  be  concentrated  by  gentle  heat  till  it  acquires  an  oily 
consistence  without  decomposition:  in  this  state  of  highest  concentration  it 
acquires  a  yellowish  tint,  emits  an  odour  of  nitric  acid,  sets  fire  to  paper  and 
other  dry  organic  matter,  and  converts  alcohol  into  acetic  acid.  When  sharply 
heated  in  a  retort,  part  of  the  acid  is  resolved  into  chlorine  and  oxygen ;  but 
another  portion,  acquiring  oxygen  from  that  which  is  decomposed,  is  converted 
into  perchloric  acid,  and  then  passes  over  into  the  receiver  in  the  form  of  a  dense 
colourless  liquid  (Serullas.)  Chloric  acid  is  easily  decomposed  by  deoxidizing 
agents.  Sulphurous  acid,  for  instance,  deprives  it  of  oxygen,  with  formation  of 
sulphuric  acid  and  evolution  of  chlorine.  By  the  action  of  hydrosulphuric  acid, 
water  is  generated,  while  sulphur  and  chlorine  are  set  free.  The  power  of 
hydrochloric  acid  in  effecting  its  decomposition  has  already  been  explained. 

Chloric  acid  is  readily  known  by  forming  a  salt  with  potassa,  which  crystal- 
lizes in  tables  and  has  a  pearly  lustre,  deflagrates  like  nitre  when  flung  on  burn- 
ing charcoal,  and  yields  peroxide  of  chlorine  by  the  action  of  concentrated 
sulphuric  acid.  Chlorate  of  potassa,  like  most  of  the  chlorates,  gives  oif  pure 
oxygen  when  heated  to  redness,  and  leaves  a  residue  of  chloride  of  potassium. 
By  this  mode  Gay-Lussac  ascertained  the  composition  of  chloric  acid,  as  stated 
in  the  preceding  table.     (An.  de  Chiraie,  xci.) 

Its  eq.  is  75-42 ;  symh.  CI  f  50,  CI,  orClOj. 

Perchloric  Mid. — The  saline  matter  which  remains  in  the  retort  after  forming 
chlorous  acid,  is  a  mixture  of  perchlorate  and  bisulphate  of  potassa ;  and  by 
washing  it  with  cold  water,  the  bisulphate  is  dissolved,  and  the  perchlorate  is 
left.  Perchloric  acid  may  be  prepared  from  this  salt  by  mixing  it  in  a  retort 
with  half  its  weight  of  sulphuric  acid,  diluted  with  one-third  of  water,  and  ap- 
plying heat  to  the  mixture.  At  the  temperature  of  ab^t  284°  F.  white  vapours 
rise,  which  condense  as  a  colourless  liquid  in  the  receiver.  This  is  a  solution 
of  perchloric  acid.  " 

The  existence  of  perchloric  acid  was  first  ascertained  by  Count  Stadion,  who 
found  it  to  be  a  compound  of  2  volumes  or  1  eq.  of  chlorine  and  7  of  oxygen ; 
and  this  view  of  its  constitution  has  been  confirmed  by  Gay-Lussac,  Serullas, 
and  Mitscherlich.  (An.  de  Ch.  et  Ph.  viii.  ix.  xlvi.  297,  and  xlix.  113.)  Ac- 
cording to  Serullas,  it  is  a  very  stable  compound :  it  may  be  heated  with  hydro- 
chloric or  sulphuric  acid  without  change,  does  not  set  fire  to  organic  substances, 
and  is  not  decomposed  by  alcohol.  When  concentrated  it  has  a  density  of  1*65, 
in  which  state  it  emits  vapour  when  exposed  to  the  air,  absorbs  hygrometric 
moisture  powerfully,  and  boils  at  392°  F.  By  admixture  with  strong  sulphuric 
acid  and  distilling,  Serullas  obtained  it  in  the  solid  form,  both  massive  and  in 
elongated  prisms.  It  hisses  when  thrown  into  water,  like  red-hot  iron  when 
quenched. 

Of  all  the  salts  of  perchloric  acid,  that  with  potassa  is  the  most  insoluble,  re- 
quiring 65  times  its  weight  of  water  at  60°  for  solution.  This  salt  is  readily 
and  safely  formed  by  adding  chlorate  of  potassa,  well  dried  and  in  fine  powder, 
in  small  portions  at  a  time,  to  an  equal  weight  of  concentrated  sulphuric  acid, 
gently  warmed  in  an  open  vessel.  The  chlorous  acid  gas  escapes  without  dan- 
ger, and  the  chlorate  is  entirely  converted  into  perchlorate  and  bisulphate  of  po- 
tassa, the  latter  of  which,  being  very  soluble,  is  easily  removed  by  cold  water. 
Serullas  finds  that  chlorate  of  potassa,  when  decomposed  by  a  low  heat,  is  con- 
verted into  chloride  of  potassium  and  perchlorate  of  potassa;  but  the  temperature 


<|2§  CHLORINE. 

must  be  carefully  managed,  otherwise  the  perchlorate  itself  would  be  resolved 
into  oxygen  and  chloride  of  potassium.  The  perchlorate  thus  procured  is  puri- 
fted  by  solution  in  hot  water  and  crystallization.*  It  is  distinguished  from  chlo- 
rate of  potassa  by  not  acquiring  a  yellow  tint  on  the  addition  of  hydrochloric  acid. 
The  primary  form  of  its  crystals,  according  to  Mitscherlich,  is  a  right  rhomboidal 
prism  isomorphus  with  premanganate  of  potassa. 

Its  eq.  u  91-42;  aymh.  CI  +  70,  CI,  or  CIO7. 

[In  reference  to  the  oxygen  compounds  of  chlorine  it  mast  be  observed  that 
our  knowledge  is  far  from  being  entirely  complete.  The  recent  elaborate  re- 
searches of  Gay-Lussac  and  Millon  have  tended  to  prove  the  existence  of  a  greater 
number  than  has  been  heretofore  recognized,  and  to  modify  our  views  respecting 
their  constitution.  These  researches  are  still  in  progress  and  require  confirma- 
tion. The  following  table  presents  the  composition  of  these  compounds  accord- 
ing to  the  views  of  Millon. 

Hypochlorous  Acid,        ....  CIO 

Clilorous  Acid,  .....  CIO5 

Hyppchloric  Acid,         ....  C104=   Cl40i6=  3CIO3 -f-  ClOr 

Chloric  Acid,             ....  C106=   ClgOio^    CIO3 -j-  0107 

Chlorochloric  Acid,        ....  CI3O13  =  2CIO3    -}-    010, 

Chloroperchloric  Acid,         .            .            .  CI3O17  =  ClOa    -f  ^ClO, 

Perchloric  Acid,             ....  CIO7] 

Quadrochloride  of  Nitrogen. — Hut,  and  Prep. — This  compound  was  discovered 
by  Dulong  in  1811.  Its  elements  have  a  feeble  mutual  affinity,  and  do  not  unite 
when  presented  to  each  other  in  their  gaseous  form.  The  condition  which  leads 
to  their  union  is  the  decomposition  of  ammonia  by  chlorine,  during  which  hydro- 
chloric acid  is  generated  ^y  chlorine  combining  with  the  hydrogen  of  ammonia ; 
while  the  nitrogen  of  that  •  alkali,  in  its  nascent  state,  enters  into  combination 
with  another  portion  of  chlorine.  A  convenient  mode  of  preparing  the  quadro- 
chloride of  nitrogen  is  the  following.  An  ounce  of  hydrochlorate  of  ammonia  is 
dissolved  in  12  or  16  ounces  of  hot  water;  and  when  the  solution  has  cooled  to 
the  temperature  of  90°,  a  glass  bottle  with  a  wide  mouth,  full  of  chlorine,  is  in- 
verted in  it.  The  solution  gradually  absorbs  the  chlorine,  and  acquires  a  yellow 
colour ;  and  in  about  20  minutes  globules  of  a  yellow  fluid  are  seen  floating  like 
oil  upon  its  surface,  which,  after  acquiring  the  size  of  a  small  pea,  sink  to  the 
bottom  of  the  liquid.  The  drops  of  the  chloride,  as  they  descend,  should  be  col- 
lected in  a  small  saucer  of  lead,  placed  for  that  purpose  under  the  mouth  of  the 
bottle.  It  is  also  readily  obtained  by  suspending  a  fragment  of  sal-ammonia  in 
a  solution  of  hypochlorous  acid. 

Prop. — It  is  one  of  the  most  explosive  compounds  yet  known,  having  been 
the  cause  of  serious  accidents  both  to  its  discoverer  and  to  Davy.  (Phil.  Trans. 
1813;  An.  de  Ch.  Ixxxvi.)  Its  specific  gravity  is  1*653.  It  does  not  congeal 
in  the  intense  cold  produced  by  a  mixture  of  snow  and  salt.    It  may  be  distilled 

*  All  possibility  of  danger,  as  first  sliown  by  Professor  Penny,  is  avoided  by  adding  the 
chlorate  to  dilute  nitric  acid,  and  applying  a  gentle  heat.  The  change  which  occurs  is 
similar  to  that  which  takes  place  when  sulphuric  acid  is  used  ;  but  in  this  case  the  oxygen 
and  chlorine  are  evolved  merely  in  a  state  of  mixture,  and  not  in  union  as  an  explosive 
compound.  The  resulting  salts,  nitrate  and  perchlorate  of  potassa,  are  readily  separated  by 
water,  on  account  of  the  much  greater  solubility  of  the  former (R.) 


CHLORINE.  229 

at  160°  ;  but  at  a  temperature  between  200°  and  212°  it  explodes.  It  appears 
from  the  investigation  of  Messrs.  Porrett,  Wilson,  and  Kirk,  that  its  mere  con- 
tact with  some  substances  of  a  combustible  nature  causes  detonation  even  at  com- 
mon temperatures.  This  result  ensues  particularly  with  oils,  both  volatile  and 
fixed.  I  have  never  known  olive  oil  fail  in  producing  the  effect.  The  products 
of  the  explosion  are  chlorine  and  nitrogen.     (Nicholson's  Journal,  xxxiv.) 

Sir  H.  Davy  analyzed  chloride  of  nitrogen  by  means  of  mercury,  which  unites 
with  chlorine,  and  liberates  the  nitrogen.  He  inferred  from  his  analysis  that  its 
elements  are  united  in  the  proportion  of  four  measures  of  chlorine  to  one  of  nitro- 
gen ;  and  it  hence  follows  that,  by  weight,  it  consists  of  4  eq.  of  chlorine  and  1 
eq.  of  nitrogen.  [Chemists  are,  however,  still  undecided,  respecting  the  true 
constitution  of  this  substance.  From  the  researches  of  Millon,  Kane,  and  others, 
it  would  appear  to  contain  hydrogen,  and  may  be  a  compound  of  chlorine  and 
amidogen  : — represented  thus,  NH2,  CL] 

Perchloride  of  Carbon. — Hist,  and  Prep. — The  discovery  of  this  compound  is 
due  to  Mr.  Faraday.  When  olefiant  gas  (a  compound  of  carbon  and  hydrogen) 
is  mixed  with  chlorine,  combination  takes  place  between  them,  and  an  oil-like 
liquid  is  generated,  which  consists  of  chlorine,  carbon,  and  hydrogen.  On  ex- 
posing this  liquid  in  a  vessel  full  of  chlorine  gas  to  the  direct  solar  rays,  the 
chlorine  acts  upon  and  decomposes  the  liquid,  hydrochloric  acid  is  set  free,  and 
the  carbon,  at  the  moment  of  separation,  unites  with  the  chlorine.  (Phil.  Trans. 
1821.) 

Prop. — Perchloride  of  carbon  is  solid  at  common  temperatures,  has  an  aromatic 
odour  approaching  to  that  of  camphor,  is  a  non-conductor  of  electricity,  and  re- 
fracts light  very  powerfully.  Its  sp.  gr.  is  exactly  double  that  of  water.  It  fuses 
at  320°,  and  after  fusion  it  is  colourless  and  very  transparent.  It  boils  at  360°, 
and  may  be  distilled  without  change,  assuming  a  crystalline  arrangement  as  it 
condenses.  It  is  sparingly  soluble  in  water,  but  dissolves  in  alcohol  and  ether, 
especially  by  the  aid  of  heat.     It  is  soluble  also  in  fixed  and  volatile  oils. 

It  burns  with  a  red  light  when  held  in  the  flame  of  a  spirit-lamp,  giving  out 
acid  vapours  and  smoke ;  but  the  combustion  ceases  as  soon  as  it  is  withdrawn. 
It  bums  vividly  in  oxygen  gas.  Alkalies  do  not  act  upon  it ;  nor  is  it  changed 
by  the  stronger  acids,  such  as  the  hydrochloric,  nitric,  or  sulphuric  acids,  even 
with  the  aid  of  heat.  When  its  vapour,  mixed  with  hydrogen,  is  transmitted 
through  a  red-hot  tube,  charcoal  is  separated,  and  hydrochloric  acid  gas  evolved. 
On  passing  its  vapour  over  the  peroxides  of  metals,  such  as  that  of  mercury  and 
copper,  heated  to  redness,  a  chloride  of  the  metal  and  carbonic  acid  are  gene- 
rated. Protoxides,  under  the  same  treatment,  yield  carbonic  oxide  gas  and  me- 
tallic chlorides.  Most  of  the  metals  decompose  it  also  at  the  temperature  of 
ignition,  uniting  with  its  chlorine,  and  causing  deposition  of  charcoal. 

The  composition  of  the  perchloride  of  carbon  was  inferred  by  Faraday  from 
the  proportions  of  chlorine  and  olefiant  gas  employed  in  its  production,  and  from 
the  quantity  of  chloride  of  copper  and  carbonic  acid  generated  when  its  vapour 
was  transmitted  over  oxide  of  copper  at  a  red  heat. 

Its  eq.  is  118-50 ;  symh.  2C  -f-  3C1,  or  Cj  CI3. 

Protochloride  of  Carbon. — When  the  vapour  of  the  perchloride  is  passed  through 
a  red-hot  glass  or  porcelain  tube,  filled  with  fragments  of  rock  crystal  to  increase 
the  quantity  of  heated  surface,  partial  decomposition  occurs,  chlorine  gas  escapes, 
and  a  vapour  which,  analyzed  by  Faraday,  by  means  of  oxide  of  copper,  proved 
to  be  protochloride  of  carbon.    At  common  temperatures  it  is  a  limpid  colourless 


230  CHLORINE. 

liquid,  which  has  a  density  of  1*5526,  does  not  congeal  at  0°  F.,  and  at  160*^  or 
170°  is  converted  into  vapour.  It  may  be  distilled  repeatedly  without  change  ; 
but  when  exposed  to  a  red  heat,  some  of  it  is  resolved  into  its  elements.  In  its 
chemical  relations  it  is  very  analogous  to  perchloride  of  carbon. 

Its  eq.  is  41-54;  symb.  C  +  CI,  or  C  CI. 

Bichloride  cf  Carbon. — The  first  sample  of  this  substance  yet  obtained  was 
brought  from  Sweden  by  M.  Julin,  and  is  said  to  have  been  formed  during  the 
distillation  of  nitric  acid  from  crude  nitre  and  sulphate  of  iron.  It  occurs  in  small, 
soft,  adhesive  fibres  of  a  white  colour,  which  have  a  peculiar  odour,  somewhat 
resembling  spermaceti.  It  fuses  on  the  application  of  heat,  and  boils  at  a  tem- 
perature between  350°  and  450°  F.  At  250°  it  sublimes  slowly,  and  condenses 
again  in  the  form  of  long  needles.  It  is  insoluble  in  water,  acids,  and  alkalies ; 
but  is  dissolved  by  hot  oil  of  turpentine  or.by  alcohol,  and  forms  acicular  crys- 
ta,ls  as  the  solution  cools.  It  burns  with  a  red  flame,  emitting  much  smoke  and 
fumes  of  hydrochloric  acid  gas.  It  has  since  been  obtained  among  the  products 
of  the  action  of  chlorine,  aided  by  light,  on  some  organic  compounds. 

The  nature  of  this  substance  is  shown  by  the  following  circumstances.  When 
its  vapour  is  exposed  to  a  red  heat,  evolution  of  chlorine  gas  ensues,  and  char- 
coal is  deposited.  A  similar  deposition  of  charcoal  is  produced  by  heating  it 
with  phosphorus,  iron,  or  tin ;  and  a  chloride  is  formed  at  the  same  time.  Po- 
tassium burns  vividly  in  its  vapour  with  formation  of  chloride  of  potassium  and 
separation  of  charcoal.  On  detonating  a  mixture  of  its  vapour  with  oxygen  gas 
over  mercury,  a  chloride  of  that  metal  and  carbonic  acid  are  generated.  By  these 
means  Phillips  and  Faraday  ascertained  its  composition.  (An.  of  Phil,  xviii. 
150).     lis  eq.  is  47-66 ;  symb.  2C  -f  CI,  or  Cj  CI. 

Chlorocarbonic  Acid  Gas, — Hist,  and  Prep. — This  compound  was  discovered  in 
1819  by  John  Davy,  who  described  it  in  the  Philosophical  Transactions  for  that 
year,  under  the  name  of  phosgene  gas.  (From  t^s  light,  and  yewativ  to  produce.) 
It  is  made  by  exposing  a  mixture  of  equal  measures  of  dry  chlorine  and  carbonic 
acid  gases  to  sunshine,  when  rapid  but  silent  combination  ensues,  and  they  con- 
tract to  one  half  their  volume.  Diffused  day-light  also  affects  their  union  slowly; 
but  they  do  not  combine  at  all  when  the  mixture  is  wholly  excluded  from  light. 

Prop. — It  is  colourless  gas,  has  a  strong  odour,  and  reddens  dry  litmus  paper. 
It  combines  with  four  times  its  volume  of  ammoniacal  gas,  forming  a  white  solid 
salt ;  so  that  it  possesses  the  characteristic  property  of  acids.  It  is  decomposed 
by  contact  with  water.  One  equivalent  of  each  compound  undergoes  decompo- 
sition ;  and  as  the  hydrogen  of  the  water  unites  with  chlorine,  and  its  oxygen 
with  carbonic  oxide,  the  products  are  carbonic  and  hydrochloric  acids.  When 
tin  is  heated  in  this  gas,  chloride  of  tin  is  generated,  and  carbonic  oxide  gas  set 
free,  which  occupies  exactly  the  same  space  as  the  chlorocarbonic  acid  which 
was  employed.  A  similar  change  occurs  when  it  is  heated  in  contact  with  anti- 
mony, zinc,  or  arsenic. 

As  chlorocarbonic  acid  gas  contains  its  own  volume  of  each  of  its  constituents, 
it  follows  that  100  cubic  inches  of  that  gas  at  the  standard  temperature  and  pres- 
sure must  weigh  106-806  grains;  namely,  76-599  of  chlorine  added  to  30-207  of 
carbonic  oxide.  Its  sp.  gr.  is  therefore  3-4427,  and  it  consists  of  35-42  parts  or 
1  eq.  of  chlorine,  and  14-15  parts  or  1  eq.  of  carbonic  oxide. 

Its  eg.  is  49-54;  symb.  C  -f-  O  f  CI,  or  CO  CI. 

Dichloride  of  Sulphur. -^ThxB  compound  was  discovered  in  the  year  1804  by 


CHLORINE.  231 

Thomson,*  and  was  afterwards  examined  by  Berthollet.f  It  is  most  conveniently- 
prepared  by  passing  a  current  of  chlorine  gas  over  flowers  of  sulphur  gently 
heated,  until  nearly  all  the  sulphur  disappears.  Direct  combination  ensues,  and 
the  product,  distilled  off  from  uncombined  sulphur,  is  obtained  under  the  form 
of  a  liquid  which  appears  red  by  reflected,  and  yellowish  green  by  transmitted 
light.  It%  density  is  1-687.  It  is  volatile  below  200°,  boils  at  280°,  yielding 
vapour  which  has  a  density  of  4*70,  and  condenses  again  without  change  in  cool- 
ing. When  exposed  to  the  air  it  emits  acrid  fumes,  which  irritate  the  eyes  pow- 
erfully, and  have  an  odour  somewhat  resembling  sea-weed,  but  much  stronger. 
Dry  litmus  paper  is  not  reddened  by  it,  nor  does  it  unite  with  alkalies.  It  acts 
with  energy  on  water : — mutual  decomposition  ensues,  with  formation  of  hydro- 
chloric and  hypos ulphurous  acids,  ajfid  deposite  of  sulphur,  by  which  the  water 
is  rendered  cloudy.  From  a  recent  analysis  by  Rose  it  consists  of  35*42  parts 
or  1  eq.  of  chlorine,  and  32.2  parts  or  2  eq.  of  sulphur  (Pog.  An.  xxi.  431.) 

Its  eq.  is  67-62 ;  symh.  38  +  CI,  or  S^  CI. 

Rose  maintains  that  the  preceding  is  the  only  chloride  of  sulphur,  arguing  that 
the  chloride  analyzed  by  Davy  was  merely  dichloride  of  sulphur  holding  chlo- 
ride in  solution.  Dumas,  on  the  other  hand,  contends,  that  when  sulphur  is 
acted  on  by  excess  of  chlorine,  a  chloride  of  sulphur  is  really  obtained,  which  is 
apt  to  retain  traces  of  the  dichloride,  and  can  only  be  purified  by  repeated  dis- 
tillation at  about  140°  F.  This  chloride  is  a  liquid  of  a  deep  reddish  brown 
tint,  and  has  a  density  of  1-62.  It  boils  at  147°,  and  the  density  of  its  vapour 
is  between  3-67  and  3.70.  By  decomposition  in  water  it  should  yield  hydro- 
chloric and  hyposulphurous  acids.     (An.  de  Ch.  et  Ph.  xlix.  205.) 

Perchloride  of  Phosphorus. — There  are  two  definite  compounds  of  chlorine  and 
phosphorus,  the  nature  of  which  was  first  satisfactorily  explained  by  Davy 
(Elements,  p.  290).  When  phosphorus  is  introduced  into  ajar  of  dry  chlorine, 
it  inflames,  and  on  the  inside  of  the  vessel  a  white  matter  collects,  which  is 
perchloride  of  phosphorus.  It  is  very  volatile,  a  temperature  much  below  212° 
being  sufficient  to  convert  it  into  vapour.  Under  pressure  it  may  be  fused,  and 
it  yields  transparent  prismatic  crystals  in  cooling. 

Water  and  perchloride  of  phosphorus  mutually  decompose  each  other;  and 
the  sole  products  are  hydrochloric  and  phosphoric  acids.  Now,  in  order  that 
these  products  should  be  formed,  consistently  with  the  constitution  of  phospho- 
ric acid,  as  stated  at  page  206,  the  perchloride  must  consist  of  31*4  parts  or  2 
eq.  of  phosphorus,  and  177-1  parts  or  5  eq.  of  chlorine.  One  equivalent  of  the 
chloride  and  5  eq.  of  water  will  then  mutually  decompose  each  other  without 
any  element  being  in  excess,  and  yield  ]  eq.  of  phosphoric,  and  5  eq.  of  hydro- 
chloric acid.  This  proportion  is  not  far  from  the  truth;  for,  according  to  Davy, 
one  grain  of  phosphorus  is  united  in  the  perchloride  with  six  of  chlorine. 

Its  eq.  is  206-4  ;   symb.  2P  -f-  5  CI,  or  PgClg. 

Sesquichioride  of  Phosphorus  may  be  made  either  by  heating  the  perchloride 
with  phosphorus,  or  by  passing  the  vapour  of  phosphorus  over  corrosive  subli- 
mate contained  in  a  glass  tube.  It  is  a  clear  liquid  like  water,  of  sp.  gr.  1-45; 
emits  acid  fumes  when  exposed  to  the  air,  owing  to  the  decomposition  of  watery 
vapour;  but  when  pure  it  does  not  redden  dry  litmus  paper.  On  mixing  it  with 
water,  mutual  decomposition  ensues,  heat  is  evolved,  and  a  solution  of  hydro- 
chloric and  phosphorous  acids  is  obtained.     It  hence  appears  to  consist  of  31*4 

*  Nicholson'8  Journal,  vol.  vi.  t  Memoires  de  Arcueil,  vol.  i. 


232  CHLORINE. 

parts  or  2  eq.  of  phosphorus,  and  106*26  parts  or  3  eq.  of  chlorine.  Its  eq.  is 
137-66 ;  symb.  2P  f  3C1,  or  P2CI3. 

"When  hydrosulphuric  acid  gas  is  transmitted  through  a  vessel  containing 
perchloride  of  phosphorus,  hydrochloric  acid  is  disengaged,  and  a  liquid  pro- 
duced which,  according  to  Serullas,  is  a  compound  of  three  equivalents  of  chlo- 
rine, one  of  phosphorus,  and  one  of  sulphur.     (An.  de  Ch.  et  Ph.  xli».  25.) 

Terchloride  of  Boron. — Davy  noticed  that  recently  prepared  boron  lakes  fire 
spontaneously  in  an  atmosphere  of  chlorine,  and  emits  a  vivid  light ;  but  he  did 
not  examine  the  product.  Berzelius  remarked,  that  if  the  boron  has  been  pre- 
viously heated,  whereby  it  is  rendered  more  compact,  the  combustion  does  not 
take  place  till  heat  is  applied.  This  observation  led  him  to  expose  boron,  thus 
rendered  dense,  in  a  glass  tube  to  a  current  of  dry  chlorine  ;  and  to  heat  it  gently 
as  soon  as  the  atmospheric  air  was  completely  expelled,  in  order  to  commence 
the  combustion.  The  resulting  compound  proved  to  be  a  colourless  gas ;  and 
on  collecting  it  over  mercury,  which  absorbed  free  chlorine^  he  procured  the 
chloride  of  boron  in  a  state  of  purity.  This  gas  is  rapidly  absorbed  by  water ; 
but  double  decomposition  takes  place  at  the  same  instant,  giving  rise  to  hydro- 
chloric and  boracic  acids  as  the  sole  products :  from  this  fact  is  inferred  the  com- 
position of  the  chloride;  for  1  eq.  of  terchloride  of  boron  or  B  -f-  3  CI,  and  3 
eq.  of  water  or  3(H  -|-  0),  correspond  to  I  eq.  of  boracic  acid  or  B  -f-  30,  and 
3  eq.  of  hydrochloric  acid  or  3(H  -|-  CI).  The  watery  vapour  of  the  atmosphere 
occasions  a  similar  change ;  so  that  when  the  gas  is  mixed  with  air  containing 
hygrometric  moisture,  a  dense  white  cloud  is  produced.  The  sp.  gr.  of  the  gas, 
according  to  Dumas,  is  3-942.  It  is  soluble  in  alcohol,  and  communicates  to  it 
an  ethereal  odour,  apparently  by  the  action  of  hydrochloric  acid.  It  unites  with 
ammoniacal  gas,  forming  a  fluid  volatile  substance,  the  nature  of  which  is  un- 
known.—(Annals  of  Phil.  xxvi.  129.) 

Durnas  finds  that  chloride  of  boron  may  be  generated  by  the  action  of  dry 
chlorine  on  a  mixture  of  charcoal  and  boracic  acid,  heated  to  redness  in  a  por- 
celain tube.  Although  neither  charcoal  nor  chlorine  can,  when  acting  alone,  de- 
compose boracic  acid,  they  do  so  readily  by  their  united  effort.  According  to 
Dumas,  two  volumes  of  chloride  of  boron,  and  three  of  carbonic  oxide  gas  are 
formed.  From  these  data  chloride  of  boron  may  be  considered  as  composed  of 
3  eq.  vol.  of  chlorine  and  1  eq.  vol.  of  boron  condensed  into  two  volumes.  Its 
sp.  gr.  is  4*079  (Dumas). 

Despretz  also  appears  to  have  invented  a  similar  process.  (Philos.  Magazine 
and  Annals,  i.  469.) 

Its  eq.  t«  117-16  ;  eq.  «o/.  =  200 ;  symb.  B  +  3Cl,  or  BCl,. 

Terchloride  of  Silicon. — When  silicon  is  heated  in  a  current  of  chlorine  gas, 
it  takes  fire,  and  is  rapidly  volatilized.  The  product  of  the  combustion  con- 
denses into  a  liquid,  which  appears  to  be  naturally  colourless,  but  to  which  an 
excess  of  chlorine  communicates  a  yellow  tint.  This  fluid  is  very  limpid  and 
volatile,  and  evaporates  almost  instantaneously  in  open  vessels  in  the  form  of  a 
white  vapour.  It  boils  at  124°,  and  bears  a  cold  of  zero  without  becoming  solid. 
It  has  a  suffocating  odour  not  unlike  that  of  cyanogen,  and  when  put  into  water 
is  converted  into  hydrochloric  and  silicic  acids,  the  latter  being  easily  obtained 
in  a  gelatinous  form  (Berzelius). 

It  may  also  be  prepared  by  the  method  proposed  by  Oersted,  which  has  been 
80  successfully  applied  in  the  formation  of  other  chlorides.  It  consists  in  mix- 
ing about  equal  parts  of  hydrated  silicic  acid  and  starch  into  a  paste  with  oil, 


CHLORINE.  233 

healing  the  mass  in  a  covered  crucible  so  as  to  char  the  starch,  introducing  the 
mixture  in  fragments  into  a  porcelain  tube,  and  then  transmitting  through  it  a 
current  of  dry  chlorine  gas  while  the  tube  is  kept  at  a  red  heat.  The  chlorine 
unites  with  silicium,  while  the  charcoal  and  oxygen  combine.  The  volatile 
chloride  is  then  agitated  with  mercury  to  separate  the  free  chlorine,  and  purified 
by  distillation. 

Its  eq.  is  128*76 ;  symb.  Si  +  3C1.,  or  Si  Clg. 

Chloro-nitrous  Gas. — When  fused  chloride  of  sodium,  potassium,  or  calcium, 
in  powder,  is  treated  with  as  much  strong  nitric  acid  as  is  sufficient  to  wet  it, 
mutual  decomposition  ensues,  and  a  new  gas,  composed  of  chlorine  and  binoxide 
of  nitrogen,  is  generated.  Its  discoverer,  Mr.  E.  Davy,  describes  it  as  a  gas  of 
a  pale  reddish  yellow  colour,  of  an  odour  similar  to  that  of  chlorine,  though  less 
pungent,  and  possessed  of  bleaching  properties.  It  fumes  on  exposure  to  the 
air,  and  is  freely  absorbed  by  water.  It  is  decomposed  by  sulphur,  phosphorus, 
mercury,  and  most  metals,  and  by  substances  in  general  which  have  an  affinity 
for  chlorine.  It  consists,  according  to  Davy,  of  equal  volumes  of  chlorine  and 
binoxide  of  nitrogen,  united  without  any  condensation. 

In  the  mutual  decomposition  of  chloride  of  sodium  and  nitric  acid,  the  pro- 
ducts appear  to  be  chloro-nitrous  and  chlorine  gases,  and  nitrate  of  soda.  Their 
formation  must  obviously  depend  on  sodium  being  oxidized  at  the  expense  of  nitric 
acid,  while  part  of  the  chlorine  unites,  at  the  moment  of  separation  from  the 
sodium,  with  binoxide  of  nitrogen.  (Phil.  Mag.  ix.  355.)  Theoretically,  it 
should  be  mixed  with  twice  its  volume  of  chlorine,  the  presence  of  which  must 
materially  obscure  the  properties  of  the  new  gas, 

ON  THE  NATURE  OF  CHLORINE. 

The  change  of  opinion  which  has  gradually  taken  place  among  chemists  con- 
cerning the  nature* of  chlorine,  is  a  remarkable  fact  in  the  history  of  the  science. 
The  hypothesis  of  BerthoUet,  unfounded  as  it  is,  prevailed  at  one  time  univer- 
sally. It  explained  phenomena  so  satisfactorily,  and  in  a  manner  so  consistent 
with  the  received  chemical  doctrine,  that  for  some  years  no  one  thought  of  call- 
ing its  correctness  into  question.  A  singular  reverse,  however,  has  taken  place  ; 
and  this  hypothesis,  though  it  has  not  hitherto  been  rigidly  demonstrated  to  be 
erroneous,  has  within  a  short  period  been  generally  abandoned,  even  by  persons 
who,  from  having  adopted  it  in  early  life,  were  prejudiced  in  its  favour.  The 
reason  of  this  will  readily  appear  on  comparing  it  with  the  opposite  theory,  and 
examining  the  evidence  in  favour  of  each. 

Chlorine,  according  to  the  new  theory,  is  maintained  to  be  a  simple  body, 
because,  like  oxygen,  hydrogen,  and  other  analogous  substances,  it  cannot  be 
resolved  into  more  simple  parts.  It  does  not  indeed  follow  that  a  body  is  simple 
because  it  has  not  hitherto  been  decomposed ;  but  as  chemists  have  no  other 
mode  of  estimating  the  elementary  nature  of  bodies,  they  must  necessarily  adopt 
this  one,  or  have  none  at  all.  Hydrochloric  acid,  by  the  same  rule,  is  considered 
to  be  a  compound  of  chlorine  and  hydrogen.  For  when  exposed  to  the  agency 
of  galvanism,  it  is  resolved  into  these  substances ;  and  by  mixing  the  two  gases 
in  due  proportion,  and  passing  an  electric  spark  through  the  mixture,  hydro- 
chloric acid  gas  is  the  product.  Chemists  have  no  other  kind  of  proof  of  the 
composition  of  water,  of  potassa,  or  of  any  other  compound. 

Very  different  is  the  evidence  in  support  of  the  theory  of  BerthoUet.    Accord- 


2&i  CHLORINE. 

ing  to  that  view,  hydrochloric  acid  gas  is  composed  of  absolute  muriatic  acid  and 
water  or  its  elements ;  chlorine  consists  of  absolute  muriatic  acid  and  oxygen ; 
and  absolute  muriatic  acid  is  a  compound  of  a  certain  unknown  base  and  oxygen 
gas.  Now  all  these  propositions  are  gratuitous.  For,  in  the  first  place,  hydro- 
chloric acid  gas  has  not  been  proved  to  contain  water.  Secondly,  the  assertion 
that  chlorine  contains  oxygen  is  opposed  to  direct  experiment,  the  most  powerful 
deoxidizing  agents  having  been  unable  to  elicit  from  that  gas  a  particle  of  oxy- 
gen. Thirdly,  the  existence  of  such  a  substance  as  absolute  muriatic  acid  is 
wholly  without  proof,  and  therefore  its  supposed  base  is  also  imaginary. 

But  this  is  not  the  only  weak  point  of  the  doctrine.  Since  chlorine  is  admitted 
by  this  theory  to  contain  oxygen,  it  was  necessary  to  explain  how  it  happens  that 
no  oxygen  can  be  separated  from  it.  For  instance,  on  exposing  chlorine  to  a 
powerful  galvanic  battery,  oxygen  gas  does  not  appear  at  the  positive  pole,  as 
occurs  when  other  oxidized  bodies  are  subjected  to  its  action ;  nor  is  carbonic 
acid  or  carbonic  oxide  evolved,  when  chlorine  is  conducted  over  ignited  charcoal. 
To  account  for  the  oxygen  not  appearing  under  these  circumstances,  it  was 
assumed  that  absolute  muriatic  acid  is  unable  to  exist  in  an  uncombined  state, 
and  therefore  cannot  be  separated  from  one  substance  except  by  uniting  with 
another.  This  supposition  was  thought  to  be  supported  by  the  analogy  of  certain 
compounds,  such  as  nitric  and  oxalic  acids,  which  appear  to  be  incapable  of 
existing  except  when  combined  with  water  or  some  other  substance.  The  anal- 
ogy, however,  is  incomplete ;  for  the  decomposition  of  such  compounds,  when 
an  attempt  is  made  to  procure  them  in  an  insulated  state,  is  manifestly  owing  to 
the  tendency  of  their  elements  to  enter  into  new  combinations. 

Admitting  the  various  assumptions  which  have  been  stated,  most  of  the  phe- 
nomena receive  as  consistent  an  explanation  by  the  old  as  by  the  new  theory. 
Thus,  when  hydrochloric  acid  gas  is  resolved  by  galvanism  into  chlorine  and 
hydrogen,  it  may  be  supposed  that  absolute  muriatic  acid  attaches  itself  to  the 
oxygen  of  the  water,  and  forms  chlorine  ;  while  the  hydrogen' of  the  water  goes 
to  the  opposite  pole  of  the  battery.  When  chlorine  and  hydrogen  enter  into 
combination,  the  oxygen  of  the  former  may  be  said  to  unite  with  the  latter ;  and 
that  hydrochloric  acid  gas  is  generated  by  the  water  so  formed  combining  with 
the  absolute  muriatic  add  of  the  chlorine.  The  evolution  of  chlorine,  which 
ensues  on  mixing  hydrochloric  acid  and  peroxide  of  manganese,  is  explained  on 
the  supposition  that  absolute  muriatic  acid  unites  directly  with  the  oxygen  of  the 
black  oxide  of  manganese. 

It  will  not  be  difficult,  after  these  observations,  to  account  for  the  preference 
shown  to  the  new  theory.  In  an  exact  science,  such  as  chemistry,  every  step  of 
which  is  required  to  be  matter  of  demonstration,  there  is  no  room  to  hesitate 
between  two  modes  of  reasoning,  one  of  which  is  hypothetical,  and  the  other 
founded  on  experiment.  Nor  is  there,  in  the  present  instance,  temptation  to 
deviate  from  the  strict  logic  of  the  science ;  for  there  is  not  a  single  phenomenon 
which  may  not  be  fully  explained  on  the  new  theory,  in  a  manner  quite  consistent 
with  the  laws  of  chemical  action  in  general. 

It  was  supposed,  indeed,  at  one  time,  that  the  sudden  decomposition  of  water, 
occasioned  by  the  action  of  that  liquid  on  the  compounds  of  chlorine  with  some 
simple  substances,  constitutes  a  real  objection  to  the  doctrine ;  but  it  will  after- 
wards appear,  that  the  acquisition  of  new  facts  has  deprived  this  argument  of  all 
its  force.  While  nothing  therefore  can  be  gained,  much  may  be  lost  by  adopting 
the  doctrine  of  Berthollet.    If  chlorine  is  regarded  as  a  compound  body,  the 


IODINE.  235 

same  opinion,  though  in  direct  opposition  to  the  result  of  observation,  ought  to 
be  extended  to  iodine  and  bromine ;  and  as  other  analogous  substances  may 
hereafter  be  discovered,  in  regard  to  which  a  similar  hypothesis  will  apply,  it  is 
obvious  that  this  view,  if  proper  in  one  case,  may  legitimately  be  extended  to 
others.  One  encroachment  on  the  method  of  strict  induction  would  consequently 
open  the  way  to  another,  and  thus  the  genius  of  the  science  would  eventually  be 
destroyed. 

An  able  attempt  was  made  some  years  ago  by  the  late  Dr.  Murray,  to  demon- 
strate the  presence  of  water  or  its  elements  as  a  constituent  part  of  hydrochloric 
acid  gas,  and  thus  to  establish  the  old  theory  to  the  subversion  of  the  new. 
The  arguments  which  he  used,  though  plausible  and  ingenious,  were  success- 
fully combated  by  Sir  H.  and  Dr.  Davy.  The  only  experiment  which  strictly 
bears  upon  the  question — that,  namely,  where  hydrochloric  acid  and  ammoniacal 
gases  were  mixed  together,  goes  far  to  demonstrate  the  absence  of  combined 
water  in  hydrochloric  acid  gas,  and  thereby  to  establish  the  views  of  Davy.* 


SECTION   XIII. 


IODINE. 


Hist. — Iodine  was  discovered  in  the  year  1812  by  M.  Courtois,  a  manufacturer 
of  saltpetre  at  Paris.  In  preparing  carbonate  of  soda  from  the  ashes  of  sea- 
weeds, he  observed  that  the  residual  liquor  corroded  metallic  vessels  powerfully  ; 
and  on  investigating  the  cause  of  the  corrosion,  he  noticed  that  sulphuric  acid 
threw  (^wn  a  dark-coloured  matter,  which  was  converted  by  the  application  of 
heat  into  a  beautiful  violet  vapour.  Struck  with  its  appearance,  he  gave  some  of 
the  substance  to  M.  Clement,  who  recognized  it  as  a  new  body,  and  in  1813 
described  some  of  its  leading  properties  in  the  Royal  Institute  of  France.  Its 
real  nature  was  soon  after  determined  by  Gay-Lussac  and  Davy,  each  of  whom 
proved  that  it  is  a  simple  non-metallic  substance,  exceedingly  analogous  to 
chlorine."!" 

Iodine  is  frequently  met  with  in  nature  in  combination  with  potassium  or 
sodium.  Under  this  form  it  occurs  in  many  salt  and  other  mineral  springs,  both 
in  England,  on  the  Continent,  and  in  North  America.  It  has  been  detected  in 
the  water  of  the  Mediterranean,  in  the  oyster  and  some  other  marine  molluscous 
animals,  in  sponges,  and  in  most  kinds  of  sea-weed.  In  some  of  these  produc- 
tions, such  as  the  Fucus  serraius  and  Fucus  digitatus,  it  exists  ready  formed,  and 
according  to  Fyfe  (Edin.  Philos.  Journal,  i.  254)  may  be  separated  by  the  action 
of  water ;  but  in  others  it  can  be  detected  only  after  incineration.  Marine  ani- 
mals and  plants  doubtless  derive  from  the  sea  the  iodine  which  they  contain. 

*  In  Nicholson's  Journal,  vols.  xxxi.  xxxii.  and  xxxiv.  Edinburgh  Philos.  Trans,  vol.  viii. 
and  Philos.  Trans,  for  1818. 

t  The  original  papers  on  this  subject  are  in  the  Annales  de  Chimie,  vols.  Ixxxviii.  xc.  and 
xci. ;  and  in  the  Philos.  Trans,  for  1814  and  1815. 


236  IODINE. 

Vauquelin  found  it  also  in  the  mineral  kingdom,  in  combination  with  silver. 
(An.  de  Ch.  et  Ph.  xxix.) 

Prep. — The  iodine  of  commerce  is  procured  from  the  impure  carbonate  of 
soda,  called  kelp,  which  is  prepared  in  large  quantity  on  the  northern  shores  of 
Scotland,  the  Hebrides,  and  west  coast  of  Ireland,  by  incinerating  sea-weeds. 
The  kelp  is  employed  by  soap-makers  for  the  preparation  of  carbonate  of  soda ; 
and  the  dark  residual  liquor  remaining  after  that  salt  has  crystallized,  contains  a 
considerable  quantity  of  iodine,  combined  with  sodium  or  potassium.  By  adding 
a  sujBicient  quantity  of  sulphuric  acid,  hydriodic  acid  is  first  generated,  and  then 
decomposed.  The  iodine  sublimes  when  the  solution  is  boiled,  and  may  be  col- 
lected in  cool  glass  receivers.  A  more  convenient  process  is  to  employ  a  mode- 
rate excess  of  sulphuric  acid,  and  then  add  to  the  mixture  some  peroxide  of 
manganese,  which  acts  on  hydriodic  in  the  same  way  as  on  hydrochloric  acid 
(Phil.  Mag.  L.  Ure).  Another  method,  proposed  by  Soubeiran,  is  by  adding  to 
the  ley  from  kelp  a  solution  made  with  the  sulphates  of  protoxides  of  copper 
and  iron  in  the  ratio  of  one  of  the  former  to  2|  of  the  latter,  as  long  as  a  white 
precipitate  appears.  The  diniodide  of  copper  is  thus  thrown  down ;  and  it  may 
be  decomposed  either  by  peroxide  of  manganese  alone,  or  by  manganese  and 
sulphuric  acid.  By  means  of  the  former,  the  iodine  passes  over  quite  dry ;  but  a 
strong  heat  is  requisite. 

Prop. — Iodine,  at  common  temperatures,  is  a  soft  friable  opaque  solid  of  a 
bluish-black  colour,  and  metallic  lustre.  It  occurs  usually  in  crystalline  scales, 
having  the  appearance  of  micaceous  iron  ore  ;  but  it  sometimes  crystallizes  in 
large  rhomboidal  plates,  the  primitive  form  of  which  is  a  rhombic  octohedron. 
The  crystals  are  best  prepared  by  exposing  to  the  air  a  solution  of  iodine  in 
hydriodic  acid.  Its  sp.  gr.  according  to  Gay-Lussac,  is  4*948 ;  but  Thomson 
found  it  only  3*0844.  At  225°  it  is  fused,  and  enters  into  ebullition  at  347° ; 
but  when  moisture  is  present,  it  is  sublimed  rapidly  even  below  the  degree  of 
boiling  water,  and  suffers  a  gradual  dissipation  at  low  temperatures.  Its  vapour 
is  of  an  exceedingly  rich  violet  colour,  a  character  to  which  it  owes  the  name 
of  Iodine.  (From 'lu-5»75,  violet-coloured.)  This  vapour  is  remarkably  dense, 
its  sp.  gr.  by  calculation,  page  140,  being  8'7011,  or  8*716  as  directly  observed 
by  Dumas.  Hence  100  cubic  inches,  at  the  standard  temperature  and  pressure, 
must  weigh  269*84  grains. 

It  is  a  non-conductor  of  electricity,  and,  like  oxygen  and  chlorine,  is  a  —  elec- 
tric. It  has  a  very  acrid  taste,  and  its  odour  is  almost  exactly  similar  to  that  of 
chlorine,  when  much  diluted  with  air.  Its  acts  energetically  on  the  animal  sys- 
tem as  an  irritant  poison,  but  is  employed  medicinally  in  very  small  doses  with 
advantage. 

It  is  very  sparingly  soluble  in  water,  requiring  about  7000  times  its  weight  of 
that  liquid  for  solution.  It  communicates,  however,  even  in  this  minute  quan- 
tity, a  brown  tint  to  the  menstruum.  Alcohol  and  ether  dissolve  it  freely,  and 
Ihe  solution  has  a  deep  reddish-brown  colour. 

Iodine  possesses  an  extensive  range  of  affinity.  It  destroys  vegetable  colours, 
though  in  a  much  less  degree  than  chlorine.  It  manifests  little  disposition  to 
combine  with  metallic  oxides  ;  but  it  has  a  strong  attraction  for  the  pure  metals, 
and  for  most  of  the  simple  non-metallic  substances,  producing  compounds  which 
are  termed  Iodides  or  lodurets.  It  is  not  inflammable ;  but  under  favorable  cir- 
cumstances may,  like  chlorine,  be  made  to  unite  with  oxygen.  A  solution  of 
the  pure  alkalies  acts  upon  it  and  gives  rise  to  decomposition  of  water;  whether 
an  hypo-iodite  and  iodide  are  first  produced,  as  in  the  case  of  chlorine,  has  not 


IODINE.  237 

yet  been  determined,  but  on  the  application  of  heat  an  iodate  and  iodide  are 
formed. 

Pure  iodine  is  not  influenced  chemically  by  the  imponderables.  Exposure  to 
the  direct  solar  rays,  or  to  strong  shocks  of  electricity,  does  not  change  its  nature. 
It  may  be  passed  through  red-hot  tubes,  or  over  intensely  ignited  charcoal,  with- 
out any  appearance  of  decomposition ;  nor  is  it  affected  by  the  agency  of  gal- 
vanism. Chemists,  indeed,  are  unable  to  resolve  it  into  more  simple  parts,  and 
consequently  it  is  regarded  as  an  elementary  principle. 

The  violet  hue  of  the  vapour  of  iodine  is  for  many  purposes  a  sufficiently  sure 
indication  of  its  presence.  A  far  more  delicate  test,  however,  was  discovered  by 
Colin  and  Gaultier  de  Claubry.  They  found  that  iodine  has  the  property  of 
uniting  with  starch,  and  of  forming  with  it  a  compound  insoluble  in  cold  water, 
which  is  recognized  with  certainty  by  its  deep  blue  colour.  This  test,  according 
to  Stromyer,  is  so  delicate,  that  a  liquid  containing  1  —  450,000th  of  its  weight 
of  iodine  receives  a  blue  tinge  from  a  solution  of  starch.  Two  precautions 
should  be  observed  to  insure  success.  In  the  first  place,  the  iodine  must  be  in 
a  free  state;  for  it  is  the  iodine  itself  only, and  not  its  compounds,  which  unites 
with  starch.  Secondly,  the  solution  should  be  quite  cold  at  the  time  of  adding 
the  starch ;  for  hot  water  dissolves  the  blue  compound,  and  forms  a  colourless 
solution.  [A  solution  of  bichloride  of  palladium,  as  first  ascertained  by  La- 
saigne,  is  also  an  exceedingly  delicate  test  for  iodine  in  any  of  its  soluble  com- 
pounds. It  indicates  its  presence  by  forming  a  dark  brown  precipitate  of  iodide 
of  palladium.] 

Berzelius  determined  the  equivalent  of  iodine  by  exposing  fused  iodide  of  sil- 
ver to  a  current  of  chlorine  gas,  whereby  the  iodine  was  expelled  and  chloride 
of  silver  generated.  Through  the  known  composition  of  chloride  of  silver  he 
inferred  that  of  the  iodide,  and  thence  found  the  eq.  of  iodine.  //  is  126*3  ;  eq. 
vol.  =  100 ;  symb.  I. 

The  composition  of  the  compounds  of  iodine  described  in  this  section  is  as 
follows :— 


Iodine. 

Equiv. 

Formulae 

Hydriodic  Acid 

126-3  leq.f   1           *leq. 

hydrogen 

=127.3. 

HflorHI. 

Oxide  of  Iodine) 
lodous  Acid      5 

Composition  unknown. 

Iodic  Acid 

126-3  1  eq.f  40         5  eq. 

oxygen 

=166-3. 

lOfi. 

Periodic  Acid 

126-3  leq.f  56         7  eq. 

do. 

=182-3. 

10,. 

Protochloride  of  Iodine  126-3  1  eq.-|-  35-42     1  eq. 

chlorine 

=161-72. 

ICl. 

Terchloride        do. 

126-3  leq.-|- 106-26    3  eq. 

do 

=232-56. 

ICI3. 

Perchloride         do. 

Composition  doubtful. 

Protiodide  ofPhos. 

126-3  1  eq.f   15-7       1  eq. 

phosphs. 

=142-0. 

PI 

Sesquiodide      do. 

378-9  3eq.-f-  31.4      2  eq. 

do. 

=410-3 

P2I3. 

Periodide           do. 

631-5  5  eq.f  31-4      2  eq, 

do. 

=662-9. 

P2I6. 

Iodide  of  Sulphur 

Composition  unknown. 

Iodide  of  Carbon 

Composition  unknown. 

Periodide  of  Carbon 

Composition  unknown. 

Teriodide  of  Nitrogen 

378  9  3  eq.f   14-15     1  eq 

.  nitrogen 

—293-05 

.  NI3. 

Hydriodic  Acid. — lodohydric  Acid. — Prep. — This  compound  is  formed  by  the 
direct  union  of  its  elements,  when  a  mixture  of  hydrogen  gas  and  iodine  vapour 
are  transmitted  through  a  porcelain  tube  at  a  red  heat.    A  more  convenient  pro- 


23S  IOI>INE. 

cess,  and  by  which  it  is  obtained  in  a  pure  state,  is  by  the  action  of  water  on 
the  periodide  of  phosphorus.  Any  convenient  quantity  of  the  iodide  is  put  into 
a  small  glass  retort,  together  with  a  little  water,  and  a  gentle  heat  is  applied. 
Mutual  decomposition  ensues  ;  the  oxygen  of  the  water  unites  with  phosphorus, 
and  its  hydrogen  with  iodine,  giving  rise  to  the  formation  of  phosphoric  and 
hydriodic  acids,  the  latter  of  which  passes  over  in  the  form  of  a  colourless  gas. 
The  preparation  of  the  iodide  requires  care ;  since  phosphorus  and  iodine  act  so 
energetically  on  each  other  by  mere  contact,  that  the  phosphorus  is  generally 
inflamed,  and  a  great  part  of  the  iodine  expelled  in  the  form  of  vapour.  This 
inconvenience  is  avoided  by  putting  the  phosphorus  into  a  tube  sealed  at  one 
end,  about  twelve  inches  long,  displacing  the  airjby  a  current  of  dry  carbonic 
acid  gas,  then  gradually  adding  the  iodine,  and  promoting  the  action  towards  the 
close  by  a  gentle  heat.  The  materials  should  be  well  dried  with  bibulous  paper, 
and  the  iodide  preserved  in  a  well-stopped  dry  vessel ;  for  even  atmospheric 
humidity  gives  rise  to  copious  white  fumes  of  hydriodic  acid.  The  proportions 
usually  employed  are  one  part  of  phosphorus  to  about  twelve  of  iodine.  Another 
process  has  been  recommended  by  F.  d'Arcet,  which  consists  in  evaporating 
hypophosphorous  acid  until  it  begins  to  yield  phosphuretted  hydrogen,  mixing 
it  with  an  equal  weight  of  iodine,  and  applying  a  gentle  heat.  Hydriodic  acid 
gas  of  great  purity  is  then  rapidly  disengaged ;  its  production  depending,  as  in 
the  former  process,  on  the  decomposition  of  water. 

Prop. — Hydriodic  acid  gas  has  a  very  sour  taste,  reddens  vegetable  blue 
colours  without  destroying  them,  produces  dense  white  fumes  when  mixed  with 
atmospheric  air,  and  has  an  odour  similar  to  that  of  hydrochloric  acid  gas. 
[Condensed  into  a  liquid  which  may  be  frozen  into  a  solid  like  ice  under  the 
influence  of  intense  cold  and  pressure.  (Page  53.)]  The  salts  which  it  forms 
with  alkalies  are  called  hydriodates.  Like  hydrochloric  acid  gas,  it  cannot  be 
collected  over  water ;  for  that  liquid  dissolves  it  in  large  quantity. 

It  is  decomposed  by  several  substances  which  have  a  strong  affinity  for  either 
of  its  elements.  Thus  oxygen  gas,  when  heated  with  it,  unites  with  its  hydro- 
gen, and  liberates  the  iodine.  Chlorine  effects  the  decomposition  instantly ; 
hydrochloric  acid  gas  is  produced,  and  the  iodine  appears  in  the  form  of  vapour. 
With  strong  nitrous  acid  it  takes  fire,  and  the  vapour  of  iodine  is  set  free.  It  is 
also  decomposed  by  mercury.  The  decomposition  begins  as  soon  as  hydriodic 
acid  gas  comes  in  contact  with  mercury,  and  proceeds  steadily,  and  even  quickly 
if  the  gas  is  agitated,  till  nothing  but  hydrogen  remains.  Gay-Lussac  ascer- 
tained by  this  method  that  100  measures  of  hydriodic  acid  gas  contain  precisely 
half  their  volume  of  hydrogen.  Assuming  it  to  consist  of  equal  volumes  of 
hydrogen  gas  and  iodine  vapour  united  without  any  condensation,  then,  since 

Grains. 
50  cubic  inches  of  the  vapour  "of  iodine  weigh  .  .  .  134-92 
50  do.  hydrogen  gas  1-0684 


100  cubic  inches  of  hydriodic  acid  gas  should  weigh  .        .        135-9884. 

These  numbers  are  obviously  in  the  ratio  of  1  to  126'3,  the  cq.  of  iodine  and 
hydrogen.  On  the  same  principles  the  density  of  the  gas  should  be  4'3850, 
which  is  probably  more  correct  than  4*443,  a  number  found  experimentally  by 
Gay-Lussac  (An.  de  Ch.  xci.  IG.)     From  these  coincidences  there  is  no  doubt 


IODINE.  239 

that  100  measures  of  hydriodic  acid  gas  contain  50  measures  of  hydrogen  gas 
and  50  of  the  vapour  of  iodine. 

When  the  gas  is  conducted  into  water  till  that  liquid  is  fully  charged  with  it, 
a  colourless  acid  solution  is  obtained,  which  emits  white  fumes  on  exposure  to 
the  air,  and  has  a  sp.  gr.  of  1-7.  It  may  be  prepared  also  by  transmitting  a 
current  of  hydrosulphuric  acid  gas  through  water  in  which  iodine  in  fine  powder 
is  suspended  ;  or  by  adding  sulphuric  acid  in  atomic  proportion  to  a  solution  of 
iodide  of  barium  (Glover.)  The  iodine,  from  having  a  greater  affinity  than  sul- 
phur for  hydrogen,  decomposes  the  hydrosulphuric  acid ;  and  hence  sulphur  is 
set  free,  and  hydriodic  acid  produced.  As  soon  as  the  iodine  has  disappeared 
and  become  colourless,  it  is  heated  for  a  short  time  to  expel  -the  excess  of  hydro- 
sulphuric acid,  and  subsequently  filtered  to  separate  free  sulphur. 

The  solution  is  readily  decomposed.  On  exposure  during  a  few  hours  to  the 
atmosphere,  the  oxygen  of  the  air  forms  water  with  the  hydrogen  of  the  acid, 
and  sets  iodine  free.  The  solution  is  found  to  have  acquired  a  yellow  tint  from 
the  presence  of  uncombined  iodine,  and  a  blue  colour  is  occasioned  by  the  addi- 
tion of  starch.  Nitric  and  sulphuric  acid  likewise  decompose  it  by  yielding 
oxygen,  the  former  being  at  the  same  time  converted  into  nitrous,  and  the  latter 
into  sulphurous  acid.  Chlorine  unites  directly  with  the  hydrogen  of  the  hydri- 
odic acid,  and  hydrochloric  acid  is  formed.  The  separation  of  iodine  in  all  these 
cases  may  be  proved  in  the  way  just  mentioned.  These  circumstances  afford  a 
sure  test  of  the  presence  of  hydriodic  acid,  whether  free  or  in  combination  with 
alkalies.  All  that  is  necessary,  is  to  mix  a  cold  solution  of  starch  with  the 
liquid,  previously  concentrated  by  evaporation  if  necessary,  and  then  add  a  few 
drops  of  strong  sulphuric  acid.  A  blue  colour  w411  make  its  appearance  if 
hydriodic  acid  is  present. 

Its  eq.  is  127-3  ;  eg.  vol.  —  200 ;  symb.  H  +  I,  or  HI. 

Oxide  of  Iodine  and  lodous  Acid. — On  mixing  the  vapour  of  iodine  and  oxygen 
gas  considerably  heated,  the  viole|t  tint  of  the  former  disappears,  and  a  yellow 
matter  of  the  consistence  of  solid  oil  is  generated,  which  Sementini  regards  as 
oxide  of  iodine  ;  and  if  the  supply  of  oxygen  be  kept  up  after  its  formation,  it  is 
converted  into  a  yellow  liquid,  which  he  supposes  to  be  iodous  acid.  From  the 
mode  in  which  the  process  is  described,  there  can  scarcely  be  a  doubt  that  some 
compound  of  iodine  and  oxygen  is  thus  formed ;  but  its  composition  and  pro- 
perties have  not  been  satisfactorily  made  out.  (Quarterly  Journ.  of  Science, 
N.  S.  i.  478.)  On  dissolving  iodine  in  a  rather  dilute  solution  of  soda,  until  the 
solution  begin  to  acquire  a  red  tint,  permanent  crystals  are  obtained  by  sponta- 
neous evaporation,  in  six-sided  prisms,  which  dissolve  in  cold  water  without 
change,  but  by  the  action  of  water  moderately  heated,  or  by  alcohol,  are  con- 
verted into  iodate  of  soda  and  iodide  of  sodium.  On  the  addition  of  an  acid, 
iodine  and  iodic  acid  were  set  at  liberty.  From  these  facts  Mitscherlich  infers 
the  crystals  to  be  iodite  of  soda.  (An.  de  Ch.  et  Ph.  xxx.  84.)  They  are  more 
probably  the  hypo-iodite. 

Iodic  Acid. — Hist,  and  Prep.-— This  acid  was  discovered  at  about  the  same  time 
by  Gay-Lussac  and  Davy;  but  the  latter  first  succeeded  in  obtaining  it  in  a  state 
of  perfect  purity.  When  iodine  is  brought  into  contact  with  the  euchlorine  of 
Davy,  immediate  action  ensues ;  the  chlorine  unites  with  one  portion  of  iodine, 
and  the  oxygen  with  another,  forming  two  compounds,  a  volatile  orange-coloured 
matter,  chloride  of  iodine,  and  a  white  solid  substance,  which  is  iodic  acid.  On 
applying  heat,  the  former  passes  oflf  in  vapour,  and  the  latter  remains  (Phil. 


240  IODINE. 

Trans,  for  1815).  Serullas  has  obtained  it,  in  the  form  of  hexagonal  laminae,  by 
evaporating  in  a  warm  place  its  solution  either  in  water,  or  in  sulphuric  or  nitric 
acids.  The  method  which  he  found  most  convenient  is  by  forming  a  solution  of 
iodate  of  soda  in  a  considerable  excess  of  sulphuric  acid,  keeping  it  at  a  boiling 
temperature  for  twelve  or  fifteen  minutes,  and  then  setting  it  aside  to  crystallize 
(Ann.  de  Ch.  et  Ph.  xliii.  216).  Iodic  acid  may  also  be  formed  by  dissolving 
perchloride  of  iodine  in  water,  and  gradually  adding  a  large  quantity  of  strong 
sulphuric  acid,  a  rise  of  temperature  being  at  the  same  time  prevented  by  the 
application  of  cold.  Iodic  acid  will  then  be  precipitated.  The  action  of  strong 
alcohol  on  moist  perchloride  produces  the  same  result :  water  and  the  perchlo- 
ride decomposed,  and  hydrochloric  and  iodic  acids  formed.  The  latter  is  left 
undissolved  by  the  zflcohol.  Another  process,  suggested  by  Mr.  Connell,  of 
Edinburgh,  is  by  boiling  iodine  in  nitric  acid.  For  this  purpose  a  pure  acid  of 
density  1-5  should  be  introduced  with  about  a  fifth  of  its  weight  of  iodine  into  a 
tube  sealed  at  one  end,  about  an  inch  wide  and  15  inches  long,  and  these  mate- 
rials be  kept  at  a  boiling  temperature  for  at  least  twelve  hours.  As  the  iodine 
rises  and  condenses  on  the  sides  of  the  tube,  it  should  be  restored  to  the  liquid, 
either  by  agitation,  or  by  help  of  a  glass  rod.  As  soon  as  the  iodine  disappears, 
the  nitric  acid  is  dissipated  by  cautious  evaporation.  It  is  also  obtained,  as 
remarked  by  Balard,  by  the  oxidizing  effect  of  hypochlorous  acid  on  iodine  ;  the 
latter  unites  with  the  oxygen  of  the  acid,  and  the  chlorine  escapes  in  the 
gaseous  state. 

Prop, — ^This  compound,  which  was  termed  oxiodine  by  Davy,  is  anhydrous 
iodic  acid.  It  is  a  white  semitransparent  solid,  which  has  a  strong  astringent 
sour  taste,  but  no  odour,  its  sp.  gr.  is  considerable,  as  it  sinks  rapidly  in  sul- 
phuric acid.  When  heated  to  the  temperature  of  about  500°  F.  it  is  fused,  and 
at  the  same  time  resolved  into  oxygen  and  iodine.  In  a  dry  air  it  is  unchanged ; 
but  in  a  moist  atmosphere  it  absorbs  humidity,  forming  a  hydrated  acid,  and 
eventually  deliquesces.  In  water  it  is  very  soluble,  and  the  solution  has  a  dis- 
tinct acid  reaction  :  the  bleaching  power  ascribed  to  it  by  Davy  is  said  by  Hiley 
not  to  be  a  property  of  pure  iodic  acid.  (Lancet  for  July,  1833.)  On  evaporating 
the  solution,  a  thick  mass  of  the  consistence  of  paste  is  left,  which  is  hydrous 
iodic  acid  ;  and  which,  by  the  cautious  application  of  heat,  may  be  rendered 
anhydrous.  It  acts  powerfully  on  inflammable  substances.  With  charcoal,  sul- 
phur, sugar,  and  similar  combustibles,  it  forms  mixtures  which  detonate  when 
heated.  It  enters  into  combination  with  metallic  oxides,  and  the  resulting  salts 
are  called  iodates.  These  compounds,  like  the  chlorates,  yield  pure  oxygen  by 
heat,  and  deflagrate  when  thrown  on  burning  charcoal. 

Iodic  acid  forms  with  the  pure  alkalies  salts  which  are  soluble  in  water ;  but 
with  lime,  baryta,  strontia,and  the  oxides  of  lead  and  silver,  it  yields  compounds 
of  very  sparing  solubility.  It  is  readily  detected  by  the  facility  with  which  it  is 
deoxidized,  an  effect  readily  produced  by  the  sulphurous,  phosphorous,  hydriodic, 
and  hydro-sulphuric  acids.  Iodine  in  each  case  is  set  at  liberty,  and  may  be 
detected  as  usual  by  starch.  Hydrochloric  and  iodic  acids  decompose  each  other, 
water  and  chloride  of  iodine  being  generated. 

Davy  ascertained  the  composition  of  iodic  acid  by  determining  the  quantity  of 
oxygen  which  the  acid  loses  when  decomposed  by  heat ;  Gay-Lussac  arrived  at 
the  same  result  by  heating  iodate  of  potasSa,  when  pure  oxygen  was  given  off 

and  iodide  of  potassium  remained.     Its  eq.  is  166*3  ;  symh.  I  -\-  50, 1,  or  IO5. 


IODINE.  241 

Periodic  Acid. — Hist,  and  Prep. — This  compound  has  been  lately  discovered 
by  Ammermiiller  and  Magnus.  (Pogg.  Annalen,  xxviii.  514.)  When  pure  soda 
is  mixed  with  a  solution  of  iodate  of  soda,  and  chlorine  gas  is  transmitted  into  it 
to  saturation,  a  sparingly  soluble  white  pulverulent  salt  is  generated,  which  sub- 
sides after  heating,  and  if  necessary,  concentrating  the  solution.  This  salt  is 
a  periodate  of  soda,  the  production  of  which  appears  to  depend  on  the  formation 
of  chloride  of  sodium,  and  the  union  of  the  oxygen  of  the  soda  with  the  iodine 
of  the  iodic  acid.  For  each  equivalent  of  periodic  acid,  2  eqs.  of  chloride  of 
sodium  should  be  generated  ;  since  the  materials  IO5,  2NaO,  2C1,  just  suffice  for 
yielding  IO7,  and  2NaCl.  On  dissolving  the  periodate  of  soda  in  dilute  nitric 
acid,  and  adding  nitrate  of  oxide  of  silver,  the  periodate  of  thislDxide  of  a  greenish- 
yellow  colour  subsides,  which  should  be  washed  with  water  acidulated  with 
nitric  acid.  This  yellow  salt  is  soluble  in  hot  dilute  nitric  acid,  and  separates 
again  on  cooling  in  small  shining  straw-yellow  crystals,  which  by  digestion  with 
warm  water  acquire,  without  dissolving,  a  reddish-brown  almost  black  colour. 
If  the  nitric  acid  solution  of  the  yellow  salt  is  so  far  concentrated  by  evaporation 
that  it  crystallizes  while  still  warm,  orange-coloured  crystals  subside.  These 
three  salts  are  readily  analyzed  by  exposure  to  a  red  heat  in  a  glass  tube,  when 
iodine  and  metallic  silver  remain  in  the  tube,  and  oxygen  gas  along  with  water, 
when  water  is  present,  is  expelled.    Their  composition  is  as  follows : — 

Oxide  of  Silver.  Periodic  Acid.  Water,  Formulae. 

Yellow  Salt     232    2  eq.  182-3     1  eq.  27    3  eq.  I07,2AgO,  3aq. 

Red  Salt  232    2  eq.  182-3    1  eq.  18    2  eq.  107,2 AgO,  2aq. 

Orange  Salt      116     1  eq.  182-3     1  eq.  0  lO^AgO. 

The  two  former  are  therefore  hydrated  subperiodates  of  oxide  of  silver,  and  the 
latter  a  neutral  periodate.  This  neutral  salt  has  the  peculiarity,  that  by  pure  cold 
water  it  is  converted  into  the  yellow  subsalt,  while  the  water  takes  up  exactly 
half  of  its  acid  without  a  trace  of  silver.  By  this  means  a  pure  solution  of 
periodic  acid  may  be  obtained. 

Prop. — Periodic  acid  is  analogous  in  composition  to  perchloric  acid,  and  has 
decided  acid  properties.  Its  solution  may  be  boiled  without  decomposition,  and 
on  evaporation  the  acid  yields  crystals,  which  do  not  change  by  exposure  to  the 
air.  By  hydrochloric  acid  it  is  reduced  to  iodic  acid  with  disengagement  of 
chlorine,  and  the  same  change  will  of  course  be  produced  by  substances  which 
decompose  iodic  acid.  When  the  heat  is  increased  beyond  212°,  (the  precise 
point  is  not  stated,)  periodic  acid  loses  oxygen,  and  iodic  acid  remains.  Thus 
is  periodic  more  easy  of  decomposition  than  iodic  acid.    Its  eq.  is  182*3;  symb. 

I  +  70,  i,'or  IO7. 

Chlorides  of  /odlene.-- Chlorine  is  absorbed  at  common  temperatures  by  dry 
iodine  with  evolution  of  heat,  and  a  solid  compound  of  iodine  and  chlorine 
results,  which  was  discovered  both  by  Davy  and  Gay-Lussac.  The  colour  of 
the  product  is  orange-yellow  when  the  iodine  is  fully  saturated  with  chlorine, 
but  is  of  a  reddish-orange  if  iodine  is  in  excess.  It  is  converted  by  heat  into  an 
orange-coloured  liquid,  which  yields  a  vapour  of  the  same  tint  on  increase  of 
temperature.  It  deliquesces  in  the  open  air,  and  dissolves  freely  in  water.  Its* 
solution  is  colourless,  very  sour  to  the  taste,  and  reddens  vegetable  blue  colours, 
but  afterwards  destroys  them.    From  its  acid  properties  Davy  gave  it  the  name 

18 


243  IQDINE. 

of  chloriodic  acid.  Gfay-Lussac,  on  the  contrary,  calls  it  chloride  of  iodine^  con- 
ceiving that  the  acidity  of  its  solution  arises  from  the  presence  of  hydrochloric 
and  iodic  acids,  which  he  supposes  to  be  generated  by  decomposition  of  water. 
From  the  observations  of  Serullas  and  Dumas,  it  appears  that  there  exist  two 
compounds  of  chlorine  and  iodine,  by  the  different  action  of  which  on  water  the 
discordant  opinions  of  Davy  and  Gay-Lussac  may  be  explained. 

This  subject  has  lately  been  examined  by  Soubeiran.  He  has  distinguished 
a  compound  of  three  eq.  of  chlorine  and  one  eq.  of  iodine,  but  doubts  the  exist- 
ence of  the  perchloride  of  iodine  of  Davy  and  Gay-Lussac  (Journal  de  Phar- 
raacie,  Feb.  1837).  This  compound  and  a  protochloride  appears,  however,  to 
have  been  previousTy  described  by  Kane  (Phil.  Mag.  x.  430).  The  protochlo- 
ride was  obtained  by  passing  a  current  of  chlorine  gas  into  water,  in  which 
iodine  was  diffu^d.  A  deep  reddish-yellow  solution  is  formed,  which  gives  off 
fumes  irritating  to  the  eyes  and  nose,  has  a  peculiar  smell  of  both  its  constituents, 
and  first  reddens  and  then  bleaches  litmus  paper.  This  terchloride  was  obtained 
by  repeatedly  distilling  the  protochloride ;  it  may  also  be  procured  by  adding  to 
the  protochloride  a  strong  solution  of  corrosive  sublimate,  which  throws  down 
iodine.  The  perchloride  is  supposed  to  contain  5  eq.  of  chlorine  and  1  eq.  of 
iodine,  from  giving  rise,  when  decomposed  by  water,  to  hydrochloric  and  iodic 
acids. 

Teriodide  of  Nitrogen, — ^From  the  weak  affinity  that  exists  between  iodine  and 
nitrogen,  these  substances  cannot  be  made  to  unite  directly.  But  when  iodine 
is  put  into  a  solution  of  ammonia,  the  alkali  is  decomposed  ;  its  elements  unite 
with  different  portions  of  iodide,  and  thus  cause  the  formation  of  hydriodic  acid 
and  iodide  of  nitrogen.  The  latter  subsides  in  the  form  of  a  dark  powder,  which 
is  characterized,  like  quadrochloride  of  nitrogen,  by  its  explosive  property.  It 
detonates  violently  as  soon  as  it  is  dried ;  and  slight  pressure,  while  moist,  pro- 
duces a  similar  effect.  Heat  and  light  are  emitted  during  the  explosion,  and 
iodine  and  nitrogen  are  set  free.  According  to  the  experiments  of  M.  Colin, 
iodide  of  nitrogen  consists  of  one  eq.  of  nitrogen  and  three  of  iodine. 

It  is  conveniently  made,  according  to  Serullas,  by  saturating  alcohol  of  0'852 
with  iodine,  adding  a  large  quantity  of  pure  ammonia,  and  agitating  the  mixture. 
On  diluting  with  water,  teriodide  of  nitrogen  subsides,  which  should  be^  washed 
by  repeated  affusion  of  water  and  decantation.  As  thus  prepared  it  is  very  finely 
divided,  and  may  be  pressed  under  water  without  detonating;  but  if,  subsequently 
to  its  formation,  it  is  put  in  contact  with  pure  ammonia,  it  will  afterwards  deto- 
nate with  the  same  facility  as  that  prepared  in  the  usual  manner.  Water  and 
teriodide  of  nitrogen  mutually  decompose  each  other,  giving  rise  to  the  formation 
of  hydriodic  and  iodic  acids  and  ammonia.  The  change  takes  place  slowly  in 
cold  water;  but  it  is  completed  in  a  few  minutes,  and  with  scarcely  any  disengage- 
ment of  nitrogen,  when  gentle  heat  is  applied.  When  a  little  nitric  or  sulphuric 
acid  is  used,  ammonia  and  iodic  acid  are  alone  produced.  (An.  de  Ch.  et  Ph. 
xlii.  201.) 

Its  eq.  393-05 ;  synib.  N  -f-  31,  or  NI3. 

Iodides  of  Phosphorus. — Iodine  and  phosphorus  combine  readily  in  the  cold, 
evolving  so  much  heat  as  to  kindle  the  ][)hosphorus,  if  the  experiment  is  made  in 
the  open  air;  but  in  close  vessels  no  light  appears.  One  of  these  compounds, 
apparently  a  proiiodide,  is  formed  of  one  part  of  phosphorus  and  7  or  8  parts  of 
iodine.  It  has  an  orange  colour,  fuses  at  212°,  sublimes  unchanged  by  heat,  and 


BROMINE.  24^ 

is  decomposed  by  water,  with  the  elements  of  which  it  gives  rise  to  hydriodic 
and  phosphorous  acids,  while  phosphorus  is  set  free.  Its  eq.  is  142'0;  symb. 
P  1 1,  or  PI. 

The  sesquiodide  is  formed  by  the  action  of  1  part  of  phosphorus  and  12  of 
iodine.  It  appears  as  a  dark  grey  crystalline  mass,  fusible  at  84°,  and  yields 
with  water  hydriodic  and  phosphorous  acids,  from  which  circumstance  its  ele- 
ments are  supposed  to  be  in  the  ratio  of  2  eq.  of  phosphorus  to  3  eq.  of  iodine. 

Its  eq.  is  410*3  ;  symh.  2P  -f-  31,  or  P2I3. 

The  periodide  is  prepared  with  1  part  of  phosphorus  and  20  of  iodine,  and  is 
a  black  compound,  fusible  at  114°.  As  by  the  action  of  water  it  yields  hydri- 
odic and  phosphoric  acids  only,  it  is  inferred  to  contain  phosphorus  and  iodine 
in  the  ratio  of  2  eq.  to  5  eq.    Thus 

1  eq.  periodide  Phos.  &  5  eq.  water    2     1  eq.  Phos.  Acid.  &  5  eq.  Hydriodic  Acid. 
P2I5+5HO  -^  PaOfifSHI. 

Its  eq.  is  662-9  ;  symh.  2P  +  5l,  or  P2I5. 

Iodide  of  Sulphur. — ^This  compound  is  formed  by  heating  gently  4  parts  of 
iodine  with  1  of  sulphur.  The  product  has  a  dark  colour  and  radiated  appear- 
ance, like  antimony,  its  elements  are  easily  disunited  by  heat. 


SECTION  XIV. 


BROMINE. 


Bromine  was  discovered  in  1826  by  Balard  of  Montpellier.  The  name  origi- 
nally applied  to  it  was  muride^  but  the  term  hrome  or  bromine,  from  |3^«/toj  graveo- 
leniia,  signifying  a  strong  or  rank  odour,  has  since  been  substituted  (An.  of  Phil. 
xviii.  381). 

Bromine  in  its  chemical  relations  bears  a  close  analogy  to  chlorine  and  iodine, 
and  has  hitherto  been  always  found  in  nature  associated  with  the  former,  and 
sometimes  also  with  the  latter.  It  exists  in  sea-water  in  the  form  of  bromide  of 
sodium  or  magnesium.  Its  relative  quantity,  however,  is  very  minute ;  and  even 
the  uncrystallizable  residue  called  bittern,  left  after  chloride  of  sodium  has  been 
separated  from  sea- water  by  crystallization,  contains  it  in  small  proportion.  It 
may  apparently  be  regarded  as  an  essential  ingredient  of  the  saline  matter  of  the 
ocean  ;  for  it  has  been  detected  in  the  waters  of  the  Mediterranean,  Baltic,  North 
Sea,  and  Frith  of  Forth.  It  has  also  been  found  in  the  waters  of  the  Dead  Sea, 
and  in  a  variety  of  salt  springs  in  Germany.  Daubeny  has  detected  it  in  several 
mineral  springs  in  England,  and  states  that  it  is  rarely  wanting  in  those  springs 
which  contain  much  common  salt,  except  that  of  Droitwich  in  Worcestershire. 
Balard  found  that  it  exists  in  marine  plants  growing  on  the  shores  of  the  Medi- 
terranean, and  has  procured  it  in  appreciable  quantity  from  the  ashes  of  sea-weeds 
that  furnish  iodine.  He  has  likewise  detected  its  presence  in  the  ashes  of  some 
animals,  especially  in  those  of  the  Janthina  violacea,  one  of  the  testaceous 
mollusca. 


244  BROMINE. 

Prep,' — ^Bromine  is  usually'extracted  from  bittern,  and  its  mode  of  preparation 
is  founded  on  the  property  which  chlorine  possesses  of  decomposing  hydrobromic 
acid,  uniting  with  its  hydrogen,  and  setting  bromine  at  liberty. "  Accordingly, 
on  adding  chlorine  to  bittern,  the  free  bromine  immediately  communicates  an 
orange-yellow  tint  to  the  liquid ;  and  on  heating  the  solution  to  its  boiling  point, 
the  red  vapours  of  bromine  are  expelled,  and  may  be  condensed  by  being  con- 
ducted into  a  tube  surrounded  with  ice.  It  was  this  change  of  colour  produced 
by  chlorine  that  led  to  the  discovery  of  bromine.  The  method  recommended  by 
Balard  for  procuring  this  substance,  as  well  as  for  detecting  the  presence  of 
hydrobromic  acid,  is  to  transmit  a  current  of  chlorine  gas  through  bittern,  and 
then  to  agitate  a  portion  of  sulphuric  ether  with  the  liquid.  The  ether  dissolves 
the  whole  of  the  bromine,  from  which  it  receives  a  beautiful  hyacinth-red  tint, 
and  on  standing  it  rises  to  the  surface.  When  the  ethereal  solution  is  agitated 
with  caustic  potassa,  its  colour  entirely  disappears,  owing  to  the  formation  of 
bromide  of  potassium  and  bromate  of  potassa,  the  former  of  which  is  obtained 
in  cubic  crystals  by  evaporation.  The  bromine  may  then  be  set  free  by  means 
of  chlorine,  or  still  better  by  sulphuric  acid  and  the  peroxide  of  manganese.  The 
process  should  be  conducted  in  a  retort,  the  beak  dipping  into  cold  water,  which 
collects  the  bromine  driven  over  by  heat.  Balard  has  subsequently  improved  the 
process  so  much,  that  it  is  now  produced  in  considerable  quantity,  and  sold  in 
Paris  as  an  article  of  commerce. 

Prop. — At  common  temperatures  bromine  is  a  liquid,  the  colour  of  which  is 
blackish-red  when  viewed  in  mass  and  by  reflected  light,  but  appears  hyacinth-red 
when  a  thin  stratum  is  interposed  between  the  light  and  the  observer.  Its  odour, 
which  somewhat  resembles  that  of  chlorine,  is  very  disagreeable,  and  its  taste 
powerful.  Its  sp.  gr.  is  about  3.  By  a  temperature  between  zero  and  — 4°  it 
is  congealed,  and  in  that  state  is  brittle.  Its  volatility  is  considerable ;  for  at 
common  temperatures  it  emits  red-coloured  vapours,  which  are  very  similar  in 
appearance  to  those  of  nitrous  acid ;  and  at  ir6*5°  it  enters  into  ebullition.  The 
sp.  gr.  of  its  vapour  was  found  by  Mitscherlich  to  be  5*54,  and  the  number  cal- 
culated (p.  140)  from  its  equivalent  is  6'3930  :  100  cubic  inches  at  60°  and  30 
inches  B.  should  weigh  167*25  grains.  It  is  a  non-conductor  of  electricity,  and 
undergoes  no  chemical  change  whatever  from  the  agency  of  the  imponderables. 
It  may  be  transmitted  through  a  red-hot  glass  tube,  and  be  exposed  to  the 
agency  of  galvanism,  without  evincing  the  least  trace  of  decomposition.  Like 
oxygen,  chlorine,  and  iodine,  it  is  a  negative  electric.  It  is  soluble  in  water, 
alcohol,  and  ether,  the  latter  being  its  best  solvent.  It  does  not  redden  litmus 
paper,  but  bleaches  it  rapidly  like  chlorine ;  and  it  likewise  discharges  the  blue 
colour  from  a  solution  of  indigo.  Its  vapour  extinguishes  a  lighted  taper ;  but 
before  going  out,  it  burns  for  a  few  seconds  with  a  flame  which  is  green  at  its 
base  and  red  at  its  upper  part.  Some  inflammable  substances  take  fire  by  con- 
tact with  bromine,  in  the  same  manner  as  when  introduced  into  an  atmosphere  of 
chlorine.  It  acts  with  energy  on  organic  matters,  such  as  wood  or  cork,  and 
corrodes  the  animal  texture ;  but  if  applied  to  the  skin  for  a  short  time  only,  it 
communicates  a  yellow  stain,  which  is  less  intense  than  that  produced  by  iodine, 
and  soon  disappears.  To  animal  life  it  is  highly  destructive,  one  drop  of  it 
placed  on  the  beak  of  a  bird  having  proved  fatal. 

From  the  close  resemblance  observable  between  chlorine  and  bromine,  Balard 
was  of  course  led  to  examine  its  relations  with  hydrogen,  and  found  that  these 
substances  may  readily  be  made  to  unite;  the  product  of  the  combination  being 


BROMINE.  <34|^ 

a  gas  very  similar  to  hydrochloric  and  hydriodic  acid  gases,  whence  it  has  re- 
ceived the  name  of  hydrobromie  acid  gas.  In  its  action  on  metals,  also,  bromine 
presents  the  closest  similarity  to  that  which  chlorine  exerts  on  the  same  sub- 
stances. Antimony  and  tin  take  fire  by  contact  with  bromine ;  and  its  union 
with  potassium  is  attended  with  such  intense  heat  as  to  cause  a  vivid  flash  of 
light,  and  often  to  burst  the  vessel  in  which  the  experiment  is  performed.  Its 
affinity  for  metallic  oxides  is  feeble.  By  the  action  of  alkalies  it  is  resolved  into 
hydrobromie  and  bromic  acids,  suffering  the  same  kind  of  change  as  chlorine  or 
iodine  when  similarly  treated. 

According  to  all  the  experiments  hitherto  made,  bromine  appears  to  be  an  ele- 
ment. It  is  so  very  similar  in  most  aspects  to  chlorine  and  iodine,  and  in  the 
order  of  its  chemical  relations  is  so  constantly  intermediate  between  them,  that 
Balard  at  first  supposed  it  to  be  some  unknown  compound  of  these  substances. 
There  seems,  however,  to  be  no  good  ground  for  the  supposition ;  but,  on  the 
contrary,  an  experiment  performed  by  De  la  Rive  aflfords  a  very  strong  argument 
against  it.  He  finds  that  when  a  compound  of  bromine  and  iodine  is  mixed  with 
starch,  and  exposed  to  the  influence  of  galvanism,  bromine  appears  at  the  -f-  and 
iodine  at  the  —  wire,  where  the  starch  acquires  a  blue  tint.  On  making  the 
experiment  with  bromine  containing  a  little  bromide  of  iodine,  the  same  appear- 
ance ensues  ;  but  if  iodine  is  not  previously  added,  the  starch  does  not  receive  a 
tint  of  blue. 

Bromine  is  in  most  cases  easily  detected  by  means  of  chlorine ;  for  this  sub- 
stance displaces  bromine  from  its  combination  with  hydrogen,  metals,  and  most 
other  bodies.  The  appearance  of  its  vapour  or  the  colbur  of  its  solution  in  ether 
will  then  render  its  presence  obvious.  Like  chlorine,  it  forms  a  crystalline 
hydrate  when  exposed  to  32°  F.  in  contact  with  water.  The  crystals  are  octo- 
hedral,  of  a  beautiful  red  tint,  and  suffer  decomposition  at  54°.     (Lowig.) 

Berzelius  determined  the  equivalent  of  bromine  in  the  same  way  as  that  of 
iodine,  namely,  by  heating  a  known  weight  of  bromide  of  silver  in  a  current  of 
chlorine  gas,  so  as  to  displace  the  bromine  and  obtain  chloride  of  silver. 
Its  eq.  is  78*4 ;  eq.  vol.  =  100 ;  symb.  Br. 
The  compounds  of  bromine  described  in  this  section  are  as  follows:— 

Bromine. 
Hydrobromie  Acid    .      78-4      1  eq.  -f-  Hydrogen 
Bromic  Acid       .      ,      78-4      1  eq.  -j-  Oxygen 
Chloride  of  Bromine       Composition  uncertain. 
Bromides  of  Iodine         Composition  uncertain. 
Bromide  of  Sulphur        Composition  uncertain. 
Protobromideof  Phosp.  78*4      1  eq.  -|-  phosph. 
Perbromide  of  Phosp.  392         5  eq.  -f-     do. 
Bromide  of  Carbon  Composition  uncertain. 

Terbromide  of  Silicon  236-2      3  eq.  +  Silicon        22-5    1  eq.  =  257-7.      SiBr^. 

Hydrobromie  jicid,  Bromohydric  Acid. — Prep. — No  chemical  action  takes  place 
between  the  vapour  of  bromine  and  hydrogen  gas  at  common  temperatures,  not 
even  by  the  agency  of  the  direct  solar  rays  ;  but  on  introducing  a  lighted  candle, 
or  a  piece  of  red-hot  iron,  into  the  mixture,  combination  ensues  in  the  vicinity 
of  the  heated  body,  though  without  extending  to  the  whole  mixture,  and  w  ithout 
explosion.  The  combination  is  readily  effected  by  the  action  of  bromine  on 
some  of  the  gaseous  compounds  of  hydrogen.    Thus,  on  mixing  the  vapour  of 


iquiv. 

Formula. 

1       1  eq.  =  79-4. 

HBr. 

40      5eq.  =  118-4. 

BrOj. 

15.7    1  eq.=    94-1. 

PBr. 

31-4   2eq.  =  423-4. 

P2B3. 

5246  BROMINE. 

bromine  with  hydriodic  acid,  hydrosulphuric  acid,  or  phosphuretted  hydrogen 
gases,  decomposition  ensues,  and  hydrobromic  acid  gas  is  generated.  It  may  be 
conveniently  made  for  experimental  purposes  by  a  process  similar  to  that  for 
forming  hydriodic  acid.  A  mixture  of  bromine  and  phosphorus,  slightly  moist- 
ened, yields,  by  the  aid  of  gentle  heat,  a  large  quantity  of  pure  hydrobromic  acid, 
gas,  which  should  be  collected  either  in  dry  glass  bottles,  or  over  mercury. 

Prop. — It  is  a  colourless  gas,  has  an  acid  taste,  and  pungent  odour.  It  irri- 
tates the  glottis  powerfully,  so  as  to  excite  cough,  and  when  mixed  with  moist 
air,  yields  white  vapours,  which  are  denser  than  those  occasioned  under  the  same 
circumstances  by  hydrochloric  acid  gas.  [May  be  liquified  and  converted  into  a 
solid  by  cold  and  pressure  (page  53)].  It  undergoes  no  decomposition  when 
transmitted  through  a  red-hot  tube,  either  alone,  or  mixed  with  oxygen.  It  is 
not  affected  by  iodine ;  but  chlorine  decomposes  it  instantly,  with  production  of 
hydrochloric  acid  gas,  and  deposition  of  bromine.  It  may  be  preserved  without 
change  over  mercury ;  but  potassium  and  tin  decompose  it  with  facility,  the 
former  at  common  temperatures,  and  the  latter  by  the  aid  of  heat.  It  is  very 
soluble  in  water.  The  aqueous  solution  may  be  made  by  treating  bromine  with 
hydrosulphuric  acid  dissolved  in  water,  or  still  better,  by  transmitting  a  current 
of  hydrobromic  acid  gas  into  pure  water.  The  liquid  becomes  hot  during  the 
condensation,  acquires  great  density,  increases  in  volume,  and.  emits  white  fumes 
when  exposed  to  the  air.  This  acid  solution  is  colourless  when  pure,  but  pos- 
sesses the  property  of  dissolving  a  large  quantity  of  bromine,  and  then  receives 
the  tint  of  that  substance. 

Chlorine  decomposes  !he  solution  of  hydrobromic  acid  in  an  instant.  Nitric 
acid  likewise  acts  upon  it,  though  less  suddenly,  occasioning  the  disengagement 
of  bromine,  and  probably  the  formation  of  water  and  nitrous  acid.  Nitro-hydro- 
bromic  acid  is  analogous  to  aqua  regia,  and  possesses  the  property  of  dissolving 
gold.  The  elements  of  sulphuric  and  hydrobromic  acids  react  on  each  other  in 
a  slight  degree;  and  hence,  on  decomposing  bromide  of  potassium  by  sulphuric 
acid,  the  hydrobromic  is  generally  mixed  with  a  little  sulphurous  acid  gas. 

The  composition  of  hydrobromic  acid  gas  is  easily  inferred  from  the  two  fol- 
lowing facts.  1,  On  decomposing  hydrobromic  acid  gas  by  potassium,  a  quan- 
tity of  hydrogen  remains,  precis*ely  equal  to  half  the  volume  of  the  gas  employed ; 
and,  2,  when  hydriodic  acid  gas  is  decomposed  by  bromine,  the  resulting  hydro- 
bromic acid  occupies  the  very  same  space  as  the  gas  which  is  decomposed. 
Hence  hydrobromic  is  analogous  to  hydriodic  and  hydrochloric  acid  gases,  in 
containing  equal  measures  of  bromine  vapour  and  hydrogen  gas  united  without 
any  change  of  volume ;  and  since 

Grains. 
50  cubic  inches  of  Bromine  vapour  weigh      ....        83-64 
60  do.  Hydrogen  gas    .        .        .        .        .        .  10684 

100  do.  Hydrobromic  acid  must  weigh  .        .        84-7084 

These  numbers  are  in  the  ratio  of  1  to  78*4,  which  is  the  composition  of  the  gas 
by  weight.     Its  sp.  gr.  is  2*731. 

Since  bromine  decomposes  hydriodic,  and  chlorine  hydrobromic  acid,  bromine, 
in  relation  to  hydrogen,  is  intermediate  between  chlorine  and  iodine ;  for  it  has 
a  stronger  affinity  for  hydrogen  than  iodine,  and  a  weaker  than  chlorine.  The 
affinity  of  bromine  and  oxygen  for  hydrogen  appears  nearly  similar ;  for  while 


BROMINE.  247 

oxygen  cannot  detach  hydrogen  from  bromine,  bromine  does  not  decompose 
watery  vapour. 

The  salts  of  hydrobromic  acid  are  termed  hydrohromates.  Like  the  free  acid, 
they  are  decomposed,  and  the  presence  of  bromine  is  detected,  by  means  of  chlo- 
rine.* On  mixing  a  soluble  bromide  with  the  nitrates  of  the  protoxides  of  lead, 
silver,  and  mercury,  white  precipitates  are  obtained,  which  are  very  similar  in 
appearance  to  the  chlorides  of  those  metals,  but  which  are  metallic  bromides. 
On  the  addition  of  chlorine,  the  vapour  of  bromine  is  evolved. 

Its  eq.  is  79-4 ;  eg.  vol.  =  200 ;  symb,  H  -|-  Br,  or  H  Br. 

Bromic  Acid, — Frep» — The  only  compound  yet  known  of  bromine  and  oxygen' 
is  that  formed  by  the  action  of  bromine  on  potassa,  when  a  change  exactly  < 
similar  to  that  produced  by  chlorine  (page  226)  ensues,  whereby  bromide  of  ' 
j)otassium  and  bromate  of  potassa  are  generated ;  and  the  latter,  being  much  less  ^ 
soluble  than  the  former,  is  readily  separated  by  evaporation.     The  bromate  of  the  J 
other  alkalies  and  alkaline  earths  may  be  prepared  in  a  similar  manner.  ^ 

The  acid  may  be  procured  in  a  separate  state  by  decomposing  a  dilute  solution 
of  bromate  of  baryta  with  sulphuric  acid,  so  as  to  precipitate  the  whole  of  the 
baryta.  The  resulting  solution  of  bromic  acid  may  be  concentrated  by  slow 
evaporation  until  it  acquire  the  consistence  of  syrup ;  but  on  raising  the  tem- 
perature, in  order  to  expel  all  the  water,  one  part  of  the  acid  is  volatilized,  and 
the  other  resolved  into  oxygen  and  bromine.  A  similar  result  took  place  when 
the  evaporation  was  conducted  in  vacuo  with  sulphuric  acid  ;  and  accordingly  all 
attempts  to  procure  anhydrous  bromic  acid  have  hitherto  failed. 

Prop. — Bromic  acid  has  scarcely  any  odour,  but  its  taste  is  very  acid,  though 
not  at  all  corrosive.  It  reddens  litmus  paper  powerfully  at  first,  and  soon  after 
destroys  its  colour.  It  is  not  affected  by  nitric  or  sulphuric  acids  except  when 
the  latter  is  highly  concentrated,  in  which  case  bromine  is  set  free,  and  efferves- 
cence, probably  owing  to  the  escape  of  oxygen  gas,  ensues.  From  the  analysis 
of  bromate  of  potassa,  bromic  acid  is  obviously  similar  in  constitution  to  iodic, 
chloric,  and  nitric  acids ;  that  is,  it  consists  of  one  equivalent  of  bromine  united 
with  five  of  oxygen.  Its  salts  are  analogous  to  the  chlorates  and  iodates.  Thus 
bromate  of  potassa  is  converted  by  heat  into  bromide  of  potassium,  with  disen- 
gagement of  pure  oxygen  gas,  deflagrates  like  nitre  when  thrown  on  burning 
charcoal,  and  forms  with  sulphur  a  mixture  which  detonates  by  percussion.  The 
acid  of  the  bromates  is  decomposed  by  deoxidizing  agents,  such  as  sulphurous 
and  hydrosulphuric  acids,  in  the  same  manner  as  the  acids  of  the  iodates.  The 
bromates  likewise  suffer  decomposition  from  the  action  of  hydrobromic  and 
hydrochloric  acids. 

Bromate  of  potassa  is  said  not  to  precipitate  the  salts  of  lead,  but  to  occasionX 
a  white  precipitate  with  nitrate  of  silver,  and  a  yellowish  white  with  protonitrate  ^ 
of  mercury ;  characters  which,  if  true,  serve  as  a  good  test  to  distinguish  bro-/ 
mate  from  iodate  and  chlorate  of  potassa. 

Its  eq.  is  118-4;  syrnb.  Br  +  50,  Br,  or  BrOj. 

Chloride  of  Bromine. — ^This  compound  may  be  formed  at  common  temperatures 
by  transmitting  a  current  of  chlorine  through  bromine,  and  condensing  the  dis- 
engaged vapours  by  means  of  a  freezing  mixture.  The  resulting  chloride  is  a 
volatile  fluid  of  a  reddish  yellow  colour,  much  less  intense  than  that  of  bromine ; 
its  odour  is  penetrating,  and  causes  a  discharge  of  tears  from  the  eyes ;  and  its 
taste  very  disagreeable.    Its  vapour  is  a  deep  yellow,  like  chlorous  acid,  and  it 


Cj^  BROMINE. 

enables  metals  to  burn  as  in  an  atmosphere  of  chlorine,  doubtless  giving  rise  to 
the  formation  of  metallic  chlorides  and  bromides. 

Chloride  of  bromine  is  soluble  in  water  without  decomposition ;  for  the  solu- 
tion possesses  the  colour,  odour,  and  bleaching  properties  of  the  compound,  and 
discharges  the  colour  of  litmus  paper  without  previously  reddening  it.  By  the 
action  of  the  alkalies  it  is  decomposed,  being  converted,  by  means  of  the  ele- 
ments of  water,  into  hydrochloric  and  bromic  acids. 

Bromide  of  Iodine. — These  substances  act  readily  on  each  other,  and  appear 
capable  of  uniting  in  two  proportions.  The  protobromide  is  a  solid,  convertible 
by  heat  into  a  reddish-brown  vapour,  which,  in  cooling,  condenses  into  crystals 
of  the  same  colour,  and  of  a  form  resembling  that  of  fern  leaves.  An  additional 
quantity  of  bromine  converts  these  crystals  into  a  fluid,  which  in  appearance  is 
like  a  strong  solution  of  iodine  in  hydriodic  acid.  This  compound  dissolves 
without  decomposition  in  water,  but  with  the  alkalies  yields  hydrobromic  and 
iodic  acids.  The  existence  of  two  bromides  of  iodine  can  scarcely  be  regarded 
as  satisfactorily  established. 

Bromide  of  Sulphur, — On  pouring  bromine  on  sublimed  sulphur,  combination 
ensues,  and  a  fluid  of  an  oily  appearance  and  reddish  tint  is  generated.  In  odour 
it  somewhat  resembles  chloride  of  sulphur,  and  like  that  compound  emits  white 
vapours  when  exposed  to  the  air ;  but  its  colour  is  deeper.  It  reddens  litmus 
paper  faintly  when  dry,  but  strongly  if  water  is  added.  Cold  water  acts  slowly 
upon  bromide  of  sulphur;  but  at  a  boiling  temperature  the  action  is  so  violent 
that  a  slight  detonation  occurs,  and  three  compounds,  hydrobomic,  hydrosulphu- 
ric,  and  sulphuric  acids  are  formed.  The  formation  of  these  substances  is  of 
course  attributable  to  decomposition  of  water,  and  the  union  of  its  elements  with 
bromine  and  sulphur.  Bromide  of  sulphur  is  likewise  decomposed  by  chlorine, 
which  unites  with  sulphur,  and  displaces  bromine. 

The  composition  of  bromide  of  sulphur  is  unknown.  It  dissolves  an  excess 
both  of  chlorine  and  sulphur,  and  its  elements  separate  from  each  other  so  readily, 
that  it  has  hitherto  been  impracticable  to  procure  a  definite  compound. 

Bromide  of  Phosphorus. — When  bromine  and  phosphorus  are  brought  into  con- 
tact in  a  flask  filled  with  carbonic  acid  gas,  they  act  suddenly  on  each  other  with 
evolution  of  heat  and  light,  and  two  compounds  are  generated ;  one,  a  crystalline 
solid,  which  is  sublimed  and  collects  in  the  upper  part  of  the  flask ;  and  the 
other,  a  fluid,  which  remains  at  the  bottom.  The  former  contains  the  most  bro- 
mine, and  the  latter  is  supposed  by  Balard  to  consist  of  single  equivalents  of  its 
elements. 

The  protobromide  retains  its  liquid  form  even  at  52°  F.  It  is  readily  converted 
into  vapour  by  heat,  and  on  exposure  to  the  air  emits  penetrating  fumes.  It  red- 
dens litmus  paper  faintly,  an  efiect  which  is  probably  owing  to  the  presence  of 
moisture.  With  water  it  acts  energetically  and  with  free  disengagement  of  heat, 
hydrobromic  acid  gas  being  evolved  when  only  a  few  drops  of  water  are  employed; 
but  if  a  large  quantity  is  used,  the  gas  is  dissolved,  and  the  acid  solution  leaves 
by  evaporation  a  residuum,  which  burns  slightly  when  dried,  and  is  converted 
into  phosphoric  acid. 

The  perbromide  is  yellow  in  its  solid  state ;  but  with  gentle  heat  it  becomes  a 
red-coloured  liquid,  which  by  increase  of  temperature  is  converted  into  a  vapour 
of  the  same  tint.  On  cooling  after  fusion  it  yields  rhombic  crystals  :  but  when 
its  vapour  is  condensed,  the  crystals  are  acicular.  It  is  decomposed  by  metals, 
probably  with  the  formation  of  metallic  bromides  and  phosphurets.     It  emits 


FLUORINE.  249 

dense  penetrating  fumes  on  exposure  to  the  air,  and  with  water  gives  rise  to  the 
production  of  hydrobromic  and  phosphoric  acids.  Hence  its  elements  should  be 
in  the  ratio  of  2  eqs.  of  phosphorus  to  5  eqs.  of  bromine. 

Chlorine  has  a  greater  affinity  for  phosphorus  than  bromine,  and  decomposes 
both  the  bromides  with  evolution  of  the  vapour  of  bromine.  These  compounds 
are  not  decomposed  by  iodine ;  but,  on  the  contrary,  bromine  decomposes  iodide 
of  phosphorus. 

Terhromide  of  Silicon, — This  compound  was  made  by  Serullas'in  precisely  the 
same  mode  as  that  described  by  forming  the  terchloride.  When  purified  from 
free  bromine  by  mercury,  and  re-distilled,  it  is  a  colourless  liquid,  which  emits 
dense  vapours  in  an  open  vessel,  being  decomposed  by  the  moisture  of  the  air, 
and  is  denser  than  strong  sulphuric  acid.  At  302°  it  enters  into  ebullition,  and 
freezes  at  10°.  Potassium,  when  gently  heated,  acts  on  it  with  such  energy  that 
detonation  ensues.  By  water  it  is  resolved  into  hydrobromic  and  silicic  acids. 
(Phil.  Mag.  and  Annals,  xi.  295.)    Its  eq.  is  257*7 ;  symb.  Si  f  SBr,  or  Si  Brj. 


SECTION  XV. 


FLUORINE. 


The  substance  to  which  this  name  is  applied,  though  long  known  to  exist  in 
various  compounds,  has  only  recently  been  obtained  in  an  insulated  form,  and 
therefore  the  properties  peculiar  to  it  in  that  state  are  but  imperfectly  known.  It 
was  first  procured  by  Baudrimont  by  passing  fluoride  of  boron  over  minium 
heated  to  redness,  and  receiving  the  gas  in  a  dry  vessel.  As  it  is  mixed  with  a 
large  quantity  of  oxygen,  his  present  method  is  to  treat  a  mixture  of  fluoride  of 
calcium  and  peroxide  of  manganese  with  strong  sulphuric  acid.  This  process, 
however,  does  not  give  h  pure  gas,  as  hydrofluoric  and  fluosilicic  acid  gases  are 
at  the  same  time  evolved.  The  presence  of  the  latter  do  not  prevent  the  obser- 
vation of  some  of  the  properties  of  fluorine.  It  is  a  gas  of  a  yellowish-brown 
colour ;  its  odour  resembles  chlorine  and  burnt  sugar  ;  it  bleaches.  It  does  not 
act  on  glass,  but  combines  directly  with  gold  (Phil.  Mag.  x.  149).  The  latter 
fact  is  confirmed  by  the  observations  of  Messrs.  Knox,  who  have  succeeded  so 
far  in  the  preparation  of  fluorine  as  to  leave  no  doubt  of  its  existence  as  a  coloured 
gas  (Phil.  Mag.  x.  107).  Its  sp.  gr.  is  1-289.  From  the  nature  of  its  com- 
pounds it  appears  to  belong  to  the  class  of  negative  electrics,  and,  like  oxygen 
and  chlorine,  to  have  a  powerful  affinity  for  hydrogen  and  metallic  substances. 
Berzelius  determined  its  eq.  by  finding  that  100  parts  of  pure  fluoride  of  calcium 
yield  with  sulphuric  acid  175  parts  of  sulphate  of  lime.  Its  eq.  is  18*68 ;  eq,  vol, 
=  100 ;  symb.  F.  ^ 

The  compounds  of  fluorine  described  in  this  section  are  the  following : — 
Fluorine.  Equiv.  Formulae. 

Hydrofluoric  acid     18-68  1  eq.-f- Hydrogen     1.      1  eq.  =  19-68.  HF. 

Fluoboric  acid  56-08  3  eq.-j- Boron  109  1  eq.  =  66-98.  BF3. 

Fluosilicic  acid        56-08  3  eq.-i" Silicon  22-5  1  eq.  =  78.58  SiFa. 


250  FLUORINE. 

Hydrofluoric  Acid. — Fluohydric  Acid. — Hist,  and  Prep. — This  acid  was  first  pro- 
cured in  its  pure  state  in  the  year  1810  by  Gay-Lussac  and  Thenard,  and  de- 
scribed in  the  second  volume  of  their  liecherckes  Physico-Chimiques.  It  is  pre- 
pared by  acting  on  the  mineral  called  fluor-»par,  which  is  a  fluoride  of  calcium, 
carefully  separated  from  siliceous  earth  and  reduced  to  fine  powder,  with  twice 
its  weight  of  concentrated  sulphuric  acid.  The  mixture  is  made  in  a  leaden  re- 
tort ;  and  on  applying  heat,  an  acid  and  highly  corrosive  vapour  distils  over, 
which  must  bb  collected  in  a  receiver  of  the  same  metal  surrounded  with  ice. 
As  the  materials  swell  up  considerably  during  the  process,  owing  to  a  quantity 
of  vapour  forcing  its  way  through  a  viscid  mass,  the  retort  should  be  capacious. 
At  the  close  of  the  operation  pure  hydrofluoric  acid  is  found  in  the  receiver,  and 
the  retort  contains  dry  sulphate  of  lime.  The  chemical  changes  are  precisely 
the  same  as  in  the  formation  of  hydrochloric  acid  gas  at  page  220,  fluorine  being 
substitute^  for  chlorine  and  calcium  for  sodium.  Thus  in  symbols  CaF  and 
HO,  SO3  =  HF  and  CaO,  SO3.  If  the  oil  of  vitriol  is  of  sufficient  strength,  all 
its  water  is  decomposed,  and  the  resulting  hydrofluoric  acid  is  anhydrous. 

Prop. — It  is  at  32°  a  colourless  fluid,  and  remains  in  that  state  at  59°  if  pre- 
served in  well-stopped  bottles ;  but  when  exposed  to  the  air,  it  flies  off"  in  dense 
white  fumes,  which  consist  of  the  acid  vapour  combined  with  the  moisture  of  the 
atmosphere.  Its  sp.  gr.  is  r0609  ;  but  its  density  may  be  increased  to  1*25  by 
gradual  additions  of  water.  Its  affinity  for  this  liquid  far  exceeds  that  of  the 
strongest  sulphuric  acid,  and  the  combination  is  accompanied  with  a  hissing 
noise,  as  when  red-hot  iron  is  quenched  by  immersion  in  water.  * 

Its  vapour  is  much  more  pungent  than  chlorine  or  any  of  the  irritating  gases. 
Of  all  known  substances,  it  is  the  most  destructive  to  animal  matter.  When  a 
drop  of  the  concentrated  acid  of  the  size  of  a  pin's  head  comes  in  contact  with 
the  skin,  instantaneous  disorganization  ensues,  and  deep  ulceration  of  a  malig- 
nant character  is  produced.  On  this  account  the  greatest  care  is  requisite  in  its 
preparation.  It  acts  energetically  on  glass.  The  transparency  of  the.  glass  is 
instantly  destroyed,  heat  is  evolved,  and  the  acid  boils,  and  in  a  short  time  en- 
tirely disappears.  A  colourless  gas,  commonly  known  by  the  name  oi  fluo-silicic 
acid  gaSf  is  the  sole  product.  This  compound  is  always  formed  when  hydro- 
fluoric acid  comes  in  contact  with  a  siliceous  substance.  For  this  reason  it  can- 
not be  preserved  in  glass ;  but  must  be  prepared  and  kept  in  metallic  vessels. 
Those  of  lead,  from  their  cheapness,  are  often  used ;  but  vessels  of  silver  or  pla- 
tinum are  preferable.  In  consequence  of  its  powerful  affinity  for  siliceous  matter, 
hydrofluoric  acid  may  be  employed  for  etching  on  glass ;  and  when  used  with 
this  intention,  it  should  be  diluted  with  three  or  four  times  its  weight  of  water. 

Hydrofluoric  acid  has  all  the  usual  characters  of  a  powerful  acid.  It  has  a 
strong  sour  taste,  reddens  litmus  paper,  and  neutralizes  alkalies,  either  forming 
salts  termed  hydrofluates,  or  most  generally  giving  rise  to  metallic  fluorides.  All 
these  compounds  are  decomposed  by  strong  sulphuric  acid  with  the  aid  of  heat, 
and  the  hydrofluoric  acid  while  escaping  may  be  detected  by  its  action  on  glass. 

On  some  of  the  metals  it  acts  violently,  especially  on  the  bases  of  the  alkalies. 
Thus  when  potassium  is  brought  in  contact  with  the  concentrated  acid,  an  ex- 
plosion attended  ^ith  heat  and  light  ensues ;  hydrogen  gas  is  disengaged,  and  a 
white  compound,  fluoride  of  potassium,  is  generated.  It  is  a  solvent  for  some 
elementary  principles  which  resist  the  action  even  of  nitro-hydrochloric  acid. 
Thus  it  dissolves  silicon,  zirconium,  and  columbium,  with  evolution  of  hydrogen 
gas ;  and  when  mixed  with  nitric  acid,  it  proves  a  solvent  for  silicon  which  has 


FLUORINE.  jt51 

been  condensed  by  heat,  and  for  titanium.  Nitro-hydrofluoric  acid,  however,  is 
incapable  of  dissolving  gold  and  platinum.  Several  oxidized  bodies,  which  are 
not  attacked  by  sulphuric,  nitric,  or  hydrochloric  acid,  are  readily  dissolved  by 
hydrofluoric  acid.  As  examples  of  this  fact,  several  of  the  weaker  acids,  such  as 
silica,  or  silicic  acid,  titanic,  columbic,  molybdic,  and  tungstic  acids  may  be 
enumerated.  (Berzelius.) 

A  different  view  of  the  compounds  of  fluorine  was  originally  taken  by  Gay- 
Lussac  and  Thenard,  and  is  still  held  by  some  chemists.  They  adopted  the  opi- 
nion that  hydrofluoric  acid  is  a  compound  of  a  certain  inflammable  principle  and 
oxygen,  and  applied  to  it  the  name  of  Jluoric  acid,  previously  introduced  by 
Scheele.  Fluor-spar  on  this  »view  is  a  fluate  of  lime,  and  when  this  salt  is  de- 
composed by  oil  of  vitriol,  the  fluoric  is  merely  displaced  by  the  sulphuric  acid, 
and  the  former  passes  off  combined  with  the  water  of  the  latter.  What  I  have 
described  as  anhydrous  hydrofluoric  acid  is,  according  to  this  hypothesis,  hy- 
drated  fluoric  acid;  and  when  acted  upon  by  potassium,  this  metal  is  oxidized  at 
the  expense  of  the  water,  and  potassa  thus  generated  unites  with  fluoric  acid, 
forming,  not  fluoride  of  potassium,  but  fluate  of  potassa.  The  equivalent  of 
fluoric  acid,  as  inferred  from  the  analysis  of  Berzelius,  is  10'68 ;  for  39*18  parts 
or  one  equivalent  of  fluor-spar  is  supposed  to  contain  28*5  parts  of  lime  (20*5 
calcium  and  8  oxygen),  thus  leaving  10*68  as  the  equivalent  of  the  acid. 

The  theory,  according  to  which  fluor-spar  is  a  compound  of  fluorine  and  cal- 
cium, originated  as  a  suggestion  with  M.  Ampere  of  Paris,  and  was  afterwards 
supported  experimentally  by  Davy.  It  was  found  that  pure  hydrofluoric  acid 
evinces  no  sign  of  containing  either  oxygen  or  water.  Charcoal  may  be  in- 
tensely heated  in  the  vapour  of  the  acid  without  the  production  of  carbonic  acid. 
"When  hydrofluoric  acid  was  neutralized  with  dry  ammoniacal  gas,  a  white  salt 
resulted,  from  which  no  water  could  be  separated ;  and  on  treating  this  salt  with 
potassium,  no  evidence  could  be  obtained  of  the  presence  of  oxygen.  On  ex- 
posing the  acid  to  the  agency  of  galvanism,  there  was  a  disengagement  at  the 
negative  pole  of  a  small  quantity  of  gas,  which  from  its  combustibility  was  in- 
ferred to  be  hydrogen ;  while  the  platinum  wire  of  the  opposite  side  of  the  bat- 
tery was  rapidly  corroded,  and  became  covered  with  a  chocolate  coloured  powder. 
Davy  explained  these  phenomena  by  supposing  that  hydrofluoric  acid  was  re- 
solved into  its  elements ;  and  that  fluorine,  at  the  moment  of  arriving  at  the 
positive  side  of  the  battery,  entered  into  combination  with  the  platinum  wire 
which  was  employed  as  a  conductor.  Unfortunately,  however,  he  did  not  succeed 
in  obtaining  fluorine  in  an  insulated  state.  Indeed,  from  the  noxious  vapours 
that  arose  during  the  experiment,  it  was  impossible  to  watch  its  progress,  and 
examine  the  different  products  with  that  precision  which  is  essential  to  the  suc- 
cess of  minute  chemical  inquiries,  and  which  Davy  has  so  frequently  displayed 
on  other  occasions. 

Though  these  researches  led  to  no  conclusive  result,  they  aff"orded  so  strong  a 
presumption  in  favour  of  the  opinion  of  Ampere  and  Davy,  that  it  was  adopted 
by  several  other  chemists.  This  view  has  received  strong  additional  support 
from  the  experiments  of  M.  Kuhlman.  (Quarterly  Journal  of  Science  for  July 
1827,  p.  255.)  It  was  found  by  this  chemist  that  fluor-spar  is  not  in  the  slight- 
est degree  decomposed  by  the  action  of  anhydrous  sulphuric  acid,  whether  at 
common  temperatures  or  at  a  red  heat.  The  experiment  was  made  both  by  trans- 
mitting the  vapour  of  anhydrous  sulphuric  acid  over  fluor-spar  heated  to  redness 
in  a  tube  of  platinum,  and   by  putting  the  mineral  into  the  liquid  acid.    In 


252  FLUORINE. 

neither  case  did  decomposition  ensue  ;  but  when  the  former  experiment  •was  re- 
peated, with  the  difference  of  employing  concentrated  hydrous  instead  of  anhy- 
drous sulphuric  acid,  evolution  of  hydrofluoric  acid  was  produced.  M.  Kuhlman 
also  transmitted  hydrochloric  acid  gas  over  fluor-spar  at  a  red  heat,  when  hydro- 
fluoric acid  was  disengaged',  without  any  evolution  of  hydrogen,  and  chloride  of 
calcium  remained.  I  am  aware  of  no  satisfactory  explanation  of  these  facts,  ex- 
cept by  regarding  fluor-spar  as  a  compound  of  fluorine  and  calcium,  and  hydro- 
fluoric acid  as  a  compound  of  fluorine  and  hydrogen.  I  shall  accordingly  adopt 
this  view  in  the  subsequent  pages,  and  never  employ  the  term  fluoric  acid  except 
when  explaining  phenomena  according  to  the  theory  of  Gay-Lussac. 

Its  eq.  is  19-68 ;  si/mb.  H  +  F,  or  HF.  % 

Fluohoric  Acid. — Prep. — ^The  chief  diflUculty  in  determining  the  nature  of  hy- 
drofluoric acid  arises  from  the  water  of  the  sulphuric  acid  which  is  employed  in 
its  prepamtion.  To  avoid  this  source  of  uncertainty,  Gay-Lussac  and  Thenard 
made  a  mixture  of  vitrified  boracic  acid  and  fluor-spar,  and  exposed  it  in  a  leaden 
retort  to  heat,  under  the  expectation  that  as  no  water  was  present,  anhydrous 
fluoric  acid  would  be  obtained.  In  this,  however,  they  were  disappointed  ;  but 
a  new  gas  came  over,  to  which  they  applied  the  term  Jiuoborie  acid  gas,  A 
similar  train  of  reasoning  led  Davy  about  the  same  time  to  the  same  discovery ; 
though  the  French  chemists  had  the  advantage  in  priority  of  publication.  An- 
other process  given  by  Dr.  Davy,  is  to  mix  1  part  of  vitrified  boracic  acid  and  2 
of  fluor-spar  with  12  parts  of  strong  sulphuric  acid,  heating  the  mixture  gently 
in  a  glass  flask  (Phil.  Trans.  1812)  ;  but  the  gas  thus  developed  contains  a  con- 
siderable quantity  of  fluosilicic  acid.  Fluoboric  acid  gas  may  also  be  formed 
by  heating  a  strong  solution  of  hydrofluoric  and  boracic  acids  in  a  metallic 
retort. 

In  the  decomposition  of  fluor-spar  by  vitrified  boracic  acid,  the  former  and 
part  of  the  latter  undergo  an  interchange  of  elements.  The  fluorine  uniting  with 
boron  gives  rise  to  fluoboric  acid  gas ;  and  by  the  union  of  calcium  and  oxygen 
lime  is  generated,  which  combines  with  boracic  acid,  and  is  left  in  the  retort  as 
borate  of  lime.  Fluoboric  acid  gas,  therefore,  is  composed  of  boron  and  fluo- 
rine. Those  who  adopt  the  theory  of  Gay-Lussac  give  a  different  explanation, 
and  regard  this  gas  as  a  compound  of  fluoric  and  boracic  acids.  The  lime  of 
fluor-spar  is  supposed  to  unite  with  one  portion  of  boracic  acid,  and  fluoric  acid 
at  the  moment  of  separation  with  another,  yielding  borate  of  lime  and  fluoboric 
acid  gas. 

Prop. — It  is  a  colourless  gas,  has  a  penetrating  pungent  odour,  and  extin- 
guishes flame  on  the  instant.  Its  sp.  gr.,  according  to  Thomson,  is  2*3622.  It 
reddens  litmus  paper  as  powerfully  as  sulphuric  acid,  and  forms  salts  with  alka- 
lies which  are  called  Jluohoratcs.  It  has  a  singularly  great  affinity  for  water. 
When  mixed  with  air  or  any  gas  which  contains  watery  vapour,  a  dense  white 
cloud,  a  combination  of  water  and  fluoboric  acid  appears,  thus  affording  an  ex- 
tremely delicate  test  of  the  presence  of  moisture  in  gases.  Water  acts  power- 
fully on  this  gas,  absorbing,  according  to  Dr.  Davy,  700  times  its  volume,  dur- 
ing which  the  water  increases  in  temperature  and  volume.  The  solution  is  limpid, 
fuming,  and  very  caustic.  On  the  application  of  heat,  part  of  the  gas  is  disen- 
gaged ;  but  afterwards  the  whole  solution  is  distilled. 

Gay-Lussac  and  Thenard  and  Dr.  Davy  "were  of  opinion  that  fluoboric  acid 
gas  is  dissolved  by  water  without  decomposition ;  but  Berzelius  denies  the  ac- 
curacy of  their  observation.    On  transmitting  the  gas  into  water  until  the  liquid 


FLUORINE.  253 

acquires  a  sharply  sour  taste,  but  is  far  from  being  saturated,  a  white  powder 
begins  to  subside ;  and,  on  cooling,  a  considerable  quantity  of  boracic  acid  is 
deposited  in  crystals.  It  appears  that  in  a  certain  state  of  dilution,  part  of  the 
fluoboric  acid  and  water  mutually  decompose  each  other,  with  formation  of  bo- 
racic and  hydrofluoric  acids.  The  latter  unites,  according  to  Berzelius,  with 
undecomposed  fluoboric  acid,  forming  what  he  has  called  horo-hydrojluric  acid. 
On  concentrating  the  liquid  by  evaporation,  the  boracic  and  hydrofluoric  acids 
decompose  each  other,  and  the  original  compound  is  reproduced. 

Fluoboric  acid  gas  does  not  act  on  glass,  but  attacks  animal  and  vegetable 
matters  with  energy,  converting  them  like  sulphuric  acid  into  a  carbonaceous 
substance.    The  action  is  most  probably  owing  to  its  affinity  for  water. 

When  potassium  is  heated  in  fluoboric  acid  gas,  the  metal  takes  fire,  and  a 
chocolate  coloured  solid,  wholly  devoid  of  metallic  lustre,  is  formed.  This  sub- 
stance is  a  mixture  of  boron  and  fluoride  of  potassium,  from  which  the  latter  is 
dissolved  by  water,  and  the  boron  is  left  in  a  solid  state. 

The  composition  of  fluoboric  acid  gas  has  not  hitherto  been  determined  by 
direct  experiment.  Dr.  Davy  ascertained  that  it  unites  with  an  equal  measure  of 
ammoniacal  gas,  forming  a  solid  salt;  and  that  it  also  combines  with  twice  and 
three  times  its  volume  of  ammonia,  yielding  liquid  compounds.  In  the  former 
salt  the  relative  weights  of  the  constituent  gases  are  in  the  ratio  of  their  specific 
gravities ;  and  if  the  compound  consists  of  one  equivalent  of  each,  it  will  be  con- 
stituted of,  ^ 

Fluoboric  acid  gas       .  .        2-3622        •        68-04  one  eq. 

Ammoniacal  gas  .  .        0*5898        •        17      one  eq. 

so  that  the  equivalent  of  the  acid  may  be  assumed  in  round  numbers  to  be  68. 
Now  supposing  this  acid  to  be  formed  of  three  eqs.  of  fluorine  and  one  of  boron, 
its  eq.  will  be  64*04,  a  number  which  approximates  to  the  preceding.  This  view 
is  consistent  with  the  composition  of  boracic  as  given  at  page  210,  and  with  the 
conversion  of  fluoboric  acid  by  water  into  hydrofluoric  and  boracic  acids. 

lis  symh,  is  B  -|-  3F,  or  BF3. 

Fluosilicic  Acid. — Prep. — ^This  gas  is  formed  whenever  hydrofluoric  and  silicic 
acids  come  in  contact ;  and  hence  pure  hydrofluoric  acid  can  be  prepared  in 
metallic  vessels  only,  and  with  fluor-spar  that  is  free  from  rock  crystal.  The 
most  convenient  method  of  procuring  it  is  to  mix  in  a  retort  one  part  of  pulverized 
fluor-spar  with  its  own  weight  of  sand  or  pounded  glass,  and  two  parts  of  strong 
sulphuric  acid.  On  applying  a  gentle  heat,  fluosilicic  acid  gas  is  disengaged 
with  effervescence,  and  may  be  collected  over  mercury. 

The  chemical  changes  attending  this  process  are  differently  explained,  accord- 
ing to  the  view  which  is  taken  concerning  the  nature  of  the  product.  In  regard- 
ing fluor-spar  as  a  compound  of  fluoric  acid  and  lime,  the  former  at  the  moment 
of  being  set  free  is  thought  to  unite  directly  with  silicic  acid,  thereby  giving  rise 
to  a  compound  of  silicic  and  fluoric  acids.  But  for  reasons  already  stated,  fluor- 
spar is  not  considered  as  fluate  of  lime ;  and  therefore  this  view  cannot  be  ad- 
mitted. It  is  inferred,  on  the  contrary,  that  when,  by  the  action  of  sulphuric 
acid  on  fluoride  of  calcium,  hydrofluoric  acid  is  generated,  the  elements  of  this 
acid  react  on  those  of  silicic  acid,  and  give  rise  to  the  production  of  water  and 
fluosilicic  acid  gas.  This  gas  is  therefore  a  fluoride  of  silicon.  It  may  occur  to 
some  whether  hydrofluoric  acid  does  not  unite  directly  with  silicic  acid ;  but  this 


254  FLUORINE. 

idea  is  inconsistent  with  the  proportion  in  which  the  elements  of  the  gas  are 
found  to  be  united. 

Prop. — It  is  a  colourless  gas  which  extinguishes  flame,  destroys  animals  that 
are  immersed  in  it,  and  irritates  the  respiratory  organs  powerfully.  It  does  not 
corrode  glass  vessels  provided  they  are  quite  dry.  When  mixed  with  atmospheric 
air  it  forms  a  white  cloud,  owing  to  the  presence  of  watery  vapour.  Its  sp.  gr. 
according  to  Thomson,  is  3'6111 ;  and  100  cubic  inches  of  it  at  60°,  and  when 
the  barometer  stands  at  30  inches,  weigh  111 '985  grains. 

Water  acts  powerfully  on  fluosilicic  acid  gas,  of  which  it  condenses,  according 
to  Dr.  Davy,  365  times  its  volume  (Phil.  Trans,  for  1812).  The  gas  suffers 
decomposition  at  the  moment  of  contact  with  water,  silicic  acid  in  the  form  of  a 
gelatinous  hydrate  being  deposited,  which  when  well  washed  is  quite  pure.  The 
liquid,  which  has  a  sour  taste,  and  reddens  litmus  paper,  contains  the  whole  of 
the  hydrofluoric  acid,  together  with  two-thirds  of  the  silicic  acid  which  was  ori- 
ginally present  in  the  gas  (Berzelius).  By  conducting  fluosilicic  acid  gas  into 
a  solution  of  ammonia,  complete  decomposition  ensues  : — hydrofluoric  acid  unites 
with  the  alkali,  forming  hydrofluate  of  ammonia,  and  all  the  silicic  acid  is  de- 
posited. On  this  fact  is  founded  the  mode  of  analyzing  fluosilicic  acid  gas 
adopted  by  Dr.  Davy  and  Thomson. 

The  solution  which  is  formed  by  fully  saturating  water  with  fluosilicic  acid 
gas  is  powerfully  acid,  and  emits  fumes  on  exposure  to  the  air.  It  is  commonly 
^nown  by  the  name  of  silicated  fluoric  acid ,-  but  a  more  appropriate  term  is  silico- 
hydrofluoric  acid.  [It  is  called  by  Berzelius  hydrofluosilicic  acid,  but  preferably 
by  Prof.  Hare  fluohydrosilicic  acid.'\  According  fo  the  experiments  of  Berzelius, 
it  appears  to  be  a  definite  compound  of  hydrofluoric  and  fluosilicic  acids  in  the 
ratio  of  3  eqs.  of  the  former  to  two  of  the  latter,  and  is  thus  expressed,  3  HF  -f- 
SSiFj.  If  evaporated  before  separation  from  the  silicic  acid  deposited  by  the 
action  of  water  on  fluosilicic  acid  gas,  this  compound  is  reproduced.  But  if 
the  solution  is  poured  off  from  the  silicic  acid  thus  deposited,  and  then  evapo- 
rated, fluosilicic  acid  gas  is  at  first  evolved,  and  subsequently  hydrofluoric  acid 
and  water  are  expelled.  The  evaporation  of  silico-hydrofluoric  acid  m  vacuo  is 
attended  by  a  similar  change,  so  that  this  acid  cannot  be  obtained  free  from 
water.  It  does  not  corrode  glass ;  but  when  evaporated  in  glass  vessels,  the 
production  of  free  hydrofluoric  acid  of  course  gives  rise  to  corrosion. 

On  neutralizing  silico-hydrofluoric  acid  with  ammonia,  and  gently  evaporating 
to  dryness,  all  the  silicic  acid  is  rendered  insoluble.  By  exactly  neutralizing 
with  carbonate  of  potassa,  a  sparingly  soluble  double  fluoride  of  silicon  and 
potassium  subsides ;  the  precipitation  is  still  more  complete  with  chloride  of 
barium,  when  the  insoluble  fluoride  of  silicon  and  barium  is  generated.  A 
variety  of  similar  compounds  may  be  obtained  either  by  double  decomposition,  or 
by  the  action  of  silico-hydrofluoric  acid  on  metallic  oxides. 

lis  eq.  is  78-58 ;  symb.  Si  +  3F,  or  SiFj. 


HYDROGEN  AND  NITROGEN.  255 


ON  THE  COMPOUNDS  OF  THE  SIMPLE  NON-METALLIC  ACIDIFIABLE 
COMBUSTIBLES  WITH  EACH  OTHER. 


SECTION  I. 

I 

HYDROGEN  AND  NITROGEN.— AMMONIAC AL  GAS. 

>  as 

Hist,  and  Prep. — ^The  aqueous  solution  of  ammonia,  under  the  name  of  sptnt 
of  hartshorn^  has  been  long  known  to  chemists ;  but  its  existence  as  a  gas  was 
first  noticed  by  Priestley,  who  described  it  in  his  works  under  the  title  of  alka- 
line air.  It  is  often  called  the  volatile  alkali  ,•  but  the  terms  ammonia  and  amrao- 
niacal  gas  are  now  usually  employed.  Although  a  product  of  the  decomposition 
of  organic  substances,  it  has  been  thought  better  to  describe  it  here,  from  its 
great  importance  in  inorganic  chemistry. 

An  abundant  supply  of  ammoniacal  gas  may  be  obtained  from  any  salt  of  am- 
monia by  the  action  of  a  pure  alkali  or  alkaline  earth  ;  but  hydrochlorate  of  ammo- 
nia and  lime,  from  economical  considerations,  are  always  employed.  The 
proportions  to  which  I  give  the  preference  are  equal  parts  of  hydrochlorate  of 
ammonia  and  well-burned  quicklime,  considerable  excess  of  lime  being  taken,  in 
order  to  decompose  the  hydrochlorate  more  expeditiously  and  completely.  The 
lime  is  slaked  by  the  addition  of  water;  and  as  soon  as  it  has  fallen  into  powder, 
it  should  be  placed  in  an  earthen  pan  and  be  covered  till  it  is  quite  cold,  in  order 
to  protect  it  from  the  carbonic  acid  of  the  air.  It  is  then  mixed  in  a  mortar  with 
the  hydrochlorate  of  ammonia,  previously  reduced  to  a  fine  powder;  and  the 
mixture  is  put  into  a  retort  or  other  convenient  glass  vessel.  Heat  is  then  ap- 
plied, and  the  temperature  gradually  increased  as  long  as  free  evolution  of  gas 
continues.    The  residue  consists  of  chloride  of  calcium  and  lime. 

The  gas,  thus  liberated,  must  be  collected  over  mercury,  as  it  is  most  rapidly 
absorbed  by  water.  Advantage  is  taken  of  this  property  to  prepare  what  is  com- 
monly though  incorrectly  termed  liquid  ammonia.  For  this  purpose  a  current  of 
gas  is  transmitted  into  distilled  water,  which  is  kept  cool  by  means  of  ice  or 
moist  cloths,  and  the  process  is  continued  as  long  as  any  gas  is  absorbed.  A 
highly  concentrated  solution  of  ammonia  is  thus  obtained.  The  most  convenient 
method  of  preparing  ammoniacal  gas  for  purposes  of  experiment  is  by  applying 
a  gentle  heat  to  the  concentrated  solution,  contained  in  a  glass  vessel.  It  soon 
enters  into  ebullition,  and  a  large  quantity  of  pure  ammonia  is  disengaged. 

Prop, — Ammonia  is  a  colourless  gas,  which  has  a  strong  pungent  odour,  and 
acts  powerfully  on  the  eyes  and  nose.  It  is  quite  irrespirable  in  its  pure  form, 
but  when  diluted  with  air,  it  may  be  taken  into  the  lungs  with  safety.  Burning 
bodies  are  extinguished  by  it,  nor  is  the  gas  inflamed  by  their  approach.    Am- 


256  HYDROGEN  AND  NITROGEN. 

monia,  however,  is  inflammable  in  a  low  degree ;  for  when  a  lighted  candle  is 
immersed  in  it,  the  flame  is  somewhat  enlarged,  and  tinged  of  a  pale  yellow 
colour  at  the  moment  of  being  extinguished ;  and  a  small  jet  of  the  gas  will  bum 
in  an  atmosphere  of  oxygen.  A  mixture  of  ammoniacal  and  oxygen  gases  deto- 
nates by  the  electric  spark ;  water  being  formed,  and  nitrogen  set  free.  A  little 
nitric  acid  is  generated  at  the  same  time,  except  when  a  smaller  quantity  of  oxy- 
gen is  employed  than  is  suflicient  for  combining  with  all  the  hydrogen  of  the 
ammonia.     (Henry,  Phil.  Trans.  1809.) 

Ammoniacal  gas  at  the  temperature  of  50°  and  under  a  pressure  equal  to  6*5 
atmospheres  becomes  a  transparent  colourless  liquid.  [In  the  experiments  of 
Mr.  Faraday  it  was  converted  into  a  transparent  crystalline  solid  (page  53.)] 
It  is  also  liquefied,  according  to  Guyton-Morveau,  under  the  common  pressure, 
by  a  cold  of  — 70°  ;  but  there  is  no  doubt  that  the  liquid  which  he  obtained  was 
a  solution  of  ammonia  in  water. 

It  has  all  the  properties  of  an  alkali  in  a  very  marked  manner.  Thus  it  has 
an  acrid  taste,  and  gives  a  brown  stain  to  turmeric  paper;  though  the  yellow 
colour  soon  reappears  on  exposure  to  the  air,  owing  to  the  volatility  of  the  alkali. 
It  combines  also  with  acids,  and  neutralizes  their  properties  completely.  All 
these  salts  suffer  decomposition  by  being  heated  with  the  fixed  alkalies  or  alka- 
line earths,  such  as  potassa  or  lime,  the  union  of  which  with  the  acid  of  the  salt 
causes  the  separation  of  its  ammonia.  None  of  the  ammoniacal  salts  can  sustain 
a  red  heat  without  being  dissipated  in  vapour  or  decomposed,  a  character  which 
manifestly  arises  from  the  volatile  nature  of  the  alkali.  If  combined  with  a  vola- 
tile acid,  such  as  the  hydrochloric,  the  compound  itself  sublimes  unchanged  by 
heat;  but  when  united  with  an  acid,  which  is  fixed  at  a  low  red  heat,  such  as 
the  phosphoric,  the  ammonia  alone  is  expelled.  It  is  here  considered  that  the 
salts  of  ammonia  are  formed  by  its  direct  union  with  acids.  Another,  and  a  very 
scientific  view  has  been  adopted  by  Berzelius.  When  an  electric  cunent  is 
passed  through  a  weak  solution  of  ammonia,  it  is  decomposed  by  the  secondary 
action,  hydrogen  from  decomposed  water  being  evolved  at  the  negative  electrode 
and  nitrogen  at  the  positive  (Faraday,  Phil.  Trans.  1834).  But  if  a  portion  of 
mercury  form  the  negative  electrode,  no  hydrogen  is  evolved,  and  the  mercury  is 
rapidly  converted  into  a  light  porous  substance,  which  has  the  lustre  and  all  the 
characters  of  an  amalgam.  As  soon  as  it  is  removed  from  the  influence  of  the 
electric  current,  rapid  decomposition  ensues,  mercury  is  reproduced,  and  hydro- 
gen and  ammoniacal  gases  are  evolved  in  the  ratio  of  one  measure  of  the  former 
to  two  of  the  latter,  according  to  the  observations  of  Gay-Lussac  and  Thenard. 
The  production  of  this  compound  is  explained  by  Berzelius  on  the  supposition 
that  ammonia  by  uniting  with  an  additional  eq.  of  hydrogen,  forms  a  compound, 
which  has  all  the  properties  of  a  metal ;  he  therefore  calls  it  ammonium.  The 
oxide  of  ammonium,  the  composition  of  which  is  represented  by  the  formula 
NH4  -f-  O,  he  considers  to  be  the  base  of  the  ammoniacal  salts.  This  view  is 
supported  by  several  facts,  which  will  be  considered  when  treating  of  the  salts. 

Hydrogen  and  nitrogen  gases  do  not  unite  directly,  and  therefore  chemists 
have  no  synthetic  proof  of  the  constitution  of  ammonia.  Its  composition,  how- 
ever, has  been  determined  analytically  with  great  exactness.  When  a  succession 
of  electric  sparks  is  passed  through  ammoniacal  gas,  it  is  resolved  into  its  ele- 
ments ;  and  the  same  effect  is  produced  by  conducting  it  through  porcelain  tubes 
heated  to  redness.  A.  Berthollet  analyzed  ammonia  in  both  ways,  and  ascer- 
tained that  200  measures  of  that  gas,  on  being  decomposed,  occupy  the  space  of 


HYDROGEN  AND  NITROGEN. 


257 


400  measures,  300  of  which  are  hydrogen,  and  100  nitrogen.  Henry  has  made 
an  analysis  of  ammonia  hy  means  of  electricity,  and  his  experiment  proves 
beyond  a  doubt  that  the  proportions  above  given  are  rigidly  exact.  (Annals  of 
Philosophy,  xxiv.  346.) 


Now  since  150  cubic  inches  of  hydrogen  weigh 
and  50  of  nitrogen 

200  cubic  inches  of  ammonia  must  weigh 
and  it  is  composed  by  weight  of 


Hydrogen 
Nitrogen 


3-205 
15083 


3 
14-15 


Grains. 
3-205 
15083 

18-288 


or  3  equivalents. 
or  1  equivalent. 


The  sp.  gr.  of  ammonia,  according  to  this  calculation,  is  0*5898,  a  number 
which  agrees  closely  with  those  ascertained  directly  by  Davy  and  Thomson. 

Ammoniacal  gas  has  a  powerful  affinity  for  water.  Owing  to  this  attraction,  a 
piece  of  ice,  when  introduced  into  a  jar  full  of  ammonia,  is  instantly  liquefied, 
and  the  gas  disappears  in  the  course  of  a  few  seconds.  Davy,  in  his  Elements, 
stated  that  water  at  50°,  and  when  the  barometer  stands  at  29*8  inches,  absorbs 
670  times  its  volume  of  ammonia,  and  that  the  solution  has  a  sp.  gr.  of  0*875 , 
According  to  Thomson,  water  at  the  common  temperature  and  pressure  takCT  up 
780  times  its  bulk.  By  strong  compression,  water  absorbs  the  gas  in  still  greater 
quantity.  Heat  is  evolved  during  its  absorption;  and  a  considerable  expansion, 
independently  of  the  increased  temperature,  occurs  at  the  same  time. 

The  concentrated  solution  of  ammonia  is  a  clear  colourless,  liquid,  of  sp.  gr. 
0*936.  It  possesses  the  peculiar  pungent  odour,  taste,  alkalinity,  and  other  pro- 
perties of  the  gas  ,itself.  On  account  of  its  great  volatility  it  should  be  pre- 
served in  well-stopped  bottles,  a  measure  which  is  also  required  to  prevent  the 
absorption  of  carbonic  acid.  At  a  temperature  of  130°  it  enters  into  ebullition, 
owing  to  the  rapid  escape  of  pure  ammonia ;  but  the  whole  of  the  gas  cannot  be 
expelled  by  this  means,  as  at  last  the  solution  itself  evaporates.  It  freezes  at 
about  the  same  temperature  as  mercury. 

The  following  table,  from  Davy's  Elements  of  Chemical  Philosophy,  shows 
the  quantity  of  real  ammonia  contained  in  100  parts  of  solutions  of  different  sp. 
gravities  at  59°  F.  and  when  the  barometer  stands  at  30  inches.  The  sp.  gr.  of 
water  is  supposed  to  be  10,000  :— 

Table  of  the  quantity  of  real  Ammonia  in  solvtions  of  diffetent  densities. 


100  parts  of 

Of  real 

100  parts  of 

Of  real 

sp.  gravity. 

c 

Ammonia. 

sp.  gravity. 

e: 

Ammonia. 

8750 

32-5 

9435 

14-53 

8875 

2 

29-25 

9476 

B 

13-46 

9000 

s 

Q 

26-00 

9513 

§ 

12-40 

9054 

u 

25-37 

9545 

u 

11-56 

9166 

2207 

9573 

10-82 

9255 

19-54 

9597 

10-17 

9326 

17-52 

9619 

9-60 

9385 

15-88 

9692 

9-50 

19 


258  COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

The  presence  of  free  ammoniacal  gas  may  always  be  detected  by  its  odour,  by 
its  temporary  action  on  yellow  turmeric  paper,  and  by  its  forming  dense  white 
fumes,  hydrochlorate  of  ammonia,  when  a  glass  rod  moistened  with  hydrochloric 
acid  is  brought  near  it. 

Besides  ammonia  and  ammonium,  another  compound  of  nitrogen  and  hydrogen 
is  believed  to  exist,  the  composition  of  which  is  represented  by  the  formula, 
NHg.  It  is  only  known  in  combination,  and  has  been  named  Amidcj  or  Ami- 
dogen.  Its  compounds,  which  are  important,  will  be  described  in  treating  of 
organic  chemistry. 

Its  eq.  is  17-15;  eq,  vol,  =  200 ;  sr/mb.  N  f  3H,  or  NH3. 


SECTION    II. 


COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

CjpEMisTS  have  for  several  years  been  acquainted  with  two  distinct  compounds 
of  carbon  and  hydrogen,  viz.  carburetted  hydrogen  and  defiant  gases ;  but  late 
researches  have  enriched  the  science  with  several  other  compounds  of  a  similar 
nature,  to  which  'much  interest  is  attached.  They  are  remarkable  for  their  num- 
ber, for  supplying  some  instructive  instances  of  isomerism,  and  for  their  tendency 
to  unite  with  and  even  neutralize  powerful  acids,  without,  in  thefr  uncombined 
state,  manifesting  any  ordinary  signs  of  alkalinity.  Several  of  them  are  particu- 
larly distinguished  by  their  chemical  affinities ;  for  although  compound,  they 
exhibit  in  their  combinations  with  other  substances  the  characteristics  of  an  ele- 
ment. They  have  hence  been  called  the  compound  radicals.  These  compound 
radicals  are  closely  associated  both  with  the  organic  and  inorganic  chemistry.  In 
the  latter  they  must  hold  a  place,  as  being  compounds  formed  by  the  direct  union 
of  two  elements ;  and  in  the  former  they  are  the  roots  or  radicals  of  the  various 
organic  products. 

Light  Carburetted  Hydrogen. — Hist, — This  gas  is  sometimes  called  heavt/ 
inflammable  air^  the  inflammable  air  of  marshes,  and  hydrocarburet.  Agreeably 
to  the  principles  of  chemical  nomenclature,  taking  carbon  as  the  electro-negative 
element,  it  is  a  dicarburei  of  hydrogen ,-  but  it  is  generally  termed  light  carbu- 
retted hydrogen.  It  is  formed  abundantly  in  stagnant  pools  during  the  sponta- 
neous decomposition  of  dead  vegetable  matter;  and  it  may  readily  be  procured 
by  stirring  the  mud  at  the  bottom  of  them,  and  collecting  the  gas,  as  it  escapes, 
in  an  inverted  glass  vessel.  In  this  state  it  is  found  to  contain  l-20th  of  carbonic 
acid  gas,  which  may  be  removed  by  means  of  lime  water  or  a  solution  of  pure 
potassa,  and  1-1 5th  or  l-20th  of  nitrogen.  This  is  the  only  convenient  method 
of  obtaining  it. 

Prop. — Colourless,  tasteless,  nearly  inodorous  ;  always  gaseous  when  uncom- 
bined ;  does  not  change  the  colour  of  litmus  or  turmeric  paper.  Water,  according 
to  Henry,  absorbs  about  l-60th  of  its  volume.  It  extinguishes  all  burning  bodies, 
and  is  unable  to  support  the  respiration  of  animals.  It  is  highly  inflammable ; 
and  when  a  jet  of  it  is  set  on  fire,  it  bums  with  a  yellow  flame,  and  with  a  much 


COMPOUNDS  OF  HYDROGEN  AND  CARBON.  259 

Stronger  light  than  is  occasioned  by  hydrogen  gas.  With  a  due  proportion  of 
atmospheric  air  or  oxygen  gas  it  forms  a  mixture  which  detonates  powerfully 
with  the  electric  spark,  or  by  the  contact  of  flame.  The  sole  products  of  the 
explosion  are  water  and  carbonic  acid. 

Dalton  first  ascertained  the  real  nature  of  light  carburetted  hydrogen  ;  and  it 
has  since  been  particularly  examined  by  Thomson,  Davy,  and  Henry.  When 
100  measures  are  detonated  with  rather  more  than  twice  their  volume  of  oxygen 
gas,  the  whole  of  the  inflammable  gas  and  precisely  200  measures  of  the  oxygen 
disappear,  water  is  condensed,  and  100  measures  of  carbonic  acid  are  produced. 
Now  100  measures  of  carbonic  acid  gas  contain  (page  188)  100  of  carbon  vapour 
and  100  of  oxygen  gas,  just  half  the  oxygen  which  had  been  employed  ;  and  the 
remaining  oxygen  requires  200  measures  of  hydrogen  to  form  water.  Hence  as, 
at  60°  F.  and  30  inches  Bar., 

Grains. 
100  cubic  inches  of  carbon  vapour  weigh   '.  .  .  13153 

200  do.  hydrogen  gas     .  .  .  .  4-2636 


100  do.  light  carburetted  hydrogen  must  weigh  17'4166 

These  weights  are  obviously  in  the  ratio  of  2  to  6*12,  as  already  assigned ;  and 
the  sp.  gr.  of  such  a  gas  qjight  to  be  0*5594,  which  is  nearly  the  quantity  found 
experimentally  by  Thomson  and  Henry. 

Light  carburetted  hydrogen  is  not  decomposed  by  electricity,  nor'  by  being 
passed  through  red-hot  tubes,  unless  the  temperature  is  very  intense,  in  which 
case  some  of  the  gas  does  suffer  decomposition,  each  volume  yielding  two 
volumes  of  pure  hydrogen  gas  and  a  deposite  of  charcoal.  Mixed  with  chlorine, 
no  action  takes  place  at  common  temperatures,  when  quite  dry,  even  if  exposed 
to  the  direct  solar  rays.  If  moist,  and  the  mixture  is  kept  in  a  dark  place,  still 
no  action  ensues  ;  but  if  light  be  admitted,  particularly  sunshine,  decomposition 
follows.  The  nature  of  the  products  depends  upon  the  proportion  of  the  gases. 
If  four  measures  of  chlorine  and  one  of  light  carburetted  hydrogen  are  present, 
carbonic  and  hydrochloric  acid  gases  will  be  produced :  two  volumes  of  chlorine 
combine  with  two  volumes  of  hydrogen  contained  in  the  carburetted  hydrogen, 
and  the  other  two  volumes  of  chlorine  decompose  so  much  water  as  will  like- 
wise give  two  volumes  of  hydrogen,  forming  hydrochloric  acid  ;  while  the  oxy- 
gen of  the  water  unites  with  the  carbon,  and  converts  it  into  carbonic  acid.  If 
there  are  three  instead  of  four  volumes  of  chlorine,  carbonic  oxide  will  be  gene- 
rated instead  of  carbonic  acid,  because  one-half  less  water  will  be  decomposed 
(Henry).  If  a  mixture  of  chlorine  and  light  carburetted  hydrogen  is  electrified 
or  exposed  to  a  red  heat,  hydrochloric  acid  is  formed,  and  charcoal  deposited. 

Its  eq.  is  8*12;  eq.  vol.=:  100;  symb.  HjC. 

It  was  first  ascertained  by  Henry  (Nicholson's  Journal,  vol.  xix.) ;  and  his 
conclusions  have  been  fully  confirmed  by  the  subsequent  researches  of  Davy, 
that  \\\Q  fire-damp  of  coal-mines  consists  almost  solely  of  light  carburetted  hydro- 
gen. This  gas  often  issues  in  large  quantity  from  between  beds  of  coal,  and  by 
collecting  in  mines,  owing  to  deficient  ventilation,  gradually  mingles  with  atmo- 
spheric air,  and  forms  an  explosive  mixture.  The  first  unprotected  light  which 
then  approaches,  sets  fire  to  the  whole  mass,  and  an  explosion  ensues.  These 
accidents,  which  were  formerly  so  frequent  and  so  fatal,  are  now  comparatively 
rare,  owing  to  the  employment  of  the  safety-lamp.     For  this  invention  we  are 


<2(M)  COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

indebted  to  Davy,  who  established  the  principles  of  its  construction  by  a  train 
of  elaborate  experiment  and  close  reasoning,  which  may  be  regarded  as  one  of 
the  happiest  efforts  of  his  genius  (Essay  on  Flame). 

Davy  commenced  the  inquiry  by  determining  the  best  proportion  of  air  and 
light  carburetted  hydrogen  for  forming  an  explosive  mixture.  When  the  in- 
flammable gas  is  mixed  with  3  or  4  times  its  volume  of  air,  it  does  not  explode 
at  all.  It  detonates  feebly  when  mixed  with  5  or  6  times  its  bulk  of  air,  and 
powerfully  when  1  to  7  or  8  is  the  proportion.  With  14  times  its  volume  it  still 
forms  a  mixture  which  is  explosive;  but  if  a  larger  quantity  of  air  be  admitted,  a 
taper  bums  in  it  only  with  an  enlarged  flame. 

The  temperature  required  for  causing  an  explosion  was  next  ascertained.  It 
was  found  that  the  strongest  explosive  mixture  may  come  in  contact  with  iron 
or  other  solid  bodies  heated  to  redness,  or  even  to  whiteness,  without  detonating, 
provided  they  are  not  in  a  state  of  actual  combustion ;  whereas  the  smallest  point 
of  flame,  owing  to  its  higher  temperature,  instantly  causes  an  explosion. 

The  last  important  step  in  the  inquiry  was  the  observation  that  flame  cannot 
pass  through  a  narrow  tube.  This  led  to  the  discovery,  that  the  power  of  tubes 
in  preventing  the  transmission  of  flame  is  not  necessarily  connected  with  any 
particular  length ;  and  that  a  very  short  one  will  have  the  efiect,  provided  its 
diameter  is  proportionally  reduced.  Thus,  a  piece  of  fine  wire  gauze,  which  may 
be  regarded  as  an  assemblage  of  short  narrow  tube^  is  quite  impermeable  to 
flame ;  and  consequently,  if  a  common  oil  lamp  be  completely  surrounded  with  a 
cage  of  such  gauze,  it  may  be  introduced  into  an  explosive  atmosphere  of  fire- 
damp and  air,  without  kindling  the  mixture.  ITiis  simple  contrivance,  which  is 
appropriately  termed  the  sc^ety-lamp,  not  only  prevents  explosion,  but  indicates 
the  precise  moment  of  danger.  When  the  lamp  is  carried  into  an  atmosphere 
charged  with  fire-damp,  the  flame  begins  to  enlarge ;  and  the  mixture,  if  highly 
explosive,  takes  fire  as  soon  as  it  has  passed  through  the  gauze,  and  burns  on  its 
inner  surface,  while  the  light  in  the  centre  of  the  lamp  is  extinguished.  When- 
ever this  appearance  is  observed,  the  miner  must  instantly  withdraw :  for  though 
the  flame  should  not  be  able  to  communicate  with  the  explosive  mixture  on  the 
outside  of  the  lamp,  as  long  as  the  texture  of  the  gauze  remains  entire,  yet  the 
heat  emitted  during  the  combustion  is  so  great,  that  the  wire,  if  exposed  to  it  for 
a  few  minutes,  would  suffer  oxidation,  and  fall  to  pieces. 

The  peculiar  op^tion  of  small  tubes  in  obstructing  the  passage  of  flame  ad- 
mits of  a  very  simple  explanation.  Flame  is  gaseous  matter  heated  so  intensely 
as  to  be  luminous ;  and  Davy  has  shown  that  the  temperature  necessary  for  pro- 
ducing this  effect  is  far  higher  than  the  white  heat  of  solid  bodies.  Now,  when 
flame  comes  in  contact  with  the  sides  of  very  minute  apertures,  as  when  wire 
gauze  is  laid  upon  a  burning  jet  of  coal  gas,  it  is  deprived,  of  so  much  heat  that 
its  temperature  instantly  falls  below  the  degree  at  which  gaseous  matter  is  lumi- 
nous ;  and  consequently,  though  the  gas  itself  passes  freely  through  the  inter- 
stices, and  is  still  very  hot,  it  is  no  longer  incandescent.  Nor  does  this  take 
place  when  the  wire  is  cold  only ; — the  effect  is  equally  certain  at  any  degree  of 
heat  which  the  flame  can  communicate  to  it.  For  since  the  gauze  has  a  large 
extent  of  surface,  and  from  its  metallic  nature  is  a  good  conductor  of  heat,  it  loses 
heat  with  great  rapidity.  Its  temperature,  therefore,  though  it  may  be  heated  to 
whiteness,  is  always  so  far  below  that  of  flame,  as  to  exert  a  cooling  influence 
over  the  burning  gas,  and  reduce  its  heat  below  the  point  at  which  it  is  incan- 
descent. 


COMPOUNDS  OF  HYDROGEN  AND  CARBON.  261 

These  principles  suggest  the  conditions  under  which  Davy's  lamp  would  cease 
to  be  safe.  If  a  lamp  with  its  gauze  red-hot  be  exposed  to  a  current  of  explosive 
mixture,  the  flame  may  possibly  pass  so  rapidly  as  not  to  be  cooled  below  the 
point  of  ignition,  and  in  that  case  an  accident  might  occur  with  a  lamp  which 
would  be  quite  safe  in  a  calm  atmosphere.  It  has  been  lately  shown  by  Messrs. 
Upton  and  Roberts,  lamp  manufacturers  of  London,  that  flame  may  in  this  way 
be  made  to  pass  through  the  safety-lamp  as  commonly  constructed ;  and  I  am 
satisfied,  from  having  witnessed  some  of  their  experiments,  that  the  observation 
is  correct.  This  then  may  account  for  accidents  in  coal-mines  where  the  safety- 
lamp  is  constantly  employed.  An  obvious  mode  of  avoiding  such  an  evil  is  to 
diminish  the  apertures  of  the  gauze ;  but  this  remedy  is  nearly  impracticable  from 
the  obstacle  which  very  fine  gauze  causes  to  the  diflfusion  of  light.  A  better 
method  is  to  surround  the  common  safety-lamp  with  a  glass  cylinder,  allowing 
air  to  enter  solely  at  the  bottom  of  the  lamp  through  wire  gauze  of  extreme  fine- 
ness, placed  horizontally,  and  to  escape  at  top  by  a  similar  contrivance.  Upton 
and  Roberts  have  constructed  a  lamp  of  this  kind,  through  which  I  have  in  vain 
tried  to  cause  the  communication  of  flame,  and  which  appears  to  me  perfectly 
secure :  should  an  accident  break  the  glass,  their  lamp  would  be  reduced  to  a 
safety-lamp  of  the  common  construction.  Davy's  lamp  thus  modified  gives  a 
much  better  light  than  without  the  glass,  just  as  all  lamps  burn  better  with  a 
shade  than  without  one.  • 

Olefiant  Gas — Hist,  and  Prep. — Discovered  in  1796  by  some  associated  Dutch 
chemists,  who  gave  it  the  name  of  olefiant  gas,  from  its  property  of  forming  an 
oil-like  liquid  with  chlorine.  It  is  prepared  by  mixing,  in  a  capacious  retort,  one 
measure  of  strong  alcohol  with  three  measures  of  concentrated  sulphuric  acid, 
and  heating  the  mixture  as  soon  as  it  is  made.  The  acid  soon  acts  upon  the 
alcohol,  effervescence  ensues,  and  olefiant  gas  passes  over.  The  chemical 
changes  which  take  place  are  of  a  complicated  nature,  and  the  products  numerous. 
At  the  commencement  of  the  process,  the  olefiant  gas  is  mixed  only  with  a  little 
ether ;  but  in  a  short  time  the  solution  becomes  dark,  the  formation  of  ether 
declines,  and  the  odour  of  sulphurous  acid  begins  to  be  perceptible:  towards  the 
close  of  the  operation,  though  olefiant  gas  is  still  the  chief  product,  sulphurous 
acid  is  freely  disengaged,  some  carbonic  acid  is  formed,  and  charcoal  in  large 
quantity  deposited.  The  olefiant  gas  may  be  collected  either  over  water  or  mer- 
cury. The  greater  part  of  the  ether  condenses  spontaneously  ;  and  the  sulphurous 
and  carbonic  acids  may  be  separated  by  washing  the  gas  with  lime  water,  or  a 
solution  of  pure  potassa.  The  olefiant  gas  in  this  process  is  derived  solely  from 
the  alcohol ;  the  theory  of  its  formation,  as  well  as  that  of  the  accompanying 
products,  will  be  given  under  the  head  of  Ether  in  the  third  part  of  this  work. 

Prop. — Colourless,  tasteless,  inodorous ;  hitherto  only  known  in  a  gaseous 
state.  Water  absorbs  about  one-eighth  of  its  volume.  Like  the  preceding  com- 
pound, it  extinguishes  flame,  is  unable  to  support  the  respiration  of  animals,  and 
is  set  on  fire  when  a  lighted  candle  is  presented  to  it,  burning  slowly  with  the 
emission  of  a  dense  white  light.  With  a  proper  quantity  of  oxygen  gas,  it 
forms  a  mixture  which  may  be  kindled  by  flame  or  the  electric  spark,  and  which 
explodes  with  great  violence.  To  burn  it  completely,  it  should  be  detonated 
with  four  or  five  times  its  volume  of  oxygen.  On  conducting  this  experiment 
with  the  requisite  care,  Henry  finds  that  for  each  measure  of  olefiant  gas,  pre- 
cisely three  of  oxygen  disappear,  deposition  of  water  takes  place,  and  two  mea- 
sures of  carbonic  acid  are  produced.    From  these  data  the  proportion  of  its 


JJHH  COMPOUNDS  OF  HYDROGEN  AND  CARBON. 

constituents  may  easily  be  deduced  in  the  following  manner : — Two  measures 
of  carbonic  acid  contain  two  measures  of  the  vapour  of  carbon,  which  must  have 
been  present  in  the  defiant  gas,  and  two  measures  of  oxygen.  Two-thirds  of 
the  oxygen  which  disappeared  are  thus  accounted  for ;  and  the  other  third  must 
have  combined  with  hydrogen.  But  one  measure  of  oxygen  requires  for  form- 
ing water  precisely  two  measures  of  hydrogen,  which  must  likewise  have  been 
contained  in  the  defiant  gas.     Hence,  as 

200  cubic  inches  of  the  vapour  of  carbon,  weigh         ... 
200  do.  hydrogen  gas,  weigh       .... 

100  cmbic  inches  of  olefiant  gas  must  weigh         ....        30-4162 

These  weights  are  in  the  ratio  12*24  or  two  equivalents  of  carbon  to  2  or  two  eq. 
of  hydrogen,  as  in  the  table.  The  sp.  gr.  of  a  gas  so  constituted  should  be 
0'9808;  whereas  the  density  found  experimentally  by  Saussure  is  0*9852,  by 
Henry  0*967,  and  by  Thomson  0*97. 

By  a  succession  of  electric  sparks  it  is  resolved  into  charcoal  and  hydrogen ; 
and  the  latter  of  course  occupies  twice  as  much  space  as  the  gas  from  which  it 
was  derived.  It  is  also  decomposed  by  transmission  through  red-hot  tubes 
of  porcelain.  The  nature  of  the  products  varies  with  the  temperature.  By 
employing  a  very  low  degree  of  heat,  it  mfy  probably  be  converted  solely 
into  carbon  and  light  carburetted  hydrogen;  and  in  this  case  no  increase  of 
volume  can  occur,  because  these  two  gases,  for  equal  bulks,  contain  the  same 
quantity  of  hydrogen.  But  if  the  temperature  is  high,  then  a  great  increase  of 
volume  takes  place ;  a  circumstance  which  indicates  the  evolution  of  free  hydro- 
gen, and  consequently  the  total  decomposition  of  some  of  the  olefiant'  gas. 

Its  eq.  is  14*24  ;  eq.  vol.  =  100  ;  symb.  2H  -|-  2C,  or  H^C^  —  28*48. 

Chlorine  acts  powerfully  on  olefiant  gas.  When  these  gases  are  mixed  toge- 
ther in  the  ratio  of  two  measures  of  the  former  to  one  of  the  latter,  they  form  a 
mixture  which  takes  fire  on  the  approach  of  flame,  and  which  burns  rapidly  with 
formation  of  hydrochloric  acid  gras,  and  deposition  of  a  large  quantity  of  charcoal. 
But  if  the  gases  are  allowed  to  remain  at  rest  after  being  mixed  together,  a  very 
different  action  ensues.  The  chlorine,  instead  of  decomposing  the  olefiant  gas, 
enters  into  direct  combination  with  it,  and  a  yellow  liquid  like  oil  is  generated. 
Wohler  has  remarked  its  production  by  the  contact  of  olefiant  gas  with  certain 
metallic  chlorides,  especially  the  perchloride  of  antimony. 

The  other  compounds  of  carbon  and  hydrogen  are  described  in  the  organic  che- 
mistry. They  belong  to  this  department  not  only  as  being  products  of  the  organic 
kingdom,  but  also  on  account  of  their  atomic  constitution ;  for  whenever  they 
are  acted  on  by  chlorine  or  any  other  dehydrodizing  agents,  one  part  of  the  hydro- 
gen, which  enters  into  their  composition,  is  shown  to  be  in  a  state  of  combina- 
tion different  from  the  rest.  Thus  evidence  is  obtained  that  these  compounds, 
although  composed  of  nothing  but  hydrogen  and  carbon,  are  not  formed  by  the 
direct  union  of  these  elements,  but  that  a  portion  of  the  hydrogen  with  the  car- 
bon forms  a  compound  radical,  which  acts  the  part  of  an  element  and  combines 
as  such  with  the  remainder  of  the  hydrogen. 


COMPOUNDS  OF  HYDROGEN  AND  SULPHUR.  263 


SECTION  III. 


COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

Sulphur  unites  with  hydrogen  in  at  least  two  proportions,  and  the  resulting 
compounds  are  thus  constituted  : — 

Hydrogen.    Sulphur.         Equiv.        Formulae. 
Hydrosulphuric  acid     -        -        1        1  eq. -{- 16-1     1  eq.  =  171  HS. 

Persulphuret  of  hydrogen  1        1  eq.  -j-  32-2  ^2  eq.  =  33-2  HSj. 

Hydrosulphuric  Jtcid^  Sulphydric  Acid. — Hist,  and  Prep, — Commonly  known 
under  the  name  of  sulphuretted  hydrogen.  It  is  best  prepared  by  heating  sesqui- 
sulphuret  of  antimony  in  a  retort,  or  other  convenient  glass  vessel,  with  four  or 
five  times  its  weight  of  strong  hydrochloric  acid ;  when,  by  an  interchange  of 
elements,  sesquichloride  of  antimony  and  hydrosulphuric  acid  are  generated,  the 
latter  of  which  escapes  with  effervescence.  The  elements  concerned  before  and 
after  the  change,  are 

1  eq.  Sesquisulphuret  of  antimony  and  3  eq.  Hydrochloric  acid 
SboSa  3HC1. 


which  yield 

3  eq.  Hydrosulphuric  acid  and  1  eq.  Sesquichloride  of  antimony. 
3H8  ^  SbjCla 

It  may  also  be  formed  by  the  action  of  sulphuric  acid  diluted  with  3  or  4  parts 
of  water  on  pretosulphuret  of  iron :  this  sulphuret  and  water  interchange  ele- 
ments, hydrosulphuric  acid  and  protoxide  of  iron  are  generated,  and  the  latter 
unites  with  sulphuric  acid,  while  the  former  in  the  state  of  gas  is  rapidly  disen- 
gaged. Hydrochloric  acid  may  be  substituted  for  the  sulphuric.  A  sulphuret 
of  iron  may  be  procured  for  the  purpose,  either  by  igniting  common  iron  pyrites, 
by  which  means  nearly  half  of  its  sulphur  is  expelled,  or  by  exposing  to  a  low 
red  heat  a  mixture  of  two  parts  of  iron  filings  and  rather  more  than  one  part  of 
sulphur.  The  materials  should  be  placed  in  a  common  earthen  or  cast-iron  cru- 
cible, and  be  protected  as  much  as  possible  from  the  air  during  the  process. 
The  sulphuret  procured  from  iron  filings  and  sulphur  always  contains  some 
uncombined  iron,  and  therefore  the  gas  obtained  from  it  is  never  quite  pure, 
being  mixed  with  a  little  free  hydrogen.  This,  however,  for  many  purposes,  is 
immaterial. 

Prop. — Colourless  gas,  which  reddens  moist  litmus  paper  feebly,  and  is  dis- 
tinguished from  all  other  gaseous  substances  by  its  offensive  taste  and  odour, 
which  is  similar  to  that  of  putrefying  eggs,  or  the  water  of  sulphurous  springs. 
Under  a  pressure  of  17  atmospheres,  at  50°,  it  is  compressed  into  a  limpid  liquid, 
which  resumes  the  gaseous  state  as  soon  as  the  pressure  is  removed.  [At  a 
much  lower  temperature  obtained  as  a  transparent  crystalline  solid  (page  53).] 
To  animal  life  it  is  very  injurious.     According  to  Dupuytren  and  Thenard,  the 


264  COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

presence  of  l-1500th  of  this  gas  in  air  is  instantly  fatal  to  a  small  bird  ;  l-lOOOth 
killed  a  middle-sized  dog ;  and  a  horse  died  in  an  atmosphere  which  contained 
l-250th  of  fts  volume. 

It  extinguishes  all  burning  bodies ;  but  the  gas  takes  fire  when  a  lighted  candle 
is  immersed  in  it,  and  burns  with  a  pale  blue  flame.  Water  and  sulphurous  acid 
are  the  products  of  its  combustion,  and  sulphur  is  deposited.  With  oxygen  gas 
it  forms  a  mixture  which  detonates  by  the  application  of  flame  or  the  electric 
spark:  if  100  measures  of  it  are  exploded  with  150  of  oxygen,  the  former  is 
completely  consumed,  the  oxygen  disappears,  water  is  deposited,  and  100  mea- 
sures of  sulphurous  acid  gas  remain  (Thomson).  From  the  results  of  this  expe- 
riment, the  composition  of  hydrosulphuric  acid  gas  may  be  inferred ;  for  it  is 
clear,  from  the  composition  of  sulphurous  acid  (page  194),  that  two-thirds  of  the 
oxygen  must  have  combined  with  sulphur;  and,  therefore,  that  the  remaining 
one- third  contributed  to  the  formation  of  water.  Consequently,  hydrosulphuric 
acid  contains  its  own  volume  of  hydrogen  gas,  and  16*66  of  the  vapour  of  sul- 
phur ;  and  since 

Grains. 
16-66  cubic  inches  of  the  vapour  of  Sulphur  weigh       .  .  .  34-361     ' 

100  cubic  inches  of  Hydrogen  gas  weigh  ....       2-1318 


100  cubic  inches  of  Hydrosulp.  acid  gas  must  weigh  .  .  36-4928 

The  sp.  gr.  of  a  gas  so  constituted  should  be  1*177,  which  agrees  with  obser- 
vation; and  its  elements  are  in  the  ratio  of  1  to  16*1,  as  already  mentioned. 

The  accuracy  of  this  view  is  confirmed  by  several  circumstances.  Thus,  ac- 
cording to  Gay-Lu^sac  and  Thenard,  the  weight  of  100  cubic  inches  of  hydro- 
sulphuric acid  gas  is  36*33  grains.  When  sulphur  is  heated  in  hydrogen  gas, 
hydrosulphuric  acid  is  generated  without  any  change  of  volume.  On  igniting 
platinum  wires  in  it  by  means  of  the  voltaic  apparatus,  sulphur  is  deposited,  and 
an  equal  volume  of  pure  hydrogen  remains ;  and'  a  similar  effdtet  is  produced, 
though  more  slowly,  by  a  succession  of  electric  sparks  (Elements  of  Davy,  p. 
282.)  Gay-Lussac  and  Thenard  found  that  on  heating  tin  in  hydrosulphuric 
acid  gas,  sulphuret  of  tin  is  formed  ;  and  when  potassium  is  heated  in  it,  vivid 
combustion  ensues,  with  formation  of  sulphuret  of  potassium.  In  both  cases, 
pure  hydrogen  is  left,  which  occupies  precisely  the  same  space  as  the  gas  from 
which  it  was  derived.     (Recherches  Physico-Chimiques,  vol.  i.) 

The  salts  of  hydrosulphuric  acid  are  called  hydrosulphaiesy  sulphydrates,  and 
sometimes  hydroaulphurets.  This  acid,  however,  rarely  unites  directl}'  with 
metallic  oxides ;  but  in  most  cases  its  hydrogen  combines  with  the  oxygen  of 
the  oxide  and  its  sulphur  with  the  metal.  All  the  hydrosulphates  which  do 
exist  are  decomposed  by  sulphuric  or  hydrochloric  acids,  and  hydrosulphuric 
acid  gas  is  disengaged  with  effervescence. 

Recently  boiled  water  absorbs  its  own  volume  of  hydrosulphuric  acid,  becomes 
thereby  feebly  acid,  and  acquires  the  peculiar  odour  and  taste  of  sulphurous 
springs.    The  gas  is  expelled  without  change  by  boiling  the  water. 

The  elements  of  hydrosulphuric  acid  may  easily  be  separated  from  one 
another.  A  solution  of  the  gas  cannot  be  preserved  in  an  open  vessel,  because 
iU  hydrogen  unites  with  the  oxygen  of  the  atmosphere,  and  sulphur  is  deposited. 
When  mixed  with  sulphurous  acid,  both  compounds  are  decomposed,  water  is 


COMPOUNDS  OF  HYDROGEN  AND  SULPHUR.  265 

generated,  and  sulphur  set  free.  On  pouring  into  a  bottle  of  the  gas  a  little 
fuming  nitric  acid,  mutual  decomposition  ensues,  a  bluish-white  flame  frequently 
appears,  sulphur  and  nitrous  acid  fumes  come  into  view,  and  water  is  generated. 
Chlorine,  iodine,  and  bromine  decompose  it,  with  separation  of  sulphur,  and  for- 
mation of  hydrochloric,  hydriodic,  and  hydrobromic  acids.  An  atmosphere 
charged  with  hydrosulphuric  acid  gas  may  be  purified  by  means  of  chlorine  in 
the  space  of  a  few  minutes. 

Hydrosulphuric  acid  gas  is  readily  distinguished  from  other  gases  by  its 
odour,  by  tarnishing  silver  with  which  it  forms  a  sulphuret,  and  by  the  character 
of  the  precipitate  which  it  produces  with  solutions  of  arsenious  acid,  tartar 
emetic,  and  salts  of  lead.  The  most  delicate  test  of  its  presence,  when  diffused 
in  the  air,  is  moist  carbonate  of  oxide  of  lead  spread  on  white  paper. 

Its  eq.  is  17*1 ;  eq.  vol.  =  100  ;  symh.  HS. 

Persulphuret  of  Hydrogen. — Hist,  and  Prep. — Discovered  by  Scheele,  but  first 
specially  described  by  Berthollet  (An.  de  Chimie,  xxv.)  When  protosulphuret 
of  potassium  (or  of  any  metal  of  the  alkalies  and  alkaline  earths)  is  mixed  in 
solution  with  sulphuric  acid,  the  oxygen  of  water  unites  with  potassium  and  its 
hydrogen  with  sulphur,  just  as  when  protosulphuret  of  iron  is  employed,  hydro- 
sulphuric acid  and  sulphate  of  potassa  being  generated  :  the  elements  K  -f-  S  and 
H  -f-  O  mutually  interchange,  and  yield  K  -f-  O  and  H  -|-  S.  If  the  potassium 
be  combined  with  two  or  more  equivalents  of  sulphur  as  in  the  so  called  liver  of 
sulphur  made  by  fusing  carbonate  of  potassa  with  half  of  its  weight  of  sulphur, 
then  one  of  two  events  will  happen :  the  hydrogen  of  the  decomposed  water 
will  either  unite  with  1  eq.  of  sulphur  and  form  hydrosulphuric  acid,  the  super- 
fluous sulphur  subsiding  in  the  form  of  a  grey  hydrate,  or  with  2  eqs.  of  sulphur, 
and  give  rise  to  persulphuret  of  hydrogen.  Now,  the  former  of  these  changes 
always  occurs  when  the  acid  is  added  to  the  persulphuret  of  potassium ;  and  the 
latter  takes  place  when  a  concentrated  solution  of  that  sulphuret  is  added  by  little 
and  little  to  the  acid,  provided  the  acid  is  in  considerable  excess,  and  the  mix-- 
lure  well  stirred  after  each  addition.  The  same  phenomena  ensue  when  hydro- 
chloric instead  of  sulphuric  acid  is  employed ;  but  then  there  are  two  sources 
from  which  hydrogen  may  be  supplied.  It  may  be  derived,  as  above,  from 
decomposed  water,  hydrochlorate  of  potassa  being  generated ;  or  hydrochloric 
acid  itself  may  be  decomposed,  its  hydrogen  uniting  with  sulphur  and  its  chlo- 
rine with  potassium.  On  all  such  occasions  I  adopt  the  latter  view,  and  will 
give  reasons.for  doing  so  in  the  section  introductory  to  the  study  of  the  metals. 

Such  are  the  principles  to  be  attended  to  in  preparing  persulphuret  of  hydrogen. 
In  practice  it  is  conveniently  made  by  boiling  equal  parts  of  recently  slaked 
lime  and  flowers  of  sulphur  with  5  or  6  parts  of  water  for  half  an  hour,  when  a 
deep  orange-yellow  solution  is  formed,  which  contains  persulphuret  of  calcium. 
Let  this  liquid  be  filtered,  and  gradually  added  cold  to  an  excess  of  hydrochloric 
acid  diluted  with  about  twice  its  weight  of  water,  briskly  stirring.  A  copious 
deposit  of  sulphur  falls  (the  sulphur  praecipitatum  of  the  London  Pharmacopceia,) 
and  persulphuret  of  hydrogen  gradually  subsides  in  the  form  of  a  yellowish 
semi-fluid  matter  like  oil.  The  change  which  ensues  in  the  formation  of  the 
yellow  solution  may  be  theoretically  represented  thus  : — 

2  eq.  lime  and  6  eq.  sulphur         2       eq.  hyposulph.  acid  and  2  eq.  bisulphuret  calcium  , 
2CaOtS6  -^  S202f2CaS2. 


26C  COMPOUNDS  OF  HYDROGEN  AND  SULPHUR. 

The  hyposulphurous  acid  exists  in  solution  united  with  lime,  and  is  decomposed 
when  hydrochloric  acid  is  added,  resolving  itself  into  sulphurous  acid  and  sul- 
phur; a  change  not  essentially  connected  with  the  production  of  persul  phuret  of 
hydrogen,  but  resulting  from  the  mode  of  preparing  the  persulphuret  of  calcium. 
It  is  probable  that  the  calcium  is  combined  with  more  than  2  eqs.  of  sulphur, 
and  that  the  deposited  sulphur  is  derived  from  that  source  as  well  as  from 
decomposed  hyposulphurous  acid. 

Prop. — ^From  the  facility  with  which  this  substance  resolves  itself  into  sul- 
phur and  hydrosulphuric  acid,  its  history  is  imperfect;  we  are  indebted  to  an 
essay  by  Thenard  for  the  principal  facts  which  are  known  (An.  de  Ch.  et  Ph. 
xlviii.  79.)  At  common  temperatures  it  is  a  viscid  liquid,  of  a  yellow  colour, 
with  a  density  of  about  1*769,  and  a  consistence  varying  between  that  of  a  vola- 
tile and  fixed  oil.  It  has  the  peculiar  odour  and  taste  of  hydrosulphuric  acid, 
though  in  a  less  degree.  Its  elements  are  so  feebly  united,  that  in  the  cold  it 
gradually  resolves  itself  into  sulphur  and  hydrosulphuric  acid,  and  suffers  the 
same  change  instantly  by  a  heat  considerably  short  of  212°  F.  Decomposition 
is  also  produced  by  the  contact  of  most  substances,  especially  of  metals,  metallic 
oxides,  even  the  alkalies,  and  metallic  sulphurets.  Thus  effervescence  from  the 
escape  of  hydrosulphuric  acid  gas  is  produced  by  peroxide  of  manganese,  silica, 
the  alkaline  earths  in  powder,  and  solutions  of  potassa  or  soda;  and  the  oxides 
of  gold  and  silver  are  reduced  by  it  with  such  energy,  that  they  are  rendered 
incandescent.  It  is  remarkable  that  the  substance  which  causes  the  decomposi- 
tion often  undergoes  no  chemical  change  whatever.  In  these  respects  persul- 
phuret of  hydrogen  bears  a  close  analogy  to  peroxide  of  hydrogen ;  and  Thenard 
has  traced  other  points  of  resemblance.  They  are  both,  for  instance,  rendered 
more  stable  by  the  presence  of  acids ;  they  both  whiten  the  tongue  and  skin 
when  applied  to  them,  and  they  are  both  possessed  of  bleaching  properties. 

The  composition  of  persulphuret  of  hydrogen  has  been  variously  stated.  Ac- 
cording to  Dal  ton  it  is  a  bisul phuret,  consisting  of  two  equivalents  of  sulphur 
and  one  of  hydrogen ;  and  this  view  of  its  composition  is  corroborated  by  Sir 
John  Herschers  analysis  of  persulphuret  of  calcium  (Eden.  Phil.  Journal,  i. 
13.)  But  Thenard  found  its  constituents  to  vary;  whence  it  is  probable  that 
hydrogen  is  capable  of  uniting  with  sulphur  in  several  proportions. 

Persulphuret  of  hydrogen  is  sometimes  regarded  as  an  acid  ;  and  on  this  sup- 
position it  may  be  termed  hydropersulpkuric  acid,  and  its  salts  hydropersiilphates. 
This  view  is  founded  on  the  hypothesis,  that  the  solutions  forme^  by  boiling 
lime  or  an  alkali  with  sulphur  contain  hyposulphite  and  hydropersulphate  of 
lime,  the  hydrogen  in  the  one  acid  and  oxygen  in  the  other  being  attributed  to 
decomposed  water,  and  not  hyposulphite  of  lime  and  persulphuret  of  calcium,  as 
I  have  supposed.  The  latter  view  is  more  consistent  with  the  fact  that  persul- 
phuret of  hydrogen  in  its  free  state  has  no  acidity,  and  exhibits  no  tendency  to 
unite  with  alkalies. 

Ai  «^.  M  =  33-2  ;  symh,  H.  Sj. 


COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS.  267 


SECTION  IV. 


HYDROGEN  AND  SELENIUM.— HYDROSELENIC  ACID. 

Selenium,  like  sulphur,  forms  a  gaseous  compound  with  hydrogen,  which  has 
distinct  acid  properties,  and  is  termed  seleniuretied  hydrogen,  hydroselenic  or 
selenhydric  add.  It  is  disengaged  by  the  action  of  dilute  sulphuric  or  hydro- 
chloric acid  on  a  protoseleniuret  of  any  of  the  more  oxidahle  metals,  such  as 
potassium,  calcium,  manganese,  or  iron,  the  explanation  being  the  same  as  in  the 
formation  of  hydrosulphuric  acid  from  protosulphuret  of  iron. 

Hydroselenic  acid  gas  is  colourless.  Its  odour  is  at  first  similar  to  that  of 
hydrosulphuric  acid ;  but  it  afterwards  irritates  the  lining  membrane  of  the  nose 
powerfully,  excites  catarrhal  symptoms,  and  destroys  for  some  hours  the  sense 
of  smelling.  It  is  absorbed  freely  by  water,  forming  a  colourless  solution,  which 
reddens  litmus  paper,  and  gives  a  brown  stain  to  the  skin.  The  acid  is  soon  de- 
composed by  exposure  to  the  atmosphere ;  for  the  oxygen  of  the  air  unites  with 
the  hydrogen  of  the  hydroselenic  acid,  and  selenium,  in  the  form  of  a  red  powder, 
subsides.  It  is  decomposed  by  nitric  acid  and  chlorine  in  the  same  manner  as 
hydrosulphuric  acid  ;  and,  like  that  gas,  it  decomposes  many  metallic  salts,  the 
Hydrogen  of  the  acid  combining  with  the  oxygen  of  the  oxide,  while  an  insoluble 
seleniuret  of  the  metal  is  generated. 

According  to  the  analysis  of  Berzelius,  hydroselenic  acid  consists  of  39*6  parts 
or  I  eq.  of  selenium,  and  1  part  or  1  eq.  of  hydrogen;  so  that  its  eq.  is  40*6;  iis 
symb.  HSe. 


SECTION   V. 

COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 


The  existence  of  two  compounds  of  phosphorus  and  hydrogen,  the  phosphu- 
retted  and  perphosphuretted  hydrogen,  have,  until  lately,  been  generally  admitted 
by  chemists.  Their  composition  and  properties  have  been  closely  studied  by 
Dumas,  Buff,  Rose,  and  Graham  (An.  de  Ch.  et  Ph.  xxxi.  113;  xli.  220;  and 
xli.  5  Phil.  Mag.  v.  401).  The  investigations  of  these  chemists  concurred  in 
proving  that  phosphuretted  hydrogen  consists  of  31*4  parts  or  2  eqs.  of  phos- 
phorus, and  3  parts  or  3  eqs.  of  hydrogen ;  while  the  discordancy  in  their  ana- 
lyses of  perphosphurettpd  hydrogen  caused  great  uncertainty  respecting  its  con- 
stitution. Thus,  although  Dumas  and  Rose  agree  that  100  measures  of  perphos- 
phuretted hydrogen  contain  150  measures  of  hydrogen,  the  former  states  that  1 


2GS  COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 

part  of  hydrogen  is  united  with  15*9  of  phosphorus,  the  latter  with  10*52,  while 
Thomson  estimates  the  quantity  at  12.  The  result  of  Rose  would  indicate  that 
the  two  compounds  of  phosphorus  and  hydrogen  are  isomeric,  being  identical  in 
composition,  and  differing  in  character  only  by  the  one  being  spontaneously  in- 
flammable, and  the  other  not  so.  The  accuracy  of  the  analytical  results  of  Rose 
have  been  recently  established  by  the  discoveries  of  Leverrier  (An.  de  Ch.  et 
Ph.  Ix.  174),  who  has  proved  that  perphosphuretted  hydrogen  is  a  mixture  of 
phosphuretted  hydrogen  with  about  ^jj  of  its  volume  of  a  spontaneously  inflam- 
mable compound,  which  he  considers  to  be  composed  of  31*4  parts  or  2  eqs.  of 
phosphorus,  and  2  parts  or  2  eqs.  of  hydrogen.  In  the  same  paper  he  establishes 
the  existence  of  a  compound  formed  of  31*4  parts  or  2  eqs.  of  phosphorus,  and  1 
part  or  1  eq.  of  hydrogen.  The  compounds  of  phosphorus  and  hydrogen  are 
therefore, 


Phos. 

Hyd.    Equiv. 

FormuliB. 

Solid  Phosphuretted  Hydrogen 

31-4  2  eq.  + 

1  1  eq.  =  32-4 

P2H. 

Inflammable                   ditto. 

31-4  2  eq.  4 

2  2  eq.  =  33-4 

PjH^. 

Gaseous                          ditto. 

31-4  2  eq.  f 

3  3  eq.  =  34-4 

P2H3. 

Solid  Phosphuretted  Hydrogen. — When  phosphuretted  hydrogen  gas,  recently 
prepared  by  the  action  of  quick-lime  and  phosphorus,  is  exposed  in  the  moist 
state  to  a  strong  diffiised  light,  or  to  the  direct  rays  of  the  sun,  the  solid  phos- 
phuretted hydrogen  is  deposited  on  the  sides  of  the  glass  vessel.  It  is  also  left 
as  an  insoluble  powder  when  phosphuret  of  potassium  is  dissolved  in  water.  As 
obtained  by  the  former  process,  it  is  a  canary  yellow  flocculent  matter,  is  insolu- 
ble in  water  and  alcohol ;  but  with  the  former,  a  slow  oxidation  takes  place,  and 
hydrogen  is  evolved.  It  is  not  altered  by  a  temperature  of  234°,  but  heated  b^ 
yond  that  point  it  is  decomposed.  When  brought  into  contact  with  chlorine  and 
nitric  acid,  it  suffers  instantaneous  decomposition.  According  to  the  analysis  of 
Leverrier,  it  is  composed  of  1  part  or  1  eq.  of  hydrogen,  and  31'4  parts  or  2  eqs. 
of  phosphorus.     Hence  its  eq.  is  32*4 ;  symb.  HP2. 

PHOSPHURETTED  HYDROGEN. 

Hiit,  and  Prep, — Discovered  by  Davy  in  1812.  It  may  be  prepared  by  seve- 
ral methods.  Davy  prepared  ft  by  heating  hydrated  phosphorous  acid  in  a  retort 
(page  204);  and  it  is  evolved  from  hydrous  hypophosphorous  acid  by  similar  treat- 
ment, and  by  the  action  of  strong  hydrochloric  acid  on  phosphuret  of  calcium  ac- 
cording to  Dumas.  It  may  also  be  obtained,  but  in  an  impure  state,  by  boiling 
phosphorus  with  a  solution  of  potassa  or  milk  of  lime.  Its  production  is  in  these 
cases  dependent  on  the  decomposition  of  water,  the  oxygen  and  hydrogen  of 
which  unite  with  different  portions  of  phosphorus,  and  phosphoric  acid,  hypo- 
phosphorus  acid  and  phosphuretted  hydrogen  are  generated. 

Prop. — A  transparent  colourless  gas  of  an  exceedingly  offensive  odour  and 
bitter  taste.  It  has  no  action  on  test  paper.  It  is  absorbed  in  small  quantity  by 
water,  but  freely  by  solutions  of  chloride  of  calcium  or  sulphate  of  the  oxide  of 
copper,  by  which  means  its  purity  may  be  ascertained.  Like  sulphuretted  hy- 
drogen, it  frequently  decomposes  metallic  salts,  giving  rise  to  the  formation  of 
water  and  a  phosphuret  of  the  metal.  But  if  the  metal  have  a  feeble  affinity  foi 
oxygen,  it  is  thrown  down  in  the  metallic  state,  and  water  and  phosphoric  acid 
are  generated.  This  is  the  case,  according  to  Rose,  with  solutions  of  gold  and 
silver. 


COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS.  269 

It  is  a  non-supportei  of  combustion,  and  is  very  destructive  to  animal  life. 
When  pure,  it  may  be  mixed  with  air  or  oxygen  gas  at  common  temperatures 
without  danger ;  but  the  mixture  detonates  with  the  electric  spark  or  at  a  temper- 
ature of  300°.  Even  diminished  pressure  causes  an  explosion ;  an  effect  which, 
in  operating  with  a  mercurial  trough,  is  produced  simply  by  raising  the  tube,  so 
that  the  level  of  the  mercury  within  may  be  a  few  inches  higher  than  at  the  out- 
side. Such  is  the  property  of  the  pure  gas,  as  obtained  from  the  hydrated  phos- 
phorous or  hypophosphorous  acids ;  but  if  it  be  procured  from  the  action  of  phos- 
phorus on  potassa  or  hydrate  of  lime,  it  is  remarkable  for  being  spontaneously 
inflammable  when  mixed  with  air  or  oxygen  gas.  If  the  beak  of  the  retort  from 
which  it  issues  is  plunged  under  water,  so  that  successive  bubbles  of  the  gas 
may  arise  through  the  liquid,  a  very  beautiful  appearance  takes  place.  Each 
bubble,  on  reaching  the  surface  of  the  water,  bursts  into  flame,  and  forms  a  ring 
of  dense  white  smoke  which  enlarges  as  it  ascends,  and  retains  its  shape,  if  the 
air  is  tranquil,  until  it  disappears.  The  wreath  is  formed  by  the  products  of  the 
combustion — metaphosphoric  acid  and  water.  If  received  in  a  vessel  of  oxygen 
gas,  the  entrance  of  each  bubble  is  instantly  followed  by  a  strong  concussion,  and 
a  flash  of  white  light  of  extreme  intensity.  It  is  remarkable  that  whatever  may 
be  the  excess  of  oxygen,  traces  of  phosphorus  always  escape  combustion;  but 
that  if  the  gas  be  previously  mixed  with  three  times  its  volume  of  carbonic  acid, 
and  be  then  mixed  with  oxiygen,  the  combustion  is  perfect.  Dalton  observed 
that  it  may  be  mixed  with  pure  oxygen  in  a  tube  three-tenths  of  an  inch  in  dia- 
meter without  taking  fire ;  but  that  the  mixture  detonates  when  an  electric  spark 
is  transmitted  through  it. 

In  consequence  of  the  combustibility  of  phosphuretted  hydrogen,  it  would  be 
hazardous  to  mix  it  in  any  quantity  with  air  or  oxygen  gas  in  close  vessels.  For 
the  same  reason  care  is  necessary  in  the  formation  of  this  gas,  lest,  in  mixing 
with  the  air  of  the  apparatus,  an  explosion  ensue,  and  the  vessel  burst.  The  risk 
of  such  an  accident  is  avoided,  when  phosphuret  of  calcium  is  used,  by  filling 
the  flask  or  retort  entirely  with  dilute  acid ;  and  in  either  of  the  other  processes, 
by  causing  the  phosphuretted  hydrogen  to  be  formed  slowly  at  first,  in  order  that 
the  oxygen  gas  within  the  apparatus  may  be  gradually  consumed.  A  very  sim- 
ple method  of  averting  all  danger  has  been  mentioned  by  Graham.  It  consists 
in  moistening  the  interior  of  the  retort  with  one  or  two  drops  of  ether,  the  vapour 
of  which,  when  mixed  with  atmospheric  air  even  in  small  proportion,  effectually 
prevents  the  combustion  of  phosphuretted  hydrogen.  The  same  effect  may  be 
produced  by  the  addition  of  several  other  bodies.  He  also  finds  that  a  gas,  which 
is  not  spontaneously  inflammable,  acquires  this  property  on  being  mixed  with 
from  yoVu  ^^  Tsh^^  ^^  i^^  volume  of  nitrous  acid.  According  to  Leverrier,  it  is 
very  probable  that  there  exists  a  compound  of  phosphorus  and  hydrogen  com- 
posed of  2  eqs.  of  each  of  its  elements,  and  that  this  compound  being  sponta- 
neously inflammable  communicates  that  property  to  phosphuretted  hydrogen  gas. 
This  opinion  is  grounded  on  the  fact  that  when  spontaneously  inflammable  phos- 
phuretted hydrogen  is  kept  for  any  length  of  time  in  a  dark  place  it  suffers  no 
change,  but  if  brought  into  a  strong  light  solid  phosphuretted  hydrogen  is  depo- 
sited, and  the  residual  gas  is  no  longer  spontaneously  inflammable.  Thus  it  ap- 
pears that  by  the  action  of  light  P2H2  is  decomposed,  and  P2H  and  P2H3  are 
formed.     The  result  of  his  analysis  supports  this  view. 

[According  to  the  still  more  recent  observations  of  H.  Rose,  perfectly  dry 
phosphuretted  hydrogen  undergoes  no  change  when  kept  either  in  the  dark  or 


370^  COMPOUNDS  OF  HYDROGEN  AND  PHOSPHORUS. 

exposed  to  sunlight.  He  therefore  rejects  the  opinion  of  Leverrier,  that  the  self- 
inflammability  of  the  gas  in  question  arises  from  its  containing  another  compound 
of  phosphorus  and  hydrogen.  From  the  researches  of  Graham  this  property 
would  seem  to  be  due  to  the  presence,  in  minute  quantity,  of  some  unknown 
compound,  perhaps,  of  phoq)horus  and  oxygen,  which  in  its  action  corresponds 
to  that  of  nitrous  acid.    The  gas  examined  by  Leverrier  was  not  dry.] 

Dumas  ascertained  the  composition  of  phosphuretted  hydrogen  by  introducing 
into  a  tube  containing  the  gas  a  fragment  of  bichloride  of  mercury,  and  applying 
heat  so  as  to  convert  it  into  vapour.  Mutual  decomposition  instantly  took  place: 
phosphuret  of  mercury  and  hydrochloric  acid  were  generated;  and  100  measures 
of  gas,  thus  decomposed,  yielded  300  measures  of  hydrochloric  acid  gas,  corre- 
sponding to  150  of  hydrogen.  The  quantity  of  hydrogen  contained  in  any  given 
volume  of  phosphuretted  hydrogen  is  thus  found ;  and  the  weight  of  the  former 
deducted  from  that  of  the  latter  gives  the  quantity  of  combined  phosphorus.  This 
inference  is  conformable  to  the  quantity  of  oxygen  required  for  the  combustion 
of  phosphuretted  hydrogen.  Thomson  affirms  that  when  this  gas  is  detonated 
with  1*5  of  its  volume  of  oxygen  gas,  the  only  products  are  water  and  phospho- 
rous acid ;  but  that  when  the  oxygen  is  in  considerable  excess,  two  volumes  dis- 
appear for  one  of  the  compound,  and  water  and  phosphoric  acid  are  generated. 
Now  the  hydrogen  contained  in  one  volume  of  phosphuretted  hydrogen  is  equal 
to  1*5,  and  it  unites  with  0*75  of  oxygen.  Hence  if  0*75,  or  |,  be  deducted  from 
1*5  and  from  2,  the  remainders,  |  and  |,  represent  the  relative  quantity  of  oxy- 
gen which  is  required  to  convert  the  same  weight  of  phosphorus  into  phosphorous 
and  phosphoric  acid.  These  numbers  are  obviously  in  the  ratio  of  3  to  5,  as 
already  stated  on  the  authority  of  Berzelius  (page  203).  The  elements  of  the 
calculation  have  been  confirmed  both  by  Dumas  and  Buff. 

Agreeably  to  these  views,  and  to  the  combining  volume  of  phosphorus  (page 
140),  100  measures  of  phosphuretted  hydrogen  gas  contain  150  of  hydrogen  gas 
and  25  of  the  vapour  of  phosphorus ;  and  hence,  as 

Grains. 

150  cubic  inches  of  Hydrogen  gas  weigh 3*1977 

25  do.  Phosphorous  vapour  weigh     ....        33-5425 


100  do.  Phosphuretted  Hydrogen  gas  should  weigh  36"7402. 

The  calculated  density  of  a  gas  so  constituted  should  be  1'1853,  which  is  nearly 
a  mean  of  the  observations  of  Dumas  and  Rose. 

If  the  equivalent  of  phosphorus  were  31*4  instead  of  15*7,  as  is  very  far  from 
improbable,  then  the  combining  volume  of  phosphorous  vapour  would  be  50 
instead  of  25  (page  140) ;  and  phosphuretted  hydrogen  would  consist  of  50 
measures  of  phosphorous  vapour  and  300  of  hydrogen  gas  condensed  into  200 
measures. 

Phosphuretted  hydrogen  has  neither  an  acid  nor  alkaline  reaction ;  but  in  its 
chemical  relations  it  inclines  to  alkalinity.  Thus  it  unites  with  hydrobromic  and 
hydriodic  acids,  forming  definite  compounds  which  crystallize  in  cubes ;  and 
Rose  finds  that  it  unites  with  metallic  chlorides,  forming  compounds  analogous 
to  those  which  ammonia  forms  with  metallic  chlorides. 

Ii8  eq.  is  34*4  ;  eq.  vol.  =  100 ;  symb.  P2H3,"or  P  H3. 


COMPOUNDS  OF  NITROGEN  AND  CARBON.  <JTf 


SECTION  VI. 

COMPOUNDS  OF  NITROGEN  AND  CARBON. 

BICARBURET   OF   NITROGEN,    OR   CYANOGEN    GAS. 

Hist,  and  Prep. — Discovered  in  1815  by  Gay-Lussac  (An.  de  Ch.  xcv.).  It  is 
prepared  by  heating  carefully  dried  bicyanide  of  mercury  in  a  small  glass  retort 
by  means  of  a  spirit  lamp.  This  cyanide,  which  was  formerly  considered  a 
compound  of  oxide  of  mercury  and  prussic  acid,  and  was  then  called  prussiaie  of 
mercury,  is  composed  of  metallic  mercury  and  cyanogen.  On  exposure  to  a  low 
red  heat  it  is  resolved  into  its  elements ;  the  cyanogen  passes  over  in  the  form  of 
gas,  and  the  metallic  mercury  is  sublimed.  The  retort,  at  the  close  of  the  pro- 
cess, contains  a  small  residue  of  a  dark  brown  matter  like  charcoal,  but  which 
Johnston  has  shown  to  consist  of  the  same  ingredients  as  the  gas  itself. 

Prop, — A  colourless  gas  possessing  a  strong  pungent  and  very  peculiar  odour. 
At  the  temperature  of  45°  and  under  a  pressure  of  3*6  atmospheres,  it  is  a  lim- 
pid liquid,  which  Kemp  finds  to  be  a  non-conductor  of  electricity,  and  which 
resumes  the  gaseous  form  when  the  pressure  is  resumed.  It  extinguishes  burn- 
ing bodies ;  but  it  is  inflammable,  and  burns  with  a  beautiful  and  characteristic 
purple  flame.  It  can  support  a  strong  heat  without  decomposition.  Water  at 
the  temperature  of  60°  absorbs  4*5  times,  and  alcohol  23  times  its  volume  of  the 
gas.  The  aqueous  solution  reddens  litmus  paper ;  but  this  effect  is  not  to  be 
ascribed  to  the  gas  itself,  but  to  the  presence  of  acids  which  are  generated  by 
the  mutual  decomposition  of  cyanogen  and  water.  It  appears  from  the  observa- 
tions of  Wohler  that  two  of  the  products  are  cyanic  acid  and  ammonia ;  which, 
uniting  together,  generate  urea  (An.  de  Ch.  et  Ph.  xliii.  73). 

The  composition  of  cyanogen  may  be  determined  by  mixing  that  gas  with  a 
due  proportion  of  oxygen,  and  inflaming  the  mixture  by  electricity.  Gay-Lussac 
ascertained  in  this  way  that  100  measures  of  cyanogen  require  200  of  oxygen  for 
complete  combustion,  that  no  water  is  formed,  and  that  the  products  are  200 
measures  of  carbonic  acid  gas  and  100  of  nitrogen.  Hence  it  follows  that  cya- 
nogen contains  its  own  bulk  of  nitrogen,  and  twice  its  volume  of  the  vapour  of 
ca^^on.     Consequently,  since 

Grains. 
100  cubic  inches  of  Nitrogen  gas  weigh         .  •  .  30*166 

200  do.  the  vapour  of  Carbon  weigh      .  .  26-306 

100  cubic  inches  of  Cyanogen  gas  must  weigh  .  .  66*472 

The  ratio  of  its  elements  by  weight  is. 


Nitrogen 

. 

30-166 

0-9727 

14-15    leq. 

Carbon 

. 

26-306        . 

.        0-8430  (2  -|-  0-4215) 

12-24    2eq. 

The  sp.  gr.  of  a  gas  so  constituted  is  0*9727  -|-  0*843  =  1*8157,  which  is  near 
1*8064,  the  number  found  experimentally  by  Gay-Lussac. 


272  COMPOUNDS  OF  NITROGEN  AND  CARBON. 

Cyanogen  is  a  bicarburet  of  nitrogen,  the  formula  of  which  is  N  +  2C,  or 
NCj ;  but  its  most  convenient  name  is  cyanogen,  proposed  by  its  discoverer,* 
which  may  be  expressed  shortly  by  Cy.    Its  eg.  is  26'39. 

Paracyanogen. — ^An  examination  of  the  brown  matter,  left  in  the  retort  after 
the  preparation  of  cyanogen  gas,  has  been  made  by  Johnston,  who  by  burning  it 
with  chlorate  of  potassa  found  it  to  contain  carbon  and  nitrogen  united  in  the 
same  ratio  as  in  cyanogen  gas.  It  is,  in  fact,  a  solid  bicarburet  of  nitrogen, 
isomeric  with  cyanogen,  but  differing  from  it  essentially  in  its  physical  and  che- 
mical relations.  On  heating  this  solid  bicarburet  in  the  open  air,  several  definie 
compounds  of  carbon  and  nitrogen  may  be  successively  obtained.  After  con- 
siderable heating,  the  ratio  of  carbon  to  nitrogen  is  as  3  to  2 ;  again  heated,  the 
proportion  becomes  as  7  to  6  ;  and  finally,  after  a  still  longer  heat,  the  ratio  of 
the  equivalents  is  as  1  to  1.  Thus  the  carbon  is  gradually  burned  away,  leaving 
the  nitrogen  fixed,  until  a  protocarburet  of  nitrogen  is  formed.  On  continuing 
the  heat  after  this  period,  both  elements  fly  off  together,  and  the  whole  is  dissi- 
pated. The  solid  bicarburet  of  cyanogen  is  also  generated,  when  a  saturated 
solution  of  cyanogen  in  alcohol  is  kept  in  contact  with  mercury ;  and  Johnston 
suggests  that  the  carbonaceous  residue  after  the  charring  of  animal  substances 
by  heat,  is  probably  in  many  cases  a  carburet  of  nitrogen,  and  not  pure  charcoal^aS 
is  commonly  thought.  (Brewster's  Journ.  N.  S.  i.  75.)  Paracyanogen  is  soluble 
in  sulphuric  and  nitric  acids,  and  forms  a  compound  with  oxygen  in  which  1  eq. 
of  oxygen  is  combined  with  4  eqs.  of  nitrogen  and  8  eqs.  of  carbon.  Hence  the 
eq.  of  paracyanogen  is  probably  105*56,  and  its  sjrmb.  N4C8. 

Mellon — Is  obtained  when  sulphuret  of  cyanogen,  melame,  melamine,  amme- 
line,  or  ammelide,  is  exposed  to  a  red  heat.  It  is  a  lemon  yellow  powder,  is 
insoluble  in  water  and  alcohol,  but  is  dissolved  and  decomposed  by  acids  and 
alkalies.  Exposed  to  a  strong  red  heat,  it  is  decomposed  and  forms  1  vol.  of 
nitrogen  and  3  vols,  of  cyanogen  gas.  It  is  one  of  the  compound  radicals.  Its 
eq,  is  93*32 ;  symh.  N4C6.     (lAeb.  An.  ix.  5.) 

Cyanogen,  though  a  compound  body,  has  a  remarkable  tendency  to  combine 
with  elementary  substances.  Thus  it  is  capable  of  uniting  with  the  simple  non- 
metallic  bodies,  and  evinces  a  strong  attraction  for  metals.  When  potassium, 
for  instance,  is  heated  in  cyanogen  gas,  such  energetic  action  ensues,  that  the 
metal  becomes  incandescent,  and  cyanide  of  potassium  is  generated.  The  affinity 
of  cyanogen  for  metallic  oxides,  on  the  contrary,  is  comparatively  feeble.  It 
enters  into  direct  combination  with  a  few  alkaline  bases  only,  and  these  com- 
pounds are  by  no  means  permanent.  From  these  remarks  it  is  apparent  that 
cyanogen  has  no  claim  to  be  regarded  as  an  acid,  as  it  has  none  of  the  properties 
of  a  compound.  It  is,  in  fact,  a  compound  radical  of  organic  chemistry,  ^d 
therefore  its  various  combinations  will  be  described  in  that  part  of  the  work. 

•  From  (cuavof,  6/utf,  and  ytvva(>)f  I  generate;  because  it  is  an  essential  ingredient  of  Prus- 
sian blue. 


COMPOUND  OF  SULPHUR,  CARBON,  ETC.  <373 


SECTION  VII. 


COMPOUND  OF  PHOSPHORUS  AND  NITROGEN.  v. 

Phosphuret  of  Nitrogen. — First  described  by  Rose  (Pogg-.  An.  xxviii.  529). 
On  saturating  either  of  the  chlorides  of  phosphorus  with  dry  ammoniacal  gas,  a 
white  solid  mass  is  obtained,  which  on  exposure  to  a  strong  red  heat  gives  rise 
to  the  formation  of  phosphuret  of  nitrogen,  hydrochloric  acid  gas  being  at  the 
same  time  evolved.  It  is  also  formed  when  the  vapour  of  either  chlorides  of 
phosphorus  are  brought  into  contact  with  sal-ammonia  heated  nearly  to  its  point 
of  sublimation. 

It  is  a  light  snow-white  powder ;  is  insoluble  in  water,  and  in  dilute  acid,  or 
alkaline  solutions.  It  is  not  changed  by  a  red  heat  in  close  vessels,  or  in  an 
atmosphere  of  chlorine,  or  the  vapour  of  sulphur ;  but  in  hydrogen  it  is  decom- 
posed with  the  formation  of  ammoniacal  gas.  It  is  composed  of  31*4  parts  or  2 
eqs.  of  phosphorus,  and  14' 15  parts  or  1  eq.  of  nitrogen. 

Its  eg.  is  45'55 ;  symb.  N  -}-  2P,  or  NPg. 


SECTION  VIII. 


COMPOUND  OF  SULPHUR,  CARBON,  ETC. 

The  compounds  described  in  this  section  are  thus  constituted  : — 

Bisulph.  of  Carbon  Carb.     6- 12  -f-  Sulp.  32-2  =  38-32.  C  -f  2  S  CSj. 

Sulph.  of  Phosphorus  Composition  uncertain.  ^ 

Bisulph.  of  Selenium  Selen.   39-6 -|- Sulp.  32-2  =71-8  Se-|-2SSeS2. 

Seleni.  of  Phosphorus  Composition  uncertain. 

Bisulphuret  of  Carbon. — Hist. — This  substance  was  discovered  accidentally 
in  the  year  1796  by  Professor  Lampadius,  who  regarded  it  as  a  compound  of  sul- 
phur and  hydrogen,  and  termed  it  alcohol  of  sulphur.  Clement  and  Desormes  first 
declared  it  to  be  a  sulphuret  of  carbon,  and  their  statement  was  fully  confirmed 
by  the  joint  researches  of  Berzelius  and  the  late  Dr.  Marcet  (Phil.  Trans.  1813). 

Prep. — Bisulphuret  of  carbon  may  be  obtained  by  heating  in  close  vessels 
native  bisulphuret  of  iron  (iron  pyrites)  with  one-fifth  of  its  weight  of  well-dried 
charcoal;  or  by  transmitting  the  vapour  of  sulphur  over  fragments  of  charcoal 
heated  to  redness  in  a  tube  of  porcelain.  The  compound,  as  it  is  formed,  should 
be  conducted  by  means  of  a  glass  tube  into  cold  water,  at  the  bottom  of  which 
it  is  collected.  To  free  it  from  moisture  and  adhering  sulphur,  it  should  be  dis- 
tilled at  a  low  temperature  in  contact  with  chloride  of  calcium. 

20 


274  COMPOUNDS  OF  SULPHUR  AND;  PHOSPHORUS. 

Prop. — It  is  a  transparent  colourless  liquid,  which  is  remarkable  for  its  high 
refractive  power.  Its  sp.  gr.  is  1-272;  of  its  vapour,  2G68.  It  has  an  acid, 
pungent,  and  somewhat  aromatic  taste,  and  a  very  fetid  odour.  It  is  exceedingly 
volatile;  its  vapour  at  63-5°  supports  a  column  of  mercury  7*36  inches  long;  and 
at  110°  it  enters  into  brisk  ebullition.  From  its  great  volatility  it  may  be  em- 
ployed for  producing  intense  cold.  It  is  very  inflammable,  and  kindles  in  the 
open  air  at  a  temperature  scarcely  exceeding  that  at  which  mercury  boils.  It 
burns  with  a  pale  blue  flame.  Admitted  into  a  vessel  of  oxygen  gas,  so  much 
vapour  rises  as  to  form  an  explosive  mixture ;  and  when  mixed  in  like  manner 
with  binoxide  of  nitrogen,  it  forms  a  combustible  mixture,  which  is  kindled  on 
the  approach  of  a  lighted  taper,  and  burns  rapidly,  with  a  large  greenish-white 
flame  of  dazzling  brilliancy.  It  dissolves  readily  in  alcohol  and  ether,  and  is 
precipitated  from  the  solution  by  water.  It  dissolves  sulphur,  phosphorus,  and 
iodine,  and  the  solution  of  the  latter  has  a  beautiful  pink  colour.  Chlorine  de- 
composes it,  with  formation  of  chloride  of  sulphur.  The  pure  acids  have  little 
action  upon  it.  By  nitro-hydrochloric  acid  it  is  changed  into  a  white  crystalline 
substance  like  camphor,  which  Berzelius  regards  as  a  compound  of  the  hydro- 
chloric, carbonic,  and  sulphurous  acids. 

Bisulphuret  of  carbon  is  a  sulphur-acid,  that  is,  unites  with  sulphur-bases  to 
constitute  compounds  analogous  to  ordinary  salts,  and  hence  called  sulphur'SaUs. 
Thus  bisulphuret  of  carbon  unites  with  sulphuret  of  potassium,  forming  a  sul- 
phur-salt, in  which  the  former  acts  as  an  acid  and  the  latter  as  a  base.  The 
same  compound  is  formed  by  the  action  of  bisulphuret  of  carbon  on  a  solution  of 
pure  potassa  :  but  in  this  case  sulphuret  of  potassium  is  .first  generated  by  an  inter- 
change of  elements  with  a  portion  of  bisulphuret  of  carbon,  carbonic  acid  being 
produced  at  the  same  time.    Thus — 

2  eq.  potassa  &  1  eq.  bisulph.  carbon  2   2  eq.  sulphuret  potassium  and  1  eq.  carb.  acid. 
2KOfCS8  S.  2KS-J-CO2. 

If  the  bisulphuret  of  carbon  is  in  sufficient  quantity,  carbonic  acid  gas  is  disen- 
gaged, and  a  neutral  compound  results.  Such  is  inferred  to  be  the  nature  of  the 
change,  agreeably  to  the  researches  of  Berzelius  on  the  sulphur-salts. 

Its  eq.  is  38  32 ;  eq.  vol.  ==  100 ;  symb,  CS,. 

Sulphuret  of  Phosphorus. — When  sulphur  and  fused  phosphorus  are  brought 
into  contact  they  unite  readily,  but  in  proportions  which  have  not  been  precisely 
determined ;  and  they  frequently  react  on  each  other  with  such  violence  as  to 
cause  an  explosion.  For  this  reason  the  experiment  should  be  made  with  a 
quantity  of  phosphorus  not  exceeding  30  or  40  grains.  The  phosphorus  is  placed 
in  a  glass  tube,  5  or  6  inches  long,  and  about  half  an  inch  wide  ;  and  when  by  a 
gentle  heat  it  is  liquefied,  the  sulphur  is  added  in  successive  small  portions.  Heat 
is  evolved  at  the  moment  of  combination,  and  hydrosulphuric  and  phosphoric 
acids,  owing  to  the  presence  of  moisture,  are  generated.  This  compound  may 
also  be  made  by  agitating  flowers  of  sulphur  with  fused  phosphorus  underwater. 
The  temperature  should  not  excoed  160°;  for  otherwise  hydrosulphuric  and  phos- 
phoric acids  would  be  evolved  so  freely  as  to  prove  dangerous,  or  at  least  to  in- 
terfere with  the  success  of  the  process. 

Sulphuret  of  phosphorus,  from  the  nature  of  its  elements,  is  highly  combustible. 
It  is  much  more  fusible  than  phosphorus.  A  compound  made  by  Faraday  with 
about  5  parts  of  sulphur  and  7  of  phosphorus,  was  quite  fluid  at  32°,  and  did  not 
solidify  at  20°  (Quarterly  Journal,  iv.). 


COMPOUNDS  OF  SELENIUM  AND  PHOSPHORUS.  275 

Bisulphuret  of  Selenium. — Sulphur  and  selenium  mix  together  in  all  propor- 
tions by  fusion,  and  therefore  by  such  means  it  is  difficult  to  procure  a  definite 
compound  ;  but  the  bisulphuret  of  an  arange  colour  was  formed  by  Berzelius  by 
precipitating  a  solution  of  selenious  acid  with  hydrosulphuric  acid.  The  sul- 
phuret  found  by  Stromeyer  among  the  volcanic  products  of  the  Lipari  isles  is 
probably  similar  in  composition.  Bisulphuret  of  selenium  fuses  at  a  heat  a  little 
above  212°,  and  at  a  higher  temperature  may  be  sublimed  without  change.  In 
the  open  air  it  takes  fire  "Wfhen  heated,  and  sulphurous,  selenious,  and  %elenic 
acids  are  the  products  of  its  combustion.  The  alkalies  and  soluble  metallic  sul- 
phurets  dissolve  it.  Nitric  acid  acts  upon  it  with  difficulty  ;  but  the  nitro-hydro- 
chloric  converts  it  into  sulphuric  and  selenious  acids.     (An.  of  Phil,  xiv.) 

Sekmuret  nf  Phosphorus. — This  compound  may  be  prepared  in  the  same  man- 
ner as  the  sulphuret  of  phosphorus  ;  but  as  selenium  is  capable  of  uniting  with 
phosphorus  in  several  proportions,  the  compound  formed  by  fusing  them  together 
can  hardly  be  supposed  to  be  of  a  definite  nature.  This  seleniuret  is  very  fusible, 
sublimes  without  change  in  close  vessels,  and  is  inflammable.  It  decomposes 
water  gradually  when  digested  in  it,  giving  rise  to  seleniuretted  hydrogen,  and 
one  of  the  acids  of  phosphorus. 

Sulphuret  of  Nitrogen. — This  compound  is  formed,  according  to  Soubeiran,  by 
the  action  of  water  on  a  compound  of  chloride  of  sulphur  and  ammonia,  SCI  -f- 
2NH3.  The  sulphuret  of  nitrogen  is  a  yellow  or  green  solid,  the  colour  of  which 
varies  according  to  the  mode  of  preparation.  It  is  converted,  by  digestion  with 
water,  entirely  into  hyposulphurous  acid  and  ammonia ;  hence  its  composition  is 
NS3  and  2NS3  t  6H0  =  2NH3  +  SS.O^. 

When  aqua  ammonias  acts  on  chloride  of  sulphur  a  red  solid  compound  is 
formed  which  is  composed  of  chloride  of  sulphur,  sulphuret  of  nitrogen,  and  am- 
monia. This  body  undergoes  spontaneous  decomposition,  and  is  converted  into 
a  yellow  pulverulent  mass  (Soubeiran).  When  this  mass,  which  consists  chiefly 
of  sulphur,  is  boiled  with  alcohol,  or  exhausted  by  percolation  with  cold  alcohol, 
the  alcohol  dissolves  a  substance  in  small  quantity,  which  may  be  had  in  white 
needles  or  cubical  crystals,  and  which  contains  92  —  93  p.  c.  sulphur  and  5  —  6 
p.  c.  nitrogen.  Gregory,  who  discovered  this  compound,  thought  that  it  might 
be  a  sulphuret  of  nitrogen.  But  in  its  analysis  he  always  obtained  a  little  hydro- 
gen, and  the  nature  of  this  substance  was  left  unsettled.  Soubei^in  is  of  opinion 
that  it  contains  sulphur,  nitrogen,  and  ammonia.  The  quantity  of  sulphur,  how- 
ever, is  so  large,  that  its  constitution  must  be  unusual ;  and  it  merits  a  careful 
examination.  Gregory  showed  that  its  solution  in  alcohol,  when  mixed  with  an 
alcoholic  solution  of  caustic  potash,  acquires  a  deep  amethyst  colour,  which  soon 
disappears,  while  ammonia  is  set  free,  pure  hyposulphate  of  potash  is  deposited, 
and  traces  of  a  volatile  compound,  probably  formed  at  the  expense  of  the  alcohol, 
are  observed. 


METALS. 


GENERAL  PROPERTIES  OF  METALS. 

Metals  are  distinguished  from  other  substances  by  the  following  properties. 
They  are  all  conductors  of  electricity  and  heat.  When  the  compounds  which 
they  form  with  oxygen,  chlorine,  iodine,  sulphur,  and  similar  substances,  are 
submitted  to  the  action  of  galvanism,  the  metals  always  appear  at  the  negative 
side  of  the  battery,  and  are  hence  said  to  be  positive  electrics.  They  are  quite 
opaque,  refusing  a  passage  to  light,  though  reduced  to  very  thin  leaves.  They 
are  in  general  good  reflectors  of  light,  and  possess  a  peculiar  lustre,  which  is 
termed  the  metallic  lustre.  Every  substance  in  which  these  characters  reside 
may  be  regarded  as  a  metal. 

The  number  of  metals,  the  existence  of  which  is  admitted  by  chemists,  amounts 
to  forty-two.  The  following  table  contains  the  names  of  those  that  have  been 
procured  in  a  state  of  purity,  together  with  the  date  at  which  they  were  discov- 
ered, and  the  names  of  the  chemists  by  whom  the  discovery  was  made. 

Table  qf  the  DiscMery  of  Metals. 


Names  of  Metals. 


Gold 

Silver 

Iron 

Copper 

Mercury 

Lead 

Tin 

Antimony 

Bismuth 

Zinc 

Arsenic 

Cobalt 

Platinum 

Nickel 

Manganese 

Tungsten 

Tellurium 

Molybdenum 

Uranium  . 

Titanium  . 

Chromium 


Authors  of  the  Discovery. 


Known  to  the  Ancients. 


Described  by  Basil  Valentine 
Described  by  Agricola  in  . 
First  mentioned  by  Paracelsus 


Brandt,  in    . 

Wood,  assay.master,  Jamaica 
Cronstedt     .        . 
Gahn  and  Scheele 
D'Elhuyart  .... 
Muller  .        .        ,        . 

Hielm  .... 

Klaproth      .... 
Gregor  .... 

Vauquelin    .... 


Dates  of  the 
Discovery. 


1490 

1530 

16th  century 

1733 

1741 
1751 
1774 
1781 
1782 
1782 
1789 
1791 
1797 


GENERAL  PROPERTIES  OF  METALS. 

Table  of  the  Discovery  of  Metals — {continued). 


277 


Names  of  Metals. 


Columbium 
Palladium 
Rhodium  . 
Iridium  . 
Osmium  . 
Cerium  . 
Potassium 
Sodium  . 
Barium 
Strontium 
Calcium  . 
Cadmium  . 
Lithium  . 
Zirconium 
Aluminium 
Glucinium 
Yttrium  . 
Thorium  . 
Magnesium 
Vanadium 
Lantanium 


Authors  of  the  Discovery. 


Hatchett 

Wollaston 

Descotils  and  Smithson  Tennant 
Smithson  Tennant 
Hisinger  and  Berzelius 

Davy 

Stromeyer 

Arfwedson 

Berzelius     .        ,        .        .        . 

Wohler 

Berzelius  .        .        .        .        . 

Bussy  .        ,        .        ,        . 

Sefstrbm 

Mosander 


Dates  of  the 
Discovery. 


1802 

1803 

1803 
1803 
1804 

1807 


1818 
1818 
1824 

1828 

1829 
1829 
1830 
1839 


Most  of  the  metals  are  remarkable  for  their  great  specific  gravity ;  some  of 
them,  such  as  gold  or  platinum,  which  are  the  densest  bodies  known  in  nature, 
being  more  than  19  times  heavier  than  an  equal  bulk  of  water.  Great  density 
was  once  supposed  to  be  an  essential  characteristic  of  metals ;  but  the  discovery 
of  potassium  and  sodium,  which  are  so  light  as  to  float  on  the  surface  of  water, 
has  shown  that  this  supposition  is  erroneous.  Some  metals  experience  an 
increase  of  density  to  a  certain  extent  when  hammered,  their  particles  being 
permanently  approximated  by  the  operation.  On  this  account,  the  density  of 
some  of  the  metals  contained  in  the  following  table  is  represented  as  varying 
between  two  extremes. 


Table  of  the  Specific  Gravity  of  Metals  at  60°  Fahr.  compared  to  Water  as  Unity. 

Platinum            .            .            2098 

Brisson. 

Gold 

19-257 

Do. 

Tungsten 

17-6 

D'Elhuyart. 

Mercury 

13-568 

Brisson. 

Palladium 

11-3  to  11-8    . 

Wollaston. 

Lead 

11-352 

Brisson. 

Silver 

10-474 

Do. 

Bismuth 

9-822 

Do. 

Uranium 

9000 

Bucholz. 

Copper 

8-895 

Hatchett. 

Cadmium 

8-604 

Stromeyer. 

Cobalt 

8-538 

HaUy. 

Arsenic 

5-8843 

Turner. 

Nickel 

8-279 

Richter. 

Iron 

7-788 

Brisson. 

Molybdenum 

7-400 

Hielm. 

Tin 

7-291 

Brisson. 

Zinc 

6-861  to7  1. 

Do. 

578 


GENfeRAL  PROPERTIES  OF  METALS. 


Ifaaganese 

6-SoO 

Aatimony 

6-702 

Tellttriam 

6115 

Tit&niam 

53 

Sodiam 

0-972^ 
0-S655 

Potassiam 

Bergmann. 

BrissoD. 

Klaproth. 

Wolla8ton. 

Gay.Lussac  and 

Thenard. 


Some  metals  possess  the  property  of  fnalkabiUiy,  that  is,  admit  of  being  beaten 
into  thin  plates  or  leaves  by  hammering.  The  malleable  metals  are  gold,  silver, 
copper,  tin,  platinam,  palladium,  cadmimn,  lead,  zinc,  iron,  nickel,  potassium, 
sodium,  and  frozen  mercury.  The  other  metals  are  either  malleable  in  a  very 
small  degree  only,  or,  like  antimony,  arsenic  and  bismuth,  are  actually  brittle. 
Gold  surpasses  all  metals  in  malleability :  one  grain  of  it  may  be  extended  so  as 
to  cover  about  52  square  inches  of  snr&ce,  and  to  have  a  thickness  not  exceed- 
ing 79}  fs^tk  of  2n  inch. 

Nearly  all  malleable  metals  may  be  drawn  oat  into  wires,  a  property  which  is 
expressed  by  the  term  ductility.  The  only  metals  which  are  remarkable  in  this 
respect  are  gold,  silver,  platinum,  iron,  and  copper.  WoUaston  devised  a  method 
by  which  gold  wire  may  be  obtained  so  fine  that  its  diameter  shall  be  only 
b^Jio^  of  an  inch,  and  that  550  feet  of  it  are  required  to  weigh  one  grain.  He 
obtained  a  platinum  wire  so  small,  that  its  diameter  did  not  exceed  ?ixii;iT<i>  ^^  ^^ 
inch  (Phil.  Trans.  1813).  It  is  singular  that  the  ductility  and  malleability  of 
the  same  metal  are  not  always  in  proporticm  to  each  other.  Iron,  for  example, 
cannot  be  made  into  fine  leaves,  but  it  may  be  drawn  into  very  small  wires. 

The  tenacity  of  metals  is  measured  by  ascertaining  the  greatest  weight  which 
a  wire  of  a  certain  thickness  can  support  without  breaking.  According  to  the 
experiments  of  Guyton-Morveau,  whose  results  are  comprised  in  the  following 
table,  iron,  in  point  of  tenacity,  surpasses  all  other  metals. 

The  diameter  of  each  wire  was  0*  787th  of  a  line. 


Iron  wire  supports 

Copper     . 

Platinam  . 

SilTer 

Gold 

Zinc 

Tin 

Lead 

According  to  some  recent  observations  of  Baudrimont,  the  process  of  anneal- 
ing destroys  the  tenacity  of  metals  to  a  considerable  extent.  Thus  he  found 
that  a  wire  of  soft  iron  which  supported  a  weight  of  26  lbs.,  on  being  annealed 
could  only  bear  12  lbs. ;  and  a  copper  wire  which  could  support  22  lbs.  was 
broken,  when  annealed,  by  9  lbs.  Numerous  experiments  with  difierent  speci- 
mens of  brass  wire  confirm  the  generality  of  the  result  (An.  de  Ch.  et  Ph.  Ix.  78). 

Metals  differ  also  in  hardness ;  but  I  am  not  aware  that  their  exact  relation  to 
each  other,  under  this  point  of  view,  has  been  determined  by  experiment!  In  the 
list  of  hard  metals  may  be  placed  titanium,  manganese,  iron,  nickel,  copper,  zinc, 
and  palladium.  Gold,  silver,  and  platinum  are  softer  than  these;  lead  is  softer 
still,  and  potassium  and  sodium  yield  to  the  pressure  of  the  fingers.  The  pro- 
perties of  elasticity  and  sonorousness  are  allied  to  that  of  hardness.  Iron  and 
copper  are  in  these  respects  the  most  conspicuous. 


Ponnds. 

549  25 

302-278 

274-32 

187- 137 

150-753 

109-54 

34-63 

27  621 

GENERAL  PROPERTIES  OF  METALS. 


279 


Many  of  the  metals  have  a  distinctly  crystalline  textore.  Iron,  for  example, 
is  fibrous;  and  zinc,i>ismnth,  and  antimony  are  lamellated.  Metals  are 'some- 
times obtained  also  in  crystals;  and  most  of  them  in  crystallizing  assume  the 
figure  of  a  cube,  the  regular  octohedron,  or  some  fonn  allied  to  it.  Gold,  silver, 
and  copper  occur  naturally  in  crystals  ;  while  others  crystallize  when  they  pass 
gradually  from  the  liquid  to  the  solid  condition.  Crystals  are  most  readily  pro- 
cured from  those  metals  which  fuse  at  a  low  temperature ;  and  bismuth,  from 
conducting  heat  less  perfectly  than  other  metals,  and  therefore  cooling  more 
slowly,  is  best  fitted  for  the  purpose.  The  process  should  be  conducted  in  the 
way  already  described  for  forming  crystals  of  sulphur. 

Metals,  with  the  exception  of  mercury,  are  solid  at  common  temperatures ;  but 
they  may  all  be  liquefied  by  heat.  The  degree  at  which  they  /u»e,  or  their  point 
of  fusion,  is  very  different  for  different  metals,  as  appears  from  the  following 
table : — 


2ViUe  <tf  the  futOrilUy  cf  d^erent  MetaU. 


Faaible  below  a 
red  heat 


Infusible  below  a 
red  heat. 


Mercury  .... 
Potassium  .... 
Sodium  .... 

Tin  .... 

Bismuth  .... 
Lead  .... 

Tellurium — rather  less  fusible 

tbao  lead  .... 
Arsenic — undetermined. 
Zinc  .... 

Antimony — a  little  below  a  red 

heat.  .... 

Cadmium       .        .        about 

Silver 

Copper 


Gold 

Cobalt — rather  less  fusible  than 

iron.  .... 

Iron,  cast       .... 
Iron,  malleable      .        .         .     ) 
Manganese    .         .         .         .     j 
Nickel — nearly  the  same  as 

cobalt. 


Fahr. 

—39°    Different  cbemiats. 

190  \  ^^1'^""^  ^^  Thenaid. 
442  ) 

497  SCrichton. 
612  ) 

Klaproth. 

773      Daniell. 


442      Stromcycr. 

1873  ) 

1996  >  Daniell. 

2016  J 


2786      DaaieU. 

Requiring  the   highest  heat  of 
smith*8  forge. 


Palladium. 
Molybdenum 
Uranium 
Tungsten 
Chromium 
Titanium 
Cerium 
Lantanium 
Osmium 
Iridium 
Rhodium 
Platinum 
VColumbium 


{ 


Almost   infiisible,   and   not 
to  be  procured  in  buttons 
by  the  heat  of  a  smith 
forge. 


■»n  F, 
Jp» 


Fusible  before  the 
oxy  .hydrogen  Mow. 
pipe- 


Infusible  in  the  heat  of  a  smith's  forge,  bnt  fasible 
before  the  oiy-hydrogen  blowpipe. 


Metals  differ  also  in  volatility.  Some  are  readily  volatilized  by  heat,  while 
others  are  of  so  fixed  a  nature  that  they  may  be  exposed  to  the  most  intense  heat 
of  a  wind  furnace  without  beino-  dissipated  in  vapour.  There  are  seven  metals,  the 
volatility  of  which  has  been  ascertained  with  certainty ;  namely,  cadmium,  mer- 
cury, arsenic,  tellurium,  potassium,  sodium,  and  zinc. 

Metals  cannot  be  resolved  into  more  simple  parts ;  and  therefore,  in  the  presoit 
state  of  chemistry,  they  must  be  regarded  as  elementary  bodies.  It  was  iormsiij 


280  GENERAL  PROPERTIES  OF  METALS. 

conceived  that  they  might  be  converted  into  each  other ;  and  this  notion  led  to 
the  vawi  attempts  of  the  alchemists  to  convert  the.  baser  n^tals  into  gold.  The 
chemist  has  now  learned  that  his  art  solely  consists  in  resolving  compound  bodies 
.into  their  elements,  and  causing  substances  to  unite  which  were  previously,  un- 
combined.  Gne  elementary  principle  cannot  assume  the  properties  peculiar  to 
another. 

Metals  have  an  extensive  range  of  affinity,  and  on  this  account  few  of  them 
are  found  in  the  earth  native,  that  is,  in  an  uncombined  form.  They  commonly 
occur  in  combination  with  other  bodies,  especially  with  oxygen  and  sulphur,  in 
which  state  they  are  said  to  be  mineralized.  It  is  a  singular  fact  in  the  chemical 
history  of  the  metals,  that  they  are  little  disposed  to  combine  in  the  metallic 
state  with  compound  bodies,  such  as  an  oxide  or  an  acid.  They  unite  readily, 
on  the  contrary,  with  elementary  substances.  Thus  they  often  combine  with 
each  other,  yielding  compounds  termed  alloys,  which  possess  all  the  characteristic 
physical  properties  of  pure  metals.  They  unite  likewise  with  the  simple  non- 
metallic  substances,  such  as  oxygen,  chlorine,  and  sulphur,  giving  rise  to  new 
bodies  in  which  the  metallic  character  is  wholly  wanting.  In  all  these  combina- 
tions the  same  tendency  to  unite  in  a  few  definite  proportions,  is  equally  con- 
spicuous as  in  that  department  of  the  science  of  which  I  have  just  completed  the 
description.  The  chemical  changes  are  regulated  by  the  same  general  laws,  and 
in  describing  them  the  same  nomenclature  is  applicable. 

The  order  which  it  is  proposed  to  follow  in  describing  the  metals  has  already 
been  explained  in  the  introduction  ;  but  before  treating  of  each  separately,  some 
general  observations  may  be  premised,  by  which  the  study  of  this  subject  will  be 
nmch  facilitated. 

Metals  are  of  a  combustible  nature,  that  is,  they  are  not  only  susceptible  of 
slow  oxidation,  but,  under  favourable  circumstances,  they  unite  rapidly  with 
oxygen,  giving  rise  to  all  the  phenomena  of  real  combustion.  Zinc  burns  with 
^  brilliant  flame  when  heated  to  full  redness  in  the  open  air ;  iron  emits  vivid 
scintillations  on  being  inflamed  in  an  atmosphere  of  oxygen  gas  ;  and  the  least 
oxidable  metals,  such  as  gold  and  platinum,  scintillate  in  a  similar  manner  when 
heated  by  the  oxy-hydrogen  blowpipe. 

The  product  either  of  the  slow  or  rapid  oxidation  of  a  metal,  when  heated  in 
the  air,  has  an  earthy  aspect,  and  was  called  a  calx  by  the  older  chemists,  the 
process  of  forming  it  being  expressed  by  the  term  ealcinaiion.  Another  method 
of  oxidizing  metals  is  by  deflagration  j  that  is,  by  mixing  them  with  nitrate  or 
chlorate  of  potassa,  and  projecting  the  mixture  into  a  red-hot  crucible.  Most 
metals  may  be  oxidized  by  digestion  in  nitric  acid ;  and  nitro-hydrochloric  acid 
is  an  oxidizing  agent  of  still  greater  power. 

Some  metals  unite  with  oxygen  in  one  proportion  only,  but  most  of  them  have 
two  or  three  degrees  of  oxidation.  Metals  differ  remarkably  in  their  relative 
forces  5f  attraction  for  oxygen.  Potassium  and  sodium,  for  example,  are  oxidized 
by  mere  exposure  to  the  air ;  and  they  decompose  water  at  all  temperatures  the 
instant  they  come  in  contact  with  it.  Iron  and  copper  may  be  preserved  in  dry 
air  without  change,  nor  can  they  decompose  water  at  common  temperatures ;  but 
they  are  both  slowly  oxidized  by  exposure  to  a  moist  atmosphere,  and  combine 
rapidly  with  oxygen  when  heated  to  redness  in  the  open  air.  Iron  has  a  stronger 
affinity  for  oxygen  than  copper  ;  for  the  former  decomposes  water  at  a  red  heat, 
whereas  the  latter  caunot  produce  that  effect.  Mercury  is  less  inclined  than 
copper  to  unite  with  oxygen.    Thus  it  may  be  exposed  without  change  to  the 


GENERAL  PROPERTIES  OF  METALS.  281 

influence  of  a  moist  atmosphere.  At  a  temperature  of  650°  or  700°  it  is  oxidized ; 
butat  a  red  heat  it. is  reduced  to  the  metallic  state,  while  oxide  of  copper  can 
sustain  the  strongest  heat  of  a  blast  furnace  without  losing  its  oxygen.  The 
affinity  of  gold  for  oxygen  is  still  weaker  than  that  of  mercury  ;  for  it  will  bear 
the  most  intense  heat  of  our  furnaces  without  oxidation. 

Metallic  oxides  suffer  reduction,  or  may  be  reduced  to  the  metallic  state  in 
several  ways : 

1.  By  heat  alone.  By  this  method  the  oxides  of  gold,  silver,  mercury,  and 
platinum,  may  be  decomposed. 

2.  By  the  united  agency  of  heat  and  combustible  matter,  Thus,  by  transmit- 
ting a  current  of  hydrogen  gas  over  the  oxides  of  copper  or  iron  heated  to  redness 
in  a  tube  of  porcelain,  water  is  generated,  and  the  metals  are  obtained  in  a  pure 
form.  Carbonaceous  matters  are  likewise  used  for  the  purpose  with  great  suc- 
cess. Potassa  and  soda,  for  example,  may  be  decomposed  by  exposing  them  to 
a  white  heat  after  being  intimately  mixed  .with  charcoal  in  fine  powder.  A  simi- 
lar process  is  employed  in  metallurgy  for  extracting  metals  from  their  ores,  the 
inflammable  materials  being  wood,  charcoal,  coke,  or  coal.  In  the  more  delicate 
operations  of  the  laboratory,  charcoal,  black  Jlux,  and  formiate  of  soda  are  pre- 
ferred. *     .  . 

3.  By  the  galvanic  battery.  This  is  a  still  more  powerful  agent  than  the  pre- 
ceding ;  since  some  oxides,  such  as  baryta  and  strontia,  which  resist  the  united 
influence  of  heat  and  charcoal,  are  reduced  by  the  agency  of  galvanism. 

4.  By  the  action  of  deoxidizing  agents  on  metallic  solutions.  Phosphorous 
acid,  for  example,  when  added»to  a  liquid  containing  oxide  of  mercury,  deprives 
the  oxide  of  its  oxygen,  metallic  mercury  subsides,  and  phosphoric  acid  is  gene- 
rated. Formic  acid  and  formiate  of  soda,  when  boiled  with  the  solutions  of  the 
oxides  of  gold,  platinum,  silver,  mercury,  &c.  reduces  the  metals.  In  like  man- 
ner, one  metal  may  be  precipitated  by  another,  provided  the  affinity  of  the  latter 
for  oxygen  exceeds  that  of  the  former.  Thus,  when  mercury  is  added  to  a  solu- 
tion of  nitrate  of  the  oxide  of  silver,  metallic  silver  is  thrown  down,  and  oxide 
of  mercury  is  dissolved  by  the  nitric  acid.  On  placing  metallic  copper  in  the 
liquid,  pure  mercury  subsides,  and  a  nitrate  of  the  oxide  of  copper  is  formed ;  and 
from  this  solution  metallic  copper  may  be  precipitated  by  means  of  iron. 

Metals,  like  the  simple  non-metallic  bodies,  may  give  rise  to  oxides  or  acids 
by  combining  with  oxygen.  The  former  are  the  most  frequent  products.  Many 
metals  which  are  not  acidified  by  oxygen  may  be  formed  into  oxides;  whereas 
one  metal  only,  arsenic,  is  capable  of  forming  an  acid  and  not  an  oxide.  All 
the  other  metals  which  are  convertible  into  acids  by  oxygen,  such  as  chromium, 
tungsten,  and  molybdenum,  are  also  susceptible  of  yielding  one  or  more  oxides. 
In  these  instances,  the  acids  always  contain  a  larger  quantity  of  oxygen  than 
the  oxides  of  the  same  metal. 

Many  of  the  metallic  oxides  have  the  property  of  combining  with  acids.  In 
some  instances  all  the  oxides  of  a  metal  are  capable  of  forming  salts  with  acids, 
as  is  exemplified  by  the  oxides  of  iron;  but,  generally,  the  protoxide  is  the  sole 
alkaline  or  salijiahle  hose.  Most  of  the  metallic  oxides  are  insoluble  in  water;  but 
all  those  that  are  soluble  have  the  property  of  giving  a  brown  stain  to  yellow 
turmeric  paper,  and  of  restoring  the  blue  colour  of  reddened  litmus. 

Oxides  sometimes  unite  with  each  other,  and  form  definite  compounds.  The 
most  abundant  ore  of  chromium,  commonly  called  chromate  of  iron,  is  an  instance 


282  GENERAL  PROPERTIES  OF  METALS. 

of  this  kind ;  and  the  red  oxide  of  manganese,  the  magnetic  oxide  of  iron,  and 
the  red  oxide  of  lead,  appear  to  belong  to  the  same  class  of  bodies. 

Chlorine  has  a  powerful  affinity  for  metallic  substances.  It  combines  readily 
with  most  metals  at  common  temperatures,  and  the  action  is  in  many  instances 
so  violent  as  to  be  accompanied  with  the  evolution  of  light.  For  example,  when 
powdered  zinc,  arsenic,  or  antimony  is  thrown  into  a  jar  of  chlorine  gas,  the 
metal  is  instantly  inflamed.  The  attraction  of  chlorine  for  metals  even  surpasses 
that  of  oxygen.  Thus,  when  chlorine  is  brought  into  contact  at  a  red  heat  with 
pure  lime,  magnesia,  baryta,  strontia,  potassa  or  soda,  oxygen  is  emitted,  and  a 
chloride  of  the  metal  is  generated,  the  elements  of  which  are  so  strongly  united 
that  no  temperature  hitherto  tried  can  separate  them.  All  other  metallic  oxides 
are,  with  few  exceptions,  acted  on  in  the  same  manner  by  chlorine,  and  in  some 
cases  the  change  takes  place  below  the  temperature  of  ignition. 

Most  of  the  metallic  chlorides  are  solid  at  common  temperatures.  They  are 
fusible  by  heat,  assume  a  crystalline  texture  in  cooling,  and  under  favourable 
circumstances  crystallize  with  regularity.  Several  of  them,  such  as  the  chlorides 
of  tin,  arsenic,  antimony,  and  mercury,  are  volatile,  and  may  be  sublimed  with- 
out change.  They  are  for  the  most  part  colourless,  do  not  possess  the  metallic 
lustre,  and  have  the  aspect  of  a  salt.  Two  of  the  chlorides  are  insoluble  in 
water,  namely,  chloride  of  silver  and  protochloride  of  mercury ;  several,  such  as 
the  chlorides  of  antimony,  arsenic  and  titanium,  are  decomposed  by  that  liquid  ; 
but  most  of  them  are  more  or  less  soluble. 

Some  of  the  metallic  chlorides,  those  especially  of  gold  and  platinum,  are  de- 
composable by  heat.  All  the  chlorides  of  the  common  metals  are  decomposed  at 
a  red  heat  by  hydrogen  gas,  hydrochloric  acid  being  disengaged  while  the  metal 
is  set  free.  Pure  charcoal  does  not  affect  their  decomposition ;  but  if  moisture 
be  present  at  the  same  time,  hydrochloric  and  carbonic  acid  gases  are  formed, 
and  the  metal  remains.  They  resist  the  action  of  anhydrous  sulphuric  acid  ;  but 
all  the  chlorides,  excepting  those  of  silver  and  mercury,  are  readily  decomposed 
by  hydrated  sulphuric  acid,  with  disengagement  of  hydrochloric  acid  gas.  The 
change  is  accompanied  with  decomposition  of  water,  the  hydrogen  of  which  com- 
bines with  chlorine,  and  its  oxygen  with  the  metal.  When  in  solution,  they  may 
be  recognized  by  yielding  with  nitrate  of  oxide  of  silver  a  white  precipitate, 
which  is  chloride  of  silver. 

Metallic  chlorides  may  in  most  cases  be  formed  by  direct  action  of  chlorine  on 
the  pure  metals.  They  are  also  frequently  procured  by  dissolving  metallic  oxides 
in  hydrochloric  acid,  evaporating  to  dryness,  and  applying  heat  so  long  as  any 
water  is  expelled.  Metallic  chlorides  are  often  deposited  from  such  solutions  by 
crystallization. 

Iodine  has  a  strong  attraction  for  metals ;  and  most  of  the  compounds  which  it 
forms  with  them  sustain  a  red  heat  in  close  vessels  without  decomposition.  But 
in  the  degree  of  its  affinity  for  metallic  substances  it  is  inferior  to  chlorine  and 
oxygen.  We  have  seen  that  chlorine  has  a  stronger  affinity  than  oxygen  for 
metals,  since  it  decomposes  nearly  all  oxides  at  high  temperatures ;  and  it  sepa- 
rates iodine  also  from  metals  under  the  same  circumstances.  If  the  vapour  of 
iodine  is  brought  into  contact  with  potassa,  soda,  protoxide  of  lead,  or  oxide  of 
bismuth,  heated  to  redness,  oxygen  gas  is  evolved,  and  the  metals  of  those  ox- 
ides will  unite  with  iodine.  But  iodine,  so  far  as  is  known,  cannot  separate 
oxygen  from  any  other  metal ;  nay,  all  the  iodides,  except  those  just  mentioned. 


GENERAL  PROPERTIES  OF  METALS.  2§3 

are  decomposed  by  exposure  to  oxygen  gas  at  the  temperature  of  ignition.  All 
the  iodides  are  decomposed  by  chlorine,  bromine,  and  concentrated  sulphuric  and 
nitric  acids ;  and  the  iodine  which  is  set  free  may  be  recognized  either  by  the 
colour  of  its  vapour,  or  by  its  action  on  starch.  The  metallic  iodides  are  gene- 
rated under  circumstances  analogous  to  those  above  mentioned  for  procuring  the 
chlorides. 

The  action  of  iodine  on  metallic  oxides,  when  dissolved  or  suspended  in  water, 
is  precisely  analogous  to  that  of  chlorine.  On  adding  iodine  to  a  solution  of  the 
pure  alkalies  or  alkaline  earths,  an  iodide  and  iodate  are  generated. 

Bromine  in  its  affinity  for  metallic  substances  is  intermediate  between  chlorine 
and  iodine ;  for  while  chlorine  disengages  bromine  from  its  combination  with 
metals,  metallic  iodides  are  decomposed  by  bromine.  The  same  phenomena  at- 
tend the  union  of  bromine  with  metals,  as  accompany  the  formation  of  metallic 
chlorides.  Thus,  antimony  and  tin  take  fire  by  contact  with  bromine,  and  its 
action  with  potassium  is  attended  with  a  flash  of  light,  and  intense  heat.  These 
compounds  have  as  yet  been  but  partially  examined.  They  may  be  formed  by 
the  action  of  bromine  on  the  pure  metals,  and  often  by  dissolving  metallic  oxides 
in  hydrobromic  acid,  and  evaporating  the  solution  to  dryness,.  Bromine  unites 
with  potassa,  soda,  and  some  other  oxides,  constituting  bleaching  compounds 
similar  to  the  chlorides  above  described.  Bromide  of  lime  is  obtained  by  the 
action  of  bromine  on  milk  of  lime,  a  yellowish  solution  being  formed  with  water, 
which  bleaches  powerfully. 

As  fluorine  has  not  hitherto  been  obtained  in  a  separate  state,  the  nature  of  its 
action  on  the  metals  is  unknown ;  but  the  chief  difficulty  of  procuring  it  in  an 
insulated  form  appears  to  arise  from  its  extremely  powerful  affinity  for  metallic 
substances,  in  consequence  of  which,  at  the  moment  of  becoming  free,  it  attacks 
the  vessels  and  instruments  employed  in  its  preparation.  The  best  mode  of  pre- 
paring the  soluble  fluorides,  such  as  those  of  potassium  and  sodium,  is  by  dis- 
solving the  carbonate  of  these  alkalies  in  hydrofluoric  acid,  and  evaporating  the 
solution  to  perfect  dryness.  The  insoluble  fluorides  are  easily  formed  by  preci- 
pitation from  the  soluble  fluorides.  They  are  without  exception  decomposed  by 
concentrated  sulphuric  acid  with  the  aid  of  heat;  and  the  hydrofluoric  acid,  in 
escaping,  may  easily  be  detected  by  its  action  on  glass. 

Sulphur,  like  the  preceding  elementary  substances,  has  a  strong  tendency  to 
unite  with  metals,  and  the  combination  may  be  effected  in  several  ways : 

1.  By  heating  the  metal  directly  with  sulphur.  The  metal,  in  the  form  of 
powder  or  filings,  is  mixed  with  a  due  proportion  of  sulphur,  and  the  mixture 
heated  in  an  earthen  crucible,  which  is  covered  to  prevent  the  access  of  air ;  or  if 
the  metal  can  sustain  a  red  heat  without  fusing,  the  vapour  of  sulphur  may  be 
passed  over  it  while  heated  to  redness  in  a  tube  of  porcelain.  The  act  of  com- 
bination, which  frequently  ensues  below  the  temperature  of  ignition,  is  attended 
by  free  disengagement  of  heat,  which  in  several  instances  is  so  great,  that  the 
whole  mass  becomes  luminous,  and  shines  with  a  vivid  light.  This  appearance 
of  combustion,  which  occurs  quite  independently  of  the  presence  of  oxygen,  is 
exemplified  by  the  sulphurets  of  potassium,  sodium,  copper,  iron,  lead,  and  bis- 
muth. 

2.  By  igniting  a  mixture  of  a  metallic  oxide  and  sulphur. 


•m-- 


284  GENERAL  PROPERTIES  OF  METALS. 

3.  By  depriving  the  sulphate  of  an  oxide  of  its  oxygen  by  means  of  heat  and 
combustible  matter.  Charcoal  or  hydrogen  gas  may  be  employed  for  the  pur- 
pose, as  will  be  described  immediately. 

4.  By  hydrosulphuric  acid,  or  a  soluble  metallic  sulphuret.  Nearly  all  the 
salts  of  the  second  class  of  metals  are  decomposed  when  a  current  of  hydrosul- 
phuric acid  gas  is  conducted  into  their  solutions.  The  salts  of  uranium,  iron, 
manganese,  cobalt,  and  nickel  are  exceptions ;  but  these  are  precipitated  by  sul- 
phuret of  potassium. 

The  sulphurets  are  opaque  brittle  solids,  many  of  which,  such  as  the  sulphu- 
rets  of  lead,  antimony,  and  iron,  have  a  metallic  lustre.  They  are  all  fusible  by 
heat,  and  commonly  assume  a  crystalline  texture  in  cooling.  Most  of  them  are 
fixed  in  the  fire ;  but  the  sulphurets  of  mercury  and  arsenic  are  remarkable  for 
their  volatility.  All  the  sulphurets,  excepting  those  of  the  first  class  of  metals, 
are  insoluble  in  water. 

Most  of  the  protosulphurets  support  an  intense  heat  without  decomposition ; 
but,  in  general,  those  which  contain  more  than  one  equivalent  of  sulphur,  lose 
part  of  it  when  strongly  heated.  They  are  all  decomposed  without  exception  by 
exposure  to  the  combined  agency  of  air  or  oxygen  gas  and  heat ;  and  the  products 
depend  entirely  on  the  degree  of  heat  and  the  nature  of  the  metal.  The  sulphuret 
is  more  or  less  converted  into  the  sulphate  of  an  oxide,  provided  the  sulphate  is 
able  to  support  the  temperature  employed  in  the  operation.  If  this  is  not  the 
case,  the  sulphur  is  evolved  under  the  form  of  sulphurous  acid,  and  a  metallic 
oxide  is  left ;  or  if  the  oxide  itself  is  decomposed  by  heat,  the  pure  metal  remains. 
The  action  of  heat  and  air  in  decomposing  metallic  sulphurets  is  the  basis  of 
several  metallurgic  processes.  A  few  sulphurets  are  decomposed  by  the  actiou 
of  hydrogen  gas  at  a  red  heat,  the  pure  metal  being  set  free  and  hydrosulphuric 
acid  evolved.  Rose  finds  that  the  only  sulphurets  which  admit  of  being  easily 
reduced  to  the  metallic  state  in  this  way  are  those  of  antimony,  bismuth,  and 
silver.  The  sulphuret  of  tin  is  decomposed  with  difficulty,  and  requires  a  very 
high  temperature.  All  the  other  sulphurets  which  he  subjected  to  this  treat- 
ment were  either  deprived  of  a  part  only  of  their  sulphur,  such  as  bisulphuret  of 
iron,  or  were  not  attacked  at  all,  as  happened  with  the  sulphurets  of  zinc,  lead, 
and  copper.    (PoggendorfTs  Annalen,  iv.  109.) 

Many  of  the  metallic  sulphurets  were  formerly  thought  to  be  compounds  of 
sulphur  and  a  metallic  oxide  ;  an  error  first  pointed  out  by  Proust,  who  demon- 
strated that  protosulphuret  of  iron,  as  well  as  the  bisulphuret,  are  compounds  of 
sulphur  and  metallic  iron  without  any  oxygen.  (Journal  de  Physique,  liii.)  He 
proved  the  same  of  the  sulphurets  of  other  metals,  such  as  mercury  and  copper. 
He  was  of  opinion,  however,  that  in  some  instances  sulphur  does  unite  with  a 
metallic  oxide.  Thus,  when  sulphur  and  peroxide  of  tin  are  heated  together, 
sulphurous  acid  is  disengaged,  and  the  residue  according  to  Proilst  is  a  sulphuret 
of  the  protoxide,  but  in  this  he  was  in  error. 

In  1817  Vauquelin  extended  these  views  to  the  compounds  formed  by  heating 
an  alkali  or  an  alkaline  earth  with  sulphur,  which  were  previously  regarded  as 
sulphurets  of  a  metallic  oxide.  He  explained  that  the  elements  of  the  alkali 
unite  with  separate  portions  of  sulphur,  forming  a  metallic  sulphuret  and  sul- 
phuric acid,  the  latter  of  which  unites  with  undecomposed  alkali.  Thus,  in  pre- 
paring the  so-called  liver  of  nulphur,  made  by  fusing  carbonate  of  potassa  with 
sulphur,  one  portion  of  the  alkali  is  completely  decomposed,  its  elements  unite 
separately  with  sulphur,  giving  rise  to  sulphuret  of  potassium  and  sulphuric  acid, 


GENERAL  PROPERTIES  OF  METALS.  285 

the  latter  of  which  combines  with  undecomposed  potassa.     Those  views  were  at 
the  same  time  supported  by  Gay-Lussac.     (An.  de  Ch.  et  Ph.  vi.) 

One  of  the  chief  arguments  adduced  by  Vauquelin  in  support  of  his  opinion 
was  drawn  from  the  action  of  charcoal  on  sulphate  of  potassa.  When  a  mixture 
of  this  salt  with  powdered  charcoal  is  ignited  without  exposure  to  the  air,  car- 
bonic oxide  and  carbonic  acid  gases  are  formed,  and  a  sulphuret  is  left,  analogous 
both  in  appearance  and  properties  to  that  which  may  be  made  by  igniting  car- 
bonate of  potassa  directly  with  sulphur.  They  are  both  essentially  the  same 
substance,  and  Vauquelin  conceived  from  the  strong  attraction  of  carbon  for  oxy- 
gen, that  both  the  sulphuric  acid  and  potassa  would  be  decomposed  by  charcoal 
at  a  high  temperature ;  and  that,  consequently,  the  product  must  be  a  sulphuret 
of  potassium. 

Berthier  has  proved  that  these  changes  do  actually  occur.  (An.  de  Ch.  et  de 
Ph.  xxii.)  He  put  a  known  weight  of  sulphate  of  baryta  into  a  crucible  lined 
with  a  mixture  of  clay  and  charcoal,  defended  it  from  contact  with  the  air,  and 
exposed  it  to  a  white  heat  for  the  space  of  two  hours.  By  this  treatmerft  it  suf- 
fered complete  decomposition,  and  it  was  found  that  in  passing  into  a  sulphuret, 
it  had  suffered  a  loss  in  weight  precisely  equal  to  the  quantity  of  oxygen  origi- 
nally contained  in  the  acid  and  earth.  This  circumstance,  coupled  with  the  fact 
that  there  had  been  no  loss  of  sulphur,  is  decisive  evidence  that  the  baryta  as 
well  as  the  acid  had  lost  its  oxygen,  and  that  a  sulphuret  of  barium  had  been 
formed.  He  obtained  the  same  results  also  with  the  sulphates  of  strontia,  lime, 
potassa,  and  soda ;  but  from  the  easy  fusibility  of  the  sulphurets  of  potassium 
and  sodium,  their  loss  of  weight  could  not  be  determined  with  such  precision  as 
in  the  other  instances. 

The  experiments  of  Berzelius,  performed  about  the  same  time,  are  exceedingly 
elegant,  and  still  more  satisfactory  than  the  foregoing.  (An.  de  Ch.  et  Ph.  xx.) 
He  transmitted  a  current  of  dry  hydrogen  gas  over  a  known  quantity  of  sulphate 
of  potassa,  heated  to  redness.  It  was  expected  from  the  strong  affinity  of  hydro- 
gen for  oxygen,  that  the  sulphate  would  be  decomposed ;  and,  accordingly,  a 
considerable  quantij;y  of  water  was  formed,  which  was  carefully  collected  and 
weighed.  The  loss  of  weight  which  the  salt  had  experienced  was  precisely 
equivalent  to  the  oxygen  of  the  acid  and  alkali ;  and  the  oxygen  of  the  water 
was  exactly  equal  to  the  loss  in  weight.  A  similar  result  was  obtained  with  the 
sulphates  of  soda,  baryta,  strontia,  and  lime. 

It  is  demonstrated,  therefore,  that  the  metallic  bases  of  the  alkalies  and  alka- 
line earths  agree  with  the  common  metals  in  their  disposition  to  unite  with  sul- 
phur. It  is  now  certain  that,  whether  a  sulphate  be  decomposed  by  hydrogen  or 
charcoal,  or  sulphur  ignited  with  an  alkali  or  an  alkaline  earth,  a  metallic  sul- 
phuret is  always  the  product.  Direct  combination  between  sulphur  and  a  metallic 
oxide  is  a  very  rare  occurrence,  nor  has  the  existence  of  such  a  compound  been 
clearly  established.  Gay-Lussac  indeed  states  that,  when  an  alkali  or  an  alka- 
line earth  is  heated  with  sulphur  in  such  a  manner  that  the  temperature  is  never 
so  high  as  a  low  red  heat,  the  product  is  really  the  sulphuret  of  an  oxide.  But 
the  facts  adduced  in  favour  of  this  opinion  are  not  altogether  satisfactory,  so  that 
the  real  nature  of  the  product  must  be  decided  by  future  observation. 

Several  of  the  metallic  sulphurets  occur  abundantly  in  nature.  Those  that  are 
most  frequently  met  with  are  the  sulphurets  of  lead,  antimony,  copper,  iron,  zinc, 
molybdenum,  and  silver. 

The  metallic  seleniurets  have  so  close  a  resemblance  in  their  chemical  rela- 


286  GENERAL  PROPERTIES  OF  METALS. 

tions  to  the  sulphurets,  that  it  is  unnecessary  to  give  a  separate  description  of 
them.  They  may  be  prepared  either  by  bringing  selenium  in  contact  with  the 
metals  at  a  high  temperature,  or  by  the  action  of  hydroselenic  acid  on  metallic 
solutions. 

Respecting  the  preceding  compounds  there  remains  one  subject,  the  conside- 
ration of  which,  as  applying  equally  to  all,  has  been  purposely  delayed.  The 
non-metallic  ingredient  of  each  is  the  radical  of  a  hydracid,  that  is,  has  the 
property  of  forming  with  hydrogen  an  acid,  which,  like  other  acids,  is  unable  to 
unite  with  metals,  but  appears  to  combine  readily  with  many  metallic  oxides. 
Owing  to  this  circumstance,  a  difficulty  arises  in  explaining  th«  action  of  such 
substances  on  water.  Thus,  when  chloride  of  potassium  is  put  into  water,  it 
may  dissolve  without  suffering  any  other  chemical  change,  and  the  liquid  accord- 
ingly contain  chloride  of  potassium  in  solution.  But  it  is  also  possible  that  the 
elements  of  this  compound  may  react  on  those  of  water,  its  potassium  uniting 
with  oxygen,  and  its  chlorine  with  hydrogen ;  and  as  the  resulting  potassa  and 
hydrochloric  acid  have  a  strong  affinity  for  each  other,  the  solution  would  of 
course  contain  hydrochlorate  of  potassa.  A  similar  uncertainty  attends  the  action 
of  water  on  other  metallic  chlorides,  and  on  the  compounds  of  metals  with 
iodine,  bromine,  SQlphur,and  similar  substances;  so  that  when  iodide,  sulphuret, 
and  cyanuret  of  potassium  are  put  into  water,  it  may  be  doubted  whether  they 
dissolve  as  such,  or  whether  they  may  not  be  converted,  by  decomposition  of 
water,  into  hydriodate,  hydrosulphate,  and  hydrocyanate  of  potassa.  This  ques- 
tion would  at  once  be  decided,  could  it  be  ascertained  whether  water  is  or  is  not 
decomposed  during  the  process  of  solution ;  but  this  is  the  precise  point  of  dif- 
ficulty, since,  from  the  operation  of  the  laws  of  chemical  union,  no  disengage- 
ment of  gas  does  or  can  take  place  by  which  the  occurrence  of  such  a  change 
may  be  indicated.  Chemists,  accordingly,  being  guided  by  probabilities,  are 
divided  in  opinion,  and  I  shall  therefore  give  a  brief  statement  of  both  view  s, 
with  the  arguments  in  favour  of  each. 

According  to  one  view,  then,  chloride  of  potassium  and  all  similar  compounds 
dissolve  in  water  without  undergoing  any  other  change,  and  are  deposited  in  their 
original  state  by  crystallization.  "When  any  hydracid,  such  as  hydrochloric  or 
hydriodic  acid,  is  mixed  with  potassa  or  any  similar  metallic  oxide,  the  acid  and 
salifiable  base  do  not  unite,  but  the  oxygen  of  the  oxide  combines  with  the 
hydrogen  of  the  acid,  and  the  metal  itself  with  the  radical  of  the  hydracid. 
This  kind  of  double  decomposition  unquestionably  takes  place  in  some  instances, 
as  when  hydrosulphuric  acid  acts  upon  acetate  of  oxide  of  lead,  the  insoluble 
sulphuret  of  lead  being  actually  precipitated;  but  it  is  also  thought  to  occur  even 
when  the  transparency  of  the  solution  is  undisturbed.  It  is  argued,  accordingly, 
that  hydrochlorate  of  potassa,  and  the  salts  of  the  hydracids  in  general,  have  no 
existence.  Thus,  when  nitrate  of  the  oxide  of  silver  is  added*  to  a  solution  of 
chloride  of  potassium,  metallic  silver  is  said  to  unite  with  chlorine,  while 
the  oxygen  of  the  oxide  of  silver  combines  with  potassium ;  so  that  nitrate  of 
potassa  and  chloride  of  silver  are  generated.  On  adding  sulphuric  acid  to  a 
solution  of  chloride  of  potassium,  hydrochloric  acid  and  potassa,  not  previously 
existing,  are  instantly  formed  in  consequence  of  the  decomposition  of  water, 
which  yields  its  hydrogen  to  chlorine,  and  its  oxygen  to  potassium  ;  exactly  as 
happens  when  concentrated  sulphuric  acid  ^  is  brought  into  contact  with  solid 
chloride  of  potassium.  It  is  further  believed  that  the  crystallized  hydrochlorate 
of  lime,  baryta,  and  strontia,  which  contain  water  or  its  elements,  are  metallic 


GENERAL  PROPERTIES  OF  METALS.  287 

chlorides  combined  with  water  of  crystallization ;  and  the  same  view  is  applied 
to  all  analogous  compounds. 

According  to  the  other  doctrine,  chloride  of  potassium  is  converted  into  hydro- 
chlorate  of  potassa  in  the  act  of  dissolving ;  and  when  the  solution  is  evaporated, 
the  elements  existing  in  the  salt  reunite  at  the  moment  of  crystallization,  and 
crystals  of  chloride  of  potassium  are  deposited.  The  same  explanation  applies 
in  all  cases,  when  the  salt  of  a  hydracid  crystallizes  without  retaining  the  ele- 
ments of  water.  Of  those  compounds  which  in  crystallizing  retain  water  or  its 
elements  in  combination,  two  opinions  may  be  formed.  Thus  crystallized  hydro- 
chlorate  of  baryta,  which  consists  of  one  equivalent  of  chlorine,  one  of  barium, 
two  of  oxygen,  and  two  of  hydrogen,  may  be  regarded  as  a  compound  either  of 
hydrochlorate  of  baryta  with  one  equivalent  of  water  of  crystallization,  or  of 
chloride  of  barium  with  two  equivalents  of  water.  When  exposed  to  heat,  two 
equivalents  of  water  are  expelled,  and  chloride  of  barium  is  left.  When  nitrate 
of  the  oxide  of  silver  is  mixed  in  solution  with  hydrochlorate  of  potassa,  the 
oxygen  of  the  oxide  of  silver  unites  with  the  hydrogen  of  the  hydrochloric  acid, 
chloride  of  silver  is  precipitated,  and  nitrate  of  potassa  remains  in  the  liquid. 
On  adding  sulphuric  acid  to  a  hydrochlorate,  hydrochloric  acid  is  simply  dis- 
placed, just  as  when  carbonic  acid  in  marble  is  separated  from  lime  by  the  action 
of  nitric  acid. 

On  comparing  these  opinions  it  is  manifest  that  both  are  consistent  with  well- 
known  affinities.  When  a  metallic  chloride  is  dissolved  in  water,  the  attraction 
of  chlorine  for  the  metal,  and  that  of  oxygen  for  hydrogen,  tend  to  prevent  che- 
mical change ;  but  the  affinities  of  the  metal  for  oxygen,  of  chlorine  for  hydro- 
gen, and  of  hydrochloric  acid  for  metallic  oxides,  co-operate  in  determining  the 
decomposition  of  water,  and  the  production  of  a  hydrochlorate.  In  favour  of 
the  latter  view,  the  following  considerations  may  be  adduced: — 1.  The  solution 
of  some  compounds,  such  as  sulphuret  of  potassium,  actually  emit  an  odour  of 
hydrosulphuric  acid.  2.  Other  compounds,  such  as  the  chlorides  of  copper, 
cobalt,  and  nickel,  instantly  acquire,  when  put  into  water,  the  colour  peculiar  to 
the  salts  of  the  oxides  of  those  metals.  3.  The  solution  of  protochloride  of 
iron,  like  the  protosulphate,  absorbs  oxygen  from  the  atmosphere ;  an  effect 
which  seems  to  indicate  the  presence  of  the  protoxide  of  iron  in  the  liquid.  4. 
In  some  instances  there  is  direct  proof  of  decomposition  of  water.  Thus  when 
sulphuret  of  aluminium  is  put  into  that  fluid,  alumina  is  generated,  and  hydro- 
sulphuric  acid  gas  disengaged  with  effervescence.  In  like  manner  chloride  and 
sulphuret  of  silicon  are  converted  by  water  into  silica  and  hydrochloric  and 
hydrosulphuric  acid.  In  these  cases  the  want  of  affinity  between  the  new  com- 
pounds causes  their  separation,  and  thus  affords  direct  proof  that  water  is  decom- 
posed. But  the  affinities  which  produce  this  change  do  not  appear  so  likely  to 
be  effective,  as  those  which  are  in  operation  when  chloride  of  potassium  is  put 
into  water ;  especially  when  it  is  considered  that  the  attraction  of  chlorine  for 
hydrogen,  and  potassium  for  oxygen,  is  aided  by  that  of  the  resulting  acid  and 
oxide  for  each  other. 

These  arguments  may  be  successively  answered  in  the  following  manner: — 
1.  That  solutions  of  cyanide  and  sulphuret  of  potassium  smell  of  hydrocyanic 
and  hydrosulphuric  acids,  because  the  carbonic  acid  of  the  atmosphere  gradually 
decomposes  them.  2.  That  metals  may  yield  with  chlorine  compounds  of  the 
same  colour  as  the  oxides  of  the  same  metals.  Thus  the  terchloride  and  ter- 
fluoride  of  chromium  have  a  red  colour  closely  resembling  that  of  chromic  acid. 


2S8  GENERAL  PROPEI^TIES  OF  METALS. 

3.  Protochloride  of  iron  may  attract  oxygen  from  the  air  because  of  its  known 
tendency  to  pass  into  the  state  of  a  sesquichloride,  a  portion  of  iron  being  at  the 
same  time  converted  into  peroxide.  4.  That  while  certain  chlorides  do  really 
decompose  water,  it  must  be  conceded  that  others  dissolve  directly  without  change. 
The  bichloride  of  platinum  and  terchloride  of  gold  are  soluble  in  ether,  forming 
solutions  which  must  be  regarded  as  chlorides  and  not  hydrochl orates,  since  pure 
ether  is  anhydrous ;  and  when  aqueous  solutions  of  these  chlorides  are  agitated 
with  ether,  ethereal  solutions  of  platinum  and  gold  are  formed,  exactly  similar 
to  those  made  with  ether  alone.  It  can  scarcely  be  doubted,  then,  that  these 
chlorides  exist  as  such  in  water.  In  favour'of  the  same  view  it  may  with  truth 
be  alleged,  that  the  chlorides  of  potassium  and  sodium  dissolve  in  and  crystal- 
lize out  of  water  without  evincing  the  least  sign  of  any  other  change  than  mere 
solution  and  mere  crystallization.  Again,  crystals  of  the  so-called  hydrochlorate 
of  baryta  become  chloride  of  barium  with  loss  of  water  by  mere  exposure  to  a  dry 
air ;  a  cause  apparently  inadequate  to  determine  the  hydrogen  of  the  acid  to  unite 
with  the  oxygen  of  the  «xide,  but  sufficient  to  explain  the  phenomena  if  the 
crystals  were  chloride  of  barium  with  water  of  crystallization. 

On  weighing  these  and  other  considerations  of  a  like  kind,  it  appears  undeniable 
that  so7»«  metallic  chlorides,  iodides,  and  similar  compounds  dissolve  as  such  in 
water:  that  all  do  so  is  a  position  which  cannot,  I  think,  be  maintained  ;  and  there- 
fore the  existence  of  such  compounds  as  hydracids  united  with  metallic  oxides, 
can  scarcely  be  denied ;  and  in  the  case  of  chloride  of  aluminium,  which  cannot 
be  recovered  from  its  solution  in  water,  but  yields  alumina  and  hydrochloric  acid, 
the  change  is  obvious  to  the  senses.  At  the  same  time  it  is  necessary,  to  avoid 
a  perpetually  recurring  two-fold  explanation,  to  adhere  consistently  to  one  view  ; 
and  the  reader  may  have  observed  that  I  have,  in  this  edition,  uniformly  gone 
on  the  supposition  that  chlorides,  and  the  same  class  of  bodies,  dissolve  as  such 
in  water.  The  considerations  which  have  led  to  this  preference  are  principally 
drawn  from  the  history  of  the  sulphur-salts. 

Chemists  are  acquainted  with  several  metallic  phosphurets ;  and  it  is  proba- 
ble that  phosphorus,  like  sulphur,  is  capable  of  uniting  with  all  the  metals. 
Little  attention,  however,  has  hitherto  been  devoted  to  their  compounds  ;  and 
for  the  greater  part  of  our  knowledge  concerning  them  we  are  indebted  to  the 
researches  of  Pelletier  and  Rose.  (An.  de  Ch.  i.  and  xiii.;  and  Pog.  An.  vi. 
205.) 

The  metallic  phosphurets  may  be  prepared  in  several  ways.  The  most  direct 
method  is  by  bringing  phosphorus  in  contact  with  metals  at  a  higher  tempera- 
ture, or  by  igniting  metals  in  contact  with  phosphoric  acid  and  charcoal.  Seve- 
ral of  the  phosphurets  may  be  formed  by  transmitting  a  current  of  phosphuretted 
hydrogen  gas  over  metallic  oxides  heated  to  redness  in  a  porcelain  tube,  when 
water  is  generated,  and  a  phosphuret  of  the  metal  remains.  By  similar  treatment 
the  chlorides  and  sulphurets  of  many  metals  may  be  decomposed,  and  phosphu- 
rets formed,  provided  the  metal  is  capable  of  retaining  phosphorus  at  a  red  heat. 
According  to  Rose,  the  phosphurets  of  copper,  nickel,  cobalt,  and  iron  are  the 
only  ones  which  admit  of  being  advantageously  prepared  by  this  method.  When 
chlorides  are  employed,  hydrochloric  acid,  and  with  sulphurets  hydrosulphuric 
acid  gas,  is  of  course  generated. 

Phosphorus  is  said  to  unite  with  metallic  oxides.  For  example,  phosphuret 
of  lime  is  said  to  be  formed  by  conducting  the  vapour  of  phosphorus  over  that 
earth  at  a  low  red  heat;  but  it  is  probable  that  in  this  instance,  as  with  a  mix- 


GENERAL  PROPERTIES  OF  METALS.  289 

ture  of  sulphur  and  an  alkali,  part  of  the  metallic  oxide  is  decomposed,  and  that 
the  product  contains  phosphuret  of  calcium  and  phosphate  of  lime. 

The  only  metallic  carburets  of  importance  are  those  of  iron,  which  will  be 
described  in  the  section  on  that  metal. 

Hydrogen  unites  with  few  metals.  The  only  metallic  hydrogurets,  or  hydu- 
rets,  known  are  those  of  zinc,  potassium,  arsenic,  antimony,  and  tellurium.  No 
definite  compound  of  nitrogen  and  a  metal  has  hitherto  been  discovered. 

The  discoveries  of  modem  chemistry  have  materially  added  to  the  number  of 
the  metals,  especially  by  associating  with  them  a  class  of  bodies  which  was 
formerly  believed  to  be  of  a  nature  entirely  different.  The  metallic  bases  of  the 
alkalies  and  earths,  previous  to  the  year  1807,  were  altogether  unknown;  and 
before  that  date  the  list  of  metals,  with  few  exceptions,  included  those  only 
which  are  commonly  employed  in  the  arts,  and  which  are  hence  often  called  the 
common  metals.  In  consequence  of  this  increase  in  number,  it  is  found  conve- 
nient, for  the  purpose  of  description,  to  arrange  them  in  separate  groups ;  and 
as  the  alkalies  and  earths  differ  in  several  respects  from  the  oxides  of  other 
metals,  it  will  be  convenient  to  describe  them  separately.  I  have  accordingly 
divided  the  metals  into  the  following  classes : — 

Class  I.  Metals  which  by  oxidation  yield  alkalies  and  earths. 
Class  II.  Metals,  the  oxides  of  which  are  neither  alkalies  nor  earths. 

Class  I.  This  class  includes  12  metals,  which  may  properly  be  arranged  in 
three  orders. 

Order  1.  Metallic  bases  of  the  alkalies,    fhey  are  three  in  number;  namely, 

Potassium,  Sodium,  Lithium. 

These  metals  have  such  a  powerful  attraction  for  oxygen,  that  they  decompose 
cold  water  and  even  ice  at  the  moment  of  contact,  and  are  oxidized  with  disen- 
gagement of  hydrogen  gas.  The  resulting  oxides  are  distinguished  by  their 
causticity  and  solubility  in  water,  and  by  possessing  alkaline  properties  in  an 
eminent  degree. 

They  are  called  alkalies,  and  their  metallic  bases  are  sometimes  termed  alkaline 
or  alkaligenous  metals. 

Order  2.  Metallic  bases  of  the  alkaliae  earths.  These  are  four  in  number ; 
namely, 

Barium,  Strontium,  Calcium,  Magnesium. 

These  metals,  excepting  magnesium,  also  decompose  water  rapidly  at  common 
temperatures.  The  resulting  oxides  are  called  alkaline  earths ;  because,  while 
in  their  appearance  they  resemble  the  earths,  they  are  similar  to  the  alkalies  in 
having  a  strong  alkaline  reaction  with  test  paper  and  in  neutralizing  acids.  The 
three  first  are  strongly  caustic,  and  baryta  and  strontia  are  soluble  in  water  to  a 
considerable  extent. 

Order  3,  Metallic  bases  of  the  earths.    These  are  five  in  number ;  namely. 

Aluminium,  Glucinium,  Yttrium. 

Thorium,  Zirconium, 

The  oxides  of  these  metals  are  well  known  as  the  pure  earths.  They  are 
white  and  of  an  earthy  appearance,  in  their  ordinary  state  are  quite  insoluble  in 

21 


290  GENERAL  PROPERTIES  OF  METALS. 

water,  and  do  not  affect  the  colour  of  turmeric  or  litmus  paper.    As  salifiable 
bases  they  are  inferior  to  the  alkaline  earths. 

Class  II.  The  number  of  the  metals  included  in  this  class  amounts  to  30. 
They  are  all  capable  of  uniting  with  oxygen,  and  generally  in  more  than  one 
proportion.  Their  protoxides  have  an  earthy  appearance,  but  with  few  excep- 
tions are  coloured.  They  are  insoluble  in  water,  and  in  general  do  not  affect  the 
colour  of  test  paper.  Most  of  them  act  as  salifiable  bases  in  uniting  with  acids, 
and  forming  salts ;  but  in  this  respect  they  are  much  inferior  to  the  alkalies  and 
alkaline  earths,  by  which  they  may  be  separated  from  their  combinations.  Several 
of  these  metals  are  capable  of  forming  with  oxygen  compounds,  which  pos- 
sess the  characters  of  acids.  The  metals  in  which  this  property  has  been  no- 
ticed are,  manganese,  arsenic,  chromium,  vanadium,  molybdenum,  tungsten, 
antimony,  columbium,  titanium,  tellurium,  gold,  and  osmium. 

The  metals  belonging  to  the  second  class  may  be  conveniently  arranged  in  the 
three  following  orders : 

Order  1.  Metals  which  decompose  water  at  a  red  heat.  They  are  seven  in 
number;  namely, 


Managnese, 

Cadmium, 

Nickel, 

Iron, 

Cobalt, 

Tin. 

Zinc, 

Order  2.  Metals  which  do  not  decompose  water  at  any  temperature,  and  the 
oxides  of  which  are  not  reduced  to  the  metallic  state  by  the  sole  action  of  heat. 
Of  these  there  are  fifteen  in  number ;  namely, 


Copper, 

Chromium, 

Cerium, 

Lead, 

Vanadium, 

Lantanium, 

Bismuth, 

Molybdenum, 

Titanium, 

Arsenic, 

Tungsten, 

Tellurium, 

Antimony, 

Uranium, 

Columbium. 

Order  3.  Metals,  the  oxides  of  which  are  decomposed  by  a  red  heat.    These 
are. 


Mercury, 

Platinum, 

Osmium, 

Siver, 

Palladium, 

Iridium. 

Gold, 

Rhodium, 

POTASSIUM.  291 


CLASS  I. 

METALS  WHICH  BY  OXIDATION  YIELD  ALKALIES  OR  EARTHS. 

ORDER  I. 

METALLIC  BASES  OF  THE  ALKALIES. 

SECTION  I. 

POTASSIUM. 

Hist,  and  Prep. — Discovered  in  the  year  1807  by  Davy,  and  the  circumstances 
which  led  to  the  discovery  have  already  been  described.  Hydrate  of  potassa, 
slightly  moistened  for  the  purpose  of  increasing  its  conducting  power,  was  made 
to  communicate  with  the  opposite  poles  of  a  galvanic  battery  of  200  double 
plates  ;  when  the  oxygen  both  of  the  water  and  the  potassa  passed  over  to  the 
positive  pole,  while  the  hydrogen  of  the  former,  and  the  potassium  of  the  latter, 
made  their  appearance  at  the  negative  pole.  By  this  process  potassium  is  ob- 
tained in  small  quantity  only ;  but  Gay-Lussac  and  Thenard  invented  a  method 
by  which  a  more  abundant  supply  may  be  procured.  (Recherches  Physico- 
Chimiques,  vol.  i.)  Their  process  consists  in  bringing  fused  hydrate  of  potassa 
in  contact  with  turnings  of  iron  heated  to  whiteness  in  a  gun-barrel.  The  iron, 
under  these  circumstances,  deprives  the  water  and  potassa  of  oxygen,  hydrogen 
gas  combined  with  a  little  potassium  is  evolved,  and  pure  potassium  sublimes, 
and  may  be  collected  in  a  cool  part  of  the  apparatus. 

Potassium  may  also  be  prepared,  as  first  noticed  by  Curaudau,  by  mixing  dry 
carbonate  of  potassa  with  half  its  weight  of  powdered  charcoal,  and  exposing  the 
mixture,  contained  in  a  gun-barrel  or  spheroidal  iron  bottle,  to  a  strong  heat. 
An  improvement  on  both  processes  has  been  made  by  Brunner,  who  decomposes 
potassa  by  means  of  iron  and  charcoal.  From  eight  ounces  of  fused  carbonate 
of  potassa,  six  ounces  of  iron  filings,  and  two  ounces  of  charcoal,  mixed  inti- 
mately and  heated  in  an  iron  bottle,  he  obtained  140  grains  of  potassium.  (Quar- 
terly Journal,  xv.  379.)  Berzelius  has  observed  that  the  potassium  thus  made, 
though  fit  for  all  the  usual  purposes  to  which  it  is  applied,  contains  a  minute 
quantity  of  carbon  ;  and  therefore,  if  required  to  be  quite  pure,  must  be  rendered 
so  by  distillation  in  a  retort  of  iron  or  green  glass.  A  modification  of  this  pro- 
cess has  been  since  described  by  Wohler,  who  eflfects  the  decomposition  of  the 
potassa  solely  by  means  of  charcoal.  The  material  employed  for  the  purpose  is 
carbonate  of  potassa  prepared  by  heating  cream  of  tartar  to  redness  in  a  covered 
crucible.  (Poggendorflf's  Annalen,  iv.  23.)  According  to  Liebig,  2  eq.  of  char- 
coal  and  1  eq.  of  carbonate  of  potassa  react  on  each  other,  and  form  1  eq.  of 
potassium  and  3  eq.  of  carbonic  oxide ;  or 

KO-I-CO2       2  K 

and  2C  ?.       and  SCO. 


292 


POTASSIUM. 


The  whole  of  the  potassium  thus  liberated  is  not,  however,  obtained  in  the 
metallic  form,  for  2  out  of  every  3  eq.  combine  with  7  out  of  the  9  eq.  of  car- 
bonic oxide  gas  at  the  same  time  produced.  The  resulting  compound  has  a  dark 
grey  colour,  and  is  recognized  by  burning  on  water  with  a  violent  flame,  and 
the  production  of  croconate  and  oxalate  of  potassa.  This  compound  is  some- 
times almost  the  sole  product  of  the  process.     (Geiger's  Pharmacie,  348.) 

Prop, — Solid  at  the  ordinary  temperature  of  the  atmosphere.  At  70°  it  is 
somewhat  fluid,  though  its  fluidity  is  not  perfect  till  it  is  heated  to  150°.  At 
50°  it  is  soft  and  malleable,  and  yields  like  wax  to  the  pressure  of  the  fingers; 
but  it  becomes  brittle  when  cooled  to  32°.  It  sublimes  at  a  low  red  heat  with- 
out undergoing  any  change,  provided  atmospheric  air  be  completely  excluded. 
Its  texture  is  crystalline,  as  may  be  seen  by  breaking  it  across  while  brittle,  and 
cubic  crystals  have  been  obtained  by  Pleischl  (Fog.  An.  xxxi.  431.)  In  colour 
and  lustre  it  is  precisely  similar  to  mercury.  At  60°  its  density  is  0*865,  so  that 
it  is  considerably  lighter  than  water.  It  is  quite  opaque,  and  is  a  good  conductor 
of  heat  and  electricity. 

The  most  prominent  chemical  property  of  potassium  is  its  afiinity  for  oxygen 
gas.  It  oxidizes  rapidly  in  the  air,  or  by  contact  with  fluids  which  contain 
oxygen.  On  this  account  it  must  be  preserved  either  in  glass  tubes  hermetically 
sealed,  or  under  the  surface  of  liquids,  such  as  naphtha,  of  which  oxygen  is  not 
an  element.  If  heated  in  the  open  air,  it  takes  fire,  and  burns  with  a  purple 
flame  and  great  evolution  of  heat.  It  decomposes  water  on  the  instant  of  touch- 
ing it;  and  so  much  heat  is  disengaged,  that  the  potassium  is  inflamed,  and 
bums  vividly  while  swimming  upon  its  surface.  The  hydrogen  unites  with  a 
little  potassium  at  the  moment  of  separation ;  and  this  compound  takes  fire  as  it 
escapes,  and  thus  augments  the  brilliancy  of  the  combustion.  When  potassium 
is  plunged  under  water,  violent  reaction  ensues,  but  without  light,  and  pure 
hydrogen  gas  is  evolved. 

The  combining  weight  or  equivalent  of  potassium  is  easily  deducible  from  the 
composition  of  potassa  and  chloride  of  potassium,  which  are  admitted  to  consist 
of  single  equivalents  of  their  elements.  Gay-Lussac,  and  Thenard,  and  Davy, 
inferred  the  composition  of  potassa  from  the  hydrogen  gas  evolved  when  a  known 
weight  of  potassium  is  oxidized  under  water,  the  volume  of  the  oxygen  which 
unites  with  the  metal  being  equal  to  half  the  volume  of  the  hydrogen.  Berzelius 
analyzed  chloride  of  potassium  by  means  of  nitrate  of  oxide  of  silver,  and  inferred 
that  39*15  is  the  eq.  of  potassium.     Its  symb.  is  K. 


nf'ii  \ 


Potassium. 


Protoxide 

Peroxide 

Chloride 

Iodide 

Bromide 

Fluoride 

Hydurets 

Carburet 

Sulphuret 

Bisulphuret 

Tersulphuret 

Quadrosulphuret 

Quintosulphuret 

Phosohureta 

Seleniurets 


3915 
3915 
3915 
3915 
3915 
39-15 


:} 


1  eq.-}- Oxygen  8 
1  eq.-f  .        •  24 
1  eq.-j-Chlor.     35-42 
I  eq.-f  Iodine  126-3 
1  eq.-f-Brom.    784 
1  eq.-j- Fluor.    18-68 


Equiv, 
leq.=  47-15 
3  eq.=  63-15 
1  eq.=  74-57 
leq.  =  165-45 
1  eq.  =117-55 
1  eq.  =   57-83 


■\ 


Composition  uncertain. 

39-15    1  eq.-i- Sulphur  16-1  1  eq.  =  55-25 

39-15    1  eq.-f  do.         32-2  2eq.=  71-35 

39-15     1  eq.^do.         48.8  3eq.=   87-45 

3915     1  eq.-f  do.         64-4  4eq.  =  103-35 

39-15     1  eq.-f  do.         80-5  5eq.  =  119-65 

Composition  and  number  uncertain. 


Formula;. 
K-f-O  or  KO. 
K-fsOor  KO3. 
K-f  CI  or  KCI. 
K-f  I  or  KI. 
K-fBr.or  KBr. 
K  +  F  or  KF. 


KfSorKS. 
KfSSorKSa. 
K-fsSorKSa. 
K-f4S  orKS4. 
K-f-5S  orKSs. 


POTASSIUM.  29^ 

Protoxide  of  Potassium. — Hist,  and  Prep. — This  compound,  commonly  called 
potash  or  poiassa,  and  by  the  Germans  kali  (an  Arabic  word),  is  always  formed 
when  potassium  is  pat  into  water,  or  when  it  is  exposed  at  common  temperatures 
to  dry  air  or  oxygen  gas.  By  the  former  method  the  protoxide  is  obtained  in  com- 
bination with  water;  and  in  the  latter  it  is  anhydrous.  In  porforming  the  last- 
mentioned  process,  the  potassium  should  be  cut  into  very  thin  slices  ;  for  other- 
wise the  oxidation  is  incomplete.  The  product,  when  partially  oxidized,  is 
regarded  by  Berzelius  as  a  distinct  oxide ;  but  most  chemists  admit  it  to  be  a 
mere  mixture  of  potassa  and  potassium. 

Prop. — Anhydrous  potassa  is  a  white  solid  substance,  highly  caustic,  which 
fuses  at  a  temperature  somewhat  above  that  of  redness,  and  bears  the  strongest 
heat  of  a  wind  furnace  without  being  decomposed  or  volatilized.  It  has  a  pow- 
erful affinity  for  water,  and  intense  heat  is  disengaged  during  the  act  of  combi- 
nation. Three  compounds  are  known;  they  are  composed  of  47*15,  or  1  eq.  of 
potassa  united  with  9,  27,  and  45  parts,  or  1,  3,  and  5  eq.  of  water  respectively. 
In  the  last  compound  a  portion  of  the  water  probably  exists  as  water  of  crystal- 
lization. 

The  protohydrate  of  potassa^  KO,  HO,  is  solid  at  common  temperatures.  It 
fuses  at  a  heat  rather  below  redness,  and  assumes  a  somewhat  crystalline  texture 
in  cooling.  It  is  not  decomposed  by  any  degree  of  heat  to  which  it  has  been 
exposed,  and  hence  was  long  considered  to  be  pure  potassa.  Its  sp.  gr.  =  1'706. 
It  is  highly  deliquescent,  and  requires  about  half  its  weight  of  water  for  solu- 
tion. It  is  soluble,  likewise,  in  alcohol.  It  destroys  all  animal  textures,  and  on 
this  account  is  employed  in  surgery  as  a  caustic.  It  was  formerly  called  lapis 
causticus,  but  is  now  termed  poiassa  and  poiassa  fusa  by  the  Colleges  of  Edin- 
burgh and  London.  This  preparation  is  made  by  evaporating  the  aqueous  solu- 
tion of  potassa  in  a  silver  or  clean  iron  capsule  to  the  consistence  of  oil,  and  then 
pouring  it  into  moulds.  In  this  state  it  is  impure,  containing  oxide  of  iron, 
together  with  chloride  of  potassium,  and  carbonate  and  sulphate  of  potassa.  It 
is  purified  from  these  substances  by  solution  in  alcohol,  and  evaporation  to  the 
same  extent  as  before  in  a  silver  vessel.  The  operation  should  be  performed  ex- 
peditiously, in  order  to  prevent,  as  far  as  possible,  the  absorption  of  carbonic 
acid.  When  common  caustic  potassa  of  the  druggists  is  dissolved  in  water,  a 
number  of  small  bubbles  of  gas  is  disengaged,  which  is  pure  oxygen.  Graham 
finds  its  quantity  to  be  variable  in  different  specimens,  and  to  depend  apparently 
on  the  impurity  of  the  specimen. 

If  the  protohydrate  be  exposed  to  the  air,  it  rapidly  becomes  moist,  but  after 
absorbing  a  certain  portion  of  water,  a  perfectly  dry  substance  is  again  obtained, 
which  is  the  ierhydraie  of  poiassa,  KO,  3H0.  It  is  very  similar  in  all  its  cha- 
racters to  the  protohydrate,  but  is  much  whiter  and  more  crystalline  in  its  tex- 
ture. The  quintohydrate,  KO,  5H0,  is  obtained  by  exposing  a  very  concentrated 
solution  of  potassa  to  an  intense  cold.  It  is  then  deposited  in  four-sided  prisms 
terminated  by  a  four-sided  pyramid,  and  sometimes  in  four-sided  tables  and 
octohedrons. 

The  aqueous  solution  of  potassa,  aqua  potassas  of  the  Pharmacopceia,  is  pre- 
pared by  decomposing  carbonate  of  potassa  by  lime.  The  best  proportions  are 
1  part  of  dry  lime  to  2  of  carbonate  of  potassa.  The  lime  is  to  be  slaked  by 
being  covered  with  boiling  water,  when  it  forms  a  very  minutely  divided  hydrate, 
in  the  form  of  a  cream,  every  particle  of  which  acts,  which  is  not  the  case  in 
dry  slaking  (Mohr).    The  carbonate  is  now  dissolved  in  not  less  than  10  parts 


?mFfii|ivmi^i^ 


mm¥ 


294 


POTASSIUM. 


of  hot  water,  and  the  cream  of  lime  is  added  by  small  portions  to  the  solution, 
and  the  mixture  boiled  after  each  addition  in  a  clean  iron  vessel.  The  lime  takes 
the  carbonic  acid,  forming  insoluble  carbonate  of  lime.  When  the  whole  lime 
has  been  added,  and  the  mixture  has  been  boiled  for  some  time,  it  is  allowed  to 
subside  in  the  covered  vessel,  and  the  solution  of  caustic  potassa  may  be  decanted 
perfectly  clear.  If  the  carbonate  have  been  pure,  the  solution  yields  by  rapid 
evaporation  pure  hydrate  of  potassa.  But  if  pearlash  be  employed,  the  sulphate 
of  potash  contained  in  it  may  be  got  rid  of  by  evaporating  till  crystals  appear; 
on  cooling,  the  sulphate  is  so  completely  deposited  that  its  presence  can  no  longer 
be  detected  in  the  liquid  (Liebig).  The  same  chemist  finds  that  a  strong  solu- 
tion of  caustic  potassa  actually  deprives  carbonate  of  lime  of  its  acid,  and  that, 
from  this  circumstance,  carbonate  of  potassa  cannot  be  rendered  quite  caustic 
by  lime,  unless  diluted  with  about  ten  times  its  weight  of  water. 
As  pure  potassa  absorbs  carbonic  acid  rapidly  when  freely  exposed  to  the 
atmosphere,  it  is  desirable  to  filter  its  solution  in  vessels 
containing  as  small  a  quantity  of  air  as  possible.  This  is 
easily  effected  by  means  of  the  filtering  apparatus  devised 
by  Donovan.  It  consists  of  two  vessels  a  and  d,  of  equal 
capacity,  and  connected  with  each  other  as  represented  in 
the  annexed  wood-cut.  The  neck  b  of  the  upper  vessel 
contains  a  tight  cork,  perforated  to  admit  one  end  of  the 
glass  tube  c  ,•  and  the  lower  extremity  of  the  same  vessel 
terminates  in  a  funnel  pipe,  which  fits  into  one  of  the  necks 
of  the  under  vessel  d  by  grinding,  luting,  or  a  tight  cork. 
The  vessel  d  is  furnished  with  another  neck  c,  which  re- 
ceives the  lower  end  of  the  tube  c,  the  junction  being  se- 
cured by  means  of  a  perforated  cork,  or  luting.  The  throat 
of  the  funnel  pipe  is  obstructed  by  a  piece  of  coarse  linen 
loosely  rolled  up,  and  not  pressed  down  into  the  pipe  itself. 
The  solution  is  then  poured  in  through  the  mouth  at  Z>,  the 
cork  and  tube  having  been  removed ;  and  the  first  droppings, 
which  are  turbid,  are  not  received  in  the  lower  vessel. 
The  parts  of  the  apparatus  are  next  joined  together,  and  the 
filtration  may  proceed  at  the  slowest  rate,  without  exposure 
to  more  air  than  was  contained  in  the  vessels  at  the  begin- 
ning of  the  process.  This  apparatus  should  be  made  of  green  in  preference  to 
white  glass,  as  the  pure  alkalies  act  on  the  former  much  less  than  on  the  latter. 
(Annals  of  Philosophy,  xxvi.  115.) 

The  mode  by  which  this  apparatus  acts  scarcely  needs  explanation.  In  order 
that  the  liquid  should  descend  freely,  two  conditions  are  required : — first,  that  the 
air  above  the  liquid  should  have  the  same  elastic  force,  and  therefore  exert  the 
same  pressure,  as  that  below  ;  and  secondly,  as  one  means  of  securing  the  first 
condition,  that  the  air  should  have  free  egress  from  the  lower  vessel.  Both 
objects,  it  is  manifest,  are  accomplished  in  the  filtering  apparatus  of  Donovan; 
since  for  every  drop  of  liquid  which  descends  from  the  upper  to  the  lower  vessel, 
a  corresponding  portion  of  air  passes  along  the  tube  c  from  the  lower  vessel  to 
the  upper.  This  apparatus  is  applicable  to  any  other  case  where  it  is  wished  to 
exclude  the  atmosphere.  Other  similar  contrivances  will  be  found  in  the  scientific 
journals,  for  which  there  is  no  space  in  this  work. 

Solution  of  potassa  is  highly  caustic,  and  its  taste  intensely  acrid.    It  pos- 


POTASSIUM.  295 

sesses  alkaline  properties  in  an  eminent  degree,  converting  the  vegetable  blue 
colours  to  green,  and  neutralizing  the  strongest  acids.  It  absorbs  carbonic  acid 
gas  rapidly,  and  is  consequently  employed  for  withdrawing  that  substance  from 
gaseous  mixtures.  When  of  the  sp.  gr.  1-25,  it  is  used  in  the  analysis  of 
organic  bodies,  to  absorb  the  carbonic  acid  formed,  the  weight  of  which  is  equal 
to  the  increase  in  the  weight  of  the  potash  apparatus.  The  solution  made  from 
pearlash,  which  has  deposited  the  sulphate  of  potash,  is  exactly  of  the  proper 
strength  for  this  purpose  (Gregory).  For  the  same  reason  it  should  be  pre- 
served in  well-closed  bottles,  that  it  may  not  absorb  carbonic  acid  from  the 
atmosphere. 

Potassa  is  employed  as  a  reagent  in  detecting  the  presence  of  bodies,  and  in 
separating  them  from  each  other.  The  solid  hydrate,  owing  to  its  strong  affinity 
for  water,  is  used  for  depriving  gases  of  hygrometric  moisture,  and  is  admirably 
fitted  for  forming  frigorific  mixtures  (page  40). 

Potassa  may  be  distinguished  from  all  other  substances  by  the  following  cha- 
racters;— 1.  If  tartaric  acid  be  added  in  excess  to  a  salt  of  potassa  dissolved  in 
cold  water,  and  the  solution  be  stirred  with  a  glass  rod,  a  white  precipitate, 
bitartrate  of  potassa,  soon  appears,  which  forms  peculiar  white  streaks  upon  the 
glass  by  the  pressure  of  the  rod  in  stirring.  2.  It  is  precipitated  by  perchloric 
acid  in  the  cold,  the  perchlorate  of  potassa  having  nearly  the  same  degree  of  solu- 
bility as  the  bitartrate.  3.  A  solution  of  chloride  of  platinum  causes  a  yellow 
precipitate,  the  double  chloride  of  platinum  and  potassium.  A  drop  or  two  of 
hydrochloric  acid  should  be  added  at  the  same  time  as  the  test,  the  mixture  be 
evaporated  to  dryness  at  212°,  and  a  little  cold  water  be  afterwards  added,  when 
the  double  chloride  is  left  in  the  form  of  small  shining  yellow  crystals.  Chlo- 
ride of  platinum  dissolved  in  alcohol  often  gives  an  immediate  precipitate,  which 
falls  of  a  pale  yellow  colour.  4.  The  alcoholic  solution  of  carbazotic  acid  throws 
down  potassa  in  deep  yellow  crystals  of  carbazotate  of  potassa,  which  is  very 
sparingly  soluble.  5.  It  yields  a  light  gelatinous  precipitate,  the  double  fluoride 
of  potassium  and  silicon  with  silicated  hydrofluoric  acid.  Of  these  tests  carba- 
zotic acid  is  the  most  delicate  in  a  solution  of  pure  potassa  ;  but  when  the  alkali 
is  combined  with  a  strong  acid,  the  chloride  of  platinum  is  preferable. 

The  following  test  has  been  recommended  by  Harkort  for  distinguishing  be- 
tween potassa  and  soda  in  minerals  : — Oxide  of  nickel,  when  fused  by  the  blow- 
pipe flame  with  borax,  gives  a  brown  glass ;  and  this  glass  if  melted  with  a 
mineral  containing  potassa,  becomes  blue,  an  effect  which  is  not  produced  by  the 
presence  of  soda. 

Its  eq.  is  47-15;  symb.  K  -\-  0,  K,  or  KO. 

Peroxide. — When  potassium  burns  in  the  open  air  or  in  oxygen  gas,  it  is  con- 
verted into  an  orange-coloured  substance,  which  is  peroxide  of  potassium.  It 
may  likewise  be  formed  by  conducting  oxygen  gas  over  potash  at  a  red  heat ;  and 
it  is  produced  in  small  quantity  when  potash  is  heated  in  the  open  air.  It  is  the 
residue  of  the  decomposition  of  nitre  by  heat  in  metallic  vessels,  provided  the 
temperature  be  kept  up  for  a  sufficient  time.  When  the  peroxide  is  put  into 
water,  it  is  resolved  into  oxygen  and  potash,  the  former  of  which  escapes  with 

effervescence,  and  the  latter  is  dissolved.  Its  eq.  is  63' 15;  symb.  K  -f-  30,  K, 
or  KO3. 

Chloride  of  Potassium, — Potassium  takes  fire  spontaneously  in  an  atmosphere  of 
chlorine,  and  burns  with  greater  brilliancy  than  in  oxygen  gas.    This  chloride  is 


296  POTASSIUM. 

generated  with  evolution  of  hydrog-en  when  potassium  is  heated  in  hydrochloric 
acid  gas ;  and  it  is  the  residue  after  the  decomposition  of  chlorate  of  potassa  by 
heat.  It  is  formed  when  potassa  is  dissolved  in  a  solution  of  hydrochloric  acid, 
and  is  deposited  by  slow  evaporation  in  anhydrous  colourless  cubic  crystals.  It 
has  a  saline  and  rather  bitter  taste,  is  insoluble  in  alcohol,  and  requires  for  solu- 
tion 3  parts  of  water  at  60°,  and  still  less  of  hot  water.  Its  eq.  is  74*57  ;  symb. 
K  +  CI,  or  K  CI. 

Iodide  of  Potassium. — Prep. — This  compound  is  formed  with  evolution  of  heat 
and  light,  when  potassium  is  heated  in  contact  with  iodine  ;  it  is  the  sole  residue 
after  decomposing  iodate  of  potassa  by  heat;  and  by  neutralizing  potassa  with 
hydriodic  acid  it  is  obtained  in  solution.  The  simplest  process  for  preparing  it 
in  quantity  is  to  add  iodine  to  a  hot  solution  of  pure  potassa  until  the  alkali  is 
neutralized,  when  iodide  of  potassium  and  iodate  of  potassa  are  generated,  eva- 
porate to  dryness,  and  expose  the  dry  mass  in  a  platinum  crucible  to  a  gentle 
red  heat  in  order  to  decompose  the  iodate.  The  fused  mass  is  then  dissolved  out 
by  water  and  crystallized.  (Gregory,  Edin.  Med.  and  Surg.  Jour.  1830.)  An- 
other process  is  to  digest  iodine  with  zinc  or  iron  filings  in  water,  and  then  de- 
compose the  resulting  iodide  of  zinc  or  iron  by  a  quantity  of  potassa  just  suffi- 
cient to  precipitate  the  oxide. 

Prop. — Iodide  of  potassium  fuses  readily  when  heated,  and  rises  in  vapour  at 
a  heat  below  full  redness,  especially  in  an  open  vessel.  It  is  very  soluble  in 
water,  requiring  only  two-thirds  of  its  weight  at  60°  for  solution,  and  in  a  moist 
atmosphere  deliquesces.  It  dissolves  also  in  strong  alcohol,  even  in  the  cold ; 
and  the  solution,  when  evaporated,  yields  colourless  cubic  crystals  of  iodide  of 
potassium. 

The  commercial  iodide  is  frequently  impure,  often  containing  chloride  of  po- 
tassium or  sodium,  and  sulphate  or  carbonate  of  potassa,  the  last  sometimes  in 
very  large  quantity.  It  is  well  to  purchase  it  in  crystals,  which  ought  not  to 
deliquesce  in  a  moderately  dry  air,  but  when  in  powder  are  completely  soluble 
in  the  strongest  alcohol. 

Iodine  is  freely  soluble  in  water  which  contains  iodide  of  potassium,  a  brown 
solution  resulting,  which  has  been  thought  to  arise  from  potassium  uniting  with 
two  or  more  equivalents  of  iodine.  No  solid  compound  of  the  kind,  however, 
has  been  obtained. 

Its  eg.  is  165*45;  symb.  K  -]-  I,  or  KI. 

Bromide  of  Potassium. — ^This  compound  is  formed  by  processes  similar  to  those 
for  preparing  the  iodide,  and  is  analogous  to  it  in  most  of  its  properties.  It  is 
very  soluble  in  water,  and  crystallizes  by  evaporation  in  anhydrous  cubic  crys- 
tals, which  fuse  readily,  and  decrepitate  when  heated  like  sea-salt.  It  is  but 
slightly  soluble  in  alcohol.     Its  eq.  is  117*55  ;  si/mb.  K  -f-  Br,  or  KBr. 

Fluoride  of  Potassium. — This  compound  is  best  formed  by  nearly  saturating 
hydrofluoric  acid  with  carbonate  of  potassa,  evaporating  to  dryness  in  platinum, 
and  igniting  to  expel  any  excess  of  acid.  The  resulting  fluoride  has  a  sharp 
saline  taste,  is  alkaline  to  test  paper,  deliquesces  in  the  air,  and  dissolves  freely 
in  water.  On  evaporating  its  solution  at  a  temperature  of  100°  it  may  be  obtained 
in  tubes  or  rectangular  four-sided  prisms,  which  deliquesce  rapidly.  The  solu- 
tion acts  on  glass  in  which  it  is  kept  or  evaporated.  Heated  with  silicic  acid  it 
forms  a  fusible  limpid  glass,  which  whon  cold  "is  opaque  and  deliquescent.  Water 
dissolves  fluoride  of  potassium,  and  the  silicic  acid  is  left. 

Its  eg.  ia  57*83 ;  symb.  K  t  F,  or  KF. 


POTASSIUM.  2^7 

Hydrogen  and  Potassium. — These  substances  unite  in  two  proportions,  forming 
in  one  case  a  solid,  and  in  the  other  a  gaseous  compound.  The  latter  is  pro- 
duced when  hydrate  of  potash  is  decomposed  by  iron  at  a  white  heat,  and  it  ap- 
pears also  to  be  generated  when  potassium  burns  on  the  surface  of  water.  It 
inflames  spontaneously  in  air  or  oxygen  gas  ;  but  on  standing  for  some  hours  over 
mercury,  the  greater  part,  if  not  the  whole  of  the  potassium,  is  deposited. 

The  solid  hyduret  of  potassium  was  made  by  Gay-Lussac  and  Thenard,  by 
heating  potassium  in  hydrogen  gas.  It  is  a  grey,  solid  substance,  which  is 
readily  decomposed  by  heat  or  contact  w4th  water.  It  does  not  inflame  sponta- 
neously in  oxygen  gas. 

Carburet  of  Potassium. — ^This  compound  has  not  been  obtained  in  a  pure  state ; 
but  it  is  thought  to  form  part  of  the  residue  in  the  preparation  of  potassium  from 
charcoal ;  for  on  pouring  that  matter  into  water,  effervescence  ensues,  owing  to 
the  escape  of  carburetted  hydrogen  gas,  and  carbonate  of  potassa  is  found  in  so- 
lution. 

Sulphurets  of  Potassium. — Potassium  unites  readily  with  sulphur  by  the  aid  of 
gentle  heat,  emitting  so  much  heat  that  the  mass  becomes  incandescent.  The 
nature  of  the  product  depends  on  the  proportions  which  are  employed.  The  pro- 
tosulphufet  is  readily  prepared  by  decomposing  sulphate  of  potassa  by  charcoal 
or  hydrogen  gas  at  a  red  heat.  It  may  be  prepared  in  the  moist  way  by  a  pro- 
cess which  will  be  mentioned  in  describing  the  sulphur-salts. 

The  protosulphuret  of  potassium  fuses  below  a  red  heat,  and  acquires  on  cool- 
ing a  crystalline  texture.  It  has  a  red  colour,  its  taste  is  at  first  strongly  alkaline 
and  then  sulphurous,  has  an  alkaline  reaction  with  test  paper,  deliquesces  on  ex- 
posure to  the  air,  and  is  soluble  in  water  and  alcohol.  Most  of  the  acids  decom- 
pose it  with  evolution  of  hydrosulphuric  acid  gas,  and  without  any  deposite  of 
sulphur.  It  takes  fire  when  heated  before  the  blowpipe,  and  quickly  acquires  a 
coating  of  sulphate  of  potassa,  which  stops  the  combustion ;  but  when  mixed  in 
fine  division  with  charcoal,  it  kindles  spontaneously,  forming  a  good  pyrophoruS. 

Its  eq.  is  bb'2b ;  symh.  K  -f-  S,  or  KS. 

The  bisulphuret  is  formed  by  exposing  a  saturated  solution  in  alcohol  of  hydro- 
sulphate  or  sulphuret  of  potassium  (KS  -}-  HS),  until  a  pellicle  begins  to  form 
upon  its  surface,  and  then  evaporating  to  dryness  without  further  exposure.  The 
first  change  consists  in  oxygen  of  the  air  uniting  with  hydrogen  of  hydrosulphu- 
ric acid,  the  sulphur  of  which  unites  with  potassium.  Then  the  formation  of 
hyposulphurous  acid  begins ;  and  as  the  hyposulphite  of  potassa  is  insoluble  in 
alcohol,  it  gives  a  pellicle  on  its  surface.  It  may  also  be  obtained  from  an 
aqueous  solution  of  the  protosulphuret.  This  compound,  when  pure,  dissolves 
in  water  without  colour ;  but  exposed  to  the  air,  oxygen  is  rapidly  absorbed,  and 
the  solution  becomes  yellow.  The  change  is  effected  by  one  half  of  the  potas- 
sium combining  with  oxygen  and  yielding  its  sulphur  to  the  remainder  by  which 
the  bisulphuret  of  potassium  and  potassa  are  formed.  Thus  2KS  yield  KSj,  and 
KO.  If  the  solution  continues  to  be  exposed,  it  again  becomes  colourless,  owing 
to  the  conversion  of  the  bisulphuret  into  hyposulphite  of  potassa. 

Its  eq.  IS  71 '35  ;  symb.  K  -j-  2S,  or  KS2. 

The  tersulphuret  is  prepared  pure  by  transmitting  the  vapour  of  bisulphuret  of 
carbon  over  carbonate  of  potassa  at  red  heat,  as  long  as  carbonic  acid  or  carbonic 
oxide  gases  are  disengaged.  It  is  also  formed  when  carbonate  of  potassa  is  heated 
to  low  redness  with  half  its  weight  of  sulphur,  until  the  mass  appears  in  tranquil 
fusion :  the  oxygen  of  3-4ths  of  the  potassa  unites  with  sulphur  to  form  sulphuric 


298  POTASSIUM. 

acid,  which  exactly  suffices  to  neutralize  l-4th  of  the  alkali,  and  all  the  carhonic 
acid  is  evolved  as  gas. — Thus 

4  eq.  Potassa  and  10  eq.  Sulphur    2     3  eq.  Tersulphuret  and  1  eq.  Sulphate. 
4K0  Sio  g.        3KS3  KO,  SO3. 

This  is  known  under  the  name  of  liver  of  sulphur  (p.  284). 

Its  eq.  is  87-45 ;  symb.  K  -|-  3S,  or  KS3. 

The  quadrosulphuret  is  prepared  hy  transmitting  the  vapour  of  bisulphuret  of 
carbon  over  sulphate  of  potassa  at  a  red  heat  until  carbonic  acid  gas  ceases  to  be 
disengaged ;  ol  by  conducting  the  same  process  with  the  tersulphuret  prepared 
by  the  second  method,  until  its  sulphuric  acid  and  potassa  are  decomposed. 

Its  eq.  is  103-55  ;  symb.  K  -j-  4S,  or  KS^. 

The  quiniosulphuret  is  formed  by  fusing  carbonate  of  potassa  with  its  own 
weight  of  sulphur,  the  residue  containing  sulphate  of  potassa  as  in  preparing  the 
tersulphuret.  Each  equivalent  of  potassium  with  five  of  sulphur,  being  the 
highest  degree  of  sulphuration  which  can  be  formed  by  fusion. 

Its  eq.  is  119-65;  symh.  K  -f-  5S,  or  KS5. 

These  four  last  sulphurets  are  deliquescent  in  the  air,  have  a  sulphurous 
odour,  and  are  soluble  in  water;  and  those  who  consider  them  to  decompose 
water  in  dissolving,  suppose  the  formation  of  corresponding  compounds  of 
hydrogen  and  sulphur.  On  decomposing  the  solutions  with  hydrochloric  or 
sulphuric  acid,  the  changes  ensue  which  have  already  been  explained  (page  264). 
As  the  solution  of  the  quintosulphuret  dissolves  sulphur,  a  still  higher  degree  of 
sulphuration  must  probably  exist. 

Two  other  compounds  of  sulphur  and  potassium,  the  composition  of  which 
are  KgS  ,  and  K2S9,  have  been  described.  The  first  of  these  is  produced  when 
sulphate  of  potassa  is  heated  in  a  stream  of  sulphuretted  hydrogen ;  and  the 
latter,  when  the  quadrosulphuret  of  potassium  is  heated  in  a  similar  manner. 
The  definite  nature  of  these  compounds  may  be  considered  doubtful. 

Phosphurets  of  Potassium. — "When  potassium  is  heated  in  phosphuretted  hydro- 
gen gas,  it  takes  fire,  phosphuret  of  potassium  is  formed,  and  hydrogen  set  free; 
and  combination  is  also  effected  by  gently  heating  phosphorus  with  potassium. 
The  number  and  proportion  of  these  compounds  have  not  yet  been  determined. 
They  decompose  water  with  formation  of  phosphuretted  hydrogen,  potassa,  and 
some  acid  of  phosphorus. 

Seleniurets  of  Potassium. — These  elements  unite  when  fused  together,  some- 
times with  explosive  violence,  forming  a  crystalline  fusible  compound  of  an  iron 
grey  colour  and  metallic  lustre.  It  dissolves  completely  in  water,  yielding  a 
deep  red  solution,  very  similar  in  taste  and  odour  to  solutions  of  sulphuret  of 
potassium.  On  adding  an  acid,  hydroselenic  acid  gas  is  evolved,  and  selenium 
deposited.  Solution  of  potassa  dissolves  selenium,  and  gives  rise  to  a  seleniuret 
of  potassium  and  selenite  of  potassa  ;  and  the  same  compounds  are  formed  when 
selenium  is  heated  with  carbonate  of  potassa. 


f 
SODIUM. 


SECTION  II. 


SODIUM. 


Hist,  and  Prep. — The  Natrium  of  the  Germans,  was  discovered  in  1807,  a 
few  days  after  the  discovery  of  potassium.  The  first  portions  of  it  were  obtained 
by  means  of  galvanism ;  but  it  may  be  procured  in  much  larger  quantity  by 
chemical  processes,  precisely  similar  to  those  described  in  the  last  section.  As 
sodium  may  be  obtained  in  much  larger  quantity  than  potassium,  owing  to  the 
fact  that  it  does  not  combine,  like  the  former,  with  carbonic  acid,  the  method  of 
preparing  sodium  as  described  by  Schoedler  (Liebig's  Annalen,  vol.  xx.  p.  2)  is 
here  briefly  noticed.  Three  pounds  of  commercial  acetate  of  soda  are  ignited, 
and  the  residue,  which  weighs  1  lb.  consisting  of  carbonate  mixed  with  charcoal, 
is  further  mixed  with  J  lb.  of  finely-powdered  charcoal  and  J  lb.  of  charcoal  in 
coarser  particles,  to  prevent  fusion  of  the  mass.  It  is  then  heated  in  the  usual 
manner  in  an  iron  bottle,  such  as  is  used  for  holding  mercury  in  commerce. 
This  process  is  so  productive  that  in  one  operation  with  the  above  quantities 
Schcedler  obtained  4i  oz.  of  pure  sodium.  As  a  quantity  half  larger  may  be 
heated  in  such  a  bottle,  it  is  possible  to  obtain  in  one  operation  upwards  of  6  oz. 
of  sodium ;  and  this  from  the  cheapest  materials.  Sodium  thus  prepared  has 
been  sold  at  three  or  four  shillings  per  ounce.  It  might  be  made  much  cheaper 
even  than  this,  and  as  it  oxidizes  less  rapidly  than  potassium,  it  is  much  better 
adapted  for  experiments  of  research. 

Prop. — It  has  a  strong  metallic  lustre,  and  in  colour  is  very  analogous  to  silver. 
It  is  so  soft  at  common  temperatures,  that  it  may  be  formed  into  leaves  by  the 
pressure  of  the  fingers.  It  fuses  at  200°,  and  rises  in  vapour  at  a  red  heat.  Its 
sp.  gr.  is  0*972.  It  soon  tarnishes  on  exposure  to  the  air,  though  less  rapidly 
than  potassium.  Like  that  metal,  it  is  instantly  oxidized  by  water,  hydrogen 
gas  in  temporary  union  with  a  little  sodium  being  disengaged.  When  thrown 
on  cold  water,  it  swims  on  its  surface,  and  is  rapidly  oxidized,  though  in  general 
without  inflaming;  but  with  hot  water  it  scintillates,  or  even  takes  fire.  Ducatel 
finds  that  the  heat  rises  high  enough  for  inflammation  with  cold  water,  if  the 
sodium  be  confined  to  one  spot,  and  the  water  rest  on  a  non-conducting  sub- 
stance, such  as  charcoal.  (Silliman's  Journal,  xxv.  90.)  In  each  case,  soda  is 
generated,  and  the  water  acquires  an  alkaline  reaction. 

The  composition  of  soda  was  determined  by  the  same  methods  as  that  of 
potassa,  and  agreeably  to  the  observations  of  Berzelius  23'3  may  be  taken  as  the 
eq.  of  sodium.  Its  symh.  is  Na.  The  composition  of  the  compounds  of  sodium 
described  in  this  section  is  as  follows . — 


Sodium. 

Equiv. 

Formulae. 

Protoxide 

23-3     1  eq.-j- Oxygen 

8 

1  eq.=  31-3 

NafO  or  Na. 

Peroxide 

46-6     2  eq.-f-do. 

24 

3  eq.=  70-6 

2Na-l-30  or  Na. 

Chloride 

23-3     1  eq.-f  Chlorine 

35-42 

1  eq.=  58-72 

Naf  CI  or  NaCi. 

Iodide 

23-3     1  eq.-f- Iodine 

126-3 

1  eq.=149-6 

Na-j-I  or  Na  I. 

300 

SODIUM. 

Bromide 
Fluoride 
Sulphuret 

Sodium. 
23-3     1  eq.-|- Bromine           78-4 
23-3     1  eq.f  Fluorine          1868 
23-3    1  eq.-j-Sulphur           16-1 

Equiv. 
1  eq.=101-7 
1  eq.=  41-98 
1  eq.=  39-4 

FormuljB. 
NafBr.  orNaBr. 
Na-j-ForNaF. 
Nats  or  Na  S. 

Soda. — Prep. — The  protoxide  of  sodium,  commonly  called  soda^  and  by  the 
Germans  natron^  is  formed  by  the  oxidation  of  sodium  in  air  or  water,  as  potassa 
is  from  potassium.  In  its  anhydrous  state  it  is  a  grey  solid,  difficult  of  fusion, 
and  very  similar  in  all  its  characters  to  potassa.  With  water  it  forms  a  solid 
hydrate,  easily  fusible  by  heat,  which  is  very  caustic,  soluble  in  water  and 
alcohol,  has  powerful  alkaline  properties,  and  in  all  its  chemical  relations  is 
exceedingly  analogous  to  potassa.  It  is  prepared  from  the  solution  of  pure  soda, 
exactly  in  the  same  manner  as  the  corresponding  preparations  of  potassa.  The 
solid  hydrate  (NaO,  HO)  is  composed  of  3 1 "3  parts  or  1  eq.  of  soda,  and  9  parts 
or  1  eq.  of  water. 

Prop. — Soda  is  readily  distinguished  from  other  alkaline  bases  by  the  follow- 
ing characters.  1.  It  yields,  with  sulphuric  acid,  a  salt  which,  by  its  taste  and 
form,  is  easily  recognized  as  Glauber's  salt,  or  sulphate  of  soda.  2.  All  its  salts 
are  soluble  in  water,  and  are  not  precipitated  by  any  reagent.  3.  On  exposing 
its  salts  by  means  of  platinum  wire  to  the  blowpipe  flame,  they  communicate  to 
it  a  rich  yellow  colour. 

Iti  eq.  ts31'3  ;  symb.  Na  -f-  0,  Na,  or  NaO. 

Peroxide  of  Sodium. — This  compound  is  formed  when  sodium  is  heated  to 
redness  in  an  excess  of  oxygen  gas.  It  has  an  orange  colour,  has  neither  acid 
nor  alkaline  properties,  and  is  resolved  by  water  into  soda  and  oxygen. 

lis  eq.  is  70-6;  symb.  2Na  +  30,  Na,  or  NagOa. 

Chloride  of  Sodium.— Hist,  and  Prep. — This  compound  may  be  formed  directly 
by  burning  sodium  in  chlorine,  by  heating  sodium  in  hydrochloric  acid  gas,  and 
by  neutralizing  soda  with  hydrochloric  acid.  It  exists  as  a  mineral  under  the 
name  of  rock  salt,  is  the  chief  ingredient  of  sea-water,  and  is  contained  in  many 
saline  springs.  From  these  sources  are  derived  the  different  varieties  of  common 
salt,  such  as  rock,  bay,  fishery,  and  stoved  salt,  which  differ  from  each  other 
only  in  degrees  of  purity  and  mode  of  preparation.  The  rock  and  bay  salt  are 
the  purest,  but  always  contain  small  quantities  of  sulphate  of  magnesia  and  lin>e, 
and  chloride  of  magnesium.  These  earths  may  be  precipitated  as  carbonate  by 
boiling  a  solution  of  salt  for  a  few  minutes  with  a  slight  excess  of  carbonate  of 
soda,  filtering  the  liquid,  and  neutralizing  with  hydrochloric  acid.  On  evapo- 
rating this  solution  rapidly,  chloride  of  sodium  crystallizes  in  hollow  four-sided 
pyramids ;  but  it  occurs  in  regular  cubic  crystals  when  the  solution  is  allowed 
to  evaporate  spontaneously.  These  crystals  contain  no  water  of  crystallization, 
but  decrepitate  remarkably  when  heated,  owing  to  the  expansion  of  water 
mechanically  confined  within  them. 

Prop. — Pure  chloride  of  sodium  has  an  agreeably  saline  taste.  It  fuses  at  a 
red  heat,  and  becomes  a  transparent  brittle  mass  on  cooling.  It  deliquesces 
slightly  in  a  moist  atmosphere,  but  undergoes  no  change  when  the  air  is  dry. 
In  pure  alcohol  it  is  insoluble.  It  requires  twice  and  a  half  its  weight  of  water 
at  60°  for  solution,  and  its  solubility  is  not  increased  by  heat.  Hydrous  sul- 
phuric acid  decomposes  it  with  evolution  of  hydrochloric  acid  gas,  and  formation 
of  sulphate  of  soda. 

The  uses  of  chloride  of  sodium  are  well  known.     Besides  its  employment  in 


SODIUM.  30?! 

seasoning  food,  and  in  preserving  meat  from  putrefaction,  a  property  which, 
when  pure,  it  possesses  in  a  high  degree,  it  is  used  for  various  purposes  in  the 
arts,  especially  in  the  formation  of  hydrochloric  acid  and  hypochlorite  of  lime. 

Its  eq.  is  58-72  ;  symh.  Na  f  CI,  or  NaCl. 

Iodide  of  Sodium. — It  is  obtained  pare  by  processes  similar  to  those  for  pre- 
paring iodide  of  potassium  ;  but  it  is  contained  in  sea-water,  in  many  salt 
springs,  and  in  the  residual  liquor  from  kelp.  It  is  a  neutral  compound,  deli- 
quescent in  the  air,  soluble  in  water  and  alcohol,  fuses  readily  by  heat,  and  is 
volatile,  though  in  a  less  degree  than  iodide  of  potassium.  Evaporated  at  123° 
it  crystallizes  from  its  aqueous  solution  in  cubes,  which  Berzelius  found  to  con- 
tain 20*23  per  cent,  of  water. 

Its  eq.  is  149-6;  symh.  Na  -f-  I,  or  Nal. 

Bromide  of  Sodium. — ^This  compound  is  very  analogous  to  sea-salt,  and  is 
associated  with  it  in  sea-salt  and  most  salt  springs.  At  86°  it  crystallizes  from 
its  aqueous  solution  in  anhydrous  cubes ;  but  at  lower  temperatures  it  separates 
in  hexagonal  tables,  which  Mitscherlich  found  to  contain  26*37  per  cent,  of  water, 
or  4  eq.  to  1  eq.  of  the  bromide. 

Its  eq.  is  101*7 ;  symb.  Na  -{-  Br,  or  NaBr. 

Fluoride  of  Sodium. — ^This  compound  is  formed  by  neutralizing  hydrofluoric 
acid  by  soda,  and  by  igniting  the  double  fluoride  of  sodium  and  silicon,  when 
the  fluoride  of  silicon  is  expelled.  When  obtained  by  the  second  process,  it 
crystallizes  from  its  aqueous  solution  in  rhomboidal  crystals,  but  is  obtained  in 
cubes,  its  proper  form,  by  a  second  crystallization :  when  carbonate  of  soda  is 
present,  it  crystallizes  in  octohedrons. 

Fluoride  of  sodium  in  crystals  is  anhydrous,  is  almost  insoluble  in  alcohol, 
and  requires  25  times  its  weight  both  of  hot  and  cold  water  for  solution.  It 
attacks  glass  vessels  when  evaporated  in  them,  and  by  fusion  unites  with  silicic 
acid,  forming  a  glass  which  is  more  fusible  than  the  pure  fluoride ;  but  water 
dissolves  out  the  fluoride,  and  leaves  the  silicic  acid. 

Its  eq.  is  41-98 ;  symb.  Na  -f-  F,  or  NaF. 

Sulphurei  of  Sodium. — The  protosulphuret  is  obtained  by  processes  similar  to 
those  for  protosulphuret  of  potassium,  to  which  in  its  taste  and  chemical  rela- 
tions it  is  very  similar.  A  concentrated  solution  of  it  yields  hydrated,  square, 
four-sided  prisms,  which,  when  heated,  fuse  in  their  water  of  crystallization,  and 
then  leave  a  white  anhydrous  mass.  It  deliquesces  in  the  air,  is  very  soluble 
in  water,  and  is  also  dissolved,  though  in  a  smaller  degree,  by  alcohol.  In  solu- 
tion it  absorbs  oxygen  very  rapidly  from  the  air,  and  passes  into  hyposulphate 
of  soda. 

Its  eq.  is  39-4  ;  symb.  Na  -f-  S,  or  NaS. 

Sodium  unites  with  sulphur  in  other  proportions ;  but  the  resulting  compounds 
have  not  been  studied. 

According  to  Gmelin  of  Tubingen,  sulphuret  of  sodium  is  the  colouring  prin- 
ciple of  lapis  lazuli^  to  which  the  colour  of  ultramarine  is  owing;  and  he  has 
succeeded  in  preparing  artificial  ultramarine  by  heating  sulphuret  of  sodium 
with  a  mixture  of  silicic  acid  and  alumina.  (An.  de  Ch.  et  Ph.  xxxvii.  409.) 
Artificial  ultramarine,  thus  prepared,  is  sold  in  Paris  at  a  moderate  price.  The 
finer  specimens  are  quite  equal  to  the  native  ultramarine,  and  much  less  expen- 
sive. 


302  LITHIUM. 


SECTION  III. 


LITHIUM. 


Davy  succeeded  by  means  of  galvanism  in  obtaining  from  lithia  a  while- 
coloured  metal  like  sodium ;  but  it  was  oxidized,  and  thus  reconverted  into 
lithia,  with  such  rapidity  that  its  properties  could  not  be  farther  examined.  Its 
eq.  inferred  from  the  composition  of  sulphate  of  lithia  by  Stromeyer  and  Thom- 
son, is  10 ;  but  the  accuracy  of  this  estimate  is  rendered  doubtful  by  the  experi- 
ments of  M.  Herrman,  according  to  which  6  is  a  nearer  estimate.  Its  symb.  is  L. 
The  compounds  of  lithium  described  in  this  section /ire  thus  constituted: — 

Lithium.  Equiv.  Formulae. 

Lithia.           -      6      1  eq.  -|-  Oxygen  .  8  1  eq.  =  14  L  -|-  0  or  LO. 

Chloride        -       6       1  eq.  -f  Chlorine  .  35-42  1  eq.  =  41-42  L  -j-  CI  or  LCI. 

Fluoride       -      6      1  eq. -f  Fluorine  .  18-68  leq.  =  24-68  L -f  F  or  LF. 

Lithia, — Hist, — This,  the  only  known  oxide  of  lithium,  was  discovered  in 
1818  by  M.  Arfwedson  (An.  de  Ch.  et  Ph.  x.)  in  a  mineral  called  petalite,-  and 
its  presence  has  since  been  detected  in  spodumene,  lepidolite,  and  in  several 
varieties  of  mica.  Berzelius  has  found  it  also  in  the  waters  of  Carlsbad  in 
Bohemia.  From  the  circumstance  of  its  having  been  first  obtained  from  an 
earthy  mineral,  Arfwedson  gave  it  the  name  of  lithion,  (from  JuQftoj,  lapideus,) 
a  term  since  changed  in  this  country  to  lithia.  It  has  hitherto  been  procured  in 
small  quantity  only,  because  spodumene  and  petalite  are  rare,  and  do  not  con- 
tain more  than  6  or  8  per  cent,  of  the  alkali.  It  is  combined  in  these  two  mine- 
rals with  silicic  acid  and  alumina,  whereas  potassa  is  likewise  present  in  lepido- 
lite and  lithion-mica,  and  therefore  lithia  should  be  prepared  solely  from  the 
former. 

Prep. — The  best  process  for  preparing  lithia  is  that  which  was  suggested  by 
Berzelius.  One  part  of  petalite  or  spodumene,  in  fine  powder,  is  mixed  inti- 
mately with  two  parts  of  fluor-spar,  and  the  mixture  is  heated  with  thr^e  or  four 
times  its  weight  of  sulphuric  acid,  as  long  as  any  acid  vapours  are  disengaged. 
The  silicic  acid  of  the  mineral  is  attacked  by  hydrofluoric  acid,  and  dissipated 
in  the  form  of  fluosilicic  acid  gas,  while  the  alumina  and  lithia  unite  with  sul- 
phuric acid.  After  dissolving  these  salts  in  water,  the  solution  is  boiled  with 
pure  ammonia  to  precipitate  the  alumina :  it  is  then  filtered  and  evaporated  to 
dryness,  and  the  dry  mass  heated  to  redness  to  expel  the  sulphate  of  ammonia. 
The  residue  is  pure  sulphate  of  lithia. 

Prop. — Lithia,  in  its  alkalinity,  in  forming  a  hydrate  with  water,  and  in  its 
chemical  relations,  is  closely  allied  to  potassa  and  soda.  It  is  distinguished  from 
them  by  its  greater  neutralizing  power,  by  forming  sparingly  soluble  compounds 
with  carbonic  and  phosphoric  acids,  and  by  its  salts,  when  heated  on  platinum 
wire  before  the  blowpipe,  tinging  the  flame  of  a  red  colour.  Also,  when  fused 
on  platinum  foil,  it  attacks  that  metal  and  leaves  a  dull  yellow  trace  round  the 
spot  where  it  lay.     It  is  distinguished  from  baryta,  strontia,  and  lime,  by  form- 


BARIUM.  303 

ing  soluble  salts  with  sulphuric  and  oxalic  acids,  and  from  magnesia  by  its  car- 
bonate, though  sparingly  soluble  in  water,  forming  with  it  a  solution  which  has 

an  alkaline  reaction.    Its  eq.  is  14  ;  symb.  L  -j-  O,  L,  or  LO. 

Chloride  of  Lithium. — It  is  readily  obtained  by  dissolving  Uthia  or  its  carbonate 
in  hydrochloric  acid.  Like  the  chlorides  of  sodium  and  potassium,  it  yields  by 
evaporation  in  a  warm  place  colourless,  anhydrous,  cubic  crystals,  which  differ 
from  those  chlorides  in  being  very  deliquescent,  dissolving  freely  in  alcohol  as 
well  as  water,  and  in  its  alcoholic  solution  burning  with  a  red  flame. 

Its  eq.  is  41*42;  si/mb.  L  -|-  CI,  or  LCI. 

The  iodide  and  bromide  of  lithium  have  not  been  examined. 

Fluoride  of  Lithium. — This  is  a  fusible  compound,  prepared  by  dissolving 
lithia  in  hydrofluoric  acid,  and  possesses  about  the  sara^  solubility  in  water  as 
the  carbonate. 


CLASS    I. 

ORDER  II. 

METALLIC  BASES  OF  THE  ALKALINE  EARTHS. 

SECTION  IV. 

BARIUM. 

Hist,  and  Prep. — Davy  discovered  barium,  the  metallic  base  of  baryta,  in  the 
year  1808,  by  a  process  suggested  by  Berzelius  and  Pontin.  It  consists  in 
forming  carbonate  of  baryta  into  a  paste  with  water,  placing  a  globule  of  mer- 
cury in  a  little  hollow  made  in  its  surface,  and  laying  the  paste  on  a  platinum 
tray  which  communicated  with  the  positive  pole  of  a  galvanic  battery  of  100 
double  plates,  while  the  negative  wire  was  in  contact  with  the  mercury.  The 
baryta  was  decomposed,  and  its  barium  combined  with  mercury.  This  amalgam 
was  then  heated  in  a  vessel  free  from  air,  by  which  means  the  mercury  was 
expelled,  and  barium  obtained  in  a  pure  form. 

Prop. — A  dark  grey  coloured  metal,  with  a  lustre  inferior  to  cast  iron.  It  is 
far  denser  than  water,  for  it  sinks  rapidly  in  strong  sulphuric  acid.  It  attracts 
oxygen  with  avidity  from  the  air,  and  in  doing  so  yields  a  white  powder,  which 
is  baryta.  It  effervesces  strongly  from  the  escape  of  hydrogen  gas  when  thrown 
into  water,  and  a  solution  of  baryta  is  produced.  It  has  hitherto  been  obtained 
in  very  minute  quantities,  and  consequently  its  properties  have  not  been  deter- 
mined with  precision. 

The  eq.  of  barium,  deduced  from  an  analysis  of  the  chloride  by  Berzelius  and 


304  BARIUM. 

myself,  is  68*7.  Its  symb.  is  Ba.  The  compositioo  of  its  compounds  described 
in  this  section  is  as  follows  : — 

Barium.  Equiv.  Formulse. 

all    Protoxide  68-7  1  eq.  +  Oxygea  8  1  eq.=»   76-7  Ba -{- 0  or  BaO. 

^fi    Peroxide  68-7  1  eq.  -f  Ditto  16  2  eq.  =   84-7  Ba  -f  20  or  BaOj. 

,j;5|;  Chloride  68-7  1  eq.  4"  Chlorine  35-42  leq.=  104-12  Ba -j- CI  or  BaCl. 

Iodide  68-7  1  eq. -j- Iodine  126-3  leq.  =  195-0  Ba -f  I  or  Bal, 

Bromide  68:7  1  eq. -f  Bromine  78-4  leq.  =  1471  Ba -f"  Br  or  BaBr. 

Fluoride  68-7  1  eq.  -f  Fluorine  18-68  1  eq.  =   87-38  Ba  -[-  F  or  BaF. 

Sulphuret  68'7  1  eq. -j"  Sulphur  161  leq.  =   84-8  Ba -f  S  or  BaS. 

*  Protoxide  of  Barium. — Hist,  and  Prep. — Bart/teg  or  Baryta,  so  called  from  the 
great  density  of  its  coippounds,  (from  |3a^uj,  heavy,)  was  discovered  in  the  year 
1774  by  Scheele.  It  is  the  sole  product  of  the  oxidation  of  barium  in  air  or 
water.  It  may  be  prepared  by  decomposing  either  the  nitrate  or  iodate  of  baryta 
at  a  red  heat ;  or  by  exposing  carbonate  of  baryta  contained  in  a  black-lead  cru- 
cible to  an  intense  white  heat,  a  process  which  succeeds  much  better  when  the 
carbonate  is  intimately  mixed  with  charcoal. 

Prop. — A  grey  powder,  the  sp.  gr.  of  which  is  about  4.  It  requires  a  very  high 
temperature  for  fusion ;  its  solution  in  water  has  a  sharp  caustic  alkaline  taste, 
converts  vegetable  blue  colours  to  green,  and  neutralizes  the  strongest  acids.  Its 
alkalinity,  therefore,  is  equally  distinct  as  that  of  potassa  or  soda ;  but  it  is  much 
less  caustic  than  those  alkalies.  In  pure  alcohol  it  is  insoluble.  It  has  an  ex- 
ceedingly strong  affinity  for  water.  When  mixed  with  that  liquid  it  slakes  in  the 
same  manner  as  quicklime,  but  with  the  evolution  of  a  more  intense  heat,  which, 
according  to  Dobereiner,  sometimes  amounts  to  incandescence.  The  result  is  a 
white  bulky  hydrate,  fusible  at  a  red  heat,  and  which  bears  the  highest  tempera- 
ture of  a  smith's  forge  without  parting  with  its  water.  It  is  composed  of  76*7 
parts  or  1  eq.  of  baryta,  and  9  parts  or  1  eq.  of  water.     HO,  BaO. 

Hydrate  of  baryta  dissolves  in  three  times  its  weight  of  boiling  water,  and  in 
twenty  parts  of  water  at  the  temperature  of  60°  F.  (Davy.)  It  is  therefore  less 
soluble  than  potassa  or  soda.  A  saturated  solution  of  baryta  in  boiling  water 
deposits,  in  cooling,  transparent,  flattened  prismatic  crystals,  which  are  composed, 
according  to  Phillips,  of  76*7  parts  or  1  eq.  of  baryta,  and  90  parts  or  10  eq.  of 
water.  Smith  states,  however,  that  the  quantity  of  water  amounts  only  to  81 
parts  or  9  eq.  He  has  also  pointed  out  the  existence  of  a  hydrate  containing 
only  2  eq.  of  water;  it  is  a  white  powder  which  is  formed  by  exposing  the  crys- 
tallized hydrate  to  the  temperature  of  a  sand  bath.  (Phil.  Mag.  and  An.  vi.  53, 
and  ix.  87.) 

The  aqueous  solution  of  baryta  is  an  excellent  test  of  the  presence  of  carbonic 
acid  in  the  atmosphere  or  in  other  gaseous  mixtures.  The  carbonic  acid  unites 
with  the  baryta,  and  a  white  insoluble  precipitate,  carbonate  of  baryta,  subsides. 

Baryta  is  distinguished  from  all  other  substances  by  the  following  characters. 
1.  By  dissolving  in  water  and  forming  an  alkaline  solution.  2.  By  all  its  solu- 
ble salts  being  precipitated  as  white  carbonate  of  baryta  by  alkaline  carbonates, 
and  as  sulphate  of  baryta,  which  is  insoluble  both  in  acid  and  alkaline  solutions^ 
by  sulphuric  acid  or  any  soluble  sulphate.  3.  By  the  characters  of  chloride  of 
barium,  formed  by  the  action  of  hydrochloric,  acid  on  baryta. 

The  readiest  method  of  preparing  the  soluble  salts  of  baryta  is  by  dissolving 
the  carbonate  in  dilute  acid.    All  of  its  soluble  salts  are  poisonous ;  and  the  car- 


BARIUM.  ,  305 

bonate,  from  being  dissolved  by  the  juices  of  the  stomach,  likewise  acts  as  a 
poison.     The  sulphate,  from  its  insolubility,  is  inert. 

Its  eq.  is  76-7  ;  symb.  Ba-fO,  Ba,  or  BaO. 

Peroxide  of  Barium. — This  oxide,  which  is  used  by  Thenard  in  preparing 
peroxide  of  hydrogen,  may  be  formed  by  conducting  dry  oxygen  gas  over  pure 
baryta  at  a  low  red  heat.  A  still  easier  process,  given  by  Wohler  and  Liebig, 
is  to  heat  pure  baryta  to  low  redness  in  a  platinum  crucible,  and  then  gradually 
to  add  chlorate  of  potassa  in  the  ratio  of  about  one  part  of  the  latter  to  four  of  the 
former.  The  oxygen  of  the  chlorate  goes  over  to  the  baryta,  and  chloride  of 
potassium  is  generated.  Cold  water  afterwards  removes  the  chloride,  and  the 
peroxide  of  barium  is  left  as  a  hydrate  with  6  eq.  of  water,  its  formula  being 
BaO^fGaq. 

Chloride  of  Barium. — It  is  generated  when  chlorine  gas  is  conducted  over 
baryta  at  a  red  heat,  oxygen  gas  being  disengaged ;  but  it  is  most  conveniently 
prepared  by  dissolving  carbonate  of  baryta  in  hydrochloric  acid  diluted  with 
about  three  times  its  weight  of  water,  or  by  decomposing  a  solution  of  sulphuret 
of  barium  with  hydrochloric  acid.  On  concentrating  its  solution,  the  chloride 
crystallizes  on  cooling  in  flat  four-sided  tables  bevelled  at  the  edges,  very  like 
crystals  of  heavy  spar.  These  crystals  consist  of  104*12  parts  or  1  eq.  of  chlo- 
ride of  barium,  and  18  parts  or  2  eq.  of  water,  its  formula  being  BaCl  -f-  2  aq. 
They  do  not  change  in  ordinary  states  of  the  air;  but  in  a  very  dry  atmosphere 
at  60°  they  lose  all  their  water,  and  recover  it  again  in  a  moist  air.  They  are 
still  more  rapidly  rendered  anhydrous  at  212°,  and  fusion  ensues  at  a  full  red 
heat.  They  are  insoluble  in  strong  alcohol ;  100  parts  of  water  dissolve  43*5  at 
60°  and  78  at  222°,  which  is  the  boiling  point  of  the  solution.  Its  eq.is  104-12; 
symh.  Ba  +  CI,  or  BaCl.  ♦ 

Iodide  of  Barium.^ — This,  compound  may  be  formed  in  the  same  way  as  iodide 
of  potassium.  It  is  very  soluble  in  water,  and  crystallizes  in  small  colourless 
needles,  which  deliquesce  slightly.  On  exposure  to  the  air  a  portion  of  car- 
bonate of  baryta  is  formed,  and  iodine  set  free,  which  probably  forms  a  periodide 
of  barium. 

Its  eq.  is  159  ;  symb.  Ba  -\-  I,  or  Bal. 

Bromide  of  Barium. — It  was  prepared  by  M.  Henry,  jun.  who  has  examined 
it,  by  boiling  protobromide  of  iron  with  moist  carbonate  of  baryta  in  exccvSS,  eva- 
porating the  filtered  solution,  and  heating  the  residue  to  redness.  The  product 
crystallizes  by  careful  evaporation  in  white  rhombic  prisms,  which  have  a  bitter 
taste,  are  slightly  deliquescent,  and  are  soluble  in  water  and  alcohoL 

Its  eq.  is  147'1 ;  symb.  Ba  -j-  Br,  or  Ba  Br. 

Fluoride  of  Barium. — On  digesting  recently  precipitated  and  moist  carbonate 
of  baryta  in  hydrofluoric  acid,  carbonic  acid  is  expelled,  and  fluoride  of  barium 
collects  in  the  form  of  a  white  powder,  which  bears  a  red  heat  without  decom- 
position. It  is  sparingly  soluble  in  water,  and  by  evaporation  separates  in  crys- 
talline grains.     It  is  soluble  in  nitric  and  hydrochloric  acids. 

Its  eq.  is  87 '38 ;  symb.  Ba  -|-  F,  or  BaF. 

Sulphuret  of  Barium. — Prep. — This  compound  may  be  formed  by  transmitting 
dry  hydrosulphuric  acid  gas  over  pure  baryta  at  a  red  heat;  and  by  the  action 
of  hydrogen  gas  or  charcoal  on  sulphate  of  baryta.  The  easiest  process  is  to  mix 
sulphate  of  baryta  in  fine  powder  into  a  paste  with  an  equal  volume  of  flour,  one- 
third  its  weight  of  finely  powdered  charcoal,  place  it  in  a  hessian  crucible  on 

23 


306  STRONTIUM. 

which  a  cover  is  luted,  and  expose  it  to  a  white  heat  for  an  hour  or  two,  raising 
the  temperature  slowly.  On  pouring  hot  water  on  the  ignited  mass,  the  sul- 
phuret  of  barium  is  dissolved,  and  may  be  separated  from  undecomposed  sulphate 
and  excess  of  charcoal  by  filtration. 

Protosulphuret  of  barium  is  very  soluble  in  hot  water,  and  the  solution  if  satu- 
rated deposits  colourless  crystals  on  cooling,  which  are  sulphuretof  barium  with 
water  of  crystallization.  The  solution  has  a  sulphurous  odour,  and  absorbs  oxy- 
gen and  carbonic  acid  from  the  air,  yielding  carbonate  and  hyposulphite  of  baryta. 
Boiled  with  sulphur  it  yields  a  yellow  solution,  and  contains  a  persulphuret  of 
barium. 

Sulphuret  of  barium  supplies  a  ready  mode  of  obtaining  pure  baryta  and  its 
salts,  when  the  carbonate  cannot  be  obtained.  Thus  its  solution  boiled  with  black 
oxide  of  copper  until  it  ceases  to  precipitate  a  salt  of  lead  black,  yields  pure 
baryta,  which  should  be  filtered  while  hot  to  separate  the  sulphuret  of  copper : 
it  is  apt  to  retain  traces  of  oxide  of  copper.  With  a  solution  of  carbonate  of 
potassa,  carbonate  of  baryta  falls,  and  sulphuret  of  potassium  remains  in  solu- 
tion ;  and  with  hydrochloric  acid  it  interchanges  elements,  by  which  hydrosul- 
phuric  acid  and  chloride  of  barium  are  formed.  The  sulphuret  of  barium  is  now 
much  used  in  organic  researches,  particularly  in  purifying  vegetable  acids,  such 
as  malic  acid  (Liebig).    Its  eq,  is  84*8 ;  si/mb,  Ba  -\-  S,  or  BaS, 


SECTION  V. 


STRONTIUM. 


Davy  discovered  the  metallic  base  of  strontia,  called  slrorUium^  by  a  process 
analogous  to  that  described  in  the  last  section.  All  that  is  known  respecting 
its  properties  is,  that  it  is  a  heavy  metal,  similar  in  appearance  to  barium,  that 
it  decomposes  water  with  evolution  of  hydrogen  gas,  and  oxidizes  quickly  in  the 
air,  being  converted  in  both  cases  into  strontia,  which  is  the  protoxide  of  the 
metal. 

The  eq.  of  strontium,  deduced  from  the  experiments  of  Stromeyer,  is  43*8;  its 
symb.  Sr.  The  composition  of  its  several  compounds  described  in  this  section 
is  as  follows  : — 

Strontium.  Equiv.  Formulse. 

Protoxide  ,  43-8  1  eq.-f-Oxygen      8  1  eq.=  51  8  Sr-fO    or  SO. 

Peroxide  .  43-8  1  eq.-f-Do.           16  2  eq.=  69-8  Sr-f-20  or  SO2. 

Chloride  .  43-8  1  eq.-j- Chlorine  35-42  1  eq.=  79-22  Sr-f  CI  or  SrCl. 

Iodide  .  43-8  1  eq.-f- Iodine    1263  1  eq.=170-l  Sr-f-I     or  Sri. 

Fluoride  .  43-8  1  eq.-f  Fluorine  18-68  1  eq.=  6248  Sr-f  F    or  Srf. 

Sulphuret  .  43-8  2  eq.-f  Sulphur   16-1  1  eq.=:  59-9  Sr-fs     or  SrS. 

Protoxide  of  Slronlium. — Hist. — From  the  close  resemblance  between  baryta 
and  strontia,  these  substances  were  once  supposed  to  be  identical.  Crawford, 
however,  and  Sulzer  noticed  a  difference  between  them;  but  the  existence  of 


STRONTIUM.  gfOy 

slrontia  was  first  established  with  certainty  in  the  year  1792  by  Hope,*  and  the 
discovery  was  made  about  the  same  time  by  Klaproth.j-  It  was  originally  ex^ 
tracted  from  strontianite,  native  carbonate  of  strontia,  a  mineral  fouifid  at  Stron- 
tian  in  Scotland ;  and  hence  the  origin  of  the  term  Strontites,  or  Strontia,  by 
which  the  earth  itself  is  designated. 

Prep,  and  Prop. — Pure  strontia  may  be  prepared  from  nitrate  and  carbonate 
of  strontia,  in  the  same  manner  as  baryta.  It  resembles  this  earth  in  appearance, 
in  infusibility,  and  in  possessing  distinct  alkaline  properties.  It  slakes  when 
mixed  with  water,  causing  intense  heat,  and  forming  a  white  solid  hydrate, 
which  consists  of  51*8  parts  or  1  eq.  of  strontia,  and  9  parts  or  1  eq.  of  water. 
Hydrate  of  strontia  fuses  readily  at  a  red  heat.  It  is  insoluble  in  alcohol.  Boiling 
water  dissolves  it  freely,  and  a  hot  saturated  solution,  on  cooling,  deposits  trans- 
parent crystals  in  the  form  of  thin  quadrangular  tables,  which  consist  of  1  eq.  of 
strontia  and  10  eq.  of  water  according  to  Phillips,  Smith  gives  its  composition  to 
be  SrO  -J-  9H0.  He  also  states  that  dried  at  212°  it  becomes  SrO  -\-  HO,  and  is 
anhydrous  on  exposure  to  a  red  heat.  It  requires  50  times  its  weight  of  water 
at  60°  degrees  for  solution,  and  twice  its  weight  at  212°  F,  (Dalton.) 

The  solution  of  strontia  has  a  caustic  taste  and  alkaline  reaction.  Like  the 
solution  of  baryta,  it  is  a  delicate  test  of  the  presence  of  carbonic  acid  in  air  or 
other  gaseous  mixtures,  forming  with  it  the  insoluble  carbonate  of  strontia. 

The  salts  of  strontia  are  best  prepared  from  the  native  carbonate.  Like  those 
of  baryta,  they  are  precipitated  by  alkaline  carbonates,  and  by  sulphuric  acid  or 
soluble  sulphates.  But  sulphate  of  strontia  is  less  insoluble  than  sulphate  of 
baryta  :  on  adding  sulphate  of  soda  in  excess  to  a  barytic  solution,  baryta  cannot 
afterwards  be  found  in  the  liquid  by  any  precipitant ;  but  when  strontia  is  thus 
treated,  so  much  sulphate  of  strontia  remains  in  solution,  that  the  filtered  liquid 
yields  a  white  precipitate  with  carbonate  of  soda.  [The  hyposulphite  of  strontia 
is  quite  soluble,  while  that  of  baryta  is  insoluble.  These  earths  may  therefore 
be  separated  by  means  of  hyposulphite  of  soda.]  The  salts  of  strontia  are  not 
poisonous  ;  and  most  of  them,  when  heated  on  platinum  wire  before  the  blow- 
pipe, communicate  to  the  flame  a  red  tint. 

Its  eq.  is  51*8  ;  symb.  Sr  -f-  O,  Sr,  or  SO. 

Peroxide  of  Strontium  is  prepared  in  the  same  way  as  peroxide  of  barium,  and, 
like  it,  is  resolved  by  dilute  acids  into  strontia  and  oxygen,  the  latter  of  which 
forms  peroxide  of  hydrogen  with  the  water. 

Chloride  of  Strontium. — This  compound  is  formed  by  processes  similar  to  those 
for  preparing  chloride  of  barium,  and  crystallizes  from  its  solution  in  colourless 
prismatic  crystals,  which  deliquesce  in  a  moist  atmosphere,  require  only  twice 
their  weight  of  water  at  60°  for  solution,  and  still  less  of  boiling  water,  and  are 
soluble  in  alcohol.  The  alcoholic  solution,  when  set  on  fire,  burns  with  a  red 
flame.  These  characters  aflford  a  certain  mode  of  distinguishing  strontia  from 
baryta.  The  crystals  consist  of  79*22  parts  or  1  eq.  of  chloride  of  strontium, 
and  81  parts  or  9  eq.  of  water,  which  are  expelled  by  heat.  The  anhydrous 
chloride  fuses  at  a  red  heat,  and  yields  a  white  crystalline  brittle  mass  on  cooling. 

Ms  eq.  is  79-22 ;  ST/mb.  Sr  f  CI,  or  SrCl. 

Iodide  of  Strontium  may  be  prepared  in  the  same  manner  as  that  of  barium. 
It  is  very  soluble  in  water,  and  fuses  without  decomposition  in  close  vessels  ;  but 
when  heated  to  redness  in  the  open  air,  iodine  escapes,  and  strontia  is  generated. 
*  Edin.  Philos.  Trans,  iv.  3.  +  Klaproth's  Contributions,  i. 


9011  CALCIUM. 

Fluoride  of  Strontium  is  obtained  in  the  same  way  as  fluoride  of  barium,  and 
is  a  white  powder  of  sparing  solubility. 

Protomlphuret  of  Strontium  is  similar  in  its  properties  and  mode  of  prepara- 
tion to  sulphuret  of  barium,  and  may  be  applied  to  similar  uses.  Strontium  also 
combines  with  more  than  one  equivalent  of  sulphur;  but  these  compounds  have 
not  been  examined. 


SECTION  VI. 


CALCIUM. 


The  existence  of  calcium,  the  metallic  base  of  lime,  was  demonstrated  by 
Davy  by  a  process  similar  to  that  described  in  the  section  on  barium.  It  is  of  a 
whiter  colour  than  barium  or  strontium,  and  is  converted  into  lime  by  being 
oxidized.     Its  other  properties  are  unknown. 

According  to  the  analysis  of  chloride  of  calcium  by  Berzelius,  the  eq.  of  cal- 
dtimis20'5;  its  symb.  is  Ga.  Its  compounds  described  in  this  section  are 
composed  as  follows  :—   •-s^^i'i  •' 


Calcium, 

!,%Wv-^'   ■ 

Formulae. 

Protoxide 

20-6  1  eq.  ■\:  Oxygen 

S 

leq.==   28-5 

Ca  -|-  0   or  CaO. 

Peroxide 

20-5  1  eq.  4" 

16-0 

2eq.=    36-5 

Caf  20orCa02. 

Chloride 

20-5  1  eq.  -jr.  Chlorine 

35-42 

1  eq.  =   55-92 

Ca  -f  CI  or  CaCl. 

Iodide 

20-5  1  eq.  -|-  Iodine 

126-3 

1  eq.  =  146-8 

Ca-j-I   orCaL 

Bromide 

20-5  1  eq.  -\-  Bromine 

78-4 

1  eq.  =   98-9 

Ca  -f  Bror  CaBr. 

Fluoride 

20-5  1  eq.  -f  Fluorine 

18-68 

leq.=    39-18 

Ca  -j-  F   or  CaF. 

Sulphuret 

20-5  1  eq.  4*  Sulphur 

16-1 

1  eq.  =    36-6 

Ca  -f  S   or  CaS. 

Bisulphuret 

20-5  1  eq.  t 

32-2 

2eq.=   52-7 

Ca  4"  28  or  CaSj. 

Quintosulphuret 

20-5  1  eq.  4- 

80-5 

5eq.=  101 

Ca  4-  5S  or  CaSg. 

Phosphuret 

. 

20-5  1  eq.  -f  Phosph. 

15-7 

1  eq.  s=   36-2 

Ca4-P   orCaP. 

Protoxide  of  Calcium. — Prep. — This  compound,  commonly  known  by  the 
name  of  lime  and  quicklime,  is  obtained  by  exposing  carbonate  of  lime  to  a 
strong  red  heat,  so  as  to  expel  its  carbonic  acid.  K  lime  of  great  purity  is 
required,  it  should  be  prepared  from  pure  carbonate  of  lime,  such  as  Iceland 
spar  or  Carrara  marble;  but  in  burning  lime  in  lime-kilns  for  making  mortar, 
common  limestone  is  employed.  The  expulsion  of  carbonic  acid  is  facilitated 
by  mixing  the  carbonate  with  combustible  substances,  in  which  case  carbonic 
oxide  is  generated,  A  current  of  air  also  greatly  facilitates  the  burning  of  lime; 
for  in  close  vessels  it  is  hardly  possible  to  expel  the  whole  carbonic  acid.  The 
effect  of  a  current  of  air  is  partly  due  to  the  diffusion  of  one  gas  in  another. 

Prop. — It  is  a  brittle  white  earthy  solid,  the  sp.  gr.  of  which  is  about  2*3.  It 
phosphoresces  powerfully  when  heated  to  full  redness,  a  property  which  it  pos- 
sesses in  common  with  strontia  and  baryta.  It  is  one  of  the  most  infusible  bodies 
known;  fusing  with  difficulty,  even  by  the  heat  of  the  oxy-hydrogen  blowpipe. 
It  has  a  powerful  affinity  for  water,  and  the  combination  is  attended  with  great 
increase  of  temperature,  and  formation  of  a  white  bulky  hydrate,  which  is  com- 


CALCIUM.  ^0^ 

posed  of  28*5  parts  or  1  eq.  of  lime,  and  9  parts  or  1  eq.  of  water.  The  pro- 
cess of  slaking  lime  consists  in  forming  this  hydrate,  and  the  hydrate  itself  is 
called  slaked  lime.  It  differs  from  the  hydrate  of  baryta  in  parting  with  its 
water  at  a  red  heat. 

Hydrate  of  lime  is  dissolved  very  sparingly  by  water,  and  it  is  a  singular  fact, 
first  noticed,  I  believe,  by  Dal  ton,  that  it  is  more  soluble  in  cold  than  in  hot 
water.    Thus  he  found  that  one  grain  of  lime  requires  for  solution 

778  grains  of  water     .  .  .  .  at    60°  F. 

972  "  ....  130° 

1270  "  .  .  .  .  212° 

And,  consequently,  on  heating  a  solution  of  lime  water,  which  has  been  prepared 
in  the  cold,  deposition  of  lime  ensues.  This  fact  was  determined  experimentally 
by  Phillips,  who  has  likewise  observed  that  water  at  32°  is  capable  of  dissolv- 
ing twice  as  much  lime  as  at  212°  F.  Owing  to  this  circumstance  pure  lime 
cannot  be  made  to  crystallize  in  the  same  manner  as  baryta  or  strontia ;  but  Gay- 
Lussac  succeeded  in  obtaining  crystals  of  lime  by  evaporating  lime  water  under 
the  exhausted  receiver  of  an  air-pump  by  means  of  sulphuric  acid.  Small  trans- 
parent crystals,  in  the  form  of  regular  hexahedrons,  were  deposited,  which  con- 
sist of  water  and  lime  in  the  same  proportion  as  in  the  hydrate  above  mentioned. 

Lime  water  is  prepared  by  mixing  hydrate  of  lime  with  water,  agitating  the 
mixture  repeatedly,  and  then  setting  it  aside  in  a  well-stopped  bottle  until  the 
undissolved  parts  shall  have  subsided.  The  substance  called  milk  or  cream  of 
lime  is  made  by  mixing  hydrate  of  lime  with  a  sufficient  quantity  of  water  to 
give  it  the  liquid  form ; — it  is  merely  lime  water  in  which  hydrate  of  lime  is 
mechanically  suspended. 

Lime  water  has  a  harsh  acrid  taste,  and  converts  vegetable  blue  colours  to 
green. — It  agrees,  therefore,  with  baryta  and  strontia  in  possessing  distinct  alka- 
line properties.  Like  the  solutions  of  these  earths,  it  has  a  strong  affinity  for 
carbonic  acid,  and  forms  with  it  an  insoluble  carbonate.  On  this  account  lime 
water  should  be  carefully  protected  from  the  air.  For  the  same  reason,  lime 
water  is  rendered  turbid  by  a  solution  of  carbonic  acid ;  but  on  adding  a  large 
quantity  of  the  acid,  the  transparency  of  the  solution  is  completely  restored, 
because  carbonate  of  lime  is  soluble  in  an  excess  of  carbonic  acid.  The  action 
of  this  acid  on  the  solutions  of  baryta  and  strontia  is  precisely  similar. 

The  salts  of  lime  which  are  easily  prepared  by  the  action  of  acids  on  pure 
marble,  are  in  many  respects  similarly  affected  by  reagents,  as  those  of  baryfti 
and  strontia.  They  are  precipitated,  for  example,  by  alkaline  carbonates.  Sul- 
phuric acid  and  soluble  sulphates  likewise  precipitate  lime  from  a  moderately 
strong  solution.  But  sulphate  of  lime  has  a  considerable  degree  of  solubility. 
Thus,  a  dilute  solution  of  a  salt  of  lime  is  not  precipitated  at  all  by  sulphuric 
acid ;  and  when  the  sulphate  of  lime  is  separated,  it  may  be  redissolved  by  the 
addition  of  nitric  acid. 

The  most  delicate  test  of  the  presence  of  lime  in  neutral  solutions  is  oxalate 
of  ammonia  or  potassa ;  for  of  all  the  salts  of  lime,  the  oxalate  is  the  most  inso- 
luble in  water.  This  serves  to  distinguish  lime  from  most  substances,  though 
not  from  baryta  and  strontia  ;  because  the  oxalates  of  baryta  and  strontia,  espe- 
cially the  latter,  are  likewise  sparingly  soluble. — All  these  oxalates  dissolve 
readily  in  water  acidulated  with  nitric  or  hydrochloric  acid.  It  is  distinguished 
from  baryta  and  strontia  by  the  fact,  that  nitrate  of  lime  yields  prismatic  crystals 


^ 


CALCIUM. 


by  evaporation,  is  deliquescent  in  a  high  decree,  and  very  soluble  in  alcohol ; 
while  the  nitrates  of  baryta  and  strontia  crystallize  in  regular  octohedrons,  or 
segments  of  the  octohedron,  undergo  no  change  on  exposure  to  the  air,  except 
when  it  is  very  moist,  and  do  not  dissolve  in  pure  alcohol. 

The  salts  of  lime,  when  heated  before  the  blowpipe,  or  when  their  solutions  in 
alcohol  are  set  on  fire,  communicate  to  the  flame  a  dull  brownish-red  colour.  ' 

lis  eq.  is  28*5 ;  st/mb.  Ca  +  O,  Ca,  or  CaO. 

Peroxide  of  Calcium. — This  oxide  is  prepared  in  the  same  way  as  peroxide  of 
barium,  and  is  similar  to  it  in  its  properties. 

Chloride  of  Calcium. — This  compound  exists  in  sea-water  and  in  many  saline 
springs,  is  the  residue  of  the  process  for  preparing  ammonia,  and  is  readily 
formed  by  dissolving  marble  or  chalk  in  hydrochloric  acid.  On  evaporating  its 
solution  to  the  consistence  of  a  syrup,  the  chloride  crystallizes  on  cooling  in 
irregular,  colourless  prismatic  crystals,  which  consist  of  55'92  parts  or  1  eq.  of 
chloride  of  calcium  and  54  parts  or  6  eq.  of  water.  By  heat  it  loses  its  water, 
and  at  a  gentle  red  heat  fuses ;  but  on  exposure  to  the  air  it  rapidly  recovers  its 
water  of  crystallization  and  then  deliquesces.  Owing  to  its  strong  affinity  for 
water,  it  is  much  used  for  frigorific  mixtures  with  snow ;  but  for  this  purpose  the 
hydrous  chloride  is  preferable,  as  prepared  by  evaporating  its  solution  so  far, 
that  the  whole  becomes  a  solid  mass  on  removal  from  the  fire,  reducing  it  when 
cold  quickly  to  powder,  and  preserving  it  in  bottles  closed  with  great  care.  It 
is  also  used  for  drying  gases,  and  ethereal  and  oily  liquids,  and,  in  organic 
analysis,  to  absorb  the  water  formed,  and  thus  determine  the  amount  of  hydro- 
gen. Chloride  of  calcium  is  very  soluble  in  alcohol,  and  forms  with  it  a  definite 
compound. 

Its  eq.  is  55*92 ;  si/mb.  Ca  -}-  CI,  or  CaCl. 

Iodide  of  Calcium. — This  compound  may  be  prepared  by  digesting  hydrate  of 
lime  with  protiodide  of  iron.  It  is  deliquescent  and  very  soluble  in  water,  sus- 
tains a  red  heat  unchanged  in  close  vessels,  but  when  heated  in  the  open  air  its 
iodine  is  replaced  by  oxygen,  and  lime  remains.  The  solution  of  iodide  of  cal- 
cium dissolves  a  large  quantity  of  iodine,  and  on  evaporating  the  brown  solution 
in  vacuo  above  a  vessel  with  dry  carbonate  of  potassa,  a  periodide  of  calcium 
crystallizes  in  large  black  prisms  of  a  metallic  lustre. 

Its  eq.  is  46*8  ;  si/mb.  Ca  -f  I,  or  Cal. 

Bromide  of  Calcium. — It  was  prepared  by  Henry  by  digesting  hydrate  of  lime 
with  a  solution  of  protobromide  of  iron,  and  crystallizes  in  acicular  crystals  which 
are  very  deliquescent,  and  extremely  soluble  in  alcohol  and  water.  It  is  very 
analogous  in  taste  and  properties  to  chloride  of  calcium,  fuses  by  heat,  but  in 
open  vessels  suffers  partial  decomposition. 

Its  eq.  is  98-9 ;  si/mb.  Ca  -|-  Br,  or  CaBr. 

Fluoride  if  Calcium. — Hist,  and  Prep. — This  is  a  natural  product,  which  fre- 
quently accompanies  metallic  ores,  especially  those  of  lead  and  tin,  often  occurs 
in  cubic  crystals,  and  is  well  known  under  the  name  of  fluor  or  Derbyshire  spar. 
The  crystals  found  in  the  lead  mines  of  Derbyshire  are  remarkable  for  the  large- 
ness of  their  size,  the  regularity  of  their  form,  and  the  variety  and  beauty  of  their 
colours.  It  may  be  prepared  artificially  by  digesting  moist,  recently  precipitated, 
carbonate  of  lime  in  an  excess  of  hydrofluoric  acid  ;  or  by  mixing  a  solution  of 
chloride  of  calcium  with  fluoride  of  potassium  or  sodium.  As  prepared  in  the 
latter  mode,  it  is  a  bulky  gelatinous  mass,  which  it  is  very  difficult  to  wash ; 


MAGNESIUM.  31 X 

"Whereas  the  former  method  gives  it  in  the  state  of  a  granular  white  powder, 
which  may  be  washed  with  ease. 

Prep. — Fluoride  of  calcium  fuses  at  a  red  heat  without  farther  change.  It  is 
insoluble  in  water,  slightly  soluble  in  hot  diluted  hydrochloric  acid,  and  is  de- 
composed by  sulphuric  acid  aided  by  gentle  heat.  It  is  in  a  small  degree  de- 
composed by  boiling  nitric  acid.  Fused  with  carbonate  of  potassa,  carbonate  of 
lime  and  fluoride  of  potassium  are  generated. 

Fluor-spar  is  much  used  in  forming  vases,  as  a  flux  in  metallurgic  processes, 
and  in  the  preparation  of  hydrofluoric  acid. 

Its  eq.  is  39-18 ;  synib.  Ca  -f-  F,  or  CaF. 

Protosulphuret  of  Calcium. — Prep. — By  reduction  from  the  sulphate  by  hydro- 
gen or  charcoal,  and  when  pure  is  white  with  a  reddish  tint,  and  is  very  spar- 
ingly soluble  in  water.  It  has  the  property,  in  common  with  sulphuret  of  barium, 
of  being  phosphorescent  after  exposure  to  light,  and  appears  to  be  the  essential 
ingredient  of  Canton's  Phosphorus. 

When  3  parts  of  slaked  lime,  1  of  sulphur,  and  20  of  water  are  boiled  together 
for  an  hour,  and  the  solution,  without  separation  from  the  sediment,  is  set  aside 
in  a  corked  flask  for  a  few  days,  a  copious  deposite  of  orange-coloured  crystals 
are  deposited,  which,  when  slowly  formed,  are  flat  quadrilateral  prisms.  These, 
from  the  analysis  of  Herschel,  appear  to  be  bisulphuret  of  calcium  with  3  eq.  of 
water.  They  are  decomposed  by  exposure  to  the  air,  and  are  of  sparing  solubi- 
lity in  water.     Symb.  CaS. 

When  either  of  the  foregoing  sulphurets  is  boiled  in  water  along  with  sulphur, 
a  yellow  solution  is  formed  containing  calcium  combined  with  5  eq.  of  sulphur. 
Symb.  CaSg. 

Phosphuret  of  Calcium. — It  is  formed  by  passing  the  vapour  of  phosphorus  over 
fragments  of  quicklime  at  a  low  red  heat,  or  by  heating  to  redness  small  pieces 
of  quicklime  in  the  bottom  of  a  tall  crucible  or  matrass,  and  dropping  into  a  hol- 
low made  in  the  centre  of  the  ignited  lime,  small  fragments  of  phosphorus, 
when  a  brown  matter  is  formed,  consisting  of  phosphate  of  lime  and  phosphuret 
of  calcium.  When  put  into  water,  mutual  decomposition  ensues,  and  phosphu- 
retted  hydrogen,  hypophosphorous  acid,  and  phosphoric  acid  are  generated. 


SECTION   VII. 


MAGNESIUM. 


Hist,  and  Prep. — The  galvanic  researches  of  Davy  demonstrated  the  existence 
of  magnesium,  though  he  obtained  it  in  a  quantity  too  minute  for  determining  its 
properties.  It  was  prepared  by  Bussy,  in  the  year  1830,  by  the  action  of  potas- 
sium on  chloride  of  magnesium.  For  this  purpose  five  or  six  pieces  of  potas- 
sium, of  the  size  of  peas,  were  introduced  into  a  glass  tube,  the  sealed  extremity 
of  which  was  bent  into  the  form  of  a  retort,  and  upon  the  potassium  were  laid 
fragments  of  chloride  of  magnesium.    The  latter  being  then  heated  to  near  its 


312  MAGNESIUM. 

point  of  fusion,  a  lamp  was  applied  to  the  potassium,  and  its  vapour  transmitted 
through  the  mass  of  heated  chloride.  Vivid  incandescence  immediately  took 
place,  and  on  putting  the  mass,  after  cooling,  into  water,  the  chloride  of  potas- 
sium with  undecomposed  chloride  of  magnesium  was  dissolved,  and  metallic 
magnesium  subsided.  These  results  have  been  since  confirmed  by  Liebig.  (An. 
de  Ch.  et  Ph.  xlvi.  435.) 

Prop. — Magnesium  has  a  brilliant  metallic  lustre,  and  a  white  colour  like  sil- 
ver, is  very  malleable,  and  fuses  at  a  red  heat.  Moist  air  oxidizes  it  superfi- 
cially ;  but  it  undergoes  no  change  in  a  dry  air,  and  may  be  boiled  in  water  with- 
out oxidation.  Heated  to  redness  in  air  or  oxygen  gas,  it  burns  with  brilliancy, 
yielding  magnesia ;  and  it  inflames  spontaneously  in  chlorine  gas.  It  is  readily 
dissolved  by  dilute  acids  with  disengagement  of  hydrogen,  and  the  solution  is 
found  to  contain  a  pure  salt  of  magnesia.  In  these  and  other  respects  it  is  more 
strikingly  analogous  to  zinc  than  any  of  the  metals  thus  far  treated  of. 

The  eq.  of  magnesium,  inferred  by  Berzelius  from  the  quantity  of  sulphate 
obtained  from  a  known  weight  of  pure  magnesia,  is  12*7  ;  its  symb.  is  Mg.  Its 
compounds  described  in  this  section  are  composed  as  follows : — 


Magnesium. 

Equiv. 

Formulae. 

Protoxide    . 

.     12-7     1  eq.-}- Oxygen        8 

1  eq.=  20-7 

Mg-|-0  or  MgO. 

Chloride       . 

,     12-7     1  eq.-|- Chlorine     35-42 

leq.:=  48-12 

MgfCl  or  MgCl. 

Iodide     .     . 

12-7    leq.-f-Iodine      126'3 

1  eq.=139 

Mg+I    orMgl. 

Bromide 

127     1  eq. -}- Bromine    78-4 

leq.=  9M 

Mg-j-Bror  MgBr. 

Fluoride      . 

,      12-7     1  eq.-j- Fluorine  18-68 

1  eq.=  31-38 

Mg-f-F   orMgF. 

Protoxide  of  Magnesium. — Prep. — ^This,  the  only  known  oxide  of  magnesium, 
commonly  known  by  the  name  of  magnesia,  is  best  obtained  by  exposing  car- 
bonate of  magnesia  to  a  very  strong  red  heat,  by  which  its  carbonic  acid  is  ex- 
pelled. It  is  a  white  friable  powder,  of  an  earthy  appearance;  and  when  pure  it 
has  neither  taste  nor  odour.  Its  sp.  gr.  is  about  2*3,  and  it  is  exceedingly  infu- 
sible. It  has  a  weaker  affinity  than  lime  for  water ;  for  though  it  forms  a  hydrate 
when  moistened,  the  combination  is  effected  with  hardly  any  disengagement  of 
heat,  and  the  product  is  readily  decomposed  by  a  red  heat.  According  to  the 
analysis  of  Stromeyer,  the  native  hydrate  contains  1  eq.  of  each  of  its  constitu- 
ents ;  and  the  results  of  the  analyses  of  Berzelius  and  Fyfe  accord  very  nearly 
with  thfs  proportion.  It  has  generally  been  thought  that  magnesia  formed  seve- 
ral hydrates;  but  the  recent  observations  of  Rees  indicate  that  the  artificial  hy- 
drates have  the  same  composition  as  the  native  (Phil.  Mag.  and  An.  x.  454). 

Prop. — Very  sparingly  soluble  in  water.  According  to  Fyfe,  it  requires  5142 
times  its  weight  of  water  at  60°,  and  36,000  of  boiling  water  for  solution.  The 
resulting  liquid  does  not  change  the  colour  of  violets  ;  but  when  pure  magnesia 
is  put  upon  moistened  turmeric  paper,  it  causes  a  brown  stain.  From  this  there 
is  na  doubt  that  the  inaction  of  magnesia  with  respect  to  vegetable  colours,  when 
tried  in  the  ordinary  mode,  is  owing  to  its  insolubility. — It  possesses  the  still 
more  essential  character  of  alkalinity,  that,  namely,  of  forming  neutral  salts  with 
acids,  in  an  eminent  degree.  It  absorbs  both  water  and  carbonic  acid  when  ex- 
posed to  the  atmosphere,  and  therefore  should  be  kept  in  well-closed  phials. 

Magnesia  is  characterized  by  the  following  properties.  With  nitric  and  hydro- 
chloric acids  it  forms  salts  which  are  soluble  in  alcohol,  and  exceedingly  deli- 
quescent. The  sulphate  of  magnesia  is  very  soluble  in  water,  a  circumstance  by 
which  it  is  distinguished  from  the  other  alkaline  earths.     Magnesia  is  precipi- 


MAGNESIUM.  513 

tated  from  its  salts  as  a  bulky  hydrate  by  the  pure  alkalies.  It  is  precipitated  as 
carbonate  of  magnesia,  by  the  carbonates  of  potassa  and  soda ;  but  the  bicarbonates, 
and  the  common  carbonate  of  ammonia,  do  not  precipitate  it  in  the  cold.  If 
moderately  diluted,  the  salts  of  magnesia  are  not  precipitated  by  oxalate  of  am- 
monia. By  means  of  this  reagent  magnesia  may  be  both  distinguished  and  sepa- 
rated from  lime.  [The  most  delicate  test  for  magnesia,  even  in  very  dilute 
solutions,  is  the  common  phosphate  of  soda,  with  the  addition  of  ammonia.  A 
white  crystalline  precipitate  of  basic  phosphate  of  magnesia  and  ammonia  is 
formed,  the  separation  of  which  is  much  promoted  by  brisk  stirring  with  a  glass 
rod.] 

Its  eq.  is  20-7 ;  symb.  Mg  -f-  O,  Mg,  or  MgO. 

Chloride. — This  compound  may  be  prepared  by  transmitting  dry  chlorine  gas 
over  a  mixture  of  magnesia  and  charcoal  at  a  red  heat ;  but  Liebig  has  given  an 
easier  process,  which  consists  in  dissolving  magnesia  in  hydrochloric  acid,  eva- 
porating to  dryness,  mixing  the  residue  with  its  own  weight  of  hydrochlorate  of 
ammonia,  and  projecting  the  mixture  in  successive  portions  into  a  platinum  cru- 
cible at  a  red  heat.  As  soon  as  the  ammoniacal  salt  is  wholly  expelled,  the 
fused  chloride  of  magnesium  is  left  in  a  state  of  tranquil  fusion,  and  on  cooling 
becomes  a  transparent  colourless  mass,  perfectly  anhydrous,  highly  deliquescent, 
and  is  very  soluble  in  alcohol  and  water. 

[When  carbonate  of  magnesia  is  neutralized  by  hydrochloric  acid,  a  chloride 
of  magnesium  is  formed  which  contains  6  eq.  of  water.  This,  howejjer,  suffers 
decomposition  when  heated,  hydrochloric  acid  escapes  and  pure  magnesia 
remains ;  so  that  it  cannot  be  obtained  in  an  anhydrous  condition.  The  chloride, 
prepared  by  Leibig's  method,  is  that  which  is  employed  in  obtaining  the  metal.] 

Its  eq.  is  48*  12  ;  symb.  MgCl. 

Iodide  of  magnesium  is  obtained  by  dissolving  magnesia  in  hydriodic  acid,  is 
very  soluble  in  water,  and  is  only  known  in  solution. 

Bromide  of  magnesium,  obtained  by  dissolving  magnesia  in  hydrobromic  acid, 
crystallizes  in  small  acicular  prisms,  which  have  a  sharp  taste,  are  deliquescent, 
and  very  soluble  in  water  and  alcohol.     It  is  decomposed  by  a  strong  heat. 

Fluoride  of  magnesium  is  prepared  by  digesting  magnesia  in  hydrofluoric  acid 
in  excess.  It  is  insoluble  in  water  and  in  excess  of  hydrofluoric  acid,  and  bears 
a  red  heat  without  decomposition. 


314  ALUMINIUM. 


CLASS   I. 

ORDER  III. 

METALLIC  BASES  OF  THE  EARTHS. 


SECTION  VIII. 

ALUMINIUM. 

Hht. — ^That  alumina  is  an  oxidized  body  was  proved  by  Davy,  who  found 
that  potassa  is  generated  when  the  vapour  of  potassium  is  brought  into  contact 
with  pure  alumina  heated  to  whiteness  ;  and  it  was  inferred,  chiefly  by  analo- 
gical reasoning,  to  be  a  metallic  oxide.  The  propriety  of  this  inference  has  been 
demonstrated  by  Wohler,  who  has  procured  aluminium,  the  metallic  base  of 
alumina,  in  a  pure  state  (Edinburgh  Journal  of  Science,  No.  xvii.  178). 

Prep. — Depends  on  the  property  which  potassium  possesses,  of  decomposing 
the  chloride  of  aluminium.  Decomposition  is  effected  by  aid  of  a  moderate 
increase  of  temperature  ;  but  the  action  is  so  violent,  and  accompanied  with  such 
intense  heat,  that  the  process  cannot  be  safely  conducted  in  glass  vessels. 
Wohler  succeeded  with  a  platinum  crucible,  retaining  the  cover  in  its  place  by 
a  piece  of  wire.  The  heat  developed  during  the  action  was  so  great,  that  the 
crucible,  though  but  gently  heated  externally,  suddenly  became  red  hot.  The 
platinum  is  scarcely  attacked  during  the  process ;  but  to  prevent  the  possibility 
of  error  from  this  source,  the  decomposition  was  also  effected  in  a  crucible  of 
porcelain.  The  potassium  employed  for  the  purpose  should  be  quite  free  from 
carbon,  and  the  quantity  operated  on  at  one  time  not  exceed  the  size  often  peas. 
The  heat  was  applied  by  means  of  a  spirit  lamp,  and  continued  until  the  action 
was  completed.  The  proportion  of  the  materials  requires  to  be  carefully  ad- 
justed ;  for  the  potassium  should  be  in  such  quantity  as  to  prevent  any  chloride 
of  aluminium  from  subliming  during  the  process,  but  not  so  much  as  to  yield  an 
alkaline  solution  when  the  product  is  put  into  water.  The  matter  contained  in 
the  crucible  at  the  close  of  the  operation  is  in  general  completely  fused,  and  of  a 
dark  grey  colour.  When  quite  cold,  the  crucible  is  put  into  a  large  glass  full  of 
water,  in  which  the  saline  matter  is  dissolved,  with  slight  disengagement  of 
hydrogen  of  an  offensive  odour ;  and  a  grey  powder  separates,  which  on  close 
inspection,  especially  in  sunshine,  is  found  to  consist  solely  of  minute  scales  of 
metal.  These  scales,  after  being  well  washed  with  cold  water,  are  pure  alumi- 
nium. The  saline  matter  removed  by  water  is  chloride  of  potassium,  and  a  con- 
siderable quantity  of  chloride  of  aluminium. 

Prop. — As  thus  formed,  it  is  a  grey  powder,  very  similar  to  that  of  platinum. 
It  is  generally  in  small  scales  or  spangles  of- a  metallic  lustre;  and  sometimes 
small,  slightly  coherent,  spongy  masses  are  observed,  whichjn  some  places 
have  the  lustre  and  white  colour  of  tin.    The  same  appearance  is  rendered  per- 


ALUMINIUM.  315 

fectly  distinct  by  pressure  on  steel,  or  in  an  agate  mortar ;  so  that  the  lustre  of 
aluminium  is  decidedly  metallic.  In  this  fused  state  it  is  a  conductor  of  elec- 
tricity, though  it  does  not  possess  this  property  when  in  the  form  of  powder. 
This  remark,  of  a  metal  conducting  the  electric  fluid  in  one  state  and  not  in 
another,  is  very  instructive ;  and  Wohler  observed  an  instance  of  the  same  kind 
in  iron,  which  in  the  state  of  fine  powder  is  a  non-conductor  of  electricity. 

Aluminium  requires  for  fusion  a  temperature  higher  than  that  at  which  cast 
iron  is  liquefied.  When  heated  to  redness  in  the  open  air,  it  takes  fire  and 
burns  with  vivid  light,  yielding  aluminous  earth  of  a  white  colour,  and  of  con- 
siderable hardness.  Sprinkled  in  powder  in  the  flame  of  a  candle,  brilliant 
sparks  are  emitted,  like  those  given  off"  during  the  combustion  of  iron  in  oxygen 
gas.  When  heated  to  redness  in  a  vessel  of  pure  oxygen  gas,  it  bums  with  an 
exceedingly  vivid  light,  and  emission  of  intense  heat.  The  resulting  alumina 
is  partially  vitrified,  of  a  yellowish  colour,  and  equal  in  haraness  to  the  native 
crystallized  aluminous  earth,  corundum.  Heated  to  near  redness  in  an  atmos- 
phere of  chlorine,  it  takes  fire,  and  chloride  of  aluminium  is  sublimed. 

Aluminium  is  not  oxidized  by  water  at  common  temperatures,  nor  is  its  lustre 
tarnished  by  lying  in  water  during  its  evaporation.  On  heating  the  water  to 
near  its  boiling  point,  oxidation  of  the  metal  commences,  with  feeble  disengage- 
ment of  hydrogen  gas,  the  evolution  of  which  continues  even  long  after  cooling, 
but  at  length  wholly  ceases.  The  oxidation,  however,  is  very  slight ;  and  even  - 
after  continued  ebullition,  the  smallest  particles  of  aluminium  appear  to  have 
suffered  scarcely  any  change. 

It  is  not  attacked  by  concentrated  sulphuric  or  nitric  acid  at  common  tempera- 
tures. In  the  former,  wiih  the  aid  of  heat,  it  is  rapidly  dissolved  with  disengage- 
ment of  sulphurous  acid  gas.  In  dilute  hydrochloric  and  sulphuric  acid,  and 
also  in  a  dilute  solution  of  potassa,  it  dissolves  with  evolution  of  hydrogen  gas. 
Ammonia  produces  a  similar  eflfect,  and  dissolves  a  large  quantity  of  alumina. 
The  hydrogen  gas  which  makes  its  appearance  is  of  course  derived  from  water, 
the  oxygen  of  which  combines  with  the  metal  so  as  to  constitute  alumina. 

From  the  composition  of  the  sulphates  of  alumina,  ascertained  by  Berzelius, 
Stromeyer,  and  Philips,  the  equivalent  of  alumina  may  be  estimated  either  at 
25  7,  or  at  51*4,  twice  that  number.  Now  chemists  have  no  direct  means  of  dis- 
covering the  atomic  constitution  of  alumina,  inasmuch  as  aluminium  combines 
with  oxygen  and  most  other  elements  in  one  proportion  only.  Thomson  assumes 
alumina  to  consist  of  single  atoms  of  its  elements :  but  most  chemists,  seeing 
that  alumina  has  little  analogy  to  protoxides  in  its  modes  of  combining,  but  that 
in  its  crystalline  form  and  all  its  chemical  relations  it  closely  resembles  peroxide 
of  iron,  have  inferred  that  the  simplest  molecule  of  alumina  contains  2  atoms  of 
aluminium  and  3  atoms  of  oxygen.  On  this  supposition  51*4  must  be  the  eq, 
of  alumina,  and  13*7  that  of  aluminium;  its  symb.  Al.  The  composition  of  its 
compounds  described  in  this  section  is  the  following : — 

Equiv.  Formulae. 

3eq.  =    51-4    2Al-|-30  or  AlzOg. 
3  eq.  =  132-66  SAl-f-SCl  or  AI2CI3. 
3  eq.  =    74-7     2Al-f-3S  or  AI2S3. 
3  eq.  =    73-5    2AI-J-3P  or  AI2P3. 
3  eq.  =  144-6    2Al-i-3Se  or  Al2Se3. 

The  composition  of  the  four  last  compounds  is  matter  of  inference  from  the 
change  which  they  respectively  undergo  by  the  action  of  water. 


2  eq. 

Aluminium. 

Sesquioxide 

26-4 -f- oxygen 

24 

Sesquichloride 

26-4 -J- chlorine 

106-26 

Sesquisulphuret 

26-4-}- sulphur 

48-3 

Sesquiphosphuret 

26-4-j-phosphs. 

47-1 

Sesquiseleniuret 

26-4-j- selenium 

1182 

316  ALUMINIUM. 

Sesquioxide  cf  Aluminium. — Hist,  and  Prep. — The  only  known  oxide  of  this 
metal,  and  is  commonly  called  alumina  or  aluminous  earth.  It  is  one  of  the 
most  abundant  productions  of  nature.  It  is  found  in  every  region  of  the  globe, 
and  in  rocks  of  all  ages,  being  a  constituent  of  the  oldest  primary  mountains,  of 
the  secondary  strata,  and  of  the  most  recent  alluvial  depositions.  The  different 
kinds  of  clay  of  which  bricks,  pipes,  and  earthenware  are  made,  consist  princi- 
pally of  silicate  of  alumina  in  a  greater  or  less  degree  of  purity.  Though  this 
earth  commonly  appears  in  rude  amorphous  masses,  it  is  sometimes  found  beau- 
tifully crystallized. — The  ruby  and  the  sapphire,  two  of  the  most  beautiful  gems 
with  which  we  are  acquainted,  are  composed  almost  solely  of  alumina. 

Pure  alumina  is  prepared  from  alum,  sulphate  of  alumina  and  potassa.  This 
salt,  as  purchased  in  the  shops,  is  frequently  contaminated  with  peroxide  of  iron, 
and  consequently  unfit  for  many  chemical  purposes ;  but  it  may  be  separated 
from  this  impurity  by  repeated  crystallization.  Its  absence  is  proved  by  the 
alum  being  soluble  without  residue  in  a  solution  of  pure  potassa;  whereas  when 
peroxide  of  iron  is  present,  it  is  either  left  undissolved  in  the  first  instance,  or 
deposited  after  a  few  hours  in  yellowish  brown  flocks.  Any  quantity  of  puri- 
fied alum  is  dissolved  in  four  or  five  times  its  weight  of  boiling  water,  a  slight 
excess  of  carbonate  of  potassa  added,  and  after  digesting  for  a  few  minutes,  the 
bulky  hydrate  of  alumina  is  collected  on  a  filter,  and  well  washed  with  hot  water. 
It  is  necessary  in  this  operation  to  digest  and  employ  an  excess  of  alkali ;  since 
otherwise  the  precipitate  would  retain  some  sulphuric  acid  in  the  form  of  a  sub- 
sulphate.  But  the  alumina,  as  thus  prepared,  is  not  yet  quite  pure ;  for  it 
retains  some  of  the  alkali  with  such  force,  that  it  cannot  be  separated  by  the 
action  of  water.  For  this  reason  the  precipitate  must  be  re-dissolved  in  dilute 
hydrochloric  acid,  and  thrown  down  by  means  of  pure  ammonia  or  its  carbonate. 
This  precipitate,  after  being  well  washed  and  exposed  to  a  white  heat,  yields 
pure  anhydrous  alumina.  Ammonia  cannot  be  employed  for  precipitating  alu- 
minous earth  directly  from  alum,  because  sulphate  of  alumina  is  not  completely 
decomposed  by  this  alkali  (Berzelius).  Liebig  precipitates  alum  with  an  excess 
of  chloride  of  barium,  evaporates  the  filtered  liquid  to  dryness,  and  ignites  the 
residue.  Water  now  dissolves  the  chlorides  of  potassium  and  barium,  and 
leaves  alumina  as  a  white  powder,  very  easily  washed.  The  washing  of  the 
hydrate,  in  the  process  first  described,  is  a  most  tedious  operation.  An  easier 
process,  proposed  by  Gay-Lussac,  is  to  expose  sulphate  of  alumina  and  ammonia 
to  a  strong  heat,  so  as  to  expel  the  ammonia  and  sulphuric  acid. 

Prop. — Alumina  has  neither  taste  nor  smell,  and  is  quite  insoluble  in  water. 
It  is  very  infusible,  though  less  so  than  lime  or  magnesia.  It  has  a  powerful 
affinity  for  water,  attracting  moisture  from  the  atmosphere  with  avidity ;  and  for 
a  like  reason,  it  adheres  tenaciously  to  the  tongue  when  applied  to  it.  Mixed 
with  a  due  proportion  of  water,  it  yields  a  soft  cohesive  mass,  susceptible  of 
being  moulded  into  regular  forms,  a  property  upon  which  depends  its  employment 
in  the  art  of  pottery.  When  once  moistened,  it  cannot  be  rendered  anhydrous, 
except  by  exposure  to  a  full  white  heat ;  and  in  proportion  as  it  parts  with  water, 
its  volume  diminishes.  Owing  to  its  insolubility,  it  does  not  affect  the  blue 
colour  of  plants.  It  appears  to  possess  the  properties  both  of  an  acid  and  of  an 
alkali : — of  an  acid,  by  uniting  with  alkaline  bases,  such  as  potassa,  lime,  and 
baryta; — and  of  an  alkali,  by  forming  salts  with  acids.  In  neither  case,  how- 
Qver,  are  its  soluble  compounds  neutral  with  respect  to  test  paper. 

Alumina  most  probably  forms  several  different  hydrates  with  water,  and  two 
have  been  described  by  Thomson.     One  of  these,  apparently  composed  of  6  eq. 


ALUMINIUM,  317 

of  water  to  one  of  alumina,  so  that  its  formula  is  AI2O3  -f-  6  aq.  was  procured  by 
exposing  precipitated  alumina  for  the  space  of  two  months  to  a  dry  air,  the  tem- 
perature of  which  did  not  exceed  60°.  The  other  is  a  terhydrate  prepared  by 
drying  the  preceding  at  a  heat  of  about  100°,  and  its  formula  is  therefore  AI2O3 
-f-  3  aq.  The  mineral  called  Gibbsite  has  a  similar  composition.  [The  mineral 
called  diaspor,  from  crumbling  to  pieces  when  heated,  is  said  to  be  also  a  hydrate 
with  2  eq.  of  water ;  its  formula  is  AI2O3  -f  aq.] 

Alumina  is  easily  recognized  by  the  following  characters.  1.  It  is  separated 
from  acids,  as  a  hydrate,  by  all  the  alkaline  carbonates  and  by  pure  arrmionia. 
2.  It  is  precipitated  by  pure  potassa  or  soda,  but  the  precipitate  is  completely 
re-dissolved  by  an  excess  of  the  alkali.  [Hydrate  of  alumina  has  a  remarkable 
attraction  for  organic  colouring  matters.  On  this  account  it  is  extensively  used  in 
the  preparation  of  lakes  and  pigments.  "When  added  to  coloured  solutions  it  pre- 
cipitates with  it  the  colouring  matters.  The  fibres  of  various  fabrics  when  impreg- 
nated with  it,  seize  hold  of  the  same  colouring  matters,  and  fix  them  perma- 
nently.— Hence  the  aluminous  salts  are  largely  used  in  dying  and  calico  printing.] 

lis  eq.  is  51-4 ;  8i/mb.  2"  Al  -f-  30,  Al,  or  AI2O3. 

Sesquichloride  of  Aluminium. — Hist. — Oersted  discovered  this  compound  by 
transmitting  dry  chlorine  gas  over  a  mixture  of  alumina  and  charcoal  heated  to 
redness.  By  acting  on  this  substance  with  an  amalgam  of  potassium  and  expel- 
ling the  mercury  by  heat,  he  obtained  metallic  matter,  which  he  believed  to  be 
aluminium ;  but  not  having  leisure  to  pursue  the  inquiry  himself,  he  requested 
Wohler  to  investigate  the  subject.  Wohler  did  not  arrive  at  any  satisfactory 
conclusion  by  the  method  suggested  by  Oersted ;  but  met  with  complete  success 
by  means  of  pure  potassium,  as  already  described. 

Prep — To  procure  chloride  of  aluminium,  Wohler  precipitated  aluminous  earth 
from  a  hot  solution  of  alum  by  means  of  potassa,  and  mixed  the  hydrate,  when 
dry,  with  pulverized  charcoal,  sugar,  and  oil,  so  as  to  form  a  thick  paste,  which 
was  heated  in  a  covered  crucible  until  all  the  organic  matter  was  destroyed.  By 
this  means  the  alumina  was  brought  into  a  state  of  intimate  mixture  with  finely 
divided  charcoal,  and  while  yet  hot,  was  introduced  into  a  tube  of  porcelain,  fixed 
in  a  convenient  furnace.  After  expelling  atmospheric  air  from  the  interior  of  the 
apparatus  by  a  current  of  dry  chlorine  gas,  the  tube  was  brought  to  a  red  heat. 
The  formation  of  chloride  of  aluminium  then  commenced,  and  continued,  with 
disengagement  of  carbonic  oxide  gas,  during  an  hour  and  a  half,  when  the  tube 
became  impervious  from  sublimed  chloride  of  aluminium  collected  within  it.  The 
process  was  then  necessarily  discontinued. 

Prop. — As  thus  formed,  chloride  of  aluminium  is  of  a  pale  greenish  yellow 
colour,  partially  translucent,  and  of  a  highly  crystalline  lamellated  texture,  some- 
what like  talc,  but  without  regular  crystals.  On  exposure  to  the  air,  it  fumes 
slightly,  emits  an  odour  of  hydrochloric  acid  gas,  and,  deliquescing,  yields  a 
clear  liquid.  When  thrown  into  water,  it  is  speedily  dissolved  with  a  hissing 
noise ;  and  so  much  heat  is  evolved,  that  the  water,  if  in  small  quantity,  is  brought 
into  a  state  of  brisk  ebullition.  The  solution  is  a  true  hydrochlorate  of  alumina, 
formed  by  decomposition  of  water ;  for  when  gently  evaporated,  hydrochloric  acid 
escapes,  and  alumina  is  gradually  deposited.  According  to  Oersted  it  is  volatile 
at  a  temperature  a  little  higher  than  212°,  and  fuses  nearly  at  the  same  degree. 

Sesquisulphuret  of  Aluminium. — Sulphur  may  be  distilled  from  aluminium  withr 
out  combining  with  it ;  but  if  a  piece  of  sulphur  is  dropped  on  aluminium  when 


318  GLUCINIUM. 

strongly  incandescent,  so  that  it  may  be  enveloped  in  an  atmosphere  of  the  vapour 
of  sulphur,  the  union  is  effected  with  a  vivid  emission  of  light.  The  resulting 
sulphuret  is  a  partially  vitrified,  semi-metallic  mass,  which  acquires  an  iron-black 
metallic  lustre  when  burnished.  Applied  to  the  tongue,  it  excites  a  pricking 
warm  taste  of  hydrosulphuric  acid.  When  put  into  pure  water,  or  on  exposure 
to  the  air,  it  is  resolved,  by  an  interchange  of  elements,  into  alumina  and  hydro- 
sulphuric  acid,  the  latter  escaping  as  gas.    It  is  to  be  presumed  that 

1  eq.  Sulphuret  and  3  eq.  Water  ^  1  eq.  Alumina  and  3  eq.  Hydrosulph.  Acid. 
Al^Sa  3H0  •^Al2203  3HS 

Wohler  finds  that  sulphuret  of  aluminium  cannot  be  generated  by  the  action 
of  hydrogen  gas  on  sulphate  of  alumina  at  a  red  heat ;  for  in  that  case  all  the  acid 
is  expelled,  without  the  aluminous  earth  being  reduced. 

Sesquiphosphuret  of  Aluminium, — When  aluminium  is  heated  to  redness  in  con- 
tact with  the  vapour  of  phosphorus,  it  takes  fire,  and  emits  a  brilliant  light.  The 
product  is  described  by  Wohler  as  a  blackish  grey  pulverulent  mass,  which  by 
friction  acquires  a  dark  grey  metallic  lustre,  and  in  the  air  smells  instantly  of 
phosphuretted  hydrogen.  By  the  action  of  water  alumina  and  phosphuretted 
hydrogen  gas  are  generated,  but  the  latter  is  not  spontaneously  inflammable.  The 
efiervescence  is  less  rapid  than  with  the  sulphuret,  but  is  increased  by  heat. 

Sesquiseleniuret  of  Aluminium. — This  compound  is  formed,  with  disengagement 
of  heat  and  light,  by  heating  to  redness  a  mixture  of  selenium  and  aluminium. 
The  product  is  black  and  pulverulent,  and  assumes  a  dark  metallic  lustre  when 
rubbed.  In  the  air  it  emits  a  strong  odour  of  hydroselenic  acid  ;  and  this  gas  is 
rapidly  disengaged  by  the  action  of  water,  which  is  speedily  reddened  by  the 
separation  of  selenium. 


SECTION  IX. 

GLUCINIUM,  YTTRIUM,  THORIUM,  ZIRCONIUM. 
GLUCINIUM. 

Glucina,  which  was  discovered  by  Vauquelin  in  the  year  1798,  has  hitherto 
been  found  only  in  three  rare  minerals,  the  euclase,  beryl,  and  emerald.  It  is  the 
only  oxide  of  a  metal  which  Wohler  succeeded  in  preparing  in  the  year  1828  by 
a  process  exactly  similar  to  that  described  in  the  last  section.  Chloride  of  glu- 
cinium is  readily  attacked  by  potassium  when  heated  with  the  flame  of  a  spirit- 
lamp,  and  the  decomposition  is  attended  with  intense  heat.  After  removing  the 
resulting  chloride  of  potassium  by  cold  water,  the  glucinium  appears  in  the  form 
of  a  greyish  black  powder,  which  acquires  a  dark  metallic  lustre  by  burnishing. 
It  may  be  exposed  to  air  and  moisture,  or  be  even  boiled  in  water,  without  oxi- 
dation. Whea  heated  in  the  open  air,  it  takes  fire  and  burns  with  a  most  vivid 
light ;  and  in  oxygen  gas  the  combustion  is  attended  with  extraordinary  splen- 
dour. The  product  in  both  cases  is  glucina,  which  is  not  at  all  fused  by  the 
intense  heat  that  accompanied  its  formation.    The  metal  is  readily  oxidized  and 


YTTRIUM.  319 

dissolved  in  sulphuric,  nitric,  or  hydrochloric  acid  with  the  aid  of  heat ;  and  the 
same  ensues,  with  disengagement  of  hydrogen  gas,  in  solution  of  p  tassa.  It  is 
not  attacked,  however,  hy  pure  ammonia.  When  moderately  heated  in  chlorine 
gas,  it  burns  with  great  splendour,  and  a  crystallized  chloride  sublimes.  Similar 
phenomena  ensue  in  the  vapour  of  bromine  and  iodine ;  and  it  unites  readily  with 
sulphur,  selenium,  phosphorus,  and  arsenic.     (Phil.  Mag.  and  Annals,  v.  392.) 

According  to  the  experiments  of  Berzelius,  glucina  contains  31*154  per  cent, 
of  oxygen,  and  consequently  its  eq.  is  26*5  on  the  supposition  that  its  constitu- 
tion is  similar  to  that  of  alumina,  with  which  it  is  closely  associated  both  in 
nature  and  in  many  of  its  properties.    Its  symb.  is  G. 

Oxide  of  Glucinium  or  Glucina. — Prep. — This  oxide  is  commonly  prepared 
from  beryl,  in  which  it  exists  to  the  extort  of  about  14  per  cent,  combined  with 
silicic  acid  and  alumina.  In  order  to  procure  it  in  a  separate  state,  the  mineral 
is  reduced  to  an  exceedingly  fine  powder,  mixed  with  three  times  its  weight  of 
carbonate  of  potassa,  and  exposed  to  a  strong  red  heat  for  half  an  hour,  so  that 
the  mixture  may  be  fused.  The  mass  is  then  dissolved  in  dilute  hydrochloric 
acid,  and  the  solution  evaporated  to  perfect  dryness ;  by  which  means  the  silicic 
acid  is  rendered  quite  insoluble.  The  alumina  and  glucina  are  then  redissolved 
in  water  acidulated  with  hydrochloric  acid,  and  thrown  down  together  by  pure 
ammonia.  The  precipitate,  after  being  well  washed,  is  macerated  with  a  large 
excess  of  carbonate  of  ammonia,  by  which  glucina  is  dissolved ;  and  on  boiling 
the  filtered  liquid,  carbonate  of  glucina  subsides.  By  means  of  a  red  heat  its 
carbonic  acid  is  entirely  expelled. 

Another  process  has  been  recommended  by  Berthier,  who  directs  the  beryl  to 
be  mixed  in  fine  powder  with  its  own  weight  of  marble,  and  the  mixture  to  be 
exposed  in  a  crucible  to  a  strong  heat.  In  this  manner  a  glass  is  obtained,  which 
when  in  fine  powder  is  attached  freely  by  hydrochloric  or  sulphuric  acid.  From 
this  solution  the  glucina  may  be  obtained  as  before. 

Prop. — Glucina  is  a  white  powder,  which  has  neither  taste  nor  odour,  and  is 
quite  insoluble  in  water.  Its  sp.  gr.  is  3.  Vegetable  colours  are  not  affected  by 
it.  The  salts  which  it  forms  with  acids  have  a  sweetish  taste,  a  circumstance 
which  distinguishes  glucina  from  other  earths,  and  from  which  its  name  is  de- 
rived (from  yxvxvj,  sweet.) 

Glucina  may  be  known  chemically  by  the  following  characters.  1.  Pure 
potassa  or  soda  precipitates  glucina  from  its  salts,  but  an  excess  of  the  alkali  redis- 
solves  it.  2.  It  is  precipitated  permanently  by  pure  ammonia  as  a  hydrate,  and 
by  fixed  alkaline  carbonates  as  a  carbonate  of  glucina.  3.  It  is  dissolved  com- 
pletely by  a  cold  solution  of  carbonate  of  ammonia,  and  is  precipitated  from  it 
by  boiling.  By  means  of  this  property,  glucina  may  be  both  distinguished  and 
separated  from  alumina. 

Its  eq.  is  11 ;  symb.  2G  -j-  30,  G,  or  G2O3. 

YTTRIUM. 

Yttrium  is  the  metallic  base  of  an  earth  which  was  discovered  in  the  year 
1794  by  Professor  Gadolin,  in  a  mineral  found  at  Ytterby  in  Sweden,  from  which 
it  received  the  name  of  Yitria.  The  metal  itself  was  prepared  by  Wohler  in 
1828  by  a  process  similar  to  that  above  described.  Its  texture,  by  which  it  is 
distinguished  from  glucinium  and  aluminium,  is  scaly,  its  colour  greyish-black, 
and  its  lustre  perfectly  metallic.  In  colour  and  lustre  it  is  inferior  to  aluminium, 


320  THORIUM. 

bearing  ii? these  respects  nearly  the  same  relation  to  that  metal,  that  iron  does  to 
tin.  It  is  a  brittle  metal,  while  aluminium  is  ductile.  It  is  not  oxidized  either 
in  air  or  water;  but  when  heated  to  redness,  it  burns  with  splendour  even  in 
atmospheric  air,  and  with  far  greater  brilliancy  in  oxygen  gas.  The  product, 
yttria,  is  white,  and  shows  unequivocal  marks  of  fusion.  It  dissolves  in  sul- 
phuric acid,  and  also,  though  less  readily,  in  solution  of  potassa,  but  it  is  not 
attacked  by  ammonia.  It  combines  with  sulphur,  selenium,  and  phosphorus. 
(Phil.  Mag.  and  Annals,  v.  393.) 

The  salts  of  yttria  have  in  general  a  sweet  taste,  and  the  sulphate  and  several 
others  have  an  amethyst  colour.  It  is  precipitated  as  a  hydrate  by  the  pure  alka- 
lies, and  is  not  redissolved  by  an  excess  of  the  precipitant;  but  alkaline  carbon- 
ates, especially  that  of  ammonia,  dissdve  in  the  cold,  though  less  freely  than 
glucina,  and  carbonate  of  yttria  is  precipitated  by  boiling.  Of  all  the  earths  it 
bears  the  closest  resemblance  to  glucina ;  but  it  is  readily  distinguished  from  it 
by  the  colour  of  its  sulphate,  by  its  insolubility  in  pure  potassa,  and  by  yielding 
a  precipitate  with  ferrocyanuret  of  potassium  (Berzelius).  The  eq,  of  yttrium,  as 
deduced  by  Berzelius,  is  32*2 ;  and  that  of  yttria,  which  is  probably  a  protoxide, 
is  40-2. 

The  synib.  of  the  iiietal  is  Y  ;  of  its  oxide  Y  +  0,  Y,  or  YO.* 

THORIUM. 

The  earthy  substance  formerly  called  thorina  was  found  by  Berzelius  to  be 
phosphate  of  yttria;  but  in  1828  he  discovered  a  new  earth,  so  similar  in  some 
respects  to  what  was  formerly  called  thorina,  that  he  applied  this  terra  to  the 
new  substance.  The  metallic  base  of  thorina  (thorium)  was  procured  by  the 
action  of  potassium  on  chloride  of  thorium,  the  decomposition  being  accompanied 
with  a  slight  detonation.  On  washing  the  mass,  thorium  is  left  in  the  form  of 
a  heavy  metallic  powder,  of  a  deep  leaden-grey  colour;  and  when  pressed  in  an 
agate  mortar,  it  acquires  metallic  lustre  and  an  iron-grey  tint.  Thorium  is  not 
oxidized  either  by  hot  or  cold  water ;  but  when  gently  heated  in  the  open  air  it 
bums  with  great  brilliancy,  comparable  to  that  of  phosphorus  burning  in  oxygen. 
The  resulting  thorina  is  as  white  as  snow,  and  does  not  exhibit  the  least  trace 
of  fusion.  It  is  not  attacked  by  caustic  alkalies  at  a  boiling  heat;  is  scarcely 
at  all  acted  on  by  nitric  acid,  and  very  slowly  by  the  sulphtiric,  but  it  is  readily 
dissolved  with  disengagement  of  hydrogen  gas  by  hydrochloric  acid. 

Thorina. — Hist,  and  Prep. — Procured  from  a  rare  Norwegian  mineral,  now 
called  thorite,  which  was  sent  to  Berzelius  by  Esmark.  It  constitutes  57'91  per 
cent,  of  the  mineral,  and  occurs  in  the  form  of  a  hydrated  silicate  of  thorina.  In 
order  to  prepare  thorina,  the  mineral  is  reduced  to  powder,  and  digested  in  hy- 
drochloric acid  ;  when  a  gelatinous  mass  is  formed,  from  which  silicic  acid  is 
separated  by  evaporating  to  dryness,  and  dissolving  the  soluble  parts  in  dilute 
acid.  The  solution  is  then  freed  from  lead  and  tin,  which  occur  in  thorina  along 
with  several  impurities,  by  hydrosulphuric  acid,  and  the  earths  are  thrown  down 
by  pure  ammonia.  The  precipitate,  after  being  well  washed,  is  dissolved  in  dilute 
sulphuric  acid,  and  the  solution  evaporated  at  a  high  temperature  till  only  a  small 

*  The  recent  researches  ofMosander  show  that  the  substance  hitherto  looked  upon  as  pure 
yttria  is  in  reality  a  mixture  containing  besides,  the  oxides  of  two  different  metals,  possess- 
ing  different  properties.  Upon  these  new  metals  he  has  conferred  the  names  of  Erbiwn 
and  Terbium.    (Phil.  Mag.  Oct.  1843.)    (R.) 


ZIRCONIUM.  321 

quantity  of  fluid  remains.  During  the  evaporation  the  greater  part  of  the  thorina 
is  deposited  as  a  sulphate ;  and  on  decanting  the  remaining  fluid,  washing  the 
residue,  and  heating  it  to  redness,  pure  thorina  remains.  (An.  de  Ch.  et  Ph. 
xliii.  5.) 

Prop. — Thorina,  when  formed  by  the  oxidation  of  thorium,  or  after  being 
strongly  heated,  is  a  white  earthy  substance,  of  sp.  gr.  9-402,  and  insoluble  in 
all  the  acids  except  the  sulphuric ;  and  it  dissolves  even  in  that  with  difficulty. 
It  is  precipitated  from  its  solutions  by  the  caustic  alkalies  as  a  hydrate,  and  in 
this  state  absorbs  carbonic  acid  from  the  atmosphere,  and  dissolves  readily  in 
acids.  All  the  alkaline  carbonates  dissolve  the  hydrate,  carbonate,  and  sub-salts 
of  thorina.    Its  exact  composition  is  not  known;  but  its  eq.  is  about  67*6. 

Thorina  is  distinguished  from  alumina  and  glucina  by  its  insolubility  in  pure 
potassa  ;  from  yttria  by  forming  with  sulphate  of  potassa  a  double  salt  which  is 
quite  insoluble  in  a  cold  saturated  solution  of  sulphate  of  potassa ;  and  from  zir- 
conia  by  the  circumstance  that  this  earth,  after  being  precipitated  from  a  hot  solu- 
tion of  sulphate  of  potassa,  is  almost  insoluble  in  water  and  the  acids.  Thorina 
is  precipitated,  also,  by  ferrocyanide  of  potassium,  which  does  not  separate  zir- 
conia  from  its  solutions.  Berzelius  has  remarked  that  sulphate  of  thorina  is 
much  more  soluble  in  cold  than  in  hot  water,  so  that  a  cold  saturated  solution 
becomes  turbid  when  heated,  and  in  cooling  recovers  its  transparency. 

Chloride  of  thorium  is  readily  prepared  by  carbonizing  an  intimate  mixture  of 
thorina  and  sugar  in  a  covered  platinum  crucible,  and  then  exposing  the  residue 
at  a  red  heat  in  a  porcelain  tube  to  a  current  of  dry  chlorine.  The  chloride, 
possessing  but  little  volatility,  collects  in  the  tube  just  beyond  the  ignited  part 
in  the  form  of  a  partially  fused,  crystalline,  white  mass.  It  is  soluble  in  water 
with  considerable  rise  of  temperature. 

When  thorium  is  heated  in  the  vapour  of  sulphur,  the  phenomena  of  combus- 
tion ensue  with  the  same  brilliancy  as  in  air,  and  a  sulphuret  results.  A  phos- 
phuret  may  be  formed  by  a  similar  process. 

ZIRCONIUM. 

Hist,  and  Prep. — The  experiments  of  Davy  proved  zirconia  to  be  an  oxidized 
body,  and  afforded  a  presumption  that  its  base,  zirconium,  is  of  a  metallic  nature; 
but  Berzelius  first  obtained  the  metal  in  1824  by  heating  with  a  spirit-lamp  a 
mixture  of  potassium  and  the  double  fluoride  of  zirconium  and  potassium,  care- 
fully dried  in  a  tube  of  glass  or  iron.  The  reduction  takes  place  at  a  tempera- 
ture below  redness,  without  emission  of  light ;  and  the  mass  is  washed  with 
boiling  water,  and  afterwards  digested  for  some  time  in  dilute  hydrochloric  acid. 
The  residue  is  pure  zirconium. 

Prop. — Zirconium,  thus  obtained,  is  in  the  form  of  a  black  powder,  which 
maybe  boiled  in  water  without  being  oxidized,  and  is  attacked  with  difficulty  by 
sulphuric,  hydrochloric,  or  nitro-hydrochloric  acids;  but  it  is  dissolved  readily, 
and  with  disengagement  of  hydrogen  gas,  by  hydrofluoric  acid.  Heated  in  the 
open  air,  it  takes  fire  at  a  temperature  far  below  incandescence,  burns  brightly, 
and  is  converted  into  zirconia.  Its  metallic  nature  seems  somewhat  questionable. 
It  may  indeed  be  pressed  out  into  thin  shining  scales  of  a  dark  grey  colour,  and 
of  a  lustre  which  may  be  called  metallic  ;  but  its  particles  cohere  together  very 
feebly,  and  it  has  not  been  procured  in  a  state  capable  of  conducting  electricity. 


322  ZIRCONIUM. 

These  points,  however,  require  further  investigation  before  a  decisive  opinion  on 
the  subject  can  be  adopted.  (Pog.  Annalen,  iv.) 

Oxide  of  Zirconium  was  discovered  in  the  year  1789  by  Klaproth  in  the  Jargon 
or  Zircon  of  Ceylon,  and  has  since  been  found  in  the  Hyacinth  from  Expailly 
in  France.  Berthier  prepares  it  by  fusing  zircon  in  fine  powder  with  litharge  in 
the  ratio  of  17  to  21,  when  a  glass  is  obtained  which  is  soluble  in  acids.  It  is 
an  earthy  substance,  resembling  alumina  in  appearance,  of  sp.  gr.  4'3,  having 
neither  taste  nor  odour,  and  quite  insoluble  in  water.  It  is  so  hard  that  it  will 
scratch  glass.  Its  colour,  when  pure,  is  white ;  but  it  has  frequently  a  tinge  of 
yellow,  owing  to  the  presence  of  iron,  from  which  it  is  separated  with  difficulty. 
It  phosphoresces  vividly  when  heated  strongly  before  the  blowpipe.  Its  salts  are 
distinguished  from  those  of  alumina  or  glucina  by  being  precipitated  by  all  the 
pure  alkalies,  in  an  excess  of  which  it  is  insoluble.  TTie  alkaline  carbonates  pre- 
cipitate it  as  carbonate  of  zirconia,  and  a  small  portion  of  it  is  redissolved  by  an 
excess  of  the  precipitant,  especially  when  a  bicarbonate  is  employed.  It  differs 
from  all  the  earths,  except  thorina,  in  being  precipitated  when  any  of  its  neutral 
salts  are  boiled  with  a  saturated  solution  of  sulphate  of  potassa,  the  zirconia 
subsiding  as  a  subsalt,  and  the  potassa  remaining  in  solution  as  a  bisulphate. 
Zirconia  is  precipitated  from  its  salts  by  pure  ammonia  as  a  bulky  hydrate,  which 
is  readily  soluble  in  acids;  but  if  this  hydrate  is  ignited,  dried,  or  even  washed 
with  boiling  water,  it  afterwards  resists  the  action  of  the  acids,  and  is  dissolved 
by  them  with  great  difficulty.  Strong  sulphuric  acid  is  then  its  best  solvent 
(Berzelius),  When  hydrated  zirconia  is  heated  to  commencing  redness,  it  parts 
with  its  water,  and  soon  after  emits  a  very  vivid  glow  for  a  short  time.  This 
phenomenon  appears  to  depend  upon  the  particles  of  the  zirconia  suddenly  ap- 
proaching each  other,  and  thus  acquiring  much  greater  density  than  it  previously 
possessed.  Oxide  of  chromium,  titanic  acid,  and  several  other  compounds  afford 
instances  of  the  same  appearance ;  and  whenever  it  takes  place  the  susceptibility 
of  the  substance  to  be  attacked  by  fluid  reagents  is  greatly  diminished  (Berze- 
lius). 

The  composition  of  zirconia  has  not  yet  been  satisfactorily  determined.  From 
some  analyses  by  Berzelius,  described  in  the  Essay  above  referred  to,  it  is  pro- 
bable that  the  eq.  of  this  earth  is  about  33*7 ;  its  symb.  2Zr  -j-  30,  ^T?  or  Zr^  O3. 

Sulphuret  of  Zirconium. — This  compound  may  be  prepared,  according  to  Ber- 
zelius, by  heating  zirconium  with  sulphur  in  an  atmosphere  of  hydrogen  gas ; 
and  the  union  is  effected  with  feeble  emission  of  light.  The  product  is  pulveru- 
lent, a  non-conductor  of  electricity,  of  a  dark  chestnut-brown  colour,  and  without 
lustre.  It  is  insoluble  in  sulphuric,  nitric,  and  hydrochloric  acid;  and  it  is 
slowly  attacked  by  nitro-hydrochloric  acid,  even  with  the  aid  of  heat.  It  is 
readily  dissolved  by  hydrofluoric  acid,  with  disengagement  of  hydrogen  gas. 


MANGANESE.  323 


CLASS   II 


METALS,  THE  OXIDES  OF  WHICH  ARE  NEITHER  ALKALIES  NOR 

EARTHS. 


ORDER  I. 

METALS  WHICH  DECOMPOSE  WATER  AT  A  RED  HEAT. 


SECTION  X. 

MANGANESE. 

Hist»  and  Prep. — The  black  oxide  of  manganese  was  described  in  the  year 
1774  by  Scheele,  as  a  peculiar  earth,  and  Gahn  subsequently  showed  that  it  con- 
tains a  new  metal,  to  which  he  gave  the  name  of  magnesium ;  a  term  since 
applied  to  the  metallic  base  of  magnesia,  and  for  which  the  words  manganesium 
and  manganium  have  been  substituted.  This  metal,  owing  doubtless  to  its 
strong  affinity  for  oxygen,  has  never  been  found  in  an  uncombined  state  in  the 
earth ;  but  its  oxides  are  very  abundant.  The  metal  may  be  obtained  by  forming 
finely  powdered  oxide  of  manganese  into  a  paste  with  oil,  laying  the  mass  in  a 
hessian  crucible  lined  with  charcoal,  luting  down  a  cover  carefully,  and  exposing 
it  during  an  hour  and  a  half,  or  two  hours,  to  the  strongest  heat  of  a  smith's 
forge. 

Prop. — A  hard  brittle  metal,  of  a  greyish-white  colour,  and  granular  texture. 
Its  sp.  gr.  according  to  John,  is  8*013.  When  pure  it  is  not  attracted  by  the 
magnet,  but  Berthier  has  lately  stated  that  it  possesses  this  property  at  very  low 
temperatures.  It  is  exceedingly  infusible,  requiring  the  highest  heat  of  a  wind 
furnace  for  fusion.  It  soon  tarnishes  on  exposure  to  the  air,  and  absorbs  oxygen 
with  rapidity  when  heated  to  redness  in  open  vessels.  It  slowly  decomposes 
water  at  common  temperatures  with  disengagement  of  hydrogen  gas ;  but  at  a 
red  heat  decomposition  is  rapid,  and  protoxide  of  manganese  is  generated. 
Decomposition  of  water  is  likewise  occasioned  by  dilute  sulphuric  acid,  and  sul- 
phate of  protoxide  of  manganese  is  the  product. 

Berzelius,  from  an  analysis  of  chloride  of  manganese,  found  27*7  as  the  eq.  of 
manganese,  a  number  which  agrees  closely  with  my  own  experiments  on  the 
same  chloride.  Its  symb.  is  Mn.  The  composition  of  the  compounds  of  man- 
ganese described  in  this  section  is  as  follows : — 


Manganese. 

Equiv. 

Formulae. 

Protoxide 

27-7    1  eq.  -f-  Oxygen 

8 

1  eq.  =    35-7 

Mn  +  0. 

Sesquioxide 

55-4    2  eq.  -f      do. 

24 

3eq.=    79-4 

2Mn  -f-  30. 

Peroxide 

27-7     1  eq.  4"      do. 

16 

2eq.=:  43-7 

Mn  f  20. 

Red  Oxide 

83-1     3  eq.  -t-     do. 

32 

4eq.  =  115-l 

3Mn  f  40. 

324 

MANGANESE. 

Manganese. 

Equiv. 

Formulae. 

Varvicite 

110-8     4eq.  t 

do. 

56 

7  eq.  =  166-8 

4Mn  -f  70. 

Manganic  Acid 

27-7     1  eq.  -|- 

do. 

24 

3eq.=  51-7 

Mn  -f-  30. 

Permang.  Acid 

55-4    2  eq.  -\- 

do. 

56 

7eq.  =  lll-4 

2Mn  -|-  70. 

Protochloride 

27-7     leq.  t 

Chlor. 

35-42 

1  eq.=:   63-12 

Mn  -|-  CI. 

Perchloride 

55-4    2eq.  t 

do. 

247-94 

7  eq.  =r  303-34 

2Mn  t  7C1. 

Perfluoride 

65-4    2eq. -f 

Fluor. 

130-76 

7eq.==186l6 

2Mn  -|-  7F. 

Protosulphuret 

27-7     1  eq.  t  Sulphur. 

16-1 

1  eq,.  =   43-8 

Mn-t-S. 

OXIDES  OF  MANGANESE. 

In  studying  metallic  oxides,  it  is  necessary  to  distinguish  oxides  formed  by 
the  direct  union  of  oxygen  and  a  metal,  from  those  that  consist  of  two  other 
oxides  united  with  each  other,  and  which  therefore,  in  composition,  partake  of 
the  nature  of  a  salt  rather  than  of  an  oxide.  An  instance  of  this  kind  of  combi- 
nation is  supplied  by  the  black  oxide  of  iron ;  and  it  is  probable  that  two  of  the 
five  compounds  enumerated  as  oxides  of  manganese  have  a  similar  constitution. 
Their  composition  has  been  particularly  investigated  by  Berzelius,  Thomson 
(First  Principles,  i.),  Arfwedson,*  Berthier,f  and  myself.:|: 

Protoxide. — Prep. — By  this  term  is  meant  that  oxide  of  manganese  which  is  a 
strong  salifiable  base,  is  contained  in  all  the  ordinary  salts  of  this  metal,  and 
which  appears  to  be  its  lowest  degree  of  oxidation.  This  oxide  maybe  formed 
by  exposing  the  peroxide,  sesquioxide,  or  red  oxide  of  manganese,  to  the  com- 
bined agency  of  charcoal  and  a  white  heat ;  or  by  exposing  either  of  the  oxides 
of  manganese  contained  in  a  tube  of  glass,  porcelain,  or  iron,  to  a  current  of 
hydrogen  gas  at  an  elevated  temperature.  The  best  material  for  this  purpose  is 
the  red  oxide  prepared  from  nitrate  of  oxide  of  manganese ;  since  the  native 
oxides,  especially  the  peroxide,  are  fully  reduced  to  the  state  of  protoxide  by 
hydrogen  with  difficulty.  The  reduction  commences  at  a  low  red  heat ;  but  to 
decompose  all  the  red  oxide,  a  full  red  heat  is  required.  The  same  compound  is 
formed  by  the  action  of  hydrogen  gas  at  an  intense  white  heat.  Wohler  and 
Liebig  have  shown  that  the  protoxide  is  also  obtained  by  fusing  chloride  of  man- 
ganese in  a  platinum  crucible  with  about  twice  its  weight  of  carbonate  of  soda, 
and  its  own  weight  of  sal-ammoniac,  and  afterwards  dissolving  the  chloride  of 
sodium  by  water. 

Prop. — Protoxide  of  manganese,  when  pure,  is  of  a  light  green  colour,  very 
near  the  mountain  green.  According  to  Forchammer  it  attracts  oxygen  rapidly 
from  the  air;  but  in  my  experiments  it  was  very  permanent,  undergoing  no 
change  either  in  weight  or  appearance  during  the  space  of  nineteen  days.  At 
600°  it  is  oxidized  with  considerable  rapidity,  and  at  a  low  red  heat  is  converted 
in  an  instant  into  red  oxide.  It  sometimes  takes  fire  when  thus  heated,  espe- 
cially when  the  mass  is  considerable.  It  unites  readily  with  acids  without  effer- 
vescence, producing  the  same  salts  as  when  the  same  acids  act  on  carbonate  of 
oxide  of  manganese.  When  it  comes  in  contact  with  concentrated  sulphuric 
acid,  intense  heat  is  instantly  evolved ;  and  the  same  phenomenon  is  produced, 
though  in  a  less  degree,  by  strong  hydrochloric  acid.  The  resulting  salt  is  the 
same  as  when  these  acids  are  heated  with  either  of  the  other  oxides  of  manga- 
nese. If  quite  pure,  the  protoxide  should  readily  and  completely  dissolve  in  cold 
dilute  sulphuric  acid,  and  yield  a  colourless  solution. 

*  Letter  from  Berzelius  in  the  An.  de  Ch.  et  Ph.  vi.  t  Ibid.  xx. 

X  Philos.  Trans,  of  Edin.  for  1828;  or  Phil.  Mag.  and  Annals,  iv. 


MANGANESE.  325 

In  order  to  prepare  a  pure  salt  of  mang-anese  from  the  common  peroxide  of 
commerce,  the  following  process  may  be  employed  : — The  solution  which  remains 
when  chlorine  is  made  by  the  action  of  muriatic  acid  on  peroxide  of  manganese 
is  rendered  neutral  by  gently  evaporating  it  to  dryness.  A  portion,  which  varies 
with  the  proportion  of  iron  present,  and  is  easily  ascertained  by  trial  on  a  small 
scale,  is  then  precipitated  by  an  excess  of  carbonate  of  soda,  and  the  mixed  pre- 
cipitate of  carbonate  of  manganese  and  peroxide  of  iron,  well  washed,  is  digested 
with  the  remainder  of  the  liquid.  The  protoxide  of  manganese  enters  the  liquid, 
expelling  the  peroxide  of  iron,  and  at  last  a  liquid  is  obtained  quite  free  from 
iron.  It  ought  to  give  a  bright  flesh-coloured  precipitate  with  hydrosulphuret  of 
ammonia,  and  a  white  with  ferrocyanide  of  potassium.  Should  the  first  drop  of 
the  former  test  cause  a  dark  precipitate,  this  is  owing  to  the  presence,  not  of 
iron,  but  of  cobalt  and  nickel,  which,  according  to  Gregory,  are  almost  uniformly 
present  in  small  quantity  in  the  oxide  of  manganese.  They  are  easily  removed 
by  adding  the  hydrosulphuret  till  it  gives  a  pure  flesh-coloured  precipitate.  If 
the  oxide,  before  being  dissolved  in  muriatic  acid,  has  been  digested  in  very 
diluted  muriatic  acid,  and  washed,  no  lime  can  be  present  in  the  solution.  The 
iron  can  only  escape  complete  precipitation  if  it  be  partly  in  the  state  of  protox- 
ide ;  but  in  preparing  chlorine  the  iron  is  fully  oxidized.  If,  however,  protoxide 
should  be  present,  it  is  readily  peroxidized  by  boiling  with  a  little  nitric  acid. 
This  process,  suggested  by  Everitt,  is  founded  on  the  fact,  that  all  carbonates  of 
protoxides,  when  digested  with  solutions  of  peroxide  of  iron,  precipitate  the 
latter ;  and  the  manganese  contained  in  the  mixed  solution  is  thus  ingeniously 
made  use  of  to  effect  its  own  purification.  (Phil.  Mag.  and  An.  vi.  193.)  Other 
less  convenient  methods,  which,  however,  yield  a  pure  product,  have  been  sug- 
gested, particularly  one  by  Faraday.     (Quart.  Joum.  vi.) 

The  salts  of  the  protoxide  of  manganese  are  in  general  colourless  if  quite  pure  ; 
but  more  frequently  they  have  a  shade  of  pink,  owing  to  the  presence  of  a  little 
red  oxide  or  permanganic  acid.  [They  are  strictly  isomorphous  with  the  salts 
of  magnesia  and  zinc]  The  protoxide  is  precipitated  from  their  solutions  as  a 
white  hydrate  by  ammonia,  or  the  pure  fixed  alkalies ;  as  white  carboHate  of  pro- 
toxide of  manganese  by  alkaline  carbonates  and  bicarbonates ;  and  as  white 
ferrocyanide  of  manganese  by  ferrocyanide  of  potassium,  a  character  by  which 
the  absence  of  iron  may  be  demonstrated.  These  white  precipitates,  with  the 
exception  of  that  obtained  by  means  of  a  bicarbonate,  very  soon  become  brown 
from  the  absorption  of  oxygen.  None  of  the  salts  of  manganese  which  contain 
a  strong  acid,  such  as  the  nitric,  or  sulphuric,  are  precipitated  by  hydrosulphuric 
acid.  With  an  alkaline  hydrosulphate,  on  the  contrary,  a  flesh-coloured  precipi- 
tate is  formed,  which  is  a  hydrated  protosulphuret  of  manganese:  when  heated 
in  close  vessels,  it  yields  a  dark-coloured  sulphuret,  and  water  is  evolved. 

Its  eq.  is  35*7 ;  symh.  Mn  -f-  0,  Mn,  or  MO. 

Sesquioxide. — Hist,  and  Prep. — ^This  oxide  occurs  nearly  pure  in  nature,  con- 
stituting the  mineral  braunite,  and  as  a  hydrate  it  is  found  abundantly,  often  in 
large  prismatic  crystals,  at  Jhlefeld  in  the  Hartz.  It  may  be  formed  artificially 
by  exposing  peroxide  of  manganese  for  a  considerable  time  to  a  moderate  red 
heat,  and  therefore  is  the  chief  residue  of  the  usual  process  for  procuring  a 
supply  of  oxygen  gas ;  but  it  is  difficult  so  to  regulate  the  degree  and  duration 
of  tlie  heat,  that  the  resulting  oxide  shall  be  quite  pure. 

Frop. — The  colour  of  the  sesquioxide  of  manganese  varies  with  the  source 


326  MANGANESE. 

from  which  it  is  derived.  That  which  is  procured  by  means  of  heat  from  the 
native  peroxide  or  hyd rated  sesquioxide,  has  a  brown  tint;  but  when  prepared 
from  nitrate  of  oxide  of  manganese,  it  is  nearly  as  black  as  the  peroxide,  and  the 
native  sesquioxide  is  of  the  same  colour.  With  sulphuric  and  hydrochloric  acids 
it  gives  rise  to  the  same  phenomenon  as  the  peroxide,  but  of  course  yields  a 
smaller  proportional  quantity  of  oxygen  and  chlorine  gases.  It  is  more  easily 
attacked  than  the  peroxide  by  cold  sulphuric  acid.  With  strong  nitric  acid  it 
yields  a  soluble  protonitrate  and  the  peroxide,  and  when  boiled  with  dilute  sul- 
phuric acid,  it  undergoes  a  similar  change.  From  the  proportion  of  oxygen  and 
manganese  in  this  oxide,  it  has  sometimes  been  regarded  as  a  compound  of  43*7 
parts  or  1  eq.  of  peroxide,  and  35*7  parts  or  1  eq.  of  protoxide  of  manganese. 
In  that  case  the  sesquioxide  would  be  constituted  like  a  salt,  and  should  have 
the  properties  of  that  class  of  compounds ;  but  Mitscherlich  has  succeeded  in 
combining  it  with  sulphuric  acid,  and  has  obtained  with  it  an  alum  similar  in 
form  and  constitution  to  those  of  peroxide  of  iron  and  alumina.  It  must  there- 
fore be  considered  as  a  direct  compound  of  2  eq.  of  manganese  and  3  eq.  of 
oxygen. 
Its  eq.  is  79-4 ;  symh.  2M  +  30,  M,  or  M2O3. 

Peroxide. — Hist,  and  Prep. — The  well-known  ore  commonly  called,  from  its 
colour,  black  oxide  of  manganese.  It  generally  occurs  massive,  of  an  earthy 
appearance,  and  mixed  with  other  substances,  such  as  siliceous  and  aluminous 
earths,  oxide  of  iron,  and  carbonate  of  lime.  It  is  sometimes  found,  on  the  con- 
trary, in  the  form  of  minute  prisms  grouped  together,  and  radiating  from  a  com- 
mon centre,  forming  the  mineral  pyrosulite.  In  these  states  it  is  anhydrous ; 
but  the  essential  ingredient  of  one  variety  of  the  earthy  mineral  called  wad  is 
hydrated  peroxide  of  manganese,  consisting  of  1  eq.  of  water  and  2  of  the  oxide. 
The  peroxide  maybe  made  artificially  by  exposing  ijitrate  of  oxide  of  manganese 
to  a  commencing  red  heat,  until  the  whole  of  the  nitric  acid  is  expelled ;  but  I 
have  never  succeeded  in  procuring  it  quite  pure  by  this  process,  because  the 
heat  required  to  drive  off  the  last  traces  of  acid  likewise  expels  some  oxygen 
from  the  peroxide.  The  hydrated  peroxide,  containing  1  eq.  of  water  and  1  of 
oxide,  is  formed  by  precipitating  the  protochloride  of  manganese  by  chloride  of 
lime ;  and  the  same  compound  results  from  the  decomposition  of  the  acids  of 
manganese,  either  in  water  or  by  dilute  acid. 

Prop. — Not  changed  by  exposure  to  the  air,  is  insoluble  in  water,  and  does 
not  unite  either  with  acids  or  alkalies.  When  boiled  with  sulphuric  acid,  it 
yields  oxygen  gas,  and  a  sulphate  of  the  protoxide  is  formed.  With  hydro- 
chloric acid,  chloride  of  manganese  is  generated,  and  chlorine  is  evolved.  The 
solution  in  both  cases  is  of  a  deep-red  colour,  provided  undissolved  oxide  is 
present;  but  if  separated  from  the  undissolved  portions,  it  is  readily  rendered 
colourless  by  heat.  The  colour  is  commonly  attributed  to  a  small  quantity  of 
the  sesquioxide  or  red  oxide  of  manganese  dissolved  by  the  free  acid  ;  but  Mr. 
Pearsall,  of  Hull,  has  gone  far  to  prove  that  it  is  owing  to  the  presence  of  per- 
manganic acid.  (R.  Inst.  Journal,  N.  S.  No.  iv.  49.)  The  action  of  sulphuric 
acid  in  the  cold  is  exceedingly  tardy  and  feeble,  a  minute  quantity  of  oxygen 
gas  is  slowly  disengaged,  and  the  acid  acquires  an  amethyst-red  tint  On  expo- 
sure to  a  red  heat,  it  is  converted,  with  Evolution  of  oxygen  gas,  into  the  sesqui- 
oxide of  manganese. 

Peroxide  of  manganese  is  employed  in  the  arts,  in  the  manufacture  of  glass, 
and  in  preparing  chlorine  for  bleaching.    In  the  laboratory  it  is  used  for  pro- 


MANGANESE.  ^ 


curing  chlorine  and  oxygen  gases,  and  in  the  preparation  of  the  salts  of  man- 
ganese. 

Bed  Oxide. — The  substance  called  red  oxide  of  manganese,  Oxidum  Manga- 
noso-Manganicum  of  Arfwedson,  occurs  as  a  natural  production,  and  may  be 
formed  artificially  by  exposing  the  peroxide  of  sesquioxide  to  a  white  heat  either 
in  close  or  open  vessels.  It  is  also  produced  by  absorption  of  oxygen  from  the 
atmosphere  when  the  protoxide  is  precipitated  from  its  salts  by  pure  alkalies,  or 
when  the  anhydrous  protoxide  or  carbonate  is  heated  to  redness.  It  is  very  per- 
manent in  the  air,  not  passing  to  a  higher  stage  of  oxidation  at  any  temperature. 
Its  colour  when  rubbed  to  the  same  degree  of  fineness  is  brownish-red  when 
cold,  and  nearly  black  while  warm.  Fused  with  borax  or  glass  it  communicates 
a  beautiful  violet  tint,  a  character  by  which  manganese  may  be  easily  detected 
before  the  blowpipe ;  and  it  is  the  cause  of  the  rich  colour  of  the  amethyst.  It 
is  acted  on  by  strong  sulphuric  and  hydrochloric  acids,  with  the  aid  of  heat,  in 
the  same  manner  as  the  peroxide  and  sesquioxide,  but  of  course  yields  propor- 
tionally a  smaller  quantity  of  oxygen  and  chlorine  gases.  By  cold  concentrated 
sulphuric  acid  it  is  dissolved  in  small  quantity,  without  appreciable  disengage- 
ment of  oxygen  gas,  and  the  solution  is  promoted  by  a  slight  increase  of  tempe- 
rature. The  liquid  has  an  amethyst  tint,  which  disappears  when  heat  is  applied, 
or  by  the  action  of  deoxidizing  substances,  such  as  protochloride  of  tin,  or  sul- 
phurous and  phosphorous  acids,  sulphate  of  protoxide  of  manganese  being  gene- 
rated. By  strong  nitric  acid,  or  when  boiled  with  dilute  sulphuric  acid,  it 
undergoes  the  same  kind  of  change  as  the  sesquioxide. 

It  may  be  doubted  whether  the  red  oxide  is  not  rather  a  kind  of  salt  composed 
of  two  other  oxides,  than  a  direct  compound  of  manganese  and  oxygen.  From 
the  ratio  of  its  elements  it  may  consist  either  of 

Sesquioxide        .        79-4  or  1  equiv.)  (Peroxide        .        43-7  or  1  equiv. 

Protoxide  .        35-7  or  1  equiv.  J  (Protoxide       .        714  or  2  equiv. 

1151  115-1 

It  contains  27*586  per  cent,  of  oxygen,  and  loses  6*896  per  cent,  when  converted 
into  the  green  oxide.  Its  eq.  is  115*1 ;  its  symh.  either  MnO  -f  Mn203,or  2MnO 
+  MnOj. 

Varvicite. — This  compound  is  known  only  as  a  natural  production,  having  been 
first  noticed  a  few  years  ago  by  Mr.  Phillips  among  some  ores  of  manganese 
found  at  Hartshill,  in  Warwickshire.  The  locality  of  the  mineral  suggested  its 
name ;  but  I  have  also  detected  it  as  the  constituent  of  an  ore  of  manganese 
from  Jhlefeld,  sent  me  by  Professor  Stromeyer.  Varvicite  was  at  first  mistaken 
for  peroxide  of  manganese,  to  which  in  the  colour  of  its  powder  it  bears  con- 
siderable resemblance ;  but  it  is  readily  distinguished  from  that  ore  by  its 
stronger  lustre,  greater  hardness,  more  lamellated  texture,  which  is  very  similar 
to  that  of  manganite,  and  by  yielding  water  freely  when  heated  to  redness.  Its 
sp.  gr.  is  4-531.  It  has  not  been  found  regularly  crystallized  ;  but  my  specimen 
from  Jhlefeld  is  in  pseudo-crystals^  possessing  the  form  of  the  six-sided  pyramid  of 
calcareous  spar.  When  strongly  heated  it  is  converted  into  red  oxide,  losing 
5*725  per  cent,  of  water,  and  7*385  of  oxygen.  It  is  probably,  like  the  red  oxide, 
a  compound  of  two  other  oxides;  and  the  proportions  just  stated  justify  the 
supposition  that  it  consists  of  2  eq.  of  peroxide  and  1  of  sesquioxide  of  manga- 


MANGANESE. 

nese,  united  in  the  mineral  with  an  eq.  of  water.  (Phil.  Mag,  and  Annals,  v. 
209,  vi.  281,  and  vii.  284.) 

It  has  been  inferred  from  some  experiments  of  Berzelius  and  John,  that  there 
are  two  other  oxides  of  manganese,  which  contain  less  oxygen  than  the  green  or 
protoxide.     We  have  no  proof,  however,  of  the  existence  of  such  compounds. 

Its  eq.  is  166-8;  symh.  probably  M2O3  -[■  2MO2. 

MaHganic  Acid, — Hist,  and  Prep. — Manganese  is  one  of  those  metals  which  is 
capable  of  forming  an  acid  with  oxygen.  Manganate  of  potassa  is  generated 
when  hydrate  or  carbonate  of  potassa  is  heated  to  redness  with  peroxide  of  man- 
ganese ;  and  nitre  may  be  used  successfully,  provided  the  heat  be  high  enough 
to  decompose  the  nitrate  of  potassa.  The  materials  absorb  oxygen  from  the  air 
when  fused  in  open  vessels  ;  but  manganate  of  potassa  is  equally  well  formed  in 
close  vessels,  one  portion  of  oxide  of  manganese  then  supplying  oxygen  to 
another.  The  product  has  been  long  known  under  the  name  of  mineral  chame- 
leon, from  the  property  of  its  solution  to  pass  rapidly  through  several  shades  of 
colour  :  on  the  first  addition  of  cold  water  a  green  solution  is  formed,  which 
soon  becomes  blue,  purple,  and  red ;  and  ultimately  a  brown  flocculent  matter, 
hydrated  peroxide  of  manganese,  subsides,  and  the  liquid  becomes  colourless. 
These  changes,  which  are  more  rapid  by  dilution  with  hot  water,  have  been 
successively  elucidated  by  Chevillot  and  Edwards,  Forchammer,  and  Mitscher- 
lich.    (An.  de  Ch.  et  Ph.  viii.,  and  xlix.  113;  and  An.  of  Phil,  xvi.) 

Prop. — The  phenomena  above  mentioned  are  owing  to  the  formation  of  man- 
ganate of  potassa  of  a  green  colour,  and  to  its  ready  conversion  into  the  red  per- 
manganate of  potassa,  the  blue  and  purple  tints  being  due  to  a  mixture  of  these 
compounds.  Manganic  acid  itself  cannot  be  obtained  in  an  uncombined  state, 
because  it  is  then  resolved  into  the  hydrated  peroxide  and  oxygen,  a  property 
which  Mitscherlich  availed  himself  of  in  analyzing  this  acid  ;  but  Mitscherlich 
has  proved  that  it  is  analogous  in  composition  to  sulphuric  acid,  and  its  salts 
isomorphous  with  the  sulphates.  Manganate  of  potassa  is  obtained  in  crystals 
by  forming  a  concentrated  solution  of  mineral  chameleon  in  cold  water,  very  pure 
and  free  from  carbonic  acid,  allowing  it  to  subside  in  a  stoppered  bottle,  and 
evaporating  the  clear  green  solution  in  vacuo  with  the  aid  of  sulphuric  acid.  All 
contact  of  paper  and  other  organic  matter  must  be  carefully  avoided,  since  they 
deoxidize  the  acid,  and  the  process  be  conducted  in  a  cool  apartment.  The  crys- 
tals are  anhydrous,  and  permanent  in  the  dry  state ;  but  in  solution  the  carbonic 
acid  of  the  air  suffices  to  decompose  the  acid,  or  even  simple  dilution  with  cold 
water.  Mixed  with  a  solution  of  potassa  the  manganate  may  be  crystallized  a 
second  time  in  vacuo  without  change. 

Its  eq.  is  51-7  ;  symb.  Mn  -j-  30,  Mn,  or  MnOj. 

Permanganic  Acid. — Prep, — Permanganate  of  potassa  is  obtained  by  heating 
a  solution  of  mineral  chameleon,  however  prepared.  A  better  process  has  been 
indicated  by  Wohler  (Pog.  An.  xxvii.  626) ;  it  consists  in  fusing  chlorate  of 
potassa  in  a  platinum  crucible,  and  then  adding  peroxide  of  manganese  in  fine 
powder.  An  improvement  on  this  has  been  proposed  by  Gregory  (Lieb.  An.  xv. 
237) :  he  recommends  4  parts  of  peroxide  of  manganese  to  be  mixed  in  fine 
powder  with  3h  parts  of  chlorate  of  potassa,  and  then  added  to  5  parts  of  hydrate 
of  potassa  dissolved  in  a  small  quantity  of  water.  The  whole  is  evaporated  to 
perfect  dryness,  powdered,  and  exposed  in  a  platinum  crucible  to  a  low  red  heat. 


MANGANESE.  g^ 

The  mass,  which  has  not  been  fused,  is  again  powdered,  and  added  to  a  large 
quantity  of  boiling  water,  which  when  clear  is  decanted  from  the  sediment  of 
peroxide  of  manganese,  rapidly  concentrated  and  allowed  to  crystallize.  The 
crystals  are  at  first  small  and  almost  black ;  but  by  washing  with  a  little  cold 
water,  and  resolution  in  the  smallest  possible  quantity  of  boiling  water,  they  are 
obtained  in  very  fine  crystals.  The  acid  may  be  obtained  by  adding  to  a  solu- 
tion of  permanganate  of  baryta  a  quantity  of  dilute  sulphuric  acid  exactly  suffi- 
cient for  precipitating  the  baryta. 

[Permanganic  acid  may  be  obtained  in  a  much  more  permanent  state,  according 
to  M.  Huenefeld,  by  washing  the  manganate  of  baryta  with  hot  water,  by  which 
it  is  resolved  into  peroxide  of  manganese  and  permanganic  of  baryta,  and  then 
treating  the  latter  with  phosphoric  acid,  in  quantity  sufficient  to  neutralize  the 
baryta.  The  free  permanganic  acid  is  separated  by  solution,  evaporated  to  dry- 
ness, and  by  resolution  and  evaporation  is  obtained  as  a  reddish  brown  crystal- 
line mass,  having  in  parts  the  lustre  of  indigo.  It  is  completely  soluble  in  water. 
(Berzelius's  Traite,  i.  522.)] 

Prop. — Has  a  rich  red  colour ;  is  more  stable  than  the  manganic  acid,  though 
still  very  prone  to  decomposition.  Contact  with  paper  or  linen  as  in  filtering, 
particles  of  cork,  organic  particles  floating  in  the  atmosphere,  decompose  it 
rapidly,  for  which  reason  Gregory  recommends  that  all  solutions  containing  it 
should  be  filtered  through  a  pledget  of  asbestus,  placed  in  the  throat  of  the  funnel. 
Colouring  matters  are  bleached  by  it;  and  in  pure  water  its  decomposition 
begins  at  86°  and  is  complete  at  212°.  On  these  occasions  oxygen  gas  is  ab- 
stracted or  given  out,  and  hydrated  peroxide  of  manganese  subsides.  Its  salts 
are  more  permanent  than  the  free  acid,  so  that  most  of  them  may  be  boiled  in 
solution,  especially  if  concentrated.  When  heated  they  give  out  oxygen  gas, 
and  are  reconverted  into  manganates.  They  deflagrate  like  nitre  with  burning 
charcoal,  and  detonate  powerfully  with  phosphorus.  Their  colour  in  solution  is 
a  rich  purple,  and  a  small  quantity  of  the  salt  imparts  this  colour  to  a  very  large 
quantity  of  water.  When  mixed  with  dilute  nitric  acid  and  boiled,  oxygen  gas 
is  evolved,  and  hydrated  peroxide  of  manganese  subsides,  from  the  respective 
quantities  of  which  Mitscherlich  ascertained  the  composition  of  the  acid.  In 
addition  to  the  remarkable  analogy  which  its  constitution  bears  to  perchloric 
acid,  Mitscherlich  finds  that  permanganate  and  perchlorate  of  potassa  are  isoraor- 
phous,  an  observation  confirmed  by  Miller. 

Its  eq,  «s  111-4;  symb.  2  Mn  -f-  70,  Mn,  or  Mn207. 

Protochloride  of  Manganese. — This  compound  is  best  prepared  by  evaporating  a 
solution  of  the  chloride  to  dryness  by  a  gentle  heat,  and  heating  the  residue  to 
redness  in  a  glass  tube,  while  a  current  of  hydrochloric  acid  gas  is  transmitted 
through  it.  The  heat  of  a  spirit-lamp  is  sufficient  for  the  purpose.  It  fuses 
readily  at  a  red  heat,  and  forms  a  pink-coloured  lamellated  mass  on  cooling.  It 
is  deliquescent,  and  of  course  very  soluble  in  water.  ^ 

Its  eq.  is  63-12;  symh,  Mn  +  CI,  or  MnCl. 

Perchloride  of  Manganese. — Hist,  and  Prep. — Dumas  discovered  this  compound, 
which  is  readily  formed  by  putting  a  solution  of  permanganic  into  strong  sul- 
phuric acid,  and  then  adding  fused  sea-salt.  The  hydrochloric  and  permanganic 
acids  mutually  decompose  each  other ;  water  and  perchloride  of  manganese  are 
generated,  and  the  latter  escapes  in  the  form  of  vapour.  The  best  mode  of  pre- 
paration is  to  form  the  green  mineral  chameleon,  and  acidulate  with  sulphuric 


MANGANESE. 

acid :  the  solution,  when  evaporated,  leaves  a  residue  of  sulphate  and  permanga- 
nate of  potassa.  This  mixture,  treated  by  strong  sulphuric  acid,  yields  a  solu- 
tion of  permanganic  acid,  into  which  are  added  small  fragments  of  sea-salt,  as 
long  as  coloured  vapour  continues  to  be  evolved.  (Edin.  Joum.  of  Science, 
viii.  179.) 

Prop. — The  perchloride,  when  first  formed,  appears  as  a  vapour  of  a  copper 
or  greenish  colour ;  but  on  traversing  a  glass  tube  cooled  to  —  4°,  it  is  condensed 
into  a  greenish-brown  coloured  liquid.  "When  generated  in  a  capacious  tube, 
its  vapour  gradually  displaces  the  air,  and  soon  fills  the  tube.  If  it  is  then 
poured  into  a  large  flask,  the  sides  of  which  are  moi^t,  the  colour  of  the  vapour 
changes  instantly  on  coming  into  contact  with  the  moisture,  a  dense  smoke  of  a 
pretty  rose-tint  appears,  and  hydrochloric  and  permanganic  acids  are  generated. 
It  is  hence  analogous  in  composition  to  permanganic  acid,  its  elements  being  in 
such  a  ratio  that 

1  eq.  perchloride  and  7  eq.  water    2     1  eq.  permang.  acid  and  7  eq.  hydrochloric  acid. 
MnjCly  7H0  T.        MnzO,  •  7HC1. 

Hence  Us  eq.  is  303*34 ;  symh.  2Mn  -|-  7C1,  or  Mn2C]7. 

Perfluoride  of  Manganese. — This  gaseous  compound,  discovered  by  Dumas  and 
Wohler  (Edin.  Joum.  of  Science,  ix.),  is  best  formed  by  mixing  common  mine- 
ral chameleon  with  half  its  weight  of  fluor-spar,  and  decomposing  the  mixture 
in  a  platinum  vessel  by  fuming  sulphuric  acid.  The  fluoride  is  then  disengaged 
in  the  form  of  a  greenish-yellow  gas  or  vapour,  of  a  more  intensely  yellow  tint 
than  chlorine.  When  mixed  with  atmospheric  air,  it  instantly  acquires  a  beau- 
tiful purple-red  colour ;  and  it  is  freely  absorbed  by  water,  yielding  a  solution  of 
the  same  red  tint.  It  acts  instantly  on  glass,  with  formation  of  fluosilicic  acid 
gas,  a  brown  matter  being  at  the  same  time  deposited,  which  becomes  of  a  deep 
purple-red  tint  on  the  addition  of  water. 

It  may  be  inferred  -from  the  experiments  of  Wohler  that  this  yellow  gas  is  a 
fluoride  of  manganese  ;  that  when  mixed  with  water  both  compounds  are  decom- 
posed, and  hydrofluoric  and  permanganic  acids  generated,  which  are  dissolved  ; 
that  a  similar  formation  of  the  two  acids  ensues  from  the  admixture  of  the  yellow 
gas  with  atmospheric  air,  owing  to  the  moisture  contained  in  the  latter ;  and 
that  by  contact  with  glass,  fluosilicic  acid  gas  is  produced,  and  anhydrous  per- 
manganic acid  deposited.  In  consequence  of  its  acting  so  powerfully  on  glass, 
its  other  properties  have  not  been  ascertained  ;  but  from  those  above  mentioned, 
its  composition  is  obviously  similar  to  that  of  the  gaseous  chloride  of  manga- 
nese. 

Its  eq.  is  186*16  ;  symh.  2Mn  -}-  7F,  or  Mn^F,. 

The  protbsulphuret  of  manganese  may  be  procured  by  igniting  the  sulphate  with 
one-sixth  of  its  weight  of  charcoal  in  powder.  (Berthier.)  It  is  also  formed  by 
the  action  of  hydrosulphuric  acid  gas  on  the  protosulphate  at  a  red  heat.  (Arf- 
wedsftn  in  An.  of  Phil.  vol.  vii.  N.  S.)  It  occurs  native  in  Cornwall  and  at 
Nagyag  in  Transylvania.  It  dissolves  completely  in  dilute  sulphuric  or  hydro- 
chloric acid,  with  disengagement  of  very  pure  hydrosulphuric  acid  gas.  Its  eq, 
is  43*8  ;  symh.  Mn  -j-  S,  or  MnS. 


IRON.  331 


SECTION  XL 


IRON. 


Hist, — Known  from  the  remotest  antiquity.  The  occurrence  of  native  iron, 
except  that  of  meteoric  origin,  which  always  contains  nickel  and  cobalt,  is  ex- 
ceedingly rare ;  and  few  of  the  specimens  said  to  be  such  have  been  well 
attested.*  In  combination,  however,  especially  with  oxygen  and  sulphur,  it  is 
abundant ;  being  contained  in  animals  and  plants,  and  being  diffused  so  univer- 
sally in  the  earth  that  there  are  few  mineral  substances  in  which  its  presence 
may  not  be  detected.  Minerals  which  contain  iron  in  such  form,  and  in  such 
quantity,  as  to  be  employed  in  the  preparation  of  the  metal,  are  called  ores  of 
iron ;  and  of  these  the  principal  are  the  following.  The  red  oxides  of  iron  in- 
cluded under  the  name  of  red  haematite ;  the  brown  haematite  of  mineralogists, 
consisting  of  hydrated  peroxide  of  iron ;  the  black  oxide,  or  magnetic  iron  ore ; 
and  carbonate  of  protoxide  of  iron,  either  pure,  or  in  the  form  of  clay  iron  ore, 
when  it  is  mixed  with  siliceous,  aluminous,  and  other  foreign  substances.  The 
two  former  occur  abundantly,  both  in  primary  and  secondary  districts ;  the  latter 
is  most  abundant  in  primary  formations,  and  is  the  source  of  the  finest  kind  of 
iron  made  in  Sweden  and  India ;  while  clay-iron  stone,  from  which  most  of  the 
English  iron  is  extracted,  occurs  in  secondary  deposites,  and  chiefly  in  the  coal 
formation. 

Prep. — The  exaction  of  iron  from  its  ores  is  effected  by  exposing  the  ore,  pre- 
viously roasted  and  reduced  to  a  coarse  powder,  to  the  action  of  charcoal,  or  coke, 
and  lime  at  a  high  temperature.  The  action  of  carbonaceous  matter  in  depriving 
the  ore  of  its  oxygen  is  obvious;  and  the  lime  plays  a  part  equally  important.  It 
acts  as  a  flux  by  combining  with  all  the  impurities  of  the  ore,  and  forming  a 
fusible  compound  called  a  slag.  The  whole  mass  being  thus  in  a  fused  state,  the 
particles  of  reduced  metal  descend  by  reason  of  their  greater  density,  and  collect 
at  the  bottom ;  while  the  slag  forms  a  stratum  above,  protecting  the  melted  metal 
from  the  action  of  the  air.  The  latter,  as  it  collects,,  runs  out  at  an  aperture  in 
the  side  of  the  furnace  :  and  the  fused  iron  is  let  off  by  a  hole  in  the  bottom,  which 
was  previously  filled  with  sand.  The  process  is  never  successful  unless  the  flux, 
together  with  the  impurities  of  the  ore,  are  in  such  proportion  as  to  constitute  a 
fusible  compound.  The  mode  of  accomplishing  this  object  is  learned  only  by 
experience ;  and  as  different  ores  commonly  differ  in  the  nature  or  quantity  of 
their  impurities,  the  workman  is  obliged  to  vary  his  flux  according  to  the  com- 
position of  the  ore  with  which  he  operates.  Thus  if  the  ore  is  deficient  in  sili- 
ceous matter,  sand  must  be  added ;  and  if  it  contain  a  large  quantity  of  lime, 

*  It  is  said  to  be  found  native  associated  with  the  platinum  of  the  Uralian  mountains,  and 
it  exists  of  undoubted  terrestrial  origin  as  a  thin  vein  of  about  two  inches  thick,  attached  to 
a  mass  of  mica  slate,  at  Canaan,  in  Connecticut.  It  contains  grophite  between  its  plates, 
and  exhibits  no  obvious  crystalline  structure,  nor  is  any  developed  by  etching  with  nitric 
acid,  as  in  most  iron  of  meteoric  origin. — (Dana's  Mineralogy,  p.  467.)    (R.) 


IRON. 

proportionally  less  of  that  earth  -will  be  required.  Much  is  often  accomplished 
by  the  admixture  of  diflferent  ores  with  each  other.  The  slag  consists  of  a  com- 
pound of  earthy  salts,  similar  to  some  siliceous  minerals,  in  which  silicic  acid  is 
combined  with  lime,  alumina,  magnesia,  protoxide  of  manganese,  and  sometimes 
oxide  of  iron.  The  most  usual  combination,  according  to  Mitscherlich,  is  bisili- 
cate  of  lime  and  magnesia,  sometimes  with  a  little  protoxide  of  iron ;  a  compound 
which  he  has  obtained  in  crystals,  having  the  precise  form  and  composition  of 
Augite.  Artificial  minerals  may  in  fact  by  such  processes  be  procured,  similar 
in  form  and  composition  to  those  which  occur  in  the  earth.  We  are  indebted  to 
Mitscherlich  for  some  valuable  facts  on  this  subject  (An.  de  Ch.  et  Ph.  xxiv. 
355). 

The  iron  obtained  by  this  process  is  the  cast  iron  of  commerce,  and  contains  a 
considerable  quantity  of  carbon,  unreduced  ore,  and  earthy  substances.  It  is  con- 
verted into  a  soft  or  malleable  iron  by  exposure  to  a  strong  heat  while  a  current 
of  air  plays  upon  its  surface.  By  this  means  any  undecomposed  ore  is  reduced, 
earthy  impurities  rise  to  the  surface  as  slag,  and  carbonaceous  matter  is  burned. 
The  exposed  iron  is  also  more  or  less  oxidized  at  its  surface,  and  the  resulting 
oxide,  being  stirred  with  the  fused  metal  below,  facilitates  the  oxidation  of  the 
carbon.  As  the  purity  of  the  iron  increases,  its  fusibility  diminishes,  until  at 
length,  though  the  temperature  continue  the  same,  the  iron  becomes  solid.  It  is 
then  subjected,  while  still  hot,  to  the  operation  of  rolling  or  hammering,  by  which 
its  particles  are  approximated,  and  its  tenacity  greatly  increased.  It  is  then  the 
malleable  iron  of  commerce.  It  is  not,  however,  absolutely  pure  ;  for  Berzelius 
has  detected  in  it  about  one-half  per  cent,  of  carbon,  and  it  likewise  contains 
traces  ^  of  silicon.  The  carbonaceous  matter  may  be  removed  by  mixing  iron 
filings  with  a  quarter  of  its  weight  of  black  oxide  of  iron,  and  fusing  the  mixture, 
confined  in  a  covered  hessian  crucible,  by  means  of  a  blast  furnace.  A  little 
powdered  green  glass  should  be  laid  on  the  mixture,  in  order  that  the  iron  may 
be  completely  protected  from  the  air  by  a  covering  of  melted  glass,  and  any  un- 
reduced oxide  dissolved.  But  the  best  and  readiest  mode  of  procuring  iron  in  a 
stat^of  perfect  purity,  is  by  transmitting  hydrogen  gas  over  the  pure  oxide  heated 
to  redness  in  a  tube  of  porcelain.  The  oxygen  of  the  oxide  unites  with  hydro- 
gen, and  the  metal  is  left  in  the  form  of  a  porous  spongy  mass. 

Prop. — Iron  has  a  peculiar  grey  colour,  and  strong  metallic  lustre,  which  is 
susceptible  of  being  heightened  by  polishing.  In  ductility  and  malleability  it  is 
inferior  to  several  metals,  but  exceeds  them  all  in  tenacity.  At  common  temper- 
atures it  is  very  hard  and  unyielding,  and  its  hardness  may  be  increased  by  being 
heated  and  then  suddenly  cooled ;  but  it  is  at  the  same  time  rendered  brittle. 
"When  heated  to  redness  it  is  remarkably  soft  and  pliable,  so  that  it  may  be  beaten 
into  any  form,  or  be  intimately  incorporated  or  welded  with  another  piece  of  red- 
hot  iron  by  hammering.  Its  texture  is  fibrous.  Its  sp.  gr.  may  be  estimated  at 
7*7 ;  but  it  varies  slightly  according  to  the  degree  with  which  it  has  been  rolled, 
hammered,  or  drawn,  and  it  is  increased  by  fusion.  In  its  pure  state  it  is  ex- 
ceedingly infusible,  requiring  for  fusion  the  highest  temperature  of  a  wind  fur- 
nace. It  is  attracted  by  the  magnet,  and  may  itself  be  rendered  permanently 
magnetic  by  several  processes ; — a  property  of  great  interest  and  importance,  and 
which  is  possessed  by  no  other  metal  excepting  nickel.  It  retains  this  quality, 
however,  only  within  certain  temperatures :  thus  iron  of  an  orange-red  heat  ceases 
to  be  attracted,  and  a  steel  magnet  loses  its  polarity  at  the  boiling  point  of  almond 
oil— a  loadstone  just  below  visible  ignition  (Faraday). 


IRON.  333 

Iron,  in  its  ordinary  state,  has  a  strong  affinity  for  oxygen.  In  a  perfectly  dry 
atmosphere  it  undergoes  no  change ;  but  when  moisture  is  present,  its  oxidation, 
or  rusting,  is  rapid.  In  the  first  part  of  the  change  carbonate  of  protoxide  of  iron 
is  generated;  but  the  protoxide  gradually  passes  into  hydrated  peroxide,  and  the 
carbonic  acid  at  the  same  time  is  evolved.  Rust  of  iron  always  contains  ammo- 
nia, a  circumstance  which  indicates  that  the  oxidation  is  probably  accompanied 
by  decomposition  of  water ;  and  Chevalier  has  observed  that  ammonia  is  also 
present  in  the  native  oxides  of  iron.  Heated  to  redness  in  the  open  air,  iron  ab- 
sorbs oxygen  rapidly,  and  is  converted  into  black  scales,  called  the  black  oxide 
of  iron ;  and  in  an  atmosphere  of  oxygen  gas  it  burns  with  vivid  scintillations. 
The  same  effect  was  observed  by  Bierley  on  exposing  a  bar  of  iron  at  a  full  white 
heat  to  the  blast  of  a  powerful  pair  of  bellows.  This  has  been  confirmed  by 
D'Arcet,  who  also  obtained  the  combustion  by  causing  the  heated  iron  to  revolve 
rapidly  through  the  air :  for  this  purpose  he  attached  one  extremity  of  the  bar  by 
means  of  wire  to  a  string,  and  then  whirled  it  rapidly  round.  Magnus  has  ob- 
served that  the  spongy  mass  obtained  by  reducing  the  oxide  of  iron  with  hydro- 
gen may  be  obtained  at  a  heat  considerably  below  that  of  redness ;  and  that  when 
the  iron,  thus  reduced,  is  exposed  to  the  air,  it  takes  fire  spontaneously,  and  the 
oxide  is  instantly  reproduced.  This  singular  property,  which  Magnus  has  also 
remarked  in  nickel  and  cobalt  prepared  in  a  similar  manner,  appears  to  depend 
on  the  extremely  divided  and  expanded  state  of  the  metallic  mass  ;  for  when  the 
reduction  is  effected  at  a  red  heat,  which  enables  the  metal  to  acquire  its  natural 
degree  of  compactness,  the  phenomenon  is  not  observed.  If  the  oxide  be  mixied 
with  a  little  alumina,  and  then  reduced  at  a  red  heat,  the  presence  of  the  earth 
prevents  that  contraction  which  would  otherwise  ensue  :  the  metal  is  in  the  same 
mechanical  condition  as  when  it  is  deoxidized  at  a  low  temperature,  and  its  spon- 
taneous combustibility  is  preserved. 

Iron  decomposes  the  vapour  of  water,  by  uniting  with  its  oxygen,  at  all  tem- 
peratures, from  a  dull  red  to  a  white  heat ;  a  singular  fact  when  it  is  considered, 
that  at  the  very  same  temperatures  the  oxides  of  iron  are  reduced  to  the  metallic 
state  by  hydrogen  gas.  (Gay-Lussac  in  An.  de  Ch.  et  de  Physique,  i.  36.) 
These  opposite  effects,  various  instances  of  which  are  known  to  chemists,  are 
accounted  for  by  a  mode  of  reasoning  similar  to  that  explained  on  a  former  occa- 
sion (page  123).  It  is  rapidly  oxidized  by  sulphuric  and  nitric  acids ;  in  the 
former  case  the  oxidation  occurs  at  the  sole  expense  of  water,  the  hydrogen  of 
which  is  at  the  same  time  evolved,  while  in  the  latter  the  nitric  acid  itself  yields 
a  part  of  its  oxygen.  The  action  of  nitric  acid  on  iron  is  attended  by  a  series  of 
very  remarkable  phenomena,  which  have  recently  been  observed  by  Professor 
Schonbein.  He  first  observed  that  nitric  acid  of  sp.  gr.  1*35,  though  capable  of 
acting  with  great  violence  on  ordinary  iron,  was  perfectly  inert  on  a  portion  of 
iron  wire  one  extremity  of  which  had  been  made  red  hot  previously  to  its  intro- 
duction into  the  acid.  He  found,  too,  that  this  indifference  to  nitric  acid  may  be 
communicated  by  mere  contact  from  one  iron  wire  to  another,  by  submersion  for 
a  few  moments  into  strong  nitric  acid,  or  by  making  it  the  positive  electrode  of 
a  galvanic  current,  the  negative  electrode  having  been  previously  introduced  into 
the  acid.  It  is  remarkable  that  under  these  circumstances  the  iron  wire  possesses 
the  properties  of  one  of  gold  or  platinum,  and  does  not  combine  with  the  oxygen 
liberated  at  its  surface.  Faraday,  who  has  examined  this  voltaic  condition  of 
iron  with  his  usual  success,  has  remarked  that  the  same  property  is  communi- 
cated to  iron  by  contact  with  platinum,  and  that  the  effect  is  not  limited  to  nitric 


334 


IRON. 


acid,  but  extends  to  varions  saline  solutions  which  are  usually  acted  on  by  iron. 
For  the  particulars  on  this  interesting  subject  the  reader  may  consult  the  original 
papers  of  Schonbein  and  Faraday  in  the  Phil.  Mag.  and  An.  ix.  53 ;  x.  133,  172, 
175,  267,  428. 

The  equivalent  of  iron  has  not  yet  been  determined  with  accuracy.  From  the 
analysis  of  its  oxides  by  Berzelius,  Stromeyer,  and  Gay-Lussac,  it  may  be  esti- 
mated at  27-16,  27-8,  and  28*3.  In  the  uncertainty  as  to  which  of  these  numbers 
is  the  most  accurate,  I  shall  continue  to  use  28,  the  number  generally  adopted  in 
this  country.  Its  symh.  is  Fe.  The  composition  of  the  compounds  of  iron  de- 
scribed in  this  section  is  as  follows : — 


Iron 

Eqniv.           Formulae. 

Protoxide 

28     leq.+Oxyg. 

8 

leq. 

=  36        Fe+O  or  FeO. 

Peroxide 

56    2  eq.-l-do. 

24 

3eq. 

=  80        2  Fe-l-30  or  FegOs. 

Bua  oxide  i^:^    :    : 

36 
80 

1  eq.) 
leq.  J 

=116        FeCH-Fe203.               ' 

Ferric  acid 

28     1  eq.-Ho. 

16 

2eq. 

=  44        Fe  +  20  or  FeO^. 

Protochloride      . 

28    1  eq.+Chlor. 

35-42 

leq. 

=63.42     Fe -fCl  or  FeCl. 

Perchloride 

66    2eq.4-do. 

106-26 

3  eq. 

=162-26  2  F4-3C1  or  FeaCl,. 

Protiodide 

28    1  eq.H-Iodine 

126-3 

leq. 

=154-3     Fe-f-I  or  Fel. 

Periodide 

56    2eq.4-do. 

378-9 

3  eq. 

=434-9     2Fe-f-3I  or  F2T3. 

Protobromide     . 

28     I  eq.+Brom. 

78-4 

leq. 

=106-4    Fe-f-Br  or  FeBr. 

Perbromide 

56    2eq.+do. 

235-2 

3  eq. 

=291-2    2  Fe-f  3Br  or  FejBrs. 

Protofluoride 

28    1  eq.+Fluor. 

18-68 

leq. 

=  46-68  Fe-I-F  or  FeF. 

Perfluoride 

56    2  eq.+Fluor. 

56-04 

3  eq. 

=112-04  2  Fe-|-3F  or  Fe^F'. 

Tetrasulphuret  . 

112  4eq.+Sulph. 

16-1 

leq. 

=128-1    4Fe+SorFe4S. 

Disulphuret 

56     2  eq.4-do. 

161 

leq. 

=  72-1    2  Fe-+-S  or  Fe^S. 

Protosulphuret   . 

28     1  eq.+do. 

16-1 

leq. 

=  44-1    Fe+S  or  FeS. 

Sesquisulphuret 

55    2  eq.4-do. 

48-4 

3  eq. 

=104-3   2Fe+3S  orFeaS'. 

Bisulphuret 

28     1  eq.-Hio. 

32-2 

2eq. 

=  60-2  Fe4-2S  or  FeSa. 

Magnetic  Pyrites 

^Bisulph.of  iron 
}  Protosulph.  of 
(     iron 

60-2 
220-5 

leq.; 
5eq.| 

t  =280-7  5FeS-hFeS«. 

Diphosphuret 

56    2  eq.4-Phosp. 

15-7 

leq. 

=  71-7  2Fe-|-P  or  FeaP. 

Perphosphuret 

84     3  eq.-|-do. 

62-8 

4eq. 

=146-8  3F-HP  or  FeaPi 

Carburets.    Constitution  not  determined. 

OXIDES  OF  IRON. 


Protoxide. — ^This  oxide  is  the  base  of  the  native  carbonate  of  iron,  and  of  the 
green  vitriol  of  commerce.  Its  existence  was  inferred  some  years  ago  by  Gay- 
Lussac  (An.  de  Ch.  vol.  Ixxx.) ;  but  it  is  doubtful  if  it  has  ever  been  obtained 
in  an  insulated  form.  Its  salts,  particularly  when  in  solutioh,  absorb  oxygen 
from  the  atmosphere  with  such  rapidity  that  they  may  even  be  employed  in  eudi- 
ometry.  This  protoxide  is  always  formed  with  evolution  of  hydrogen  gas  when 
metallic  iron  is  put  into  dilute  sulphuric  acid  ;  and  its  composition  may  be  deter- 
mined by  collecting  and  measuring  the  gas  which  is  disengaged. 

Protoxide  of  iron  is  precipitated  from  its  salts  as  a  white  hydrate  by  pure  alka- 
lies, as  a  white  carbonate  by  alkaline  carbonates,  and  as  a  white  ferrocyanide  by 
ferrocyanide  of  potassium.  The  two  former  precipitates  become  first  green  and 
then  red,  and  the  latter  green  and  blue,  by  exposure  to  the  air.  The  solution  of 
gall-nuts  produces  no  change  of  colour.     Hydrosulphuric  acid  does  not  act  if 


IRON.  §g| 

the  protoxide  is  united  with  any  of  the  stronger  acids ;  but  alkaline  hydrosul- 
phates  cause  a  black  precipitate,  protosulphuret  of  iron. 

Its  eq.  is  36 ;  si/mb,  Fe  +  O,  Fe,  or  FeO. 

Peroxide. — Sesquioxide. — Hist,  and  Prep. — ^The  red  or  peroxide  is  a  natural 
product,  known  to  mineralogists  under  the  name  of  red  haematite.  It  sometimes 
occurs  massive,  at  other  times  fibrous,  and  occasionally  in  the  form  of  beautiful 
rhomboidal  crystals.  It  may  be  made  chemically  by  dissolving  iron  in  nitro- 
hydrochloric  acid,  and  adding  an  alkali.  The  hydrate  of  the  red  oxide  of  a 
brownish-red  colour  subsides,  which  is  identical  in  composition  with  the  mineral 
called  brown  hsematite,  and  consists  of  80  parts  or  1  eq.  of  the  peroxide,  and  18 
parts  or  2  eq.  of  water. 

Prop. — Is  not  attracted  by  the  magnet.  Fused  with  vitreous  substances  it 
communicates  to  them  a  red  or  yellow  colour.  It  combines  with  most  of  the 
acids,  forming  salts,  the  greater  number  of  which  are  red.  Its  presence  may  be 
detected  by  very  decisive  tests.  The  pure  alkalies,  fixed  or  volatile,  precipitate 
it  as  the  hydrate.  Alkaline  carbonates  have  a  similar  effect,  peroxide  of  iron  not 
forming  a  permanent  salt  with  carbonic  acid.  "With  ferrocyanide  of  potassium  it 
forms  Prussian  blue.  Sulphocyanide  of  potassium  causes  a  deep  blood-red,  and 
infusion  of  gall-nuts  a  black  colour.  Hydrosulphuric  acid  converts  the  peroxide 
into  protoxide  of  iron,  with  deposition  of  sulphur.  These  reagents,  and  espe- 
cially ferrocyanide  and  sulphocyanide  of  potassium,  afford  an  unerring  test  of  the 
presence  of  minute  quantities  of  peroxide  of  iron.  On  this  account  it  is  cus- 
tomary, in  testing  for  iron,  to  convert  it  into  the  peroxide,  an  object  which  is 
easily  accomplished  by  boiling  the  solution  with  a  small  quantity  of  nitric  acid. 
[The  sesquioxide  of  iron  and  its  compounds  are  strictly  isomorphous  with  alu- 
mina and  the  compounds  of  that  earth,  and  very  analogous  to  them  in  properties.] 

Its  eq.  is  80 ;  symb.  2Fe  +  30,  Ff,  or  Fe^Oa. 

Black  or  Magnetic  Oxide. — Hist,  and  Prep. — This  substance,  the  oxidum  fer- 
Toso-ferricum  of  Berzelius,  long  supposed  to  be  protoxide  of  iron,  contains  more 
oxygen  than  the  protoxide,  and  less  than  the  red-oxide.  It  cannot  be  regarded 
as  a  definite  compound  of  iron  and  oxygen ;  but  it  is  composed  of  the  two  real 
oxides.  It  occurs  native,  frequently  crystallized  in  the  form  of  a  regular  octo- 
hedron  and  dodecahedron ;  and  it  is  not  only  attracted  by  the  magnet,  but  is  itself 
sometimes  magnetic.  It  is  always  formed  when  iron  is  heated  to  redness  in  the 
open  air ;  and  is  likewise  generated  by  the  contact  of  watery  vapour  with  iron  at 
elevated  temperatures.  The  composition  of  the  product,  however,  varies  with 
the  duration  of  the  process  and  the  temperature  which  is  employed.  Thus, 
according  to  Bucholz,  Berzelius,  and  Thomson,  100  parts  of  iron,  when  oxi- 
dized by  steam,  unite  with  nearly  30  of  oxygen ;  whereas  in  a  similar  experiment 
performed  by  Gay-Lussac,  37'8  parts  of  oxygen  were  absorbed.  The  oxide  of 
Gay-Lussac  has  the  composition  stated  in  the  table ;  and  Berzelius  thinks  that 
of  magnetic  iron  ore  to  be  similar.  This  has  been  satisfactorily  confirmed  by 
Abich,  by  precipitating  a  mixture  of  the  two  oxides  from  their  solution  in  sul- 
phuric acid,  in  which  they  were  contained  in  their  equivalent  proportions.  The 
green  precipitate  which  falls  he  found  to  be  as  highly  magnetic  as  the  native 
magnetic  iron  ore,  and  to  suffer  no  change  on  exposure  to  the  atmosphere.  But 
if  the  protoxide  were  contained  in  the  solution  in  greater  quantity,  its  presence 
in  the  precipitate  as  such  was  indicated  by  the  production  of  the  hydrated  per- 


336  IRON. 

oxide  on  exposure  to  the  air.  An  excess  of  the  peroxide  diminished  the  mag- 
netic effects.  (An.  de  Ch.  et  Ph.  Ix.  369.)  Gregory  has  observed,  that  when 
a  solution  of  protosulphate  of  iron  is  divided  into  two  equal  parts,  one  of  which 
is  peroxidized,  then  mixed  with  the  other,  and  precipitated  by  ammonia  at  a  boil- 
ing heat,  a  black  oxide  is  obtained,  which  does  not  attract  oxygen  in  drying,  and 
is  highly  magnetic.  Its  composition  must  be  2FeO  -|-  Fe203 ;  as  the  two  solu- 
tions contain  equal  quantities  of  iron ;  and  Gregory  suggests  that  it  may  occur 
native  as  a  variety  of  magnetic  iron  ore.  Wohler  (Liebig's  Annalen,  xxii.  56) 
erroneously  gives  the  above  proportions  for  forming  thecommon  magnetic  oxide, 
FeO,  -f-  Fe^Oj ;  to  obtain  which  1  part  of  protosulphate  should  be  mixed  with 
2  of  the  same  salt  peroxidized  by  nitric  acid.  M.  Mosander  states,  that  on  heat- 
ing a  bar  of  iron  in  the  open  air,  the  outer  layer  of  the  scales  contains  a  greater 
quantity  of  peroxide  than  the  inner  layer.  The  former  consists  of  1  eq.  of  per- 
oxide to  4  of  the  protoxide,  and  in  the  latter  are  contained  1  eq.  of  peroxide  to 
6  eq.  of  protoxide.  The  inner  layer  seems  uniform  in  composition ;  but  the 
outer  is  variable,  its  more  exposed  parts  being  richer  in  oxygen. 

The  nature  of  the  black  oxide  is  farther  elucidated  by  the  action  of  acids.  On 
digesting  the  black  oxide  in  sulphuric  acid,  an  olive-coloured  solution  is  formed, 
containing  two  salts,  sulphate  of  the  peroxide  and  protoxide,  which  may  be  sepa- 
rated from  each  other  by  means  of  alcohol.  (Proust  and  Gay-Lussac.)  The 
solution  of  these  mixed  salts  gives  green  precipitates  with  alkalies,  and  a  very 
deep  blue  ink  with  infusion  of  gall-nuts.  The  black  oxide  of  iron  is  the  cause 
of  the  dull  green  colour  of  bottle  glass. 

Its  eq.  ts  116 ;  symh.  FeO  f  FeA- 

\^Ferric  Acid. — Hist,  and  Prep. — This  remarkable  compound,  recently  disco- 
vered by  M.  Fremy,  has  not  yet  been  obtained  isolated,  but  only  in  combination 
with  potassa  and  some  other  bases.  The  ferrate  of  potassa  is  most  easily  pro- 
cured in  solution,  by  exposing  one  part  of  the  sesquioxide  of  iron  and  four  parts 
of  dry  nitrate  of  potassa  to  a  full  red  heat  in  a  covered  crucible  for  an  hour. 
The  resulting  reddish  violet  coloured  mass  when  dissolved  in  water  forms  a  deep 
amethystine  red  solution  of  ferrate  of  potassa.  It  is  likewise  obtained,  accord- 
ing to  Fremy,  by  passing  a  current  of  chlorine  through  a  solution  of  potassa  in 
which  is  suspended  hydrated  sesquioxide  of  iron ;  the  liquid  assumes  a  fine 
purplish  colour,  and  the  sesquioxide  of  iron  is  dissolved.  When  the  potassa  is 
in  excess  the  ferrate  of  potassa  is  precipitated  as  an  insoluble  black  powder. 
This  powder  is  very  soluble  in  water  and  imparts  to  it  a  reddish  violet  tint. 
This  solution  gradually  decomposes,  evolves  oxygen  and  precipitates  the  sesqui- 
oxide of  iron.  By  heat  the  decomposition  is  hastened,  and  at  a  boiling  tempe- 
rature it  is  instantaneous.  Its  decomposition  is  likewise  promoted  by  the  presence 
of  finely  divided  substances,  and  by  several  metallic  oxides  as  those  of  silver 
and  manganese  ;  in  other  respects  it  resembles  the  peroxide  of  hydrogen.  It  is 
decomposed  by  all  the  acids,  and  the  liberated  ferric  acid  is  immediately  resolved 
into  oxygen  and  the  sesquioxide  of  iron,  the  solution  at  the  same  time  becoming 
colourless ;  a  property  which  serves  to  distinguish  the  ferrate  from  the  manganate 
of  potassa.  It  is  likewise  decomposed  by  most  organic  bodies,  even  by  the  con- 
tact of  paper,  and  hence  cannot  be  filtered.  It  precipitates  the  salts  of  baryta, 
giving  rise  to  an  insoluble  ferrate  of  baryta- of  a  deep  crimson  colour;  but  the 
salts  of  lime,  magnesia,  or  strontia,  are  not  precipitated  by  it.  From  all  its 
properties  it  is  seen  to  be  strikingly  analogous  to  the  manganate  of  potassa,  and 
its  constitution  is  correctly  inferred  to  be  similar  in  containing  an  acid  repre- 


IRON.  337 

sented  by  the  formula  Fe  -f-  30  or  Fe  O3.    (Berzelius,  Rapport,  1842,  and  An. 
de  Chim.,  1844.)] 

Proiochloride  of  Iron. — Prep. — ^This  compound  is  formed  by  transmitting  dry 
hydrochloric  acid  gas  over  iron  at  a  red  heat,  when  hydrogen  gas  is  evolved,  and 
the  surface  of  the  iron  is  covered  with  a  white  crystalline  protochloride,  which 
at  a  stronger  heat  is  sublimed.  Also,  on  acting  with  hydrochloric  acid  on  iron, 
which  is  dissolved  with  evolution  of  hydrogen  gas,  evaporating  to  dryness,  and 
heating  to  redness  in  a  tube  without  exposure  to  the  air,  a  grey  crystalline  pro- 
tochloride is  left;  but  it  contains  some  protoxide  formed  by  an  interchange  of 
elements  between  the  last  portions  of  water  and  the  chloride,  hydrochloric  acid 
being  also  generated. 

Prop, — It  dissolves  freely  in  water,  yielding  a  pale  green  solution,  from  which 
rhomboidal  prisms  of  the  same  colour  are  obtained  by  evaporation.  The  crystals 
contain  four  equivalents  of  water  of  crystallization,  deliquesce  by  exposure  to 
the  air,  owing  to  the  formation  of  perchloride,  and  are  soluble  in  alcohol  as  well 
as  water.  The  aqueous  solution  absorbs  oxygen  from  the  air,  and  becomes  yel- 
low from  the  formation  of  perchloride  of  iron :  one  portion  of  iron  takes  oxygen 
from  the  air,  and  yields  its  chlorine  to  another  portion  of  iron,  whereby  perchlo- 
ride and  peroxide  of  iron  are  generated,  and  the  latter  falls  as  an  ochreous  sedi- 
ment combined  with  some  of  the  perchloride.  A  solution  of  the  protochloride 
of  iron  dissolves  binoxide  of  nitrogen  with  the  same  phenoipena  as  the  protosul- 
phate,  a  circumstance  favourable  to  the  view  entertained  by  many  that  protochlo- 
ride of  iron  is  converted  by  water  into  hydrochlorate  of  the  protoxide. 
lU  eg,  is  63-42 ;  symb.  Fe  f  CI,  or  FeCl. 

Perchloride  or  Sesquichloride  of  Iron, — It  is  formed  by  the  combustion  of  iron 
wire  in  dry  chlorine  gas,  and  by  transmitting  that  gas  over  iron  moderately 
heated,  when  it  is  obtained  in  small  iridescent  plates  of  a  red  colour,  which  are 
volatile  at  a  heat  a  little  above  212°,  deliquesce  readily,  and  dissolve  in  water, 
alcohol,  and  ether.  On  agitating  ether  with  a  strong  aqueous  solution  of  the 
perchloride,  the  ether  abstracts  a  part  of  it,  and  acquires  a  gold-yellow  colour. 
The  readiest  mode  of  obtaining  a  solution  of  the  perchloride  is  to  dissolve  per- 
oxide of  iron  in  hydrochloric  acid.  On  concentrating  to  the  consistence  of  syrup 
and  cooling,  it  separates  as  red  crystals,  which  by  distillation  yield  at  first  water 
and  hydrochloric  acid,  and  then  anhydrous  perchloride  of  iron,  leaving  a  com- 
pound of  peroxide  and  perchloride  of  iron  in  crystalline  laminae.  The  formation 
of  peroxide  appears  due  to  an  interchange  of  elements  between  it  and  water. 
The  same  kind  of  interchange  ensues  between  the  vapours  of  water  and  the  per- 
chloride at  a  high  temperature ;  and  this  is  probably  the  source,  as  Mitscherlich 
suggests,  of  the  crystals  of  peroxide  of  iron  found  in  volcanic  products. 

Its  eg.  is  162-26 ;  st/mb.  2Fe  -f-  301,  or  FeaClg. 

Protiodide  of  Iron, — It  exists  as  a  pale  green  solution  when  iodine  is  digested 
with  water  and  iron  wire,  the  latter  being  in  excess ;  and  on  evaporating  the 
solution,  without  exposure  to  the  air,  to  dryness  and  heating  moderately,  the 
protiodide  is  fused,  and  on  cooling  becomes  an  opaque  crystalline  mass  of  an 
iron-grey  colour  and  metallic  lustre*  It  is  deliquescent  and  very  soluble  in 
water  and  alcohol.  Its  aqueous  solution  attracts  oxygen  rapidly  from  the  air, 
undergoing  the  same  kind  of  change  as  the  protochloride  :  to  preserve  a  solution 
of  protiodide  as  such  a  long  piece  of  iron  wire  should  be  kept  permanently  in  the 
liquid.  [The  presence  of  honey,  or  other  saccharine  substance,  in  the  propor- 
tion of  one  part  to  three  of  the  solution,  is  said  to  protect  it  from  the  action  of 

24 


338  IRON. 

oxygen.]     This  compound  has  been  very  successfully  employed  in  medical  prac- 
tice by  my  colleague  Dr.  A,  T.  Thomson. 

Its  eq.  is  154'3  ;  symb.  Fe  -|-  I,  or  Fel. 

The  periodidCf  of  a  yellow  or  orange  colour  according  to  the  strength  of  the 
solution,  is  obtained  by  freely  exposing  a  solution  of  the  protiodide  to  the  air,  or 
digesting  iron  wire  with  excess  of  iodine,  gently  evaporating,  and  subliming  the 
periodide.  It  is  a  volatile  red  compound,  deliquescent,  and  soluble  in  water  and 
alcohol.     Its  eq.  is  434*9  ;  symb.  2Fe  -f  31,  or  FCilg. 

The  bromides  of  iron  are  formed  under  similar  conditions  to  the  chlorides  and 
iodides,  and  are  very  analogous  to  them  in  their  properties. 

Protojluoride  of  Iron  is  best  prepared  by  dissolving  iron  in  a  solution  of  hydro- 
fluoric acid,  out  of  which  it  crystallizes  as  the  acid  becomes  saturated,  in  small 
white  square  tables,  which  are  sparingly  soluble  in  water,  and  become  pale 
yellow  by  the  action  of  the  air.  By  heat  they  part  with  their  water  of  crystal- 
lization, and  afterwards  bear  a  red  heat  without  decomposition.     (Berzelius.) 

Its  eq.  is  46*68  ;  symb.  Fe  -f  F,  or  FeF. 

The  perfluoride  is  formed  by  dissolving  peroxide  of  iron  in  hydrofluoric  acid, 
and  yields  a  colourless  solution  even  when  saturated.  By  evaporation  it  is  left 
as  a  crystalline  mass  of  a  pale  flesh-colour,  and  of  a  mild  astringent  taste.  It  is 
sparingly  soluble  in  water.    Its  eq.  is  112*04;  symb.  2Fe  -^  3F,  or  FcaFg. 

Sulphureis  of  Iron. — These  elements  have  for  each  other  a  remarkably  strong 
affinity,  and  unite  under  various  circumstances  and  in  several  proportions.  The 
two  lowest  degrees  of  sulphuration,  the  ietrasulphuret  and  disulphuretj  were  pre- 
pared by  Arfwedson  by  transmitting  a  current  of  hydrogen  gas  at  a  red  heat  over 
the  anhydrous  disulphate  of  peroxide  of  iron  to  procure  the  tetrasulphuret,  and 
over  anhydrous  sulphate  of  protoxide  of  iron  for  the  disulphuret.  In  both  cases 
sulphurous  acid  and  water  are  evolved,  and  the  resulting  sulphurets  are  left  as 
greyish  black  powders  susceptible  of  a  metallic  lustre  by  friction.  They  both 
dissolve  in  dilute  sulphuric  acid  with  evolution  of  hydrogen  and  hydrosulphuric 
acid  gases. 

Protosulphuret  of  Iron  is  prepared  by  heating  thin  laminsB  of  iron  to  redness 
with  sulphur  in  a  covered  hessian  crucible,  and  continuing  the  heat  until  any 
excess  of  sulphur  is  expelled.  The  iron  is  found  with  a  crust  of  protosulphuret, 
which  is  brittle,  of  a  yellowish-grey  colour  and  metallic  lustre,  and  is  attracted 
by  the  magnet.  When  pure  it  is  completely  dissolved  by  dilute  sulphuric  acid, 
yielding  pure  hydrosulphuric  acid.  The  protosulphuret  of  iron  exists  in  nature 
as  an  ingredient  in  variegated  copper  pyrites  ;  and  it  falls  on  mixing  hydrosul- 
phate  of  ammonia  with  sulphate  of  protoxide  of  iron  as  a  black  precipitate, 
which  oxidizes  rapidly  by  absorbing  oxygen  from  the  air  as  soon  as  the  excess 
of  hydrosulphate  of  ammonia  is  removed  by  washing. 

Its  eq.  is  44*1 ;  symb.  Fe  -|-  S,  or  FeS. 

The  sesquisulphuret  is  formed  in  the  moist  way  by  adding  perchloride  of  iron 
drop  by  drop  to  hydrosulphate  of  ammonia  or  sulphuret  of  potassium  in  excess, 
and  falls  as  a  black  precipitate,  which  is  oxidized  readily  by  the  air.  In  the 
dry  way  it  is  slowly  produced  by  the  actidfct  of  hydrosulphuric  acid  gas  on  per- 
oxide of  iron  at  a  heat  not  exceeding  212°,  water  being  also  formed  ;  and  by  the 
action  of  the  same  gas  on  the  hydrated  peroxide  at  common  temperatures.  This 
sulphuret,  when  anhydrous,  has  a  yellowish  grey  colour,  is  not  attracted  by  the 
magnet,  and  dissolves  in  dilute  sulphuric  or  hydrochloric  acid,  yielding  hydro- 
sulphuric acid  and  a  residue  of  bigulphuret  of  iron  (Berzelius). 


IRON. 

lis  eq.  is  104-3 ;  symb,  2Fe  +3S,  or  FeS^- 

Bisulphuret  of  iron,  iron  pyrites  of  mineralogists,  exists  abundantly  in  the 
earth.  It  occurs  in  cubes  or  some  allied  form,  has  a  yellow  colour,  metallic 
lustre,  a  density  of  4*981,  and  is  so  hard  that  it  strikes  fire  with  steel.  Some 
varieties  have  a  white  colour ;  but  these  usually  contain  arsenic.  Others  occur 
in  rounded  nodules,  have  a  radiated  structure  divergent  from  a  common  centre, 
are  often  found  in  beds  of  clay,  and  are  much  disposed  by  the  influence  of  air 
and  moisture  to  yield  sulphate  of  oxide  of  iron  :  these  are  suspected  by  Berzelius 
to  be  compounds  of  protosulphuret  and  bisulphuret  of  iron. 

Bisulphuret  of  iron  is  not  attacked  by  any  of  the  acids  except  the  nitric,  and 
its  best  solvent  is  the  nitro-hydrochloric  acid.  Heated  in  close  vessels  it  gives 
off  nearly  half  its  sulphur,  and  is  converted  into  magnetic  iron  pyrites.  By  heat 
and  air  together  it  yields  peroxide  of  iron.  Its  eq.  is.  60*2  ;  symh.  Fe  -]-  2S,  or 
FS2. 

Magnetic  iron  pyrites. — ^This  is  a  natural  product,  termed  magnetic  pyrites, 
from  being  attracted  by  the  magnet,  and  was  formerly  regarded  as  protosulphuret 
of  iron  ;  but  Stromeyer  has  shown  that  its  elements  are  in  such  a  ratio,  that  it 
maybe  regarded  as  a  compound  of  bisulphuret  and  protosulphuret.  It  is  formed 
by  heating  the  bisulphuret  to  redness  in  close  vessels,  by  fusing  iron  filings 
with  half  their  weight  of  sulphur,  or  by  rubbing  sulphur  upon  a  rod  of  iron 
heated  to  whiteness.  It  is  soluble  in  dilute  sulphuric  acid,  yielding  hydrosul- 
phuric  acid  gas  and  a  residue  of  sulphur.  It  is  much  more  oxidable  by  air  and 
moisture  than  the  pure  bisulphuret.    Its  eq.  is  280*7  ;  symh.  5FeS  -f-  FeS^. 

Diphosphuret  of  Iron. — It  is  prepared  by  exposing  the  phosphate  of  protoxide 
of  iron  to  a  strong  heat  in  a  covered  crucible  lined  with  charcoal,  the  excess  of 
phosphorus  being  dissipated  in  vapour.  It  is  a  fused  granular  mass,  of  the 
colour  and  lustre  of  iron,  but  very  brittle,  and  is  not  attacked  by  hydrochloric 
acid.  It  is  sometimes  contained  in  metallic  iron,  to  the  properties  of  which  it  is 
very  injurious  by  rendering  it  brittle  at  common  temperatures.  Its  eq.  is  71*7; 
symh.  2Fe  +  P,  or  Fe^P. 

The  perphosphuret  has  been  obtained  by  Rose  by  the  action  of  phosphuretted 
hydrogen  gas  on  sulphuret  of  iron  at  a  moderate  temperature,  and  resembles  the 
former  in  its  properties. 

Its  eq.  is  146*8  ;  symh.  3Fe  -f-  4P,  or  Fe3P4. 

Cktrhurets  of  Iron. — Carbon  and  iron  unite  in  very  various  proportions ;  but 
there  are  three  compounds  very  distinct  from  each  other — namely,  graphite,  cast 
or  pig  iron,  and  steel. 

Graphite,  also  known  under  the  names  of  plumbago  and  black  lead,  occurs  not 
unfrequently  as  a  mineral  production,  and  is  found  in  great  purity  at  Borrowdale 
in  Cumberland.  It  may  be  made  artificially  by  exposing  iron  with  excess  of 
charcoal  to  a  violent  and  long-continued  heat;  and  it  is  commonly  generated  in 
small  quantity  during  the  preparation  of  cast  iron.  Pure  specimens  contain 
about  four  or  five  per  cent,  of  iron,  but  sometimes  its  quantity  amounts  to  10 
per  cent.  Most  chemists  believe  the  iron  to  be  chemically  united  with  the  char- 
coal ;  but  according  to  the  researches  of  Karsten  of  Berlin,  native  graphite  is 
only  a  mechanical  mixture  of  charcoal  and  iron,  while  artificial  graphite  is  a  real 
carburet. 

Graphite  is  exceedingly  unchangeable  in  the  air,  and,  like  charcoal,  is  attacked 
with  difiiculty  by  chemical  reagents.  It  may  be  heated  to  any  extent  in  close 
vessels  without  change;  but  if  exposed  at  the  same  time  to  the  air,  its  carbon  is 


340  i^ON. 

entirely  consumed,  and  oxide  of  iron  remains.  It  has  an  iron  grey  colour, 
metallic  lustre,  and  granular  texture ;  and  it  is  soft  and  unctuous  to  the  touch. 
Its  chief  use  is  in  the  manufacture  of  pencils  and  crucibles,  and  in  burnishing 
iron  to  protect  it  from  rust. 

Cast  iron  is  the  product  of  the  process  for  extracting  iron  from  its  ores,  and 
is  commonly  regarded  as  a  real  compound  of  iron  and  charcoal.  It  always  con- 
tains impurities,  such  as  charcoal,  undecomposed  ore,  and  earthy  matters,  which 
are  often  visible  by  mere  inspection  ;  and  sometimes  traces  of  chromium,  man- 
ganese, sulphur,  phosphorus,  and  arsenic  are  present.  It  fuses  readily  at  2786° 
(Daniell,)  which  is  a  full  red  heat,  and  in  cooling  it  acquires  a  crystalline 
granular  texture.  The  quantity  of  different  specimens  is  by  no  means  uniform  ; 
and  two  kinds,  white  and  grey  cast  iron,  are  in  particular  distinguished  from 
each  other.  The  former  is  exceedingly  hard  and  brittle,  sometimes  breaking 
like  glass  from  sudden  change  of  temperature ;  while  the  latter  is  softer  and 
much  more  tenacious.  This  diflference  appears  owing  to  the  mode  of  combina- 
tion, rather  than  to  a  difference  in  the  proportion  of  carbon ;  for  the  white  variety 
may  be  converted  into  the  grey  by  exposure  to  a  strong  heat  and  cooling  slowly, 
and  the  grey  may  be  changed  into  the  white  by  being  heated  and  rapidly  cooled. 
According  to  Karsten  the  carbon  of  the  latter  is  combined  with  the  whole  mass 
of  iron,  and  amounts  as  a  maximum  to  5*25  per  cent. ;  but  in  some  specimens 
its  proportion  is  considerably  less.  The  former,  on  the  contrary,  contains  from 
3*  16  to  4'65  per  cent,  of  carbon,  of  which  about  three-fourths  are  in  the  state  of 
graphite,  and  are  left  as  such  after  the  iron  is  dissolved  by  acids ;  while  the 
remaining  fourth  is  in  combination  with  the  whole  mass  of  metal,  constituting 
a  carburet  which  is  very  similar  to  steel.  Grey  cast  iron  may  hence  be  regarded 
as  a  kind  of  steel,  in  which  graphite  is  mechanically  mixed. 

Steel  is  commonly  prepared  in  this  country  by  the  process  of  cementation, 
which  consists  in  filling  a  large  furnace  with  alternate  strata  of  bars  of  the  purest 
malleable  iron  and  powdered  charcoal,  closing  every  aperture  so  as  perfectly  to 
exclude  atmospheric  air,  and  keeping  the  whole  during  several  days  at  a  red 
heat.  By  this  treatment  the  iron  gradually  combines  with  from  1'3  to  1*75  per 
cent,  of  carbon,  its  texture  is  greatly  changed,  and  its  surface  is  blistered.  It  is 
subsequently  hammered  at  a  red  heat  into  small  bars,  and  may  be  welded  either 
with  other  bars  of  steel  or  with  malleable  iron.  Mackintosh,  of  Glasgow,  has 
introduced  an  elegant  process  of  forming  steel  by  exposing  heated  iron  to  a  cur- 
rent of  coal  gas,  when  carburretted  hydrogen  is  decomposed,  its  carbon  enters 
into  combination  with  iron,  and  hydrogen  gas  is  evolved. 

In  ductility  and  malleability  it  is  far  inferior  to  iron;  but  exceeds  it  greatly 
in  hardness,  sonorousness,  and  elasticity.  Its  texture  is  also  more  compact,  and 
it  is  susceptible  of  a  higher  polish.  It  sustains  a  full  read  heat  without  fusing, 
and  is  therefore  less  fusible  than  cast  iron ;  but  it  is  much  more  so  than  mal- 
leable iron.  By  fusion  it  forms  cast  steel,  which  is  more  uniform  in  composition 
and  texture,  and  possesses  a  closer  grain,  than  ordinary  steel. 


ZINC.  341 


i 


SECTION  XII. 

ZINC— CADMIUM. 
ZINC. 

Jlist.  and  Prep. — This  metal  was  first  mentioned  under  the  term  zinetum  in 
the  sixteenth  century  by  Paracelsus ;  but  it  was  probably  known  at  a  much 
earlier  period.  In  commerce  it  is  often  called  spelter,  and  is  obtained  either  from 
calamine,  native  crabonate  of  zinc,  or  from  the  native  sulphuret,  zinc  blende  of 
mineralogists.  It  is  procured  from  the  former  by  heat  and  carbonaceous  matters ; 
and  from  the  latter  by  a  similar  process  after  the  ore  has  been  previously  oxi- 
dized by  roasting,  that  is,  by  exposure  to  the  air  at  a  low  red  heat.  Its  prepara- 
tion affords  an  instance  of  what  is  called  distillation  hy  descent.  The  furnace  or 
crucible  for  reducing  the  ore  is  closed  above,  and  in  its  bottom  is  fixed  an  iron 
tube,  the  upper  aperture  of  which  is  in  the  interior  of  the  crucible,  and  its  lower 
terminates  just  above  a  vessel  of  water.  The  vapour  of  zinc,  together  with  all 
the  gaseous  products,  passes  through  this  tube,  and  the  zinc  is  condensed.  The 
first  portions  are  commonly  very  impure,  containing  cadmium  and  arsenic,  the 
period  of  their  disengagement  being  indicated  by  what  the  workmen  call  the 
Irown  blaze  ,•  but  when  the  blue  blaze  begins,  that  is,  when  the  metallic  vapour 
burns  with  a  bluish  white  flame,  the  zinc  is  collected.  As  thus  obtained,  it  is 
never  quite  pure :  it  frequently  contains  traces  of  charcoal,  sulphur,  cadmium, 
arsenic,  lead,  and  copper ;  and  iron  is  always  present.  It  may  be  freed  from 
these  impurities  by  distillation, — by  exposing  it  to  a  white  heat  in  an  earthen 
retort,  to  which  a  receiver  full  of  water  is  adapted ;  but  the  first  portions,  as 
liable  to  contain  arsenic  and  cadmium,  should  be  rejected. 

Prop. — It  has  a  strong  metallic  lustre,  and  a  bluish  white  colour.  Its  texture 
is  lamellated,  and  its  sp.  gr.  about  7.  It  is  a  hard  metal,  being  acted  on  by  the 
file  with  diflSculty.  At  low  or  high  degrees  of  heat  it  is  brittle;  but  at  tempera- 
tures between  210°  and  300°,  it  is  both  malleable  and  ductile,  a  property  which 
enables  zinc  to  be  rolled  or  hammered  into  sheets  of  considerable  thinness.  Its 
malleability  is  considerably  diminished  by  the  impurities  which  the  zinc  of  com- 
merce contains.  It  fuses  at  773°  (Daniell),  and  when  slowly  cooled  crystallizes 
in  four  or  six-sided  prisms.  Exposed  in  close  vessels  to  a  white  heat,  it  sublimes 
unchanged. 

Zinc  undergoes  a  slight  change  by  the  action  of  air  and  moisture,  becoming 
coated  with  a  thin  grey  film  of  suboxide  which  seems  to  protect  the  metal  be- 
neath. When  fused  in  open  vessels  it  absorbs  oxygen,  and  forms  the  white 
oxide,  called  flowers  of  zinc.  Heated  to  full  redness  in  a  covered  crucible,  it 
bursts  into  flame  as  soon  as  the  cover  is  removed,  and  burns  with  a  brilliant 
white  light.  The  combustion  ensues  with  such  violence,  that  the  oxide  as  it  is 
formed  is  mechanically  carried  up  into  the  air.  The  heat  at  which  it  begins  to 
burn  is  estimated  by  Daniell  at  941°  F.    Zinc  is  readily  dissolved  by  dilute  sul- 


342 


ZINC. 


phuric  or  hydrochloric  acid,  by  the  substitution  for  hydrogen  which  is  evolved, 
and  which  often  contains  a  small  quantity  of  metallic  zinc  in  combination. 

Gay-Lussac  and  Berzelius  found  that  the  protoxide  of  zinc  consists  of  100 
parts  of  metallic  zinc  and  24'8  of  oxygen,  being  a  ratio  of  32*3  to  8.  Its  other 
combinations  justify  the  adoption  of  32'3  as  the  eq.  of  zinc ;  its  symb.  is  Zn. 
The  composition  of  its  compounds  described  in  this  section  is  as  follows  : — 


Zinc. 

Equir. 

Formulae. 

Protoxide 

32-3     1  eq.-l"  Oxygen 

8, 

1  eq.=  40-3 

Zn-j-O  or  Z^. 

Peroxide 

Composition  uncertain. 

Chloride 

32-3     1  eq.-|- Chlorine 

35-42 

1  eq.=  67-72 

Zn-f-Cl  or  ZnCI. 

Iodide 

32-3     1  eq.-j- Iodine 

126-3 

1  eq.==158-6 

Zn-j-I  or  Znl. 

Bromine 

32-3     1  eq.-f  Bromine 

•78-4 

1  eq.==110-7 

Zn+Br  or  ZnBr, 

Fluoride 

32-3     1  eq.-f-Fluorine 

18-68 

1  eq.=  60-98 

Zn-4-F  or  ZnF. 

Sulphuret 

32-3     1  eq.+Sulphur 

161 

1  eq.=  48-4 

Zn+S  or  ZnS. 

Protoxide  of  Zinc. — ^This  is  the  only  oxide  of  zinc  which  acts  as  a  salifiable 
base,  and  the  only  one  of  known  composition.  It  is  generated  during  the  solu- 
tion of  zinc  in  dilute  sulphuric  acid,  and  may  be  obtained  in  a  dry  state  by  col- 
lecting the  flakes  which  rise  during  the  combustion  of  zinc,  or  by  heating  the 
carbonate  to  redness.  At  common  temperatures  it  is  white ;  but  when  heated  to 
low  redness  it  assumes  a  yellow  colour,  which  gradually  disappears  on  cooling. 
It  is  quite  fixed  in  the  fire.  It  is  insoluble  in  water,  and  therefore  does  not  afiect 
the  blue  colour  of  plants  ;  but  it  is  a  strong  salifiable  base,  forming  regular  salts 
with  acids,  most  of  which  are  colourless.  It  combines  also  with  some  of  the 
alkalies. 

The  presence  of  zinc  is  easily  recognized  by  the  following  characters: — The 
oxide  is  precipitated  from  its  solutions  as  a  white  hydrate  by  pure  potassa  or 
ammonia,  and  as  carbonate  by  carbonate  of  ammonia,  but  is  completely  redis- 
solved  by  an  excess  of  the  precipitant.  The  fixed  alkaline  carbonates  precipi- 
tate it  permanently  as  white  carbonate  of  oxide  of  zinc.  Hydrosulphate  of 
ammonia  causes  a  white  precipitate,  a  hydrated  sulphuret  of  zinc.  Hydrosul- 
phuric  acid  acts  in  a  similar  manner,  if  the  solution  is  quite  neutral ;  but  it  has 
no  effect  if  an  excess  of  any  strong  acid  is  present. 

Its  eq.  is  40*3 ;  symh,  Zn  +  O,  Zn,  or  ZnO. 

When  metallic  zinc  is  exposed  for  some  time  to  air  and  moisture,  or  is  kept 
under  water,  it  acquires  a  superficial  coating  of  a  grey  matter,  which  Berzelius 
describes  as  a  sub -oxide.  It  is  probably  a  mixture  of  metallic  zinc  and  the 
white  oxide,  into  which  it  is  resolved  by  the  action  of  acids.  The  peroxide  is 
prepared,  according  to  Thenard,  by  acting  on  hydrated  white  oxide  of  zinc  with 
peroxide  of  hydrogen  diluted  with  water.  It  resolves  itself  so  readily  into  oxy- 
gen and  the  oxide  already  described,  that  it  cannot  be  preserved  even  under  the 
surface  of  water ;  and  its  composition  is  quite  unknown. 

Chloride  of  Zinc. — This  compound  is  formed,  with  evolution  of  heat  and  light, 
when  zinc  filings  are  introduced  into  chlorine  gas  ;  and  it  is  readily  prepared  by 
dissolving  zinc  in  hydrochloric  acid,  evaporating  to  dryness,  and  heating  the 
residue  in  a  tube  through  which  dry  hydrochloric  acid  gas  is  transmitted.  It  is 
colourless,  fusible  at  a  heat  a  little  above  212°,  has  a  soft  consistence  at  com- 
mon temperatures,  hence  called  hutttr  of  zinc,  sublimes  at  a  red  heat,  and  deli- 
quesces in  the  air. 

Its  eq.  is  67-72;  symb.  Zn  +  CI,  or  ZnCl. 


CADMIUM. 

Iodide  of  Zinc  is  prepared  by  digesting  iodine  in  water  with  zinc  filings  in 
excess.  A  colourless  solution  results,  which  by  evaporation  yields  a  deliquescent 
iodide.  By  heat  in  close  vessels  it  may  be  sublimed,  and  then  crystallizes  in 
biilliant  needles ;  but  if  heated  in  the  open  air,  oxide  of  zinc  is  formed,  and 
iodine  expelled.  If  zinc  is  digested  in  water  with  an  excess  of  iodine,  a  brown 
solution  results,  which  probably  contains  a  biniodide. 

Its  eq.  is  158-6 ;  symb.  Zn  -f-  I,  or  Znl. 

Bromide  of  Zinc  may  be  formed  by  a  process  similar  to  that  for  the  iodide,  but 
its  properties  have  not  been  studied. 

Its  eq.  is  110*7 ;  si/mb.  Zn  -|-  Br,  or  ZnBr. 

Fluoride  of  Zinc  is  obtained  by  acting  directly  on  oxide  of  zinc  with  hydro- 
fluoric acid,  and  is  a  white  compound  of  sparing  solubility. 

Its  eq.  is  50-98 ;  symb.  Zn  -|-  F,  or  ZnF. 

Sulphurei  of  Zinc. — This  compound  is  well  known  to  mineralogists  under  the 
name  of  zinc  blende^  and  occurs  in  dodecahedral  crystals  or  some  allied  form. 
Its  structure  is  lamellated,  lustre  adamantine,  and  colour  variable,  being  some- 
times, yellow,  red,  brown,  or  black.  It  may  be  formed  artificially  by  igniting  in 
a  closed  crucible  a  mixture  of  oxide  of  zinc  and  sulphur,  or  sulphate  of  oxide  of 
zinc  and  charcoal,  or  by  drying  the  hydrated  sulphuret  of  zinc.  Its  eq.  fe  48*4 ;  I 
symb,  Zn  -\-  S,  or  ZnS. 

CADMIUM. 

Hist. — Cadmium,  so  called  (from  xaSfieuxi  a  term  applied  to  calamine,  and  to 
the  volatile  matters  which  rise  from  the  furnace  in  preparing  brass)  because  it 
is  associated  with  zinc,  was  discovered  in  the  year  1817,  by  Stromeyer,  in  an 
oxide  of  zinc  which  had  been  prepared  for  medical  use  ;  and  he  has  since  found 
it  in  several  of  the  ores  of  that  metal,  especially  in  a  radiated  blende  from  Bohe- 
mia, which  contains  about  five  per  cent,  of  cadmium.  The  late  Dr.  Clarke 
detected  its  existence  in  some  of  the  zinc  ores  of  Derbyshire,  and  in  the  common 
zinc  of  commerce.  Herapath  has  found  it  in  considerable  quantity  in  the  zinc 
works  near  Bristol.  During  the  reduction  of  calamine  by  coal,  the  cadmium, 
which  is  very  volatile,  flies  off  in  vapour  mixed  with  soot  and  some  oxide  of 
zinc,  and  collects  in  the  roof  of  the  vault,  just  above  the  tube  leading  from  the 
crucible.  Some  portions  of  this  substance  yielded  from  12  to  20  per  cent,  of 
cadmium.     (An.  of  Phil.  xiv.  and  xvii.) 

Prep. — The  process  by  which  Stromeyer  separates  cadmium  from  zinc  or 
other  metals  is  the  following.  The  ore  of  cadmium  is  dissolved  in  dilute  sul- 
phuric or  hydrochloric  acid,  and  after  adding  a  portion  of  free  acid,  a  current 
of  hydrosulphuric  acid  gas  is  transmitted  through  the  liquid,  by  which  means 
the  cadmium  is  precipitated  as  a  sulphuret,  while  the  zinc  continues  in  solution. 
The  sulphuret  of  cadmium  is  then  decomposed  by  nitric  acid,  and  the  solution 
evaporated  to  dryness.  The  dry  nitrate  is  dissolved  in  water,  and  an  excess  of 
carbonate  of  ammonia  added.  The  white  carbonate  of  oxide  of  cadmium  sub- 
sides, which,  when  heated  to  redness,  yields  a  pure  oxide.  By  mixing  this 
oxide  with  charcoal,  and  exposing  the  mixture  to  a  red  heat,  metallic  cadmium 
is  sublimed. 

A  very  elegant  process  for  separating  zinc  from  cadmium  was  proposed  by 
Wollaston.  The  solution  of  the  mixed  metals  is  put  into  a  platinum  capsule, 
and  a  piece  of  metallic  zinc  is  placed  in  it.    If  cadmium  is  present,  it  is  rediwed, 


344  CADMIUM. 

and  adheres  so  tenaciously  to  the  capsule,  that  it  may  be  washed  "with  water 
without  danger  of  being  lost.  It  may  then  be  dissolved  either  by  nitric  or  dilute 
hydrochloric  acid. 

Prop. — Cadmium,  in  colour  and  lustre,  has  a  strong  resemblance  to  tin,  but  is 
somewhat  harder  and  more  tenacious.  It  is  very  ductile  and  malleable.  Its  sp. 
gr.  is  8*604  before  being  hammered,  and  8.694  afterwards.  It  melts  at  about  the 
same  temperature  as  tin,  and  is  nearly  as  volatile  as  mercury,  condensing  like  it 
into  globules  which  have  a  metallic  lustre.  Its  vapour  has  no  odour.  When 
heated  in  the  open  air,  it  absorbs  oxygen,  and  is  converted  into  an  oxide.  Cad- 
mium is  readily  oxidized  and  dissolved  by  nitric  acid,  which  is  its  proper  solvent. 
Sulphuric  and  hydrochloric  acids  act  upon  it  less  easily,  and  the  oxygen  is  then 
derived  from  water. 

The  eq.  of  cadmium,  deduced  from  Stromeyer's  analysis  of  its  oxide,  is  55*8. 
Its  symb,  is  Cd.  The  composition  of  its  compounds  described  in  this  section  is 
as  follows ; — 


Cadmium. 

Equiv. 

Formulae. 

Oxide  of  Cadm. 

66-8     1  eq.+Oxygen        8 

1  eq.==  638 

Cd+0  or  CdO. 

Chl#ride  . 

55-8     1  eq.-hChlorine    35-42 

1  eq.=:  91-22 

Cd+Cl  or  CdCl. 

Iodide      . 

55-8    1  eq.+Iodine      126-3 

1  eq.=182-l 

Cd-HI  or  Cdl. 

Sulphuret 

65-8    1  eq.+Sulphur      16-1 

1  eq.=  71-9 

Cd+S  or  CdS. 

Oxide  of  Cadmium, — This,  the  only  known,  oxide  of  cadmium  is  prepared  by 
igniting  its  carbonate,  has  an  orange  colour,  is  fixed  in  the  fire,  and  is  insoluble 
in  water.  It  has  no  action  on  test  paper,  but  is  a  strong  alkaline  base,  forming 
neutral  salts  with  acids.  It  is  precipitated  as  a  white  hydrate  by  pure  ammonia, 
but  is  redissolved  by  excess  of  that  alkali.  It  is  precipitated  permanently  by 
pure  potassa  or  soda  as  a  hydrate,  and  by  all  the  alkaline  carbonates  as  carbonate 
of  oxide  of  cadmium. 

Its  eg.  is  63-8 ;  si/mb.  Cd  -f-  0,  Cd,  or  CdO. 

Chloride  of  Cadmium. — By  dissolving  oxide  of  cadmium  in  hydrochloric  acid 
and  concentrating  duly,  the  chloride  with  water  of  crystallization  crystallizes  in 
transparent  four-sided  rectangular  prisms,  which  lose  their  water  by  heat  and 
even  in  a  dry  air,  fuse  at  a  heat  short  of  redness,  and  acquire  a  lamellated  texture 
in  cooling.    At  a  high  temperature  it  is  sublimed. 

Its  eg.  is  91-22;  si/mb.  Cd  +  CI,  or  CdCl. 

Iodide  of  Cadmium  may  be  formed  in  the  same  manner  as  iodide  of  zinc,  is 
soluble  in  water  and  alcohol,  and  crystallizes  by  evaporation  in  large,  colourless, 
transparent,  hexagonal  tables,  which  do  not  change  in  the  air,  and  have  a  pearly 
lustre.  By  heat  they  lose  water,  and  then  fuse.  Us  eg.  is  182*1 ;  symb,  Cd  -}- 1, 
or  Cdl. 

Sulphuret  (f  Cadmium  occurs  in  mixture  or  combination  in  some  kinds  of  zinc 
blende,  and  is  easily  prepared  by  the  action  of  hydrosulphuric  acid  on  a  salt  of 
cadmium.  It  has  a  yellowish-orange  colour,  and  is  distinguished  from  the  sul- 
phurets  of  arsenic  by  being  insoluble  in  pure  potassa,  and  by  sustaining  a  white 
heat  without  subliming  (Stromeyer). 

Its  eg.  is  71*9;  ayw6  Cd  +  S,  or  CdS. 


COBALT.  345 


SECTION  XIII. 

COBALT.— NICKEL. 
COBALT. 

Hist. — This  metal  is  met  with  in  the  earth  chiefly  in  combination  with  arsenic, 
constituting  an  ore  from  which  all  the  cobalt  of  commerce  is  derived.  It  is  a 
constant  ingredient  of  meteoric  iron,  though  in  very  small  quantity.  (Stromeyer.) 
Gregory  has  detected  it  also  in  many  specimens  of  native  peroxide  of  manganese. 
Its  name  is  derived  from  the  term  Kohold^  an  evil  spirit,  applied  to  it  by  the  Ger- 
man miners  at  a  time  when  they  were  ignorant  of  its  value,  and  considered  it 
unfavourable  to  the  presence  of  valuable  metals. 

Frep. — When  native  arseniuret  of  cobalt  is  broken  into  small  pieces,  and  ex- 
posed in  a  reverberatory  furnace  to  the  united  action  of  heat  and  air,  its  elements 
are  oxidized,  most  of  the  arsenious  acid  is  expelled  in  the  form  of  vapour,  and 
an  impure  oxide  of  cobalt,  called  zaffre,  remains.  This  is  dissolved  in  hydro- 
chloric acid,  and  a  current  of  hydrosulphuric  acid  gas  is  transmitted  through  the 
solution  until  the  arsenious  acid  is  completely  separated  in  the  form  of  orpiment. 
The  filtered  liquid  is  then  boiled  with  a  little  nitric  acid,  in  order  to  convert  the 
protoxide  into  peroxide  of  iron,  and  an  excess  of  carbonate  of  potassa  is  added. 
The  precipitate  consisting  of  peroxide  of  iron  and  carbonate  of  protoxide  of  cobalt, 
after  being  well  washed  with  water,  is  digested  in  a  solution  of  oxalic  acid, 
which  dissolves  the  oxide  of  iron  and  leaves  the  oxide  of  cobalt  in  the  form  of  an 
insoluble  oxalate.  (Laugier.)  On  heating  this  oxalate  in  a  retort  from  which 
atmospheric  air  is  excluded,  a  large  quantity  of  carbonic  acid  is  evolved,  and  a 
black  powder,  metallic  cobalt,  is  left.  (Thomson  in  Annals  of  Philosophy,  N. 
S.  i.)  The  pure  metal  is  easily  procured  also  by  passing  a  current  of  dry  hydro- 
gen gas  over  oxide  of  cobalt  heated  to  redness  in  a  tube  of  porcelain.  In  this 
state  it  is  porous,  and  if  formed  at  a  low  temperature  it  inflames  spontaneously, 
as  stated  in  the  section  on  iron. 

Prop. — A  brittle  metal,  of  a  reddish-grey  colour,  and  weak  metallic  lustre.  Its 
density,  according  to  my  observation,  is  7*834.  It  fuses  at  a  heat  rather  lower 
than 'iron,  and  when  slowly  cooled  it  crystallizes.  It  lias  long  been  considered 
to  be  attracted  by  the  magnet,  but  Faraday  denies  that  it  possesses  this  property 
when  pure.  It  undergoes  little  change  in  the  air,  but  absorbs  oxygen  when 
heated  in  open  vessels.  It  is  attacked  with  difliculty  by  sulphuric  or  hydrochloric 
acid,  but  is  readily  oxidized  by  means  of  nitric  acid.  Like  iron  and  the  other 
metals  of  this  order,  it  decomposes  water  at  a  red  heat  with  disengagement  of 
hydrogen  gas.     (Despretz.) 

According  to  the  analyses  by  Rothoif  of  the  oxides  of  cobalt,  its  equivalent  is 
inferred  to  be  29-5  (An.  of  Phil.  iii.  356).  Its  symb.  is  Co.  The  composition 
of  its  compounds  described  in  this  section  is  as  follows  :— 

Cobalt.  Equiv.  Formulae. 

Protoxide        .        29-5  1  eq.+Oxygen    8        1  eq.=  37-5        Co+O  or  CoO. 
I  Oxide  .        88-5  3  eq.+    •  32        4  eq.=120-5      3Co+40  or  Co'O*. 


346  COBALT. 

Cobalt.  Equiv.  Fonnulae. 

Peroxide         .  690  2  eq.+    .  24  3  eq.=  830  2Co-|-30  or  C02O3. 

Chloride  .  29-5  1  eq.H-Chlorine35-42  1  eq.=  64-92  Co-J-Cl  or  ClCo.       , 

Protosulphuret  29-5  1  eq.+Sulphur  16*1  1  eq.5=  45-6  Co+S  or  CoS. 

Sesquisulphuret  59     2  eq.-|-    •  48-3  3  eq.=I07-3  2Co+3S  or  C02S3. 

Bisulphuret     .  295  1  eq.+    .  32-2  2  eq.=  61-7  Co-|-2S  or  C0S2. 

Subphosphuret  88-5  3  eq.+Phosph.  31-4  2  eq.=:ll9-9  3Co4-2  P  or  CoaPa- 

Protoxide  (f  CohaU. — Prepared  by  decomposing  carbonate  of  the  protoxide  by 
heat  in  a  vessel  from  which  atmospheric  air  is  excluded.  It  is  of  an  ash-grey 
colour,  and  is  the  basis  of  the  salts  of  cobalt,  most  of  which  are  of  a  pink  hue. 
When  heated  to  redness  in  open  v^sels  it  absorbs  oxygen,  and  is  converted  into 
the  peroxide.  It  is  easily  recognized  by  giving  a  blue  tint  to  borax  when  melted 
with  it ;  and  is  employed  in  the  arts,  in  the  form  of  smalt,  for  communicating  a 
similar  colour  to  glass,  earthenware,  and  porcelain.  It  is  precipitated  from  its 
salts  by  pure  potassa  as  a  blue  hydrate,  which  absorbs  oxygen  from  the  air,  and 
gradually  acquires  a  dirty  green  tint.  Pure  ammonia  likewise  causes  a  blue  pre- 
cipitate, which  is  redissolved  by  the  alkali  if  in  excess.  It  is  thrown  down  as  a 
pale  pink  carbonate  by  carbonate  of  potassa,  soda,  or  ammonia ;  but  an  excess  of 
the  last  redissolves  it  with  facility.  Hydrosulphuric  acid  produces  no  change, 
unless  the  solution  is  quite  neutral,  or  the  oxide  is  combined  with  a  weak  acid. 
Alkaline  hydrosulphates  always  precipitate  it  as  black  protosulphuret  of  cobalt. 

Its  eq.  is  37*5 ;  symb.  Co  -|-  O,  Co,  or  CoO. 

I  Oxide  of  Cobalt. — It  is  said  that  when  protoxide  of  cobalt,  or  the  nitrate,  car- 
bonate, or  oxalate  of  that  oxide,  is  gently  ignited  in  an  open  fire,  peroxide  of 
cobalt  results ;  but  M.  Hess  has  lately  shown  that  the  oxide  then  obtained  is 
analogous  in  composition  to  the  red  oxide  of  manganese.  The  peroxide  of  cobalt 
is  converted  into  it,  with  loss  of  oxygen,  by  a  full  red  heat,  whether  exposed  to 
the  air  or  not ;  so  that  of  the  oxides  of  cobalt  it  is  the  most  stable.  The  same 
compound  is  obtained  as  a  dirty  green  hydrate  by  the  action  of  the  air  on  the 
hydrated  protoxide.  It  is  probably  a  compound  of  peroxide  and  protoxide  of 
cobalt,  since  3Co  -f-  40  obviously  contain  the  elements  CoO  -f-  CojOg.  This 
intermediate  oxide  is  of  a  dark  brown  colour,  and  does  not  unite  with  acids  or 
alkalies  (Pog.  Annalen,  xxvi.  542). 

Its  eq.  is  120'5 ;  symh.  CoO  -|-  C02O3. 

Peroxide. — Is  obtained  as  a  black  hydrate  containing  2  eq.  of  water,  C02O3  -f- 
2H0,  when  chloride  of  cobalt  in  solution  is  decomposed  by  hypochlorite  of  lime, 
or  chlorine  is  transmitted  into  water  in  which  hydrated  protoxide  of  cobalt  is 
suspended.    In  this  case 

3  eq.  Protoxide  &  1  eq.  Chlorine        2         1  eq.  Peroxide  &  1  eq.  Chloride 
3  CoO  CI  -^  C02OS  CoCl 

This  hydrate  has  a  black  colour  and  yields  the  black  anhydrous  peroxide  by 
exposure  to  a  heat  of  600°  or  700° ;  but  it  is  difficult  to  drive  off  all  the  water, 
without  also  losing  oxygen.  It  combines  with  none  of  the  acids,  and  when  di- 
gested with  hydrochloric  acid  it  emits  chlorine  gas,  and  chloride  of  cobalt  is  gen- 
erated. 

Its  eq  is  83-0 ;  syvih.  2Co  +  30,  Co,  oV  C02O3. 

When  a  salt  of  cobalt  is  treated  with  pure  ammonia  in  close  vessels,  part  of  the 
cobalt  is  dissolved,  and  part  subsides  in  form  of  a  blue  powder.  On  admitting 
atmospheric  air,  this  substance  passes  to  a  higher  state  of  oxidation,  and  is  gra- 


NICKEL.  347 

dually  dissolved.  If  nitrate  of  cobalt  is  used,  a  double  salt  may  be  obtained  in 
crystals,  which  M.  Gmelin,  to  whom  we  are  indebted  for  these  remarks,  believes 
to  consist  of  nitrate  and  cobaltate  of  ammonia.  Of  the  existence  of  this  acid, 
however,  Winkelblech,  who  has  examined  the  subject,  could  obtain  no  evidence 
(Lieb.  An.  xiii.  253). 

Chloride  of  Cobalt. — It  is  obtained  in  solution  on  dissolving  metallic  cobalt,  its 
protoxide  or  either  of  the  other  oxides  in  hydrochloric  acid,  with  evolution  of 
hydrogen  gas  with  the  first  and  of  chlorine  with  the  latter.  It  yields  a  pink- 
coloured  solution,  and  by  evaporation  small  crystals  of  the  same  colour  contain- 
ing water  of  crystallization.  When  deprived  of  water  its  colour  is  blue,  a  cha- 
racter on  which  is  founded  its  use  as  a  sympathetic  ink  :  when  letters  are  written 
with  a  dilute  solution  of  the  chloride,  the  colour  is  so  pale  that  it  is  invisible  in 
the  cold ;  but  on  heating  gently  the  letters  appear  of  a  blue  colour,  and  disappear 
as  soon  as  the  chloride  has  recovered  its  moisture  from  the  atmosphere.  When 
iron  or  nickel  is  present  the  dry  chloride  of  cobalt  is  green  instead  of  blue. 

Its  eq.  is  64-92 ;  symb,  Co  -|-  CI,  or  CoCl. 

Sulphur ets. — Cobalt  appears  to  unite  with  sulphur  in  three  proportions ;  the 
first  being  a  protosulphuret,  the  second  a  sesquisulphuret,  and  the  third  a  bisul- 
phuret.  The  protosulphuret  may  be  formed  in  the  dry  way  either  by  throwing 
fragments  of  sulphur  on  red-hot  cobalt,  or  by  igniting  protoxide  of  cobalt  with 
sulphur ;  and  it  is  thrown  down  as  a  black  precipitate  from  the  salts  of  cobalt 
by  alkaline  hydrosulphates,  or  even  by  hydrosulphuric  acid  gas  if  the  salt  is 
quite  neutral,  or  the  oxide  united  with  any  of  the  feebler  acids.  It  has  a  grey 
colour,  a  metallic  lustre,  and  a  crystalline  texture. 

Its  eq.  45*6 ;  symb,  Co  -f-  S,  or  CoS. 

Arfwedson  has  observed  that  when  hydrogen  gas  is  transmitted  over  sulphate 
of  oxide  of  cobalt  heated  to  redness,  water  and  sulphurous  acid  are  evolved,  and 
a  compound  remains,  called  an  oxysulphuret^  consisting  of  oxide  of  cobalt  united 
with  sulphuret  of  cobalt.  When  this  substance  is  exposed  to  hydrosulphuric 
acid  gas  at  a  red  heat,  the  oxide  is  decomposed,  and  the  sesquisulphuret  is 
formed. 

Its  eq.  is  107*3  ;  syrnb.  2Co  +  3S,  or  C02S3. 

The  bisulphuret  is  prepared,  according  to  Setterberg,  by  heating  2  parts  of 
carbonate  of  oxide  of  cobalt  intimately  mixed  with  3  parts  of  sulphur.  The 
process  is  conducted  in  a  glass  retort,  and  the  heat  continued  as  long  as  sulphur 
is  expelled  ;  but  the  temperature  should  not  be  sufiered  to  reach  that  of  redness. 

Its  eq.  61-7;  symb.  Co  +  2S,  or  C0S2. 

Subphosphurei  of  Cobalt. — Rose  obtained  this  phosphuret  by  the  action  of 
hydrogen  gas  on  subphosphate  of  oxide  of  cobalt  he&ted  in  a  tube,  water  being 
also  generated.    In  this  case 

1  eq.  Phosphate  and  8  eq.  Hydrogen        2         1  eq.  Phosphuret  and  8  eq.  water 
3(Co  +  0)  f  (2?  t  50)        8H  |,  3Co  +  2P  8(H  +  0). 

This  phosphuret  is  pulverulent  and  of  a  grey  colour,  and  is  also  obtained  by 
the  action  of  phosphuretted  hydrogen  gas  on  chloride  of  cobalt. 
Its  eq.  is  119-9 ;  symb.  3Co  -f  2P,  or  C03P2. 

NICKEL. 

Hist,  and  Prep. — Nickel  is  a  constituent  of  meteoric  iron,  and,  according  to 
Gregory,  of  native  peroxide  of  manganese ;  but  its  principal  ore  is  the  copper- 


348  NICKEL. 

coloured  mineral  of  Westphalia,  termed  Jcujfernichtlj  copper-nickel ;  nickel  being 
an  epithet  of  detraction,  applied  by  the  older  German  miners,  because  the  mine- 
ral looked  like  an  ore  of  copper,  and  yet  they  could  extract  none  from  it.  The 
preparations  of  nickel  may  either  be  prepared  from  copper-nickel,  which  is  an 
arseniuret  of  nickel  containing  small  quantities  of  sulphur,  copper,  cobalt,  and 
iron,  or  from  the  artificial  arseniuret  called  speiss,  a  metallurgic  production  ob- 
tained in  forming  smalt  from  the  roasted  ores  of  cobalt.  Various  processes  have 
been  devised  for  procuring  a  pure  salt  of  nickel,  but  the  following  appears  to  me 
as  simple  and  perhaps  as  successful  as  any.  After  reducing  speiss  to  fine  pow- 
der, it  is  digested  in  sulphuric  acid,  to  which  a  fourth  part  of  nitric  acid  is  added  ; 
and  when  the  solution  is  saturated  with  nickel,  it  is  set  aside  for  several  hours 
in  order  that  arsenious  acid  may  separate,  and  is  then  filtered.  The  clear  liquid 
is  subsequently  mixed  with  a  solution  of  sulphate  of  potassa,  and  set  aside  to 
crystallize  spontaneously ;  when  a  double  salt,  sulphate  of  oxide  of  nickel  and 
potassa,  is  deposited.  Thomson,  who  proposed  this  process,  states  that  the 
crystals  thus  obtained  are  quite  free  from  arsenic  and  iron,  and  contain  no  impuri- 
ties except  copper  and  cobalt.  The  former  is  precipitated  as  sulphuret  by  a 
current  of  hydrosulphuric  acid  gas,  a  little  free  sulphuric  acid  being  previously 
added ;  and  at  the  same  time  any  traces  of  arsenic,  if  present,  would  likewise 
subside  as  orpiment.  The  filtered  liquid  is  then  heated  to  expel  free  hydrosul- 
phuric acid,  and  the  oxides  of  nickel  and  cobalt  precipitated  by  carbonate  of 
potassa.  The  separation  of  these  oxides  may  then  be  efiected  by  the  method 
suggested  by  Berthier ;  namely,  by  precipitating  them  together  by  pure  potassa, 
and,  after  washing  the  mixed  hydrates,  suspending  them  in  water  through  which 
chlorine  gas  is  transmitted  to  saturation.  All  the  cobalt  and  generally  some 
nickel  is  converted  into  peroxide  and  thus  rendered  insoluble ;  while  the  greater 
part  of  the  nickel  is  dissolved  in  the  form  of  chloride,  and  may  be  removed 
from  the  insoluble  peroxides  by  filtration.  The  metal  may  be  prepared  either  by 
heating  the  oxalate  in  close  vessels,  or  by  the  combined  action  of  heat  and  char- 
coal or  hydrogen  on  oxide  of  nickel. 

Prop. — It  is  of  a  white  colour,  intermediate  between  that  of  tin  and  silver.  It 
has  a  strong  metallic  lustre,  and  is  both  ductile  and  malleable.  It  is  attracted 
by  the  magnet,  and  like  iron  may  be  rendered  magnetic  at  common  temperatures, 
but  loses  this  power  at  630°  (Faraday).  Its  sp.  gr.  after  fusion  is  about  8*279, 
and  is  increased  to  near  9*0  by  hammering. 

Nickel  is  very  infusible,  but  less  so  than  pure  iron.  It  suffers  no  change  at 
common  temperatures  by  exposure  to  air  and  moisture  ;  but  it  absorbs  oxygen  at 
a  red  heat,  though  not  rapidly,  and  is  partially  oxidized.  It  decomposes  water 
at  the  same  temperature.  Hydrochloric  and  sulphuric  acids  act  upon  it  with  dif- 
ficulty ;  but  by  nitric  acid  it  is  readily  oxidized,  and  forms  a  nitrate  of  the  pro- 
toxide of  nickel. 

From  the  analyses  of  the  oxides  of  nickel  by  Rothoff  and  Tupputi  the  eq.  of 
nickel  may  be  estimated  at  29*5.  Its  symb.  is  Ni.  The  composition  of  its  com- 
pounds described  in  this  section  is  as  follows  : — 


Nickel. 

Equiv. 

Formulx. 

Protoxide 

29-5  1  eq.  4- Oxygen 

a 

1  eq. 

=    37-5 

Ni  +  0  or  NiO. 

Peroxide 

690  2  eq.-4-     do. 

24 

3eq. 

=   830 

2Ni-f-30orNij03- 

Chloride 

29-5  1  eq.  -j-  Chlorine 

35-42 

leq. 

=   64-92 

Ni  -i-  CI  or  NiCl. 

Disulphuret 

59      2  eq.  -f  Sulphur 

16-1 

leq. 

=    75- 1 

2Ni  4  S  or  Ni2S. 

ProtoBulphuret 

29-5  1  eq.  t     do. 

161 

1  eq. 

==   45-6 

Ni  +  S  or  NiS. 

Subphosphuret 

88-5  3  eq.  -f-  Phosphorus 

31-4 

2eq. 

=  119-9 

3Ni  -f-  2P  or  Ni3P2. 

NICKEL.  349 

Protoxide  cf  Nickel. — This  oxide  may  be  formed  by  heating  the  carbonate, 
oxalate,  or  nitrate  to  redness  in  an  open  vessel,  and  is  then  of  an  ash-^rey 
colour ;  but  after  exposure  to  a  white  heat,  its  colour  is  a  dull  olive-green.  It 
is  not  reducible  by  heat  unaided  by  combustibles.  It  is  not  attracted  by  the 
magnet.  It  is  a  strong  alkaline  base,  and  nearly  all  its  salts  have  a  green  tint. 
It  is  precipitated  as  a  hydrate  of  a  pale-green  colour  by  the  pure  alkalies,  but  is 
redissolved  by  ammonia  in  excess ;  as  a  pale  green  carbonate  by  alkaline  carbon- 
ates, but  is  dissolved  by  an  excess  of  carbonate  of  ammonia ;  and  as  a  black 
sulphuret  by  alkaline  hydrosulphates.  Hydrosulphuric  acid  occasions  no  pre- 
cipitate, unless  the  solution  is  quite  neutral,  or  the  oxide  combined  with  a  weak 

acid.    Its  eq.  is  37*5 ;  syml.  Ni  -j-  O,  Ni,  or  NiO. 

Peroxide. — It  is  formed  by  transmitting  chlorine  gas  through  water  in  which 
the  hydrate  of  the  protoxide  is  suspended.  It  has  a  black  colour,  does  not  unite 
with  acids,  is  decomposed  by  a  red  heat,  and  with  hot  hydrochloric  acid  forms 
the  chloride  with  disengagement  of  chlorine  gas. 

Its  eq,  is  83-0 ;  syjnb,  2  Ni  -|-  30,  Ni,  or  NizOg. 

Thenard  succeeded  in  preparing  a  peroxide  by  the  action  of  peroxide  of  hydro- 
gen on  hydrated  protoxide  of  nickel ;  but  it  is  uncertain  whether  the  composition 
of  this  peroxide  is  identical  with  that  above  described,  or  different.  Two  sub- 
oxides have  likewise  been  enumerated ;  but  their  existence  is  exceedingly  pro- 
blematical. 

Chloride  of  Nickel. — ^This  compound  is  formed  by  acting  with  hydrochloric 
acid  on  metallic  nickel,  its  protoxide,  or  peroxide,  hydrogen  gas  being  evolved 
with  the  former,  and  chlorine  with  the  latter.  It  forms  an  emerald  green  solu- 
tion, and  by  evaporating  yields  crystals  of  the  same  tint,  which  lose  water  or 
deliquesce  according  as  the  air  is  dry  or  moist.  In  its  anhydrous  stdte  it  is  yel- 
low ;  but  a  small  admixture  with  cobalt  causes  a  green  tint.  At  a  low  red  heat 
it  sublimes  and  condenses  in  brilliant  scales  of  a  gold-yellow  colour. 

Its  eq.  is  64*92  ;  symh.  Ni  -f-  CI,  or  NiCl. 

Protosulphuret  of  nickel  is  formed  by  processes  similar  to  those  described  for 
preparing  protosulphuret  of  cobalt.  The  precipitated  sulphuret  is  dark  brown 
or  nearly  black,  and  is  dissolved  by  hydrochloric  acid  with  evolution  of  hydro- 
sulphuric  ;  while  that  procured  in  the  dry  way  is  of  a  greyish  yellow  colour,  and 
requires  for  solution  nitric  or  nitro-hydrochloric  acid.  It  occurs  as  a  natural  pro- 
duction in  very  delicate  acicular  crystals,  the  haarkies  of  the  Germans,  Its  eq.  is 
45-6 ;  symb.  Ni  -{-  S,  or  NiS. 

Arfwedson  obtained  the  disulphuret  by  transmitting  hydrogen  gas  over  sul- 
phate of  oxide  of  nickel  at  a  red  heat.  It  is  of  a  lighter  yellow  and  more  fusible 
than  the  other. 

Its  eq.  is  75*  1 ;  symb.  2Ni  -f-  S,  or  Ni  S. 

Subphosphuret  of  Nickel. — Rose  obtained  it  by  the  action  of  hydrogen  gas  on 
subphosphate  of  oxide  of  nickel,  the  same  change  ensuing  as  with  cobalt ;  and 
it  is  generated  by  the  action  of  phosphuretted  hydrogen  gas  on  chloride  of  nickel. 
It  Ras  a  black  colour,  is  insoluble  in  hydrochloric  acid,  but  dissolves  in  nitric 
acid.     Heated  by  the  blowpipe  it  burns  with  flame.  y 

Its  eq.  is  119-9 ;  symb.  3  Ni  +  2P,  or  Ni'Pi. 


8S0 


TIN. 


SECTION  XIV. 


TIN. 


Hist,  and  Prep. — ^Tin  was  known  to  the  ancients,  who  obtained  it  principally, 
if  not  solely,  from  Cornwall,  The  tin  of  coramerce  is  distinguished  into  two 
varieties,  called  block  and  grain  tin,  both  of  which  are  procured  from  the  native 
oxide  by  means  of  heat  and  charcoal.  In  Cornwall,  which  has  been  celebrated 
for  its  tin  mines  during  many  centuries,  the  ore  is  both  extracted  from  veins, 
and  found  in  the  form  of  rounded  grains,  among  beds  of  rolled  materials,  which 
have  been  deposited  by  the  action  of  water.  These  grains,  commonly  called 
stream  tin,  contain  a  very  pure  oxide,  and  yield  the  purest  kind  of  grain  tin.  An 
inferior  sort  is  prepared  by  heating  bars  of  tin,  extracted  from  the  common  ore, 
to  very  near  their  point  of  fusion,  when  the  more  fusible  parts,  which  are  the 
purest,  flow  out;  and  the  less  fusible  portions  constitute  block  tin.  The  usual 
impurities  are  iron,  copper  and  arsenic. 

Prop. — It  has  a  white  colour,  and  a  lustre  resembling  that  of  silver.  The 
brilliancy  of  its  surface  is  but  very  slowly  impaired  by  exposure  to  the  atmo- 
sphere, nor  is  it  oxidized  even  by  the  combined  agency  of  air  and  moisture.  Its 
malleability  is  very  considerable;  for  the  thickness  of  common  tin-foil  does  not 
exceed  1-1 000th  of  an  inch.  In  ductility  and  tenacity  it  is  inferior  to  several 
metals.  It  is  soft  and  inelastic,  and  when  bent  backwards  and  forwards  emits 
a  peculiar  crackling  noise.  Its  sp.  gr.  is  about  7'291.  At  442°  it  fuses,  and  if 
exposed  at  the  same  time  to  the  air,  its  surface  tarnishes,  and  a  grey  powder  is 
formed.  When  heated  to  whiteness,  it  takes  fire  and  burns  with  a  white  flame, 
being  converted  into  peroxide  of  tin. 

The  eq.  of  tin  deduced  by  Berzelius  from  his  analysis  of  its  oxides  is  57'9 ;  its 
symb.  is  Sn.  The  composition  of  the  compounds  of  tin  described  in  this  section 
is  as  follows : — 


Tin. 

Equiv.               FormulsB. 

Protoxide 

57-9 

1  eq.-f- Oxygen     8 

1  eq.=  65-9    Sn-fOorSnO. 

Sesquioxide 

105-8 

2eq.-H    .      .    24 

3eq.  =  129-8    2Snf  30orSn203. 

Binoxide 

57-9 

1  eq.-j-     .      .     16 

2  eq.  =  73-9     Sn-f-20  or  SnO^. 

Protochloride 

67-9 

1  eq.-|- Chlorine  35-72 

1  eq.==   93-32  Sn-f  CI  or  SnCl. 

Bichloride 

57-9 

I  eq.-f-     .      .    70-84 

2  eq.  =  128-74  Sn-f  2C1  or  SnClj. 

Protiodide 

67-9 

1  eq.-j-Iodine  126-3 

leq.  =  184-2     Sn-florSnI. 

Biniodide 

67-9 

1  eq.-l-     .      .  252-6 

2eq.  =  310-5     Snt2IorSnI». 

ProtoBulphurel 

;  57-9 

1  eq.-f  Sulphur  16-1 

leq.=   740    Sn-fSorSnS. 

Sesquisulph. 

115-8 

2eq.t     .      .    48  3 

3  eq.=  164-1     2Sn-|-3S  or  Sn2S3. 

Bisulphuret 

57-9 

leq.+     .      .     32-2 

2eq.=   901     Sn-j-2SorSnS2. 

TerBulphuret 

57-9 

.  1  eq.-f  Phosph.  47.1, 

3  eq.  =  1050    Sn-f  3P  or  SnP». 

Protoxide  of  Tin. — Prep. — When  chloride  of  tin  in  solution  is  mixed  with  an 
alkaline  carbonate,  hydrated  oxide  of  tin  falls,  which  may  be  obtained  as  such 
in  a  dry  form  by  washing  with  warm  water,  and  drying  at  a  heat  not  above  196°, 


TIN.  861 

with  the  least  possible  exposure  to  the  air.  The  best  mode  of  obtaining  the 
anhydrous  oxide  is  by  heating  the  hydrate  to  redness  in  a  tube  from  which  air 
is  excluded  by  a  current  of  carbonic  acid  gas.  The  same  oxide  is  formed  when 
tin  is  kept  for  some  time  fused  in  an  open  vessel. 

Prop. — Its  sp.  gr.  is  G*666.  At  common  temperatures  it  is  permanent  in  the 
air ;  but  if  touched  by  a  red-hot  body  it  takes  fire,  and  is  converted  into  the 
peroxide.  It  is  dissolved  by  the  sulphuric  and  hydrochloric  acids,  as  also  by 
dilute  nitric  acid ;  and  the  pure  fixed  alkalies  likewise  dissolve  it.  From  the 
alkaline  solution  metallic  tin  is  gradually  deposited,  and  peroxide  of  tin  remains 
in  solution.  Its  salts  are  remarkably  prone  to  absorb  oxygen,  both  from  the  air 
and  from  compounds  which  yield  oxygen  readily.  Thus  it  converts  peroxide  of 
iron  into  protoxide,  and  throws  down  mercury,  silver,  and  platinum  in  the  metal- 
lic state  from  their  salts.  With  a  solution  of  gold  it  causes  a  purple  precipitate, 
the  purple  of  Cassius,  which  appears  to  be  a  compound  of  peroxide  of  tin  and  prot- 
oxide of  gold.  By  this  character  protoxide  of  tin  is  recognized  with  certainty. 
It  is  thrown  down  by  hydrosulphuric  acid  as  black  protosulphuret  of  tin. 

Its  eq.  ts  65*9 ;  symb.  Sn  -f-  0,  Sn,  or  SnO. 

Sesquioxide  of  Tin, — Fuchs  has  lately  succeeded  in  preparing  this  oxide  by 
mixing  recently  precipitated  and  moist  hydrated  peroxide  of  iron  with  a  solution 
of  protochloride  of  tin  as  free  as  possible  from  hydrochloric  acid ;  when,  by  an 
interchange  of  elements 

1  eq.  perox.  iron  &  2  eq.  chloride  of  tin    2     1  eq.  sesquiox.  tin  &  2  eq.  chlo.  iron. 
FeaOa  2SnCl  •£  Sn203  2FeCl 

The  sesquioxide  falls  as  a  slimy  grey  matter,  and  in  general  rather  yellow  from 
adhering  oxide  of  iron.  Berzelius  obtained  it  purer  by  using  a  solution  made  by 
saturating  hydrochloric  acid  as  far  as  possible  with  hydrated  peroxide  of  iron. 
The  se^uioxide  of  tin,  while  moist,  is  soluble  in  hydrochloric  acid,  and  the 
solution  strikes  the  purple  of  Cassius  with  gold  ;  and  it  is  readily  soluble  in  a 
solution  of  ammonia,  which  distinguishes  it  from  the  protoxide  of  tin,  just  as  its 
action  on  gold  does  from  the  binoxide  (Pog.  Annalen,  xxviii,  443.) 

Its  eq.  is  129-8  ;  symh.  2Sn  -f-  30,  ^,  or  SnaOa. 

Peroxide  cf  Tin. — Prep. — Most  conveniently  by  the  action  of  nitric  acid  on 
metallic  tin.  The  acid  in  its  most  concentrated  state,  does  not  act  easily  upon 
tin ;  but  when  a  small  quantity  of  water  is  added,  violent  effervescence  takes 
place  owing  to  the  evolution  of  nitrous  acid  and  binoxide  of  nitrogen,  and  a 
white  powder,  the  hydrated  peroxide,  is  produced.  On  edulcorating  this  sub- 
stance, and  heating  it  to  redness,  watery  vapour  is  expelled,  and  the  pure  per- 
oxide, of  a  straw  yellow  colour,  remains.  In  this  process  ammonia  is  generated, 
a  circumstance  which  proves  water  as  well  as  nitric  acid  to  be  decomposed. 
Peroxide  of  tin  may  likewise  be  obtained  by  precipitation  from  a  solution  of  per- 
chloride  of  tin  by  potassa,  ammonia,  or  the  alkaline  carbonates  ;  but  in  this  case 
it  falls  as  a  very  bulky  hydrate,  different  from  the  other  hydrate  both  in  appear- 
ance and  several  of  its  chemical  properties.  Thus  the  latter  dissolves  readily 
in  sulphuric,  nitric,  and  hydrochloric  acid,  even  when  diluted;  while  the  former 
is  completely  insoluble  in  the  same  acids,  even  when  concentrated.  It  unites, 
indeed,  with  hydrochloric  acid,  and  the  compound  is  soluble  in  pure  water. 

Prop. — It  has  very  little  disposition  in  any  state  to  unite  with  acids,  and  when 
dissolved  by  them  is  very  apt  to  separate  itself  spontaneously  as  a  gelatinous 


352  TIX. 

hydrate.  It  acts  the  part  of  a  feeble  acid :  it  reddens  litmus  when  its  hydrate 
moistened  is  laid  upon  it,  and  it  unites  with  the  pure  alkalies,  forming  soluble 
compounds  which  are  called  stannaies. 

Peroxide  of  tin  is  recognized  by  its  insolubility  in  acids  in  its  anhydrous 
state ;  by  separating  from  its  solution  by  means  of  hydrochloric  acid  as  a  bulky 
hydrate  by  any  of  the  alkalies  or  alkaline  carbonates,  which  is  easily  and  com- 
pletely dissolved  by  pure  potassa  or  soda  in  excess ;  and  by  yielding  with  hydro- 
sulphuric  acid  the  yellow  bisulphuret  of  tin,  which  is  also  soluble  in  pure  potassa. 
Peroxide  of  tin,  when  melted  with  glass,  forms  a  white  enamel. 

Its  eq.  73-9;  st/mb,  Sn  +  20,  Sn,  or  SO^. 

Protochloride  of  T^n. — ^This  compound  is  obtained  by  transmitting  hydrochloric 
acid  gas  over  metallic  tin  heated  in  a  glass  tube,  when  hydrogen  gas  is  evolved ; 
or  by  distilling  a  mixture  either  of  granulated  tin  with  an  equal  weight  of  bichlo- 
ride of  mercury,  of  an  amalgam  of  tin  with  calomel,  urging  the  heat  till  the 
mercury  is  expelled.  In  this  state  it  is  a  grey  solid,  of  a  resinous  lustre,  which 
fuses  below  redness,  and  at  a  high  temperature  sublimes.  It  is  obtained  by  crys- 
tallization from  a  concentrated  solution  of  the  chloride  in  crystals,  which  are 
sometimes  in  small  white  needles,  and  at  others  in  large  transparent  prisms,  and 
consist  of  93'32  parts  or  1  eq.  of  protochloride  of  tin  and  2V  parts  or  3  eq,  of 
water.  On  heating  these  crystals,  they  not  only  lose  water,  but  reaction  ensues 
between  the  elements  of  water  and  the  chloride,  hydrochloric  acid  gas  is  evolved, 
and  protoxide  of  tin  remains  combined  with  the  chloride.  The  same  kind  of  com- 
pound is  formed  when  a  large  quantity  of  the  water  is  poured  upon  the  crystals  : 
the  solution  contains  protochloride  of  tin  and  hydrochloric  acid,  and  a  white 
powder  subsides  which  consists  of  1  eq.  of  the  protochloride,  1  eq.  of  protoxide, 
and  2  eqs.  of  water  (Berzelius). 

A  solution  of  protochloride  of  tin  is  obtained  by  healing  granulated  tin  in 
strong  hydrochloric  acid  as  long  as  hydrogen  gas  continues  to  be  evolved.  This 
solution  is  much  employed  as  a  deoxidizing  agent,  being  more  powerful  than 
the  sulphate  or  nitrate  of  the  protoxide;  owing  apparently  to  the  tendency  of  the 
protochloride  of  tin  to  resolve  itself  into  bichloride  and  metallic  tin,  the  latter 
taking  oxygen  or  chlorine  from  any  metallic  solutions  which  yield  them  readily. 
Its  eq.  is  93-32;  synJ).  Sn  -f-  CI,  or  SnCl. 

Bichloride  of  Tin, — When  protochloride  of  tin  is  heated  in  chlorine  gas,  or  on 
distilling  a  mixture  of  8  parts  of  granulated  tin  with  24  of  bichloride  of  mercury, 
a  very  volatile  colourless  liquid  passes  over,  which  is  bichloride  of  tin.  In  an 
open  vessel  it  emits  dense  white  fumes,  caused  by  the  moisture  of  the  air,  and 
hence  it  was  formerly  called  the  fuming  liquor  of  Libavius,  who  discovered  it. 
At  248°  it  boils  and  the  sp.  gr.  of  its  vapour  was  found  by  Dumas  to  be  9*1997. 
With  one-third  of  its  weight  of  water  it  forms  a  solid  hydrate,  and  in  a  larger 
quantity  of  water  dissolves. 

The  solution  of  bichloride  of  tin,  commonly  called  permuriate  of  tin,  is  much 
used  in  dyeing,  and  is  prepared  by  dissolving  tin  in  nitro-hydrochloric  acid.  The 
process  requires  care;  for  if  the  action.be  very  rapid,  as  is  sure  to  happen  if 
strong  acid  be  employed  and  much  tin  added  at  once,  the  peroxide  will  be  spon- 
taneously deposited  as  a  bulky  hydrate,  and  be  subsequently  redissolved  with 
great  difficulty.  But  the  operation  will  rarely  fail,  if  the  acid  is  made  with  two 
measures  of  hydrochloric  acid,  one  of  nitric  acid,  and  one  of  water,  and  if  the  tin 


TIN.  35^ 

is  gradually  dissolved,  one  portion  disappearing  before  another  is  added.  The 
most  certain  mode  of  preparation,  however,  is  to  prepare  a  solution  of  the  proto- 
chloride,  and  convert  it  into  the  bichloride  either  by  chlorine,  or  by  gentle  heat 
and  nitric  acid. 

Its  eq.  is  128-74 ;  symb.  Sn  +  2C1,  or  SnCl^. 

Iodides  of  Tin. — The  protiodide  is  formed  by  heating  granulated  tin  with 
about  25  times  its  weight  of  iodine,  and  is  a  brownish  red,  translucid  substance, 
very  fusible,  volatile  at  a  high  temperature,  and  soluble  in  water. 

Its  eq.  is  184*2 ;  symb.  Sn  -\-  I,  or  SnI. 

The  periodide  is  prepared  by  dissolving  in  hydriodic  acid  the  hydrate  of  the 
peroxide  precipitated  by  alkalies  from  the  bichloride.  It  crystallizes  in  yellow 
crystals  of  a  silky  lustre,  which  are  resolved  by  boiling  water  into  hydriodic 
acid  and  peroxide  of  tin. 

Its  eq.  is  3 10*  5;  symb.  Sn  -f  2l,  or  Snl^. 

Protosulphuret  of  Tin. — This  compound  iS  prepared  by  pouring  melted  tin 
upon  its  own  weight  of  sulphur,  and  stirring  rapidly  with  a  stick  during  the  ac- 
tion ;  as  some  tin  usually  escapes  the  sulphur  from  the  latter  being  rapidly  ex- 
pelled, the  product  should  be  pulverized,  mixed  with  its  weight  of  sulphur,  and 
projected  in  successive  portions  into  a  hot  hessian  crucible,  and  then  heated  to 
redness.  It  is  a  brittle  compound,  of  bluish  grey,  nearly  black,  colour  and  metal- 
lic lustre,  which  fuses  at  a  red  heat,  and  acquires  a  lamellated  texture  in  cooling. 
It  is  dissolved  by  hydrochloric  acid  with  evolution  ^f  hydrosulphuric  acid.  The 
same  sulphuret  is  obtained  in  the  moist  way  by  adding  hydrosulphuric  acid  to  a 
solution  of  protochloride  of  tin. 

Its  eq.  is  74*0 ;  symb,  Sn  -j-  S,  or  SnS. 

The  Sesquisulphuret  is  formed  by  mixing  the  protosulphuret  in  fine  powder 
with  a  third  of  its  weight  of  sulphur,  and  heating  the  mixture  to  low  redness 
until  sulphur  ceases  to  escape.  Its  colour  is  of  a  deep  greyish  yellow,  it  is  re- 
converted by  a  strong  heat  into  the  protosulphuret,  and  dissolves  in  hydrochloric 
acid  gas,  yielding  hydrosulphuric  acid  gas  and  a  residue  of  bisulphuret  of  tin. 

Its  eq.  is  164-1 ;  symb.  2Sn  -f-  SS,  or  ^n^^^. 

Bisulphuret  of  Tin,  formerly  called  mosaic  gold,  is  prepared  by  heating  in  a 
glass  or  earthen  retort  a  mixture  of  2  parts  of  peroxide  of  tin,  2  of  sulphur,  and 
1  part  of  sal-ammoniac,  and  maintaining  a  low  red  heat  until  sulphurous  acid 
ceases  to  be  evolved.  These  materials  are  sometimes  employed  without  sal- 
ammoniac,  but  Berzelius  says  that  the  latter  is  essential  for  obtaining  the  bisul- 
phuret. The  product,  when  successfully  prepared,  is  in  crystalline  scales,  and 
sometimes  even  in  regular  six-sided  tables,  of  a  golden  yellow  colour  and  metal- 
lic lustre.  It  is  soluble  in  pure  potassa  and  in  its  carbonate  by  boiling  ;  but  its 
only  solvent  among  the  acids  is  the  nitro-hydrochloric.  The  bisulphuret  is  ob- 
tained as  a  bulky  hydrate  of  a  dirty  yellow  colour  by  the  action  of  hydrosulphuric 
acid  or  hydrosulphate  of  ammonia  on  bichloride  of  tin  in  solution. 

Its  eq.  is  90.1 ;  symb.  Sn  -f  2S,  or  SnS^. 

Terphosphuret  of  Tin. — Rose  formed  this  compound  by  acting  on  a  solution 
of  protochloride  of  tin  by  phosphuretted  hydrogen.  It  is  readily  oxidized  by  the 
action  of  the  air. 

Its  eq.  is  105-0 ;  symb.  Sn  +  3P,  or  SnP^. 

25 


354  COPPER. 


CLASS  II 


ORDER  II. 

METALS  WHICH  DO  NOT  DECOMPOSE  WATER    AT  ANY  TEMPERA- 
:,  TURe',  and  the  oxides  of  which  ARE  NOT  REDUCED  TO  THE 
METALLIC  STATE  BY  THE  SOLE  ACTION  OF  HEAT. 


SECTION  XV. 

COPPER. 

Hist,  and  Prep, — One  of  the  most  abundant  of  the  metals,  and  was  well 
known  to  the  ancients.  Native  copper  is  by  no  means  uncommon,  being  found 
more  or  less  in  most  copper  mines  :  it  occurs  in  large  amorphous  masses  in  some 
parts  of  America,  and  is  so|[ietimes  met  with  in  octohedral  crystals,  or  in  some 
of  the  forms  allied  to  the  octohedron.  Stromeyer  has  lately  discovered  it  in 
several  specimens  of  meteoric  iron,  but  in  a  quantity  not  exceeding  2-lOOOths 
of  the  mass.  The  eopper  of  commerce  is  extracted  chiefly  from  the  native  sul- 
phuret;  especially  from  copper  pyrites,  a  double  sulphuret  of  iron  and  copper. 
The  first  part  of  the  process  consists  in  roasting  the  ore,  so  as  to  burn  off  some 
of  the  sulphur,  and  leave  the  remainder  as  a  subsulphate  of  the  oxides  of  iron 
and  copper.  The  mass  is  next  heated  with  some  unroasted  ore  and  siliceous 
substances,  by  which  means  much  of  the  iron  unites  in  the  state  of  black  oxide 
with  silicic  acid,  and  rises  as  a  fusible  slag  to  the  surface;  while  most  of  the 
copper  returns  to  the  state  of  sulphuret.  It  is  then  subjected  to  long-continued 
roasting,  when  the  greater  part  of  the  sulphur  escapes  as  sulphurous  acid,  and 
the  metal  is  oxidized  ;  after  which  it  is  reduced  by  charcoal,  and  more  of  the 
iron  separated  as  a  silicate  by  the  addition  of  sand.  Lastly,  the  metal  is  strongly 
heated  while  a  current  of  air  plays  upon  its  surface :  the  impurities,  chiefly  sul- 
phur and  iron,  being  more  oxidable  than  copper,  combine  with  oxygen  by  pre- 
ference, and  the  copper  is  at  length  left  in  a  state  of  purity  sufficient  for  the 
purposes  of  commerce. 

Prop. — Distinguished  from  all  other  metals,  titanium  excepted,  by  having  a 
red  colour.  It  receives  a  considerable  lustre  by  polishing.  Its  density,  when 
fused,  is  8*667,  and  it  is  increased  by  hammering.  It  is  both  ductile  and  malle- 
able, and  in  tenacity  is  inferior  only  to  iron.  It  is  hard  and  elastic,  and  conse- 
quently sonorous.  Its  point  of  fusion  is  1996°  F.  according  to  Daniell,  being 
less  fusible  than  silver  and  more  so  than  gold. 

It  undergoes  little  change  in  a  perfectly  dry  atmosphere,  but  is  rusted  in  a 
short  time  by  exposure  to  air  and  moisture,  being  converted  into  a  green  sub- 
stance, subcarbonate  of  the  black  oxide  of  copper.  At  a  red  heat  it  absorbs 
oxygen,  and  is  converted  into  black  scales  of  oxide.  It  is  attacked  with  diffi- 
culty by  hydrochloric  and  sulphuric  acids,  and  not  at  all  by  solutions  of  the 


COPPER. 


vegetable  acids,  if  atmospheric  air  be  excluded  ;  but  if  air  have  free  access,  the 
metal  absorbs  oxygen  with  rapidity,  the  attraction  of  the  acid  for  the  oxide  of 
copper  co-operating  with  that  of  the  copper  for  oxygen.  Nitric  acid  acts  with 
violence  on  copper,  forming  a  nitrate  of  the  black  oxide. 

The  most  trustworthy  experiments  for  determining  the  eq.  of  copper  are  those 
of  Berzelius  on  the  reduction  of  the  black  oxide  by  means  of  hydrogen  gas  at  a 
red  heat.  According  to  the  best  of  his  analyses,  8  parts  of  oxygen  unite  with 
31*6  parts  of  copper  to  constitute  the  black  oxide;  and,  therefore,  if  this  oxide 
be  formed  of  an  atom  of  oxygen  united  with  an  atom  of  copper,  the  eq.  of  this 
metal  will  be  31 '6.  This  opinion,  which  I  have  adopted,  is  maintained  by 
Thomson,  Berzelius,  and  many  Continental  chemists.  Others  consider  it  as  a 
binoxide,  regarding  red  oxide  of  copper  as  the  real  protoxide  ;  and  these  take 
twice  31-6  or  63*2  as  an  eq.  of  copper.  The  principal  arguments  in  favour  of 
the  former  view  are  these : — 1,  the  red  oxide  has  very  much  the  character  of  a 
suboxide,  a  term  frequently  used  to  designate  an  oxide  which  has  little  or  no 
tendency  to  unite  with  acids,  and  which  contains  less  than  one  atom  of  oxygen 
to  one  atom  of  metal;  2,  the  product  of  the  eq.  and  specific  heat  of  most  metals 
is  a  constant  quantity,  and  copper  coincides  with  the  law,  provided  the  black 
oxide  contain  an  atom  of  each  element;-  3,  the  salts  of  the  black  oxide  are 
isomorphous  with  the  salts  of  protoxide  of  iron,  which  gives  a  strong  presump- 
tion that  these  oxides  possess  the  same  atomic  constitution. 

Its  symh.  is  Cu. 

The  composition  of  the  compounds  described  in  this  section  is  as  follows  : — 


Copp 

er. 

Equiv. 

Formulae. 

Red  or  Dioxide 

63-2 

2  eq.-f- Oxygen 

8 

1  eq.=  71-2 

2Cu-f-0. 

Black  or  Protoxide 

31-6 

1  eq.+do. 

8 

I  eq.=  39-6 

Cu-i-0.' 

Superoxide 

31-6 

1  eq.-|-do. 

16 

2  eq.=  47-6 

Cut  20. 

Dichloride 

63-2 

2  eq.-f  Chlorine 

35-42 

1  eq.=  98-62 

2CU-J-C1. 

Chloride 

31-6 

1  eq.-|-do. 

35-42 

1  eq.=:  66-02 

Cu-fCl. 

Diniodide 

63-2 

2  eq.-j- Iodine 

126-3 

1  eq.=189-5 

2CutI. 

Disulphuret     • 

63-2 

2  eq.-f  Sulphur 

16-1 

1  eq.=  79-3 

2Cu-tS. 

Sulphuret 

31-6 

1  eq.-j- Sulphur 

16-1 

1  eq.=  47-7 

Cu-fs. 

Triphosphuret 

94-8 

3  eq. -[-Phosphorus 

15-7 

1  eq.=110.5 

3CufP. 

Subsesquiphosph.    . 

94- S 

3  eq.+do. 

31-4 

2  eq.=126-2 

3Cu-f-2P. 

Red  Oxide  or  Dioxide. — Hist,  and  Prep. — ^This  compound  occurs  native  in  the 
form  of  octohedral  crystals,  and  is  found  of  peculiar  beauty  in  the  mines  of 
Cornwall.  It  may  be  prepared  artificially  by  heating  in  a  covered  crucible  a 
mixture  of  31-6  parts  of  copper  filings  with  39*6  of  the  black  oxide ;  or  still 
better  by  arranging  thin  copper  plates  one  above  the  other  with  interposed  strata 
of  the  black  oxide,  and  exposing  them  to  a  red  heat  carefully  protected  from  the 
air.  Another  method  is  by  boiling  a  solution  of  acetate  of  protoxide  of  copper 
with  sugar,  when  the  suboxide  subsides  as  a  red  powder ;  and  another  is  to  fuse 
at  a  low  red  heat  the  dichloride  of  copper  with  about  an  equal  weight  of  car- 
bonate or  bicarbonate  of  soda,  subsequently  dissolving  the  sea-salt  by  water, 
and  drying  the  red  powder. 

In  this  case,  by  an  interchange  of  elements, 


1  eq.  Dichloride  of  Copper    CU2CI    2     1  eq.  Red  Oxide CU2O 

and  1  eq.  Soda    ....    NaO      "^    and  1  eq.  Chloride  of  Sodium         .    NaCl. 


356  COPPER. 

Malaguti  recommends  the  following  process  : — 100  parts  of  sulphate  of  copper 
and  57  of  carbonate  of  soda,  both  in  crystals,  are  fused  at  a  gentle  heat ;  and  the 
mass  left  when  all  water  is  expelled,  is  pulverized  and  mixed  with  25  parts  of 
copper  filings.  The  mixture  is  pressed  into  a  crucible  and  exposed  for  20 
minutes  to  a  white  heat.  The  result  is  again  pulverized  and  carefully  w^ashed 
(An.  de  Ch.  et  Ph.  liv.  216). 

Prop. — The  red  oxide  of  copper  has  a  sp.  gr.  of  6*093,  and  in  colour  is  very 
similar  to  copper.  It  may  be  preserved  in  a  dry  atmosphere;  but  at  a  red  heat 
it  absorbs  oxygen  and  is  converted  into  the  protoxide.  Dilute  acids  act  on  it 
very  slowly;  and  the  resulting  solution,  as  is  indicated  by  its  tint,  does  not 
arise  from  the  union  of  the  red  oxide  itself  with  the  acid,  but  from  its  being 
resolved,  like  other  sub-oxides,  into  metal  and  a  protoxide.  With  strong  nitric 
acid  it  is  oxidized,  binoxide  of  nitrogen  escapes,  and  a  nitrate  of  the  black  oxide 
is  formed.  Strong  hydrochloric  acid  forms  with  it  a  colourless  solution,  from 
which  alkalies  throw  it  down  as  a  hydrate  of  an  orange  tint.  In  this  state  it 
readily  absorbs  oxygen  from  the  air.  The  red  oxide  of  copper  is  soluble  in 
ammonia,  and  the  solution  is  quite  colourless ;  but  it  becomes  blue  with  sur- 
prising rapidity  by  free  exposure  to  air,  owing  to  the  formation  of  the  black  oxide. 

Its  eg.  is  71-2;  symb.  2Cu  +  O,  or  Cufi. 

Black  Oxide  or  Protoxide, — Hist  and  Prep, — This  compound,  the  copper  black 
of  mineralogists,  is  sometimes  found  native,  being  formed  by  the  spontaneous 
oxidation  of  other  ores  of  copper.  It  may  be  prepared  artificially  by  calcining 
metallic  copper,  by  precipitation  from  the  salts  of  copper  by  means  of  pure 
potassa,  and  by  heating  nitrate  of  copper  to  redness. 

Prop, — It  varies  in  colour  from  a  dark  brown  to  a  bluish-black,  according  to 
the  mode  of  formation :  its  sp.  gr.  is  6*401.  It  undergoes  no  change  by  heat 
alone,  but  is  readily  reduced  to  the  metallic  state  by  heat  and  combustible  mat- 
ter;  and  is  hence  much  employed  as  an  oxidizing  agent  in  the  analysis  of 
organic  substances.  It  is  insoluble  in  water,  and  does  not  affect  the  vegetable 
blue  colours ;  it  combines  with  nearly  all  the  acids,  forming  salts  which  have  a 
green  or  blue  tint.  It  is  soluble  likewise  in  ammonia,  forming  with  it  a  deep 
blue  solution,  a  property  by  which  protoxide  of  copper  is  distinguished  from  all 
other  substances.  Its  salts  are  distinguished  from  most  substances  by  their 
colour,  and  are  easily  recognized  by  reagents.  When  pure  soda  or  potassa  is 
mixed  with  a  solution  of  sulphate  of  the  protoxide,  a  greenish-blue  disulphate  at 
first  subsides ;  but  as  soon  as  the  alkali  is  added  in  excess,  a  blue  bulky  hydrate 
of  the  oxide  is  formed,  which  is  decomposed  by  boiling,  and  consequently 
becomes  black.  Pure  ammonia  also  throws  down  the  disulphate  when  carefully 
added ;  but  an  excess  of  the  alkali  instantly  redissolves  the  precipitate,  and 
forms  a  deep  blue  solution.  Alkaline  carbonates  cause  a  bluish-green  precipi- 
tate, carbonate  of  the  protoxide,  which  is  redissolved  by  an  excess  of  carbonate 
of  ammonia.  It  is  precipitated  as  a  dark  brown  sulphuret  by  hydrosulphuric 
acid,  and  as  a  reddish-brown  ferrocyanide  by  ferrocyanide  of  potassium.  It  is 
thrown  down  of  a  yellowish-white  colour  by  albumen,  and  M.  Orfila  has  proved 
that  this  compound  is  inert,  so  that  albumen  is  an  antidote  to  poisoning  by 
copper. 

Copper  is  separated  in  the  metallic  state  hy  a  rod  of  iron  or  zinc.  The  copper 
thus  obtained,  after  being  digested  in  a  dilute  solution  of  hydrochloric  acid,  is 
almost  chemically  pure. 

The  best  mode  of  detecting  copper,  when  supposed  to  be  present  in  mixed 


COPPER.  357 

fluids,  is  by  hydrosulphuric  acid.  The  sulphuret,  after  being  collected,  and 
heated  to  redness  in  order  to  char  organic  matter,  should  be  placed  on  a  piece 
of  porcelain,  and  be  digested  in  a  few  drops  of  nitric  acid.  Sulphate  of  protoxide 
of  copper  is  formed,  which,  when  evaporated  to  dryness,  strikes  the  character- 
istic deep  blue  tint  on  the  addition  of  ammonia;  but  the  most  delicate  test  of 
black  oxide  of  copper  in  solution  is  ferrocyanide  of  potassium. 

Its  eq»  is  39*6  ;  symb.  Cu  +  O,  Ca,  or  CuO. 

Superoxide. — ^This  oxide  was  prepared  by  Thenard  by  the  action  of  peroxide  of 
hydrogen  diluted  with  water  on  the  hydrated  black  oxide.  It  suffers  spontaneous 
decomposition  underwater;  but  it  maybe  dried  in  vacuo  by  means  of  sulphuric 
acid. 

Its  eq.  is  47*6 ;  symb.  Cu  +  20,  Cu,  or  CuO^. 

Bichloride, — Prep. — When  copper  filings  are  introduced  into  an  atmosphere  of 
chlorine  gas,  the  metal  takes  fire  spontaneously,  and  both  the  chlorides  are  gene- 
rated. The  dichloride  may  be  conveniently  prepared  by  heating  copper  filings 
with  twice  their  weight  of  corrosive  sublimate.  In  this  way  it  was  originally 
made  by  Boyle,  who  termed  it  resin  of  copper,  from  its  resemblance  to  common 
resin.  Proust,  who  called  it  white  muriate  of  copper,  procured  it  by  the  action  of 
protochloride  of  tin  on  chloride  of  copper  ;  and  also  by  decomposing  the  chloride 
by  heat,  air  being  excluded.  It  is  slowly  deposited  in  crystalline  grains  when 
the  green  solution  of  chloride  of  copper  is  kept  in  a  corked  bottle  in  contact  with 
metallic  copper. 

Prop. — The  dichloride  of  copper  is  fusible  at  a  heat  just  below  redness,  and 
bears  a  red  heat  in  close  vessels  without  subliming.  It  is  insoluble  in  water,  but 
dissolves  in  hydrochloric  acid,  and  is  precipitated  unchanged  by  water  as  a  white* 
powder.  Its  colour  varies  with  the  mode  of  preparation,  being  white,  yellow,  or 
dark  brown.  It  is  apt  to  absorb  oxygen  from  the  atmosphere,  forming  a  green- 
coloured  compound  of  oxide  and  chloride  of  copper ;  a  change  to  which  the 
dichloride  prepared  in  the  moist  way  is  peculiarly  prone. 

Its  eq.  is  98-62  ;  symb.  2Cu  +  CI,  or  Cu^Cl. 

Chloride. — The  chloride  of  copper  is  obtained  in  solution  of  a  green  colour  by 
dissolving  protoxide  of  copper  in  hydrochloric  acid,  and  crystallizes  by  due  con- 
centration in  blue  prismatic  needles,  containing  two  eq,  of  water;  Cu  CI  -f-  2 
HO,  which  are  deliquescent  and  very  soluble  in  alcohol.  V/hen  heated  they 
fuse,  lose  water,  and  the  anhydrous  chloride  in  form  of  a  yellow  powder  is  left ; 
but  the  heat  must  not  exceed  400°,  as  beyond  that  degree  the  chloride  loses  half 
its  chlorine,  and  is  converted  into  the  dichloride.  Its  tq,  is  66'02  ;  symb.  Cu  -+- 
CI,  or  CuCl. 

Diniodide  of  Copper. — This  substance  is  obtained  by  adding  iodide  of  potassium 
to  a  solution  made  of  the  sulphates  of  the  protoxides  of  copper  and  iron,  both  in 
crystals,  in  the  ratio  of  1  to  2|,  when  the  protoxide  of  iron  takes  the  oxygen  of 
the  oxide  of  copper  and  the  iodine  the  metallic  copper,  forming  a  white  precipi- 
tate, the  diniodide.  It  may  be  dried,  and  will  bear  a  high  temperature  in  close 
vessels,  without  change ;  but  if  heated  with  the  oxides  of  iron,  manganese,  or 
copper,  iodine  is  expelled  and  the  copper  oxidized. 

Its  eq.  is  189*5;  symb.  2Cu  -\- 1,  or  Cu^I. 

Iodide  of  Copper  is  scarcely  known.  For  on  mixing  a  salt  of  oxide  of  copper 
with  iodide  of  potassium,  iodine  is  set  free  and  the  diniodide  of  copper  falls.  A 
small  quantity  of  iodide  of  copper  remains  in  solution. 


358  COPPER. 

Sulphurets  of  Copper. — Tlie  dimlphuret  is  a  natural  production,  well  known 
to  mineralogists  under  the  name  of  copper  glance ;  and  in  combination  with  pro- 
tosulphuret  of  iron,  it  is  a  constituent  of  variegated  copper  ore.  It  is  formed 
artificially  by  heating  copper  filings  with  a  third  of  their  weight  of  sulphur,  the 
combination  being  attended  wuth  such  free  disengagement  of  heat,  that  the  mass 
becomes  vividly  luminous. 

Its  eg.  is  79-3  ;  symb.  2Cu  +  S,  or  Cu^S. 

Sulphuret  of  Copper  is  formed  by  the  action  of  hydrosulphuric  acid  on  a  salt 
of  copper.  When  ignited  without  exposure  to  the  air,  it  loses  half  of  its  sul- 
phur, and  is  converted  into  the  disulphuret. 

Its  eq.  is  47*7 ;  symb,  Cu  +  S,  or  CuS. 

Phosphurets  of  Copper. — Rose  states  that  the  triphosphuret  is  generated  by 
the  action  of  phosphuretted  hydrogen  gas  on  dlchloride  of  copper,  the  mutual 
interchange  of  elements  being  such  that 

3  eq.  Dichloride  of  Copper  SCujCl    2     2  eq.  Triphosphuret  SCujP. 

and  1  eq.  Phosphuretted  Hyd.       P2H8      >,    and  3  eq.  Hydrochl.  Acid  3  HCl. 

The  subsesquiphosphuret  is  formed  by  a  similar  interchange  between  chloride 
of  copper  and  phosphuretted  hydrogen,  so  that 

3  eq.  Chloride  of  Copper      3CuCl    2     1  ®<1'  Subsesquiphosphuret  CujPj 

and  1  eq.  Phosp.  Hyd.  PgHj    -^    and  3  eq.  Hydrochl.  Acid  3HCI. 

Rose  obtained  the  protosulphuret  by  the  action  of  hydrogen  gas  on  phosphate 
of  protoxide  of  copper  at  a  red  heat.  All  these  phosphurets  resemble  each  other, 
being  pulverulent,  of  a  grey  colour,  insoluble  in  hydrochloric  acid,  oxidized  and 
dissolved  by  nitric  acid,  and  burn  with  a  phosphorous  flame  before  the  blowpipe. 
A  phosphuret  of  copper  is  also  obtained  by  transmitting  phosphuretted  hydrogen 
gas  through  a  solution  of  sulphate  of  oxide  of  copper ;  but  the  dark  precipitate 
which  falls  seems  to  be  a  variable  mixture  of  diflferent  phosphurets,  phosphoric 
acid  being  generated  at  the  same  time.     (An.  de  Ch.  et  Ph.  li.  47.) 


SECTION  XVI. 


LEAD. 


Hist,  and  Prep. — ^This  metal  was  well  known  to  the  ancients.  As  a  native 
production  it  is  very  rare ;  but  in  combination  with  sulphur  it  occurs  in  great 
quantity.  All  the  lead  of  commerce  is  extracted  from  the  native  sulphuret,  the 
galena  of  mineralogists.  This  ore,  in  the  state  of  a  coarse  powder,  is  heated  in 
a  reverberatory  furnace;  when  part  of  it  is  oxidized,  yielding  sulphate  of  prot- 
oxide of  lead,  sulphuric  acid,  which  is  evolved,  and  free  oxide  of  lead.  These 
oxidized  portions  then  react  on  sulphuret  of  lead  :  by  the  reaction  of  two  eq.  of 


LEAD.  35^ 

oxide  of  lead  and  one  of  the  sulphuret,  three  eq.  of  metallic  lead  and  one  of  sul- 
phurous acid  result ;  while  one  equivalent  of  the  sulphuret  and  one  of  sulphate 
mutually  decompose  each  other,  giving  rise  to  two  eq.  of  sulphurous  acid  and 
two  of  metallic  lead.  The  slag  which  collects  on  the  surface  of  the  fused  lead 
contains  a  large  quantity  of  sulphate  of  protoxide  of  lead,  and  is  decomposed  by 
the  addition  of  quicklime,  the  oxide  so  separated  reacting  as  before  on  sulphuret 
of  lead.    The  lead  of  commerce  commonly  contains  silver,  iron,  and  copper. 

Prop. — It  has  a  bluish-grey  colour,  and  when  recently  cut,  a  strong  metallic 
lustre  ;  but  soon  tarnishes  by  exposure  to  the  air,  acquiring  a  superficial  coating 
of  carbonate  of  protoxide  of  lead.  (Christison.)  Its  sp.  gr.  is  11*381.  It  is 
soft,  flexible,  and  inelastic.  It  is  both  malleable  and  ductile,  possessing  the 
former  property  in  particular  to  a  considerable  extent.  In  tenacity,  it  is  inferior 
to  all  ductile  metals.  It  fuses  at  about  612°,  and  when  slowly  cooled  forms 
octohedral  crystals.  It  may  be  heated  to  whiteness  in  close  vessels  without 
subliming. 

Lead  absorbs  oxygen  quickly  at  high  temperatures.  When  fused  in  open 
vessels,  a  grey  film  is  formed  upon  its  surface,  which  is  a  mixture  of  metallic 
lead  and  protoxide  ;  and  when  strongly  heated,  it  is  dissipated  in  fumes  of  the 
protoxide.  In  distilled  water,  previously  boiled  and  preserved  in  close  vessels, 
it  undergoes  no  change ;  but  in  open  vessels  it  is  oxidized  with  considerable 
rapidity,  yielding  minute,  shining,  brilliantly  white,  crystalline  scales  of  car- 
bonate of  the  protoxide,  the  oxygen  and  carbonic  acid  being  derived  from  the 
air.  The  presence  of  saline  matter  in  water  retards  the  oxidation  of  the  lead ; 
and  some  salts,  even  in  very  minute  quantity,  prevent  it  altogether.  The  pro- 
tecting influence,  exerted  by  certain  substances,  was  first  noticed  by  Guyton 
Morveau ;  but  it  has  been  minutely  investigated  by  Christison  of  Edinburgh, 
who  has  discussed  the  subject  in  his  excellent  Treatise  on  Poisons.  He  finds 
that  the  preservative  power  of  neutral  salts  is  materially  connected  with  the  inso- 
lubility of  the  compound  which  their  acid  is  capable  of  forming  with  lead.  Thus, 
phosphates  and  sulphates,  as  well  as  chlorides  and  iodides,  are  highly  preserva- 
tive ;  so  small  a  quantity  as  1 -30,000th  part  of  phosphate  of  soda  or  iodide  of 
potassium  in  distilled  water  preventing  the  corrosion  of  lead.  In  a  preservative 
solution  the  metal  gains  weight  during  some  weeks,  in  consequence  of  its  surface 
gradually  acquiring  a  superficial  coating  of  carbonate,  which  is  slowly  decom- 
posed by  the  saline  matter  of  the  solution.  The  metallic  surface  being  thus 
covered  with  an  insoluble  film,  which  adheres  tenaciously,  all  further  change 
ceases.  Many  kinds  of  spring  water,  owing  to  the  salts  which  they  contain,  do 
not  corrode  lead  ;  and  hence,  though  intended  for  drinking,  it  may  be  safely  col- 
lected in  leaden  cisterns.  Of  this,  the  water  of  Edinburgh  is  a  remarkable 
instance. 

Lead  is  not  attacked  by  the  hydrochloric  or  the  vegetable  acids,  though  their 
presence,  at  least  in  some  instances,  accelerates  the  absorption  of  oxygen  from 
the  atmosphere  in  the  same  manner  as  with  copper.  Cold  sulphuric  acid  does 
not  act  upon  it ;  but  when  boiled  in  that  liquid,  the  lead  is  slowly  oxidized 
at  the  expense  of  the  acid.  The  only  proper  solvent  for  lead  is  nitric  acid. 
This  reagent  oxidizes  it  rapidly,  and  forms  with  its  oxide  a  salt  which  crystal- 
lizes in  opaque  octohedrons  by  evaporation. 

From  my  experiments  on  the  composition  of  the  protoxide  of  lead,  and  of  the 
nitrate  and  sulphate  of  that  oxide,  I  have  deduced  103-6  as  the  eq.  a  number 
which  agrees  very  closely  with  the  researches  of  Berzelius  on  the  same  subject. 


360 


LEAD. 


(Phil.  Trans.  1833,  part  ii.)    Its  symb.  is  Pb.    The  composition  of  its  com- 
pounds described  in  this  section  is  as  follows  :— 


Lead. 

Equiv. 

Formula;. 

Dinoxide 

?e7-2    2  eq.  -|-. Oxygen 

8 

1  eq.  =  215-2 

2Pb  -j-  0  or  PbjO. 

Protoxide 

103-6     1  eq.  -f      ... 

.      8 

1  eq.  =  111-6 

Pb  t  0  or  PbO. 

Sesquioxide 

207-2    2eq.  +       .    .     . 

.    24 

3  eq.  =  231-2 

2Pb  f  30  or  PbjOs. 

Peroxide 

103-6     1  eq.  t      ... 

,    16 

J?eq.  =  119-6 

Pb  4  20  or  PbOg. 

Red  Oxide 

;310-8    3  eq. -f       .    .    . 
torProtoi.  223-2  or2  eq.  -f- 

•    3'          ^^^•^342-8 
Peroi.  119-6  leq.) 

,    f3Pb-f-40. 
'   j2Pb0-t-Pb02. 

Chloride 

103-6     1  eq.  -|-  Chlorine 

35-42 

1  eq.  =  139-02 

Pb  -j-  CI. 

Iodide 

103'6    1  eq. -f-  Iodine 

1263 

leq.  =  229-9 

Pb-j-L 

Bromide 

103-6     1  eq.  -j-  Bromine 

78-4 

1  eq.  =  182 

Pb  -j-  Br. 

Fluoride 

103-6     1  eq.  -j-  Fluorine 

18-68 

1  eq.  =  122-28 

Pb  +  F. 

Sulphuret 

103-6     leq.  +  Sulphur 

16-1 

1  eq.  =  119-7 

Pb  +  S. 

Phosphuret 
'Carburet 

>  Composition  uncertain. 

Dinoxide  of  Lead. — ^Dulong  observed  that  on  heating  dry  oxalate  of  protoxide 
of  lead  in  a  glass  tube  to  low  redness,  air  being  excluded,  a  mixture  of  carbonic 
acid  and  carbonic  oxide  gases  is  evolved,  and  a  suboxide  remains  of  a  dark  grey, 
nearly  black,  colour.  Boussingault  has  lately  proved  that  it  is  a  dinoxide.  It 
does  not  unite  with  acids,  but  is  resolved  by  them  into  a  salt  of  the  protoxide 
with  separation  of  metallic  lead.  (An.  de  Ch.  et  Ph.  liv.  263.)  Its  eq.  is  215-2; 
symh.  2Pb  -f  0,  or  Pb  O. 

Protoxide. — Prep. — This  oxide  is  prepared  on  a  large  scale  by  collecting  the 
grey  film  which  forms  on  the  surface  of  melted  lead,  and  exposing  it  to  heat  and 
air  until  it  acquires  a  uniform  yellow  colour.  In  this  state  it  is  the  massicot  of 
commerce ;  and  when  partially  fused  by  heat  the  term  litharge  is  applied  to  it. 
As  thus  procured  it  is  always  mixed  with  the  red  oxide.  It  may  be  obtained 
pure  by  adding  ammonia  to  a  cold  solution  of  nitrate  of  protoxide  of  lead  until  it 
is  faintly  alkaline,  washing  the  precipitated  subnitrate  with  cold  water,  and  when 
dry,  heating  it  to  moderate  redness  for  an  hour  in  a  platinum  crucible.  An  open 
fire  should  be  used,  and  great  care  taken  to  prevent  combustible  matter  in  any 
form  from  contact  with  the  oxide. 

Prop. — It  is  red  while  hot,  but  has  a  rich  lemon-yellow  colour  when  cold,  is 
insoluble  in  water,  fuses  at  a  bright  red  heat,  and  is  fixed  and  unchangeable  in 
the  fire.  Its  sp.  gr.  is  9-4214.  The  fused  protoxide  has  a  highly  foliated  tex- 
ture, and  is  very  tough,  so  as  to  be  pulverized  with  difficulty.  By  transmitted 
light  it  is  yellow ;  but  by  reflected  light  it  appears  green  in  some  parts  and  yel- 
low in  others.  Heated  with  combustible  matters  it  parts  with  ox)'^gen,  and  is 
reduced.  From  its  insolubility  it  does  not  change  the  vegetable  colours  under 
common  circumstances ;  but  when  rendered  soluble  by  a  small  quantity  of  acetic 
acid,  it  has  a  distinct  alkaline  reaction.  It  unites  with  acids,  and  is  the  base  of 
all  the  salts  of  lead,  most  of  which  are  of  a  white  colour,  and  isomorphous  with 
the  salts  of  baryta  and  strontia.  From  its  solutions  it  is  precipitated  by  pure 
alkalies  as  a  white  hydrate,  which  is  redissolved  by  potassa  in  excess  ;  as  a  white 
carbonate,  which  is  the  well-known  pigment  white  lead^  by  alkaline  carbonates; 
as  a  white  sulphate  by  soluble  sulphates ;  as  a  dark  brown  sulphuret  by  hydro- 
sulphuric  acid ;  and  as  yellow  iodide  of  lead  by  hydriodic  acid  or  iodide  of  potas- 
eium. 


LEAD.  361 

With  regard  to  the  poisonous  property  of  the  salts  of  lead,  a  remarkable  fact 
has  been  observed  by  my  colleague  Dr.  A.  T.  Thomson,  who  has  proved  that  of 
all  the  ordinary  preparations  of  lead,  the  carbonate  is  by  far  the  most  virulent 
poison.  Any  salt  of  lead  which  is  easily  convertible  into  the  carbonate,  as  for 
instance  the  subacetate,  is  also  poisonous ;  but  he  has  given  large  doses  of  the 
nitrate  of  the  protoxide  and  chloride  of  lead  to  rabbits  without  producing  percep- 
tible inconvenience.  He  finds  that  acetate  of  protoxide  of  lead,  mixed  with 
vinegar  to  prevent  the  formation  of  any  carbonate,  may  be  freely  and  safely  ad- 
ministered in  medical  practice. 

The  best  method  of  detecting  the  presence  of  lead  in  wine  or  other  suspected 
mixed  fluids  is  by  means  of  hydrosulphuric  acid.  The  sulphuret  of  lead,  after 
being  collected  on  a  filter  and  washed,  is  to  be  digested  in  nitric  acid  diluted  with 
twice  its  weight  of  water,  until  the  dark  colour  of  the  sulphuret  disappears.  The 
solution  of  the  nitrate  should  then  be  brought  to  perfect  dryness  on  a  watch-glass, 
in  order  to  expel  the  excess  of  nitric  acid,  and  the  residue  be  redissolved  in  a 
small  quantity  of  cold  water.  On  dropping  a  particle  of  iodide  of  potassium  into 
a  portion  of  this  liquid,  yellow  iodide  of  lead  will  instantly  appear. 

Protoxide  of  lead  unites  readily  with  earthy  substances,  forming  with  them  a 
transparent  colourless  glass.  Owing  to  this  property  it  is  much  employed  for 
glazing  earthenware  and  porcelain.  It  enters  in  large  quantity  into  the  composi- 
tion of  flint  glass,  which  it  renders  more  fusible,  transparent,  and  uniform.      0 

Lead  is  separated  from  its  salts  in  the  metallic  state  by  iron  or  zinc.  The  best 
way  of  demonstrating  this  fact  is  by  dissolving  one  part  of  acetate  of  protoxide 
of  lead  in  24  of  water,  and  suspending  a  piece  of  zinc  in  the  solution  by  means 
of  a  thread.  The  lead  is  deposited  upon  the  zinc  in  a  peculiar  arborescent  form, 
giving  rise  to  the  appearance  called  arbor  saturni. 

Its  eq,  is  IIVG ;  symh.  Pb  +  O,  Pb,  or  PbO. 

Bed  Oxide. — Prep. — This  compound,  the  minium  of  commerce,  is  employed  as 
a  pigment,  and  in  the  manufacture  of  flint  glass.  It  is  formed  by  oxidizing  lead 
by  heat  and  air  without  allowing  it  to  fuse,  and  then  exposing  it  in  open  vessels 
to  a  temperature  of  600°  or  700°,  while  a  current  of  air  plays  upon  its  surface. 
It  slowly  absorbs  oxygen  and  is  converted  into  minium. 

Prop. — This  oxide  does  not  unite  with  acids.  When  heated  to  redness,  it 
gives  oflf  pure  oxygen  gas,  and  is  reconverted  into  the  protoxide.  When  digested 
in  nitric  acid  it  is  resolved  into  protoxide  and  peroxide  of  lead,  the  former  of 
which  unites  with  the  acid,  while  the  latter  remains  as  an  insoluble  powder. 
From  the  facility  with  which  this  change  is  efiected  even  by  acetic  acid,  most 
chemists  consider  red  lead,  not  so  much  as  a  definite  compound  of  lead  and  oxy- 
gen, but  as  a  salt  composed  of  the  protoxide  and  peroxide,  as  stated  at  page  360. 
This  oxide  has  been  long  considered  as  a  sesquioxide,  an  error  first  corrected  by 
Dalton  (New  System  of  Chemistry,  ii.  41),  whose  observation  has  been  con- 
firmed by  Dumas  and  Phillips.  (An.  de  Ch.  et  Ph.  xlix.  398,  and  Phil.  Mag. 
N.  S.  iii.  125.)  Dumas  shows  that  the  minium  is  not  uniform  in  composition, 
but  consists  of  variable  mixtures  of  the  protoxide  with  real  red  lead.  The  former 
may  be  oxidized  by  continued  exposure  to  air  and  heat,  and  may  be  dissolved  by 
acetic  acid  very  much  diluted  with  cold  water. 

Its  eq.  is  342-8 ;  symb.  2  PbO  +  PbOj. 

Sesquioxide. — Winkelblech  (Ann.  der  Pharm.  xxi.  29)  has  proved  the  existence 
of  this  compound.    It  is  prepared  by  adding  hypochlorite  of  soda  to  a  solution  of 


362  LEAD* 

protoxide  of  lead  in  caustic  potash.  It  forms  a  reddisli-yellow  insoluble  powder, 
which  is  resolved  by  heat  and  by  acids  into  protoxide  and  oxygen.  Its  eg.  is 
231*2 ;  si/mb,  PbaOg.  Red  lead  may  be  a  compound  of  1  at.  sesquioxide  and  1  at. 
protoxide,  Pb^Og,  PbO  =  PbaO^. 

Peroxide, — Prep, — This  oxide  may  be  obtained  by  the  action  of  nitric  acid  on 
minium,  as  just  mentioned ;  by  fusing  protoxide  of  lead  with  chlorate  of  potassa, 
at  a  temperature  short  of  redness,  and  removing  the  chloride  of  potassium  by  so- 
lution in  water;  and  by  transmitting  a  current  of  chlorine  gas  through  a  solution 
of  acetate  of  the  protoxide  of  lead,  or  the  protoxide  suspended  in  water.  In  the 
last  the  reaction  is  such,  that 

1  eq.  Chlorine  and  2  eq.  Protoz.  Lead  "B   1  eq.  Perox.  Lead  and  1  eq.  Chloride  Lead 
CI  2Pba  -2  pbOa  PbCl. 

The  chloride  is  removed  by  washing  with  warm  water. 

Prep. — It  is  of  a  puce  colour,  is  insoluble  in  water,  and  is  resolved  by  strong 
ox-acids,  such  as  the  sulphuric  and  nitric,  into  a  salt  of  the  protoxide  and  oxygen 
gas.  With  hydrochloric  acid  it  yields  chlorine  gas  and  chloride  of  lead.  At  a 
red  heat  it  emits  oxygen  gas  and  is  converted  into  the  protoxide. 

Its  eq.  is  119-6;  symJ.  Pb  -f-  20,  Pb,  or  PbO^. 
%Chioride  of  Lead. — ^This  compound,  sometimes  called  horn  lead,  is  slowly 
formed  by  the  action  of  chlorine  gas  on  thin  plates  of  lead,  and  may  be  obtained 
more  easily  by  adding  hydrochloric  acid  or  a  solution  of  sea-salt  to  acetate  or 
nitrate  of  oxide  of  lead  dissolved  in  water.  This  chloride  dissolves  to  a  consi- 
derable extent  in  hot  water,  especially  when  acidulated  with  hydrochloric  acid, 
and  separates  on  cooling  in  small  acicular  anhydrous  crystals  of  a  white  colour. 
It  fuses  at  a  temperature  below  redness,  and  forms  as  it  cools  a  semi-transparent 
mass,  which  has  a  density  of  5*133.  It  bears  a  full  red  heat  in  close  vessels 
without  subliming ;  but  in  open  vessels  it  smokes  from  spurious  evaporation, 
loses  some  of  its  chlorine  and  absorbs  oxygen,  yielding  an  oxychloride  of  a  yel- 
low colour.  [It  combines  in  several  proportions  with  oxide  of  lead  and  forms  a 
number  of  basic  compounds — as  the  bibasic  chloride  PbCl  -|-  2PbO  a  crystalline 
mineral  found  in  Somersetshire,  England.  The  iribasic  chloride  of  lead  PbCl  -|- 
3PbO  -f-  3H0,  precipitated  by  ammonia  from  a  solution  of  chloride  of  lead ;  and 
the  surbasic  chloride  of  lead  formed  by  digesting  1  part  of  common  salt  with  7 
parts  of  oxide  of  lead,  and  fusing  the  resulting  oxichloride.  In  this  form  it  con- 
stitutes a  beautiful  yellow  pigment,  known  as  Turner's  patent  yellow.]  Its  eq. 
is  139-02 ;  symb.  Pb  -\-  CI,  or  PbCl. 

Iodide  of  Lead  is  easily  formed  by  mixing  a  solution  of  hydriodic  acid  in  excess 
with  the  nitrate  of  protoxide  of  lead  dissolved  in  water;  and  it  is  of  a  rich  yellow 
colour.  It  is  dissolved  by  boiling  water,  forming  a  colourless  solution,  and  is 
deposited  on  cooling  in  yellow  crystalline  scales  of  a  brilliant  lustre. 

Its  eq.  is  229*9 ;  symb.  Pb  +  I,  or  Pbl. 

Bromide  of  Lead. — It  falls  as  a  white  crystalline  powder,  of  sparing  solubility 
in  water,  when  a  soluble  salt  of  lead  is  mixed  with  bromide  of  potassium  in  so- 
lution. Exposed  to  heat  it  fuses  into  a  red  liquid  which  becomes  yellow  when 
cold. 

Its  eq.  is  182 ;  symb.  Pb  -\-  Br,  or  PbBr. 

Fluoride  of  Lead  is  formed  by  mixing  hydrofluoric  acid  with  acetate  of  protox- 
ide of  lead,  and  falls  as  an  uncrystalline  white  powder  of  very  sparing  solubi- 


ARSENIC.  363 

lity.  It  is  soluble  in  nitric  and  hydrochloric  acids,  but  is  decomposed  whfen  the 
solution  is  evaporated. 

Its  eq.  is  122-28  ;  symh.  Pb  +  F,  or  PbF. 

Sulphureis  of  Lead. — It  is  probable  that  lead  unites  with  sulphur  in  several  dif- 
ferent proportions ;  but  the  only  one  of  these  compounds  well  known  to  chemists 
in  the  native  sulphuret,  galena,  which  occurs  in  cubic  crystals,  or  in  forms  allied 
to  the  cube.  It  may  be  formed  artificially  by  fusing  lead  with  sulphur,  or  by  the 
action  of  hydrosulphuric  acid  on  a  salt  of  lead. 

Its  eq.  is  119-7 ;  symb.  Pb  -f  S,  or  PbS. 

Phosphuret  of  Lead  has  been  little  examined.  It  may  be  formed  by  heating  phos- 
phate of  oxide  of  lead  with  charcoal,  by  mixing  a  solution  of  phosphorus  in  alco- 
hol or  ether  with  the  solution  of  a  salt  of  lead,  or  by  the  action  of  phosphuretted 
hydrogen  on  a  similar  solution. 

Carburet  of  Lead  may  be  obtained  by  reducing  oxide  of  lead  in  a  state  of  fine 
division  and  intimate  admixture  with  charcoal.  It  is  also  generated,  when  salts 
of  lead,  which  contain  a  vegetable  acid,  are  decomposed  by  heat  in  close  vessels. 
(Berzelius.) 


SECTION  XVII. 


ARSENIC. 


Hist,  and  Prep. — Metallic  arsenic  sometimes  occurs  native  but  more  fre- 
quently it  is  found  in  combination  with  other  metals,  and  especially  with  cobalt 
and  iron.  On  roasting  these  arsenical  ores  in  a  reverberatory  furnace,  the  arsenic, 
from  its  volatility,  is  expelled,  combines  with  oxygen  as  it  rises,  and  condenses 
into  thick  cakes  on  the  roof  of  the  chimney.  The  sublimed  mass,  after  being 
purified  by  a  second  sublimation,  is  the  virulent  poison  known  by  the  name  of 
arsenic  or  white  oxide  of  arsenic.  From  this  substance  the  metal  itself  is  procured 
by  heating  it  with  charcoal.  The  most  convenient  process  is  to  mix  the  white 
oxide  with  about  twice  its  weight  of  black  flux,  and  expose  the  mixture  to  a  red 
heat  in  a  hessian  crucible,  over  which  is  luted  an  empty  crucible  for  receiving 
the  metal.  The  reduction  is  easily  eflfected,  and  metallic  arsenic  collects  in  the 
upper  crucible,  which  should  be  kept  cool  for  the  purpose  of  condensing  the 
vapour. 

Prop. — An  exceedingly  brittle  metal,  of  a  strong  metallic  lustre,  and  white 
colour,  running  into  steel  grey.  Its  structure  is  crystalline,  and  when  slowly 
sublimed  it  is  said  to  crystallize  in  rhomb ohedrons.  Its  sp.  gr.  is  5-8843.  When 
heated  to  356°  it  sublimes  without  previously  liquefying ;  for  its  point  of  fusion 
is  far  above  that  of  its  sublimation,  and  has  not  hitherto  been  determined.  Its 
vapour  has  a  strong  odour  of  garlic  ;  a  property  which  affords  a  distinguishing 
character  for  metallic  arsenic,  as  it  is  not  possessed  by  any  other  metal,  with  the 
exception  perhaps  of  zinc,  which  is  said  to  emit  a  similar  odour  when  thrown  in 
powder  on  burning  charcoal,  an  effect,  however,  most  probably  due  to  the  pre- 
sence of  arsenic  in  the  zinc.     In  close  vessels  it  may  be  sublimed  without 


364 


ARSENIC. 


change;  but  if  atmospheric  air  be  admitted,  it  is  rapidly  converted  into  the  white 
oxide.  According  to  Hahneman  it  is  slowly  oxidized  and  dissolved  by  being 
boiled  in  water.  In  general  it  speedily  tarnishes  by  exposure  to  air  and  moisture, 
acquiring  upon  its  surface  a  dark  film  which  is  extremely  superficial ;  but  Ber- 
zelius  remarks  that  he  has  kept  some  specimens  in  open  vessels  for  years  with- 
out loss  of  lustre,  while  others  are  oxidized  through  their  whole  substance,  and 
fall  into  powder.  It  has  lately  been  suggested  (Liebig's  Annalen,  1840),  that 
this  effect  is  owing  to  the  presence  of  potassium,  derived  from  the  black  flux. 
The  arsenic  sublimed  from  the  cakes  which  occur  in  commerce  is  permanent  in 
the  air.  The  product  of  this  spontaneous  oxidation,  which  is  known  abroad 
under  the  name  oijly  powder^  is  supposed  by  Berzelius  to  be  an  oxide ;  but  it  is 
more  generally  regarded  as  a  mixture  of  white  oxide  and  metallic  arsenic. 

The  eq.  of  arsenic,  as  inferred  by  Berzelius  from  the  composition  of  arsenious 
and  arsenic  acids,  is  37*7.  Its  symb.  is  As.  The  compounds  of  this  metal  de- 
scribed in  this  section  are  thus  constituted : — 


Arsenic. 

Equiv. 

Formulae. 

Arsenious  Acid 

75-4 

2  eq.-|- Oxygen 

24 

3  eq.=:  99-4 

2A8t30orA8203. 

Arsenic  Acid 

75-4 

2  eq.-fdo. 

40 

6  eq.=115-4 

2A8-J-60  or  AS2O6. 

Protochloride 

37-7 
75-4 

1  eq. -J- Chlorine 

35-42 

1  eq.=  73-12 
3  eq.=181-66 

As-f  CI  or  AsCl. 

Sesquichloride 

2  eq.+do. 

106-26 

2AS+3C1  or  A82CIS. 

Periodide 

75-4 

2  eq.+Iodine 

631.5 

5  eq.=706-9 

2As4-5I  or  Asjls. 

Sesquibromide 

75-4 

2  eq.-f-Bromine 

235-2 

3  eq.=313-6 

2A8-f-3Bror  AsjBrj. 

Protohydaret 

37-7 

1  eq.+Hydrogen    1 

1  eq.=  38-7 

As+H  or  AsH. 

Arseniur.  Hydro. 

75-4 

2  eq.+do. 

3 

3  eq.=  78-4 

2A8-I-3H  or  AsjHs. 

Protosulphuret 

37-7 

1  eq.-}-Sulphur 

16-1 

1  eq.=  53-8 

As-f-S  or  AsS. 

Sesquisulphuret 

75-4 

2  eq.+do. 

483 

3  eq.=123-7 

2A8-I-3S  or  A82S3. 

Persulphuret 

75-4 

2  eq.+do. 

80-5 

5  eq,=155-9 

2A8-f5S  or  AsaS,. 

Arsenious  Acid, — Prep. — This  compound,  frequently  called  white  arsenic  and 
white  oxide  of  arsenic^  is  always  generated  when  arsenic  is  heated  in  open  ves- 
sels, and  may  be  prepared  by  digesting  the  metal  in  dilute  nitric  acid.  The 
white  arsenic  of  commerce  is  derived  from  the  native  arseniurets  of  cobalt,  being 
sublimed  during  the  roasting  of  these  ores  for  the  preparation  of  zaffre,  and  it  is 
purified  by  a  second  sublimation  in  iron  vessels. 

Prop. — It  is  commonly  sold  in  the  state  of  a  fine  white  powder;  but  when  first 
sublimed,  it  is  in  the  form  of  brittle  masses,  more  or  less  transparent,  colourless, 
of  a  vitreous  lustre,  and  conchoidal  fracture.  This  glass,  which  may  also  be  ob- 
tained by  fusion,  gradually  becomes  opaque  without  undergoing  any  apparent 
change  of  constitution,  either  with  respect  to  water  or  any  other  substance  ;  but 
the  change  is  certainly  promoted  by  exposure  to  the  atmosphere.  Its  sp.  gr.  is 
3'7.  At  380°  it  is  volatilized,  yielding  vapours  which  do  not  possess  the  odour 
of  garlic,  and  which  condense  unchanged  on  cold  surfaces.  Its  point  of  fusion 
is  rather  higher  than  that  at  which  it  sublimes ;  and  therefore,  in  order  to  be  fused, 
it  must  either  be  heated  under  pressure,  or  its  temperature  be  suddenly  raised 
above  380°.  Arsenious  acid  is  dimorphous,  that  is,  susceptible  of  assuming  two 
crystalline  forms  belonging  to  different  systems  of  crystallization.  By  slow 
sublimation  in  a  glass  tube  it  is  always  obtained  in  distinct  octohedral  crystals 
of  adamantine  lustre  and  perfectly  transparent.  Its  unusual  form  is  that  of  six- 
sided  scales  derived  from  a  rhombic  prism,  and  was  first  lately  found  by  Wohler 
among  the  products  in  a  manufacture  of  smalt :  the  conditions  for  enabling  it  to 


ARSENIC.  355 

assume  this  form  are  unknown,  and  by  subliming  the  crystals,  they  crystallized 
in  octohedrons.     (An.  de  Ch.  et  Ph.  li.  201.) 

The  taste  of  arsenious  acid  is  stated  differently  by  different  persons.  It  is 
prevalently  thought  to  be  acrid  ;  but  I  am  satisfied  from  personal  observation  that 
it  may  be  deliberately  tasted  without  exciting  more  than  a  very  faint  impression 
of  sweetness,  and  perhaps  of  acidity.  The  acrid  taste  ascribed  to  it  has  probably 
been  confounded  with  the  local  inflammation,  by  which  its  application,  if  of  some 
continuance,  is  followed.  (Christison  on  Poisons.)  It  reddens  vegetable  blue 
colours  feebly,  an  effect  which  is  best  shown  by  placing  the  acid  in  powder  on 
moistened  litmus  paper.  It  combines  with  salifiable  bases,  forming  salts  which 
are  termed  arsenites. 

According  to  the  experiments  of  Klaproth  and  Bucholz,  1000  parts  of  boiling 
water  dissolve  77*75  of  arsenious  acid ;  and  the  solution,  after  having  cooled  to 
60°  F.,  contains  only  30  parts.  The  same  quantity  of  water  at  60°,  when  mixed 
with  the  acid  in  powder,  dissolves  only  two  parts  and  a  half.  Guibourt  has 
lately  observed  that  the  transparent  and  opaque  varieties  of  arsenic  differ  in  solu- 
bility. He  found  that  1000  parts  of  temperate  water  dissolve,  during  36  hours, 
9-Q  of  the  transparent,  and  12-5  of  the  opaque  variety:  that  the  same  quantity  of 
boiling  water  dissolves  97  parts  of  the  transparent  variety,  retaining  18  when 
cold,  but  takes  up  115  of  the  opaque  variety,  and  retains  29  on  cooling.  By  the 
presence  of  organic  substances,  such  as  milk  or  tea,  its  solubility  is  materially 
impaired.     (Christison  on  Poisons.) 

When  metallic  arsenic  is  sharply  heated  with  hydrate  of  potassa,  pure  hydrogen 
gas  is  evolved,  and  a  mass  is  left  consisting  of  arseniuret  of  potassium  and  arsenite 
of  potassa  ;  facts,  which  prove  that  a  portion  of  arsenic  is  oxidized,  and  derives 
its  oxygen  partly  from  water  and  partly  from  potassa.  If  the  heat  is  raised  to  red- 
ness, the  arsenious  acid  is  resolved  into  arsenic  acid  and  metal,  the  former  remain- 
ing as  an  arseniate,  while  the  latter  is  expelled.  Similar  phenomena  ensue  with 
the  hydrates  of  soda,  baryta,  and  lime ;  except  that  with  the  two  latter  no  arsenic 
acid  is  produced.     (Soubeiran  in  An.  de  Ch.  et  Ph.  xliii.  410.) 

Its  eq.  99-4 ;  symh.  2As  f  30,  As,  or  As^Og. 

The  frequent  exhibition  of  arsenious  acid  as  a  poison  renders  the  detection  of 
this  compound  an  object  of  great  importance  to  medical  practitioners  as  well  as 
to  the  chemist.  In  this  as  in  all  similar  inquiries,  the  object  to  be  held  in  view 
is  the  discovery  of  a  few  decisive  characters,  by  means  of  which  the  poison  may 
be  distinguished  from  all  other  bodies,  and  when  present  but  in  small  quantity, 
either  in  pure  water,  or  in  any  fluids  likely  to  be  met  with  in  the  stomach,  may 
with  certainty  be  detected.  The  attention  should  be  fixed  on  one  or  ^o  tests 
of  admitted  value,  and  all  others  be  set  aside.  With  this  feeling  I  shall  indicate 
the  mode  of  applying  the  four  principal  tests,  namely,  the  ammonio-nitrate  of 
silver,  ammonio-sulphate  of  copper,  hydrosulphuric  acid,  and  hydrogen  gas. 

1.  Ammonio-nitrate  of  Silver. — Arsenious  acid  is  not  precipitated  by  nitrate  of 
oxide  of  silver  unless  an  alkali  is  present,  to  neutralize  the  nitric  acid.  Ammonia 
is  commonly  employed  for  the  purpose ;  but  as  arsenite  of  oxide  of  silver  is  very 
soluble  in  ammonia,  an  excess  of  the  alkali  would  retain  the  arsenite  in  solution. 
To  remedy  this  inconvenience,  Hume,  of  Long  Acre,  proposed  to  employ  the 
ammoniacal  nitrate  of  silver,  which  is  made  by  dropping  ammonia  into  a  rather 
strong  solution  of  lunar  caustic  till  the  oxide  of  silver  at  first  thrown  down  is 
nearly  all  dissolved.    The  liquid  thus  prepared  contains  the  precise  quantity  of 


366  ARSENIC.  • 

ammonia  which  is  required  ;  and  when  mixed  with  arsenious  acid,  two  neutral 
salts  result,  the  soluble  nitrate  of  ammonia,  and  the  insoluble  yellow  arsenite  of 
oxide  of  silver.  Ammoniacal  nitrate  of  silver  likewise  diminishes  the  risk  of 
fallacy  that  might  arise  from  the  presence  of  phosphoric  acid.  Phosphate  of 
oxide  of  silver  is  so  very  soluble  in  ammonia,  that  when  a  neutral  phosphate  is 
mixed  with  the  ammoniacal  nitrate  of  silver,  the  resulting  phosphate  is  held 
almost  entirely  in  solution  by  the  free  ammonia. 

This  test,  however,  even  in  its  improved  state,  is  still  liable  to  objection.  For 
when  arsenious  acid  in  small  proportion  is  mixed  with  sea  salt,  or  animal  and 
vegetable  infusions,  the  arsenite  of  oxide  of  silver  either  does  not  subside  at  all, 
or  is  precipitated  in  so  impure  a  state  that  its  characteristic  colour  cannot  be 
distinguished.  Several  methods  have  been  proposed  for  obviating  this  source  of 
fallacy ;  but  Christison  has  shown,  that  this  test,  taken  singly,  cannot  be  relied 
on  in  practice. 

2.  Ammonio-sulphaie  cf  copper,  which  is  made  by  adding  ammonia  to  a  solu- 
tion of  sulphate  of  oxide  of  copper  until  the  precipitate  at  first  thrown  down  is 
nearly  all  redissolved,  occasions  with  arsenious  acid  a  green  precipitate,  which 
,  has  been  long  used  as  a  pigment  under  the  name  of  ScheeWs  green.  This  test, 
though  well  adapted  for  detecting  arsenious  acid  dissolved  in  pure  water,  is 
very  fallacious  when  applied  to  mixed  fluids.  Christison  has  proved  that  am- 
moniacal sulphate  of  copper  produces  in  some  animal  and  vegetable  infusions, 
containing  no  arsenic,  a  greenish  precipitate,  which  may  be  mistaken  for 
Scheele's  green:  whereas  in  other  mixed  fluids,  such  as  tea  and  porter,  to 
which  arsenic  has  been  previously  added,  it  occasions  none  at  all,  if  the  arseni- 
ous acid  is  in  small  quantity.  In  some  of  these  liquids,  a  free  vegetable  acid  is 
doubtless  the  solvent;  for  arsenite  of  oxide  of  copper  is  also  dissolved  by  tannic 
acid,  and  perhaps  by  other  vegetable  as  well  as  some  animal  principles. 

3.  When  a  current  of  hydrosulphuric  acid  gas  is  conducted  through  a  solution 
of  arsenious  acid,  the  fluid  immediately  acquires  a  yellow  colour,  and  in  a  short 
time  becomes  turbid,  owing  to  the  formation  of  orpiment,  the  sesquisulphuret 
of  arsenic.  The  precipitate  is  at  first  partially  suspended  in  the  liquid  ;  but  as 
soon  as  free  hydrosulphuric  acid  is  expelled  by  heating  the  solution,  it  subsides 
perfectly,  and  may  easily  be  collected  on  a  filter.  One  condition,  however, 
must  be  observed  in  order  to  ensure  success,  namely,  that  the  liquid  does  not 
contain  a  free  alkali ;  for  sulphuret  of  arsenic  is  dissolved  with  remarkable 
facility  by  pure  potassa  or  ammonia.  To  avoid  this  fallacy,  it  is  necessary  to 
acidulate  the  solution  with  a  little  acetic  or  hydrochloric  acid.  Hydrosulphuric 
acid  likewise  acts  on  arsenic  in  all  vegetable  and  animal  fluids  if  previously 
boiled,  filtered,  and  acidulated. 

But  it  does  not  necessarily  follow,  because  hydrosulphuric  acid  causes  a  yel- 
low precipitate,  that  arsenic  is  present ;  since  there  are  not  less  than  four  other 
substances,  namely,  selenium,  cadmium,  tin,  and  antimony,  the  sulphurets  of 
which,  judging  from  their  colour  alone,  might  possibly  be  mistaken  for  orpi- 
ment. From  these  and  all  other  substances  whatever,  the  sulphuret  of  arsenic 
may  be  thus  distinguished. — On  drying  the  sulphuret,  mixing  it  with  black  flux, 
and  heating  the  mixture  contained  in  a  glass  tube  to  redness  by  means  of  a 
spirit-lamp,  decomposition  ensues,  and  a  metallic  crust  of  an  iron-grey  colour 
externally,  and  crystalline  on  its  inner  surface,  is  deposited  on  the  cool  part  of 
the  tube.  This  character  alone  is  quite  satifactory ;  but  it  is  easy  to  procure 
additional  evidence,  by  reconverting  the  metal  into  arsenious  acid,  so   as  to 


ARSENIC.  367 

obtain  it  in  the  form  of  resplendent  octohedral  crystals.  This  is  done  by  holding 
that  part  of  the  tube  to  which  the  arsenic  adheres  about  three-fourths  of  an  inch 
above  a  very  small  spirit-lamp  flame,  so  that  the  metal  may  be  slowly  sublimed. 
As  it  rises  in  vapour,  it  combines  with  oxygen,  and  is  deposited  in  crystals 
within  the  tube.  The  character  of  these  crystals  with  respect  to  volatility,  lustre, 
transparency,  and  form,  is  so  exceedingly  well  marked,  that  a  practised  eye  may 
safely  identify  them,  though  their  weight  should  not  exceed  the  100th  part  of  a 
grain.    This  experiment  does  not  succeed  unless  the  tube  be  quite  clean  and  dry. 

The  only  circumstance  which  occasions  a  difficulty  in  the  preceding  process, 
is  the  presence  of  organic  substances,  which  cause  the  precipitate  to  subside 
imperfectly,  render  filtration  tedious,  and  froth  up  inconveniently  during  the 
reduction.  Hence,  if  so  abundant  as  materially  to  impede  filtration  and  prevent 
the  liquid  from  becoming  clear,  they  should  be  removed  before  hydrosulphuric 
acid  is  employed.  This  is  often  sufficiently  efiiBcted  by  acidulating  with  acetic 
acid,  by  which  caseous  and  albuminous  substances  are  coagulated ;  but  a  more 
complete  separation  is  accomplished  by  evaporating  the  solution  at  a  moderate 
heat  to  dryness,  redissolving  anew  by  boiling  successive  portions  of  distilled 
water  on  the  residue,  and  then  filtering  the  solution  after  it  has  cooled.  Most 
of  the  organic  matters  are  thus  rendered  insoluble.  It  is  of  course  necessary 
towards  the  close  of  the  desiccation  to  guard  against  too  high  a  temperature, 
since  otherwise  the  arsenic  itself  might  be  expelled.  (Christison  on  Poisons, 
2nd  edition,  252). 

The  black  flux  employed  in  the  processes  for  reducing  arsenic,  is  prepared  by 
deflagrating  a  mixture  of  bitartrate  of  potassa  with  rather  less  than  half  its 
weight  of  nitre.  The  nitric  and  tartaric  acids  undergo  decomposition,  and  the 
solid  product  is  charcoal  derived  from  tartaric  acid,  and  pure  carbonate  of  potassa. 
As  it  contains  a  deliquescent  salt,  it  should  be  kept  in  well-stopped  bottles. 
When  this  substance  is  employed  in  the  reduction  of  arsenious  acid  or  its  salts, 
the  charcoal  is  of  course  the  decomposing  agent ;  but  the  alkali  is  of  use  in 
retaining  the  arsenious  acid  until  the  temperature  is  sufficiently  high  for  its  de- 
composition. With  sulphuret  of  arsenic,  on  the  contrary,  the  alkali  is  the  active 
principle,  the  potassium  of  which  unites  with  sulphur  and  liberates  the  arsenic ; 
but  the  charcoal  operates  usefully  by  facilitating  the  decomposition  of  the  alkaline 
carbonate.  The  whole  of  the  arsenic,  however,  is  not  sublimed  ;  but  part  of  it 
enters  into  union  with  potassium,  and  remains  with  the  flux. 

4.  For  the  application  of  hydrogen  in  testing  for  arsenic  we  are  indebted  to 
the  ingenuity  of  Marsh  (Edinburgh  New  Phil.  Journ.  October,  1836).  Its  em- 
ployment is  dependent  on  the  fact,  that  whenever  hydrogen  in  the  nascent  state 
is  brought  into  contact  with  any  compound  of  oxygen  and  arsenic,  the  latter  is 
instantly  decomposed,  and  water  and  a  gaseous  compound  of  arsenic  and  hydro- 
gen, the  arseniuretted  hydrogen,  are  generated.  If  the  gas  be  inflamed  as  it 
escapes  into  the  air  through  a  fine  tube,  it  burns  with  the  production  of  the 
vapour  of  water,  while  metallic  arsenic  or  arsenious  acid  is  deposited,  according 
as  the  supply  of  oxygen  be  more  or  less  abundant.  Hence  if  a  piece  of  cold 
window-glass  be  held  in  the  flame,  its  surface  is  instantly  covered  with  a  thin 
coating  of  metallic  arsenic ;  but  if  the  flame  be  made  to  burn  in  the  centre  of  a 
glass  tube  open  at  both  extremities,  the  inner  surface  of  the  latter  is  covered  in 
the  course  of  half  a  minute  with  arsenious  acid.  If  the  tube  be  held  obliquely 
against  it,  both  depositions  take  place,  and  on  bringing  the  tube,  while  still 
warm,  to  the  nose  a  peculiar  odour  of  arsenic  is  readily  perceived. 


368  ARSENIC. 

The  experiment  is  made  in  the  following  manner.  The  suspected  substances, 
if  in  the  solid  form,  such  as  bread,  must  first  be  boiled  with  a  few  ounces  of 
distilled  water,  and  the  clear  solution  while  still  hot  is  to  be 
separated  from  the  solid  parts  by  filtration.  The  same  process 
must  be  adopted  with  very  thick  soups,  or  the  contents  of  the 
stomach  ;  while  thin  soups,  wine,  beer,  coffee,  tea,  and  similar 
fluids  require  no  previous  preparation.  The  liquid  is  then  mixed 
with  a  few  ounces  of  dilute  sulphuric  acid,  and  introduced  into 
the  apparatus  represented  by  the  accompanying  woodcut.  This 
consists  of  two  parts,  a  cylindrical  glass  vessel  a,  and  a  capped 
bell  jar  furnished  with  a  stop-cock  and  small  gas-burner ;  to  the 
'stop-cock  is  suspended  a  string,  to  which  a  fragment  of  zinc  c, 
reaching  nearly  to  the  bottom  of  the  bell  jar,  is  attached.  The 
stop-cock  h  being  open,  when  the  liquid  to  be  examined  is  poured  into  a  it  rises 
in  the  bell  jar,  and  so  much  must  be  used  that  the  latter  is  almost  full.  By  the 
action  of  the  dilute  acid  on  the  zinc  hydrogen  is  rapidly  evolved,  and  after  per- 
mitting a  small  quantity  to  escape  in  order  to  ensure  the  removal  of  atmospheric 
air  from  the  vessel,  the  stop-cock  is  turned,  and  the  gas  allowed  to  accumulate 
in  the  bell  jar.  On  burning  it  the  presence  of  arsenic  is  readily  recognized  by 
the  characters  above  stated,  and  by  the  light  blue  tint  it  communicates  to  the 
flame.  The  extreme  delicacy  of  this  method  has  been  recently  amply  attested 
by  Liebig  and  Mohr  in  their  valuable  journal  (Lieb.  Annal.  xxiii.  217).  To 
avoid  every  source  of  fallacy,  however,  several  precautions  are  necessary :  the 
most  important  are — to  ensure  the  perfect  purity  of  the  reagents  used,  as  arsenic 
is  commonly  contained  both  in  the  zinc  and  sulphuric  acid  of  commerce ;  to 
employ  a  fresh  piece  of  zinc  with  each  experiment,  as  a  portion  of  the  arsenic 
in  the  solution  is  deposited  as  a  metallic  crust  on  the  zinc,  which  is  thus  ren- 
dered impure ;  and  to  prove  experimentally  the  purity  of  the  apparatus  before 
each  experiment.  Liebig  recommends  that  a  fragment  of  porcelain  be  held  in 
the  flame  instead  of  the  window-glass,  as  a  very  thin  film  of  metallic  arsenic  is 
better  seen  on  the  white  opaque  ground  than  on  the  transparent  glass.  He  ob- 
serves, too,  that  owing  to  the  rapid  evolution  of  the  gas,  other  metals,  as  for 
example  iron,  which  may  be  contained  in  the  solution,  being  carried  up  by  the 
hydrogen  and  deposited  on  the  porcelain,  may  prove  a  source  of  error  to  the 
inexperienced.  For  this  reason  he  recommends  that  the  gas,  instead  of  being 
burnt  by  the  jet,  be  transmitted  through  a  fine  tube  of  difficultly  fusible  glass  ; 
on  bringing  a  part  of  the  glass  to  a  red-heat  by  a  spirit-lamp  flame,  the  arseni- 
uretted  hydrogen  is  decomposed  as  it  passes,  and  the  metallic  arsenic  is  deposited 
just  beyond  the  heated  part  of  the  glass,  while  other  metals  are  deposited  in  the 
hot  parts  themselves. 

It  was  hoped  that  this  test  might  prove  infallible  even  in  the  hands  of  inex- 
perienced chemists;  but  according  to  a  recent  discovery  of  Mr.  L.  Thompson, 
antimony  combines  with  hydrogen,  forming  with  it  a  gaseous  compound  which 
is  similar  to  arseniuretted  hydrogen  in  the  mode  of  its  production,  in  the  colour 
of  its  flame  when  burnt,  and  in  the  deposition  of  a  metallic  crust  on  a  cold  sur- 
face. The  two  gases  may  nevertheless  be  readily  distinguished  by  decomposing 
them  by  means  of  heat  while  passing  through  a  fine  tube,  as  was  proposed  by 
Liebig  for  arseniuretted  hydrogen;  for  although  the  metallic  crusts  are  very 
similar,  yet  by  attention  to  the  directions  of  page  36G,  the  crust  of  arsenic  cannot 
be  mistaken  for  that  of  antimony.    For  by  bringing  the  spirit-lamp  flame  under 


ARSENIC.  ae9 

the  crust  when  the  stream  of  hydrogen  has  ceased  to  pass  along  the  tube,  if  it  be 
arsenic  it  rapidly  volatilizes  and  condenses  again  on  the  neighbouring  cool  parts 
of  the  tube;  the  antimonial  crust,  on  the  contrary,  when  thus  heated,  fuses,  runs 
into  small  globules,  and  assumes  the  appearance  of  mercury.  If  the  tube  be 
now  detached  from  the  vessel  in  which  the  hydrogen  is  generated,  and  the 
flame  of  the  spirit-lamp  cautiously  applied  to  the  metal,  the  arsenic  volatilizes 
without  fumes,  and  distinct  octohedral  crystals  of  arsenious  acid  are  formed  on 
the  upper  parts  of  the  tube  ;  with  antimony,  on  the  contrary,  dense  white  fumes 
are  produced  and  an  amorphous  white  powder  is  deposited.  The  different  char- 
acters of  the  two  substances  may  be  carried  still  further ;  if  the  tube  be  boiled 
in  a  small  quantity  of  pure  water,  the  arsenious  acid  is  dissolved,  and  the  first 
two  tests  may  be  successfully  employed ;  the  antimony,  on  the  contrary,  is 
insoluble. 

Arsenic  Acid. — This  compound  is  made  by  dissolving  arsenious  acid  in  con- 
centrated nitric,  mixed  with  a  little  hydrochloric  acid,  distilling  in  glass  till  it 
acquires  the  consistence  of  syrup,  and  then  exposing  it  in  a  platinum  crucible  for 
some  time  to  a  heat  somewhat  short  of  low  redness  to  expel  the  nitric  acid.  The 
acid  thus  prepared  has  a  sour  metallic  taste,  reddens  vegetable  blue  colours,  and 
with  alkalies  forms  neutral  salts,  which  are  termed  arseniaies.  It  is  much  more 
soluble  in  water  than  arsenious  acid,  dissolving  in  five  or  six  times  its  weight  of 
cold,  and  in  a  still  smaller  quantity  of  hot  water.  It  forms  irregular  grains  when 
its  solution  is  evaporated,  but  does  not  crystallize.  If  strongly  heated,  it  fuses 
into  a  glass  which  is  deliquescent.  When  urged  by  a  very  strong  red  heat,  it  is 
resolved  into  oxygen  and  arsenious  acid.    It  is  an  active  poison. 

Arsenic  acid  is  decomposed  by  hydrosulphuric  acid  gas,  and  yields  a  sulphuret 
of  arsenic  very  like  orpiment  in  colour,  but  containing  a  greater  proportional 
quantity  of  sulphur.  The  soluble  arseniates,  when  mixed  with  the  nitrates  of 
lead  and  silver,  form  insoluble  arseniates,  the  former  of  which  has  a  white,  and 
the  latter  a  brick-red  colour.  They  dissolve  readily  in  dilute  nitric  acid,  and 
when  heated  with  charcoal  yield  metallic  arsenic. 

Its  eq..  is  115*4 ;  si/mb,  2  As  -f  50,  As,  or  As^O^. 

Protochloride  of  Arsenic. — It  is  prepared,  according  to  Dumas,  by  introducing 
into  a  tubulated  retort  a  mixture  of  arsenious  acid  with  ten  times  its  weight  of 
concentrated  sulphuric  acid  ;  and  after  raising  its  temperature  to  near  212°,  frag- 
ments of  sea-salt  are  thrown  in  by  the  tubular.  If  the  salt  is  added  in  succes- 
sive small  portions,  scarcely  any  hydrochloric  acid  gas  is  evolved,  and  the  pure 
chloride  may  be  collected  in  cooled  vessels.  Towards  the  end  of  the  process  a 
little  water  frequently  passes  over  with  the  chloride;  but  this  hydrated  portion 
does  not  mix  with  the  anhydrous  chloride,  but  swims  on  its  surface.  The 
hydrate  may  be  decomposed,  and  a  pure  chloride  obtained,  by  distilling  the  mix- 
ture from  a  sufficient  quantity  of  concentrated  sulphuric  acid.  Dumas  considers 
this  compound  a  protochloride  of  arsenic,  so  that  it  is  probably  different  from 
that  obtained  by  means  of  corrosive  sublimate.  (Quarterly  Journal  of  Science, 
N.  S.  i.  235.) 

Its  eq.  is  73-12  ;  symb.  As  +  CI,  or  AsCl. 

Sesquichloride  of  Arsenic. — When  arsenic  in  powder  is  thrown  into  a  jar  full 
of  dry  chlorine  gas,  it  takes  fire,  and  sesquichloride  of  arsenic  is  generated ;  and 
the  same  compound  may  be  formed  by  distilling  a  mixture  of  six  parts  of  cor- 
rosive sublimate  with  one  of  arsenic.    It  is  a  colourless  volatile  liquid,  which 

26 


370  ARSENIC. 

fumes  strongly  on  exposure  to  the  air,  hence  called  fuming  liquor  of  arsenic,  and 
is  resolved  by  water  into  hydrochloric  and  arsenious  acids.     (Davy.) 

Its  eq»  is  181'66;  symb.  2As4-3Cl,  or  As^Cl^. 

Periodide  cf  Arsenic  is  formed  by  bringing  its  elements  into  contact,  and  pro- 
moting union  by  gentle  heat.  They  form  a  deep  red  compound,  which  is  resolved 
into  arsenic  and  hydriodic  acids  by  the  action  of  water.  (Plisson  in  An.  de  Ch. 
et  Ph.  xxxix.  266.) 

Its  eq,  is  706-9  ;  symb.  2As-h  51,  or  AsJ^. 

Sesquibromide  of  Arsenic. — The  elements  of  this  compound  unite  at  the  moment 
of  contact,  with  vivid  evolution  of  heat  and  light.  Serullas  prepared  it  by  adding 
dry  arsenic  to  bromine  as  long  as  light  was  emitted,  the  former  being  added  in 
successive  small  quantities,  to  prevent  the  temperature  from  rising  too  high.  The 
bromide  is  then  distilled,  and  then  collected  in  a  cool  receiver.  (An.  de  Ch.  et 
Ph.  xxxviii.  318.) 

This  compound  is  solid  at  or  below  68°,  liquefies  between  68°  and  77°,  and 
boils  at  428°.  As  a  liquid  it  is  transparent  and  slightly  yellow,  and  yields  long 
prisms  by  evaporation.  By  water  it  is  resolved  into  arsenious  and  hydrobromic 
acids. 

Its  eq,  is  313*6 ;  symb.  2As  +  3Br,  or  As^Brg. 

Protohyduret  of  Arsenic. — This  compound,  which  is  solid  and  of  a  brown 
colour,  was  discovered  by  Davy  as  well  as  Gay-Lussac  and  Thenard.  The  former 
prepared  it  by  attaching  a  piece  of  arsenic  to  the  negative  wire  during  the  decom- 
position of  water  by  galvanism ;  and  the  French  chemists,  by  the  action  of  water 
on  an  alloy  of  potassium  and  arsenic. 

Its  eq,  is  38*7 ;  symbi  As  H-  H,  or  AsH. 

Arseniuretted  Hydrogen. — This  gas,  which  was  discovered  by  Scheele,  has 
been  studied  by  Proust,  Trommsdorf,  and  others,  but  especially  by  Stromeyer. 
It  is  generally  made  by  digesting  an  alloy  of  tin  and  arsenic  in  hydrochloric 
acid  ;  but  as  thus  prepared  it  is  always  mixed  with  free  hydrogen.  Soubeiran 
generated  it  by  fusing  arsenic  with  its  own  weight  of  granulated  zinc,  and 
decomposing  the  alloy  with  strong  hydrochloric  acid.  The  gas  thus  developed, 
is  quite  free  from  hydrogen,  being  absorbed  without  residue  by  a  saturated  solu- 
tion of  sulphate  of  oxide  of  copper.  Its  sp.  gravity,  according  to  Dumas,  is 
2*695.  It  is  colourless,  and  has  a  fetid  odour  like  that  of  garlic.  It  extinguishes 
bodies  in  combustion,  but  is  itself  kindled  by  them,  and  burns  with  a  blue  fiame. 
It  instantly  destroys  small  animals  that  are  immersed  in  it,  and  is  poisonous  to 
man  in  a  high  degree,  having  proved  fatal  to  a  German  philosopher,  the  late  M. 
Gehlen,  and  others.  Water  absorbs  one-fifth  of  its  volume,  and  acquires  the 
odour  of  the  gas.     It  is  altogether  destitute  of  the  properties  of  an  acid. 

Arseniuretted  hydrogen  is  decomposed  by  various  agents.  It  suflTers  gradual 
decomposition  when  mixed  with  atmospheric  air,  water  being  formed,  and  metal- 
lic arsenic,  together  with  a  little  oxide,  deposited.  With  nitric  acid,  water  is 
generated,  and  a  deposite  of  metal  takes  place,  which  is  subsequently  oxidized. 
Chlorine  decomposes  it  instantly  \^ith  disengagement  of  heat  and  light,  hydro- 
chloric acid  being  generated,  and  the  metal  set  free.  With  iodine  it  yields 
hydriodic  acid  gas  and  iodide  of  arsenic,  and  sulphur  and  phosphorus  produce 
analogous  changes.  By  its  action  on  salts  of  the  easily  reducible  metals,  such 
as  silver  and  gold,  the  metal  is  revived,  and  its  oxygen  uniting  with  the  elements 
of  the  gas  constitutes  arsenious  acid  and  water.    With  salts  of  copper  the  pro- 


ARSENIC.  371 

ducts  are  water  and  arseniuret  of  copper ;  and  with  several  other  metallic  salts 
its  action  is  similar. 

Soubeiran  observed  that  arseniuretted  hydrogen  in  a  glass  tube  is  completely 
decomposed  by  the  heat  of  a  spirit-lamp,  and  that  its  hydrogen  occupies  one  and 
a  half  as  much  space  as  when  in  combination.  He  has  also  confirmed  the  obser- 
vation of  Dumas,  that  when  mixed  with  oxygen,  and  detonated  by  the  electric 
spark,  each  volume  of  the  gas,  in  forming  water  and  arsenious  acid,  requires  one 
and  a  half  its  volume  of  oxygen  gas.  The  oxygen,  therefore,  is  equally  divided 
between  the  arsenic  and  hydrogen  ;  and  arseniuretted  hydrogen  consists  of  one 
eq.  of  arsenic  and  one  and  a  half  of  hydrogen.  By  volume,  it  is  composed  of 
half  a  volume  of  the  vapour  of  arsenic,  and  one  and  a  half  of  hydrogen,  con- 
densed into  one  measure.     (An.  de  Ch.  et  Ph.  xliii.  407.) 

Its  eq.  is  78 '4  ;  syml.  2 As  -f-  3H,  or  As^  H^. 

Sulphurets  of  Arsenic. — Sulphur  unites  with  arsenic  in  at  least  three  propor- 
tions, forming  compounds,  two  of  which  occur  in  the  mineral  kingdom,  and  are 
well  known  by  the  names  of  realgar  and  orpiment.  Realgar  or  the  protosulphuret 
may  be  formed  artificially  by  heating  arsenious  acid  with  about  half  its  weight  of 
sulphur,  until  the  mixture  is  brought  into  a  state  of  perfect  fusion.  The  cooled 
mass  is  crystalline,  transparent, and  of  a  ruby-red  colour;  and  maybe  sublimed 
in  close  vessels  without  change. 

Its  eq.  is  53*8  ;  symb.  As  +  S,  or  AsS. 

Orpiment,  or  sesquisulphuret  of  arsenic  may  be  prepared  by  fusing  together 
equal  parts  of  arsenious  acid  and  sulphur;  but  the  best  mode  of  obtaining  it 
quite  pure  is  by  transmitting  a  current  of  hydrosulphuric  acid  gas  through  a 
solution  of  arsenious  acid.  Orpiment  has  a  rich  yellow  colour,  fuses  readily 
when  heated,  and  becomes  crystalline  on  cooling,  and  in  close  vessels  may  be 
sublimed  without  change.  It  is  dissolved  with  great  facility  by  the  pure  alkalies, 
and  yields  colourless  solutions. 

Orpiment  is  employed  as  a  pigment,  and  is  the  colouring  principle  of  the  paint 
called  King's  yellow.  Braconnot  has  proposed  it  likewise  for  dyeing  silk, 
woollen,  or  cotton  stuffs  of  a  yellow  colour  ;  the  cloth  being  soaked  in  a  solu- 
tion of  orpiment  in  ammonia,  and  then  suspended  in  a  warm  apartment.  The 
alkali  evaporates,  and  leaves  the  orpiment  permanently  attached  to  the  cloth. 
(An.  de  Ch.  et  Ph.  xii.) 

Its  eq.  is  123-7  ;  symb.  2 AS  +  3S,  or  K^^^^. 

Persulphuret  of  arsenic  is  prepared  by  transmitting  hydrosulphuric  acid  gas 
through  a  moderately  strong  solution  of  arsenic  acid  ;  or  by  saturating  a  solution 
of  arseniate  of  potassa  or  soda  with  the  same  gas,  and  acidulating  with  hydro- 
chloric or  acetic  acid.  The  oxygen  of  the  acid  unites  with  the  hydrogen  of  the 
gas,  and  persulphuret  of  arsenic  subsides.  In  colour  it  is  very  similar  to  orpi- 
ment, is  dissolved  by  pure  alkalies,  fuses  by  heat,  and  may  be  sublimed  in  close 
vessels  without  decomposition. 

Its  eq.  is  155'9;  symb.  2As  -f-  5S,  or  As^Sg. 

The  experiments  of  Orfila  have  proved  that  the  sulphurets  of  arsenic  are  poi- 
sonous, though  in  a  much  less  degree  than  the  arsenious  acid.  The  precipitated 
sulphuret  is  more  injurious  than  the  native  orpiment.  The  only  antidote  of  arse- 
nious acid  is  hydrated  peroxide  of  iron  (Bunsen),  the  effects  of  which  have  been 
amply  tested  in  Germany,  and  lately  elucidated  by  Dr.  D.  Maclagan.  (Edin. 
Med.  and  Surg.  Journal,  1840.)  It  acts  by  forming  an  insoluble  arsenite  or  ar- 
seniate ;  and  must  be  used  in  the  moist  state,  never  having  been  dried  ;  and  also 


372-  ANTIMONT. 

in  large  quantity.    The  late  edition  (1840)  of  the  Edinburgh  Pharmacopoeia  gives 
a  process  for  preparing  it  for  this  object.* 


SECTION  XVIII. 


ANTIMONY. 


Hist, — First  made  known  as  a  metal  in  the  15th  century  by  Basil  Valentine, 
and  is  said  to  derive  its  name  {anii-nnoine,  anti-monk)  from  having  proved  fatal 
to  some  monks  to  whom  it  was  given  as  a  medicine.  It  sometimes  occws  native ; 
but  its  only  ore  which  is  abundant,  and  from  which  the  antimony  of  commerce  is 
derived,  is  the  sulphuret.  This  ore,  the  stibium  of  the  ancients,  was  long  re- 
garded as  the  metal  itself,  and  was  called  antimony,  or  crude  antimony;  while  the 
pure  metal  was  termed  the  regulus  of  antimony. 

Fr^. — Either  by  heating  the  native  sulphuret  in  a  covered  crucible  with  half 
its  weight  of  iron  filings ;  or  by  mixing  it  with  two-thirds  of  its  weight  of  cream 
of  tartar  and  one-third  of  nitre,  and  throwing  the  mixture,  in  small  successive  por- 
tions, into  a  red-hot  crucible.  By  the  first  process  the  sulphur  unites  with  iron,  and 
in  the  second  it  is  expelled  in  the  form  of  sulphurous  acid ;  while  the  fused  anti- 
mony, which  in  both  cases  collects  in  the  bottom  of  the  crucible,  may  be  drawn 
off  and  received  in  moulds.  The  antimony,  thus  obtained,  is  not  absolutely  pure; 
and  therefore,  for  chemical  purposes,  should  be  procured  by  heating  the  oxide 
with  an  equal  weight  of  cream  of  tartar. 

Prop. — A  brittle  metal,  of  a  white  colour,  running  into  bluish-grey,  and  is  pos- 
sessed of  considerable  lustre.  Its  sp.  gr.  is  nearly  6'7.  At  810°  it  fuses,  and 
on  cooling  acquires  a  highly  lamellated  texture,  and  sometimes  yields  crystals : 
like  arsenic,  but  unlike  most  other  metals,  its  primary  form  is  rhombohedron.  It 
is  volatile  at  a  very  intense  temperature.  Its  surface  tarnishes  by  exposure  to 
the  atmosphere ;  and  by  the  continued  action  of  air  and  moisture,  a  dark  matter 
is  formed,  which  Berzelius  regards  as  a  definite  compound.  It  appears,  how- 
ever, to  be  merely  a  mixture  of  the  sesquioxide  and  metallic  antimony.  Heated 
to  a  white  or  even  full  red  heat  in  a  covered  crucible,  and  then  suddenly  exposed 

*  This  hydrate  is  readily  obtained  by  adding  ammonia  in  excess  to  the  neutral  sulphate  of 
the  sesquioxide  of  iron,  or  indeed  any  red  salt  §r  tincture  of  iron,  and  washing  the  precipi- 
tate with  water.  According  to  the  observations  of  Mr.  Wm.  Proctor,  the  pulpy  hydrate 
thus  formed,  becomes  more  dense  and  loses  somewhat  of  its  susceptibility  of  reaction  with 
arsenious  acid  by  keeping,  and  should  therefore  be  used  as  an  antidote  in  a  recent  state. 
(Amer.  Jour,  of  Phar.  vol.  iv.  p.  29.)  (R.) 

According  to  Duflos  this  preparation  is  totally  ineffectual  as  an  antidote,  when  the  acids 
of  arsenic  are  combined  with  bases  as  in  Fowler's  solution,  and  the  arseniate  of  potassa  em- 
ployed in  calico  printing.  In  such  cases,  and  i]\deed  when  any  doubt  exists  as  to  the  state 
of  combination  of  the  arscniacal  poison,  he  recommends  the  peracetate  of  iron,  with  excess 
of  base,  largely  diluted  with  water.  This  liquid  he  states  precipitates  arsenious  and  arsenic 
acid  from  all  their  solutions,  either  free  or  combined  with  any  base.  (Joum.  de  Ch.  Med. 
Nov.  1844.)  (R.) 


ANTIMONY. 


99$ 


eq.  Antimony. 

Equiv. 

Formulae. 

129-2-t-Oxygen 

24 

3eq.    =153.2 

2Sb-f-30or  Sb203. 

129-2t     do. 

32 

4eq.    =161-2 

2Sb-f-40  or  Sb^. 

129-2+    do. 

40 

5  eq.    =169-2 

2Sbt50  or  SbaOg. 

129-2+Chlorine 

106-26 

3eq.    =235-46 

2Sb+3Cl  or  SbjCls. 

129-2+     do. 

141-68 

4eq.    =270-88 

2Sb+4Cl  or  SbgC^. 

129-2+    do. 

177-1 

5  eq.    =306-3 

2Sb+5  CI  or  SbaClg. 

Composition  uncertain. 

129-2 -[-Sulphur 

48-3 

3eq.    =177-5 

2Sb+3S  or  SbjSs. 

129-2+    do. 

64-4 

4eq.    =193-6 

2Sb  +  4S  or  Sb2S4. 

129-2+    do. 

80-5 

5eq.    =209-7 

2Sb+5S  or  SbjSg. 

'Sesquichloride 
■'Sesquioxide 

570-92 
1378-8 

9  ec|:}  =1949-72 

2Sb2Cl3+9Sba03. 

[Sesquisulphuret 
•  Sesquioxide 

355 
153-2 

2  eq.  1=508.2 

Sb2SH-Sb203  . 

to  the  air,  it  inflames,  and  burns  with  a  white  light.  During  the  combustion,  a 
white  vapour  rises,  which  condenses  on  cool  surfaces,  frequently  in  the  form  of 
small  shining  needles  of  silvery  w^hiteness.  These  crystals  were  formerly  called 
argentine  flowers  cf  antimony,  and  in  chemical  works  are  generally  described  as 
binoxide  of  antimony ;  but  they  are  correctly  considered  by  Berzelius,  as  the  ses- 
quioxide. 

From  the  experiments  of  Berzelius  on  the  composition  of  the  oxide  and  acids 
of  antimony  (An.  de  Ch.  et  Ph.  xvii.),  the  eq.  of  that  metal  maybe  estimated  at 
64*6.    The  composition  of  the  compounds  described  in  this  section  is  as  follows  : 

2 
Sesquioxide 
Antimonious) 

Acid  5 

Antimonic      > 

Acid  5 

Sesquichloride 
Bichloride 
Perchloride 
Bromide 
Sesquisulphuret 
Bisulphuret 
Persulphuret 
Oxychloride 

of  Antimony 
Oxysulphuret 

of  Antimony 

Sesquioxide. — When  sesquichloride  of  antimony,  made  by  boiling  the  native 
sulphuret  in  hydrochloric  acid,  is  poured  into  water,  a  white  curdy  precipitate 
subsides,  formerly  called  powder  of  Algaroih,  which  consists  of  sesquioxide  of 
antimony  combined  with  undecomposed  chloride.  On  decomposing  the  latter  by 
digestion  with  carbonate  of  potassa,  and  then  washing  with  water,  the  sesquiox- 
ide is  obtained  in  a  state  of  purity.  It  may  also  be  procured  by  adding  carbonate 
of  potassa  or  soda  to  a  solution  of  tartar  emetic,  and  by  sublimation  during  the 
combustion  of  antimony.  When  slowly  sublimed  it  condenses  in  fine  needles  of 
silvery  whiteness.  It  occurs  as  a  mineral,  the  oxide  of  antimony  of  mineralo- 
gists, the  primary  form  of  which  is  a  right  rhombic  prism,  isomorphous  with  the 
crystals  of  arsenious  acid  lately  observed  by  Wohler. 

Prop, — When  prepared  in  the  moist  way,  it  is  a  white  powcler  with  a  some- 
what dirty  appearance.  When  heated  it  acquires  a  yellow  tint,  and  at  a  dull  red 
heat  in  close  vessels  it  is  fused,  yielding  a  yellow  fluid,  which  becomes  an  opaque 
greyish  crystalline  mass  on  cooling.  Its  sp.  gr.  is  S'SGG.  It  is  very  volatile, 
and  if  protected  from  atmospheric  air  may  be  sublimed  without  change.  When 
heated  in  open  vessels  it  absorbs  oxygen ;  and  when  the  temperature  is  suddenly 
raised,  and  the  oxide  is  porous,  it  takes  fire  and  burns.  In  both  cases  antimo- 
nious acid  is  generated.  It  is  the  only  oxide  of  antimony  which  forms  regular 
salts  with  acids,  and  is  the  base  of  the  medicinal  preparation,  tartar  emetic,  the 
tartrate  of  antimony  and  potash.  Most  of  its  salts,  however,  are  either  insoluble 
in  water,  or,  like  chloride  of  antimony,  are  decomposed  by  it,  owing  to  the  affi- 
nity of  that  fluid  for  the  acid  being  greater  than  that  of  the  acid  for  oxide  of  anti- 
mony. This  oxide  is  therefore  a  feeble  base ;  and,  indeed,  possesses  the  pro- 
perty of  uniting  with  alkalies.    To  the  foregoing  remark,  however,  tartrate  of 


374  ANTIMONY. 

antimony  and  potassa  is  an  exception  ;  for  it  dissolves  readily  in  water  without 
change.  By  excess  of  tartaric  or  hydrochloric  acid,  the  insoluble  salts  of  anti- 
mony may  be  rendered  soluble  in  water. 

The  presence  of  antimony  in  solution  is  easily  detected  by  hydrosulphuric  acid. 
This  gas  occasions  an  orange-coloured  precipitate,  hydrated  sesquisulphuret  of 
antimony,  which  is  soluble  in  pure  potassa,  and  is  dissolved  with  disengagement 
of  hydrosulphuric  acid  gas  by  hot  hydrochloric  acid,  forming  a  solution  from 
which  the  white  oxychloride  is  precipitated  by  water. 

In  trying  the  effect  of  reagents  on  solutions  of  oxide  of  antimony^  it  is  conve- 
nient to  employ  tartar  emetic,  from  its  property  of  dissolving  in  pure  water  with- 
out decomposition.  From  a  solution  of  this  salt,  when  moderately  concentrated, 
a  little  pure  potassa  throws  down  the  oxide,  but  excess  of  the  alkali  redissolves 
the  precipitate.  The  oxide  is  more  perfectly  separated  by  alkaline  carbonates. 
Lime  water  causes  a  white  precipitate,  a  mixed  tartrate  of  lime  and  oxide  of 
antimony ;  and  earthy  and  metallic  salts  decompose  tartar  emetic  by  forming, 
like  lime,  sparingly  soluble  compounds  with  tartaric  acid.  Decomposition  is 
also  occasioned  by  most  acids,  which  throw  down  a  sparingly  soluble  salt  of 
antimony  and  cream  of  tartar;  and  a  recently  made,  pretty  strong,  infusion  of 
gall-nuts,  gives  a  yellowish  white  precipitate,  which  consists  of  tannic  acid  and 
oxide  of  antimony.  But  these  appearances  are  by  no  means  to  be  relied  on  as 
tests  of  the  presence  of  antimony  :  a  mixture  of  other  substances  might  be  simi- 
larly influenced  by  the  same  reagents ;  in  a  moderately  dilute  solution  of  tartar 
emetic  most  of  them  produce  no  effect  whatever ;  and  the  too  free  addition  of  a 
pure  alkali  or  of  an  acid,  even  to  a  strong  solution,  may  altogether  prevent  that 
precipitate  from  forming,  which  a  smaller  quantity  of  the  same  reagents  would 
have  produced.  The  only  certain  method  of  bringing  the  antimony  into  view, 
even  in  a  very  weak  solution,  is  to  acidulate  with  tartaric  acid,  and  then  transmit 
through  the  liquid  a  current  of  hydrosulphuric  acid  gas.  The  hydrated  sesqui- 
sulphuret of  antimony,  of  a  characteristic  orange-red  colour,  is  immediately 
formed. 

The  detection  of  antimony  in  mixed  fluids,  as  when  tartar  emetic  is  mixed 
with  articles  of  food,  is  conducted  in  the  following  manner.  The  substances 
are  first  digested  in  water  acidulated  with  about  a  drachm  of  hydrochloric  and 
tartaric  acids,  which  coagulate  some  organic  matters,  and  give  complete  solubility 
to  the  oxide  of  antimony.  Through  the  filtered  liquid,  hydrosulphuric  acid  is 
then  transmitted,  when  the  orange-red  sesquisulphuret  of  antimony  subsides, 
which  preserves  its  characteristic  tint  even  when  deposited  from  coloured  solu- 
tions, and  may  be  further  recognized  by  solution  in  hot  hydrochloric  acid  and 
precipitation  by  water.  The  metal  itself  may  in  general  be  obtained  by  placing 
the  dry  sulphuret  in  a  glass  tube,  transmitting  through  it  a  current  of  hydrogen 
gas,  and  then,  when  all  the  atmospheric  air  is  displaced,  heating  the  sulpuuret 
by  the  flame  of  a  spirit-lamp.  The  sulphur  is  carried  off  in  the  form  of  hydro- 
sulphuric acid  gas,  and  the  metallic  antimony,  recognizable  by  its  lustre,  remains. 
The  metal  is  principally  found  where  the  sulphuret  lay;  but  if  the  current  of 
gas  during  the  reduction  happen  to  be  rapid,  it  causes  mechanically  a  spurious 
sublimation  of  antimony,  which  lines  part  of  the  tube  with  a  thin  film  of  metal. 
When  much  organic  matter  is  mixed  with  the  sulphuret,  the  metal  is  sometimes 
indistinctly  seen.  In  that  case  it  should  be  dissolved  in  a  few  drops  of  nitro- 
hydrochloric  acid  with  heat,  and  be  precipitated  by  water  :  it  may  then  be  redis- 
solved  by  tartaric  acid,  and  again  precipitated  with  its  characteristic  tint  by 


ANTIMONY.  375 

hydrosulphuric  acid.  Orfila  recommends  that  the  metal  should  be  obtained  from 
the  sulphuret  by  fusion  with  black  flux ;  but  I  have  elsewhere  shown  this  pro- 
cess to  be  very  precarious,  and  my  opinion  is  supported  by  the  experience  of 
Christison.  (Treatise  on  Poisons,  2d  Ed.  429.)  It  may  be  detected,  when 
present  even  in  small  quantity,  by  decomposing  the  antimoniuretted  hydrogen 
formed  as  described  under  Arsenic,  where  the  characters  by  which  it  is  distin- 
guished from  arsenic  are  given. 

Its  eq,  is  153-2  ;  symh.  2Sb+  30,  Sb,  or  Sb^Og. 

Aniimonious  Acid. — When  metallic  antimony  is  digested  in  strong  nitric  acid, 
the  metal  is  oxidized  at  the  expense  of  the  acid,  and  hydrated  antimonic  acid  is 
formed;  and  on  exposing  this  substance  to  a  red  heat,  it  gives  out  water  and  oxy- 
gen gas,  and  is  converted  into  antimonious  acid.  It  is  also  generated  when  the 
oxide  is  exposed  to  heat  in  open  vessels.  Thus,  on  heating  sulphuret  of  anti- 
mony with  free  exposure  to  the  air,  sulphurous  acid  and  oxide  of  antimony  are 
generated  ;  but  on  continuing  the  roasting  after  all  the  sulphur  is  burned,  the  oxide 
gradually  absorbs  oxygen  and  passes  into  antimonious  acid.  Hence  this  acid  is 
formed  in  the  process  of  preparing  the  pubis  antimonialis  of  the  pharmacopoeia. 
Antimonious  acid  is  white  while  cold,  but  acquires  a  yellow  tint  when  heated, 
is  very  infusible,  and  fixed  in  the  fire,  two  characters  by  which  it  is  readily  dis- 
tinguished from  the  oxide.  It  is  insoluble  in  water,  and  likewise  in  acids  after 
being  heated  to  redness.  It  combines  in  definite  proportions  with  alkalies,  and 
its  salts  are  called  antimonites.  Antimonious  acid  is  precipitated  from  these  salts 
by  acids  as  a  hydrate,  which  reddens  litmus  paper,  and  is  dissolved  by  hydro- 
chloric and  tartaric  acids,  though  without  appearing  to  form  with  them  definite 
compounds. 

Its  eq.  is  161-2  ;  symh,  2Sbf  40,  Sb,  or  Sb204. 

Antimonic  Acid,  sometimes  c^We^  peroxide  of  antimony,  is  obtained  as  a  whitfe 
hydrate,  either  by  digesting  the  metal  in  strong  nitric  acid,  or  by  dissolving  it 
in  nitro-hydrochloric  acid,  concentrating  by  heat  to  expel  excess  of  acid,  and 
throwing  the  solution  into  water.  When  recently  precipitated  it  reddens  litmus 
paper,  and  may  then  be  dissolved  in  water  by  means  of  hydrochloric  or  tartaric 
acid.  It  does  not  enter  into  definite  combination  with  acids,  but  with  alkalies 
forms  salts,  which  are  called  antimoniates.  When  the  hydrated  peroxide  is  ex- 
posed to  a  temperature  of  500°  or  600°  F.  the  water  is  evolved,  and  the  anhy- 
drous acid  of  a  yellow  colour  remains.  In  this  state  it  resists  the  action  of  acids. 
When  exposed  to  a  red  heat  it  parts  with  oxygen,  and  is  converted  into  antimo- 
nious acid. 

Its  eq.  is  1 69-2 ;  symh.  2Sb  -f-  50,  Sb,  or  Sb^O^. 

Chlorides  of  Antimony. — When  antimony  in  powder  is  thrown  into  a  jar  of 
chlorine  gas,  combustion  ensues,  and  the  sesquichloride  of  antimony  is  generated. 
The  same  compound  may  be  formed  by  distilling  a  mixture  of  antimony  with 
about  twice  and  a  half  its  weight  of  corrosive  sublimate,  when  the  volatile  ses- 
quichloride of  antimony  passes  over  into  the  recipient,  and  metallic  mercury 
remains  in  the  retort.  At  common  temperatures  it  is  a  soft  solid,  thence  called 
hutter  of  antimony,  which  is  liquefied  by  gentle  heat,  and  crystallizes  on  cooling. 
It  deliquesces  on  exposure  to  the  air ;  and  when  mixed  with  water,  hydrochloric 
acid  and  sesquioxide  are  generated,  and  the  latter,  combined  with  undecomposed 
chloride  subsides. 

Its  eq.  is  235-46;  symh  2Sb  f  3C1,  or  Sb^Cl^. 


376  ANTIMONY. 

The  bichloride  (f  antimony  is  formed  by  acting  on  hydrated  antimonious  by 
hydrochloric  acid,  when  a  solution  is  formed,  which  appears  to  be  a  compound 
of  bichloride  of  antimony  and  hydrochloric  acid.  It  possesses  little  permanence, 
and  on  the  addition  of  water  antimonious  acid  subsides,  and  hydrochloric  acid 
lemains  in  solution.  - 

The  perchloride  IB  generated  by  passing  dry.  chlorine  gas  over  heated  metallic 
antimony.  Jt  is  a  transparent  volatile  liquid,  which  emits  fumes  on  exposure  to 
the  air.  Mixed  with  water,  it  is  converted  into  hydrochloric  and  hydrated  anti- 
monic  acid,  which  subsides.     (Rose,  in  the  Annals  of  Philosophy,  N.  S.  x.) 

Bromide  of  Antimony. — The  union  of  bromine  and  antimony  is  attended  with 
disengagement  of  heat  and  light,  and  the  compound  is  readily  obtained  by  distil- 
lation, as  in  the  process  for  preparing  bromide  of  arsenic.  It  is  solid  at  common 
temperatures,  is  fused  at  206°,  and  boils  at  518°  F.  It  is  colourless,  and  crys- 
tallizes in  needles ;  it  attracts  moisture  from  the  air,  and  is  decomposed  by 
water. 

Sesquisulphurei  of  Antimony. — ^This  is  by  far  the  most  abundant  ore  of  anti- 
mony, and  is  hence  employed  in  making  the  preparations  of  antimony.  Though 
compact  or  earthy,  it  sometimes  occurs  in  acicular  crystals  and  in  rhombic  prisms. 
Its  sp.  gr.  is  4-62,  colour  red-grey,  and  'its  lustre  metallic.  When  heated  in 
close  vessels,  it  enters  into  fusion  without  undergoing  any  other  change.  It  may 
be  formed  artificially  by  fusing  together  antimony  and  sulphur,  or  by  transmit- 
ting a  current  of  hydrosulphuric  acid  gas  through  a  solution  of  tartar  emetic :  in 
this  case  it  falls  as  a  hydrate  of  an  orange-red  colour,  and  does  not  acquire  its 
dark  colour  till  its  water  is  expelled  by  heat. 
Its  eq.  is  177-5  ;  symb.  2Sb  +  3S,  or  ^h^^* 

The  bisulphuret  is  formed,  according  to  Rose  by  transmitting  hydrosulphuric 
acid  gas  through  a  solution  of  antimonious  acid  in  dilute  hydrochloric  acid.  (An. 
of  Phil.  N.  S.  X.) 

Its  eq.  is  193-6 ;  symb.  2Sb  +  4S,  or  Sb^S^. 

Rose  formed  the  persulphurei  by  the  action  of  hydrosulphuric  acid  on  a  solu- 
tion of  antimonic  acid.  The  golden  sulphuret,  prepared  by  boiling  sulphuret  of 
antimony  and  sulphur  in  solution  of  potassa,  a  process  which  is  not  adopted  by 
either  of  our  colleges,  is  a  persulphuret.  Its  eq,  209-7;  syw6. 2Sb-|-5S,  or  Sb^S^. 
Oxychloride  cf  Antimony. — This  compound  has  lately  been  studied  by  Mala- 
guti  and  Johnston.  When  an  acid  solution  of  the  sesquichloride  of  antimony  is 
thrown  into  a  large  quantity  of  water,  a  white  voluminous  precipitate  forms. 
Allowing  it  to  subside,  it  contracts  considerably  during  thirty  or  forty  hours,  and 
then  consists  of  a  thick  bed  of  minute  crystals.  These  crystals  are  small  pris- 
matic needles,  of  a  white  colour  and  brilliant  lustre ;  they  are  decomposed  by 
boiling  in  water,  by  continued  washings,  and  by  the  alkaline  carbonates,  being 
thus  converted  into  sesquioxide.  They  have  been  analyzed  by  Johnston,  accord- 
ing to  whom  they  are  composed  of  2  eq.  of  the  sesquichloride  united  with  9  eq. 
of  the  sesquioxide;  a  composition  which  corresponds  closely  with  the  analysis 
of  Malaguti.     Hence  the  eq.  is  1949-72 ;  symb.  'iiShp\^-\.9^hfi^, 

Oxysulphuret  of  Antimony. — Hist,  and  Prep. — Rose  has  shown  that  this  com- 
pound occurs  in  the  mineral  kingdom,  being  the  red  antimony  ore  (rolhspies- 
glanzerz)  of  mineralogists.  The  pharmaceutic  preparations  known  by  the  terms 
glass,  livery  and  crocus  of  antimony,  are  of  a  similar  nature,  though  less  definite 
in  composition.  They  are  made  by  roasting  the  native  sulphuret,  so  as  to  form 
sulphurous  acid  and  oxide  of  antimony,  and  then  vitrifying  the  oxide  together 


ANTIMONY.  377 

with  undecomposed  ore,  by  means  of  a  strong  heat.  The  product  will  of  course 
differ  according  as  more  or  less  of  the  sulphuret  escapes  oxidation  during  the 
process. 

When  sulphuret  of  antimony  is  boiled  in  a  solution  of  potassa  or  soda,  a 
liquid  is  obtained,  from  which,  on  cooling,  an  orange-red  matter  called  Kermes 
mineral  is  deposited ;  and  on  subsequently  neutralizing  the  cold  solution  with 
an  acid,  an  additional  quantity  of  a  similar  substance,  the  golden  sulphuret  of  the 
pharmacopoeia,  subsides.  These  compounds  may  also  be  obtained  by  igniting 
sulphuret  of  antimony  with  an  alkali  or  alkaline  carbonate,  and  treating  the  pro- 
duct with  hot  water ;  or  by  boiling  the  mineral  in  a  solution  of  carbonate  of  soda 
or  potassa.  The  finest  kermes  is  obtained,  according  to  M.  Cluzel,  from  a  mix- 
ture of  four  parts  of  sulphuret  of  antimony,  90  of  crystallized  carbonate  of  soda, 
and  1000  of  water.  These  materials  are  boiled  for  half  or  three  quarters  of  an 
hour;  the  hot  solution  is  filtered  into  a  warm  vessel,  in  order  that  it  may  cool 
slowly ;  and  after  24  hours  the  deposit  is  collected  on  a  filter,  moderately 
washed  with  cold  water,  and  dried  at  a  temperature  of  70°  or  80°  F. 

Prop. — Very  great  diversity  of  opinion  has  long  existed  among  chemists  as  to 
the  nature  of  kermes.  Berzelius  and  Rose  gave  experiments  to  show  that  it  is 
a  hydrated  sesquisulphuret,  differing  from  the  native  sulphuret  solely  in  being 
combined  with  water.  Subsequently  Gay-Lussac  and  others  observed  that 
kermes  contains  oxide  of  antimony,  which  may  be  removed  by  digestion  with 
cream  of  tartar ;  and  Gay-Lussac  inferred  from  the  quantity  of  water  formed 
when  kermes,  previously  rendered  anhydrous,  is  lieduced  by  hydrogen  gas,  that 
it  is  a  hydrated  oxysulphuret,  identical,  when  deprived  of  its  water,  with  the  red 
ore  of  antimony  above  referred  to.  Still  more  recently  Berzelius  has  explained, 
that  the  ordinary  process  for  making  kermes  leads  to  the  sepaiation  of  a  com- 
pound of  oxide  of  antimony  and  potassa,  which  tenaciously  adheres  to  kermes, 
but  is  not  chemically  united  with  it :  he  rightly  argues  that  the  question  is  not, 
whether  oxide  of  antimony  is  sometimes  or  generally  present  in  kermes,  but 
whether  the  latter  can  exist  without  oxide  of  antimony.  This  question  he  has 
answered  affirmatively.  He  fused  sulphuret  of  antimony  with  black  flux,  boiled 
the  residue  in  water,  and  set  aside  the  solution  to  cool :  a  perfect  kermes  was 
deposited,  which  he  considers,  and  I  apprehend  with  good  reason,  to  be  quite  free 
from  oxide  of  antimony.     (Pog.  Annalen,  xx.  364.) 

The  theory  of  the  preparation  of  kermes,  as  given  by  Berzelius,  is  the  follow- 
ing. When  sesquisulphuret  of  antimony  is  fused  with  potassa,  part  of  each 
interchanges  elements  with  the  other  in  such  a  ratio  that 

1  eq.  Sesquisulphuret  of  Ant.  Sb2S3  2      1  eq.  Sesquioxide  of  Antimony        Sb203 

and  3  eq.  Potassa  3K0  -^    and  3  eq.  Sulphuret  of  Potassium    3KS. 

The  sulphuret  of  potassium  unites  with  undecomposed  sesquisulphuret  of 
antimony,  forming  a  sulphur-salt  which  will  be  again  referred  to  hereafter,  and 
sesquioxide  of  antimony  with  undecomposed  potassa ;  and  on  adding  hot  water 
both  compounds  are  dissolved,  and  coexist  independently  of  each  other  in  the 
solution.  As  the  solution  cools,  the  sesquisulphuret  of  antimony  subsides,  sim- 
ply because  the  solvent  power  of  sulphuret  of  potassium  is  thereby  diminished  ; 
but  a  variable  quantity  of  potassa  and  sesquioxide  of  antimony  falls  with  the 
deposit,  and  cannot  be  entirely  removed  by  washing  with  water.  The  cold  solu- 
tion still  contains  a  double  sulphuret  of  antimony  and  potassium,  together  with 
sesquioxide  of  antimony  united  with  potassa :  on  acidulating  with  sulphuric  acid, 


378  CHROMIUM. 

the  sulphuret  of  potassium  is  resolved,  by  decomposition  of  water,  into  potassa 
and  hydrosulphuric  acid,  and  the  sesquioxide  of  antimony  is  deprived  of  its 
potassa ;  and  therefore  the  sesquisulphuret  and  sesquioxide  of  antimony,  both 
losing  at  the  same  instant  the  principles  which  gave  them  solubility,  are  thrown 
down  either  in  combination  or  in  mixture  with  each  other.  Berzelius  believes 
the  same  change  to  occur  when  the  ingredients  are  boiled  instead  of  fused 
together.  The  golden  sulphuret  differs  from  kermes,  in  the  absence  of  potassa, 
in  containing  more  oxide  of  antimony,  and  perhaps  in  being  or  containing  an 
oxysulphuret.  It  commonly  contains  free  sulphur,  derived  apparently  from  the 
oxidizing  influence  of  the  air  on  the  sulphuret  of  potassium.  When  alkaline 
carbonates  are  employed  instead  of  pure  alkalies,  the  same  phenomena  ensue, 
except  that  carbonic  acid  is  evolved. 
//»  eq.  is  508-2 ;  si/mb,  2Sb2S3  -f  ^\0^. 


SECTION  XIX. 

CHBOMIUM.— VANADIUM. 

CHROMIUM. 

Hist. — Discovered  in  the  year  1797  by  Vauquelin  in  a  beautiful  red  mineral, 
the  native  dichromate  of  oxide  of  lead.  (An.  de  Ch.  xxv.  and  Ixx.)  It  has 
since  been  detected  in  the  mineral  called  chromaie  of  iron,  a  compound  of  the 
oxides  of  chromium  and  iron,  which  occurs  abundantly  in  several  parts  of  the 
Continent,  in  America,  and  at  Unst  in  Shetland.  (Hibbert.)  It  derived  its 
name  from  y^»/*a,  colour,  owing  to  its  remarkable  tendency  to  form  coloured 
compounds. 

Frep. — By  exposing  the  oxide  of  chromium  mixed  with  charcoal  to  the  most 
intense  heat  of  a  smith's  forge;  but  owing  to  its  strong  affinity  for  oxygen,  the 
reduction  is  extremely  difficult.  A  better  process,  that  of  Vauquelin,  is  to  mix 
the  dry  chloride  into  a  paste  with  oil,  place  the  mass  in  a  crucible  lined  with 
charcoal,  lute  on  a  cover,  and  to  expose  it  for  an  hour  to  a  very  strong  heat. 
Liebig  has  obtained  the  metal  in  the  form  of  a  black  powder,  which  acquires  the 
metallic  aspect  from  pressure,  by  heating  the  compound  of  terchloride  of  chro- 
mium and  ammonia  to  redness,  and  transmitting  over  it  dry  ammoniacal  gas ;  the 
chlorine  unites  with  the  hydrogen  of  the  ammonia,  hydrochloric  acid  and  nitro- 
gen gases  are  evolved,  and  pulverulent  chromium  remains.  A  still  more  conve- 
nient process  is  to  decompose  the  sesquichlorido  by  heat  and  ammoniacal  gas, 
in  which  case  the  metal  has  a  chocolate-brown  colour.  In  this  finely  divided  state 
it  takes  fire  when  heated  in  the  open  air.  .  (An.  de  Ch.  et  Ph.  xlviii.  297.) 

Prop. — As  obtained  by  Vauqueiin*s  process  it  has  a  white  colour  with  -a.  shade 
of  yellow,  and  a  distinct  metallic  lustre.  It  is  brittle,  very  infusible,  and  with 
difficulty  attacked  by  acids,  even  by  the  nitro-hydrochloric.  Its  sp.  gr.  has  been 
stated  at  5*9  ;  but  Thomson  found  it  a  little  above  5.    When  fused  with  nitre  it 


CHROMIUM.  379 

is  oxidized  and  converted  into  chromic  acid.     With  a  smaller  quantity  of  oxy- 
gen it  forms  the  green  oxide. 

From  the  experiments  of  Berzelius  and  Thomson  the  eq.  of  chromic  acid  may 
be  estimated  at  52 ;  and  as  the  salts  of  this  acid  are  isomorphous  with  the  sul- 
phates and  seleniates,  it  is  inferred  that  chromic  acid  has  the  same  atomic  con- 
stitution as  sulphuric  and  selenic  acids,  or  consists  of  1  eq.  of  chromium  and 
3  eq.  of  oxygen.  Berzelius  has  moreover  remarked  that  when  the  acid  is  con- 
verted into  the  green  oxide  of  chromium,  it  parts  with  exactly  half  of  its  oxygen. 
Hence,  24  deducted  from  52,  leaves  28  as  the  eq.  of  chromium.  Its  synib.  is  Cr. 
The  composition  of  its  compounds  described  in  this  section  is  as  follows  : — 


Chromium. 

Equiv. 

Formulae, 

Sesquioxide 

56    2  eq.  -|-  Oxygen 

24 

3  eq.  =   80 

2Cr+30orCr203. 

Chromic  Acid 

28    leq.t     .    . 

24 

3  eq.  =   52 

Cr  +  30  or  OrOj. 

Sesquichloride 

56    2  eq.  -|-  Chlorine 

106-26 

3  eq.  =  162-262 

Cr  -+-  3C1  or  CrjCla. 

Sesquifluoride 

66    2  eq.  -f  Fluorine 

5604 

3  eq.==  112-04 

2Cr-+-3ForCr2Fs. 

Perfluoride 

Composition  unknown. 

Sesquisulphuret 

56    2  eq.  -f-  Sulphur 

48-3 

3  eq.  =  104-3 

2Cr-+-3S  or  CraSj. 

Protophosphuret 

28     1  eq.  -f  Phosphs. 

15-7 

1  eq.=   43-7 

Cr  -f  P  or  CrP. 

Oxy-chloride  CrOa 

104    2eq. -|-CrCl3 

106-26 

leq.  =  210-26 

CrCh  -\-  4Cr03. 

Sesquioxide  of  Chromium, — Prep. — ^This,  the  commonly  known  oxide  of  chro- 
mium, is  prepared  by  dissolving  chromate  of  potassa  in  water,  and  mixing  it  with  a 
solution  of  nitrate  of  protoxide  of  mercury,  when  an  orange-coloured  precipitate, 
chromate  of  that  oxide,  subsides.  On  heating  this  salt  to  redness  in  an  earthen 
crucible,  the  mercury  is  dissipated  in  vapour,  and  the  chromic  acid  is  resolved 
into  oxygen  and  oxide  of  chromium.  It  may  also  be  obtained  in  small  tabular 
crystals  by  exposing  the  bichromate  of  potassa  to  a  strong  red  heat ;  one  eq.  of 
chromic  acid  loses  oxygen,  while  the  other  forms  a  neutral  salt  with  the  potassa. 
The  latter  is  readily  removed  from  the  insoluble  oxide  by  boiling  water.  Woh- 
ler  has  succeeded  in  obtaining  this  oxide  in  fine  crystals  by  conducting  the  vapour 
of  the  oxychloride  of  chromium  (formerly  terchloride  of  chromium)  through  a 
red-hot  glass  tube,  when  it  is  decomposed,  oxide  of  chromium  is  deposited  in 
fine  crystals,  and  a  mixture  of  oxygen  and  chlorine  gj^ses  is  evolved. 

Prep. — As  obtained  by  either  of  the  first  processes,  it  is  a  green  powder ;  but 
the  crystals  of  Wohler  are  black  and  possess  a  strong  metallic  lustre,  and  are 
identical  in  form  and  very  similar  in  appearance  to  specular  iron  ore  :  it  is  as  hard 
as  corundum ;  and  has  a  sp.  gr.  of  5*21 ;  its  powder  has  the  common  green  colour 
of  oxide  of  chromium.     (Pog.  An.  xxxiii.  341.) 

It  is  insoluble  in  water,  and  after  being  strongly  heated,  resists  the  action  of 
the  most  powerful  acids.  Deflagrated  with  nitre,  or  fused  with  chlorate  of  po- 
tassa, it  is  oxidized  to  its  maximum,  and  is  thus  reconverted  into  chromic  acid. 
Fused  with  borax  or  vitreous  substances,  it  communicates  to  them  a  beautiful 
green  colour,  a  property  which  aflfords  an  excellent  test  of  its  presence,  and  ren- 
ders it  exceedingly  useful  in  the  arts.  The  emerald  owes  its  colour  to  the  pre- 
sence of  this  oxide. 

Oxide  of  chromium  is  a  salifiable  base,  and  its  salts,  which  have  a  green  colour, 
may  be  easily  prepared  in  the  following  manner.  To  a  boiling  solution  of  chro- 
mate of  potassa  in  water,  equal  measures  of  strong  hydrochloric  acid  and  alcohol 
are  added  in  successive  small  portions,  until  the  red  tint  of  the  chromic  acid  dis- 
appears entirely,  and  the  liquid  acquires  a  pure  green  colour.     On  pouring  an 


380  CHROMIUM. 

excess  of  pure  ammonia  into  this  solution,  a  pale  green  bulky  hydrate  subsides, 
which  consists  of  1  eq.  of  the  oxide  and  26  eq.  of  water.  (Thomson.)  The 
oxide,  in  this  state,  is  readily  dissolved  by  acids.  On  expelling  the  water  by 
heat,  the  sudden  approximation  of  the  particles,  which  abruptly  occurs  at  a  cer- 
tain temperature,  causes  such  intense  evolution  of  heat  that  the  whole  mass  be- 
comes vividly  incandescent. 

The  anhydrous  oxide  is  formed  when  bichromate  of  potassa  is  briskly  boiled 
with  sugar  and  a  little  hydrochloric  acid.  At  first  a  brown  matter  falls,  consist- 
ing of  the  acid  and  oxide  of  chromium ;  but  subsequently  the  green  oxide  appears 
in  the  form  of  a  finely  divided  powder.  If  the  bichromate  and  sugar  are  employed 
without  hydrochloric  acid,  the  brown  matter  is  the  only  solid  product,  and  on 
boiling  this  compound  with  a  little  carbonate  of  potassa,  a  greenish-blue  carbon- 
ate of  chromium,  of  a  very  fine  colour,  is  obtained.  For  this  mode  of  preparation 
I  am  indebted  to  my  late  pupil,  Mr.  Thomas  Thomson,  of  Clitheroe,  near  Man- 
chester. 

Its  eq.  is  80 ;  symb.  2Cr  +  30,  Cr,  or  Cr  O3. 

Chromic  Acid. — Prep. — This  acid  is  best  prepared  by  transmitting  the  gaseous 
fluoride  of  chromium  into  water  contained  in  a  vessel  of  silver  or  platinum,  when 
by  mutual  decomposition  of  the  gas  and  the  water,  hydrofluoric  and  chromic  acids 
are  generated :  the  former  is  then  expelled  by  evaporating  the  solution  to  dryness, 
and  the  latter  in  a  pure  state  remains.  If  the  gas  is  conducted  into  a  silver  ves- 
sel which  is  only  moistened  with  water,  and  the  aperture  of  which  is  closed  by 
a  piece  of  moist  paper,  the  chromic  acid  is  obtained  in  the  form  of  acicular  crys- 
tals of  a  cinnabar  red  colour,  w^hich  are  so  voluminous  and  abundant  as  to  fill  the 
interior  of  the  vessel.  Another  method  of  preparing  chromic  acid  has  been  sug- 
gested by  Arnold  Maus,  which  consists  in  decomposing  a  hot  concentrated  solu- 
tion of  bichromate  of  potassa  by  silicated  hydrofluoric  acid.  The  chromic  acid, 
after  being  separated  from  the  sparingly  soluble  fluoride  of  silicon  and  potassium, 
is  evaporated  to  dryness  in  a  platinum  capsule,  and  then  redissolved  in  the  small- 
est possible  quantity  of  water.  By  this  means  the  last  portions  of  the  double 
salt  are  rendered  insoluble,  and  the  pure  chromic  acid  may  be  separated  by  decanta- 
tion.  The  acid  must  not  be  filtered  in  this  concentrated  state,  as  it  then  corrodes 
paper  like  sulphuric  acid,  and  is  converted  into  chromate  of  the  green  oxide  of 
chromium.  Asbestus,  however,  might  be  used  for  filtering  this  acid,  in  the  same 
way  as  the  permanganic  acid.  (Gregory.)  When  it  is  wished  to  prepare  a  large 
quantity  of  chromic  acid  by  this  process,  porcelain  vessels  may  be  safely  em- 
ployed in  the  first  part  of  the  operation,  provided  care  is  taken  to  add  a  quantity 
of  silicated  hydrofluoric  acid  not  quite  sufl5cient  for  precipitating  the  whole  of 
the  potassa.     (Edinburgh  Journal  of  Science,  viii.  175.) 

It  was  formerly  prepared  by  digesting  chromate  of  baryta  or  oxide  of  lead  in 
dilute  sulphuric  acid,  the  quantity  of  the  latter  being  regulated  with  the  view  of 
decomposing  the  chromate  without  being  in  excess.  A  dark  ruby-red  solution 
is  thus  obtained,  which  by  evaporation  yields  irregular  crystals,  and  was  sup- 
posed to  contain  pure  chromic  acid  ;  but  Gay-Lussac  showed  that  the  acid  when 
|hus  procured  is  never  pure,  being  intimately  combined  with  sulphuric  acid.  On 
endeavouring  to  expel  the  latter  by  heatj  the  chromic  acid  itself  yields  oxygen, 
and  is  more  or  less  completely  converted  into  sulphate  of  the  green  oxide. 

Prop. — Pure  dry  chromic  acid  is  black  while  warm,  and  of  a  dark  red  colour 
when  cold.  It  is  very  soluble  in  water,  rendering  it  red  or  yellow  according  to 
the  degree  of  dilution ; — when  the  solution  is  concentrated  by  heat  and  allowed 


CHROMIUM.  381 

to  cool,  it  deposits  red  crystals,  which  deliquesce  readily  in  the  air.  In  alcohol 
it  is  also  soluble,  but  the  action  of  heat  or  light  causes  its  conversion  into  the 
green  oxide.  Its  taste  is  sour,  and  with  alkalies  it  acts  as  a  strong  acid.  It  is 
converted  into  the  green  oxide,  with  evolution  of  oxygen,  by  exposure  to  a  strong 
heat.  It  yields  a  chloride  when  boiled  with  hydrochloric  acid  and  alcohol,  and 
the  direct  solar  rays  have  a  similar  effect  when  hydrochloric  acid  is  present :  the 
mutual  action  sets  chlorine  free,  and  hence  the  solution  acquires  the  property  of 
dissolving  gold.  With  sulphurous  acid  it  forms  a  sulphate  of  the  oxide ;  and  it 
is  more  or  less  completely  converted  into  the  oxide  by  being  boiled  with  sugar, 
starch,  or  various  other  organic  principles.  It  destroys  the  colour  of  indigo,  and 
of  most  vegetable  and  animal  colouring  matters ;  a  property  advantageously  em- 
ployed in  calico-printing,  and  which  manifestly  depends  on  the  facility  with 
which  it  is  deprived  of  oxygen.  ^ 

Chromic  acid  is  characterized  by  its  colour,  and  by  forming  coloured  salts 
with  alkaline  bases.  The  most  important  of  these  salts  is  chromate  of  oxide  of 
lead,  which  is  found  native  in  small  quantity,  and  is  easily  prepared  by  mixing 
chromate  of  potassa  with  a  soluble  salt  of  lead.  It  is  of  a  rich  yellow  colour,  and 
is  employed  in  the  arts  of  painting  and  dyeing  to  a  great  extent.  When  heated 
to  redness,  it  is  also  much  used  as  the  oxidizing  agent  in  the  ultimate  analysis 
of  organic  substances.     (Liebig.) 

When  sulphurous  acid  gas  is  transmitted  into  a  solution  of  chromate  or  bichro- 
mate of  potassa,  a  brown  precipitate  subsides,  which  was  long  regarded  as  a  dis- 
tinct oxide  of  chromium ;  but  Thomson  has  proved  that  it  is  the  green  oxide  com- 
bined with  a  little  chromic  acid.  The  acid  may  in  a  great  measure  be  washed 
away  by  means  of  water,  and  by  ammonia  it  is  entirely  removed ;  but  the  best 
mode  of  separating  it,  is  to  dissolve  the  brown  matter  with  hydrochloric  acid, 
and  then  precipitate  the  green  oxide  by  ammonia.  The  brown  compound  may  be 
formed  by  boiling  a  solution  of  bichromate  of  potassa  with  alcohol;  and  it  is  also 
rapidly  generated,  when  bichromate  of  potassa  is  gently  boiled  with  sugar  and  a 
very  little  hydrochloric  acid. 

Its  eq,  is  52 ;  symb.  Cr  +  30,  Cr,  or  CrOj, 

Sesqutchloride  of  Chromium. — It  is  prepared  by  transmitting  dry  chlorine  gas 
over  a  mixture  of  oxide  of  chromium  and  charcoal  heated  to  redness  in  a  tube  of 
porcelain,  when  the  sesquichloride  gradually  collects  as  a  crystalline  sublimate 
of  a  peach-purple  colour,  which  in  thin  layers  is  transparent,  but  in  thicker  masses 
is  opaque.  Another  method  is  to  evaporate  the  green  solution  of  this  chloride 
gently  to  dryness  at  a  temperature  of  212°,  when  a  green  powder  remains,  con- 
sisting of  1  eq.  of  the  sesquichloride  and  3  eq.  of  water  (CrjCla  -+-  3  H),  these 
elements  being  exactly  in  the  ratio  to  form  oxide  of  chromium  and  hydrochloric 
acid.  On  raising  the  temperature  above  212°,  no  water  is  lost  until  it  reaches 
400° ;  the  powder  then  begins  to  swell  up  from  the  escape  of  water,  the  colour 
changes  from  green  to  the  red  of  peach-blossoms,  and  pure  sesquichloride  remains. 
This  part  of  the  process  should  be  conducted  in  a  tube  from  which  air  is  ex- 
cluded by  a  current  of  dry  carbonic  acid  gas.  These  phenomena  are  quoted  by 
Liebig  as  favouring  the  notion  that  the  green  solution  and  powder  are  a  hydro- 
chlorate  of  an  oxide,  and  not  a  chloride  with  water.  Gregory  has  shown  ( Joum. 
de  Pharm.)  that  the  pink  powder,  first  obtained  by  Kemp  from  the  action  of 
chloride  of  sulphur  on  oxychloride  of  chromium,  is  an  isomeric  modification  of 
the  sesquichloride  above  described.    It  is  not  crystalline,  and  quite  insoluble  in 


382  CHROMIUM. 

water ;  but  by  long  exposure  to  air  it  passes  slowly  into  the  soluble  state.  Being 
formed  at  a  high  temperature,  it  probably  differs  from  the  soluble  variety  as  ig- 
nited alumina,  peroxide  of  iron,  or  sesquioxide  of  chromium,  do  from  the  same 
oxides  previous  to  ignition.  The  existence  of  this  modification  has  lately  been 
confirmed  by  Rose.     (Annalen  der  Pharm.  1840.) 

The  sesquichloride  of  chromium  dissolves  slowly,  forming  a  deep  green  solu- 
tion. The  same  may  be  prepared  by  directly  dissolving  the  hydrated  oxide  in 
hydrochloric  acid ;  or  by  digesting  chromate  of  oxide  of  lead  in  strong  hydro- 
chloric acid,  adding  a  little  alcohol  from  time  to  time  to  promote  the  deoxidation 
of  chromic  acid,  and  then  separating  the  resulting  chloride  of  chromium  from  that 
of  lead  by  strong  alcohol,  which  together  with  any  excess  of  hydrochloric  acid  is 
ultimately  expelled  by  evaporating  to  dryness.  Traces  of  lead  which  may  have 
been  dissolved  ^e  easily  precipitated  by  hydrosulphuric  acid. 

Its  eq.  is  162-26;  symb,  2Cr  +  3  CI,  or  CraClj. 

[In  some  recent  researches  on  the  compounds  of  chromium,  M.  Peligot  an- 
nounces the  discovery  of  a  protochloride  CIO,  which  it  seems  had  escaped  the 
observation  of  chemists.  He  states  that  it  is  always  formed  in  the  preparation 
of  the  sesquichloride  when  a  current  of  dry  chlorine  is  passed  over  a  mixture  of 
the  oxide  of  chromium  and  charcoal,  heated  to  redness.  In  this  process,  it  pre- 
cedes the  formation  of  the  sesquichloride,  and  appears  as  a  sublimate  in  the  form 
of  very  fine  sparkling  white  crystals  which  are  mingled  with  more  or  less  carbon 
and  oxide  of  chromium.  But  it  may  be  procured  in  a  state  of  perfect  purity  by 
passing  hydrogen  over  the  violet  sesquichloride  contained  in  a  tube  of  hard  glass. 
A  considerable  rise  of  temperature  attends  the  reaction,  hydrochloric  acid  escapes, 
and  the  protochloride  remains  in  the  tube  as  a  white  crystalline  mass,  having  the 
same  form  as  the  mass  of  sesquichloride  originally  used.  The  analyses  of  these 
crystals  show  them  to  be  composed  of  single  equivalents  of  chlorine  and  chro- 
mium. 

The  protochloride  readily  dissolves  in  water,  the  solution  being  attended  by  a 
considerable  rise  of  temperature.  The  solution  is  at  first  blue  in  colour,  but  by 
exposure  to  the  air,  soon  becomes,  green,  oxygen,  at  the  same  time,  being  ab- 
sorbed with  great  rapidity. 

The  solubility  in  water  which  has  heretofore  been  attributed  to  the  sublimed 
sesquichloride,  M.  Peligot  states,  is  due  to  the  presence  of  the  protochloride 
which  accompanies  it ;  thq^ormer  according  to  his  observations  being  entirely 
insoluble  in  cold  or  hot  water  as  well  as  remarkably  indifferent  to  the  action  of 
most  of  the  powerful  acids.  Even  aqua  regia  does  not  affect  it.  In  a  solution, 
however,  of  water,  containing  only  a  minute  quantity  of  the  protochloride,  it  dis- 
solves with  surprising  facility.  The  solution  thus  obtained  possesses  all  the  pro- 
perties of  that  of  the  hydrated  sesquichloride  of  chromium  prepared  in  the  moist 
way,  viz.  by  the  action  of  hydrochloric  acid  and  alcohol  on  chromic  acid  or  the 
chromate  of  lead. 

In  the  same  researches,  M.  Peligot  obtained  a  protoxide  of  chromium  CrO, 
and  an  intermediate  oxide  CrgO^,  or  CrO  +  Cr^Oa,  analogous  to  the  magnetic 
oxide  of  Iron.     (Compt.  Rendus,  t.  xix.  p.  609  et  734.)] 

Sesqui/luoride  of  Chromium  is  formed  by  dissolving  the  oxide  in  hydrofluoric 
acid,  and  evaporating  the  solution  to  dryness,  when  the  sesquifluoride  remains  as 
a  green  crystalline  residue,  which  is  soluble  in  water.  Its  eq.  is  112*04 ;  symb. 
2Cr+3F,orC^F3. 

Perfluoride  of  Chromium, — Discovered  by  Unverdorben  in  1825  (Ed.  Journ.  of 


CHROMIUM.  383 

Science,  iv.  129).  When  a  mixture  of  3  parts  of  fluor-spar  and  4  of  chromate  of 
oxide  of  lead  is  distilled  with  5  parts  of  fuming  or  even  common  sulphuric  acid 
in  a  leaden  or  silver  retort,  a  red-coloured  gas  is  disengaged,  which  acts  rapidly 
upon  glass,  with  deposition  of  chromic  acid  and  formation  of  fluosilicic  acid  gas. 
It  is  decomposed  by  water,  and  the  solution  is  found  to  contain  a  mixture  of 
hydrofluoric  and  chromic  acids.  The  watery  vapour  of  the  atmosphere  effects 
its  decomposition,  so  that  when  mixed  with  air,  red  fumes  appear,  owing  to  the 
separation  of  minute  crystals  of  chromic  acid. 

The  red  colour  of  terfluoride  of  chromium  naturally  excites  the  suspicion  that 
the  gas  itself  may  consist,  not  of  fluoride  of  chromium,  but  of  hydrofluoric  and 
chromic  acids ;  and  its  production  by  means  of  hydrous  sulphuric  acid  is  con- 
sistent with  this  idea.  But  since  the  gas  may  also  be  formed  from  fluor-spar, 
chromate  of  oxide  of  lead,  and  anhydrous  sulphuric  acid,  it  is  clear  that  this  view 
is  inadmissible.  It  was  formerly  considered  to  be  composed  of  1  eq.  of  chromium 
and  3  eq.  of  fluorine,  and  was  hence  described  as  the  terfluoride.  H.  Rose  has 
shown,  however,  that  its  elements  approximate  more  closely  to  the  ratio  of  1  to 
5  rather  than  1  to  3 ;  but  its  true  constitution  is  not  yet  satisfactorily  deter- 
mined.   It  is  perhaps  CrFj. 

Sulphurel  of  Chromium  may  be  formed  by  transmitting  the  vapour  of  bisul- 
phuret  of  carbon  over  oxide  of  chromium  at  a  white  heat ;  by  heating  in  close 
vessels  an  intimate  mixture  of  sulphur  and  the  hydrated  oxide;  by  fusing  the 
oxide  with  a  persulphuret  of  potassium,  and  dissolving  the  soluble  parts  in  water ; 
or  by  transmitting  hydrosulphuric  acid  gas  aided  by  heat  over  the  sesquichloride 
of  chromium.  It  cannot  be  prepared  in  the  moist  way.  It  is  of  a  dark  grey 
colour,  and  acquires  metallic  lustre  by  friction  in  a  mortar.  It  is  readily  oxidized 
when  heated  in  the  open  air,  and  is  dissolved  by  nitric  or  nitro-hydrochloric  acid. 

Its  eq.  is  104-3;  symb,  2Cr  -f-  3S,  or  CrjSj. 

Phosphuret  of  Chromium. — Rose  prepared  this  compound  by  acting  on  the 
sesquichloride  of  chromium  by  phosphuretted  hydrogen  gas  at  a  red  heat.  By 
mutual  interchange  of  elements 

1  eq.  Sesquichloride  Cr2Cl3    2     2  eq.  Phosphuret  2CrP. 

and  1  eq.  Phosphur.  Hyd.  P2H3        I,    and  3  eq.  Hydrochloric  Acid.       3HC1. 

This  phosphuret  is  black,  insoluble  in  hydrochloric  acid,  feebly  attacked  by 
nitric  and  nitro-hydrochloric  acid,  and  burns  before  the  blowpipe  with  a  flame  of 
phosphorus. 

Its  eq.  is  43-7;  symb.  Cr  f  P,  or  CrP. 

Another  phosphuret  of  a  grey  colour  may  be  formed  by  exposing  the  phosphate 
of  oxide  of  chromium  to  a  strong  heat  in  a  covered  crucible  lined  with  charcoal. 
Its  composition  is  unknown. 

Oxy chloride  of  Chromium. — Hist. — Discovered  by  Unverdorben  at  the  same 
time  as  the  perfluoride  of  chromium  ;  it  was  long  considered  and  described  as 
the  terchloride,  until  Rose  pointed  out  its  real  constitution.  (Pog.  An.  xxvii. 
565.) 

Prep. — By  the  action  of  fuming  sulphuric  acid  on  a  mixture  of  about  equal 
weights  of  chromate  of  oxide  of  lead  and  chloride  of  sodium.  Wohler  recom- 
mends the  following  process  :  10  parts  of  chloride  of  sodium  are  fused  in  a  com- 
mon crucible  with  16-9  parts  of  the  neutral  chromate  of  potassa,  the  fused  salts 
are  thrown  upon  a  clean  stone,  and  the  mass  when  cold  is  broken  into  coarse 


384  VANADIUM. 

fragments.  These  are  to  be  introduced  into  a  capacious  tubulated  retort,  to 
which  a  receiver  kept  cold  by  moistened  paper  is  adapted.  Twelve  parts  of 
fuming  sulphuric  acid  are  then  added  to  the  fused  salts,  when  an  energetic  action 
commences,  and  in  a  few  minutes,  the  oxychloride  is  formed  and  distilled  over 
without  the  application  of  external  heat.     (Pog.  An.  xxxiii.  343.) 

Prop, — It  is  a  heavy  red  liquid,  exceedingly^  volatile,  yielding  abundant  red 
vapours  when  exposed  to  the  air.  By  water  it  is  instantly  decomposed  into 
hydrochloric  and  chromic  acids.  Its  vapour  is  decomposed  by  a  red  heat  into 
oxide  of  chromium,  oxygen,  and  chlorine,  as  observed  by  Wohler,  who  has  thus 
confirmed  the  composition  of  the  oxychloride  as  stated  by  Rose.  The  latter 
chemist  found  it  was  composed  of  2  eq.  of  chromic  acid  and  1  eq.  of  a  perchlo- 
Tide ;  and  the  former,  that  2  eq.  of  the  oxychloride  produced  3  eq.  of  the  oxide 
of  chromium,  3  eq.  of  oxygen,  and  6  eq.  of  chlorine.    In  symbols, 


2  {CrCl3-|-2Cr05)         yield        ^30, 


(  3Cr203. 
30. 
6C1. 


Its  eq.  is  210-26 ;  symb.  CrClj  +  SCrOa. 

Millon  considers  it  as  chromic  acid  in  which  1  eq.  oxygen  is  replaced  by 

CI  "J 

chlorine,  Cr   p.    >  .    The  same  ingenious  chemist  has  extended  this  view  to  the 

bleaching  compounds  of  chlorine.    Thus  bleaching  powder,  commonly  viewed 

as  CaO,  CIO  -f-  CaCl,  may  be  viewed  as  an  oxychloride  of  calcium,  Ca^    >  . 

For  further  details,  I  must  refer  to  the  foreign  journals,  as  I  have  not  been  able 
to  obtain  the  original  memoir.    (Editor). 

VANADIUM. 

Hist, — Vanadium,  so  called  from  Vanadis,  the  name  of  a  Scandinavian  deity, 
was  discovered  in  the  year  1830  by  Sefstrom,  of  Fahlun,  in  iron  prepared  from 
the  iron-ore  of  Taberg  in  Sweden.  The  state  in  which  it  occurs  in  the  ore  is 
unknown ;  but  Sefstrom  separated  it  from  the  iron  by  dissolving  the  latter  in 
hydrochloric  acid,  when  a  black  powder  came  into  view  containing  a  small  quan- 
tity of  vanadium,  together  with  iron,  copper,  cobalt,  silex,  alumina,  and  lime. 
He  afterwards  found  a  more  abundant  source  in  the  slag  or  cinder  formed  during 
the  conversion  of  the  cast-iron  of  Taberg  into  malleable  iron.  Soon  after  Sef- 
strom's  discovery,  the  same  metal  was  found  by  Johnston,  of  Durham,  in  a 
mineral  from  Wanlockhead  in  Scotland,  where  it  occurs  as  a  vanadiate  of  oxide 
of  lead.  A  similar  mineral,  found  at  Zimapan  in  Mexico,  was  examined  in  the 
year  1801  by  Professor  del  Rio,  who,  in  the  belief  of  having  discovered  a  new 
metal,  gave  it  the  name  of  Eryihronium,  apparently  from  the  red  colour  of  its 
acid ;  but  as  Collet  Descotils,  on  being  appealed  to,  declared  the  mineral  to  be 
chromate  of  lead,  Del  Rio  abandoned  his  own  opinion  in  deference  to  a  higher 
atrthority.  Thus  have  three  persons  noticed  the  existence  of  vanadium,  without 
the  knowledge  of  each  other's  labours ;  but  the  merit  of  being  the  first  discoverer 
is  fairly  due  to  Sefstrom.* 

Prep, — From  the  slag  above-mentioned  vanadic  acid  may  be  obtained  by  the 


•Phil.  Mag.  and  Annals,  x.  321.    An.  de  Ch.  ct  Ph.  xlvii.  337.    Brewster's  Journal,  r 
318,  N.  S.    Poggendorflf 's  Annalen,  xxii.  1. 


1 


VANADIUM.  335 

following  process,  contrived  by  Sefstrom  and  improved  by  Berzelius.  The  slag 
in  fine  powder,  mixed  with  its  own  weight  of  nitre  and  twice  its  weight  of  car- 
bonate of  potassa,  is  strongly  ignited  for  the  space  of  one  hour.  The  soluble 
parts  are  then  removed  by  boiling  water,  and  the  solution,  after  being  filtered 
and  neutralized  with  colourless  nitric  acid,  is  precipitated  by  chloride  of  barium 
or  acetate  of  lead.  The  precipitate,  which  consists  of  vanadiate  and  phosphate 
of  baryta  or  oxide  of  lead,  zirconia,  alumina,  and  silicic  acid,  is  decomposed, 
while  still  moist,  by  digestion  with  strong  sulphuric  acid ;  to  the  deep-red  solu- 
tion, alcohol  is  then  added,  when  by  continued  digestion  ether  is  disengaged, 
and  all  the  vanadic  acid  converted  into  the  salifiable  oxide,  the  solutions  of  which 
are  blue  ; — a  change  effected  in  order  the  more  completely  to  remove  the  vanadic 
acid  from  the  insoluble  matters.  The  blue  liquid  is  then  evaporated  ;  and  when 
it  acquires  a  syrupy  consistence,  it  is  mixed  in  a  platinum  crucible  with  a  little 
hydrofluoric  acid,  and  sharply  heated  in  an  open  fire.  By  this  means  the  silicic 
acid,  which  can  only  be  got  rid  of  in  this  way,  is  converted  into  the  gaseous 
fluoride  of  silicon,  the  sulphuric  acid  expelled,  and  the  oxide  reconverted  into 
the  acid  of  vanadium. 

The  vanadic  acid  still  contains  phosphoric  acid,  alumina,  and  zirconia.  For 
its  further  purification  it  is  fused  with  nitre  added  in  successive  small  portions, 
until,  on  cooling  a  small  quantity,  the  red  tint  is  found  to  have  disappeared.  In 
this  process  the  acid  of  the  nitre  is  displaced  by  the  phosphoric  and  vanadic 
acids,  the  object  being  to  cause  those  acids  to  unite  with  potassa  without  em- 
ploying an  excess  of  nitre.  The  vanadiate  and  phosphate  of  potassa  are  then 
taken  up  by  as  small  a  quantity  of  water  as  will  suffice,  and  into  the  filtered 
liquid  a  piece  of  sal-ammoniac,  larger  than  can  be  dissolved  by  it,  is  introduced  : 
as  it  dissolves,  vanadiate  of  ammonia,  insoluble  in  a  saturated  solution  of  sal- 
ammoniac,  subsides  as  a  white  powder,  leaving  the  phosphoric  acid  in  the  liquid. 
The  vanadiate  of  ammonia  should  be  first  washed  with  a  solution  of  sal-ammo- 
niac, and  then  with  alcohol  of  sp.  gr.  0*86. 

By  heating  this  salt  in  an  open  platinum  crucible,  vanadic  acid  is  obtained ; 
but  the  temperature  ought  to  be  kept  below  that  of  redness,  and  the  mass  be 
well  stirred  until  it  acquires  a  dark  red  colour.  Heated  in  close  vessels  the 
vanadiate  of  ammonia  is  converted  principally  into  the  salifiable  oxide  ;  though 
some  of  the  protoxide  and  acid  are  mixed  with  it.  With  the  zirconia  and  alu- 
mina, left  by  the  water  after  fusion  with  nitre,  some  vanadium  remains  :  it  may 
be  extracted  by  fusion  with  sulphur  and  carbonate  of  potassa,  when  a  double 
sulphuret  of  vanadium  and  potassium  is  generated,  which  is  soluble  in  water. 
On  adding  sulphuric  acid  to  the  solution,  sulphuret  of  vanadium  is  precipitated. 

The  preparation  of  vanadium  from  the  native  vanadiate  of  lead  is  much  less 
complicated  than  the  process  above  described.  It  suffices  to  dissolve  the  ore, 
as  Johnston  advises,  in  nitric  acid,  and  to  precipitate  the  lead  by  hydrosulphuric 
acid,  which  also  throws  down  any  arsenic  that  may  be  present.  As  vanadic  acid 
is  deoxidized  by  hydrosulphuric  acid,  a  blue  solution  is  formed;  but  by  evapo- 
rating to  dryness  the  acid  is  reproduced.  The  residue  is  then  dissolved  by  a 
solution  of  ammonia,  and  the  vanadiate  of  ammonia  precipitated  as  before  by  a 
piece  of  sal-ammoniac.  The  vanadic  acid  is  thus  separated  from  arsenic,  phos- 
phoric, and  hydrochloric  acids,  with  which  in  the  ore  of  Wanlockhead  it  is  gene- 
rally associated. 

The  attempts  of  Berzelius  to  reduce  vanadic  acid  to  the  metallic  state  by  the 
agency  of  hydrogen  or  charcoal  at  high  temperatures  proved  unsuccessful,  as  the 

37 


386 


VANADIUM. 


protoxide  alone  was  obtained.  He  procured  the  metal,  however,  in  the  form  of 
a  heavy  black  powder,  by  placing  fragments  of  fused  vanadic  acid  and  potassium 
of  equal  size  in  alternate  layers  in  a  porcelain  crucible,  the  potassium  being 
in  the  largest  proportion :  a  cover  was  then  luted  on,  and  heat  applied  by  means 
of  a  spirit-lamp.  The  reduction  took  place  suddenly  and  with  violence;  and 
when  the  mass  had  cooled,  the  potassa  and  redundant  potassium  were  separated 
by  water.  But  Berzelius  succeeded  better  by  a  process  similar  to  that  of  H. 
Rose  for  procuring  metallic  titanium.  The  liquid  chloride  of  vanadium  is  intro- 
duced into  a  glass  bulb  blown  in  a  barometer  tube,  and  through  it  is  transmitted 
dry  ammoniacal  gas  until  a  white  saline  mass  is  produced,  during  the  formation 
of  which  the  gas  is  rapidly  absorbed,  and  heat  disengaged.  A  spirit  lamp  flame 
is  then  applied,  which  expels  a  quantity  of  hydrochlorate  of  ammonia,  and  metal- 
lic vanadium  is  left  adhering  to  the  interior  of  the  bulb.  The  production  of 
hydrochloric  aeid  is  obviously  owing  to  chlorine  leaving  the  vanadium  and 
uniting  with  the  hydrogen  of  part  of  the  ammonia. 

Prop. — The  pulverulent  vanadium,  produced  by  means  of  potassium,  has  but 
little  of  the  tenacity  and  appearance  of  a  metal,  though  under  strong  pressure  it 
assumes  a  lustre  like  that  of  graphite.  Heated  in  the  open  air  to  commencing 
redness  it  takes  fire,  and  is  converted  into  the  black  protoxide.  It  conducts  elec- 
tricity, however,  and  is  strongly  electro-negative  in  relation  to  zinc.  As  procured 
by  Rose's  process  the  vanadium  has  a  strong  metallic  lustre  and  a  white  colour 
considerably  resembling  silver,  but  still  more  like  molybdenum.  It  is  so  ex- 
tremely brittle  that  it  cannot  be  removed  from  the  glass  bulb  without  falling  into 
powder.  It  is  not  oxidized  either  by  air  or  water ;  although  by  continued  expo- 
sure to  the  air  its  lustre  gradually  grows  weaker,  and  it  acquires  a  reddish  tint. 
It  is  not  dissolved  by  boiling  sulphuric,  hydrochloric,  or  hydrofluoric  acid;  but 
by  nitric  and  nitro-hydrochloric  acid  it  is  attacked,  and  the  solution  has  a  beau- 
tiful dark  blue  colour.  It  is  not  oxidized  by  being  boiled  with  caustic  potash, 
nor  by  carbonated  alkalies  at  a  red  heat. 

The  eq.  of  vanadium,  according  to  the  analysis  of  its  oxides  by  Berzelius,  is 
68-5;  its  symb  is  V  ;  and  its  compounds  described  in  this  section  are  thus  con- 
stituted : — 


Vana 

idium. 

Equiv. 

Formulae. 

Protoxide 

68-5 

1  eq.-|- Oxygen        8 

1  eq.=  76-5 

V-fO     orVO. 

Binoxide 

68-5 

leq.f     do.         16 

2  eq.=  84-5 

V-f-20  orVOi. 

Vanadic  Acid 

68-5 

1  eq.-j-     do.          24 

3  eq.=  92-5 

V-f30  orVOj. 

Bichloride 

68-5 

1  eq.-|- Chlorine    70-84 

2  eq.=l  39-34 

V-i-2Cl  or  VCI2. 

Terchloride 

68-5 

1  eq.-i"     do.       106-26 

3  eq.=l74-76 

V-f3ClorVCl3. 

Bibromide 

68-5 

1  eq.-f- Bromine  156-8 

2  eq.=225-3 

V-f2Bror  VBrj. 

Bisulphurct 

68-5 

1  eq.-f-Sulphur     32-2 

2  eq.=100-7 

V-I-2S  orVSa. 

Teraulphuret 

68-5 

1  eq--f-    do.         48-3 

3eq.=ll6-8 

V+3S  orVSa. 

Protoxide. — ^This  compound  is  readily  formed  from  vanadic  acid  by  the  com- 
bined agency  of  heat  and  charcoal  or  hydrogen  gas.  By  means  of  the  latter 
Berzelius  found  that  the  reduction  is  effected  as  perfectly  at  a  temperature  short 
of  ignition,  as  at  the  strongest  heat  of  a-  wind  furnace.  When  prepared  from 
fused  vanadic  acid,  the  protoxide  retains  the  crystalline  structure  of  the  acid, 
and  has  a  black  colour  and  a  semi-metallic  lustre;  but  it  is  easily  broken  down 
into  a  fine  black  powder.     When  rendered  coherent  by  compression  it  possesses 


VANADIUM.  887 

a  property  very  unusual  in  oxides,  that  of  conducting  electricity,  and  in  relation 
to  zinc  of  being  as  strongly  electro-negative  as  silver  or  copper. 

It  is  very  infusible.  When  heated  in  open  vessels  it  takes  fire  and  burns  like 
tinder,  being  converted  into  the  binoxide.  On  exposure  to  air  and  moisture  it 
is  slowly  oxidized,  a  process  which  is  best  seen  by  putting  it  into  water,  when 
the  liquid  gradually  acquires  a  green  tint.  In  both  cases  the  oxygen  is  derived 
from  the  atmosphere.  A  similar  change  occurs  in  acid  and  alkaline  solutions, 
which,  with  the  exception  of  nitric  acid,  do  not  dissolve  it  even  at  a  boiling  tem- 
perature. Heated  in  nitric  acid  oxidation  ensues  with  escape  of  nitric  oxide  gas, 
and  a  blue  nitrate  of  the  binoxide  of  vanadium  is  generated.  The  character  of 
an  alkaline  base  seems  wholly  wanting  in  the  protoxide,  and  hence  Berzelius 

considers  it  as  a  sub-oxide.     Its  eq.  is  76*5 ;  symb.  V  -f-  0,  V,  or  VO. 

Binoxide. — Prep. — Best  prepared,  in  the  dry  way,  by  heating  to  full  redness 
an  intimate  mixture  of  10  parts  of  the  protoxide  with  12  of  vanadic  acid  in  a 
vessel  filled  with  carbonic  acid,  or  from  which  combustible  matter  on  one  hand, 
and  oxygen  gas  on  the  otlier,  are  carefully  excluded.  From  the  salts  of  the  bin- 
oxide, and  especially  the  sulphate,  it  is  precipitated  as  a  greyish-white  hydrate 
by  means  of  a  very  slight  excess  of  carbonate  of  soda.  The  residual  solution  is 
colourless  when  the  process  has  been  properly  conducted  :  it  remains  blue,  from 
undecomposed  salt,  if  an  insufficient  quantity  of  alkali  is  used  ;  it  is  brown  when 
the  alkaline  carbonate  is  too  freely  employed,  because  some  of  the  binoxide  is 
then  dissolved  by  the  free  alkali ;  and  if  the  solution  contained  vanadic  acid,  its 
colour  after  precipitation  is  green.  The  presence  of  the  latter  is  avoided  by  trans- 
mitting hydrosulphuric  acid  gas  into  the  solution,  whereby  vanadic  acid  is  effec- 
tually converted  into  the  binoxide,  but  the  redundant  gas  should  be  expelled  by 
gentle  heat  before  the  oxide  is  precipitated.  As  the  hydrate,  while  moist,  readily 
absorbs  oxygen,  and  hence  acquires  a  tint  of  brown,  it  must  be  washed  and  dried 
without  exposure  to  the  air.  When  thus  prepared  it  retains  its  grey  tint.  By 
exposure  to  heat  in  a  vessel  from  which  the  air  is  excluded,  it  gives  out  water, 
and  acquires  all  the  characters  of  the  oxide  prepared  in  the  dry  way. 

Prop. — A  black  pulverulent  substance,  very  infusible,  insoluble  in  water,  and 
free  from  any  acid  or  alkaline  reaction.  When  heated  in  the  open  air  it  is  con- 
verted into  vanadic  acid,  and  when  moist  it  gradually  suflfers  the  same  change 
at  ordinary  temperatures.  It  is  dissolved  by  acids  more  readily  as  a  hydrate  than 
after  being  heated  to  redness, and  forms  salts,  most  of  which  have  a  blue  colour, 
and  are  more  or  less  soluble  in  water.  They  may  all  be  conveniently  formed  by 
the  direct  action  of  acids  on  the  hydrated  oxide.  The  nitrate  may  be  made  by 
acting  on  vanadium,  or  either  of  its  oxides,  by  nitric  acid  ;  the  salt,  when  diluted 
with  water,  may  be  boiled  without  change;  but  when  evaporated  even  sponta- 
neously, the  blue  colour  passes  through  green  into  red,  owing  to  the  production 
of  vanadic  acid.  The  sulphate  is  easily  prepared  by  dissolving  vanadic  acid  in 
warm  sulphuric  acid  diluted  with  an  equal  weight  of  water,  decomposing  the 
vanadic  acid  by  hydrosulphuric  acid,  concentrating  the  solution  in  order  that  the 
salt  may  be  deposited,  and  washing  away  adhering  sulphuric  acid  by  means  of 
alcohol.  The  deoxidation  of  vanadic  acid  in  the  preceding  process  may  also  be 
effected  by  adding  pure  oxalic  acid  as  long  as  carbonic  acid  gas  is  evolved. 

The  salts  of  the  binoxide  of  vanadium  are  distinguished  by  their  blue  colour, 
by  yielding  with  the  alkalies  or  their  carbonates  in  very  slight  excess  the  hydrated 


388  VANADIUM. 

binoxide,  which  becomes  red  by  oxidation,  and  by  forming  with  solution  of  gall- 
nuts  a  black  compound,  a  tannate  of  the  binoxide,  very  similar  to  ink. 

The  binoxide  is  disposed  to  act  the  part  of  an  acid  by  uniting  with  alkaline 
bases,  with  which  it  forms  definite,  and  in  some  cases  crystalline,  compounds. 
On  digesting  the  hydrated  binoxide  in  pure  potassa  or  ammonia,  combination  is 
readily  effected,  and  a  dark  brown  solution  is  formed.  These  compounds,  though 
soluble  in  water,  are  very  sparingly  so  in  strong  and  cold  alkaline  solutions,  and 
may  be  precipitated  by  them.  Most  of  the  other  salts  formed  by  the  binoxide 
and  salifiable  bases  are  insoluble  in  water,  and  may  be  formed  from  the  preceding 
by  way  of  double  decomposition.    ., 

lU  eq.  is  84*5  ;  8i/7nb.  V  -f-  20,  V,  or  Voj. 

Vanadic  Acid. — When  vanadiate  of  ammonia,  prepared  as  already  mentioned, 
is  heated  in  close  vessels,  the  acid  is  decomposed  by  the  hydrogen  of  the  ammo- 
nia, and  binoxide  of  vanadium  is  formed,  mixed  with  a  little  protoxide  and  un- 
decomposed  acid.  If  the  salt  is  heated  in  an  open  vessel  and  well  stirred,  the 
whole  mass  acquires  a  dark  red  colour,  and  pure  vanadic  acid  is  obtained  :  but  a 
red  heat  should  be  avoided,  since  fusion  would  thereby  be  occasioned,  and  free 
exposure  of  every  part  to  the  atmosphere  prevented.  Its  colour  in  the  state  of 
fine  powder  is  a  light  rust-yellow  ;  but  the  fused  acid  is  red  with  a  shade  of 
orange,  and  has  a  strong  lustre.  By  light  transmitted  through  thin  layers  it  ap- 
pears yellow.  In  the  fire  it  is  fixed,  and  is  not  decomposed  by  a  very  strong 
heat,  provided  combustible  matters  are  excluded.  It  fuses  at  a  heat  lower  than 
that  of  redness,  and  crystallizes  readily  as  it  cools.  In  the  act  of  becoming 
solid  it  contracts  considerably  in  volume,  and  emits  so  much  heat  of  fluidity  that 
the  acid,  after  ceasing  to  be  luminous,  is  again  rendered  incandescent,  and 
remains  so  until  the  congelation  is  complete. 

It  is  tasteless,  insoluble  in  alcohol,  and  very  slightly  soluble  in  water,  which 
takes  up  rather  less  than  I-lOOth  of  its  weight  acquiring  a  yellow  colour  and  an 
acid  reaction.  Heated  with  combustible  matter  it  is  deoxidized,  being  converted 
into  the  protoxide  or  binoxide  or  mixtures  of  these  oxides.  In  solutions  it  is 
deprived  of  oxygen  by  all  deoxidizing  agents,  such  as  alcohol,  sugar,  and  most 
organic  substances,  including  the  oxalic  and  several  vegetable  acids,  by  hydro- 
sulphuric  acids,  and  most  of  the  other  hydracids,  not  excepting  the  hydrochloric, 
by  sulphurous  and  phosphorous  acids,  and  even  by  nitrous  acid.  Like  molybdic 
and  tungstic  acids  it  is  disposed  to  act  as  a  base  to  such  of  the  stronger  acids  as 
do  not  decompose  it,  and  to  form  with  them  definite  compounds,  which  are  solu- 
ble in  water.  It  unites  on  this  principle  with  sulphuric  and  phosphoric  acid  ; 
and  Berzelius  has  remarked  a  compound  of  the  phosphoric,  silicic,  and  vanadic 
acids,  a  sort  of  double  salt,  in  which  the  latter  acid  is  a  base  to  the  two  former, 
and  which  crystallizes  in  scales ;  it  is  formed  in  Sefstrom's  process  for  preparing 
vanadic  acid,  and  its  solubility  opposes  a  great  obstacle  to  the  separation  of 
vanadic  from  silicic  acid. 

Vanadic  acid  unites  with  salifiable  bases  often  in  two  or  more  proportions, 
forming  soluble  salts  with  the  alkalies,  and  in  general  sparingly  soluble  salts 
with  the  other  metallic  oxides.  Those  with  excess  of  acid  are  commonly  of  a 
red  or  orange-red  colour.  Most  of  the  neutral  salts  are  yellow  :  but  it  is  singu- 
lar that  the  neutral  vanadiates  of  the  alkalies,  the  alkaline  earths,  and  the  oxides 
of  lead,  zinc,  and  cadmium  may  be  yellow  at  one  time  and  colourless  at  another 
without  suffering  any  appreciable  change  in  composition.     Thus,  on  neutralizing 


VANADIUM..^ 

vanadic  acid  with  ammonia  a  yellow  salt  is  obtained,  the  solution  of  which  gra- 
dually becomes  colourless  if  kept  for  some  hours,  and  suffers  the  same  change 
rapidly  when  heated.  The  solution,  as  it  is  coloured  or  colourless,  gives  a  yel- 
low or  white  residue  by  evaporation,  and  a  yellow  or  white  precipitate  with  a  salt 
of  baryta  or  oxide  of  lead.  These  changes  appear  to  be  of  the  same  kind  as 
those  already  noticed  in  the  description  of  phosphoric  acid. 

Vanadic  acid  unites  in  different  proportions  with  binoxide  of  vanadium,  and 
forms  compounds  which  are  soluble  in  pure  water,  but  sparingly  so  in  saline 
solutions,  and  which  are  purple,  green,  yellow,  or  orange,  according  as  the  acid 
is  in  a  smaller  or  larger  proportion.  They  are  best  formed  by  exposing  the 
hydrated  binoxide  to  the  atmosphere,  when  these  different  colours  successively 
appear,  as  a  gradually  increasing  quantity  of  the  acid  is  generated. 

Vanadic  acid  is  distinguished  from  all  other  acids  except  the  chromic  by  its 
colour,  and  from  this  acid  by  the  action  of  deoxidizing  substances,  which  give  a 
blue  solution  with  the  former  and  a  green  with  the  latter.  When  heated  with 
borax  in  the  reducing  flame  of  the  blowpipe,  both  of  the  acids  yield  a  green 
glass ;  but  in  the  oxidizing  flame  the  bead  becomes  yellow  if  vanadium  is  pre- 
sent, while  the  green  colour  produced  by  chromium  is  permanent. 

Its  eq.  is  92-5  ;  symb.  V  +  30,  V,  or  VO3. 

Chlorides. — The  bichloride  is  prepared  by  digesting  a  mixture  of  the  vanadic 
and  hydrochloric  acids,  deoxidizing  any  undecomposed  vanadic  acid  by  hydro- 
sulphuric  acid,  and  evaporating  the  solution  to  dryness.  A  brown  residue  is 
obtained,  which  yields  a  blue  solution  with  water,  part  being  left  as  an  insoluble 
sub-salt.  It  may  also  be  generated  by  acting  directly  on  the  ignited  binoxide 
with  strong  hydrochloric  acid.  As  thus  obtained  its  solution  is  brown  instead 
of  blue,  though  in  composition  it  seems  identical  with  the  preceding.  Its  eq.  is 
139-34  ;  symb.  V  +  2C1,  or  VCl^. 

The  terchloride  may  be  formed  by  transmitting  a  current  of  dry  chlorine  gas 
over  a  mixture  of  protoxide  of  vanadium  and  charcoal  heated  to  a  low  redness, 
when  the  terchloride  passes  over  in  vapour,  and  condenses  in  the  form  of  a  yel- 
low liquid,  from  which  free  chlorine  may  be  removed  by  a  current  of  dry  air.  It 
is  converted  by  water  into  hydrochloric  and  vanadic  acid,  and  atmospheric 
humidity  produces  the  same  change,  which  is  indicated  by  the  escape  of  red 
fumes.     Its  eq.  is  174-76;  symb.  V  -f  3C1,  or  VCl^. 

A  bibromide  of  vanadium  may  be  formed  in  the  same  manner  as  the  bichloride, 
substituting  the  hydrobromic  for  hydrochloric  acid.  Similar  compounds  may  be 
procured  with  iodine,  fluorine,  and  cyanogen,  by  dissolving  binoxide  of  vanadium 
in  hydriodic,  hydrofluoric,  and  hydrocyanic  acid. 

Sulphurets. — When  the  binoxide  of  vanadium  is  heated  to  redness  in  a  current 
of  hydrosulphuric  acid  gas,  it  is  converted  into  protoxide,  and  both  water  and 
sulphur  are  obtained  :  on  continuing  the  process,  the  protoxide  is  decomposed, 
hydrogen  gas  and  water  pass  over,  and  bisulphuret  of  vanadium  is  generated. 
This  compound  may  also  be  procured  by  mixing  sulphate  of  ammonia  with  a 
salt  of  the  binoxide  of  vanadium  until  the  precipitate  at  first  formed  is  redis- 
solved,  and  then  decomposing  the  deep  purple-coloured  solution  by  sulphuric  or 
hydrochloric  acid.  The  bisulphuret  of  a  brown  colour  subsides,  which  becomes 
black  when  it  is  dried.  It  is  unchanged  at  common  temperatures  by  exposure  to 
the  air,  but  takes  fire  when  heated.  In  the  hydrated  state  it  is  dissolved  by  alka- 
lies and  alkaline  sulphurets;  but  it  is  insoluble  in  acids,  with  the  exception  of 


hw  whiA  it  IB  MJMf  ted  aMo  Kilphale  ^i  the 


Wfc«ik3p4r:-_^__:..  <:mittBd  ihvnisfc  an  aqueous  soladon  of 

iTiiDed,  consisting  of  hydiated  bin- 
salphnr.     But  if  a  solution  of  tbd- 
ialated  by  hydrochloric  or  salphnric 
hMu  -ides.    Its  colour  is  of  a  much 

tke  nami  himek  in  drying,  and  is 

hjm  mi  kHt  :  saeis  into  ifae  hiaii|ifcmm,  with  loss  of  water 

it  li  soluc..  _  „^:^lies  and  alkaliae  saipliarets,  and  is  oxidized 
bjahxieaeid. 

mi  ^mamtnmj  «f  a  hmium  gtu}  eoloar,  may  be  formed  by 

ci  Ike  binnwirte  a£  ▼■■adi—  mixed  with  a 

rf     ^ 


SECTION  XX. 


MOLYBDENUM— TCNG9rrEX.—C0LOIBirM. 


SaL  ami  iV(p.-.-THK  |»iBfei|ial  one  of  laiiljIiiiiiMi  isike  solplmv^ 
■•kaf  ■■atriKB  Ar  piphile,aaidwa»im  didiapBihcd  from  h  in  1778  by 
Ike  imd  m  ja  iiblMa  i J  la  a  ■epairtg  tata  hy  Hjchn.    Wken  tins 

esidae  is  bnairly  bralir  d  m  svier  to  ezpsl  salpksne  acid, 
01  tks  iatm  of  a  wkite  kesvj  powder.  From  tkis  acid 
■sy  ke  oktaiMd  hj  OTpssi^  it  vidi  ^areoal  Is  Ike 
straM^eat  kest  of  a  aandi's  fiHgs;  m  kj  rnwiTtisg  ovar  it  a  ement  of 
fai9M«kileslaBi*g^kealediBatBb*«f  pMeeku*  (Benetias.) 

iB  As  £ma  of  B^aljkdbia  «f  «ZBde  of  lead. 

cfto  it  baa  only  beea  obtained  is  a  state  of  saflufiMaoB.    lalkisfiMmit  kasasp. 
gr.ia^kykaliiiis»6l5andfiC3<.    Wfaca kesled  in spca vessels  it  absoibs 

msd  ky  Ike  ^titm  of  ckknine  eg  nitaa^ydmrikkrtri  s>id.    b  knsduw  degioee 

Bcssdias  iilMiiM  tks  «^  of  ■eljbdi— ■  t  47-7.    fU  wgmk.U  Mo.    Tke 


Acid 


Moiybdena. 

' 

EqviT.            Fonools. 

477  1eq.  +  0.yS« 

8 

1  ©q.  =  56-7      Mo  -|-  0  or  MoO. 

47-7  1  «|.  +     do. 

1« 

J  eq.  =   63-7      Mo  -f  20<w  MoO^. 

47^  1  e,.  -f-     do. 

34 

Seq.ss   71-7      Mot»><»'*''^- 

47-7  leq.-f-CMarise 

3»^ 

leq  s   ga-U    Mo  +  CiorMcCL 

MOLYBDENUM.  ^jf^ 

Molybdenum.  Equiv.  Formulae. 

Bichloride  47-7  1  eq.  -|-  Chlorine  70-84  2  eq.  =  118-54    Mo  -j-  2C1  or  MoClj. 

Bisulphuret  47-7  1  eq.  -f  Sulphur  322  2  eq.  =    79-9      Mo  -f-  2S  or  M0S2. 

Tersulphuret  47-7  1  eq.  -f     do.  483  3  eq.  =   96-0      Mo  -f  3S  or  M0S3. 

Persulphuret  477  1  eq.  -f     do.  64-4  4  eq.  =  112-1       Mo  -f"  4S  or  M0S4. 

OxychlorideiMoOa  143.4  2  eq.  -(-  M0CI3  153-96  1  eq.  =  297-36  2MoO  -f-  M0CI3. 

Protoxide  of  Molybdenum. — On  dissolving  molybdate  of  potassa  or  soda  in  a 
small  quantity  of  water,  adding  hydrochloric  acid  until  the  molybdic  acid  at  first 
thrown  down  is  redissolved,  and  digesting  with  a  piece  of  pure  metallic  zinc, 
the  latter  deoxidizes  the  molybdic  acid,  the  liquid  changes  to  blue,  red,  and 
black,  and  then  contains  chloride  of  zinc  and  protochloride  of  molybdenum. 
From  the  black  solution  pure  potassa  throws  down  the  protoxide  of  molybdenum 
as  a  black  hydrate,  an  excess  of  the  alkali  being  used  in  order  to  hold  the  zinc 
in  solution.  The  hydrate  is  washed  with  the  least  possible  exposure  to  the  air, 
and  dried  in  vacuo  by  sulphuric  acid.  When  heated  to  low  redness  in  the  open 
air  it  takes  fire  and  is  converted  into  the  binoxide;  but  if  not  exposed  to  the  air 
it  becomes  incandescent  at  the  moment  of  losing  its  water,  like  hydrated  oxide 
of  chromium.  The  anhydrous  oxide  is  black  and  insoluble  in  acids ;  but  in  the 
state  of  hydrate,  acids  dissolve  it.  The  recently  precipitated  hydrate  is  soluble 
in  the  cold  by  carbonate  of  ammonia,  but  in  none  of  the  other  alkalies. 

Its  eq.  is  55*7  ;  symb.  Mo  +  O,  Mo,  or  MoO. 

Binoxide  of  Molybdenum. — Prep. — Obtained  as  a  deep  brown  anhydrous  pow- 
der by  mixing  molybdate  of  soda  with  half  its  weight  of  sal-ammoniac  in  fine 
powder,  projecting  the  mixture  into  a  red-hot  crucible,  which  is  to  be  instantly 
covered,  and  the  heat  continued  until  vapours  of  sal-ammoniac  cease  to  appear. 
In  this  process  chloride  of  sodium  is  generated,  and  molybdic  acid  is  reduced  by 
the  ammonia  to  the  state  of  binoxide :  by  adding  water  to  the  mass  when  cold 
chloride  of  sodium  is  dissolved,  and  the  dark  brown,  nearly  black,  binoxide  left. 
The  hydrate,  of  a  rust-brown  colour,  may  be  formed  by  digesting  molybdenum  in 
powder  with  molybdic  acid  dissolved  in  hydrochloric  acid,  until  the  liquid 
acquires  a  deep  red  colour,  and  then  adding  ammonia ;  or  by  adding  ammonia  to 
a  solution  of  the  bichloride ;  or  digesting  with  metallic  copper  a  solution  of 
molybdic  in  hydrochloric  acid  until  a  deep  red  solution  is  formed,  and  employing 
an  excess  of  ammonia  in  order  to  keep  oxide  of  copper  in  solution. 

Prop. — The  anhydrous  binoxide  is  insoluble  in  acids  and  is  changed  into 
molybdic  acid  by  strong  nitric  acid.  The  hydrate  is  very  like  hydrated  peroxide 
of  iron,  reddens  litmus  paper  when  placed  on  it,  is  dissolved  by  acids  with 
which  it  forms  red  salts,  insoluble  in  the  alkalies,  but  dissolves  in  alkaline  car- 
bonates. It  is  soluble,  though  sparingly,  in  pure  water,  so  that  it  should  be 
washed  after  precipitation  by  a  solution  of  sal-ammoniac,  which  salt  is  afterwards 
removed  by  alcohol.  On  exposure  to  the  air,  the  hydrate  absorbs  oxygen  and 
becomes  blue  at  its  surface :  this  blue  compound  is  more  soluble  in  water  than 
the  hydrate,  and  was  supposed  by  Bucholz  to  be  a  distinct  acid,  which  he  termed 
molybdous  acid  ,•  but  Berzelius  has  shown  that  it  is  a  bimolybdate  of  the  binox- 
ide.  (Berzelius.) 

Its  eq.  is  63-7 ;  symb.  Mo  +  20,  Mo,  or  MoO^. 

Molybdic  Mid. — Prep. — When  sulphuret  of  molybdenum  is  roasted  in  an  open 
crucible  kept  at  a  low  red  heat,  and  constantly  stirred  until  sulphurous  acid 


MOLYBDENUM. 

ceases  to  escape,  a  dirty  yellow  powder  is  left,  which  contains  impure  molybdic 
acid.  The  acid  is  taken  up  by  amnionia  and  the  filtered  solution  evaporated  to 
dryness ;  it  is  again  taken  up  by  a  little  dilute  ammonia  and  filtered  ;  it  is  then 
purified  by  crystallization.  On  heating  gently  in  an  open  platinum  crucible, 
taking  care  to  prevent  fusion,  the  ammonia  is  expelled,  and  pure  acid  remains. 
It  is  also  obtained  by  oxidizing  the  binoxide  with  nitric  acid. 

Pr(yp, — As  thus  formed,  it  is  a  white  powder,  of  sp.  gr.  3-49,  fusible  by  a  red 
heat  into  a  yellow  liquid,  which  bears  a  strong  red  heat  in  closed  vessels  with- 
out subliming,  but  in  an  open  crucible  rises  with  the  cuirent  of  air,  and  collects 
on  cold  surfaces  in  colourless  crystalline  scales.  It  requires  570  times  its  weight 
of  water  for  solution,  which  nevertheless  has  an  acid  reaction.  It  is  soluble  in 
the  alkalies,  forming  colourless  molybdates,  from  which  molybdic  acid  is  pre- 
cipitated by  the  stronger  acids,  though  an  excess  of  the  acids  dissolves  it;  but 
after  exposure  to  a  red  heat  it  is  insoluble  in  acids. 

Chlorides. — Berzelius  has  described  three  chlorides  of  molybdenum  which  he 
considered  analogous  in  composition  to  the  oxides ;  but  his  terchloride  has  re- 
cently been  shown  by  Rose  to  be  an  oxychloride  which  has  the  same  constitu- 
tion as  the  oxychloride  of  chromium.     (Pog.  An.  xl.  395.) 

The  protochloride  is  formed  by  dissolving  the  hydrated  protoxide  in  hydro- 
chloric acid,  when  it  forms  a  deep  nearly  black  coloured  solution,  whiQli  leatves  a 
black  viscid  mass  by  evaporation.  ^        .         .^ 

Its  eq.  is  83-12;  symb.  Mo  +  CI,  or  MoCl.  '     ''    '  ' 

The  bichloride  is  obtained  as  above  mentioned,  and  yields  a  red  solution.  It 
is  obtained  in  the  anhydrous  state  by  gently  heating  molybdenum  in  powder  in 
dry  chlorine  gas,  atmospheric  air  being  excluded.  The  metal  takes  fire  at  its 
surface,  but  it  is  soon  extinguished,  after  which  the  chlorine  is  replaced  by  a  red 
vapour  of  such  intensity  that  it  is  completely  opaque  in  a  vessel  -|  inch  in  diam- 
eter :  this  vapour  condenses  in  the  cooler  parts  of  the  apparatus  brilliant  black 
crystals  just  like  those  of  iodine,  which  are  very  fusible,  and  sublime  at  a  gentle 
heat.  Exposed  to  dry  oxygen  gas  it  is  transformed  gradually  into  oxychloride 
of  molybdenum  and  molybdic  acid.  With  water  the  bichloride  acts  violently 
from  the  intense  heat  evolved,  and  the  whole  is  dissolved. 

Its  eg.  is  1 18*54  ;  symb.  Mo  -f-  2C1,  or  MoCl^. 

Sulphurets. — Molybdenum  combines  with  sulphur  in  three  proportions.  The 
lowest  grade  is  the  bisulphuret^  which  is  the  moet  common  ore  of  molybdenum, 
and  is  usually  associated  with  ores  of  tin,  has  a  lead-grey  colour  and  metallic 
lustre  resembling  graphite,  for  which  it  was  formerly  mistaken.  Its  density  varies 
from  4*138  to  4*569.  It  bears  a  strong  heat  in  close  vessels  without  change  or 
fusion;  but  it  is  oxidized  by  nitric  acid  or  by  the  joint  action  of  heat  and  air. 
Its  eq.  7S.79-9 ;  symb.  Mo  +  2S,  or  MoS^. 

The  tersulphuret  is  obtained  by  saturating  molybdate  of  potassa,  soda,  or  am- 
monia with  hydrosulphuric  acid  gas,  and  adding  hydrochloric  acid,  when  the 
tersulphuret  falls  of  a  deep  brown  colour,  which  becomes  black  on  drying.  It 
is  partially  oxidized  when  dried  in  the  air.  By  heat  in  close  vessels  it  is  changed 
into  the  bisulphuret  with  loss  of  sulphur.  • 

lis  cq.  is  9G ;  symb.  Mo  -f  3S,  or  MoS^. 

The  persulphuret  is  made  by  boiling  the  Sulphur-salt  formed  of  tersulphuret  of 
molybdenum  and  sulphuret  of  potassium  for  a  long  time  with  the  bisulphuret  of 
molybdenum,  when  a  precipitate  collects  which  is  to  be  well  washed  with  cold 


tungsten;  393 

water.  It  is  a  sulphur-salt  composed  of  persulphuret  of  molybdenum  and  sul- 
phuret  of  potassium,  which  forms  with  boiling  water  a  deep  red  solution,  from 
which  on  the  addition  of  hydrochloric  acid  the  persulphuret  subsides. 

Its  eq.  is  112-1 ;  symh.  Mo  -j-  4S,  or  MoS^. 

Oxychloride  of  Molybdenum. — Formerly  described  as  a  terchloride.  It  is  ob- 
tained by  heating  the  binoxide  in  a  current  of  dry  chlorine.  It  is  white  with  a 
shade  of  yellow,  sublimes  at  a  heat  short  of  redness,  and  condenses  into  crystal- 
line scales.  It  dissolves  in  water,  but  the  solution  is  slightly  milky  from  the 
separation  of  molybdic  acid.  From  its  composition,  which  has  been  recently 
determined  by  Rose,  it  would  appear  that 

3  eq.  of  Binoxide  and  3  eq.  of  Chlorine    2     1  eq.  of  Oxychloride 
3  M0O2  3C1  -^        M0CI3+2M0O3. 

Its  eq,  is  297-36  ;  symb,  M0CI3      2M0O3. 

TUNGSTEN. 

It  derives  its  name  from  the  Swedish  words  Tung  Sten,  heavy  stone,  from  the 
density  of  its  ores  :  and  it  is  called  Wolfram  from  the  mineral  of  that  name, 
which  is  a  tungstate  of  the  oxides  of  iron  and  manganese.  This  metal  may  be 
procured  in  the  metallic  state  by  exposing  tungslic  acid  to  the  action  of  charcoal 
or  dry  hydrogen  gas  at  a  red  heat ;  but  though  the  reduction  is  easily  effected, 
an  exceedingly  intense  temperature  is  required  for  fusing  the  metal.  Tungsten 
has  a  greyish-white  colour,  and  considerable  lustre.  It  is  brittle,  nearly  as  hard 
as  steel,  and  less  fusible  than  manganese.  Its  sp.  gr.  is  near  17'4.  When  heated 
to  redness  in  the  open  air  it  takes  fire,  and  is  converted  into  tungstic  acid ;  and 
it  undergoes  the  same  change  by  the  action  of  nitric  acid.  Digested  with  a  con- 
centrated solution  of  pure  potash,  it  is  dissolved  with  disengagement  of  hydrogen 
gas,  and  tungstate  of  potash  is  generated. 

Chemists  are  acquainted  with  two  compounds  of  this  metal  and  oxygen ; 
namely,  the  dark  brown  oxide,  and  the  yellow  acid  of  tungsten  ;  and  according  to 
the  analyses  of  Berzelius,  (An.  de  Ch.  et  Ph.  xvii.)  the  oxygen  of  the  former  is 
to  that  of  the  latter  in  the  ratio  of  two  to  three.  From  the  composition  of  the 
latter,  and  assuming  that  it  contains  three  atoms  of  oxygen,  the  eq.  of  tungsten 
is  99*7.  Its  symb.  is  W.  Its  compounds  described  in. this,  section  are  thus 
constituted  : — .  >t  js  ts  hi 

.[.  Tungsten.  Equiv.        Formulae. 

2  eq.=l  15-7      W4-20  or  WO2. 

3  eq.=223-4  2W+30  or  W2O3. 
3  eq.=123-7  W+30  or  WO3. 
2  eq.=170-54     W+2C1  or  WClj. 

2  eq.=  131-9       W+2S  or  WSj. 

3  eq.=148-0      W-I-3S  or  WS2. 
Oxychloride  2W02257.4    2  eq.+WClg     205-96     1  eq.=463-36    WC]r+.2W03. 

Binoocide. — Prep, — By  the  action  of  hydrogen  gas  on  tungstic  acid  at  a  low 
red  heat ;  but  the  best  mode  of  procuring  it,  both  pure  and  in  quantity,  is  that 
recommended  by  Wohler.  (Quarterly  Journal  of  Science,  xx.  177.)  This  pro- 
cess consists  in  mixing  Wolfram  in  fine  powder  with  twice  its  weight  of  car- 
bonate of  potassa,  and  fusing  the  mixture  in  a  platinum  crucible.    The  resulting 


Binoxide 

99-7 

1  eq.+Oxygen 

16 

Blue  Oxide 

199-4 

2  eq.+ditto 

24 

Tungstic  Acid 

99-7 

1  eq.+ditto 

24 

Bichloride 

99-7 

1  eq.-|-Chlorine 

70-84 

Bisulphuret 

99-7 

1  eq.+Sulphur 

32-2 

Persulphuret 

99-7 

1  eq.+ditto 

48-3 

394  TUNGSTEN. 

tungstate  of  potassa  is  dissolved  in  hot  water,  mixed  with  about  half  its  weight 
of  hydrochlorate  of  ammonia  in  solution,  evaporated  to  dryness,  and  exposed  in 
a  hessian  crucible  to  a  red  heat.  The  mass  is  well  washed  with  boiling  water, 
and  the  insoluble  matter  digested  in  dilute  potassa  to  remove  any  tungstic  acid. 
The  residue  is  oxide  of  tungsten.  It  appears  that  in  this  process  the  tungstate 
of  potassa  and  hydrochlorate  of  ammonia  mutually  decompose  each  other,  so  that 
the  dry  mass  consists  of  chloride  of  potassium  and  tungstate  of  ammonia.  The 
elements  of  the  latter  react  on  each  other  at  a  red  heat,  giving  rise  to  water, 
nitrogen  gas,  and  oxide  of  tungsten  ;  and  this  compound  is  protected  from  oxida- 
tion by  the  fused  chloride  of  potassium  with  which  it  is  enveloped.  This  oxide 
is  also  formed  by  putting  tungstic  acid  in  contact  with  zinc  in  dilute  hydrochlo- 
ric acid.  The  tungstic  acid  first  becomes  blue,  and  then  assumes  a  copper  colour; 
but  the  oxide  in  this  state  can  with  difficulty  be  preserved,  as  by  exposure  to  the 
air,  and  even  under  the  surface  of  water,  it  absorbs  oxygen,  and  is  reconverted 
into  tungstic  acid. 

Prop. — When  prepared  by  means  of  hydrogen  gas,  it  has  a  brown  colour,  and 
when  polished  acquires  the  colour  of  copper ;  but  when  procured  by  Wohler's 
process,  it  is  nearly  black.  It  does  not  unite,  so  far  as  is  known,  with  acids ; 
and  when  heated  to  near  redness,  it  lakes  fire,  and  yields  tungstic  acid. 

Its  eq,  is  115-7 ;  symb,  W  t  SO,  W,  or  WO^'. 

Tungstic  Acid, — Prep, — Conveniently  by  digesting  native  tungstate  of  lime, 
very  finely  levigated,  in  nitric  acid  ;  by  which  means  nitrate  of  lime  is  formed, 
and  tungstic  acid  separated  in  the  form  of  a  yellow  powder.  Long  digestion  is 
required  before  all  the  lime  is  removed ;  but  the  process  is  facilitated  by  acting 
upon  the  mineral  alternately  by  nitric  acid  and  ammonia.  The  tungstic  acid  is 
dissolved  readily  by  that  alkali,  and  may  be  obtained  in  a  separate  state  by  heat- 
ing the  tungstate  of  ammonia  to  redness.  Tungstic  acid  may  also  be  prepared 
by  the  action  of  hydrochloric  acid  on  Wolfram.  It  is  also  obtained  by  heating 
the  brown  oxide  to  redness  in  open  vessels. 

Prop. — Tungstic  acid  is  of  a  yellow  colour,  is  insoluble  in  water,  and  has  no 
action  on  litmus  paper.  With  alkaline  bases  it  forms  salts  called  tungstales,  which 
are  decomposed  by  the  stronger  acids,  the  tungstic  acid  in  general  falling  com- 
bined with  the  acid  by  which  it  is  precipitated.  When  strongly  heated  in  open 
vessels  it  acquires  a  green  colour,  and  becomes  blue  when  exposed  to  the  action 
of  hydrogen  gas  at  a  temperature  of  500°  or  600°  F.  The  blue  compound,  ac- 
cording to  Berzelius,  is  a  tungstate  of  the  oxide  of  tungsten;  and  the  green  colour 
is  probably  produced  by  an  admixture  of  this  compound  with  the  yellow  acid. 

Its  eq.  is  123-7 ;  symb,  W  +  30,  W,  or  WO3. 

Malaguti  finds  that  the  blue  compound,  formed  in  the  manner  stated  above,  is 
never  constant  in  its  composition ;  but  he  obtained  a  definite  compound  by  heating 
tungstic  acid  by  the  flame  of  a  spirit-lamp  in  a  current  of  dry  hydrogen.  Accord- 
ing to  his  analysis  it  contains  17-72  per  cent,  of  oxygen ;  and  he  considers  it  a 
distinct  acid,  the  constitution  of  which  is  represented  by  the  symb.  2W  +  50,  or 
WjOj.     (An.  de  Ch.  et  Ph.  Ix.  271.) 

Chlorides  (f  Tunfrsten. — Tungsten  and  chlorine  unite  in  two  proportions.  When 
metallic  tungsten  is  heated  in  chlorine  gas,  it  takes  fire,  and  yields  the  bichlo- 
ride. The  compound  appears  in  the  form  of  delicate  jieedles,  of  a  deep  red 
colour  resembling  wool,  but  more  frequently  as  a  deep-red  fused  mass  which  has 


COLUMBIUM.  395 

the  brilliant  fracture  of  cinnabar.  When  heated,  it  fuses,  boils,  and  yields  a  red 
vapour.  By  water  it  is  changed  into  hydrochloric  acid  and  oxide  of  tungsten. 
It  is  entirely  dissolved  by  solution  of  pure  potassa,  with  disengagement  of  hydro- 
gen gas,  yielding  tungstate  of  potassa  and  chloride  of  potassium.  A  similar 
change  is  produced  by  ammonia,  except  that  some  oxide  of  tungsten  is  left  un- 
dissolved. 

Its  eq,  is  170-54  ;  symb.  W  -f-  2C1,  or  WCl^. 

Another  chloride  has  been  described  by  Wohler.  It  is  formed  at  the  same 
time  as  the  first;  by  the  action  of  water  it  is  converted  into  hydrochloric  and 
tungstic  acids.  It  is  the  most  beautiful  of  all  these  compounds,  existing  in  long 
transparent  crystals  of  a  fine  red  colour.  It  is  very  fusible  and  volatile,  and  its 
vapour  is  red  like  that  of  nitrous  acid.  The  difference  between  this  compound 
and  the  chloride  first  described  is  not  ye^  satisfactorily  determined ;  for  although 
the  analysis  of  Malaguti  in  his  paper  aboVe  referred  to  would  indicate  its  consti- 
tution to  be  similar  to  that  of  his  blue  oxide,  and  therefore  W2CI5,  still  the  errors 
into  which  he  fell  in  reference  to  the  terchloride  throw  suspicion  on  this  result. 
The  production  of  tungstic  acid  by  its  decomposition  with  water  strengthens  this 
suspicion. 

Sulphurets  of  Tungsten. — The  protosulphuret  is  obtained  as  a  black  powder  by 
transmitting  hydrosulphuric  acid  gas,  or  the  vapour  of  sulphur,  over  tungstic  acid 
heated  to  whiteness  in  a  tube  of  porcelain.  The  persulphuret  is  prepared  by  dis- 
solving tungstic  acid  in  a  solution  of  sulphuret  of  potassium  or  hydrosulphate  of 
ammonia,  and  adding  an  excess  of  hydrosulphuric  acid.  It  falls  as  a  brown  pre- 
cipitate, which  becomes  black  in  drying.  It  is  soluble  to  a  certain  extent  in 
water  which  is  free  from  saline  matter. 

Oxychloride  of  Tungsten — Formerly  described  as  the  terchloride.  It  was  dis- 
covered by  Wohler,  and  prepared  by  heating  the  binoxide  of  tungsten  in  a  stream 
of  dry  chlorine  gas.  The  action  is  attended  with  the  appearance  of  combustion, 
dense  fumes  arise,  and  a  thick  sublimate  is  obtained  in  the  form  of  scales,  like 
native  boracic  acid.  It  is  volatile  at  a  low  temperature  without  previous  fusion. 
According  to  Rose,  who  has  determined  its  composition,  (Pog.  An.  xl.  395,)  it 
is  resolved  when  suddenly  heated  into  tungstic  acid,  the  bichloride  of  tungsten, 
and  chlorine. 

Its  eq.  is  463'36;  symb.  WCl   -f-  2W0  ;  or,  as  in  the  case  of  the  corresponding 

CI  ? 
compound  of  chromium,    W      V  • 

COLUMBIUM. 

Hist. — This  metal  was  discovered  in  1801  by  Hatchett,  who  detected  it  in  a 
black  mineral  belonging  to  the  British  Museum,  supposed  to  have  come  from 
Massachusetts  in  North  America ;  and  from  this  circumstance  applied  to  it  the 
name  of  columhium.  About  two  years  after,  M.  Ekeberg,  a  Swedish  chemist, 
extracted  the  same  substance  from  tantalite  and  yttro-iantalite ;  and,  on  the  sup- 
position of  its  being  different  from  columhium,  described  it  under  the  name  of 
tantalum.  The  identity  of  these  metals,  however,  was  established  in  the  year 
1809  by  Wollaston. 

Prep. — Columbic  acid  is  with  difficulty  reduced  to  the  metallic  state  by  the 
action  of  heat  and  charcoal ;  but  Berzelius  succeeded  in  obtaining  this  metal  by 
the  same  process  which  he  employed  in  the  preparation  of  zirconium  and  silicon, 


396  COLUMBIUM. 

namely,  by  heating  potassium  with  the  double  fluoride  of  potassium  and  colum- 
bium.  On  washing  the  reduced  mass  with  hot  water,  in  order  to  remove  the 
fluoride  of  potassium,  columbium  is  left  in  the  form  of  a  black  powder. 

Prop. — As  a  powder  it  does  not  conduct  electricity ;  but  in  a  denser  state  it  is 
a  perfect  conductor.  By  pressure  it  acquires  a  metallic  lustre,  and  has  an  iron- 
grey  colour.  It  is  not  fusible  at  the  temperature  at  which  glass  is  fused.  "When 
heated  in  the  open  air  it  takes  fire  considerably  below  the  temperature  of  ignition, 
and  glows  with  a  vivid  light,  yielding  columbic  acid.  It  is  scarcely  at  all  acted 
on  by  the  sulphuric,  hydrochloric,  or  nitro-hydrochloric  acid  ;  whereas  it  is  dis- 
solved with  heat  and  disengagement  of  hydrogen  gas  by  hydrofluoric  acid,  and 
still  more  easily  by  a  mixture  of  nitric  and  hydrofluoric  acids.  It  is  also  con- 
verted into  columbic  acid  by  fusion  with  hydrate  of  potassa,  the  hydrogen  gas 
of  the  water  being  evolved. 

From  the  experiments  of  Berzelius  on  the  composition  of  the  oxide  and  acid  of 
columbium,  its  eq.  may  be  estimated  at  185.  Its  symh,  is  Ta.  The  compounds 
described  in  this  section  are  thus  constituted  : — 

Columbium.  Equiv.  Formulae. 

Binoxide        .        185     1  eq.+Oxygen        16        2  eq.=  201  Ta+20  or  TaOs. 

Columbic  Acid      185     1  eq.-+-    .     .  24        3  eq.=  209  Ta+30  or  TaOs. 

Terchloride  185    1  eq.+Chlorine     10626   3  eq-=  291-26       Ta+3C1  or  TaClj. 

Terfluoride    .       185    1  eq.+Fluorine      5604   3  eq.=  241-04       Ta4-3F  or  TaFa. 

Sulphuret       .       Composition  uncertain. 

Oxide  cf  Columbium. — It  is  generated  by  placing  columbic  acid  in  a  crucible 
lined  with  charcoal,  luting  carefully  to  exclude  atmospheric  air,  and  exposing  it 
for  an  hour  and  a  half  to  intense  heat.  The  acid,  where  in  direct  contact  with 
charcoal,  is  entirely  reduced :  but  the  film  of  metal  is  very  thin.  The  interior 
portions  are  pure  oxide  of  a  dark  grey  colour,  very  hard  and  coherent.  When 
reduced  to  powder  its  colour  is  dark  brown.  It  is  not  attacked  by  any  acid,  even 
by  the  nitro-hydrofluoric ;  but  it  is  converted  into  columbic  acid  either  by  fusion 
with  hydrate  of  potassa,  or  deflagration  with  nitre.  When  heated  to  low  redness 
it  takes  fire  and  glows,  yielding  a  light  grey  powder ;  but  in  this  way  it  is  never 
completely  oxidized.  Berzelius  states  that  this  oxide,  in  union  with  protoxide 
of  iron  and  a  little  protoxide  of  manganese,  occurs  at  Kimito  in  Finland,  and  may 
be  distinguished  from  the  other  ores  of  columbium  by  yielding  a  chestnut-brown 
powder. 

Its  eg.  is  201 ;  symb.  Ta  -+-  20,  Ta,  or  TaO^^. 

Columbic  Acid. — Columbium  exists  in  most  of  its  ores  as  an  acid,  united  either 
with  the  oxides  of  iron  and  manganese,  as  in  tantalite,  or  with  the  earth  yttria, 
as  in  the  yttro-tantalite.  This  acid  is  obtained  by  fusing  its  ore  with  three  or 
four  times  its  weight  of  carbonate  of  potassa,  when  a  soluble  columbate  of  that 
alkali  results,  from  which  columbic  acid  is  precipitated  as  a  white  hydrate  by 
acids.     Berzelius  also  prepares  it  by  fusion  with  bisulphate  of  potassa. 

Hydrated  columbic  acid  is  tasteless,  and  insoluble  in  water ;  but  when  placed 
on  moistened  litmus  paper,  it  communicates  a  red  tinge.  It  is  dissolved  by  the 
sulphuric,  hydrochloric,  and  some  vegetable  acids;  but  it  does  not  diminish  their 
acidity,  or  appear  to  form  definite  compounds  with  them.  With  alkalies  it  unites 
readily  ;  and  though  it  does  not  neutralize  their  properties  completely,  crystallized 
salts  may  be  obtained  by  evaporation.  W^hen  the  hydrated  acid  is  heated  to  red- 
ness, water  is  expelled,  and  the  anhydrous  columbic  acid  remains.  In  this  state 
it  is  attacked  by  alkalies  only. 


URANIUM.  397 

Its  eq.  is  209  ;  symb,  Ta  +  30,  Ta,  or  TaO^. 

Perchloride  of  Columbtum. — When  columbium  is  heated  in  chlorine  gas,  it  takes 
fire  and  burns  actively,  yielding  a  yellow  vapour,  which  condenses  in  the  cold 
parts  of  the  apparatus  in  the  form  of  a  white  powder  with  a  tint  of  yellow.  Its 
texture  is  not  in  the  least  crystalline.  By  contact  with  water,  it  is  converted, 
with  a  hissing  noise  and  increase  of  temperature,  into  columbic  and  hydrochloric 
acids.     Hence  its  eq.  is  considered  to  be  291*26 ;  symb.  Ta  +  3C1,  or  TaCl  . 

Terfluoride  of  Columbium. — Hydrofluoric  acid  takes  up  hydrated  columbic  acid, 
and  forms  with  it  a  compound  of  terfluoride  of  columbium  and  hydrofluoric  acid, 
which,  by  evaporation  at  76°,  is  deposited  in  crystals,  which  are  soluble  in  water, 
and  effervesce  in  the  air.  By  gently  evaporating  the  solution,  an  uncrystalline 
mass,  white  and  opaque  is  left,  which  Berzelius  considers  to  be  the  terfluoride 
of  columbium.  By  water  part  of  it  is  converted  into  columbic  and  hydrofluoric 
acids,  the  latter  soluble  and  the  former  insoluble ;  but  both  of  these  acids  retain 
some  terfluoride  in  combination.     Its  eq.  is  241'04 ;  symb.  Ta  +  3F,  or  TaF  . 

Sulphurei  of  Columbium. — This  compound,  first  prepared  by  Rose,  is  generated, 
with  the  phenomena  of  combustion,  when  columbium  is  heated  to  commencing 
redness  in  the  vapour  of  sulphur  ;  or  by  transmitting  the  vapour  of  bisulphuret  of 
carbon  over  columbic  acid  in  a  porcelain  tube  at  a  white  heat,  carbonic  oxide 
being  also  evolved.* 


SECTION  XXL 

URANIUM.-.CERIUM.— LANTANIUM. 
URANIUM. 

Hist,  and  Prep, — This  metal  was  discovered  in  1789  by  the  German  analyst 
Klaproth,  who  named  it  after  the  new  planet  Uranus,  the  discovery  of  which  took 
place  in  the  same  year.  It  was  obtained  from  a  mineral  of  Saxony,  called  from 
its  black  colour  pitchblende,  which  consists  of  protoxide  of  uranium  and  oxide  of 
if  on.  From  this  ore  the  uranium  may  be  conveniently  extracted  by  the  following 
process.  After  heating  the  mineral  to  redness,  and  reducing  it  to  fine  powder,  it 
is  digested  in  pure  nitric  acid  diluted  with  three  or  four  parts  of  water,  taking 
the  precaution  to  employ  a  larger  quantity  of  the  mineral  than  the  nitric  acid 
present  can  dissolve.  By  this  mode  of  operating,  the  protoxide  is  converted  into 
peroxide  of  uranium,  which  unites  with  the  nitric  acid  almost  to  the  total  exclu- 
sion of  the  iron.  A  current  of  hydrosulphuric  acid  gas  is  then  transmitted 
through  the  solution,  in  order  to  separate  lead  and  copper,  the  sulphurets  of 
which  are  always  mixed  with  pitchblende.  The  solution  is  boiled  to  expel  free 
hydrosulphuric  acid,  and  after  being  concentrated  by  evaporation,  is  set  aside  to 
crystallize.  The  nitrate  of  peroxide  of  uranium  is  gradually  deposited  in  flat- 
tened four-sided  prisms  of  a  beautiful  lemon-yellow  colour. 

*  Professor  H.  Rose  has  recently  discovered  two  new  metals  in  the  Tantalite  of  Bava- 
ria, which  he  calls  Niobium  and  Pelopium.    (Comptes  Rendus,  Dec.  1844.)  (R.) 


398  uranium: 

Prop. — The  properties  of  metallic  uranium  are  as  yet  known  imperfectly.  It 
was  prepared  by  Arfwedson  by  conducting  hydrogen  gas  over  the  protoxide  of 
uranium  heated  in  a  glass  tube.  The  substance  obtained  by  this  process  was 
crystalline,  of  a  metallic  lustre,  and  of  a  reddish-brown  colour.  It  suffered  no 
change  on  exposure  to  air  at  common  temperatures ;  but  when  heated  in  open 
vessels,  it  absorbed  oxygen,  and  was  reconverted  into  the  protoxide.  From  its 
lustre  it  was  inferred  to  be  metallic  uranium. 

From  the  experiments  of  Arfwedson  and  Berzelius  on  the  oxides  of  uranium, 
the  eq.  of  the  metal  may  be  estimated  at  217.  (An.  of  Ph.  N.  S.  vii.  258)  ;  its 
symb.  is  U.    Its  compounds  described  in  this  section  are  thus  constituted  : — 

Uranium.  Equiv.  Formulae. 

Protoxide  217     1  eq.  + Oxygen        8  leq.  =  225         U -]- O  or  UO. 

Peroxide  434    2  eq.  +    do.  24  3  eq.  =  458        2U  +  30  or  U2O3. 

Protochloride  217     1  eq.  +  Chlorine    35-42  leq.  =252-42    U  +  ClorUCl. 

Perchloride  434    2  eq.  +    do.        106-26  3  eq.  =  640-26  2U  +  3C1  or  U2CI3. 

Solphuret  Composition  unknown. 

Protoxide. — ^This  oxide  is  of  a  very  dark  green  colour,  and  is  obtained  by 
exposing  nitrate  of  the  peroxide  to  a  strong  heat.  It  is  exceedingly  infusible, 
and  bears  any  temperature  hitherto  tried  without  change.  It  unites  with  acids, 
forming  salts  of  a  green  colour.  It  is  readily  oxidized  by  nitric  acid,  yielding  a 
nitrate  of  the  peroxide.  The  protoxide  is  employed  in  the  arts  by  giving  a  black 
colour  to  porcelain. 

Its  eq.  is  225 ;  symb.  U  -\-  0,U,  or  UO. 

Peroxide  of  Uranium  is  of  a  yellow  or  orange  colour,  and  most  of  its  salts 
have  a  similar  tint.  It  not  only  combines  with  acids,  but  likewise  unites  with 
alkaline  bases,  a  property  which  was  first  noticed  by  Arfwedson.  It  is  precipi- 
tated from  acids  as  a  yellow  hydrate  of  pure  alkalies,  fixed  or  volatile ;  but  retains 
a  portion  of  these  bases  in  combination.  It  is  thrown  down  as  a  carbonate  by 
alkaline  carbonates,  but  is  redissolved  by  an  excess  of  carbonate  of  soda  or 
ammonia,  a  circumstance  which  affords  an  easy  method  of  separating  uranium 
from  iron.  It  is  not  precipitated  by  hydrosulphuric  acid,  but  acquires  a  green 
tint  from  partial  deoxidation.  With  ferrocyanide  of  potassium  it  gives  a  brown- 
ish-red precipitate,  very  like  ferrocynnuret  of  copper. 

Peroxide  of  uranium  is  decomposed  by  a  strong  heat,  and  converted  into  the 
protoxide.  From  its  affinity  for  alkalies,  it  is  difficult  to  obtain  it  in  a  state  of 
perfect  purity.  It  is  employed  in  the  arts  for  giving  an  orange  colour  to  porcelain. 

Its  eq,  is  458 ;  st/mb.  2U  -f-  30,  U,  or  11,03. 

Chlorides. — These  compounds  are  obtained  in  solution  by  dissolving  the  cor- 
responding oxides  in  hydrochloric  acid.  The  protochloride  is  green,  very  solu- 
ble, and  does  not  crystallize.  The  perchloride  is  yellow,  deliquescent,  soluble 
in  alcohol,  ether,  and  water,  and  yields  yellow  solutions. 

Sulphuret  if  Uranium  may  be  formed  by  transmitting  the  vapour  of  bisulphuret 
of  carbon  over  protoxide  of  uranium  strongly  heated  in  a  tube  of  porcelain. 
(Rose.)  It  is  of  a  dark-grey  or  nearly  black  colour,  is  converted  into  protoxide 
of  uranium  when  heated  in  the  open  air,  and  is  readily  dissolved  by  nitric  acid. 
Hydrochloric  acid  attacks  it  feebly. 


BISMUTH.  399 

CERIUM.— LANTANIUM. 

Cerium,  named  after  the  planet  Ceres,  w'as  discovered  in  the  year  1803  by 
Hisinger  and  Berzelius,  in  a  rare  Swedish  mineral  known  by  the  name  of  Cerite, 
and  its  existence  was  recognized  about  the  same  time  by  Klaproth.  Thomson 
has  since  found  it  to  the  extent  of  thirty-four  per  cent,  in  a  mineral  from  Green- 
land, called  Mlantte,  in  honour  of  the  late  Mr.  Allan,  who  first  distinguished  it 
as  a  distinct  species. 

Very  lately,  Mosander  has  shown  that  the  oxide  commonly  considered  as  oxide 
of  cerium  contains  a  large  proportion  of  the  oxide  of  a  new  m€tal,  to  which  he 
has  given  the  name  of  Lantanium  (from  Txiv^avco,  I  lurk,  it  having  lain  concealed 
in  the  ores  of  cerium).  The  properties  and  compounds  of  this  new  metal  have 
not  yet  been  fully  investigated,  and  of  course  those  of  pure  cerium  are  equally 
unknown.  There  is,  however,  a  great  analogy  between  them,  each  forming  two 
oxides,  both  of  which  unite  with  acids.  The  carbonates  of  both  protoxides  are 
white  and  insoluble;  the  sulphates  soluble  and  cry  stall  izable. 

By  the  following  process  the  two  oxides  may  be  conveniently  separated.  The 
mixed  oxide  is  dissolved  in  nitric  acid,  the  solution  evaporated  to  dryness,  and 
the  residue  calcined.  The  oxide  is  now  powdered,  and  digested  in  weak  nitric 
acid  (1  of  acid  to  50  or  100  of  water),  which  dissolves  the  oxide  of  lantanium, 
and  leaves  the  oxide  of  cerium  undissolved.  The  former  may  be  precipitated  as 
carbonate  by  a  carbonated  alkali ;  the  latter  may  be  dissolved  by  a  strong  acid, 
and  also  converted  into  carbonate.  It  would  be  absurd,  in  the  present  state  of 
our  knowledge,  to  give  details  as  to  the  compounds  of  these  two  metals,  which 
cannot  possibly  be  correct. 

The  symbol  of  cerium  is  Ce;  that  of  lantanium  will  be  La.  Both  metals  are 
more  closely  allied  to  yttrium  and  zirconium  than  to  any  others.* 


SECTION  XXII. 

BISMUTH.— TITANIUM.— TELLURIUM. 

BISMUTH. 

HisL  and  Prep. — This  metal  was  known  to  the  ancients,  though  often  con- 
founded by  them  with  lead  and  tin ;  but  it  appears  to  have  derived  the  name  of 
bismuth,  or  properly  wismuth,  from  the  German  miners.  It  occurs  in  the  earth 
both  native  and  in  combination  with  other  substances,  such  as  sulphur,  oxygen, 
and  arsenic.  That  which  is  employed  in  the  arts  is  derived  chiefly  from  native 
bismuth,  and  commonly  contains  small  quantities  of  sulphur,  iron,  and  copper. 
It  may  be  obtained  pure  for  chemical  purposes  by  heating  the  oxide  or  subnit'rate 
to  redness  along  with  charcoal. 

*  Mosander  has  still  more  recently  announced  the  existence  of  another  new  metal  asso- 
ciated with  cerium  and  lantanium,  which  he  calls  Didym  or  Didymium.    (R.) 


400  BISMUTH. 

Prop. — Bismuth  has  a  reddish-white  colour  and  considerable  lustre.  Its  struc- 
ture is  highly  lamellated,  and  when  slowly  cooled  it  crystallizes  in  cubes  or 
octohedrons.  Its  density  is  about  10.  It  is  brittle  when  cold,  but  may  be  ham- 
mered into  plates  while  warm.  At  476°  it  fuses,  and  sublimes  in  close  vessels 
at  a  red  heat.     It  is  a  less  perfect  conductor  of  heat  than  most  other  metals. 

Bismuth  undergoes  little  change  by  exposure  to  air  at  common  temperatures. 
When  fused  in  open  vessels,  its  surface  becomes  covered  with  a  grey  film,  which 
is  a  mixture  of  metallic  bismuth  with  the  oxide  of  the  metal.  Heated  to  its 
subliming  point,  it  bums  with  a  bluish  white  flame,  and  emits  copious  fumes  of 
oxide  of  bismuth.  The  metal  is  attacked  with  difficulty  by  hydrochloric  or  sul- 
phuric acid,  but  it  is  readily  oxidized  and  dissolved  by  nitric  acid. 

The  eq.  of  bismuth,  deduced  by  Lagerhjelm  from  the  composition  of  its  pro- 
toxide, is  71  (An.  of  Phil.  iv.  357);  its  symh.  is  Bi.  Its  compounds  described 
in  this  section  are  thus  constituted : — 


Bismuth. 

Equiv. 

Formulse. 

Protoxide 

71     1  eq.-f- Oxygen 

8 

1  eq.=  79 

BifO  or  BIO. 

Peroxide 

142    2eq.-|-do. 

24 

3  eq.=l66 

2Bi-f30orBi203. 

Chlorine 

71     1  eq. -[-Chlorine 

35-42 

1  eq.=106-42 

Bi-f-Cl  or  BiCl. 

Bromide 

71     1  eq.-f-Bromine 

78-4 

1  eq.=149-4 

Bi-f-Br  orBiBr. 

Sulphuret 

71     1  eq.-|- Sulphur 

16-1 

1  eq.=i  87-1 

Bi-f-S  or  BiS. 

Protoxide  of  Bismuth^-'^ThiB  compound  is  readily  prepared  by  heating  to  red- 
ness the  nitrate  or  subnitrate  of  oxide  of  bismuth.  Its  colour  is  yellow;  at  a 
full  red  heat  it  is  fused  into  a  brown  liquid,  which  on  cooling  becomes  a  yellow 
transparent  glass  of  sp.  gr.  8*211.  At  intense  temperatures  it  is  sublimed.  It 
unites  with  acids,  and  most  of  its  salts  are  white. 

"When  nitrate  of  oxide  of  bismuth,  either  in  solution  or  in  crystals,  is  put  into 
water,  a  copious  precipitate,  the  subnitrate,  of  a  beautifully  white  colour,  sub- 
sides, which  was  formerly  called  the  magisiery  of  bismuth.  From  its  whiteness 
it  is  sometimes  employed  as  a  paint  for  improving  the  complexion ;  but  it  is  an 
inconvenient  cosmetic,  owing  to  the  facility  with  which  it  is  blackened  by  hydro- 
sulphuric  acid.  If  the  nitrate  with  which  it  is  made  contains  no  excess  of  acid, 
and  a  large  quantity  of  water  is  employed,  nearly  the  whole  of  the  bismuth  is 
separated  as  a  subnitrate. — By  this  character  bismuth  may  be  both  distinguished 
and  separated  from  other  metals. 

Its  eq.  is  79 ;  symb.  Bi  ^  O,  Bi,  or  BiO. 

Peroxide. — This  oxide  was  first  noticed  by  Bucholz  and  Brandes,  but  its 
nature  and  composition  have  been  recently  examined  by  A.  Stromeyer.  It  is 
generated  when  hydrate  of  potassa  is  fused  at  a  moderate  heat  with  protoxide  of 
bismuth ;  but  the  best  mode  of  preparation  is  first  to  prepare  the  protoxide  by 
igniting  the  subnitrate,  and  then  gently  heating  it  for  some  time  in  a  solution  of 
chloride  of  potassa  or  soda.  After  washing  with  water,  any  unchanged  protoxide 
is  dissolved  by  a  solution  made  with  1  part  of  nitric  acid  (quite  free  from  nitrous 
acid)  and  9  of  water. 

As  thus  prepared,  peroxide  of  bismuth  is  a  heavy  powder  of  a  brown  colour, 
very  like  peroxide  of  lead,  manifests  little  disposition  to  unite  either  with  acids 
or  alkalies,  and  is  reconverted  by  heat  with  loss  of  oxygen  into  the  protoxide. 
Heated  with  sulphuric  or  phosphoric  acid,  it  gives  off  oxygen  gas,  and  a  sulphate 
or  phosphate  of  the  protoxide  is  formed ;  and  with  hydrochloric  acid  chlorine  is 


TITANIUM.  HH 

evolved,  and  the  protochloride  produced  (An.  de  Ch.  et  Ph.  li.  267).     lis  eq.  is 

166  ;  symb.  2Bi  +  30,  5i'  or  81203. 

Chloride  of  Bismuth. — When  bismuth  in  fine  powder  is  introduced  into  chlorine 
gas,  it  takes  fire,  bums  with  a  pale  blue  light,  and  is  converted  into  a  chloride, 
formerly  termed  hulter  of  bismuth.  It  may  be  prepared  conveniently  by  heating 
two  parts  of  corrosive  sublimate  vs^ith  one  of  bismuth,  and  afterwards  expelling 
the  excess  of  the  former,  together  with  the  metallic  mercury,  by  heat. 

Chloride  of  bismuth  is  of  a  greyisb-white  colour,  opaque,  and  of  a  granular 
texture.  It  fuses  at  a  temperature  a  little  above  that  at  which  the  metal  itself  is 
liquefied,  and  bears  a  red  heat  in  close  vessels  without  subliming. 

Its  eq,  is  106-42  ;  symh.  Bi  +  CI,  or  BiCl. 

Bromide  of  Bismuth  is  prepared  by  heating  the  metal  with  a  large  excess  of 
bromine  in  a  long  tube;  when  a  grey-coloured  bromide  results,  similar  in  its 
aspect  to  fused  iodine.  At  392°  it  enters  into  fusion,  and  at  a  low  red  heat  sub- 
limes. With  water  it  is  converted  into  oxide  of  bismuth  and  hydrobromic  acid, 
the  former  of  which  combines  with  some  undecomposed  bromide  of  bismuth  as 
an  oxybromide.      (SeruUas.) 

Its  eq.  is  149*4  ;  symb.  Bi  -f-  Br,  orBiBr. 

Sulphuret  of  Bismuth. — This  sulphuret  is  found  native,  and  may  be  formed 
artificially  by  fusing  bismuth  with  sulphur,  or  by  the  action  of  hydrosulphuric 
acid  on  the  salts  of  bismuth.    It  is  of  a  lead-grey  colour  and  metallic  lustre. 

Its  eq.  is  87*1 ;  symb.  Bi  -j-  S,  or  BiS. 

TITANIUM. 

Hist. — This  metal  was  first  recognized  as  a  new  substance  by  Mr.  Gregor  of 
Cornwall,  and  its  existence  was  afterwards  established  by  Klaproth,  who  fanci- 
fully gave  it  the  name  of  Titanium,  after  the  Titans  of  ancient  fable.  (Contri- 
butions, i.)  But  the  properties  of  the  metal  were  not  ascertained  in  a  satisfactory 
manner  until  the  year  1822,  when  Wollaston  was  led  to  examine  some  minute 
crystals  which  were  found  in  a  slag  at  the  bottom  of  a  smelting  furnace  at  the 
great  iron  works  at  Merthyr  Tydvil  in  Wales,  and  presented  to  him  by  Buck- 
land.  (Philosophical  Transactions,  1823.)  These  crystals,  which  have  since 
been  found  at  other  iron  works,  are  of  a  cubic  form,  and  in  colour  and  lustre 
resemble  burnished  copper.  They  are  found  in  the  blast  furnaces,  and  are  pro- 
bably derived  principally  from  the  hearth-stone,  which  contains  them  abundantly. 
They  conduct  electricity,  and  are  attracted  slightly  by  the  magnet,  a  property 
which  seems  owing  to  the  presence  of  a  minute  quantity  of  iron.  Their  sp.  gr. 
is  5*3  ;  and  their  hardness  is  so  great,  that  they  scratch  a  polished  surface  of 
rock  crystal.  They  are  exceedingly  infusible ;  but  when  exposed  to  the  united 
action  of  heat  and  air,  their  surface  becomes  covered  with  a  purple-coloured 
film,  which  is  an  oxide.  They  resist  the  action  of  nitric  and  nitro-hydrochloric 
acids,  but  are  completely  oxidized  by  being  strongly  heated  with  nitre.  They 
are  then  converted  into  a  white  substance,  which  possesses  all  the  properties  of 
titanic  acid. 

Prep. — Liebig  prepares  metallic  titanium  by  putting  fragments  of  recently 
made  chloride  of  titanium  and  ammonia  in  a  glass  tube  half  an  inch  wide  and 
two  or  three  feet  long,  transmitting  through  it  a  current  of  perfectly  dry  ammo- 
nia, and  when  atmospheric  air  is  entirely  displaced,  applying  heat  until  the  glass 
softens.      Complete  decomposition  ensues,  nitrogen  gas  is  disengaged,  hydro- 

28 


402  TITANIUM. 

chlorate  of  ammonia  sublimes,  and  metallic  titanium  is  left  in  the  state  of  a  deep 
blue-coloured  powder.  If  exposed  to  the  air  while  warm,  it  is  apt  to  take  fire. 
The  eq.  of  titanium,  determined  by  Rose  from  his  analysis  of  the  bichloride, 
is  24*3  ;  its  symb.  is  Ti.  The  composition  of  its  compounds  described  in*  this 
section  is  as  follows  : — 

1  eq.  Titanium.  Equiv.  Formulae. 

Oxide  (probably)        24-3 -j- Oxygen  8  1  eq.=32-3  Ti-fO    or  TiO- 

Titanic  Acid      .        24-3-|-do.  16  2  eq.=40-3  Ti+20  or  TiO^. 

Bichloride  .        24-3 -f- Chlorine  70-84  2  eq.=96-14  Ti4-2C1  or  TiClj. 

Bisulphuret       .        24-3 -J- Sulphur  32-2  2  eq.=56-5  T1+2S  or  TiSj. 

Oxide  of  Titanium. — When  titanic  is  exposed  to  a  strong  heat  in  a  black-lead 
crucible,  a  mass  is  obtained,  the  exterior  crust  of  which  is  metallic  titanium,  but 
the  interior  parts  consist  of  the  supposed  protoxide.  As  thus  prepared  it  is  a 
black  mass,  which  has  an  earthy  fracture,  is  quite  insoluble  in  all  acids,  and  is 
very  difficult  to  oxidize.  Oxide  of  titanium  is  formed  in  the  moist  way,  when  a 
fragment  of  zinc  or  iron  is  introduced  into  a  solution  of  titanic  acid  in  hydro- 
chloric acid.  The  solution  soon  acquires  a  purple  tint,  and  after  a  time  the 
whole  of  the  titanic  acid  is  thrown  down  in  the  form  of  a  deep  purple  powder. 
This  cannot  be  collected,  owing  to  the  facility  with  which  it  is  reconverted  into 
titanic  acid  ;  hence  its  composition  and  chemical  properties  are  unknown. 

Titanic  .Acid. — Hist,  and  Prep. — ^This  compound,  called  also  peroxide  of  tita- 
nium, has  been  carefully  studied  by  H.  Rose,  who  first  pointed  out  its  acid  pro- 
perties. It  occurs  in  a  nearly  pure  state  in  the  minerals  rutile  and  anatase,  which 
are  remarkable  for  presenting  the  same  chemical  compound  crystallized  in  uncon- 
nected forms.  It  also  exists  in  titanite  or  sphene  as  titanate  and  silicate  of  lime, 
and  menaccanite  as  titanate  of  the  oxides  of  iron  and  manganese,  in  the  latter  of 
which  titanium  was  originally  discovered  by  Gregor.  It  is  best  prepared  from 
rutile.  The  mineral,  after  being  reduced  to  an  exceedingly  fine  powder,  is  fused 
in  a  platinum  crucible  with  three  times  its  weight  of  carbonate  of  potash,  and  the 
mass  afterwards  washed  with  water  to  remove  the  excess  of  alkali.  A  grey  mass 
remains,  which  consists  of  potash  and  titanic  acid.  This  compound  is  dissolved 
in  concentrated  hydrochloric  acid ;  and  on  diluting  with  water,  and  boiling  the 
solution,  the  greater  part  of  the  titanic  acid  is  thrown  down.  It  is  then  collected 
on  a  filter,  and  well  washed  with  water  acidulated  with  hydrochloric  acid.  In 
this  state  it  is  not  qmte  pure;  but  contains  a  little  oxide  of  manganese  and  iron, 
derived  from  the  rutile.  The  best  mode  of  separating  these  impurities  is  to 
digest  the  precipitate,  while  still  moist,  with  hydrosulphate  of  ammonia,  which 
converts  the  oxides  of  iron  and  manganese  into  sulphurets,  but  does  not  act  on 
the  titanic  acid.  The  two  sulphurets  are  readily  dissolved  by  dilute  hydrochloric 
acid  ;  and  the  titanic  acid,  after  being  collected  on  a  filter  and  well  washed  as 
before,  may  be  dried  and  heated  to  redness.  This  method,  proposed  by  Rose 
of  Berlin,  has  been  thus  simplified  by  himself.  Either  rutile  or  titaniferous 
iron,  after  being  pulverized  and  washed,  is  exposed  in  a  porcelain  tube  at  a  very 
strong  red  heat  to  a  current  of  hydrosulphuric  acid  gas,  which  acts  upon  the 
oxide  of  iron,  giving  rise  to  water  and  sulphuret  of  iron.  As  soon  as  water 
ceases  to  appear,  the  process  is  discontinued,  the  mass  digested  in  hydrochloric 
acid  to  remove  the  iron,  and  the  titanic  acid  separated  from  adhering  sulphur  by 
heat.  A  little  iron  is  still  usually  retained ;  but  the  whole  may  be  removed  by 
a  repetition  of  the  same  process.     (An.  de  Ch.  et  Ph.  xxiii.  and  xxxviii.  131.) 


TELLURIUM.  4^ 

Prop, — Titanic  acid,  when  pure,  is  quite  white.  It  is  exceedingly  infusible ; 
and  after  being  once  ignited  it  ceases  to  be  soluble  in  acids,  except  in  the  hydro- 
fluoric. In  its  chemical  relations  it  is  analogous  to  silicic  acid,  being  a  feeble 
acid,  insoluble  in  water,  without  action  on  test  paper,  but  combining  with  me- 
tallic oxides.  In  the  state  of  hydrate,  as  when  precipitated  from  hydrochloric 
acid  by  boiling,  or  when  combined  with  an  alkali  after  fusion,  it  has  a  singular 
tendency  to  pass  through  the  pores  of  a  filter  when  washed  with  pure  water ; 
but  the  presence  of  a  little  acid,  alkali,  or  salt,  prevents  this  inconvenience. 

If  previously  ignited  with  carbonate  of  potassa,  titanic  acid  is  soluble  in  dilute 
hydrochloric  acid  ;  but  it  is  retained  in  solution  by  so  feeble  an  attraction,  that 
it  is  precipitated  merely  by  boiling.  It  is  likewise  thrown  down  by  the  pure 
and  carbonated  alkalies,  both  fixed  and  volatile.  A  solution  of  gall-nuts  causes 
an  orange  red  colour,  which  is  very  characteristic  of  titanic  acid  ;  an  effect  which 
appears  owing  to  tannic,  and  not  to  gallic  acid.  When  a  rod  of  zinc  is  sus- 
pended in  the  solution,  a  purple-coloured  powder,  probably  the  protoxide,  is  pre- 
cipitated which  is  gradually  converted  into  titanic  acid.     Its  eq.  is  40*3;  symh. 

Ti  +  20,Ti,  or  TiO^. 

Bichloride  of  Titanium. — This  substance  was  discovered  in  the  ye?ir  1824  by 
Mr.  Grforge  of  Leeds,  by  transmitting  dry  chlorine  gas  over  metallic  titanium  at 
a  red  heat.  Rose  prepared  it  for  his  analysis  by  heating  a  mixture  of  titanic  acid 
and  charcoal  in  a  tube,  through  which  dry  chlorine  gas  was  passing:  the  result- 
ing bichloride  was  purified  from  adhering  free  chlorine  by  agitation  either  with 
mercury  or  potassium,  and  repeated  distillation.  At  common  temperatures  it  is 
a  transparent  colourless  fluid,  of  considerable  sp.  gr.,  boils  violently  at  a  tem- 
perature a  little  above  212°,  and  condenses  again  without  change.  Dumas  has 
shown  that  the  density  of  its  vapour  may  be  estimated  at  6*G15.  In  open  ves- 
sels it  is  attacked  by  the  moisture  of  the  atmosphere,  and  emits  dense  white 
fumes  of  a  pungent  odour  similar  to  that  of  chlorine,  but  not  so  offensive.  On 
adding  a  few  drops  of  water  to  a  few  drops  of  the  liquid,  combination  ensues 
with  almost  explosive  violence,  from  the  evolution  of  intense  heat;  and  if  the 
water  is  not  in  excess  a  solid  hydrate  is  obtained.  On  exposure  to  the  air  it 
deliquesces,  and  on  adding  water  the  greater  part  is  dissolved.  The  bichloride, 
when  exposed  to  an  atmosphere  of  dry  ammonia,  absorbs  a  large  quantity  of  the 
gas,  and  becomes  solid.  It  was  from  this  compound  Liebig  prepared  metallic 
titanium. 

Its  eq,  is  95-14 ;  symb.  Ti  +  3C1,  or  TiCl^. 

Bisulphuret  of  Titanium. — This  compound  was  discovered  by  Rose,  who  pre- 
pared it  by  transmitting  the  vapour  of  bisulphuret  of  carbon  over  titanic  acid, 
heated  to  whiteness  in  a  tube  of  porcelain.  It  occurs  in  thick  green  masses, 
which  by  the  least  friction  acquire  a  dark  yellow  colour  and  metallic  lustre. 
When  heated  in  the  open  air  it  is  converted  into  sulphurous  and  titanic  acids. 
By  acids  it  is  slowly  decomposed,  and  is  dissolved  by  hydrochloric  acid  with 
disengagement  of  hydrosulphuric  acid  gas. 

Its  eq.  is  56-5  ;  symb,  Ti  -f-  2S,  or  TiS^. 

TELLURIUM. 

Hist. — A  rare  metal,  hitherto  found  only  in  the  gold  mines  of  Transylvania, 
and  even  there  in  very  small  quantity.  Its  existence  was  inferred  by  Miiller  in 
the  year  1782,  and  fully  established  in  1798  by  Klaproth,  who  gave  it  the  name 


404  TELLURIUM. 

of  tellurium^  from  iellxis,  the  earth,  suggested  by  the  source  from  which  he  drew 
the  name  of  uranium.  (Contributions,  iii.)  It  occurs  in  the  metallic  state, 
chiefly  in  combination  with  gold  and  silver. 

Prop. — It  has  a  tin-white  colour  running  into  lead-grey,  a  strong  metallic 
lustre,  and  lamellated  texture.  It  is  very  brittle,  and  its  density  is  6'2578.  It 
fuses  at  a  temperature  below  redness,  and  at  a  red  heat  is  volatile.  When 
heated  before  the  blowpipe  it  takes  fire,  bums  rapidly  with  a  blue  flame  bor- 
dered with  green,  and  is  dissipated  in  grey-coloured  pungent  inodorous  fumes. 
The  odour  of  decayed  horse-radish  is  sometimes  emitted  during  the  combustion, 
and  was  thought  by  Klaproth  to  be  peculiar  to  tellurium ;  but  Berzelius  ascribes 
it  solely  to  the  presence  of  selenium. 

From  some  experiments  of  Berzelius  the  eq.  of  tellurium  is  64*2 ;  its  symb.  is 
Te.    The  compounds  described  in  this  section  are  thus  constituted  : — 


leq. 

.  Tellurium. 

Equiv. 

Formulae. 

Tellurous  Acid 

64-2 -f  Oxygen    . 

,     16 

2  eq.=  80-2 

Te-^-20  or  TeOz. 

iTelluric  Acid 

64-2t     .     .      . 

24 

3  eq.=  88-2 

Te4-30  or  TeOs. 

Chloride 

64-2 -j- Chlorine  . 

35-42 

1  eq.=  99-62 

Te-j-Cl   orTeCl. 

Bichloride 

64-2-1-    ;    .     . 

70-84 

2  eq.:=135-04 

Te-J-2ClorTeC]2. 

Bisulphuret 

64-2 -(-Sulphur    . 

32-2 

2  eq.=  96-4 

Tet2S  orTe^. 

Persulphuret  Composition  uncertain. 

H>drotelluric  Acid  64-2 -f- Hydrogen       1  1  eq.=  65-2        Te-|-H    or  TeH. 

Tellurous  Acid. — This  compound,  also  called  oxide  of  tellurium,  is  generated 
by  the  action  of  nitric  acid  on  tellurium,  by  which  acid  it  is  dissolved;  but  the 
solution  possesses  such  little  permanence  that  mere  effusion  of  water  precipitates 
part  of  it,  and  the  rest  is  obtained  by  evaporating  to  dryness.  In  this  state  it  is 
a  white  granular  anhydrous  powder,  which  slowly  reddens  moist  litmus  paper, 
and  is  insoluble  in  water  and  acids.  By  pure  potassa  or,  soda  in  solution  it  is 
dissolved,  and  is  rendered  soluble  by  fusion  with  the  alkaline  carbonates,  forming 
with  those  alkalies  crystallizable  salts.  Acids  added  in  slight  excess  to  the  alka- 
line solutions  throw  down  tellurous  acid  as  a  white  flaky  hydrate,  which  if 
washed  in  ice-cold  water,  and  dried  at  a  temperature  not  exceeding  53°,  may  be 
preserved  unchanged.  In  this  state  it  is  freely  soluble  in  acids,  in  ammonia,  in 
the  alkaline  carbonates,  from  which  it  expels  carbonic  acid,  and  even  to  con- 
siderable extent  in  pure  water.  Its  aqueous  solution  reddens  litmus  paper:  it 
becomes  turbid  at  68°,  and  the  acid  which  falls  is  no  longer  soluble  in  acids. 
In  these  properties  tellurous  acid  closely  resembles  the  titanic  and  several  other 
feeble  acids,  which  have  a  soluble  hydrated  state  easily  convertible  into  an  in- 
soluble anhydrous  one.  Its  salts  are  precipitated  black  by  hydrosulphuric  acid, 
bisulphuret  of  tellurium  being  formed.  It  is  deoxidized  and  metallic  tellurium 
falls  as  a  black  powder,  when  a  piece  of  zinc,  tin,  iron  or  antimony  is  left  in  its 

Bolution.     Its  eq.  is  80-2  ;  symb.  Te  f  20,  Tc,  or  TeO^. 

Telluric  Acid. — The  process  which  Berzelius  recommends  for  preparing  this 
compound  is  either  to  deflagrate  tellurous  acid  with  nitre,  or  to  mix  pure  potassa 
freely  with  a  solution  of  tellurite  of  potassa,  and  to  saturate  fully  with  chlorine. 
Nitric  acid  in  slight  excess  and  a  little  chloride  of  barium  are  added,  in  order  to 
precipitate  any  traces  of  sulphuric  and  selenic  acids;  and  after  separating  the 
precipitate  by  filtration,  the  liquid  is  exactly  neutralized  with  ammonia,  and  chlo- 
ride of  barium  added  as  long  as  it  causes  a  precipitate.    The  tellurate  of  baryta 


TELLURIUM.  4f|5 

is  washed,  dried  by  a  gentle  heat,  and  then  digested  with  a  fourth  of  its  weight 
of  strong  sulphuric  acid  previously  diluted  with  water :  the  filtered  solution  is 
then  concentrated  by  a  water  bath,  and  on  cooling  or  subsequent  spontaneous 
evaporation  yields  hydrated  telluric  acid  in  the  form  of  flat  six-sided  prisms. 
Adhering  sulphuric  acid  is  removed  by  alcohol. 

This  hydrate  consists  of  1  eq.  of  acid  and  3  eq.  of  water.  When  heated  at 
212°  it  loses  2  of  its  eq.  of  water;  and  on  heating  still  further  all  its  water  is 
expelled,  and  the  anhydrous  acid  of  a  lemon-yellow  colour  remains.  In  this  state 
it  is  insoluble  in  all  fluids,  whereas  the  hydrated  acid  is  soluble  in  water ;  and 
the  salts  of  the  former  differ  from  those  which  the  latter  forms  with  the  same 
bases.  Hence  heat  modifies  the  character  of  telluric  acid  much  in  the  same  way 
as  that  of  phosphoric  acid.  At  a  heat  beyond  that  required  to  render  it  anhy- 
drous, telluric  acid  loses  oxygen  and  is  reduced  to  tellurous  acid.  (Pog.  Annalen. 
xxviii.  392.) 

Its  eq.  is  88-2 ;  symb.  Te  -\-  30,  f  e,  or  TeOg. 

Chloride. — Rose  obtained  it  by  passing  a  feeble  current  of  chlorine  gas  over 
tellurium  at  a  strong  heat,  when  the  chloride  passes  over  as  a  violet  vapour, 
which  at  first  condenses  into  a  black  liquid,  and  when  quite  cold  becomes  a  solid 
of  the  same  colour.  By  the  action  of  water  it  deposits  metallic  tellurium,  and 
the  bichloride  is  dissolved. 

Its  eq.  «s  99-62  ;  symh.  Te  -f-  CI,  or  TeCl. 

Bichloride. — Rose  obtained  this  in  the  same  manner  as  the  preceding  chloride, 
except  using  a  lower  heat  and  a  more  liberal  supply  of  chlorine.  The  bichloride 
is  also  volatile,  and  after  being  purified  from  free  chlorine  by  agitation  with  mer- 
cury, and  a  second  distillation,  it  condenses  into  a  white  crystalline  solid.  By 
a  gentle  heat  it  yields  a  brown  liquid,  but  recovers  its  whiteness  on  cooling. 
(Pog.  Annalen,  xxi.  443.) 

Its  eq.  is  135-04;  symb.  Te  +  2C1,  orTeClj. 

Bisulphuret. — This  compound  falls  of  a  dark  brown,  nearly  black  colour,  when 
hydrosulphuric  acid  gas  is  transmitted  through  a  solution  of  bichloride  of  tellu- 
rium, tellurous  acid,  or  any  soluble  tellurite.  This  sulphuret  is  what  Berzelius 
calls  a  sulphur-acid,  forming  a  soluble  sulphur-salt  by  uniting  with  sulphuret  of 
potassium.  Hence  a  solution  of  caustic  potassa  dissolves  bisulphuret  of  tellu- 
rium, producing  the  same  kind  of  change  as  on  sulphuret  of  antimony. 

Its  eq.  96-4 ;  symh.  Te  f  2S,  or  TeSz. 

Persulphuret. — This  compound  falls  of  a  deep  yellow  colour,  when  a  salt  of 
telluric  acid  is  mixed  in  solution  with  persulphuret  of  potassium.  Its  existence 
is  but  transient,  as  it  is  quickly  transformed  into  bisulphuret  and  becorries  black. 

Hydrolelluric  Acid. — This  gas,  discovered  by  Davy  in  1809,  is  formed  by  act- 
ing with  hydrochloric  acid  on  an  alloy  of  tellurium  with  zinc  or  tin.  It  has  the 
properties  of  a  feeble  acid,  very  analogous  in  odour,  and  apparently  in  composi- 
tion, to  hydrosulphuric  acid  ;  it  is  absorbed  by  water,  forming  a  claret-coloured 
solution ;  and  it  precipitates  many  metallic  salts,  yielding  an  alloy  of  tellurium 
with  the  other  metal.  It  is  deprived  of  its  hydrogen  by  chlorine,  nitric  acid,  or 
oxygen  of  the  atmosphere,  tellurium  being  separated. 

Its  eq.  is  65-2 ;  symh.  Te  +  H,  or  TeH- 


406  MERCURY  OR  QUICKSILVER. 


CLASS    II 


ORDER   III. 

METALS,  THE  OXIDES  OF  WHICH  ARE  REDUCED  TO  THE  METALLIC 
STATE  BY  RED  HEAT. 


SECTION  XXIII. 

MERCURY  OR  QUICKSILVER. 

Hist,  and  Prep. — This  metal  was  well  known  to  the  ancients.  The  principal 
mines  from  which  it  is  obtained  are  those  of  Idria  in  Carniola  and  Almaden  in 
Spain,  where  it  is  found  both  in  the  native  state  and  combined  with  sulphur  as 
cinnabar,  the  latter  being  the  most  abundant.  From  this  ore  the  metal  is 
extracted  by  heating  it  with  lime  or  iron  filings,  by  which  means  the  mercury  is 
volatilized  and  the  sulphur  retained.  As  prepared  on  a  large  scale  it  is  usually 
mixed  in  small  quantity  with  other  metals,  from  which  it  may  be  purified  by 
cautious  distillation. 

Prop. — Distinguished  from  all  other  metals  by  being  fluid  at  common  tem- 
peratures. It  has  a  tin-white  colour  and  strong  metallic  lustre.  It  becomes  solid 
at  a  temperature  which  is  39  or  40  degrees  below  zero ;  and  in  congealing,  it 
evinces  a  strong  tendency  to  crystallize  in  octohedrons.  It  contracts  greatly  at 
the  moment  of  congelation;  for  while  its  density  at  47°  is  13*545,  that  of  frozen 
mercury  is  15*612.  When  solid  it  is  malleable,  and  may  be  cut  with  a  knife. 
At  662°  or  near  that  degree,  it  enters  into  ebullition,  and  condenses  again  on 
cool  surfaces  into  metallic  globules. 

Mercury,  if  quite  pure,  is  not  tarnished  in  the  cold  by  exposure  to  air  and 
moisture ;  but  if  it  contain  other  metals,  the  amalgam  of  those  metals  oxidizes 
readily,  and  collects  as  a  film  upon  its  surface.  It  is  said  to  be  oxidized  by  long 
agitation  in  a  bottle  half  full  of  air,  and  the  oxide  so  formed  was  called  by  Boer- 
haave  Ethiops  per  se ;  but  it  is  very  probable  that  the  oxidation  of  mercury 
observed  under  these  circumstances  was  solely  owing  to  the  presence  of  other 
metals.  When  exposed  to  air  or  oxygen  gas,  while  in  the  form  of  vapour,  it 
slowly  absorbs  oxygen,  and  is  converted  into  peroxide  of  mercury. 

The  only  acids  that  act  on  mercury  are  the  sulphuric  and  nitric  acids.  The 
former  has  no  action  whatever  in  the  cold ;  but  on  the  application  of  heat,  the 
mercury  is  oxidized  at  the  expense  of  tlte  acid,  pure  sulphurous  acid  gas  is  dis- 
engaged, and  a  sulphate  of  mercury  is  generated.  Nitric  acid  acts  energetically 
upon  mercury  both  with  and  without  the  aid  of  heat,  oxidizing  and  dissolving  it 
with  evolution  of  binoxide  of  nitrogen. 


MERCURY.  4^ 

From  some  late  analyses  on  the  peroxide  and  chlorides  of  mercury,  I  have 
inferred  that  its  equivalent  is  202*  (Phil.  Trans.  1833,  part  ii.) ;  its  symb.  is 
Hg.     The  composition  of  its  compounds  described  in  this  section  is  as  follows  : 

Mercury.  Equiv.  Formulae. 

Protoxide  202  1  eq.  +  Oxygen          8  1  eq.  =  210  Hg  +  OorHgO. 

Peroxide  202  1  eq.  +    do.             16  2eq.  =  218           Hg4-20orHg02. 

Protochloride  202  1  eq.  + Chlorine      35-42  leq.  =  237-42      Hg  +  ClorHgCl. 

Bichloride  202  leq.+    do.            70-84  2  eq.  =  272-84      Hg+ 2CI  or  HgClg. 

Iodide  202  1  eq.  -\-  Iodine  126-3  1  eq,  =  328-3  Hg  + 1  or  Hgl. 

Sesquiodide  404  2  eq. -\-     do.  378-9  3eq.  =  782-9  2Hg  +  31  or  Hgjla. 

Biniodide  202  1  eq. -j-     do.  252  6  2eq.  =  454'6  Hg  +  2IorHgl2. 

Brotobromide  202  1  eq.  +  Bromine     784  leq.  =  280-4  Hg  +  BrorHgBr. 

Bibromide  202  1  eq. -f-     do.  156-8  2  eq.  =  358-8  Hg  +  2Br  or  HgBrg. 

Protosulphuret  202  1  eq. -|- Sulphur       16-1  leq.  =218-1  Hg  +  SorHgS. 

Bisulphuret  202  1  eq.  +    do.  32-2  2  eq.  =  234-2  Hg  +  2S  or  HgS2. 

loduretted  bichloride  (     HgClg  54568     20  eq.     )  xcoo.i  onw^ri    _j_  t 

of  Mercury  \         J  126-3       leq.     J  =   5583  1  20HgC1.2  + 1. 

lodo-bicbloride  of       C     HgClz        10913-6    40  eq.     J  _  110^0.9  .ftxrari  O-HaT 
Mercury*  \     Ugh  454-6      leq.     J  =  11368  2  40HgCl2-f-Hgl2- 


Protoxide. — Prep. — Best  by  the  process  recommended  by  Donovan  (An.  of 
Phil,  xiv.)  :  this  consists  in  mixing  calomel  briskly  in  a  mortar  with  pure  potassa 
in  excess,  so  as  to  effect  its  decomposition  as  rapidly  as  possible ;  the  protoxide 
is  then  washed  with  cold  water,  and  dried  spontaneously  in  a  dark  place.  These 
precautions  are  rendered  necessary  by  the  tendency  of  the  protoxide  to  resolve 
itself  into  the  peroxide  and  metallic  mercury,  a  change  which  is  easily  effected 
by  heat,  by  the  direct  solar  rays,  and  even  by  daylight.  It  is  on  this  account 
very  difficult  to  procure  protoxide  of  mercury  in  a  state  of  absolute  purity. 

Prop. — A  black  powder,  which  is  exceedingly  prone  to  decomposition,  is  inso- 
luble in  water,  unites  with  acids,  but  is  a  weak  alkaline  base.  It  is  precipitated 
from  a  solution  of  its  salts,  of  which  the  nitrate  is  the  most  interesting,  as  the 
black  protoxide  of  pure  alkalies ;  as  a  white  carbonate,  which  soon  becomes  dark 
from  the  loss  of  carbonic  acid,  by  alkaline  carbonates ;  as  calomel  by  hydro- 
chloric acid  or  any  soluble  chloride ;  and  as  the  black  protosulphuret  by  hydro- 
sulphuric  acid.  Of  these  tests,  the  action  of  hydrochloric  acid  is  the  most 
characteristic.  The  oxide  is  reduced  to  the  metallic  state  by"  copper,  phosphorous 
acid,  or  protochloride  of  tin. 

Its  eq.  is  210;  symb.  Hg  -j-  O,  Hg,  or  HgO. 

Peroxide. — Prep. — Either  by  the  combined  agency  of  heat  and  air,  as  already 
mentioned,  or  by  dissolving  mercury  in  nitric  acid,  and  exposing  the  nitrate  so 
formed  to  a  temperature  just  sufficient  for  expelling  the  whole  of  the  nitric  acid. 
It  is  commonly  known  by  the  name  of  red  precipitate.  The  peroxide  prepared 
from  the  nitrate  almost  always  contains  a  trace  of  nitric  acid,  which  may  be 
detected  by  heating  it  in  a  clean  glass  tube  by  means  of  a  spirit-lamp  :  a  yellow- 

*  Some  chemists  regard  the  black  oxide  of  mercury  as  a  suboxide  2HgO,  and  the  red 
oxide  as  the  true  protoxide,  HgO  ;  according  to  which  view  the  equivalent  of  mercury  is 
assumed  to  be  101,  or  one  half  the  number  adopted  in  the  text.  There  are  no  positive  data 
by  which  to  decide  this  point,  as  we  are  ignorant  of  any  isomorphous  relations  between 
mercury  and  copper  or  that  class  of  metals  to  which  the  latter  belongs.    (R.) 


408  MERCURY. 

ring,  formed  of  subnitrate  of  oxide  of  mercury,  collects  within  the  tube  just 
above  the  part  which  is  heated.     (Clark.) 

As  thus  prepared,  it  is  commonly  in  the  form  of  shining  crystalline  scales  of 
a  nearly  black  colour  while  hot,  but  red  when  cold  :  when  very  finely  levigated, 
the  peroxide  has  an  orange  colour.  It  is  soluble  to  a  small  extent  in  water, 
forming  a  solution  which  has  an  acrid  metallic  taste,  and  communicates  a  green 
colour  to  the  blue  infusion  of  violets.  When  heated  to  redness,  it  is  converted 
into  metallic  mercury  and  oxygen.  Long  exposure  to  light  has  a  similar  effect. 
(Guibourt.) 

Some  of  the  neutral  salts  of  this  oxide,  such  as  the  nitrate  and  sulphate,  are 
converted  by  water,  especially  at  a  boiling  temperature,  into  insoluble  yellow 
subsalts,  leaving  a  strongly  acid  solution,  in  which  a  little  of  the  original  salt  is 
dissolved.  This  oxide  is  separated  from  all  acids  as  a  yellow  hydrate,  by  the 
pure  fixed  alkalies.  Carbonate  of  potash  or  soda  causes  a  dirty  brownish  red 
precipitate.  Ammonia  and  its  carbonate  cause  a  white  precipitate,  which  is  a 
double  salt,  consisting  of  one  equivalent  of  the  acid,  three  equivalents  of  the 
peroxide,  and  one  equivalent  of  ammonia.  The  oxide  is  readily  reduced  to  the 
metallic  state  by  metallic  copper.  Hydrosulphuric  acid,  phosphoroi^  acid,  and 
protochloride  of  tin,  reduce  the  peroxide  into  the  protoxide  ;  and  when  added  in 
larger  quantity,  the  first  throws  down  a  black  sulphuret,  and  the  two  latter 
metallic  mercury.  The  action  of  hydrosulphuric  acid  on  a  solution  of  corrosive 
sublimate  is,  however,  peculiar;  for  at  first  it  occasions  a  white  precipitate 
which,  according  to  Rose,  is  a  compound  of  two  equivalents  of  bisulphuret  to 
one  of  bichloride  of  mercury.  This  gas  acts  on  bibromide  and  biniodide  of 
mercury  in  a  similar  manner.     (An.  de  Ch.  et  Ph.  xl.  46.) 

Its  eq.  is  218  ;  si/mb.  Hg  -f-  20,  Hg,  or  HgO^. 

Protochloride. — Frep. — Protochloride  of  mercury,  or  calomel^  is  a  rare  mineral 
production,  called  horn  silver,  which  occurs  crystallized  in  quadrangular  prisms 
terminated  by  pyramids.  It  is  always  generated  when  chlorine  comes  in  contact 
with  mercury  at  common  temperatures ;  and  also  by  the  contact  of  metallic  mer- 
cury and  the  bichloride.  It  may  be  made  by  precipitation,  by  mixing  nitrate  of 
protoxide  of  mercury  in  solution  with  hydrochloric  acid  or  any  soluble  chloride. 
It  is  more  commonly  prepared  by  sublimation.  This  is  conveniently  done  by 
mixing  272*84  parts  or  1  eq.  of  the  bichloride  with  202  parts  or  1  eq.  of  mer- 
cury, until  the  metallic  globules  entirely  disappear,  and  then  subliming.  When 
first  prepared  it  is  always  mixed  with  some  corrosive  sublimate,  and  therefore 
should  be  reduced  to  powder  and  well  washed  before  being  employed  for  che- 
mical or  medical  purposes. 

Prop. — When  obtained  by  sublimation  it  is  in  sejmi-transparent  crystalline 
cakes ;  but  as  formed  by  precipitation,  it  is  a  white  powder.  Its  sp.  gr.  is  7'2. 
At  a  heat  short  of  redness,  but  higher  than  the  subliming  point  of  the  bichloride, 
it  rises  in  vapour  without  previous  fusion;  but  during  the  sublimadon  a  portion 
is  always  resolved  into  mercury  and  the  bichloride.  It  is  yellow  while  warm, 
but  recovers  its  whiteness  on  cooling.  It  is  distinguished  from  the  bichloride  by 
not  being  poisonous,  by  having  no  taste,  and  by  being  exceedingly  insoluble  in 
water.  Acids  have  little  effect  upon  it;  but- pure  alkalies  decompose  it,  separat- 
ing the  black  protoxide  of  mercury.  When  calomel  is  boiled  in  a  solution  of 
hydrochlorate  of  ammonia,  it  is  converted  into  corrosive  sublimate  and  metallic 
mercury.  Chloride  of  sodium  has  a  similar  effect,  though  in  a  less  degree.  Its 
eq.  is  237-42;  si/mb.  Hg-|-  CI,  or  HgCl. 


MERCURY.  409 

Bichloride. — Prep. — When  mercury  is  heated  in  chlorine  gas,  it  takes  fire,  and 
burns  with  a  pale  red  flame,  forming  the  well-known  medicinal  preparation  and 
virulent  })oison  corrosive  sublimate  or  bichloride  of  mercury.  It  is  prepared  for 
medical  purposes  by  subliming  a  mixture  of  bisulphate  of  the  peroxide  of  mer- 
cury with  chloride  of  sodium  or  sea-salt.  The  exact  quantities  required  for 
mutual  decomposition  are  298*2  parts  or  1  eq.  of  the  bisulphate,  to  117'44  parts 
or  2  eq.  of  the  chloride.     Thus, 


Bisulphate  of  Mercury  1  eq. 

Sulphuric  Acid        .  80-2  or  2  eq.  2SO3. 

Peroxide  of  Mer.     .        218     or  1  eq,  HgOg. 


298-2  Hg02t2S03 


Chloride  of  Sodium.  2  eq. 

Chlorine        .        70-84  or  2  eq.  2C1. 

Sodium  .        46-6    or  2  eq.  2Na. 


177-44  2NaCl. 


And  by  mutual  interchange  of  elements  they  produce 


Bichloride  of  Mercury  1  eq. 

Mercury        .  202       or  1  eq.  Hg. 

Chlorine        .  70-84  or  2  eq.  2C1. 


272.84  HgClj 


Sulphate  of  Soda  2  eq. 

Soda    .    .        62-6  or  2  eq.  .        2  NaO. 

Sulphuric  Ac.  80-2  or  2  eq.  .        2SO3. 

142-8  2NaO,S03. 


The  products  have  exactly  the  same  weight  (272*84  +  142*8  =  415*64)  as 
the  compounds  (298*2  +  117*44  =  415*64)  from  which  they  were  prepared. 

Prop. — When  obtained  by  sublimation,  it  is  a  semi-transparent  colourless  sub- 
stance, of  a  crystalline  texture.  It  has  an  acrid,  burning  taste,  and  leaves  a 
nauseous  metallic  flavour  on  the  tongue.  Its  sp.  gr.  is  5*2.  When  exposed  to 
a  heat  short  of  incandescence,  it  is  fused,  enters  into  ebullition  from  the  rapid 
formation  of  vapour,  and  is  deposited  without  further  change  on  cool  surfaces  as 
a  white  crystalline  sublimate.  It  requires  twenty  times  its  weight  of  cold,  and 
only  twice  its  weight  of  boiling  water  for  solution,  and  is  deposited  from  the 
latter,  as  it  cools,  in  the  form  of  prismatic  crystals.  Strong  alcohol  and  ether 
dissolve  it  in  the  same  proportion  as  boiling  water ;  and  it  is  soluble  in  half  its 
weight  of  concentrated  hydrochloric  acid  at  the  temperature  of  70°.  With  the 
chlorides  of  potassium  and  sodium,  hydrochlorate  of  ammonia,  and  several  other 
bases,  it  enters  into  combination,  forming  double  salts,  which  are  more  soluble 
than  the  chloride  itself.  When  its  solution  in  water  is  agitated  with  ether,  the 
latter  abstracts  the  bichloride,  and  rises  with  it  to  the  surface  of  the  former,  thus 
affording  strong  evidence  of  the  bichloride  having  existed  as  such  in  the  water. 
Its  aqueous  solution  is  gradually  decomposed  by  light,  calomel  being  deposited. 

The  pure  and  carbonated  fixed  alkalies  throw  down  the  peroxide  of  mercury, 
from  a  solution  of  corrosive  sublimate.  Ammonia,  on  the  contrary,  causes  the 
deposition  of  a  white  matter,  which  is  commonly  known  under  the  name  of  the 
white  precipitate.  This  substance  has  been  recently  examined  by  Kane.  (Trans. 
Irish  Academy,  xvii.)  He  finds  that  on  adding  a  slight  excess  of  ammonia  just 
one  half  of  the  chlorine  of  the  corrosive  sublimate  falls,  the  other  half  remaining 
in  the  solution  with  ammonia.  The  precipitate  nevertheless  does  not  contain 
calomel,  as  is  proved  by  its  complete  solubility  in  hydrochloric  and  nitric  acids. 
From  his  analysis  it  is  composed  of 

Mercury  ,        .        .        78-6        Ammonia 6-77 

Chlorine  .        .        .        13-85      Hygrometric  water,  loss,  &  oxygen        0-78 

Its  atomic  constitution  would  appear  from  this  analysis  to  contain  the  compound 
radical  which  is  the  base  of  the  amides.     By  the  action  of  boiling  water,  it  loses 


410  MERCURY. 

half  its  chlorine  and  ammonia,  peroxide  of  mercury  being  at  the  same  time  formed, 
and  a  canary-yellow  powder  is  produced.  Kane  finds  that  on  treating  calomel 
with  ammonia,  it  too  loses  only  one  half  its  chlorine,  and  a  compound  analogous 
to  white  precipitate  is  obtained. 

The  presence  of  mercury  in  a  fluid  supposed  to  contain  corrosive  sublimate, 
may  be  detected  by  concentrating  and  digesting  it  with  an  excess  of  pure  potassa. 
Oxide  of  mercury,  which  subsides,  is  then  sublimed  in  a  small  glass  tube  by 
means  of  a  spirit-lamp,  and  obtained  in  the  form  of  metallic  globules.  But  in 
cases  of  poisoning,  when  the  bichloride  is  mixed  with  organic  substances,  Chris- 
tison  recommends  that  the  liquid,  without  previous  filtration,  be  agitated  with  a 
fourth  of  its  volume  of  ether,  which  separates  the  poison  from  the  aqueous  part, 
and  rises  to  the  surface.  The  ethereal  solution  is  then  evaporated  on  a  watch- 
glass,  the  residue  dissolved  in  hot  water,  and  the  mercury  precipitated  in  the 
metallic  state  by  protochloride  of  tin  at  a  boiling  temperature.  If,  as  is  probable, 
most  of  the  poison  is  already  converted  into  calomel,  and  thereby  rendered  inso- 
luble, as  many  vegetable  fibres  should  be  picked  out  as  possible,  and  the  whole 
at  once  digested  with  protochloride  of  tin.  The  organic  substances  are  then 
dissolved  in  a  hot  solution  of  caustic  potassa,  and  the  insoluble  parts  washed  and 
sublimed  to  separate  the  mercury.     (Christison  on  Poisons.) 

A  very  elegant  method  of  detecting  the  presence  of  mercury  is  to  place  a  drop 
of  the  suspected  liquid  on  polished  gold,  and  to  touch  the  moistened  surface  with 
a  piece  of  iron  w^ire  or  the  point  of  a  penknife,  when  the  part  touched  instantly 
becomes  white,  owing  to  the  formation  of  an  amalgam  of  gold.  This  process 
was  originally  suggested  by  Sylvester,  and  has  since  been  simplified  by  Paris. 
(Medical  Jurisprudence,  by  Paris  and  Fonblanque.) 

Many  animal  and  vegetable  solutions  convert  bichloride  of  mercury  into  calo- 
mel, a  portion  of  hydrochloric  acid  being  set  free  at  the  same  time.  Some  sub- 
stances effect  this  change  slowly ;  while  others,  and  especially  albumen,  produce 
it  in  an  instant.  Thus,  when  a  solution  of  corrosive  sublimate  is  mixed  with 
albumen,  a  white  flocculent  precipitate  subsides,  which  Orfila  has  shown  to  be 
a  compound  of  calomel  and  albumen,  and  which  he  has  proved  experimentally  to 
be  inert.  (Toxicologic,  vol.  i.)  Consequently  a  solution  of  the  white  of  eggs 
is  an  antidote  to  poisoning  by  corrosive  sublimate.  The  muscular  and  membra- 
nous parts,  even  of  a  living  animal,  produce  a  similar  effect ;  and  the  causti- 
city of  corrosive  sublimate  seems  owing  to  the  destruction  of  the  animal,  fibre, 
by  which  the  decomposition  of  the  bichloride  is  accompanied,  and  which  consti- 
tutes an  essential  part  of  the  chemical  change.* 

Its  eg.  is  272-84 ;  symb.  Hg  f  CI,  or  HgCl^. 

Protiodide  of  Mercury. — This  compound  is  obtained  by  mixing  nitrate  of  prot- 
oxide of  mercury  in  solution  with  iodide  of  potassium.  It  is  a  green  powder, 
insoluble  in  water,  and  disposed  to  resolve  itself  under  the  influence  of  heat  or 
solar  light  into  mercury  and  the  biniodide.  However,  when  the  heat  is  quickly 
supplied,  it  is  fused  and  sublimed  without  material  change. 

*  M.  Mialhi  proposes  the  moist  recently  precipitated  sulphuret  of  iron  as  an  antidote  for 
corrosive  sublimate,  and  its  value  in  this  respect  is  said  to  have  been  tested  by  M.  Orfila. 
When  added  to  mixtures  containing  the  minutest  trace  of  corrosive  sublimate,  decomposi- 
tion  ensues  immediately,  from  the  reaction  of  two  equivalents  of  the  sulphuret  of  iron  with 
one  of  the  bichloride  of  mercury,  giving  rise  to  two  eq.  of  the  chloride  of  iron  and  1  eq.  of 
the  bisulphuret  of  mercury,  thus  HgCl2  and  2FeS  yield  HgSj  and  2FeCl.  The  bisulphuret  of 
mercury  is  inert.     (R.) 


MERCURY.  411 

Us  eg.  is  328-3 ;  symb.  Hg  +  I,  or  Hgl. 

Sesquiodide. — This  compound  falls  as  a  yellow  powder  when  iodide  of  potas- 
sium is  added  in  solution  to  the  mixed  nitrates  of  the  protoxide  and  peroxide  of 
mercury,  the  latter  being  in  excess.  The  precipitate  is  digested  with  a  solution 
of  sea-salt,  which  takes  up  any  biniodide  which  may  have  fallen. 

Its  eq.  is  782-9 ;  symb,  2Hg  -f-  31,  or  Hgjg. 

Biniodide. — This  compound  is  formed  by  mixing  nitrate  of  the  peroxide  or 
bichloride  of  mercury  with  iodide  of  potassium  in  solution,  and  falls  as  a  rich 
red-coloured  powder  of  a  tint  which  vies  in  beauty  with  that  of  vermilion,  though, 
unfortunately,  the  colour  is  less  permanent.  Though  insoluble  in  water,  it  dis- 
solves freely  in  an  excess  of  either  of  its  precipitants.  If  taken  up  in  a  hot  so- 
lution of  nitrate  of  peroxide  of  mercury,  the  biniodide  crystallizes  out  on  cooling 
in  scales  of  a  beautiful  red  tint.  The  same  crystals  separate  from  a  solution  in 
iodide  of  potassium;  but  if  the  liquid  be  concentrated,  a  double  iodide  of  mer- 
cury and  potassium  subsides. 

The  biniodide,  w^hen  exposed  to  a  moderate  heat,  gradually  becomes  yellow  ; 
and  the  particles,  though  previously  in  powder,  acquire  a  crystalline  appearance. 
At  about  400°  it  forms  a  yellow  liquid,  which  slowly  sublimes  in  small  trans- 
parent scales,  or  in  large  rhombic  tables,  when  a  considerable  quantity  is  sub- 
limed. The  crystals  retain  their  yellow  colour  at  60°  if  kept  very  tranquil ;  but 
if  the  temperature  be  below  a  certain  point,  or  they  are  rubbed  or  touched,  they 
quickly  become  red.  This  phenomenon  is  entirely  due  to  a  change  in  molecular 
arrangement :  the  different  colours  so  often  witnessed  in  the  same  substances  at 
different  temperatures,  as  in  peroxide  of  mercury  and  the  protoxides  of  lead  and 
zinc,  appear  to  be  phenomena  of  the  same  nature. 

Its  eq.  454-6 ;  symb.  Hg  -\-  21,  or  Hgl^. 

loduretted  Bichloride  of  Mercury. — This  compound  has  recently  been  described 
by  Lassaigne.  (An.  de  Ch.  et  Ph.  Ixiii.  106.)  It  is  formed  by  adding  to  an 
alcoholic  solution  of  iodine  a  solution  of  corrosive  sublimate,  when  the  deep 
colour  of  the  iodine  gradually  disappears,  and  a  colourless  solution  is  obtained. 
It  is  remarkable,  that  in  this  combination  the  iodine  cannot  be  detected  by  starch 
and  chlorine  or  sulphurous  acid,  as  in  its  other  combinations.  The  compound  is 
decomposed  by  heat,  but  may  be  obtained  in  crystals  by  evaporating  a  concen- 
trated solution  at  a  moderate  temperature.     Its  eq.  is  5583-1 ;  symb.  20HgCl2  -|-  I. 

lodo-bichloride  of  Mercury. — This  compound  was  described  by  Boullay.  (An. 
de  Ch.  et  Ph.  xxxvi.  366.)  It  is  formed  by  dissolving  biniodide  of  mercury  in 
corrosive  sublimate,  when  a  colourless  crystalline  compound  is  obtained.  It  is 
composed  of  40  eq.  of  the  bichloride  and  one  of  the  biniodide. 

Its  eq.  is  11368-2;  symb.  40HgCl2  +  Hgl^. 

Protobromide  of  Mercury. — It  is  precipitated  as  a  white  insoluble  powder  by 
mixing  nitrate  of  protoxide  of  mercury  with  bromide  of  potassium.  Its  eq.  is 
280-4;  symb.  Hg  +  Br,  or  HgBr. 

The  bibromide  is  a  white  crystallizable  compound,  soluble  in  water  and  alco- 
hol, fusible  and  volatile,  and  in  many  respects  analogous  to  the  bichloride.  It  is 
formed  by  acting  on  peroxide  of  mercury  with  hydrobromic  acid,  or  digesting  the 
preceding  compound  with  bromine.  ' 

Its  eq.  is  358-8 ;  symb.  Hg  +  2Br,  or  HgBr^. 

Sulphurets  of  Mercury. — The  protosulphuret  may  be  prepared  by  transmitting 
a  current  of  hydrosulphuric  acid  gas  through  a  dilute  solution  of  nitrate  of  prot- 
oxide of  mercury,  or  through  water  in  which  calomel  is  suspended.  It  is  a  black- 


412  SILVER. 

coloured  substance,  which  is  oxidized  by  digestion  in  strong  nitric  acid.  When 
exposed  to  heat  it  is  resolved  into  the  bisulphuret  and  metallic  mercury.  Its  eq. 
IS  218-1 ;  symb.  Hg  -f-  S,  or  HgS. 

The  bisulphuret  is  formed  by  fusing  sulphur  with  about  six  times  its  weight 
of  mercury,  and  subliming  in  close  vessels.  When  procured  by  this  process  it 
has  a  red  colour,  and  is  known  by  the  name  of  factitious  cinnabar.  Its  tint  is 
greatly  improved  by  being  reduced  to  powder,  in  which  state  it  forms  the  beau- 
tiful pigment  vermilion.  It  may  be  obtained  in  the  moist  way  by  pouring  a  solu- 
tion of  corrosive  sublimate  into  an  excess  of  hydrosulphate  of  ammonia.  A 
black  precipitate  subsides,  which  acquires  the  usual  red  colour  of  cinnabar  when 
sublimed.  The  black  precipitate  formed  by  the  action  of  hydrosulphuric  acid  on 
bicyanuret  of  mercury,  is  likewise  a  bisulphuret.  Cinnabar,  as  already  men- 
tioned, occurs  native. 

When  equal  parts  of  sulphur  and  mercury  are  triturated  together  until  metallic 
globules  cease  to  be  visible,  the  dark-coloured  mass  called  Ethiops  mineral 
results,  which  Mr.  Brande  has  proved  to  be  a  mixture  of  sulphur  and  bisul- 
phuret of  mercury.     (Journal  of  Science,  vol.  xviii.  p.  294.) 

Cinnabar  is  not  attacked  by  alkalies,  or  any  simple  acid ;  but  it  is  dissolved 
by  the  nitro-hydrochloric,  with  formation  of  sulphuric  acid  and  peroxide  of 
mercury. 

Its  eq.  is  234*2 ;  symb,  Hg  -f  2S,  or  HgS^. 


SECTION  XXIV. 


SILVER. 


Hist. — This  metal  was  known  to  the  ancients.  It  frequently  occurs  native  in 
silver  mines,  both  massive  and  in  octohedral  or  cubic  crystals.  It  is  also  found 
in  combination  with  gold,  tellurium,  antimony,  copper,  arsenic,  and  sulphur. 
In  the  state  of  sulphuret  it  so  frequently  accompanies  galena,  that  the  lead  of 
commerce  is  rarely  quite  free  from  traces  of  silver. 

Prep, — Silver  is  extracted  from  its  ores  by  two  processes  which  are  essentially 
distinct ;  one  of  them  being  contrived  to  separate  it  from  lead,  the  other,  the  pro- 
cess by  amalgamation,  being  especially  adapted  to  those  ores  which  are  free  from 
lead.  The  principle  of  its  separation  from  lead  is  founded  on  the  different  oxida- 
bility  of  lead  and  silver,  and  on  the  ready  fusibility  of  litharge.  The  lead 
obtained  from  those  kinds  of  galena  which  are  rich  in  sulphuret  of  silver  is  kept 
at  a  red  heat  in  a  flat  furnace,  with  a  draught  of  air  constantly  playing  on  its 
surface :  the  lead  is  thus  rapidly  oxidized  ;  and  as  the  oxide,  at  the  moment  of 
it»  formation,  is  fused,  and  runs  off  through  an  aperture  in  the  side  of  the  fur- 
nace, the  prdtiuction  of  litharge  goes  on.  uninterruptedly  until  all  the  lead  is 
removed.  The  button  of  silver  is  again  fused  in  a  smaller  furnace,  resting  on  a 
porous  earthen  dish,  made  with  lixiviated  wood-ashes,  called  a  test,  the  porosity 
of  which  is  so  great,  that  it  absorbs  any  remaining  portions  of  litharge  which 
may  be  formed  on  the  silver. 


SILVER.  413 

Mr.  Pattinson  of  Newcastle  has  taken  out  a  patent  for  a  new  and  ingenious 
process,  whereby  the  extraction  of  silver  from  lead  is  much  facilitated.  .  The 
lead  is  melted* and  allowed  to  cool  slowly.  The  crystals  wfiich  form  first  are 
much  richer  in  silver  than  the  original  mass.  They  are  removed  by  means  of  a 
perforated  ladle,  and  the  process  is  repeated  both  with  them  and  with  the  residue, 
till  there  is  obtained,  on  the  one  hand,  lead  almost  free  of  silver,  while  on  the 
other,  the  whole  silver  is  collected  in  combination  with  a  small  part  of  the  lead. 
This  mixture  is  then  subjected  to  cupellation,  which  from  its  smaller  bulk  is 
more  easily  and  rapidly  accomplished. 

The  ores  commonly  employed  in  the  process  of  amalgamation,  which  has  been 
long  used  at  Freyberg  in  Saxony,  and  is  extensively  practised  in  the  silver  and 
gold  mines  of  South  America,  are  native  silver  and  its  sulphuiet.  At  Freyberg 
the  ore  in  fine  pow^der  is  mixed  with  sea-salt,  and  carefully  roasted  in  a  reverbe- 
ratory  furnace.  The  production  of  sulphuric  acid  leads  to  the  formation  of  sul- 
phate of  soda,  while  the  chlorine  of  the  sea-salt  combines  with  silver.  The 
roasted  mass  is  ground  to  a  fine  powder,  and,  together  with  mercury,  water,  and 
fragments  of  iron,  is  put  into  barrels,  which  are  made  to  revolve  by  machinery. 
In  this  operation,  intended  to  insure  perfect  contact  between  the  materials,  chlo- 
ride of  silver  is  decomposed  by  the  iron,  the  silver  unites  with  the  mercury,  and 
the  chloride  of  iron  is  dissolved  by  the  water.  The  mercury  is  then  squeezed 
through  leathern  bags,  the  pores  of  which  permit  the  pure  mercury  to  pass,  but 
retain  the  amalgam  of  silver.  The  combined  mercury  is  then  distilled  off  in 
close  vessels,  and  the  metals  obtained  in  a  separate  state. 

Goldsmiths'  silver  commonly  contains  copper  and  traces  of  gold,  the  latter 
appearing  in  dark  flocks  when  the  metal  is  dissolved  in  nitric  acid.  It  may  be 
obtained  pure  for  chemical  use  by  placing  a  clean  piece  of  copper  in  a  solution 
of  nitrate  of  oxide  of  silver,  washing  the  precipitate  with  pure  water,  and  then 
digesting  it  in  ammonia,  in  order  to  remove  any  adhering  copper.  A  better  pro- 
cess is  to  decompose  chloride  of  silver  by  means  of  carbonate  of  potassa.  For 
this  purpose  precipitate  a  solution  of  nitrate  of  oxide  of  silver  with  chloride  of 
sodium,  wash  the  precipitate  with  water,  and  dry  it.  Then  put  twice  its  weight 
of  carbonate  of  potassa  into  a  clean  hessian  or  black-lead  crucible,  heat  it  to  red- 
ness, and  throw  the  chloride  by  successive  portions  into  the  fused  alkali.  Effer- 
vescence takes  place  from  the  evolution  of  carbonic  acid  and  oxygen  gases,  chlo- 
ride of  potassium  is  generated,  and  metallic  silver  subsides  to  the  bottom.  The 
pure  metal  may  be  granulated  by  pouring  it  while  fused  from  a  height  of  seven 
or  eight  feet  into  a  vessel  of  water. 

Prop. — It  has  the  clearest  white  colour  of  all  the  metals,  and  is  susceptible  of 
receiving  a  lifstre  surpassed  only  by  polished  steel.  In  malleability  and  ductility 
it  is  inferior  only  to  gold,  and  its  tenacity  is  considerable.  It  is  very  soft  when 
pure,  so  that  it  may  be  cut  with  a  knife.  Its  density  after  being  hammered  is 
10*51.  At  a  full  red  heat,  corresponding  to  1873°  F.  according  to  Daniell,  it 
enters  into  fusion.  It  does  not  rust  by  exposure  to  air  and  moisture.  When 
fused  in  open  vessels  it  absorbs  oxygen  in  considerable  quantity,  amounting 
sometimes  to  22  times  its  volume ;  but  it  parts  with  the  whole  of  it  in  the  act 
of  becoming  solid.  This  fact,  first  noticed  by  M.  Lucas,  has  been  studied  by 
Gay-Lussac,  who  attributes  to  it  the  peculiarly  beautiful  aspect  of  granulated 
silver :  he  observed  the  absorption  and  subsequent  evolution  of  oxygen  to  be 
most  abundant  in  the  purest  silver,  and  is  entirely  prevented  by  a  very  small  per 
centage  of  copper.     If  silver  is  heated  to  redness,  without  fusing,  in  contact  with 


414 


SILVER. 


glass  or  porcelain,  it  readily  absorbs  oxygen,  and  tbe  oxide  fuses  with  the  earthy 
matters,  forming  a  yellow  enamel.  When  silver  in  the  form  of  leaves  or  fine 
wire  is  intensely  heated  by  means  of  electricity,  galvanism,  or  the  *oxy-hydrogen 
blowpipe,  it  burns  with  vivid  scintillations  of  a  greenish-white  colour. 

The  only  pure  acids  that  act  on  silver  are  the  sulphuric  and  nitric  acids,  by 
both  of  which  it  is  oxidized,  forming  with  the  first  a  sulphate,  and  with  the 
second  a  nitrate  of  oxide  of  silver.  It  is  not  attacked  by  sulphuric  acid  unless 
by  the  aid  of  heat.  Nitric  acid  is  its  proper  solvent,  and  forms  with  its  oxide  a 
salt,  which,  after  fusion,  is  known  by  the  name  of  lunar  caustic. 

From  recent  experiments  on  the  composition  of  the  chloride  and  nitrate  of  the 
oxide  of  silver,  I  have  deduced  108  as  the  eq.  of  silver,  an  estimate  closely  cor- 
responding with  the  previous  researches  of  Berzelius.  (Phil.  Trans.  1833,  part 
ii.)  Its  symb.  is  Ag.  The  compounds  of  silver  described  in  this  section  are 
thus  constituted  : — 


Dioxide 

Oxide 

Chloride 

Iodide 

Sulphuret 


Silver.  Equiv.  Formulae. 

216    2  eq.+Oxygen  8  1  eq.=224-2  Ag+0  or  Ag20. 

108     1  eq.4-0xygen  8  1  eq.=116  Ag+0  or  AgO. 

108    1  eq.+Chlorine  35-42  1  eq.=143-42  Ag+Cl  or  AgCl. 

108     1  eq.+Iodine  126-3  1  eq.=234-3  Ag-J-I   or  Agl. 

108     1  eq.+Sulphur  161  1  eq.=124-l  AgfS  or  AgS. 


[Dioxide  of  Silver,  suboxide. — ^This  oxide  is  obtained,  according  to  Wohler,  by 
passing  a  current  of  hydrogen  gas  over  the  citrate  of  the  protoxide,  heated  to 
212°.  The  protoxide  of  this  salt  loses  one  half  of  its  oxygen  and  is  thereby 
reduced  to  the  dioxide  which  remains  in  combination  with  one  half  of  the  citrate 
as  a  sub-salt,  which  along  with  the  free  citric  acid,  forms  a  dark  brown  solu- 
tion in  water.  The  dioxide  is  precipitated  from  this  solution  by  potassa  as  a 
black  powder,  wliich  is  very  easily  decomposed  and  quite  soluble  in  ammonia. 
A  solution  of  the  sub-salt  is  immediately  resolved  by  heat  into  metallic  silver 
which  is  precipitated,  and  a  protosalt  which  remains  in  solution.] 

Oxide  of  Silver. — ^This  oxide  is  best  procured  by  mixing  a  solution  of  pure 
baryta  with  nitrate  of  oxide  of  silver  dissolved  in  water,  [or,  according  to  Gre- 
gory, by  boiling  recently  precipitated  .chloride  of  silver  with  a  strong  solution  of 
caustic  potassa.  By  the  first  method  it  is  brown  in  colour,  by  the  second  jet 
black.]  It  is  insoluble  in  water,  and  completely  reduced  by  a  red  heat.  It  is 
separated  from  its  solution  in  nitric  acid  by  pure  alkalies  and  alkaline  earths  as 
the  brown  oxide,  which  is  redissolved  by  ammonia  in  excess;  by  alkaline  car- 
bonates as  a  white  carbonate,  which  is  soluble  in  an  excess  of  carbonate  of  am- 
monia ;  as  a  dark  brown  sulphuret  by  hydrosulphuric  acid ;  and  as  a  white  curdy 
chloride  of  silver,  which  is  turned  violet  by  light,  and  is  very  soluble  in  ammo- 
nia, by  hydrochloric  acid  or  any  soluble  chloride.  By  the  last  character,  silver 
may  be  both  distinguished  and  separated  from  other  metallic  bodies. 

Silver  is  precipitated  in  the  metallic  state  by  most  other  metals.  When  mer- 
cury is  employed  for  this  purpose,  the  silver  assumes  a  beautiful  arborescent 
appearance,  called  arbor  Dianse.  A  very  good  proportion  for  the  experiment  is 
20  grains  of  lunar  caustic  to  6  drachms  or  an  ounce  of  water.  The  silver  thus 
deposited  always  contains  mercury. 

When  oxide  of  silver,  recently  precipitated  by  baryta  or  lime-water,  and  sepa- 
rated from  adhering  moisture  by  bibulous  paper,  is  left  in  contact  for  10  or  12 


SILVER.  415 

hours  with  a  strong  solution  of  ammonia,  the  greater  part  of  it  is  dissolved ;  but 
a  black  powder  remains  which  detonates  violently  from  heat  or  percu^on. 
This  substance,  which  was  discovered  by  Berthollet,  (An.  de  Chimie,  i!)  ap- 
pears to  be  a  compound  of  ammonia  and  oxide  of  silver ;  for  the  products  of  its 
detonation  are  metallic  silver,  water,  and  nitrogen  gas.  It  should  be  made  in 
very  small  quantity  at  a  time,  and  dried  spontaneously  in  the  air. 

On  exposing  a  solution  of  oxide  of  silver  in  ammonia  to  the  air,  its  surface 
becomes  covered  with  a  pellicle,  which  Faraday  considers  to  be  an  oxide  con- 
taining a  smaller  proportion  of  oxygen  than  that  just  described.  This  opinion 
he  has  made  highly  probable ;  but  further  experiments  are  requisite  before  the 
existence  of  this  oxide  can  be  regarded  as  certain. 

Its  eq.  is  116 ;  symh.  Ag  -|-  0,  Ag,  or  AgO. 

Chloride  of  Silver. — Prep. — ^This  compound,  which  sometimes  occurs  in  silver 
mines,  and  constitutes  the  horn  silver  of  mineralogists,  is  always  generated  when 
silver  is  heated  in  chlorine  gas,  and  may  be  prepared  conveniently  by  mixing 
hydrochloric  acid,  or  any  soluble  chloride,  with  a  solution  of  nitrate  of  oxide  of 
silver.  As  formed  by  precipitation  it  is  quite  white;  but  by  exposure  to  the 
direct  solar  rays  it  becomes  violet,  and  almost  black,  in  the  course  of  a  few 
minutes;  and  a  similar  effect  is  slowly  produced  by  diffused  day-light.  On  this 
principle  is  founded  Mr.  Talbot's  method  of  photography.  Hydrochloric  acid  is 
set  free  during  this  change,  and,  according  to  Berthollet,  the  dark  colour  is  owing 
to  separation  of  oxide  of  silver.     (Statique  Chimique,  vol.  i.  p.  195.) 

Prop. — It  is  insoluble  in  water,  and  is  dissolved  very  sparingly  by  the  strongest 
acids  ;  but  it  is  soluble  in  ammonia.  Hyposulphurous  acid  likewise  dissolves  it. 
At  a  temperature  of  about  500°  it  fuses,  and  forms  a  semitransparent  horny  mass 
on  cooling,  which  has  a  density  of  5"524.  It  bears  any  degree  of  heat,  or  even 
the  combined  action  of  pure  charcoal  and  heat,  without  decomposition ;  but 
hydrogen  gas  decomposes  it  readily  with  formation  of  hydrochloric  acid.  Its  eq. 
is  143.42  ;  symb.  Ag-|-  CI,  or  AgCl. 

Iodide  of  Silver. — This  compound  is  formed  when  iodide  of  potassium  is 
mixed  with  a  solution  of  nitrate  of  oxide  of  silver.  It  is  of  a  greenish-yellow 
colour,  and  is  insoluble  in  water  and  ammonia.  A  film  of  this  compound  on  the 
surface  of  a  polished  plate  of  silver,  constitutes  the  substance  which  receives  the 
impressions  of  light  in  Daguerre's  beautiful  invention  of  the  Daguerreotype. 

Its  eq.  is  234*3  ;  sj/mb.  Ag  -f-  I,  or  Agl. 

Sulphurei  of  Silver. — Silver  has  a  strong  affinity  for  sulphur.  This  metal  tar- 
nishes rapidly  when  exposed  to  an  atmosphere  containing  hydrosulphuric  acid 
gas,  owing  to  the  formation  of  a  sulphuret.  On  transmitting  a  current  of  this 
gas  through  a  solution  of  lunar  caustic,  a  dark  brown  precipitate  subsides,  which 
is  a  sulphuret  of  silver.  Thesilver  glance  of  mineralogists  is  a  similar  compound, 
and  the  same  sulphuret  may  be  prepared  by  heating  thin  plates  of  silver  with 
alternate  layers  of  sulphur.  This  sulphuret  is  remarkable  for  being  soft  and 
even  malleable. 

Its  eq.  is  124*1 ;  symb.  Ag  -f-  S,  or  AgS. 

Silver  unites  also  by  the  aid  of  heat  with  phosphorus,  forming  a  soft,  brittle, 
crystalline  compound. 


416  GOLD. 


SECTION  XXV. 


GOLD. 


Hist,  and  Prep. — Gold  appears  to  have  been  known  to  the  earliest  races  of 
man,  and  to  have  been  esteemed  by  them  as  much  as  by  the  moderns.  It  has 
hitherto  been  found  only  in  the  metallic  state,  either  pure  or  in  combination  with 
other  metals.  It  occurs  massive,  capillary,  in  grains,  and  crystallizes  in  octo- 
hedrons  and  cubes,  or  their  allied  forms.  It  is  sometimes  found  in  primary 
mountains ;  but  more  frequently  in  alluvial  depositions,  especially  among  sand 
in  the  beds  of  rivers,  having  been  washed  by  water  out  of  disintegrated  rocks  in 
which  it  originally  existed.  There  are  few  countries  in  which  gold  washings 
have  not  formerly  existed ;  but  the  principal  supply  of  gold  is  from  South  Ame- 
rica, from  the  gold  mines  of  Hungary,  and  from  the  Uralian  mountains  of  Siberia, 
especially  on  the  Asiatic  side  of  the  chain,  where  separate  masses  in  sand  have 
been  found  weighing  18  or  20  pounds.  Rich  deposits  of  gold  appear  also  to 
exist  in  some  of  the  southern  provinces  of  North  America.  Gold  is  generally 
separated  from  accompanying  impurities  by  the  process  of  amalgamation,  similar 
to  that  described  in  the  last  section ;  by  which  means  it  is  freed  from  iron  and  all 
associated  metals,  excepting  silver.  In  Hungary  the  gold  is  purified  by  cupel- 
lation.  The  silver,  which  in  variable  quantity  is  present  in  native  gold,  may  be 
brought  into  view  by  dissolving  the  gold  in  nitro-hydrochloric  acid.  The  best 
mode  of  separation  consists  in  fusing  the  gold  with  so  much  silver  that  the 
former  may  constitute  one-fourth  of  the  mass  :  nitric  acid  will  then  dissolve  all 
the  silver  and  leave  the  gold.  The  silver  may  also  be  removed  by  digestion  in 
sulphuric  acid. 

Prop. — Gold  is  the  only  metal  which  has  a  yellow  colour,  a  character  by  which 
it  is  distinguished  from  all  other  simple  metallic  bodies.  It  is  capable  of  receiv- 
ing a  high  lustre  by  polishing,  but  is  inferior  in  brilliancy  to  steel,  silver,  and 
mercury.  In  ductility  and  malleability  it  exceeds  all  other  metals ;  but  it  is 
surpassed  by  several  in  tenacity.  Its  density  is  19*3;  when  pure  it  is  exceed- 
ingly soft  and  flexible  ;  and  it  fuses  according  to  Daniell  at  2016°. 

Gold  may  be  exposed  for  ages  to  air  and  moisture  without  change,  nor  is  it 
oxidized  by  being  kept  in  a  state  of  fusion  in  open  vessels.  When  intensely 
ignited  by  means  of  electricity  or  the  oxy-hydrogen  blowpipe,  it  burns  with  a 
greenish-blue  flame,  and  is  dissipated  in  the  form  of  a  purple  powder,  which  is 
supposed  to  be  an  oxide. 

Gold  is  not  oxidized  or  dissolved  by  any  of  the  pure  acids ;  for  it  may  be 
boiled  even  in  nitric  acid  without  undergoing  any  change.  Its  best  solvents  are 
chlorine  and  nitro-hydrochloric  acid ;  and  it  appears  from  the  observations  of  Davy 
that  chlorine  is  the  agent  in  both  cases,  ^ince  nitro-hydrochloric  acid  does  not 
dissolve  gold,  except  when  it  gives  rise  to  the  formation  of  chlorine.  It  is  to 
be  inferred,  therefore,  that  the  chlorine  unites  directly  with  the  gold.  It  is  also 
readily  attacked  by  fluorine. 

The  most  convenient  method  of  dissolving  it  is  to  digest  fragments  of  the 


GOLD. 


417 


metal  in  a  mixture  composed  of  two  measures  of  hydrochloric  and  one  of  nitric 
acid,  until  the  acid  is  saturated.  The  excess  of  acid  is  then  expelled  by  evapo- 
rating the  orange-coloured  solution  until  a  ruby-red  liquid  remains,  which  is  the 
neutral  terchloride  of  gold.  On  adding  water,  the  chloride  is  dissolved,  forming 
a  solution  of  a  gold-yellow  colour. 

The  eq.  of  gold,  estimated  from  the  analysis  of  the  terchloride  by  Berzelius,  is 
199'2;  its  symb.  is  Au.  The  composition  of  its  compounds  described  in  this 
section  is  as  follows  : — 


1 

eq.  of  Gold. 

Equiv. 

Formulae. 

Protoxide 

199-2  + Oxygen 

8 

1  eq.=207-2 

Au-|-0    or  AuO. 

Binoxide 

199-2fdo. 

16 

2eq.=115-2 

Au-t-20  or  Au02. 

Peroxide 

199-2-t-do. 

24 

3  eq.=123-2 

Au-i-30or  AuOg. 

Protochloride 

199-2  4"  Chlorine 

35-42 

1  eq.=234-62 

Au-|-Cl  orAuCl. 

Terchloride 

199-2+do. 

106-26 

3  eq.=305-46 

Au  4-301  or  AuClg 

Protiodide 

199-2 -f  Iodine 

126-3 

1  eq.=325-5 

Au-f-I     or  Aul. 

Teriodide 

199-24-do. 

378-9 

3  eq.=5781 

Au-|-3I  or  Aulg. 

Tersulphuret 

199-2+Sulphur 

48-3 

3  eq.=247-5 

Au-f-3S  or  AuSg. 

Protoxide  of  Gold. — It  is  obtained  by  the  action  of  a  cold  solution  of  potassa 
on  the  protochloride  of  gold,  and  is  separated  as  a  green  precipitate,  which  is 
partially  soluble  in  the  alkaline  solution.  It  spontaneously  changes  soon  after 
its  preparation  into  metallic  gold  and  the  peroxide. 

Us  eq.  is  207*2;  symh.  Au  -f-  0,  Au,  or  AuO. 

The  binoxide  is  supposed  to  be  the  purple  oxide  which  is  formed  by  the  com- 
bustion of  gold  ;  but  its  composition  has  not  been  demonstrated  by  analysis. 

Peroxide. — Prep. — This,  the  only  well  known  oxide  of  gold,  is  prepared  by 
the  action  of  alkalies  on  the  terchloride,  but  is  obtained  quite  pure  with  difficulty. 
Pelletier  recommends  that  it  should  be  formed  by  digesting  a  solution  of  the 
terchloride  with  pure  magnesia,  washing  the  precipitate  with  water,  and  removing 
the  excess  of  magnesia  by  dilute  nitric  acid.  It  is  apt,  however,  to  retain  mag- 
nesia, and  I  am  informed  by  Wagner,  of  Pesth  in  Hungary,  that  the  most  certain 
mode  of  procuring  the  peroxide  is  the  following.  Dissolve  one  part  of  gold  in 
the  usual  way,  render  it  quite  neutral  by  evaporation,  and  redissolve  in  12  parts 
of  water:  to  the  solution  add  one  part  of  carbonate  of  soda  dissolved  in  twice  its 
weight  of  water,  and  digest  at  about  170°.  Carbonic  acid  gradually  escapes, 
and  the  hydrated  peroxide  of  a  brownish-red  colour  subsides.  After  being  well 
washed  it  is  dissoved  in  colourless  nitric  acid  of  specific  gravity  1*4,  and  the 
solution  decomposed  by  admixture  with  water.  The  hydrated  peroxide  is  thus 
obtained  quite  pure,  and  is  rendered  anhydrous  by  a  temperature  of  212°. 

Prop. — Yellow  in  a  state  of  hydrate,  and  nearly  black  when  anhydrous,  is 
insoluble  in  water,  and  completely  decomposed  by  solar  light  or  a  red  heat. 
Hydrochloric  acid  dissolves  it  readily,  yielding  the  common  solution  of  gold  ; 
but  it  forms  no  definite  compound  with  any  acid  which  contains  oxygen.  It  may 
indeed  be  dissolved  by  nitric  and  sulphuric  acids ;  but  the  affinity  is  so  slight 
that  the  oxide  is  precipitated  by  the  addition  of  water.  It  combines,  on  the  con- 
trary, with  alkaline  bases,  such  as  potassa  and  baryta,  apparently  forming  regular 
salts,  in  which  it  acts  the  part  of  a  weak  acid.  This  property,  which  constitutes 
the  difficulty  of  procuring  peroxide  of  gold  quite  pure,  induced  Pelletier  to  deny 
that  the  peroxide  of  gold  is  a  salifiable  base,  and, to  propose  for  it  the  name  of 

29 


418  GOLD. 

auric  acid^  its  compounds  with  alkalies  being  called  auraies.     (An.  de  Ch.  et 
Ph.  XV.) 

When  recently  precipitated  peroxide  of  gold  is  kept  in  strong  ammonia  for 
about  a  day,  a  detonating  compound  of  a  deep  olive  colour  is  generated,  analo- 
gous to  the  fulminating  silver  described  in  the  last  section.  According  to  the 
,  analysis  of  Dumas,  its  elements  are  in  the  ratio  of  1  eq.  of  gold,  2  of  nitrogen, 
6  of  hydrogen,  and  3  of  oxygen,  as  expressed  by  the  symbols  Au  -f-  N^  +  Hg 
+  0  .  With  regard  to  the  mode  in  which  these  elements  are  arranged,  different 
opinions  may  be  formed.  Dumas  thinks  the  real  combination  is  indicated  by 
the  formula  AuN^  +  NH^  +  3H0,  being  a  hydrated  nituret  of  gold  united  with 
ammonia ;  but  it  appears  more  simple  to  consider  it  as  a  di-aurate  of  ammonia, 
expressed  by  the  formula  AuO^  -\-  2NH^.  Its  detonation  should  give  rise  to 
metallic  gold,  water,  nitrogen,  and  ammonia.  A  similar  compound  is  obtained, 
and  this  is  the  ordinary  mode  of  procuring  fulminating  gold,  by  digesting  terchlo- 
ride  of  gold  with  an  excess  of  ammonia:  a  yellow  precipitate  subsides,  the  fulmi- 
nating ingredient  of  which  appears  identical  with  that  above  described  ;  but  a 
subchloride  of  gold  and  ammonia  falls  at  the  same  time,  and  adheres  so  obsti- 
nately that  it  cannot  be  wholly  removed  by  boiling  water.  Fulminating  gold 
may  be  dried  at  212°;  but  friction,  or  a  heat  suddenly  raised  to  about  290°  or 
upwards,  produces  a  violent  detonation.  It  is  best  to  make  it  in  small  quantities 
at  a  time,  and  to  dry  it  in  the  open  air.    (kn.  de  Ch.  et  Ph.  xliv.  167.) 

lis  eq.  is  123*2 ;  symb.  Au  -f-  30,  Au,  or  AuO^. 

Chlorides  of  Gold. — On  concentrating  the  solution  of  gold  to  a  sufficient  extent 
by  evaporation,  the  terchloride  may  be  obtained  in  ruby-red  prismatic  crystals, 
which  are  very  fusible.  It  deliquesces  on  exposure  to  the  air,  and  is  dissolved 
readily  by  water  without  residue.  It  is  also  soluble  in  alcohol  and  ether ;  and 
the  latter  withdraws  it  from  the  aqueous  solution.  It  begins  to  lose  chlorine  at 
a  temperature  of  about  400°,  being  changed  into  a  brown  dry  mass,  which  is  a 
mixture  of  the  protocliloride  and  terchloride,  soluble  in  water.  At  about  600° 
the  terchloride  is  completely  resolved  into  the  yellow  insoluble  protochloride, 
which  by  boiling  in  water  is  changed  into  metallic  gold  and  the  soluble  terchlo- 
ride. At  a  red  heat  the  protochloride  loses  its  chlorine  altogether,  and  metallic 
gold  remains.     Its  eq.  is  234*62 ;  st/mb.  Au  -f-  CI,  or  AuCl. 

The  terchloride  of  gold  is  the  usual  and  most  convenient  form  of  obtaining  a 
solution  of  gold  and  examining  its  properties  in  that  state.  On  adding  to  the 
solution  sulphate  of  protoxide  of  iron,  a  brown  precipitate  ensues,  which  is  gold 
in  very  fine  division,  and  the  solution  contains  sesquisulphate  of  peroxide  and 
perchloride  of  iron.    The  action  is  such  that 

6  eq.  Sulphate  of  Protoxide  oflron    ....        6  (FeO,  SO3.) 
and  1  eq.  Terchloride  of  Gold  ...  Au  CI3. 

yield 

2  eq.  Sesquisulphate  of  Peroxide  oflron        ....        ScFegOa,  3SO3.) 
1  eq.  Perchloride  oflron,  FegCla,  and  1  eq.  of  Gold  .  Au. 

The  precipitate  when  duly  washed  with  dilute  hydrochloric  acid,  in  order  to  sejy^- 
rate  adhering  iron,  is  gold  in  a  state  of  perfect  purity.  A  similar  reduction  is  effected 
by  most  of  the  metals,  and  by  sulphurous  and  phosphorous  acids,  and  by  oxalic 
acid  with  escape  of  carbonic  acid  gas.  W^hen  a  piece  of  charcoal  is  immersed  in 
a  solution  of  gold,  and  exposed  to  the  direct  solar  rays,  its  surface  acquires  a  coat- 


GOLD.  4f§ 

ing  of  metallic  gold ;  and  ribands  may  be  gilded  by  moistening  them  with  a  diKite 
solution  of  gold,  and  exposing  them  to  a  current  of  hydrogen  or  phosphuretted 
hydrogen  gas.  When  a  strong  aqueous  solution  of  gold  is  shaken  in  a  phial  with 
an  equal  volume  of  pure  ether,  two  fluids  result,  the  lighter  of  which  is  an  ethe- 
real solution  of  gold.  From  this  liquid  flakes  of  metal  are  deposited  on  stand- 
ing, especially  by  exposure  to  light,  and  substances  moistened  with  it  receive  a 
coating  of  metallic  gold.*  The  reduction  in  most  of  these  instances  is  owing  to 
the  chlorine  quitting  the  gold  in  obedience  to  some  stronger  attraction  :  metals 
deprive  it  directly  of  its  chlorine ;  and  deoxidizing  agents  do  so  indirectly  by 
combining  with  the  oxygen  of  water,  while  its  hydrogen  acts  on  the  chlorine. 

When  protochloride  of  tin  is  added  to  a  dilute  aqueous  solution  of  gold,  a  pur- 
ple-coloured precipitate,  called  the  purple  of  Cassius,  is  thrown  down ;  and  the 
same  substance  may  be  prepared  by  fusing  together  150  parts  of  silver,  20  of  gold, 
and  35*  1  of  tin,  and  acting  on  the  alloy  with  nitric  acid,  which  dissolves  out  the 
silver  and  leaves  a  purple  residue,  containing  the  tin  and  gold  which  were  em- 
ployed. To  prevent  the  oxidation  of  the  tin  during  fusion,  the  three  metals  should 
be  projected  into  a  red-hot  black-lead  crucible,  which  contains  a  little  melted 
borax.  When  the  powder  of  Cassius  is  fused  with  vitreous  substances,  such  as 
flint-glass,  or  a  mixture  of  sand  and  borax,  it  forms  with  them  a  purple  enamel, 
which  is  employed  in  giving  pink  colours  to  porcelain.  The  essential  cause  of 
the  colour  is  probably  a  compound  of  the  purple  or  supposed  binoxide  of  gold 
with  earthy  matters,  similar  to  the  enamel  formed  by  glass  and  oxide  of  silver ; 
the  oxide  of  tin  is  not  essential,  since  finely  divided  metallic  gold  alone  will  give 
the  same  tint  of  purple.  Fuchs  has  shown  that  the  purple  of  Cassius  is  best 
prepared  by  means  of  sesquioxide  of  tin  dissolved  in  hydrochloric  acid. 

The  chemical  nature  of  the  purple  of  Cassius  is  very  obscure.  From  its  for- 
mation by  protochloride  of  tin  it  is  inferred  to  contain  peroxide  of  tin  and  gold 
either  in  the  metallic  state  or  oxidized  to  a  degree  inferior  to  the  peroxide.  Ac- 
cording to  Berzelius  its  sole  loss  when  heated  to  redness  is  7'65  per  cent,  of 
water,  and  the  residue  has  a  brick-red  colour,  arising  from  a  mechanical  mixture 
of  metallic  gold  and  peroxide  of  tin,  a  statement  which  is  confirmed  by  Gay- 
Lussac.  (An.  de  Ch.  et  Ph.  xlix.  396.)  The  proportion  of  these  products  cor- 
responds to  5  equivalents  of  peroxide  of  tin,  1  of  gold,  and  6  of  water.  Never- 
theless, the  purple  of  Cassius,  as  is  indicated  both  by  its  colour  and  its  solubi- 
lity in  ammonia,  is  not  a  mechanical  mixture  of  these  ingredients ;  nor  can  it 
well  be  regarded  as  a  chemical  compound  of  gold  and  peroxide  of  tin,  since  no 
definite  compound  of  the  kind  is  known  to  chemists.  The  more  probable  sup- 
position is,  that  it  is  a  hydrated  double  salt,  composed  of  peroxide  of  tin  as  the 
acid,  united  with  protoxide  of  tin  and  binoxide  of  gold  as  bases,  in  such  propor- 
tion that  the  oxygen  of  the  gold  exactly  sufiices  to  convert  the  protoxide  into 
peroxide  of  tin.  A  compound  of  this  nature  is  expressed  by  the  formula  2(SnO, 
SnO J  +  (AuO^,  SnO J  +  6H0. 

Its  eq.  is  305*46 ;  symb.  Au  -|-  3C1,  or  AUCI3. 

Sulphur  et  of  Gold. — On  transmitting  a  current  of  hydrosulphuric  acid  gas 
through  a  solution  of  gold,  a  black  precipitate  is  formed,  which  is  a  sulphuret. 
It  is  resolved  by  a  red  heat  into  gold  and  sulphur. 

Its  eq.  is  247*5 ;  symb.  Au  -\-  3S,  or  AuS^. 

*  With  respect  to  the  revival  of  gold  from  its  solutions,  the  reader  may  consult  an  Essay 
on  combustion,  by  Mrs.  Fulhame,  and  a  paper  by  Count  Rumford,  in  the  Philosophical 
Transactions  for  1798. 


420  PLATINUM. 

The  compounds  of  gold  with  the  other  non-metallic  bodies  have  been  little  ex- 
amined. 

Iodides  of  Gold. — ^These  compounds  have  recently  been  studied  by  Johnston 
(Phil.  Mag.  and  An.  ix.  266.)  The  protiodide  falls  as  a  greenish-yellow  pow- 
der, when  iodide  of  potassium  is  added  in  excess  to  a  solution  of  the  terchloride 
of  gold.  Though  insoluble  in  water,  it  dissolves  in  a  dilute  hot  solution  of  iodide 
of  potassium,  from  which  it  crystallizes  on  cooling  in  golden  yellow  scales  with 
triangular  and  square  faces.  These  crystals  generally  contain  about  12  per  cent, 
of  metallic  gold  mechanically  mixed  with  them.  They  gradually  lose  iodine  at 
common  temperatures,  freely  at  150°,  and  are  almost  wholly  decomposed  at  230°, 

Its  eg.  is  325*5 ;  symb,  Au  +  I,  or  Aul. 

The  teriodide  is  formed  when  terchloride  of  gold  is  added  to  a  solution  of 
iodide  of  potassium.  It  fells  as  a  dark  green  precipitate,  which  is  insoluble  in 
water,  but  is  soluble  in  hydriodic  acid  and  in  solutions  of  the  iodides  of  potas- 
sium and  sodium.  It  is  very  prone  to  decomposition  from  the  easy  loss  of  io- 
dine. It  is  a  haloid  acid,  and  forms  crystallizable  compounds  with  haloid  bases. 
Thus,  on  setting  aside  the  solution  formed  by  digesting  it  in  iodide  of  potassium, 
the  auro-iodide  of  potassium  is  deposited  in  dark  brownish-red,  nearly  black 
needles.  These  crystals  are  anhydrous,  are  more  stable  than  the  teriodide,  and 
may  be  dried  at  100°  without  decomposition.  The  corresponding  salt  of  sodium 
is  deliquescent.     Its  eq,  is  578*1 ;  symb.  Au  -^  31,  or  Aul^. 


SECTION  XXVI. 


PLATINUM. 


Hist. — This  valuable  metal  occurs  only  in  the  metallic  state,  associated  or 
combined  with  various  other  metals,  such  as  copper,  iron,  lead,  titanium,  chro- 
mium, gold,  silver,  palladium,  rhodium,  osmium,  and  iridium.  It  has  hitherto 
been  found  chiefly  in  Brazil,  Peru,  and  other  parts  of  South  America,  in  the  form 
of  rounded  or  flattened  grains  of  a  metallic  lustre  and  white  colour,  mixed  with 
sand  and  other  alluvial  depositions.  The  particles  rarely  occur  so  large  as  a  pea; 
but  they  are  sometimes  larger,  and  a  specimen  brought  from  South  America  by 
Humboldt  was  rather  larger  than  a  pigeon's  egg^  and  weighed  1088*6  grains.  In 
the  year  1826,  however,  Boussingault  discovered  it  in  a  syenitic  rock  in  the  pro- 
vince of  Antioquia  in  South  America,  where  it  occurs  in  veins  associated  with 
gold.  Rich  mines  of  gold  and  platinum  have  also  been  discovered  in  the  Ura- 
lian  Mountains.     (Edinburgh  Journal  of  Science,  v.  323.) 

Prop. — Pure  platinum  has  a  white  colour  very  much  like  silver,  but  of  infe- 
rior lustre.  It  is  the  heaviest  of  known  metals,  its  density  after  forging  being  about 
21*25,  and  21*5  in  the  state  of  wire.  Its  malleability  is  considerable,  though  far  less 
than  that  of  gold  and  silver.  It  may  be  drawn  into  wires,  the  diameter  of  which 
does  not  exceed  the  2000th  part  of  an  inch.    It  is  a  soft  metal,  and  like  iron  ad- 


PLATINUM.  421 

mits  of  being  welded  at  a  high  temperature.  Wollaston*  observed  that  it  is  a 
less  perfect  conductor  of  heat  than  several  other  metals. 

Platinum  undergoes  no  change  from  the  combined  agency  of  air  and  moisture ; 
and  it  may  be  exposed  to  the  strongest  heat  of  a  smith's  forge  without  suffering 
either  oxidation  or  fusion.  On  heating  a  small  wire  of  it  by  means  of  galvanism 
or  the  oxy-hydrogen  blowpipe,  it  is  fused,  and  afterwards  bums  with  the  emis- 
sion of  sparks.  Smithson  Tennant  showed  that  it  is  oxidized  when  ignited  with 
nitre  (Phil.  Trans.  1797) ;  and  a  similar  effect  is  occasioned  by  pure  potassa  and 
lithia.  It  is  not  attacked  by  any  of  the  pure  acids.  Its  solvents  are  chlorine  or 
solutions,  such  as  nitro-hydrochloric  acid,  which  supply  chlorine ;  and  it  is  dis- 
solved with  greater  difficulty  than  gold. 

The  remarkable  property  observed  by  Dobereiner  in  spongy  platinum  of  caus- 
ing the  union  of  oxygen  and  hydrogen  gases,  was  formerly  mentioned ;  a  pro- 
perty which  Dulong  and  Thenard  showed  to  be  also  possessed,  though  in  a  lower 
degree,  by  platinum  in  its  compact  form  of  wire  or  foil,  and  by  several  other 
metals.  (An.  de  Ch.  et  Ph.  xxiii.  and  xxiv.)  Faraday  (Phil.  Trans.  1834,  part 
i.)  has  lately  discussed,  with  his  wonted  ability  and  success,  both  the  conditions 
required  for  the  effective  action  of  platinum,  and  the  cause  of  the  phenomenon. 
The  sole  conditions  are  purity  of  the  gases  and  perfect  cleanliness  of  the  plati- 
num. By  cleanliness  is  meant  perfect  absence  of  foreign  matter,  pure  water 
excepted  ;  and  this  condition  is  easily  secured  by  fusing  pure  potassa  on  its  sur- 
face, washing  off  the  alkali  by  pure  water,  then  dipping  the  platinum  in  hot  oil 
of  vitriol,  and  again  washing  with  water.  In  this  state  platinum  foil  acts  so 
rapidly  at  common  temperatures  on  oxygen  and  hydrogen  gases  mixed  in  the 
ratio  of  1  to  2,  that  it  often  becomes  red  hot  and  kindles  the  mixture.  Handling 
the  platinum,  wiping  it  with  a  towel,  or  exposing  it  to  the  atmosphere  for  a  few 
days,  suffices  to  soil  the  surface  of  the  metal,  and  thereby  diminish  or  prevent  its 
action.  These  phenomena  are  supposed  to  result  from  the  concurring  influence 
of  two  forces,  the  self-repulsive  energy  of  similar  gaseous  particles,  and  the 
adhesive  attraction  exerted  between  them  and  the  platinum.  Each  gas,  repulsive 
to  itself  and  not  repelled  by  the  platinum,  comes  into  the  most  intimate  contact 
with  that  metal,  and  both  gases  are  so  condensed  upon  its  surface  that  they  are 
brought  within  the  sphere  of  their  mutual  attraction  and  combine.  Faraday  has 
given  several  instances,  similar  to  those  which  I  had  occasion  to  describe  some 
years  ago  (Jameson's  Journal,  xi.  99  and  311),  where  the  action  of  platinum  is 
retarded  or  altogether  prevented  by  small  quantities  of  certain  gases,  such  as 
hydrosulphuric  acid,  carbonic  oxide,  and  defiant  gases.  One  would  be  tempted 
to  suppose  that  these  gases  act  by  soiling  the  metallic  surface,  though  in  some 
respects  this  explanation  is  not  satisfactory. 

When  solutions  of  platinum  are  heated  with  various  deoxidizing  agents,  such 
as  formic  acid,  formiates,  alcohol  with 'alkalies,  &c.,  or  when  an  alloy  of  zinc 
and  platinum  is  acted  on  by  nitric  acid,  platinum  is  obtained  as  a  finely  divided 
black  powder,  which  absorbs  oxygen  without  chemically  combining  with  it,  and 
transfers  it  to  combustible  substances,  thus  indirectly  acting  as  a  powerful  oxi- 

*  The  reader  will  find,  in  the  Philosophical  Transactions  for  1829,  some  important  direc- 
tions by  Dr.  Wollaston,  both  as  to  the  mode  of  extracting  platinum  from  its  ores,  and  of 
communicating  to  the  pure  metal  its  highest  degree  of  malleability.  The  essay  receives 
additional  interest  from  being  one  of  those  which  were  composed  during  the  last  illness  of 
this  truly  illustrious  philosopher. 


422  PLATINUM. 

dizing  agent.  In  this  way  alcohol  and  pyroxylic  spirit  may  be  converted  into 
acetic  and  formic  acids,  sulphurous  acid  into  sulphuric  acid,  &c.  (Dobereiner.) 
The  eq.  of  platinum,  deduced  by  Berzelius  from  the  analysis  of  the  bichloride, 
is  98*8 ;  its  symb.  is  Pt.  The  composition  of  its  compounds  described  in  this 
section  is  as  follows  : — 


Platinum. 

Equiv. 

Formulae. 

Protoxide 

98-8 

1  eq.  +  Oxygen 

8 

1  eq.  =  106-8 

Pt  +  O      orPtO. 

Binoxide 

98-8 

leq.+    .    . 

16 

2  eq.  =  114-8 

Pt  +  20    orPtOa. 

Sesquioxide  7 

197-6 

2eq.+    .    . 

24 

3eq.  =  221-6 

2PtH-30    orPtjOs. 

Protochloride 

98-8 

1  eq.  + Chlorine 

35-42 

1  eq.  =  134-22 

Pt  +  CI     or  PtCl. 

Bichloride 

98-8 

leq.+    .     . 

70-84 

2  eq.  =  169-64 

Pt  +  2C1  orPtCR 

Protiodide 

98-8 

1  eq.  +  Iodine 

126-3 

1  eq.  =  225-1 

Pt  + 1      or  PtI. 

Biniodide 

98-8 

leq.-f    .     . 

252-6 

2  eq.  =  351-4 

Pt  +  2I     orPtlj. 

Protosulphuret  98-8     1  eq. -+- Sulphur  16-1        leq.==  114-9        Pt  +  S      or  PtS. 

Bisulphuret       98-8     1  eq.-J-    .    .  32-2        2eq.=  1310        Pt4-2S    or  PtS2. 

Protoxide  of  Platinum. — ^This  oxide  is  prepared  by  digesting  protochloride  of 
platinum  in  a  solution  of  pure  potassa,  avoiding  a  large  excess  of  the  alkali, 
since  it  dissolves  a  portion  of  the  oxide  and  thereby  acquires  a  green  colour.  In 
this  state  it  is  a  hydrate  which  loses  first  its  water  and  then  oxygen  when  heated, 
and  dissolves  slowly  in  acids,  yielding  solutions  of  a  brownish-green  tint. 

Its  eq.  is  106-8 ;  si/mb.  Pt  +  CI,  Pt,  or  PtO. 

Binoxide. — ^This  oxide  is  prepared  with  difiiculty,  owing  to  its  disposition, 
like  peroxide  of  gold,  to  act  rather  as  an  acid  than  an  alkaline  base,  and  either 
to  fall  in  combination  with  any  alkali  by  which  it  is  precipitated,  or  to  remain 
with  it  altogether  in  solution.  Berzelius  recommends  that  it  should  be  prepared 
by  exactly  decomposing  sulphate  of  binoxide  of  platinum  with  nitrate  of  baryta, 
and  adding  pure  soda  to  the  filtered  solution,  so  as  to  precipitate  about  half  of 
the  oxide ;  since  otherwise,  a  sub-salt  would  subside.  The  oxide  falls  in  the 
form  of  a  bulky  hydrate,  of  a  yellowish-brown  colour  :  it  resembles  rust  of  iron 
when  dry,  and  is  nearly  black  when  rendered  anhydrous. 

Its  eq.  is  114-8;  symb.  Pt  +  20,  Pt,  or  PtO^. 

Sesquioxide. — ^This  oxide,  of  a  grey  colour,  is  prepared,  according  to  its  dis- 
coverer, Mr.  E.  Davy,  by  heating  fulminating  platinum  with  nitrous  acid  ;  but  the 
nature  of  the  compound  so  formed  has  not  yet  been  decisively  determined.  (Phil. 
Trans.  1820.) 

Protochloride. — When  the  bichloride  is  heated  to  450°,  half  of  its  chlorine  is 
expelled,  and  the  protochloride  of  a  greenish-grey  colour  remains.  It  is  insolu- 
ble in  water,  sulphuric  acid,  and  nitric  acid ;  but  hydrochloric  acid  partially  dis- 
solves it,  yielding  a  red  solution.  At  a  red  heat  its  chlorine  is  driven  off,  and 
metallic  platinum  is  left.    It  is  dissolved  by  a  solution  of  the  bichloride. 

Its  eq.  is  134-22 ;  symb.  Pt  -f-  CI,  or  PtCl. 

Bichloride  (f  Platinum. — ^This  chloride  is  obtained  by  evaporating  the  solution 
of  platinum  in  nitro-hydrochloric  acid  to  dryness  at  a  very  gentle  heat,  when  it 
remains  as  a  red  hydrate,  which  becomes  brown  when  its  water  is  expelled.  It 
is  deliquescent,  and  very  soluble  in  water,  alcohol,  and  ether ;  its  solution,  if  free 
from  the  chlorides  of  palladium  and  iridium,  being  of  a  pure  yellow  colour.  Its 
ethereal  solution  is  decomposed  by  light,  metallic  platinum  being  deposited. 


PLATINUM.  423 

A  solution  of  platinum  is  recognized  by  the  following  characters.  When  to 
an  alcoholic  or  concentrated  aqueous  solution  of  the  bichloride  a  solution  of 
chloride  of  potassium  is  added,  a  crystalline  double  chloride  of  a  pale  yellow 
colour  subsides,  which  is  insoluble  in  alcohol,  and  sparingly  soluble  in  water  ; 
at  a  red  heat  it  yields  chlorine  gas,  and  the  residue  consists  of  metallic  platinum 
and  chloride  of  potassium.  With  a  solution  of  hydrochlorate  of  ammonia  a 
similar  yellow  salt  falls,  which  when  ignited  leaves  pure  platinum  in  the  form  of 
a  delicate  spongy  mass,  the  power  of  which  in  kindling  an  explosive  mixture  of 
oxygen  and  hydrogen  gases  has  already  been  mentioned. 

lis  eq.  is  169-64;  symb.  Pt  +  2C1,  or  PtCl^. 

Protiodide  of  Platinum. — Lassaigne  prepared  this  compound  by  digesting  the 
protochloride  of  platinum  in  a  rather  strong  solution  of  iodide  of  potassium,^ 
when  the  protiodide  gradually  appeared  in  the  form  of  a  black  powder,  which  is 
insoluble  in  water  and  alcohol.  It  is  unchanged  by  the  sulphuric,  nitric,  and 
hydrochloric  acids,  decomposed  by  the  alkalies,  and  at  a  red  heat  gives  off  its 
iodine.     Its  eq.  is  225*1 ;  symh.  Pt  -f- 1,  or  PtI. 

Periodide  of  Platinum. — Lassaigne  prepares  this  compound  by  the  action  of 
iodide  of  potassium  on  a  rather  dilute  solution  of  bichloride  of  platinum.  At 
first  the  liquid  acquires  an  orange-red  and  then  a  claret  colour,  without  any  pre- 
cipitation ;  but  when  the  solution  is  boiled  a  black  precipitate  subsides,  which 
should  be  washed  with  hot  water  and  dried  ai'  a  heat  not  exceeding  212°.  This 
biniodide  is  a  black  powder,  sometimes  crystalline,  is  tasteless  and  inodorous, 
insoluble  in  water,  and  may  be  boiled  in  water  without  change.  By  alcohol  it  is 
sparingly  dissolved,  especially  when  heated.  Acids  act  feebly  upon  it ;  but  it  is 
decomposed  by  alkalies,  and  begins  to  lose  iodine  at  270°.  (An.  de  Ch.  et  Ph. 
li.  113.)     Its  eq.  is  351-4  ;  symh.  Pt  -+-  21,  or  Ptl^. 

Protosulphuret  of  Platinum. — It  is  formed  by  heating  in  a  retort  the  yellow 
ammoniacal  chloride  of  platinum  with  half  its  weight  of  sulphur  until  all  the 
sal-ammoniac  and  excess  of  sulphur  is  expelled.  The  protosulphuret  is  then 
left  as  a  grey  powder  of  a  metallic  lustre.  It  may  also  be  formed  by  the  action 
of  hydrosulphuric  acid  on  protochloride  of  platinum. 

Its  eq.is  114-9  ;  symh.  Pt  -\-  S,  or  PtS.  f£« 

Bisulphuret. — It  is  formed  as  a  brown  precipitate,  which  becomes  black  when 
dried,  by  letting  fall  a  solution  of  bichloride  of  platinum  drop  by  drop  into  a 
solution  of  sulphuret  of  potassium,  or  by  transmitting  hydrosulphuric  acid  gas 
into  a  solution  of  the  double  chloride  of  platinum  and  sodium.  (Berzelius.)  It 
should  be  dried  in  vacuo  by  aid  of  sulphuric  acid,  since  by  exposure  to  the  air  in 
a  moist  state  sulphuric  acid  is  generated. 

Its  eq.  is  130;  symh.  Pt  -|-  2S,  or  PtS^. 

Fulminating  platinum  may  be  prepared  by  the  action  of  ammonia  in  slight 
excess  on  a  solution  of  sulphate  of  oxide  of  platinum.  (E.  Davy.)  It  is  analo- 
gous to  the  detonating  compounds  which  ammonia  forms  with  the  oxides  of  gold 
and  silver. 


424  PALLADIUM. 


SECTION   XXVII. 


PALLADIUM.— RHODIUM.— OSMIUM.— IRIDIUM. 

The  four  metals  to  be  described  in  this  section  are  all  contained  in  the  ore  of 
platinum,  and  have  hitherto  been  procured  in  very  small  quantity.  When  the 
ore  is  digested  in  nitro-hydrochloric  acid,  the  platinum,  together  with  palladium, 
rhodium,  iron,  copper,  and  lead,  is  dissolved ;  while  a  black  powder  is  left  con- 
sisting of  osmium  and  iridium,  mixed  in  general  with  a  considerable  quantity 
of  titanate  of  iron,  and  siliceous  minerals. 

PALLADIUM. 

Hist,  and  Prep, — Discovered  in  1803,  by  Wollaston  (Phil.  Trans.  1804  and 
1805).  On  adding  bicyanuret  of  mercury  dissolved  in  water  to  a  neutral  solu- 
tion of  the  ore  of  platinum,  either  before  or  after  the  separation  of  that  metal  by 
hydrochlorate  of  ammonia,  a  yellowish-white  flocculent  precipitate  is  gradually 
deposited,  which  is  cyanuret  of  palladium.  When  this  compound  is  heated  to 
redness,  the  cyanogen  is  expelled,  and  pure  palladium  remains.  In  order  to 
obtain  it  in  a  malleable  state,  the  metal  should  be  heated  with  sulphur,  and  the 
resulting  sulphuret  purified  by  cupellation  in  an  open  crucible  with  borax  and  a 
little  nitre.  It  is  then  roasted  at  a  low  red  heat  on  a  flat  brick,  and  when  reduced 
to  a  pasty  consistence,  it  is  pressed  into  a  square  or  oblong  perfectly  flat  cake. 
It  is  again  to  be  roasted  very  patiently,  at  a  low  red  heat,  until  it  becomes 
spongy  on  the  surface ;  and  when  quite  cold,  it  is  condensed  by  frequent  tap- 
pings with  a  light  hammer.  By  alternate  roastings  and  tappings  the  sulphur  is 
hurned  off,  and  the  metal  rendered  sufficiently  dense  to  be  laminated.  Thus  pre- 
pared it  is  rather  brittle  while  hot,  which  Wollaston  supposed  to  arise  from  a 
small  remnant  of  sulphur.     (Phil.  Trans.  1829,  p.  7.) 

Prop. — It  resembles  platinum  in  colour  and  lustre.  It  is  ductile  as  well  as 
malleable,  and  is  considerably  harder  than  platinum.  Its  sp.  gr.  varies  from 
11*3  to  11'8.  In  fusibility  it  is  intermediate  between  gold  and  platinum,  and  is 
dissipated  in  sparks  when  intensely  heated  by  the  oxy-hydrogen  blowpipe.  At 
a  red  heat  in  oxygen  gas  its  surface  acquires  a  fine  blue  colour,  owing  to  super- 
ficial oxidation  ;  but  the  increase  of  weight  is  so  slight  as  not  to  be  appreciated. 
It  is  oxidized  and  dissolved  by  nitric  acid,  and  even  the  sulphuric  and  hydro- 
chloric acids  act  upon  it  by  the  aid  of  heat;  but  its  proper  solvent  is  nitro-hydro- 
chloric acid.  Its  oxide  forms  beautiful  red-coloured  salts,  from  which  metallic 
palladium  is  precipitated  by  sulphate  of  protoxide  of  iron,  and  by  all  the  metals 
described  in  the  foregoing  sections,  excepting  silver,  gold,  and  platinum. 

From  the  analysis  by  Berzelius  of  the  double  chloride  of  palladium  and 
potassium  the  eq.  of  palladium  is  inferred  to  be  53-3.  Its  symb.  is  Pd.  The 
composition  of  its  compounds  described  in  this  section  is  as  follows  :  — 


# 

RHODIUM. 

i 

Palladium. 

Equiv. 

Formulae 

Protoxide 

53-3     1  eq.+Oxygen 

8             1  eq.=  61-3 

Pd+O  or  PdO. 

Binoxide 

53-3     leq.4-do. 

16            2  eq.=  69-3 

Pd-l-20  or  PdOa. 

Protochloride 

53-3     1  eq.+Chlorine 

35-42       1  eq.=  88-72 

Pd+Cl  or  PdCl. 

Bichloride 

53-3     1  eq.+do. 

70-84       2  eq.=124-14 

Pd+2Cl'or  PdCl2. 

425 


Protosulphuret   53*3     1  eq.+Sulphur         16- 


1  eq.=  69-4        Pd+S  or  PdS. 


Protoxide  of  Palladium. — ^This  oxide  is  obtained  as  a  hydrate  of  a  deep  brown 
colour  by  decomposing  its  salts  with  an  excess  of  carbonate  of  potassa  or  soda ; 
and,  by  washing  and  heating  to  low  redness,  the  anhydrous  protoxide  of  a  black 
colour  is  left.  It  is  also  obtained  by  heating  the  nitrate  at  a  low  red  heat.  In 
the  anhydrous  state  it  is  dissolved  with  difficulty  by  acids.  When  strongly 
heated  it  parts  with  its  oxygen.  Berzelius  says  it  falls  from  its  salts  on  the 
addition  of  the  alkalies  as  a  sub-salt,  which  is  dissolved  by  the  alkali  in  excess. 

Its  eq.  is  61-3 ;  symb.  Pd  f  0,  Pd,  or  PdO. 

Binoxide. — To  prepare  this  oxide  Berzelius  recommends  that  a  solution  of 
potassa  or  its  carbonate  in  excess  should  be  poured  by  little  and  little  on  the 
solid  bichloride  of  palladium  and  potassium,  and  the  materials  be  well  inter- 
mixed :  water  is  not  first  added,  because  it  decomposes  the  double  chloride  ;  and 
the  alkali  is  not  added  all  at  once,  because  the  binoxide  would  then  be  dissolved 
at  first,  and  afterwards  separate  out  as  a  gelatinous  hydrate,  which  could  not  be 
purified  by  washing.  When  prepared  with  the  foregoing  directions,  the  binoxide 
is  obtained  as  a  hydrate  of  a  deep  yellowish-brown  colour,  which  retains  a  little 
potassa  in  combination;  but  on  heating  the  solution  to  212°  the  alkali  is  dis- 
solved, and  the  anhydrous  black  oxide  left. 

Its  eq.  is  69-3 ;  symb.  Pd  -f-  20,  Pd,  or  PdO^. 

Protochloride  of  Palladium. — It  is  obtained  by  evaporating  to  dryness  a  solu- 
tion of  palladium  in  nitro-hydrochloric  acid,  being  left  as  a  brown  crystalline 
hydrate,  which  becomes  black  when  its  water  is  expelled.  It  loses  its  chlorine 
when  strongly  heated,  and  is  soluble  in  water.  Its  eq.  is  88*72 ;  symb.  Pd  -f- 
Cl,  or  PdCl. 

The  bichloride  is  formed  by  digesting  the  protochloride  in  nitro-hydrochloric 
acid,  and  exists  only  in  solution,  the  colour  of  which  is  of  so  deep  a  brown  as 
to  appear  nearly  black.  It  is  readily  distinguished  from  the  protochloride  by 
yielding  with  chloride  of  potassium  a  double  chloride  of  a  red  colour;  whereas 
that  formed  with  the  protochloride  is  yellow. 

Its  eq.  is  124-14;  symb.  Pd  +  2C1,  or  PdClg. 

Protosulphuret  of  Palladium. — It  is  readily  formed  by  heating  the  metal  with 
sulphur,  and  is  a  fusible  brittle  compound  of  a  grey  colour.  Its  eq.  is  69*4 ;  synA, 
Pd  -t-  S,  or  PdS. 

RHODIUM. 


Hist,  and  Prep. — ^This  metal  was  discovered  by  Wollaston  at  the  time  he  was 
occupied  with  the  discovery  of  palladium.  On  immersing  a  thin  plate  of  clean 
iron  into  the  solution  from  which  palladium  and  the  greater  part  of  the  platinum 
have  been  precipitated,  the  rhodium,  together  with  small  quantities  of  platinum, 
copper,  and  lead,  is  thrown  down  in  the  metallic  state;  and  on  digesting  the 
precipitate  in  dilute  nitric  acid,  the  two  last  metals  are  removed.  The  rhodium 
and  platinum  are  then  dissolved  by  means  of  nitro-hydrochloric  acid,  and  the 


426  RHODIUM. 

solution,  after  being  mixed  with  some  chloride  of  sodium,  is  evaporated  to  dry- 
ness. Two  double  chlorides  result,  that  of  platinum  and  sodium,  and  of  rhodium 
and  sodium,  the  former  of  which  is  soluble,  and  the  latter  insoluble  in  alcohol ; 
and  they  may  therefore  be  separated  from  each  other  by  this  menstruum.  The 
double  chloride  of  rhodium  is  then  dissolved  in  water,  and  metallic  rhodium 
precipitated  by  insertion  of  a  rod  of  zinc. 

Prop, — Thus  procured,  it  is  in  the  form  of  a  black  powder,  which  requires 
the  strongest  heat  that  can  be  produced  in  a  wind  furnace  for  fusion,  and  when 
fused  has  a  white  colour  and  metallic  lustre.  It  is  brittle,  is  extremely  hard, 
and  has  a  sp.  gr.  of  about  11.  It  attracts  oxygen  at  a  red  heat,  a  mixture  of 
peroxide  and  protoxide  being  formed.  It  is  not  attacked  by  any  of  the  acids 
when  in  its  pure  state  ;  but  if  alloyed  with  other  metals,  such  as  copper  or  lead, 
it  is  dissolved  by  nitro-hydrochloric  acid,  a  circumstance  which  accounts  for  its 
presence  in  the  solution  of  crude  platinum.  It  is  oxidized  by  being  ignited 
either  with  nitre,  or  bisulphate  of  potash.  When  heated  with  the  latter,  sul- 
phurous acid  gas  is  evolved,  and  a  double  sulphate  of  peroxide  of  rhodium  and 
potash  is  generated,  which  dissolves  readily  in  hot  water,  and  yields  a  yellow 
solution.  The  presence  of  rhodium  in  platinum,  iridium,  and  osmium  may  thus 
be  detected,  and  by  repeated  fusion  a  perfect  separation  be  accomplished.  (Ber- 
zelius.) 

Chemists  are  acquainted  with  two  oxides  of  rhodium.  The  protoxide  is  black, 
and  the  peroxide,  which  is  the  base  of  the  salts  of  rhodium,  is  of  a  yellow 
colour.     Most  of  its  salts  are  either  red  or  yellow. 

From  the  composition  of  the  double  chloride  of  rhodium  and  potassium  Berze- 
lius  considers  52*2  as  the  eq.  of  rhodium  ;  its  symh,  is  R,  and  its  compounds 
described  in  this  section  are  thus  constituted  : — 


Rhodium. 

Equiv. 

Formulae. 

Protoxide 

62-2    1  eq.-f- Oxygen               8 

1  eq.=  60-2 

R-j-G  or  RO. 

Peroxide 

104-4    2eq.4do.                    24 

3  eq.5=128-4 

2Rt30orR203. 

Protochloride 

52-2     1  eq.tChlorine        3542 

1  eq.=  87-62 

RfCl  or  RCl. 

Perchloride 

104-4    2eq.-f-do.              106-26 

3  eq.=210-66 

2R+3C1  or  R2CI3. 

Sulphuret 

Probably  a  protosulphuret. 

Oxides  of  Rhodium. — The  first  grade  of  oxidation  has  not  yet  been  insulated. 
The  peroxide  is  generated  when  pulverulent  rhodium  is  heated  to  redness  in  a 
silver  crucible  mixed  with  hydrate  of  potassa  and  a  little  nitre,  when  the  rho- 
dium is  oxidized  and  acquires  a  coffee-brown  colour.  To  remove  the  potassa 
united  with  the  peroxide,  the  mass  is  first  washed  with  water  and  then  digested 
in  hydrochloric  acid,  when  it  acquires  a  greenish-grey  colour,  and  is  left  as  a 
pure  hydrate  of  the  peroxide.  In  this  state  ii  is  insoluble  in  acids.  If  an  ex- 
cess of  carbonate  of  potassa  or  soda  is  added  to  the  double  chloride  of  rhodium 
and  potassium,  and  the  solution  is  evaporated,  a  gelatinous  hydrate  falls ;  but 
on  attempting  to  dissolve  in  acid  the  potassa  combined  with  the  peroxide,  the 
latter  is  also  dissolved. 

Its  eq.  is  128-4  ;  symh.  2R  +  30,  R,  or  Hp^. 

Chlorides  of  Rhodium. — The  only  chloride  which  has  yet  been  insulated  is  the 
perchloride,  which  Berzelius  obtained  by  adding  to  a  solution  of  the  double 
chloride  of  rhodium  and  potassium  silico-hydrofluoric  acid  as  long  as  the  double 
fluoride  of  potassium  and  silicon  was  generated,  after  which  the  filtered  liquid 


IRIDIUM  AND  OSMIUM.  427 

was  evaporated  to  dryness,  and  redissolved  in  water.  This  perchloride  when 
dry  has  a  dark  brown  colour,  is  uncrystalline,  and  decomposed  by  a  full  red  heat 
into  chlorine  and  metallic  rhodium.  It  deliquesces  in  the  air  into  a  brown 
liquid,  and  its  aqueous  solution  has  a  fine  red  colour,  whence  its  name  of  rho- 
dium (from  |jo5ov,  a  rose)  is  derived.     (An.  de  Ch.  et  Ph.  xl.  51.) 

Its  eq.  is  210-66 ;  st/mb.  2R  +  3 CI,  or  R^Clg. 

Sulphur  et  of  Rhodium. — It  may  be  formed  by  heating  rhodium  directly  with 
sulphur,  fuses  at  a  white  heat  without  decomposition,  and  has  a  bluish-grey 
colour,  with  a  metallic  lustre.  Wollaston  made  use  of  it  for  procuring  the  metal 
in  a  coherent  state,  in  the  same  manner  as  sulphuret  of  palladium. 

IRIDIUM  AND  OSMIUM. 

Hist. — These  metals  were  discovered  by  the  late  Mr.  Tennant  in  the  year  1803 
(Phil.  Trans.  1804),  and  the  discovery  of  iridium  was  made  about  the  same  time 
by  Descotils  in  France.  The  black  powder  mentioned  at  the  beginning  of  this 
section  is  a  compound  of  iridium  and  osmium,  an  alloy  which  Wollaston  detected 
in  the  form  of  flat  white  grains  among  fragments  of  crude  platinum.  This  alloy, 
which  is  quite  insoluble  in  nitro-hydrochloric  acid,  is  the  source  from  which 
iridium  and  osmium  are  extracted. 

Osmium  and  Iridium. — Prep. — These  metals  are  obtained  from  the  pulveru- 
lent residue  of  the  ores  of  platinum,  after  that  metal  together  with  palladium  and 
rhodium  have  been  removed  by  digestion  in  nitro-hydrochloric  acid.  Wollaston 
has  recommended  the  following  process  (Phil.  Trans.  1829,  p.  8).  The  residue 
is  ground  into  a  fine  powder  with  a  third  of  its  weight  of  nitre,  and  the  mixture 
heated  to  redness  in  a  silver  crucible  until  it  is  reduced  to  a  pasty  state,  when 
the  characteristic  odour  of  oxide  of  osmium  will  be  perceptible.  Dissolve  the 
soluble  parts,  which  contain  oxide  of  osmium  in  combination  with  potassa,  in 
the  smallest  possible  quantity  of  water,  and  acidulate  the  solution,  introduced 
into  a  retort,  with  sulphuric  acid  diluted  with  its  own  weight  of  water.  By  dis- 
tilling rapidly  into  a  clean  receiver  as  long  as  osmic  fumes  pass  over,  the  acid 
will  be  collected  on  its  sides  in  the  form  of  a  white  crust ;  and,  there  melting, 
it  will  run  down  in  drops  beneath  the  watery  solution,  forming  a  fluid  flattened 
globule  at  the  bottom.  As  the  receiver  cools,  the  acid  becomes  solid  and  crys- 
tallizes. Osmium  is  precipitated  from  the  solution  of  its  acid  by  all  the  metals, 
excepting  gold  and  silver.  A  convenient  mode  of  reduction  is  to  agitate  it  with 
mercury,  adding  hydrochloric  acid  to  decompose  the  protoxide  of  mercury  which 
is  formed,  and  then  expelling  the  mercury  and  calomel  by  heat.  The  osmium  is 
left  as  a  black  porous  powder  which  acquires  metallic  lustre  by  friction. 

The  insoluble  parts  contain  the  iridium  as  oxide  in  combination  with  potassa. 
On  digesting  the  mass  in  hydrochloric  acid,  a  blue  solution  is  obtained  ;  but  it 
afterwards  becomes  of  an  olive-green  hue,  and  subsequently  acquires  a  deep-red 
tint.  This  variety  of  colour,  which  suggested  the  name  of  iridium  (Iris,  the 
rainbow),  is  owing  to  the  successive  production  of  different  compounds.  The 
iridium  may  be  precipitated  from  the  solution  by  any  metal  except  gold  and  pla- 
tinum, or  it  may  be  obtained  by  exposing  the  chloride  to  a  red  heat.  Wohler 
has  proposed  a  very  elegant  process  by  which  both  metals  may  be  obtained  on  a 
large  scale  (Pog.  An.  xxi.  161).  The  great  advantage  of  his  method  is,  that  it 
leaves  the  titanate  of  iron  and  other  foreign  minerals  undecomposed.  He  mixes 
the  residue  with  an  equal  weight  of  fused  sea-salt  in  fine  powder.    The  mixture 


428  OSMIUM,    iim 

is  introduced  into  a  long  and  wide  green  glass  tube,  which  is  connected  at  one 
extremity  with  an  apparatus  for  developing  chlorine,  at  the  other  with  a  tubulated 
receiver.  The  latter  is  furnished  with  a  small  tube,  the  extremity  of  which  is 
made  to  dip  into  a  weak  solution  of  ammonia.  The  tube  containing  the  mixture 
of  salt  and  ore  being  then  brought  to  a  low  red  heat,  the  chlorine  is  developed 
and  the  gas  transmitted  in  a  moderate  stream  through  the  glowing  mass,  by 
which  in  the  first  part  of  the  process  it  is  abundantly  and  completely  absorbed. 
The  operation  is  to  be  continued  until  the  chlorine  is  observed  to  pass  pretty 
freely  into  the  solution  of  ammonia.  The  changes  which  occur  are  owing  to  the 
formation  of  two  haloid  acids,  by  the  combination  of  the  chlorine  with  both 
metals  of  the  ore ;  and  as  these  instantly  combine  with  the  chloride  of  sodium, 
two  soluble  salts,  the  iridio-chloride  of  sodium,  and  the  osmio-chloride  of  sodium, 
are  produced.  But  by  the  moisture  of  tlie  chlorine  gas  the  latter  compound  is 
decomposed,  the  chloride  of  osmium  giving  rise  to  the  formation  of  osmic  and 
hydrochloric  acids,  and  the  deposition  of  a  part  of  the  osmium  in  the  metallic 
state.  This  by  again  combining  with  chlorine  gives  rise  to  a  repetition  of  the 
same  changes,  and  to  the  production  of  an  additional  quantity  of  osmic  acid, 
which,  being  volatile,  passes  on  and  is  deposited  in  crystals  in  the  receiver. 
The  solution  of  ammonia  prevents  the  loss  of  any  acid  which  might  escape  con- 
densation. The  solid  matter  in  the  tube  is  then  digested  in  water,  when  a  deep 
brown  solution  is  obtained,  and  the  clear  liquid  is  separated  by  decantation  from 
the  insoluble  parts,  which  consists  principally  of  titanate  of  iron.  As  the  solu- 
tion still  contains  some  osmic  acid,  it  is  submitted  to  a  distillation  until  one-half 
has  passed  over  into  a  weak  solution  of  ammonia.  The  remainder  is  then  eva- 
porated in  an  open  dish,  while  carbonate  of  soda  is  at  the  same  time  added  in 
successive  portions  until  a  considerable  excess  is  present.  On  evaporating  to 
dryness  a  black  mass  is  obtained,  which  is  to  be  exposed  to  a  low  red  heat  in  a 
hessian  crucible.  When  cold,  the  saline  matter  is  removed  by  boiling  water, 
and  the  sesquioxide  of  iridium  is  left  in  the  form  of  a  black  powder.  It  is  readily 
reduced  to  the  metallic  state  by  a  stream  of  hydrogen  gas. 

Osmium. — As  obtained  by  precipitation  it  is  a  black  porous  powder,  which 
acquires  a  metallic  lustre  by  friction.  After  exposure  to  a  very  gentle  heat,  its 
sp.  gr.  is  7.  It  takes  fire  when  heated  in  the  open  air,  and  is  readily  oxidized 
and  dissolved  by  fuming  nitric  acid  :  but  a  red  heat  gives  it  greater  compactness, 
and  in  that  state  it  ceases  to  be  attacked  by  acids,  and  may  be  freely  heated 
without  oxidation.  In  its  densest  state  Berzelius  found  its  sp.  gr.  to  be  10.  (An. 
de  Ch.  et  Ph.  xl.  257,  andixlii.  185.)     Its  symb.  is  Os. 

Berzelius,  from  his  late  researches  on  the  compounds  of  osmium,  considers 
99'7  to  be  its  eq.,  and  gives  the  composition  of  its  oxides,  chlorides,  and  sul- 
phurets,  as  follows; — 

Osmium.  Equiv.  Formulae. 

Protoxide           99-7  1  eq.-J-Oxygen  8  1  eq.=:107-7      Os+O  or  OsO. 

Sesquioxide      199-4  2  eq.-+-do-  24  3  eq.=223-4    208+30  or  O82O3. 

Binoxide             997  1  eq.-|-do.  16  2  eq.=115-7      08+20  or  OsOj. 

Teroxide            99-7  1  eq.-+-do.  24  3  eq.=123-7      Os+30  or  OsOj. 

Osmic  Acid        99-7  1  eq.+do.  32'  4  eq.=131-7      Os+40  or  Os04. 

Protochloride     99-7  1  eq.+Chlorine   35-42  1  eq.==13512    Os+Cl  or  OsCl. 

Scsquichlor.      199-4  2  eq.+do.  106-26  3  eq.=205-66  20s+3CI  or  OS2CI3. 

Bichloride          99-7  1  eq.+do.  70-84  2  eq.=170-54    Os+2Cl  or  OsClj. 

Terchloride       997  1  eq.-|-do.  106-26  3  eq.=205-96    08+3C1  or  OsCJj. 


IRIDIUM.  '  429 

Osmium.  Equiv.  Formulae. 

Protosulphuret  99-7     1  eq.+Sulphur  16-1  1  eq.=115-8      Os-f-S  or  Os  or  OsS.' 

Sesquisulph.     199-4    2  eq-H-do.  48-3  3  eq.=247-7    203+38  or  Os^Sg. 

Bisulphuret        99-7     1  eq.+do.  32-2  2  eq.=131-9      Os+2S  or  OsSg. 

Tersulphuret     99-7    1  eq.+do.  48-3  3  eq.=148-0      Os+3S  or  OsSg. 

Oxides  of  Osmium. — For  a  minute  description  of  these  compounds  I  refer  to 
the  essays  of  Berzelius  above  cited.  The  protoxide  is  precipitated  by  pure  alka- 
lies from  the  protochloride,  and  falls  as  a  deep  green,  nearly  black,  hydrate, 
which  is  soluble  in  acids,  and  detonates  when  heated  with  combustible  matter. 
The  binoxide  is  thrown  down  as  a  hydrate  of  a  deep  brown  colour,  when  a  satu- 
rated solution  of  the  bichloride  is  heated  with  carbonate  of  soda.  It  retains  a 
little  alkali  in  combination ;  but  the  soda  is  easily  removed  by  dilute  hydrochlo- 
ric acid,  without  the  oxide  being  dissolved.  The  teroxide  is  prepared  in  like 
manner  from  the  terchloride.  [This,  according  to  MM.  Fremy  and  Claus,  com- 
bines with  potassa,  forming  a  very  beautiful  salt,  which  crystallizes  in  regular 
octohedrons  having  a  black,  garnet,  or  rose-red  colour,  according  to  the  quick- 
ness of  their  formation.  They  therefore  rank  this  oxide  with  the  metallic  acids, 
under  the  name  of  osmious  acid.]  The  sesquioxide  has  not  been  obtained  in  a 
separate  state  ;  but  it  is  procured  in  combination  with  ammonia  when  the  binox- 
ide is  treated  with  a  large  excess  of  pure  ammonia,  nitrogen  gas  being  disen- 
gaged at  the  same  time. 

The  highest  stage  of  oxidation  is  the  volatile  acid,  which  is  the  product  of  the 
oxidation  of  osmium  by  acids,  by  combustion,  or  by  fusion  with  nitre  or  alkalies; 
and  it  may  be  procured  by  the  process  above  mentioned  in  colourless  transparent 
elongated  crystals,  or  as  a  colourless  solution  in  water.  Its  vapour  is  very  acrid, 
exciting  cough,  irritating  the  eyes,  and  producing  a  copious  flow  of  saliva ;  and 
its  odour  is  disagreeable  and  pungent,  somewhat  like  that  of  chlorine ;  a  pro- 
perty which  suggested  the  name  of  Osmium  (from  offjwj;,  odour.)  It  does  not 
combine  with  acids :  on  the  contrary,  though  it  has  no  acid  reaction,  it  unites 
with  alkalies,  and  the  compound  sustains  a  strong  heat  without  decomposition. 
When  touched,  it  communicates  a  stain  which  cannot  be  removed  by  washing. 
With  the  infusion  of  gall-nuts  it  yields  a  purple  solution,  which  afterwards  ac- 
quires a  deep  blue  tint ;  a  character  which  forms  a  sure  and  extremely  delicate 
test  for  peroxide  of  osmium.  By  sulphurous  acid  it  is  deoxidized,  and  the  colour 
of  the  solution  passes  through  the  shades  of  yellow,  orange,  brown,  green,  and 
lastly  blue,  when  it  resembles  sulphate  of  indigo.  These  changes  correspond  to 
sulphates  of  the  different  oxides  of  osmium,  the  last  or  blue  oxide  being  a  com- 
pound of  protoxide  and  sesquioxide  of  osmium. 

Chlorides  of  Osmium. — Berzelius  has  described  four  chloriJes  of  osmium,  cor- 
responding to  the  four  first  degrees  of  oxidation  above  mentioned.  When  osmium 
is  heated  in  a  tube  in  a  current  of  dry  chlorine  gas,  a  deep  green  sublimate  is 
formed,  which  is  the  protochloride.  On  continuing  the  process  it  yields  a  red 
sublimate,  which  is  the  bichloride.  For  the  remaining  details,  which  are  rather 
minute,  I  may  refer  to  the  essay  already  cited.  Several  of  these  chlorides  yield 
double  compounds  with  sodium,  potassium,  and  ammonia. 

Osmium  unites  with  sulphur  in  the  dry  way,  or  when  precipitated  from  the 
chlorides  by  hydrosulphuric  acid.  The  sulphurets  obviously  correspond  to'  the 
number  of  the  oxides.     (Berzelius.) 

Iridium, — Prop. — A  brittle  metal,  and  apt  to  fall  into  powder  when  burnished ; 
but  with  care  it  may  be  polished,  and  then  acquired  the  ap  pearance  of  platinum. 


430  IRIDIUM. 

Of  all  known  metals  it  is  the  most  infusible  :  Children,  by  means  of  his  large 
galvanic  battery,  fused  it  into  a  globule  of  a  brilliant  metallic  lustre  and  white 
colour,  having  a  density  of  18*68  ;  but  the  attempts  at  fusion  by  Berzelius  were 
unsuccessful.  Breithaupt  states  that  the  sp.  gr.  of  native  iridium,  lately  found 
in  the  Russian  mines  of  platinum,  although  not  quite  free  from  lighter  metals, 
varies  from  23  to  26.*  This  would  make  iridium  the  heavest  of  metals.  It  is 
also,  according  to  Breithaupt,  the  hardest  and  the  most  indestructible  by  acids. 
Hence,  if  it  could  be  easily  wrought  it  would  be  invaluable  for  the  edges  of 
delicate  balances.  It  is  oxidized  at  a  red  heat  in  the  open  air,  if  in  a  state  of 
fine  division,  but  not  otherwise ;  and  it  is  attacked  with  difficulty  even  by  nitro- 
hydrochloric  acid. 

The  eq.  of  iridium  is  estimated  by  Berzelius  at  98*8,  being  identical  with  that 
of  platinum.  It  forms  with  oxygen  four  oxides  exactly  analogous  in  composi- 
tion to  the  four  first  oxides  of  osmium  in  the  foregoing  table,  and  its  four  chlo- 
rides correspond  to  those  of  osmium.  Its  sulphurets  have  been  little  examined, 
but  they  doubtless  correspond  to  the  oxides.  (An.  de  Ch.  et  Ph.  xl.  257,  and 
xliii.  185.)    Its  symb.  is  Ir. 

Oxides  of  Iridium. — ^The  protoxide,  sesquioxide,  and  teroxide,  are  precipitated 
by  alkalies  from  the  chloride,  to  which  each  is  respectively  proportional.  The 
protoxide  is  greenish-grey  as  a  hydrate,  and  black  when  anhydrous.  The  ses- 
quioxide is  bluish-black  in  the  dry  state,  and  deep  brown  as  a  hydrate.  The 
hydrated  teroxide  is  of  a  yellowish-brown  or  greenish  colour.  The  binoxide 
has  not  hitherto  been  insulated.  Berzelius  has  not  fully  decided  the  nature  of 
the  compound  which  is  considered  as  the  blue  oxide,  that  which  forms  a  blue 
solution  with  acids ;  but  he  believes  it  to  be  a  compound  of  the  protoxide  and 
sesquioxide.  This  variety  of  oxides,  together  with  the  facility  with  which  they 
appear  to  pass  from  one  to  the  other,  amply  accounts  for  the  diversity  of  tints 
sometimes  observed  in  solutions  of  iridium. 

Chlorides  of  Iridium. — The  protochloride  is  obtained  as  a  light  powder  of  a 
deep  olive-green  colour,  by  transmitting  chlorine  gas  over  pulverulent  iridium 
heated  to  a  commencing  red  heat.  When  heated  to  redness  its  chlorine  is 
expelled.  It  is  insoluble  in  water,  and  but  sparingly  dissolved  by  acids,  even 
the  nitro-hydrochloric ;  but  when  the  hydrated  protoxide  is  digested  in  hydro- 
chloric acid,  the  protochloride  is  reproduced  and  dissolved,  forming  probably  a 
soluble  compound  of  the  protochloride  and  hydrochloric  acid.  Its  solution  is  a 
mixture  of  brown,  green,  and  yellow.     (Berzelius.) 

The  sesquichhride  is  best  obtained  by  calcining  iridium  with  nitre,  digesting 
the  product  in  nitric  acid,  and,  after  washing,  dissolving  the  residual  oxide  in 
hydrochloric  acid.  Its  solution  has  a  dark  yellowish-brown  tint,  which  is  so 
intense  that  a  small  quantity  renders  water  opaque.  By  evaporation  it  yields  a 
black  mass,  wholly  uncrystalline,  and  deliquescent  in  the  air. 

The  bichloride  is  formed  by  digesting  at  a  moderate  heat  the  sesquichloride  in 
nitro-hydrochloric  acid.  It  is  deliquescent  and  very  soluble,  yielding  a  solution 
of  a  dark  reddish-brown  colour.  When  its  solution  is  evaporated  to  dryness, 
except  at  a  heat  not  exceeding  104°,  it  loses  chlorine,  and  is  reconverted  into 
the  sesquichloride. 

The  ierchloride  has  not  been  obtained  in  a  separate  form,  but  only  as  a  double 
chloride  of  potassium.    It  appears  to  be  the  principal  compound  formed  in  the 

*  Prefessor  Hare  has  repeatedly  fused  it  by  means  of  his  oxyhydrogen  blowpipe,  and 
fotuad  iu  sp.  gr.  to  be  31-8. 


ON  METALLIC  COMBINATIONS.  431 

process  above  given  for  extracting  iridium  from  its  ore,  and  is  recognized  by  its 
rose-red  tint. 

Iridium  has  a  considerable*  affinity  for  carbon,  combining  with  it  when  a  piece 
of  metal  is  held  in  the  flame  of  a  spirit-lamp.  The  resulting  carburet  contains 
19*8  per  cent,  of  carbon. 

IRuthenium  is  the  name  given  by  M.  Claus  to  a  new  metal  which  he  discov- 
ered about  two  years  ago  in  the  platinum  residues.  It  had  escaped  the  notice  of 
chemists  from  the  close  resemblance  of  its  double  chloride  with  potassium  to  the 
similar  double  salt  of  iridium.  He  has  recently  obtained  the  metal  in  perfect 
purity,  and  states  that  its  highest  chloride  is  of  a  fine  orange  colour,  and  its 
solution  in  water,  unlike  any  of  the  other  platina  metals,  is  precipitated  by  ammo- 
nia at  common  temperatures.  When  a  plate  of  zinc  is  immersed  in  this  chloride, 
previously  acidified  by  a  little  hydrochloric  acid,  the  metal  is  after  some  time 
precipitated  in  the  form  of  a  black  powder.  (Jour,  de  Pharm.  et  de  Ch.  Juin. 
1845.)] 


SECTION  XXVIII. 


ON  METALLIC  COMBINATIONS. 


Having  completed  the  history  of  the  individual  metals,  and.  of  the  compounds 
resulting  from  their  union  with  the  simple  non-metallic  bodies,  I  shall  treat 
briefly  in  the  present  section  of  the  combinations  of  the  metals  with  each  other. 
These  compounds  are  called  alloys ;  and  to  those  alloys,  of  which  mercury  is  a 
constituent,  the  term  amalgam  is  applied.  It  is  probable  that  each  metal  is 
capable  of  uniting  in  one  or  more  proportions  with  every  other  metal,  and  oh  this 
supposition  the  number  of  alloys  would  be  exceedingly  numerous.  This  depart- 
ment of  chemistry,  however,  owing  to  its  having  been  cultivated  with  less  zeal 
than  most  other  branches  of  the  science,  is  as  yet  limited,  and  our  knowledge 
concerning  it  imperfect.  On  this  account  I  shall  mention  those  alloys  only  to 
which  some  particular  interest  is  attached, 

Metals  do  not  combine  with  each  other  in  their  solid  state,  owing  to  the  influ- 
ence of  chemical  affinity  being  counteracted  by  the  force  of  cohesion.  It  is 
necessary  to  liquefy  at  least  one  of  them,  in  which  case  they  always  unite,  pro- 
vided their  mutual  attraction  is  energetic.  Thus,  brass  is  formed  when  pieces 
of  copper  are  put  into  melted  zinc ;  and  gold  unites  with  mercury  at  common 
temperatures  by  mere  contact. 

Metals  appear  to  unite  with  one  another  in  every  proportion,  precisely  in  the 
same  manner  as  sulphuric  acid  and  water.  Thus  there  is  no  limit  to  the  number 
of  alloys  of  gold  and  copper.  It  is  certain,  however,  that  metals  have  a  tendency  to 
combine  in  definite  proportion ;  for  several  atomic  compounds  of  this  kind  occur 
native.  The  crystallized  amalgam  of  silver,  for  example,  is  composed,  accord- 
ing to  the  analysis  of  Klaproth,  of  64  parts  of  mercury  and  36  of  silver ;  num- 
bers which  are  so  nearly  in  the  ratio  of  202  to  108,  that  the  amalgam  may  be 
inferred  to  contain  one  eq.  of  each  of  its  elements.  It  is  indeed  possible  that 
the  variety  of  proportion  in  alloys  is  rather  apparent  than  real,  arising  from  the 
mixture  of  a  few  definite  compounds  with  each  other,  or  with  uncombined  metal ; 


432  ON  METALLIC  COMBINATIONS. 

an  opinion  not  only  suggested  by  the  mode  in  which  alloys  are  prepared,  but  in 
some  measure  supported  by  observation.  Thus,  on  adding  successive  small 
quantities  of  silver  to  mercury,  a  great  variety  of  fluid  amalgams  are  apparently 
produced ;  but,  in  reality,  the  chief,  if  not  the  sole  compound,  is  a  solid  amal- 
gam, which  is  merely  diffused  throughout  the  fluid  mass,  and  may  be  separated 
by  pressing  the  liquid  mercury  through  a  piece  of  thick  leather. 

This  view  is  strengthened  by  some  late  experiments  by  Rudberg  (An.  de  Ch. 
et  Ph.  xlviii.  363).  He  finds  that  variable  mixtures  of  metals  in  cooling  after 
fusion  have  generally  two  periods  when  the  thermometer  is  stationary.  In  alloys 
of  lead  and  tin  one  of  these  points  is  uniformly  at  368|°  for  all  mixtures,  while 
the  other  point  varies  according  as  one  or  the  other  metal  is  predominant,  and  is 
near  the  fusing  point  of  the  predominating  metal.  From  this  it  is  inferred  that 
the  latter  point  is  caused  by  the  congelation  of  the  predominating  metal,  and  the 
constant  point  is  the  congealing  temperature  of  an  alloy  of  uniform  composition 
present  in  all  the  mixtures.  This  alloy  is  composed  of  3  eq.  of  tin  and  1  eq.  of 
lead,  its  congealing  point  being  368 J°.  In  variable  mixtures  of  bismuth  and  tin 
the  constant  point  is  289^°,  which  is  the  congealing  temperature  of  an  alloy 
composed  of  single  eq.  of  tin  and  bismuth. 

Alloys  are  analogous  to  metals  in  their  chief  physical  properties.  They  are 
opaque,  possess  the  metallic  lustre,  and  are  good  conductors  of  heat  and  elec- 
tricity. They  often  diflfer  materially  in  some  respects  from  the  elements  of  which 
they  consist.  The  colour  of  an  alloy  is  sometimes  different  from  that  of  its  con- 
stituents, of  which  brass  is  a  remarkable  example.  The  hardness  of  a  metal  is 
in  general  increased  by  being  alloyed,  and  for  this  reason  its  elasticity  and 
sonorousness  are  frequently  improved.  The  malleability  and  ductility  of  metals, 
on  the  contrary,  are  usually  impaired  by  combination.  Alloys  formed  of  two 
brittle  metals  are  always  brittle ;  and  an  alloy  composed  of  a  ductile  and  a  brittle 
metal  is  generally  brittle,  especially  if  the  latter  predominate.  An  alloy  of  two 
ductile  metals  is  sometimes  brittle. 

The  density  of  an  alloy  is  sometimes  less,  sometimes  greater,  than  the  mean 
density  of  the  metals  of  which  it  is  composed. 

The  fusibility  of  metals  is  greatly  increased  by  being  alloyed.  Thus  pure 
platinum,  which  cannot  be  completely  fused  in  the  most  intense  heat  of  a  wind 
furnace,  forms  a  very  fusible  alloy  with  arsenic. 

The  tendency  of  metals  to  unite  with  oxygen  is  considerably  augmented  by 
being  alloyed.  This  effect  is  particularly  conspicuous  when  dense  metals  are 
liquefied  by  combination  with  quicksilver.  Lead  and  tin,  for  instance,  when 
united  with  mercury,  are  soon  oxidized  by  exposure  to  the  atmosphere  ;  and  even 
gold  and  silver  combine  with  oxygen,  when  the  amalgams  of  those  metals  are 
agitated  with  air.  The  oxidability  of  one  metal  in  an  alloy  appears  in  some 
instances  to  be  increased  in  consequence  of  a  galvanic  action.  Thus,  Faraday 
observed  that  an  alloy  of  steel  with  100th  of  its  weight  of  platinum  was  dis- 
solved with  effervescence  in  dilute  sulphuric  acid,  which  was  so  weak  that  it 
scarcely  acted  on  common  steel ;  an  eflect  which  he  ascribes  to  the  steel  in  the 
alloy  being  rendered  positive  by  the  presence  of  the  platinum.  De  la  Rive  has 
noticed  a  similar  instance  in  commercial  zinc,  the  oxidability  of  which  is  in- 
creased by  the  presence  of  small  quantities  of  iron.  In  these  cases,  however, 
the  effect  is  due  rather  to  one  metal  being  mechanically  enveloped  in  another 
than  to  actual  combination. 


433 

^"''-"Trr  -  AMALGAMS.    ■  ";  , '     .f^r.  —  rn  [.:.-:  ..• 

Quicksilver  unites  with  potassium  when  agitated  in  a  glass  tube  with  that 
metal,  forming  a  solid  amalgam.  When  the  amalgam  is  put  into  water,  the  po- 
tassium is  gradually  oxidized,  hydrogen  gas  is  disengaged,  and  the  mercury  re- 
sumes its  liquid  form.  A  similar  compound  may  be  obtained  with  sodium. 
These  amalgams  may  also  be  procured  by  placing  the  negative  wire  in  contact 
with  a  globule  of  mercury  during  the  process  of  decomposing  potassa  and  soda 
by  galvanism. 

A  solid  amalgam  of  tin  is  employed  in  making  looking-glasses;  and  an  amal- 
gam made  of  one  part  of  lead,  one  of  tin,  two  of  bismuth,  and  four  parts  of  mer- 
cury, is  used  for  silvering  the  inside  of  hollow  glass  globes.  This  amalgam  is 
solid  at  common  temperatures ;  but  is  fused  by  a  slight  degree  of  heat. 

The  amalgam  of  zinc  and  tin,  used  for  promoting  the  action  of  the  electrical 
machine,  is  made  by  fusing  one  part  of  zinc  with  one  of  tin,  and  then  agitating 
the  liquid  mass  with  two  parts  of  hot  mercury  placed  in  a  wooden  box.  Mer- 
cury evinces  little  disposition  to  unite  with  iron,  and,  on  this  account,  it  is  usually 
preserved  in  iron  bottles. 

The  amalgam  of  silver,  as  already  mentioned,  is  a  mineral  production.  The 
process  of  separating  silver  from  its  ores  by  amalgamation,  practised  on  a  large 
scale  at  Freyberg  in  Germany,  is  founded  on  the  affinity  of  mercury  for  silver. 
On  exposing  the  amalgam  to  heat,  the  quicksilver  is  volatilized,  and  pure  silver 
remains. 

Gold  unites  with  remarkable  facility  with  mercury,  forming  a  white-coloured 
compound.  An  amalgam  composed  of  one  part  of  gold  and  eight  of  mercury  is 
employed  in  gilding  brass.  The  brass,  after  being  rubbed  with  nitrate  of  oxide 
of  mercury,  in  order  to  give  it  a  thin  film  of  quicksilver,  is  covered  with  the  amal- 
gam of  gold,  and  then  exposed  to  heat  for  the  purpose  of  expelling  the  mercqry. 

ALLOYS  OF  ARSENIC.  ■'■•-'  '■-■■'  ^  '^^ 

Arsenic  has  a  tendency  to  render  the  metals,  with  which  it  is  alloyed,  both 
brittle  and  fusible.  It  has  the  property  of  destroying  the  colour  of  gold  and  cop- 
per. An  alloy  of  copper,  with  a  tenth  part  of  arsenic,  is  so  very  similar  in  ap- 
pearance to  silver,  that  it  has  been  substituted  for  it.  The  whiteness  of  this  alloy 
affords  a  rough  mode  of  testing  it  for  arsenic ;  for  if  arsenious  acid  and  charcoal 
be  heated  between  two  plates  of  copper,  a  white  stain  afterwards  appears  upoii 
its  surface,  owing  to  the  formation  of  an  arseniuret  of  copper. 

The  presence  of  arsenic  in  iron  has  a  very  pernicious  effect ;  for  even  though 
in  small  proportion  it  renders  the  iron  brittle,  especially  when  heated. 

The  alloy  of  tin  and  arsenic  is  employed  for  forming  arseniuretted  hydrogen 
gas  by  the  action  of  hydrochloric  acid.  The  tin  of  commerce  sometimes  contains 
a  minute  quantity  of  this  alloy. 

An  alloy  of  platinum  with  ten  parts  of  arsenic  is  fusible  at  a  heat  a  little  above 
redness,  and  may  therefore  be  cast  in  moulds.  On  exposing  the  alloy  to  a  gra- 
dually increasing  temperature  in  open  vessels,  the  arsenic  is  oxidized  and  expel- 
led, and  the  platinum  recovers  its  purity  and  infusibility. 

ALLOYS  OF  TIN,  LEAD,  ANTIMONY,  AND  BISMUTH. 

Tin  and  lead  unite  readily  when  fused  together,  constituting  a  solder,  of  which 
two  kinds  are  distinguished.     The  alloy  called  jine  solder,  consists  of  two  parts 

30 


434  ALtoVs. 

of  tin  and  one  of  lead,  fuses  at  about  360*^,  and  is  much  employed  in  tinning  cop- 
per. The  coarse  solder  contains  l-4th  of  tin,  fuses  at  about  500°,  and  is  the  sub- 
Stance  used  for  soldering  by  glaziers.  Thus,  by  varying  the  relative  quantity  of 
the  metals,  a  solder  of  different  fusibility  may  be  obtained.  The  process  of  hard 
soldering  or  brazings  by  which  two  surfaces  of  copper  are  cemented  together,  is 
done  with  hard  solder,  which  is  made  by  fusing  together  brass  and  zinc :  the 
popper  requires  to  be  heated,  when  this  solder  is  used,  to  near  its  point  of  fusion. 

It  has  been  observed  by  Kupfer  that  most  of  the  alloys  of  tin  and  lead,  made 
in  atomic  proportion,  have  a  sp.  gr.  less  than  their  calculated  density;  from  which 
it  is  manifest  that  they  expand  in  uniting.  The  amalgams  of  lead  and  tin,  on 
the  contrary,  occupy  less  space,  when  combined,  than  their  elements  did  pre- 
viously. 

Tin  alloyed  with  small  quantities  of  antimony,  copper,  and  bismuth,  forms  the 
best  kind  of  pewter.     Inferior  sorts  contain  a  large  proportion  of  lead. 

Tin,  lead,  and  bismuth,  form  an  alloy  which  is  fused  at  a  temperature  below 
212°.  The  best  proportion,  according  to  D'Arcet,  is  8  parts  of  bismuth,  5  of 
lead,  and  3  of  tin. 

An  alloy  of  three  parts  of  lead  to  one  of  antimony  constitutes  the  aubstancQ.  of 
which  types  for  printing  are  made. 

A  native  alloy  of  antimony  and  nickel,  found  at  Andreasberg  in  the  Harz,  was 
found  by  Stromeyer  to  consist  of  29*5  parts  or  1  eq.  of  nickel|  and  64*4  parts  or 
1  eq.  of  antimony. 

ALLOYS  OF  COPPER. 

Copper  forms  with  tin  several  valuable  alloys,  which  are  characterized  by  their 
sonorousness.  Bronze  is  an  alloy  of  copper  with  about  eight  or  ten  per  cent,  of 
tin,  together  with  small  quantities  of  other  metals  which  are  not  esseptial  to  tHe 
compound.      Cannons  are  cast  with  an  alloy  of  a  similar  kind.  "' 

The  best  bell-metal  is  composed  of  80  parts  of  copper  and  20  of  tin ; — the  In- 
dian gong,  celebrated  for  the  richness  of  its  tones,  contaips  copper  and  tin  in  this 
proportion.  A  specimen  of  English  bell-metal  was  found  by  Dr.  Thomson  to 
consist  of  80  parts  of  copper,  10*1  of  tin,  5*6  of  zinc,  and  4*3  of  lead.  Lead  and 
aptimony,  though  in  small  quantity,  have  a  remarkable  effect  in  diminishing  the 
elasticity  and  sonorousness  of  the  compound.  Speculum-metal,  with  which  mir- 
rors for  telescopes  are  made,  consists  of  about  two  parts  of  copper  and  one  of  tin. 
The  whiteness  of  the  alloy  is  improved  by  the  addition  of  a  little  arsenic.  '*' 

Copper  and  zinc  unite  in  several  proportions,  forming  alloys  of  great  import-^ 
ance  in  the  arts.  The  best  brass  consists  of  four  parts  of  copper  to  one  of  zinc  i 
and  when  the  latter  is  in  a  greater  proportion,  compounds  are  generated  which' 
are  called  Tombac,  J)uichgold,2Lnd  Pinchbeck.  The  white  copper  of  the  Chinese, 
which  is  the  same  as  the  German  silver  of  the  present  day,  is  composed,  accord- 
ing to  the  analysis  of  Fyfe,  of  40*4  parts  of  copper,  25'4  of  zinc,  31'6  of  nickel, 
and  2*0  of  iron. 

The  art  of  tinning  copper  consists  in  covering  that  metal  with  a  thin  layer  of 
tin,  in  order  to  protect  its  surface  from  rusting.  For  this  purpose,  pieces  of  tin 
are  placed  upon  a  well-polished  sheet  of  copper,  which  is  heated  sufficiently  for 
fusing  the  tin.  As  soon  as  the  tin  liquefies,  it  is  rubbed  over  the  whole  sheet 
of  copper,  and  if  the  process  is  skilfully  conducted,  adheres  uniformly  to  its  sur- 
face. The  oxidation  of  the  tin,  a  circumstance  which  would  entirely  prevent 
the  success  of  the  operation,  is  avoided  by  employing  fragments  of  resin  or 


ALLOYS.  435 

muriate  of  ammonia,  and  regulating  the  temperature  with  great  care.  The  two 
metals  do  not  actually  combine ;  but  the  adhesion  is  certainly  owing  to  their 
actual  affinity. — Iron,  which  has  a  weaker  attraction  than  copper  for  tin,  is 
tinned  with  more  difficulty  than  that  metal. 

ALLOYS  OF  STEEL. 

Messrs.  Stodart  and  Faraday  have  succeeded  in  making  some  very  important 
alloys  of  steel  with  other  metals.  (Phil.  Trans,  for  1822.)  Their  experiments 
induced  them  to  believe  that  the  celebrated  Indian  steel,  called  wootz,  is  an  alloy 
of  steel  with  small  quantities  of  silicon  and  aluminium  ;  and  they  succeeded  in 
preparing  a  similar  compound,  possessed  of  all  the  properties  of  wootz.  They 
ascertained  that  silver  combines  with  steel,  forming  an  alloy,  which,  although  it 
contains  only  l-500th  of  its  weight  of  silver,  is  superior  to  wootz  or  the  best 
cast  steel  in  hardness.  The  alloy  of  steel  with  100th  part  of  platinum,  though  less 
hard  than  that  with  silver,  possesses  a  greater  degree  of  toughness,  and  is  there- 
fore highly  valuable  when  tenacity  as  well  as  hardness  is  required.  The  alloy 
of  steel  with  rhodium  even  exceeds  the  two  former  in  hardness.  The  compound 
of  steel  with  palladium,  and  of  steel  with  iridium  and  osmium,  is  likewise  ex- 
ceedingly hard  ;  but  these  alloys  cannot  be  employed  extensively,  owing  to  the 
rarity  of  the  metals  of  which  they  are  composed. 

ALLOYS  OF  SILVER.  ;^ 

Silver  is  capable  of  uniting  with  most  other  metals,  and  suffers  greatly  in  mal- 
leability and  ductility  by  their  presence.  It  may  contain  a  large  quantity  of 
copper  without  losing  its  white  colour.  The  standard  silver  for  coinage  contains 
about  l-13th  part  of  copper,  which  increases  its  hardness,  and  thus  renders  it 
more  fit  for  coins  and  many  other  purposes. 

ALLOYS  OF  GOLD. 

The  presence  of  other  metals  in  gold  has  a  remarkable  effect  in  impairing  its 
malleability  and  ductility.  The  metals  which  possess  this  property  in  the  greatest 
degree  are  bismuth,  lead,  antimony,  and  arsenic.  Thus,  when  gold  is  alloyed 
■with  1-1 920th  part  of  its  weight  of  lead,  its  malleability  is  surprisingly  dimin- 
ished. A  very  small  proportion  of  copper  has  an  influence  over  the  colour  of 
gold,  communicating  to  it  a  red  tint,  which  becomes  deeper  as  the  quantity  of 
copper  increases.  Pure  gold,  being  too  soft  for  coinage  and  many  purposes  in 
the  arts,  is  always  alloyed  either  with  copper  or  an  alloy  of  copper  and  silver, 
which  increases  the  hardness  of  the  gold  without  materially  affecting  its  colour 
or  tenacity.     Gold  coins  contain  about  l-12th  of  copper. 

Nearly  all  the  gold  found  in  nature  is  alloyed  more  or  less  with  silver.  In  a 
late  elaborate  investigation  into  the  constituents  of  the  Uralian  ores  of  gold,  G. 
Rose  found  one  specimen  with  0*16  percent,  of  silver,  and  another  with  38-38 
per  cent. ;  but  most  of  the  specimens  contained  8  or  9  per  cent,  of  silver.  It  has 
bt3en  maintained  that  the  native  alloys  of  gold  and  silver  are  usually  in  atomic 
proportion.  This  statement,  however,  has  been  amply  disproved  by  G.  Rose  : 
these  metals  appear  to  beisomorphous,  and  hence,  like  other  isomorphons  bodies, 
they  crystallize  with  each  other  in  proportions  altogether  indefinite.  (Pog.  An. 
xxiii.  161.) 


SALTS. 


GENERAL  REMARKS  ON  SALTS. 


The  preceding  pages  contain  the  description  either  of  elementary  principles, 
or  of  compounds  immediately  resulting  from  the  union  of  those  elements.  These 
compounds  are  chiefly  bi-elementary,  that  is,  arise  from  the  union  of  two  ele- 
ments; their  constituents  are  regarded,  according  to  the  electro-chemical  theory, 
possessing  opposite  electric  energies,  and  as  combined  by  virtue  of  such  ener- 
gies; and  the  names  applied  to  them  are  partly  constructed  in  reference  to  this 
theory.  Thus  in  compounds  of  oxygen  and  chlorine,  chlorine  and  iodine,  sul- 
phur and  potassium,  the  term  expressive  of  the  genus  or  class  of  bodies  to  which 
each  compound  belongs,  is  derived  from  the  electro-negative  element ;  so  that 
we  do  not  say,  chloride  of  oxygen,  iodide  of  chlorine,  and  potassiuret  of  sulphur, 
— but,  oxide  of  chlorine,  chloride  of  iodine,  and  sulphuret  of  potassium;  because 
oxygen  has  a  higher  electro-negative  energy  than  chlorine,  chlorine  than  iodine, 
and  sulphur  than  potassium.  The  metals  as  a  class  are  electro-positive  to  the 
non-metallic  elements ;  but  in  relation  to  each  other  some  of  the  metals  are  elec- 
tro-positive, and  others  electro-negative.  To  the  former  belong  those  metals, 
the  oxides  of  which  are  strong  alkaline  bases,  such  as  potassium,  sodium,  and 
calcium  ;  and  among  the  latter  are  enumerated  those,  such  as  arsenic,  antimony, 
and  molybdenum,  which  are  prone  to  form  acids  when  they  unite  with  oxygen. 

Some  of  the  bi-elementary  compounds  above  referred  to,  though  composed  of 
very  energetic  elements,  are  themselves  chemically  indifferent,  manifesting  little 
disposition  to  unite  with  any  other  body  whatever;  of  which  the  peroxides  of 
manganese  and  lead,  and  some  of  the  chlorides  are  examples.  Others,  on  the 
contrary,  are  surprisingly  energetic  in  their  chemical  relations,  and  have  an  ex- 
tensive range  of  affinity.  The  most  remarkable  instances  of  this  are  found  among 
those  oxidized  bodies  called  acids  and  alkalies^  the  characters  of  which  fixed  the 
attention  of  chemists  long  before  their  composition  was  understood.  The  acids 
and  alkalies,  however,  are  indiflferent  to  elementary  substances:  their  affinities 
are  exerted  towards  each  other,  and  by  upiting  they  give  rise  to  compounds 
more  complex  than  themselves,  as  containing  at  least  three  elements,  and  which 
are  known  by  the  name  of  salts.  Acids  and  alkalies  possess  opposite  electric 
energies  in  relation  to  each  other,  the  former  being  —  and  the  latter  -f-.  The 
electric  energies  evinced  by  them  are  related  to  the  electric  energies  of  their 


GENERA.L  REMARKS  ON  SALTS.  437 

elements.  Thus  acids  generally  abound  in  the  electro-neg^ative  oxygen,  and  if 
they  contain  a  metal,  it  is  usually  an  electro-negative  metal ;  whereas  the  pow- 
erful alkalies  are  the  protoxides  of  electro-positive  metals.    . 

Acids  and  alkalies  neutralize  each  other  more  or  less  completely,  so  that  the 
resulting  salt  is  generally  neither  acid  nor  alkaline,  and  is  far  less  energetic  as 
a  chemical  agent  than  acids  and  alkalies.  Most  of  them,  however,  unite  in  defi- 
nite proportion  with  certain  substances,  such  as  water,  alcohol,  ammonia,  and 
with  other  salts,  forming  the  extensive  family  of  double  salts.  To  these  com- 
pounds the  electro-chemical  theory  may  be  extended  :  the  two  simple  salts  which 
constitute  a  double  salt,  may  be  viewed  as  two  molecules  united  by  virtue  of 
electric  energies  of  an  opposite  character. 

In  the  early  period  of  modern  chemistry  an  acid  was  considered  to  be  an  oxi- 
dized body  which  has  a  sour  taste,  reddens  litmus  paper,  and  neutralizes  alka- 
lies. But  subsequent  experience  has  shown  the  propriety  of  extending  the  defi- 
nition of  an  acid.  For,  first,  the  discovery  of  the  hydracids  proved  that  oxygen 
is  not  essential  to  acidity.  Secpndly,  some  compounds,  owing  to  their  insolu- 
bility, neither  taste  sour  nor  redden  litmus,  and  yet  from  their  chemical  relations 
are  regarded  as  acids.  Thirdly,  some  acknowledged  acids,  such  as  the  carbonic 
and  hydrosulphuric,  are  unable  fully  to  destroy  the  alkaline  reaction  of  potassa. 
Facts  of  this  kind  have  induced  chemists  to  consider  as  acids  all  those  com- 
pounds which  unite  with  potassa  or  ammonia,  and  give  rise  to  bodies  similar 
in  their  constitution  and  general  character  to  the  salts  which  the  sulphuric  or 
some  admitted  acid  forms  with  those  alkalies. 

A  similar  extension  is  given  to  the  notion  of  alkalinity,  the  characters  of  which, 
as  exhibited  in  their  most  perfect  form  in  potassa  and  soda,  are  causticity,  a 
peculiar  pungent  alkaline  taste,  alkaline  reaction  with  test  paper,  and  power  both 
of  neutralizing  acids  and  of  forming  with  them  neutral  saline  compounds.  Of 
these,  chemists  agree  to  consider  the  last  as  the  most  characteristic,  and  place 
among  the  allialine  or  salifiable  bases  all  those  bodies  which  unite  definitely  with 
admitted  acids,  such  as  the  sulphuric  and  nitric,  and  form  with  them  compounds 
analogous  in  constitution  to  the  salts  which  admitted  alkalies  form  with  the 
acids.  Thus,  magnesia  is  a  very  strong  alkaline  base,  seeing  that  20'7  parts  of 
it  neutralize  as  much  sulphuric  acid  as  47  of  potassa;  and  yet  magnesia,  from 
being  insoluble  is  all  but  tasteless,  and  has  barely  any  alkaline  reaction. 

The  progress  of  chemistry,  which  ha§  gradually  developed  sounder  views  ot 
the  nature  of  acids  and  alkalies,  is  also  causing  an  extension  in  the"  idea  of  a 
salt.  The  great  mass  of  the  salts  are  compounds  of  oxidized  bodies,  both  the 
acid  and  the  base  containing  oxygen.  But  ammonia,  though  not  an  oxide,  has 
all  the  characters  of  alkalinity  in  an  eminent  degree,  and  its  compounds  with 
acids  were  at  once  admitted  into  the  list  of  salts.  Then  came  the  discovery  of 
the  hydracids,  such  as  the  hydrochloric  and  hydriodic,  which  are  so  powerfully 
acid,  that  their  compounds  with  alkaline  bases  were  readily  adopted  as  salts. 
Hence  arose  the  division  of  the  salts  as  a  class  into  two  orders,  one  containing 
the  oxygen  or  oxy-salts,  and  the  other  the  hydrogen  or  hydro-salts.  Again,  the 
gaseous  terfluoride  of  boron,  which  contains  neither  oxygen  nor  hydrogen,  com- 
bines definitely  with  ammonia,  and  forms  with  it  a  neutral  compound,  which  was 
esteemed  a  salt  as  soon  as  it  was  known. 

The  notion  of  a  salt  has  of  late  been  still  further  extended.  Chemists  have 
long  known  that  metallic  sulphurets  occasionally  combine  together,  and  consti- 
tute what  is  called  a  double  sulphurei.     In  these  compounds  Berzelius,  whose 


438  GENEEAL  REMARKS  ON  SALTS. 

labours  have  greatly  added  to  their  number,  has  traced  an  exact  analogy  with  the 
salts,  and  applied  to  them  the  name  oi sulphur-salts.  The  simple  sulphurets  by 
the  union  of  wliich  a  sulphur-salt  is  formed,  are  bi-elementary  compounds,  strictly 
analogous  in  their  constitution  to  acids  and  alkaline  bases,  and  which,  like  them, 
are  capable  of  assuming  opposite  electric  energies  in  relation  to  each  other. 
jElectro-positive  sulphurets,  termed  sulphur  basesy  are  usually  the  protosulphurets 
of  electro-positive  metals,  and  thereibre  correspond  to  the  alkaline  bases  of  those 
metals;  and  the  electro-negative  sulphurets,  sulphur-acids^  are  the  sulphurets  of 
electro-negative  metals,  and  are  proportional  in  composition  to  the  acids  which 
the  same  metals  form  with  oxygen.  Hence,  if  the  sulphur  of  a  sulphur-salt  were 
replaced  by  an  equivalent  quantity  of  oxygen,  an  oxy-salt  would  result.  (An. 
de  Ch.  et  Ph.  xxxii.  60.) 

The  compounds  which  Berzelius  has  enumerated  as  sulphur-acids,  are  the  sul- 
phurets of  arsenic,  antimony,  tungsten,  molybdenum,  tellurium,  tin,  and  gold. 
To  these  he  has  added  the  sulphurets  of  several  other  substances  not  metallic, 
such  as  sulphnret  of  selenium,  bisulphuret  of  carbon,  and  the  hydrosulphuric 
and  hydrosulphocyanic  acids.  He  mentions,  also,  that  just  as  two  electro-posi- 
tive oxides  may  combine,  one  becoming  electro-negative  in  regard  to  the  other, 
so  may  a  sulphur-salt  be  generated  by  the  union  of  electro-positive  sulphurets. 
The  native  double  sulphuret  of  copper  and  iron,  and  a  considerable  number  of 
similar  compounds,  are  instances  of  this  nature.  These  analogies  are  rendered 
much  closer  by  the  facts  that  hydrosulphuric  and  hydrosulphocy.anic  acids  act 
as  hydro-acids  with  ammonia,  and  as  sulphur-acids  with  sulphur-bases;  and  that 
all  the  sulphurets  which  are  remarkable  as  sulphur-acids,  have  likewise  the  pro- 
perty of  combining  with  ammonia. — I  shall  accordingly  place  the  double  sul- 
phurets as  a  third  order  of  the  class  of  salts,  and  describe  them  under  the  name 
of  sulphur-salts. 

A  fourth  order  of  salts  has  been  formed  by  Berzelius,  comprising  for  the  most 
part  bi-elementary  compounds,  which  consist  of  a  metal  on  the  one  hand,  and  of 
chlorine,  iodine,  bromine,  fluorine,  and  the  radicals  of  the  hydracids  on  the  other. 
He  has  applied  to  them  the  name  of  haloid-salts  (from  d?tj  sea-salt,  and  ftSoj 
form),  because  in  constitution  they  are  analogous  to  sea-salt.  The  whole  series 
of  the  metallic  chlorides,  iodides,  bromides,  and  fluorides,  such  as  chloride  of 
sodium,  iodide  of  potassium,  and  fluor-spar,  as  well  as  the  cyanides,  sulpho- 
cyanides,  and  ferrocyauides,  are  included  in  the  list  of  haloid-salts.  (An.  de 
Ch.  et  Ph.  xxxii.  60.)  The  reader  will  at  once  perceive  that  these  haloid-salts, 
as  bi-elementary  compounds,  differ  in  composition  from  other  salts,  and  are  analo- 
gous to  oxides  and  sulphurets. 

The  preceding  pages  contain  an  account  of  the  different  classes  of  compounds 
which  have  been  termed  salts.  But  since  the  last  edition  of  this  work  was  pub- 
lished, new  views  on  this  important  class  of  bodies  have  begun  to  prevail.  The 
researches  ^f  Graham  on  the  phosphates,  those  of  Liebig  on  the  constitution  of 
the  organic  acids  and  their  salts,  and  the  experiments  of  Dumas,  Clark,  Fremy, 
Thaulow,  Peligot,  and  many  others,  have  gradually  converged  to  the  point  of 
recalling  to  the  recollection  of  chemists  certain  profound  views,  first  suggested 
by  Davy  in  regard  to  chloric  and  iodic  acids  and  their  salts,  and  afterwards 
applied  (apparently  without  previous  knowledge  of  what  Davy  had  done)  by 
Dulong  to  the  salts  of  oxalic  acid.  These  views  have  the  inestimable  advantage 
of  uniting  all  acids  into  one  series,  and  all  salts  into  another;  nay,  these  two 
series  may  even  be  considered  as  one.    I  shall  here  briefly  explain  them ;  but  in 


GENERAL  REMARKS  ON  SALTS.  439 

describing  tiie  salts  individually,  I  shall  retain  the  usual  views  of  the  constitu- 
tion of  acids  and  salts,  as  the  former  have  been  thus  described  in  the  preceding 
part  of  this  volume,  and  the  chemical  world  is  not  yet  ripe  for  a  complete  change 
in  the  theory  of  salts.  The  new  views,  however,  are  making  such  rapid  pro- 
gress, and  are  so  closely  entwined  with  the  details  of  every  part  of  chemistry, 
that  a  knowledge  of  them  is  indispensable  to  the  student. 

In  regard  to  acids,  then,  the  first  point  to  be  noticed  is,  that  all  so-called  oxy- 
gen acids,  in  the  free,  or  what  may  be  called  the  active  state,  contain  hydrogen. 
On  referring  to  the  description  of  the  mineral  acids  it  will  be  found,  for  example, 
that  they  are  described  as  combining  with  water  when  separated  from  their  com- 
bining actions.  Oil  of  vitriol  is  SOg,HO ;  nitric  acid  NO^,HO,  &c.  The  latter, 
indeed,  cannot  exist  in  the  supposed  anhydrous  state,  NO^  ;  and  this  is  the  case 
with  a  large  majority  of  all  known  acids.  Sulphuric  acid  and  phosphoric  acid, 
no  doubt,  may  be  obtained  anhydrous,  So^  and  PgO^;  but  it  is  worthy  of  especial 
notice,  that  in  this  state  they  do  not  possess  the  properties  of  these  acids,  and  only 
acquire  them  on  the  addition  of  water.  The  compound  of  dry  sulphuric  acid 
and  ammonia,  SO^,NH^,  is  not  sulphate  of  ammonia,  but  a  distinct  compound. 
Moreover,  these  anhydrous  acids  combine  with  water  with  the  -greatest  vehe* 
mence,  and  then  assume  their  active  characters.  The  principal  exceptions  are 
carbonic  acid  and  chromic  acid  ;  but,  on  the  other  hand,  none  of  the  organic 
acids  can  exist  without  water,  that  is,  without  hydrogen. 

It  is  obvious  that  hydrogen  is  essential  to  the  hydracids.  Now  the  view  which 
I  wish  here  to  explain  considers  both  these  classes  of  acids  as  hydracids,  and 
thus  unites  in  one  class  or  series  bodies  having  the  most  perfect  analogy  in  pro- 
perties. According  to  this  view,  therefore,  the  general  formula  of  a  hydracid  is 
X  -f-  H  :  X  being  an  acid-radical  which  may  be  either  simple  or  compound. 
Thus  in  hydrochloric,  hydriodic,  and  hydrosulphuric  acids  respectively,  X  is 
represented  by  CI, I,  or  S.  In  hydrocyanic  and  hydrosulphocyanic  acids,  X  is 
represented  by  Cy  =  C^N,  and  by  CyS^  =  C^NS^,  respectively. 

In  the  hydrated  oxygen  acids  of  the  preceding  pages,  to  which  alone,  and  not 
to  the  anhydrous  acids,  this  theory  applies,  X  is  always  a  compound,  and  always 
contains  oxygan.  Thus  in  hydrated  sulphuric  acid,  commonly  so  called,  and 
represented  by  80^,110,  X  is  represented  by  SO^*:  in  nitric  acid,  NO^Ht),  X  = 
NOg;  and  in  metaphosphoric  acid,  P20^,H0,  X=  PgOgi  and  the  true  formulae 
of  these  acids  are  SO^,H,NOg,H  and  P^O^,!!,  respectively. 

Further,  among  the  organic  acids  to  be  afterwards  described,  we  find  a  corres- 
ponding constitution.  In  acetic  acid  (hydrated)  CJ^l^O^,¥LO,  X  =  C^H^O^;  in 
hydrated  formic  acid,  C2H03,HO,  X  ==  C^HO^,  &c. 

The  next  point  to  be  noticed  is,  that  acids  exist,  the  general  formula  of  which 
is  X  -f  H„ ;  that  is,  in  which  X  combines  with  two  or  more  equivalents  of  H, 
and  which  are  called  polybasic  acids.  Those  acids,  above  described,  in  which 
there  is  1  eq.  of  H,  are  called  monobasic  acids.  Where  2  eq.  of  H  are  present 
the  acid  is  bibasic  ;  with  3  eq.  of  H,  tribasic,  and  so  on.  The  reason  of  this 
nomenclature  will  appear  when  we  come  to  salts. 

Examples  of  this  kind  are,  pyrophosphoric  acid,  P20^,2HO,  which  is  bibasic, 
its  true  formula  being  ^fi^->^2'^  phosphoric  acid,  P^^j^SHO,  which  is  a  tri- 
basic acid,    P^O  ,H  ;    and    arsenic   acid,    As20j,3HO ;    also   a   tribasic   acid, 

But  it  is  among  the  organic  acids  that  we  find  the  most  numerous  and  striking 


440  GENERAL  REMARKS  ON  SALTS. 

examples  of  polybasic  acids.    The  following  table  contains  the  fonnulse  of  some 
of  these. 

Meconic  acid  .  .  .  C^H  Oi,  +  3H0  (tribasic)  =  CuH  0,4+  Hg-  ^^ 

Cyanuric  acid  .  .  .  Cya    O3  :f- 3H0  (tribasic)  =  Cya    Oe   -|- H3.  ^ 

Citric  acid     ....  CaHsO,,  -f-  3H0  (tribasic)  =  C,2H50i4  + H3. 

Tannic  acid  .  .  .  CigHgOg   -f  3H0  (tribasic)  =  CisHjOu  -f-  H3. 

Tartaric  acid  .  .  .  Cg  H^Ojo  +  2H0  (bibasic)  =  Cg  H^0,2 -f"  Hg. 

Komenic  acid  .  .  .  CijHaOg  +  2H0  (bibasic)  =  CizHjOjo  "l"  H2.  *i 

Fulminicacid  .  .  .  Cyz    Oj  +  2H0  (bibasic)  =  Cyj    O4   -f  H2.  ^ 

Mucic  acid    .  .  .  .  '  CiaHgOu  -f  2H0  (bibasic)  =C,2H80i6  -|-  Hj.  ^ 


Moreover  there  are  also  polybasic  acid^  which  contain  no  oxygen,  analogous 
in  this  respect  to  hydrochloric  and  hydrocyanic  acids.  Thus  ferrocyanic  acid  is 
represented  by  Cy^Fe  -f  H^  ;  and  ferrideyanic  acid  is  Cy^Fe2+  H^. 

It  will  be  obvious  at  a  glance,  that  this  theory  of  acids  possesses  the  advan- 
tages of  simplicity  and  of  uniting  in  classification  a  vast  number  of  bodies, 
similar  in  properties,  which  have  formerly  been  arbitrarily  separated.  But  the 
chief  advantage  attending  it  is,  that  it  enables  us  to  effect  the  same  union  into 
one  class  of  all  the  salts  of  the  acids  containing  hydrogen.  It  is  in  examining 
the  salts,  moreover,  that  we  find  the  strongest  arguments  in  favour  of  the  theory 
as  applied  to  acids. 

A  salt  is  formed,  whenever  one  of  these  acids  is  neutralized  by  a  metallic 
oxide,  by  ammonia,  or  by  an  organic  base,  or  combines  with  them,  without  being 
neutralized. 

Now,  when  a  salt  is  thus  formed,  one  phenomena  constantly  occurs  ;  this  is 
the  separation  of  water.  In  the  simplest  case,  namely,  where  the  hydracid  of 
an  elementary  body  acts  on  a  metallic  protoxide,  the  origin  of  the  water  is  quite 
obvious.  When  hydrochloric  acid,  for  example,  acts  on  oxide  of  silver,  chloride 
of  silver  is  formed,  and  water  is  eliminated  :  HCl  -f  AgO  =  AgCl  -f  HO. 
There  is  here  no  doubt  that  the  water  is  produced  by  the  reaction. 

But  when  hydrated  sulphuric  acid  acts  on  the  same  oxide,  although  the  phe- 
nomena are  exactly  the  same,  a  different  explanation  is  commoj^ly  given ;  and 
the  water  is  assumed  to  have  pre-existed  in  the  acid,  thus,  80^,110  4-  AgO  ^ 
S03,AgOtHO. 

It  is  contrary  to  all  sound  principles  of  reasoning  to  adopt  two  explanations  of 
facts  precisely  similar;  where  one  will  suffice,  and  only  one  explanation  of  "the 
former  case  is  possible,  we  must  apply  the  same  explanation  to  the  latter.  This 
is  Clone  by  the  new  theory  ;  and  the  following  formulae  will  show  the  identity  of 
the  reaction  in  the  two  cases  : — 

H,C1  f  Ag,0  =  Ag,Cl  4-  H,0. 
H,S04  +  AgO=  Ag,S0«  -j-  HO. 

In  both  cases  the  water  is  formed  by  the  union  of  the  hydrogen  of  the  acid  with 
the  oxygen  of  the  oxide ;  and  consequently  in  both  cases  the  hydrogen  of  the 
acid  has  been  replaced  by  the  metal. 

Here,  then,  is  the  theory  of  salts.  A  salt  is  formed  when  the  hydrogen  of  the 
acid  is  replaced  by  its  equivalent  of  a  metal.  Consequently,  acids  may  be  viewed 
as  the  hydrogen  salts  of  their  radicals,  and  thus  acids  and  salts,  in  regard  to 
their  constitution,  will  form  but  one  class. 


GENERAL  REMARKS  ON  SALTS.  441 

As  the  metals  replace  hydrogen  equivalent  for  equivalent,  it  is  ohvious  that 
polyhasic  acids  will  form  poly  basic  salts.  This  has  already  been  illustrated 
under  phosphoric  acid,  but  other  examples  may  be  given.  Thus,  when  cyanuric 
acid  acts  on  oxide  of  silver,  3  atoms  of  the  latter  are  required  for  one  of  the 
former,  (Cy30^  +  H3)  +  3AgO  =  (Cy30g  t  Ag^)  +  3H0.  With  fulminic  acid 
2  atoms  are  required,  (Cy^O^  +  hJ  +  2AgO  =  (Cy^O^  +  AgJ  -f-  2H0.  It  is 
unnecessary  here  to  multiply  these  examples. 

One  remarkable  consequence,  deducible  from  the  theory  under  consideration 
is,  that  those  oxides  which  most  easily  lose  oxygen  should  most  readily  replace 
by  their  metal  the  hydrogen  of  the  acid.  This  is  found  to  be  the  case.  For 
example,  potash  can  only  replace  by  potassium  2  of  the  3  eq.  of  hydrogen  in 
cyanuric  acid,  and   1  of  the  2    eq.  of  hydrogen  in  fulminic  acid,   forming  the 

K    C  K  7 

compounds,    Cy  O.,  2  3  and   Cy„0^„  >  while  with  oxide  of  silver,  an  easily 

3    oj[-[     ^  2    4J-1  y 

reducible  oxide,  the  replacement  as  before  mentioned,  is  complete.  This  fact 
furnishes  an  almost  irresistible  argument  for  the  existence  of  hydrogen,  as  such, 
in  acids ;  and  further  explains  the  formerly  unaccountable  fact,  that  the  salts 
formed  by  the  action  of  oxide  of  silver  on  organic  acids  are  always  anhydrous. 
In  the  case  of  phosphoric  and  arsenic  acids  also,  oxide  of  silver  forms  anhy- 
drous salts,  or,  in  other  words,  replaces  the  hydrogen  entirely,  with  much  greater 
facility  than  potash  or  soda. 

Another  obvious  consequence  of  this  theory  is,  that  the  neutralizing  power  of 
an  acid  depends  entirely  on  the  number  of  equivalents  of  hydrogen  replaceable 
by  metals.  Take,  for  example,  hydrosulphuric  acid,  S  +  H;  and  add  to  the 
radical  oxygen,  &c.,  in  almost  any  proportion,  the  neutralizing  power  remains 
unchanged,  as  the  following  table  shows  : — 

X= 

Hydrosulphuric  acid         .        .         .  S         "hH. 

Sulphurous  acid       ....  SO3     -|-H. 

Sulphuric  acid  .        .        .        .  S04     -^H. 

Hyposulphurous  acid        .         .         .  S2O3   "f-H. 

Hyposulphuric  acid  .         .         .  S2O6   -|-H. 

Hydrosulphocyanic  acid  .         ,         .  SjCy  -J-H.  .^ 

Chlorosulphuric  acid         .         .         .  SO3CI-I-H.  (Regnault,) 

Nitrosulphuric  acid  .        .        .  SNOs-j-H.  (Pelouze.) 

No  substances  can  be  more  different  in  composition  than  the  above;  yet  they 
all  neutralize  exactly  the  same  quantity  of  base  ;  a  fact  readily  explained,  when 
it  is  considered  that  neutral  salts  result  from  the  complete  replacement  of  the 
hydrogen  by  metals.  . 

The  salts  of  ammonia  form  no  exception  to  our  theory.  They  always  contain 
1  at.  of  water,  essential  to  their  existence.  Thus,  sulphate  of  ammonia,  anhy- 
drous, contains  S03,NH3,HO=S03,NH^O  =  SO^  +  NH^.  In  this  last  formula, 
NH^  represents  the  supposed  metal  ammonium,  which,  if  it  be  a  metal,  only 
differs  from  ordinary  metals  in  being  compound,  just  as  cyanogen,  a  compound 
acid,  radical,  differs  from  chlorine.* 

*  This  theory  respecting  the  constitution  of  acids  and  salts,  although  captivating  on 
account  of  its  apparent  simplicity,  has  not  met  the  views  of  some  distinguished  chemists. 
It  is  ably  opposed  in  a  paper  entitled,  "An  effort  to  refute  the  argument  in  favor  of  the 


443  GENERAL  REMARKS  ON  SALTS. 

I  shall  resume  this  subject  when  treating  of  the  organic  acids;  and  meantime 
I  return  to  the  description  of  the  salts,  according  to  the  views  still  prevailing, 
with  which  the  student  must  also  make  himself  well  acquainted,  as  they  per- 
vade all  chemical  works. 

Consistently  with  the  views  developed  in  the  first  part  of  this  section,  I  have 
grouped  together  all  saline  compounds  which  have  a  certain  similarity  of  com- 
position into  one  great  class  of  salts,  which  is  divided  into  the  four  following 
orders : — 

Order  I.  The  oxy-salts.  This  order  includes  no  salt  the  acid  or  base  of 
whjch  is  not  an  oxidized  body. 

Order  II.  The  hydro-salts.  This  order  includes  no  salt  the  acid  or  base  of 
which  does  not  contain  hydrogen. 

Order  III.  The  sulphur-salts.  This  order  includes  no  salt  the  electro-positive 
or  negative  ingredient  of  which  is  not  a  sulphuret. 

Order  IV.  The  haloid-salts.  This  order  includes  no  salt  the  electro-positive 
or  negative  ingredient  of  which  is  not  haloidal.* 

The  nomenclature  of  the  first  order  of  salts  was  explained  on  a  former  occa- 
sion. The  insufliciency  of  the  division  into  neutral^  super,  and  swi-salts  will  be 
made  apparent  by  the  following  remarks.  In  the  first  place,  some  alkaline  bases 
form  more  than  one  super-salt,  in  which  case  two  or  more  different  salts  would 
be  included  under  the  same  name.  Secondly,  some  salts  have  an  acid  reaction, 
and  might  therefore  be  denominated  super-salts,  although  they  do  not  contain  an 
excess  of  acid.  Nitrate  of  oxide  of  lead,  for  instance,  has  the  property  of  red- 
dening litmus  paper ;  whereas  it  consists  of  1  eq.  of  oxide  of  lead  and  I  ex{.  of 
pitric  acid,  and  therefore  in  composition  is  precisely  analogous  to  nitrate  of 
potassa,  which  is  a  neutral  salt.  This  fact  was  noticed  some  years  ago  ^  Ber- 
zelius,  who  accounted  for  the  circumstance  in  the  following  manner: — The 
colour  of  litmus  is  naturally  red,  and  it  is  only  rendered  blue  by  the  colouiing 
matter  combining  with  an  alkali.  If  an  acid  be  added  to  the  blue  compound,  the 
colouring  matter  is  deprived  of  its  alkali^  and  thus,  being  set  free,  resumes  its 
red  tint.  Now  on  bringing  litmus  paper  in  contact  with  a  salt,  the  acid  and  base 
of  which  have  a  weak  attraction  for  each  other,  it  is  possible  that  the  alkali  con- 
tained in  the  litmus  paper  may  have  a  stronger  affinity  for  the  acid  of  the  salt 
than  the  base  has  with  which  it  was  combined ;  and  in  that  case  the  alkali  of 
the  litmus  being  neutralized,  its  red  colour  will  necessarily  be  restored.  It  is 
hence  apparent  that  a  salt  may  have  an  acid  reaction  without  having  an  excess 
of  acid. 

The  nomenclature  of  the  hydro-salts  is  framed  on  the  same  principles  as  that 
applied  to  the  salts  which  contain  oxygen.  With  respeet  to  the  third  and  fourth 
orders  of  salts  no  general  principle  of  nomenclature  has  yet  been  agreed  on. 
Berzelius  has  extended  to  them  the  same  nomenclature  which  he  employs  for 
the  oxy-salts,  and  some  chemists  seem  disposed  to  follow  his  example ;  but  as 

existence  in  amphide  salts  of  radicals,"  by  Robert  Hare,  M.  D.,  Professor  of  Chemistry, 
University  of  Pennsylvania,"  &c.     (R.) 

*Thi8  order  of  salts  is  founded  upon  the  assumption  that  the  binary  compounds  which 
form  them  have  opposite  electro.chemical  relations,  and  act  relatively  to  each  other  as  acids 
and  bases.  This  doctrine  was  proposed  by  BornsdorfT^An.  de  Ch.  et  de  Ph.  xliv,  189),  and 
entertained  by  Professor  Hare,  before  he  became  aware  that  Bornsdorff  held  similar  opmions. 
More  recently  he  has  ably  advocated  it  in  a  letter  to  Proliessor  Silliraau  on  tlic  Borzelian 
oomeuciature.    June,  1834.    (R.) 


GENERAL  REMARKS  ON  SALTS.  443 

new  views  are  apt  to  be  obscured,  and  tbeir  intrinsic  value  overlooked,  by  being 
expressed  in  new  language,  I  shall  confine  myself  as  much  as  possible  to  terms 
with  which  every  chemist  is  familiar.  It  is  worthy  of  consideration  whether 
the  nomenclature  of  the  sulphur  and  haloid  salts,  instead  of  being  purposely 
assimilated  to  that  of  the  other  salts,  should  not  designedly  be  kept  distinct,  in 
order  the  more  readily  to  distinguish  between  analogous  compounds. 

Nearly  all  salts  are  solid  at  common  temperatures,  and  most  of  them  are 
capable  of  crystallizing.  The  colour  of  salts  is  very  variable,  having  no  neces- 
sary connection  with  the  colour  of  their  elements.  Salts  composed  of  a  colour- 
less acid  and  base  are  colourless;  but  a  salt,  though  formed  of  a  coloured  oxide 
or  acid,  may  be  colourless;  or,  if  coloured,  the  tint  may  differ  from  that  of  both 
its  constituents. 

All  soluble  salts  are  more  or  less  sapid,  while  those  that  are  insoluble  in 
water  are  insipid.  Few  salts  are  possessed  of  odour:  the  most  remarkable  one 
for  this  property  is  carbonate  of  ammonia. 

Salts  differ  remarkably  in  their  affinity  for  water.  Thus  some  salts,  such  as 
the  nitrates  of  lime  and  magnesia,  are  deliquescent^  that  is,  attract  moisture  from 
the  air,  and  become  liquid.  Others,  which  have  a  less  powerful  attraction  for 
water,  undergo  no  change  when  the  air  is  dry,  but  become  moist  in  a  humid 
atmosphere ;  and  others  may  be  exposed  without  change  to  an  atmosphere  loaded 
with  watery  vapour. 

Salts  differ  likewise  in  the  degree  of  solubility  in  water.  Some  dissolve  in 
less  than  their  weight  of  water;  while  others  require  several  hundred  times  their 
weight  of  this  liquid  for  solution,  and  others  are  quite  insoluble.  This  difference 
depends  on  two  circumstances,  namely,  on  their  affinity  for  water,  and  on  their 
cohesion  ;  their  solubility  being  in  direct  ratio  with  the  first,  and  in  inverse 
ratio  with  the  second.  One  salt  may  have  a  greater  affinity  for  water  than 
another,  and  yet  be  less  soluble ;  an  effect  with  may  be  produced  by  the  cohesive 
power  of  the  salt  which  has  the  stronger  attraction  for  water  being  greater  than 
that  of  the  salt  which  has  a  less  powerful  affinity  for  that  liquid.  The  method 
proposed  by  Gay-Lussac  for  estimating  the  relative  degrees  of  affinity  of  salts 
for  water  (An.  de  Ch.  Ixxxii.)  is  by  dissolving  equal  quantities  of  salts  in  equal 
quantities  of  water,  and  applying  heat  to  the  solutions.  That  salt  which  has 
the  greatest  affinity  for  the  menstruum  will  retain  it  with  most  force,  and  will 
therefore  require  the  highest  temperature  for  boiling. 

Salts  which  are  soluble  in  water  crystallize  more  or  less  regularly  when  their 
solutions  are  evaporated.  If  the  evaporation  is  rendered  rapid  by  heat,  the  salt 
is  usually  deposited  in  a  confused  crystalline  mass  ;  but  if  it  take  place  slowly, 
regular  crystals  are  formed.  The  best  mode  of  conducting  the  process  is  to  disr 
solve  a  salt  in  hot  water,  and  when  it  has  become  quite  cold  to  pour  the  saturated 
solution  into  an  evaporating  basin,  which  is  to  be  set  aside  for  several  days  or 
weeks  without  being  moved.  As  the  water  evaporates,  the  salt  assumes  the 
solid  form ;  and  the  slower  the  evaporation,  the  more  regular  are  the  crystals. 
Some  salts  which  are  much  more  soluble  in  hot  than  in  cold  water,  crystallize 
with  considerable  regularity  when  a  boiling  saturated  solution  is  slowly  cooled. 
The  form  which  salts  assume  in  crystallizing  is  constant  under  the  same  cItt 
cumstances,  and  constitutes  an  excellent  character  by  which  they  may,be  dis- 
tinguished from  one  another. 

Many  salts  during  the  act  of  crystallizing  unite  chemically  with  a  definite  por- 
tion of  water,  which  forma  an  essential  part  of  the  crystal,  but  not  of  the  salt, 


444  GENERAL  REMARKS  ON  SALTS. 

and  IS  termed  water  of  trystallizaiion.  The  quantity  of  combined  water  is  very 
variable  in  different  saline  bodies,  but  is  uniform  in  the  same  salt.  A  salt  may 
contain  more  than  half  its  weight  of  water,  and  yet  be  quite  dry.  On  exposing 
a  salt  of  this  kind  to  heat,  it  is  dissolved,  if  soluble,  in  its  own  water  of  crystal- 
lization, undergoing  what  is  termed  the  watery  fusion.  By  a  strong  heat,  the 
whole  of  the  water  is  expelled;  for  no  salt  can  retain  its  water  of  crystallization 
when  heated  to  redness.  Some  salts,  such  as  sulphate  and  phosphate  of  soda, 
lose  a  portion  of  their  water,  and  crumble  down  into  a  white  powder,  by  mere 
exposure  to  the  air;  a  change  which  is  called  efflorescence.  The  tendency  of 
salts  to  undergo  this  change  depends  on  the  dryness  and  coldness  of  the  air;  for 
a  salt  which  effloresces  rapidly  in  a  moderately  dry  and  warm  atmosphere,  may 
often  be  kept  without  change  in  one  which  is  dgmp  and  cold. 

The  water  of  crystallization  is  retained  by  a  very  feeble  affinity,  as  is  proved 
by  the  phenomena  of  efflorescence,  and  by  the  facility  with  which  such  water  is 
separated  from  the  saline  matter  by  a  moderate  heat,  or  by  exposure  to  the 
vacuum  of  an  air-pump  at  common  temperatures.  It  is  frequently  observed, 
however,  that  a  portion  of  the  water  is  retained  with  such  obstinacy  that  it  can- 
not be  expelled  by  a  temperature  short  of  that  at  which  the  salt  is  totally  decom- 
posed. This  water,  as  in  the  case  of  the  hydrated  acids,  is  considered  to  act  the 
part  of  a  base,  and  is  hence  commonly  called  basic  water,  as  has  already  been 
explained  in  the  section  on  phosphorus.  But  from  the  observations  of  Graham 
it  would  appear  that  the  water  thus  retained  does  not  always  act  the  part  of  a 
base,  but  is  in  a  peculiar  state  of  combination,  characteristically  different  both 
from  basic  water  and  water  of  crystallization  (Ph.  Tr.  Ed.  xii.  297).  In  his 
original  paper  he  distinguished  it  as  saline  water  ;  but  in  a  recent  report  read  to 
the  meeting  of  the  British  Association  in  Liverpool,  he  has  called  it  constitu- 
tional water.  It  is  readily  distinguished  from  water  of  crystallization,  by  being 
retained  by  a  stronger  affinity,  and  by  being  essential  to  the  existence  of  the  salt 
of  which  it  constitutes  a  part.  From  basic  water  it  differs  by  not  being  removed 
from  its  combinations  even  by  the  most  powerful  alkalines,  whereas  it  is  readily 
removed,  and  its  place  in  the  compound  assumed  by  certain  anhydrous  salts :  it 
is  also  expelled  from  an  acid  more  readily  than  the  basic  water.  From  an  ex- 
ample the  character  of  water  in  these  different  states  of  combination  will  be 
readily  understood.  The  crystals  of  the  common  phosphate  of  soda  are  com- 
posed of  1  eq.  of  phosphoric  acid,  2  eq.  of  soda,  and  25  eq.  of  water.  On 
exposing  them  to  a  temperature  of  212®,  24  eq.  of  the  water  are  readily  expelled  ; 
but  the  25th  eq.  is  retained  with  such  power,  that  a  red  heat  is  necessary  to 
effect  its  complete  separation.  By  the  loss  of  the  24  eq.  of  water,  the  crystalline 
form  and  texture  of  the  salt  is  entirely  destroyed,  but  the  residual  amorphous 
mass  has  all  the  properties  of  the  common  phosphate;  whereas  by  the  loss  of 
the  25ih,  an  entirely  different  salt,  the  pyrophosphate  of  soda,  is  produced.  It 
will  hence  appear,  that  the  24  eq.  of  water  which  were  lost  at  212°  were  only 
essential  to  the  existence  of  the  crystal,  while  the  loss  of  the  25th  eq.  affected 
that  of  the  salt. 

The  same  thing  is  observed  in  the  case  of  sulphate  of  oxide  of  zinc.  Its  com- 
mon crystals  are  composed  of  1  eq.  of  sulphuric  acid,  1  eq.  of  oxide  of  zinc,  and 
7  eq.  of  water,  six  of^  which  are  readily  lost  at  212°,  the  crystal  being  at  the 
same  time  destroyed,  while  the  7ih  eq.  is  not  expelled  until  the  temperature 
rises  above  410°.  Thus  far  the  7th  eq.  of  water  in  sulphate  of  zinc  appears 
analogous  to  the  25th  in  the  common  phosphate  of  soda ;  but  Graham  has  pointed 


GENERAL  REMARKS  ON  SALTS.  445 

out  the  remarkable  difference  that  in  the  latter  salt  the  eq.  of  water  is  readily 
removed  from  its  combination  by  an  eq.  of  any  base  which  supplies  its  place  in 
the  compound  ;  while  in  sulphate  of  zinc,  ihe  eq.  of  water  is  not  affected  by 
bases,  but  may  be  removed  by  anhydrous  sulphates,  which  occupy  its  place  and 
give  rise  to  the  formation  of  double  salts.  The  former,  as  acting  the  part  of  a 
base,  is  called  basic  water;  the  latter,  as  influencing  the  constitution  of  a  salt,  is 
called  constitutional  water.  The  difference  is  denoted  in  symbols,  by  writing  the 
basic  water,  as  is  the  case  with  all  bases,  on  the  left  side  of  the  acid  with  which 
it  is  combined,  and  the  constitutional  water  on  the  right.  Hence  the  syrab.  of 
the  crystals  of  phosphate  of  soda  is  2NaO,  HO.  F^0^-^2A  aq. ;  and  of  the  sul- 
phate of  zinc,  ZnO  SO  HO  +  6  aq.  In  the  phosphate  the  water  may  be  re- 
moved by  soda,  forming  3NaO.  ^fi^  +  24  aq. ;  in  the  sulphate,  by  anhydrous 
sulphate  of  potassa,  forming  the  double  salt  ZnO  SO^  (KO  SO^)  +  6  aq. 

In  pursuing  the  study  of  this  subject,  Graham  has  been  led  to  the  conclusion 
that  all  salts  are  neutral  in  their  constitution  with  the  exception  of  certain  classes. 
Thus  he  finds  that  the  bisulphate  of  potassa  is  a  double  salt,  formed  by  the  con- 
stitutional water  of  sulphate  of  water  being  replaced  by  sulphate  of  potassa : 
thus 

HO  SO3HO    2     HO  SO  (KO3  SO3. 
&  Kg  SO3    •?.        &  HO. 

To  illustrate  the  constitution  of  a  subsalt,  the  nitrates  were  selected.  Nitric 
acid  of  sp.  gr.  1*42  he  considers  to  be  nitrate  of  water  with  3  eq.  of  constitutional 
water.  Its  symb.  is  therefore  HO  NO^.  3H0.  But  water  corresponds  with  the 
class  of  isomorphous  oxides  of  which  magnesia,  the  oxides  of  zinc  or  of  copper, 
may  be  taken  as  the  type.  Hence  these  oxides  are  capable  of  supplying  the 
place  of  water  in  either  state  of  combination,  as  is  seen  in  the  neutral  and  sub- 
nitrate  of  copper,  in  the  former  of  which  the  basic  water  is  replaced  by  an  eq.  of 
oxide  of  copper,  while  in  the  sub-salt  the  3  eq.  of  constitutional  water  are  replaced 
by  3  eq.  of  oxide  of  copper.  Their  constitution  is  therefore  represented  by  the 
formulae 

KuO  NO5.  3H0. 
And  HO  NO5.  3KuO. 

In  applying  these  views  in  other  cases,  however,  difficulties  arise,  owing  to 
the  existence  of  anhydrous  bisalts,  as  the  anhydrous  bisulphate  and  bichromate 
of  potassa.  These  are  accounted  for  by  Graham,  by  supposing  the  existence  of 
a  class  of  bodies,  called  by  him  basic  adjuncts,  which  admit  of  being  attached  to 
the  oxide  of  hydrogen,  or  to  the  oxides  of  metals  —  the  only  true  bases.  The 
arguments  in  support  of  this  view  are  principally  drawn  from  the  composition  of 
the  ammoniacal  salts  :  it  must  be  remembered,  however,  that  the  whole  subject 
is  in  many  respects  hypothetical,  and  has  not  yet  been  sufficiently  tested  by  ex- 
periment. 

Salts,  in  crystallizing,  frequently  enclose  mechanically  within  their  texture 
particles  of  water,  by  the  expansion  of  which,  when  heated,  the  salt  is  bursty 
with  a  crackling  noise  into  smaller  fragments.  This  phenomenon  is  known  by 
the  name  of  decrepitation.  Berzelius  has  correctly  remarked  that  those  crystals 
decrepitate  most  powerfully,  such  as  the  nitrates  of  baryta  and  oxide  of  lead, 
which  contain  no  water  of  crystallization. 

The  atmospheric  pressure  is  said  to  have  considerable  influence  on  the  crys- 


446  ON  CRYSTALLIZATION. 

tallization  of  salts.  If,  for  example,  a  concentrated  solution,  composed  of  about 
three  parts  of  sulphate  of  soda  in  crystals,  and  two  of  water,  is  made  to  boil 
briskly,  and  the  flask  which  contains  it  is  then  tightly  corked,  while  its  upper 
part  is  full  of  vapour,  the  solution  will  cool  down  to  the  temperature  of  the  air 
without  crystallizing,  and  may  in  that  state  be  preserved  for  months  without 
thange.  Before  removal  of  the  cork,  the  liquid  may  often  be  briskly  agitated 
without  losing  its  fluidity ;  but  on  readmitting  the  air,  crystallization  commonly 
commences,  and  the  whole  becomes  solid  in  the  course  of  a  few  seconds.  The 
admission  of  the  air  sometimes,  indeed,  fails  in  causing  the  effect;  but  it  may  be 
produced  with  certainty  by  agitation  or  the  introduction  of  a  solid  body.  The 
theory  of  this  phenomenon  is  not  very  apparent.  Gay-Lussac  has  shown  that  it 
does  not  depend  on  atmospheric  pressure  (An.  de  Ch.  vol.  Ixxxvii.)  ;  for  he  finds 
that  the  solution  may  be  cooled  in  open  vessels  without  becoming  solid,  provided 
its  surface  be  covered  with  a  film  of  oil ;  and  I  have  frequently  succeeded  in  the 
same  experiment  without  th^  use  of  oil,  by  causing  the  air  of  the  flask  to  com- 
fiiunicaie  with  the  atmosphere  by  means  of  a  moderately  narrow  tube.  It  appears 
from  some  experiments  of  Graham  {Phil.  Trans.  Edin.  1828),  that  the  influence 
of  the  air  maybe  ascribed  to  its  uniting  chemically  with  water:  for  he  has  proved 
that  gases  which  are  more  freely  absorbed  than  atmospheric  air,  act  more  rapidly 
in  producing  crystallization.  Indeed,  the  rapidity  of  crystallization,  occasioned 
by  the  contact  of  gaseous  matter,  seems  proportional  to  the  degree  of  its  affinity 
for  water. 

The  same  quantity  of  water  may  hold  several  different  salts  in  solution,  pro- 
Tided  they  do  not  mutually  decompose  each  other.  The  solvent  power  of  watet 
■with  respect  to  one  salt  is,  indeed,  sometimes  increased  by  the  presence  of  an- 
other, owing  to  combination  taking  place  between  the  two  salts. 

Most  salts  produce  cold  during  the  act  of  solution,  especially  when  they  are 
dissolved  rapidly  and  in  large  quantity.  The  greatest  reduction  of  temperature 
is  occasioned  by  those  which  contain  water  of  crystallization. 

All  the  oxy-salts  are  decomposed  by  voltaic  electricity,  provided  they  are  either 
moistened  or  in  solution.  The  acid  appears  at  the  positive  pole  of  the  battery, 
and  the  oxide  at  its  opposite  extremity ;  or  if  the  oxide  is  of  easy  reduction,  the 
metal  itself  goes  over  to  the  negative  side,  and  its  oxygen  accompanies  the  acid 
to  the  positive  wire. 

The  hydro-salts,  and  doubtless  also  the  sulphur  and  haloid-salts,  are  subject 
to  a  similar  change ;  but  the  phenomena  as  respects  the  two  last  orders  of  salts 
have  been  little  examined. 

ON  CRYSTALLIZATION. 

The  particles  of  liquid  and  gaseous  bodies,  during  the  formation  of  solids, 
sometimes  cohere  together  in  an  indiscriminate  manner,  and  give  rise  to  irregular 
shapeless  masses ;  but  more  frequently  they  attach  themselves  to  each  other  in  a 
certain  order,  so  as  to  constitute  solids  possessed  of  a  symmetrical  form.  The 
•process  by  which  such  a  body  is  produced  is  called  crystallizalion ;  the  solid 
itself  is  termed  a  crystal;  and  the  sciencei^he  object  of  which  is  to  study  the  form 
of  crystals,  is  crystallographi/. 

Most  bodies  crystallize  under  favourable  circumstances.  The  condition  by 
which  the  process  is  peculiarly  favoured  is  the  slow  and  gradual  change  of  a 
fluid  into  a  solid,  the  arrangement  of  the  particles  being  at  the  same  time  undis- 


ON  CRYSTALLIZATION. 


447 


turbed  by  motion.  This  is  exemplified  during  the  slow  cooling  of  a  fused  mass 
of  sulphur  or  bismuth,  or  the  spontaneous  evaporation  of  a  saline  solution ;  and 
the  origin  of  the  numerous  crystals,  which  are  found  in  the  mineral  kingdom, 
may  be  ascribed  to  the  influence  of  the  same  cause. 

.  All  substances  are  limited  in  the  number  of  their  crystalline  forms.  Thus, 
calcareous  spar  crystallizes  in  rhombohedrons,  fluor-spar  in  cubes,  and  quartz  in 
six-sided  pyramids  ;  and  these  forms  are  so  far  peculiar  to  those  substances,  that 
fluor-spar  never  crystallizes  in  rhombohedrons  or  six-sided  pyramids,  nor  calca- 
reous spar  or  quartz  in  cubes.  Crystalline  form  may  therefore  serve  as  a  ground 
of  distinction  between  different  substances.  It  is  accordingly  employed  by  min- 
eralogists for  distinguishing  one  mineral  species  from  another ;  and  it  is  very 
serviceable  to  the  chemist  as  affording  a  physical  character  for  salts.  On  this 
account  I  have  thought  it  would  be  useful,  before  describing  the  individual  salts, 
to  introduce  a  few  pages  on  crystallization;  but  from  the  great  extent  of  the  sub- 
ject, which  now  constitutes  a  separate  science,  my  remarks  must  necessarily  be 
limited,  and  comprehend  little  else  than  a  brief  outline  of  its  more  important 
principles.  To  those  who  are  desirous  of  more  ample  information,  I  may  recom- 
mend the  "  Elements  of  Crystallography,"  by  Gustav.  Rose,  or  Mr.  Whewell's 
Essay  in  the  Phil,  Trans,  of  London  for  1825. 

Every  perfect  crystal  is  bound  by  plane  surfaces,  which  are  called  its  faces. 
The  straight  line  formed  by  the  intersection  of  two  faces  is  called  an  edge;  the 
meeting  of  three  or  more  edges  in  a  point  forms  a  solid  angle.  Thus  in  the 
octohedron,  fig.  1,  the  bounding  planes  are  the  faces,  the  lines  formed  by  their 
intersection  the  edges,  the  meeting  of  four  of  whieh  in  the  same  point  produces 
a  solid  angle  of  the  crystal. 

The  forms  of  crystals  are  exceedingly  diversified.  They  are  divided  by  crys- 
tallographers  into  simple  and  compound  :  a  simple  form  has  all  its  faces  equal 
and  similar  to  each  other,  while  a  compound  form  is  bounded  by  at  least  two 
different  classes  of  faces.     Thus,  figs.  1,  2,  and  3,  are  simple  forms;  for  the 


Fig.  1. 


Fig.  2. 


Fig.  3. 


■ 


first  is  bounded  by  eight  faces,  each  of  which  is  an  equilateral  triangle,  the 
second  by  six  squares,  and  the  third  by  twelve  equal  and  similar  rhombi.  The 
forms  represented  by  4,  5,  and  6,  are,  on  the  contrary,  compound  crystals :  for 
fig.  4  is  composed  of  ^wo  classes  of  faces,  eight  which  are  hexagonal,  and 
six  square ;  while  fig.  6  contains  three  classes,  eight  faces  being  hexagonal,  six 
octagonal,  and  twelve  quadratic.  This  division  into  compound  and  simple  is  not 
artificial,  but  is  founded  on  the  fact  that  the  compound  forms  are  really  produced 
by  the  combinatibn  of  two  or  more  of  the  simple  crystals,  as  will  bo  seen  by  a 
careful  inspection  of  the  forms  and  relative  situations  of  the  faces  in  the  accom- 


448 


ON  CRYSTALLIZATION. 


panying  fiorures.     The  character  of  the  faces  in  figures  1,  2,  and  3,  which  repre- 
sent respectively  the  regular  octohedron,  the  cube,  and  the  rhombic  dodecahedron, 


Fig.  5. 


Fig.  4. 


is  too  obvious  to  demand  comment;  but  to  obtain  a  correct  idea  of  the  relative 
positions  of  the  faces  in  these  three  forms  requires  a  more  careful  investigation. 
It  will  be  observed  that  in  each  of  these  figures  three  right  lines,  which  are 
equal  in  length,  perpendicular  to  each  other,  and  pass  through  the  centre  of  the 
crystal,  may  be  obtained  ;— *in  the  octohedron  by  joining  the  opposite  angles,  in 
the  cube  by  joining  the  centres  of  the  opposite  faces,  and  in  the  rhombic  dode- 
cahedron by  connecting  the  opposite  angles  formed  by  the  meeting  of  four  edges, 
these  angles  being  six  in  number  and  corresponding  in  situation  to  the  six  angles 
of  the  octohedron.     The  lines  around  which  the  different  parts  of  the  crystals 
are  thus  symmetrically  grouped  are  called  crystalline  axes.     Hence  the  above 
forms  are  connected  by  being  possessed  of  the  same  axes  of  crystallization,  and 
proceeding  from  these  three  equal  and  rectangular  axes,  either  the  octohedron, 
the  cube,  or  the  rhombic  dodecahedron  may  be  constructed,  the  resulting  form 
being  solely  dependent  on  the  law  in  accordance  with  which  planes  are  symmetri- 
cally arranged  or  grouped  around  the  axes.   The  octohedron  (fig.  1)  results  from 
the  law  that  every  plane  shall  pass  through. an  extremity  of  each  axis  :  it  will  be 
evident  that  one,  and  only  one,  plane,  fulfilling  the  required  condition,  may  be 
introduced  into  each  of  the  eight  octants  formed  by  the  intersection  of  the  three 
axes.    This  law,  therefore,  limits  the  number  of  faces  to  eight ;    and  as  these 
intersect  each  other  in  the  lines  joining  the  extremities  of  the  axes,  each  face  is 
an  equilateral  triangle,  and  the  resulting  form  is  the  regular  octohedron.     The 
cube  (fig.  2)  results  from  the  law  that  each  plane  shall  pass  through  an  extremity 
of  one  axis,  and  be  parallel  to  the  other  two  :  as  each  of  the  three  axes  has  two 
extremities,  six,  and  only  six,  planes  can  be  grouped  around  them  in  accordance 
with  this  law,  and  by  their  intersection  the  hexahedron,  or  cube,  as  it  is  more 
commonly  called,  is  produced.     In  a  similar  manner  may  the  rhombic  dodeca- 
hedron (fig.  3)  be  shown  to  be  formed  according  to  the  law  that  each  plane  shall 
pass  through  the  extremities  of  two  axes,  and  be  parallel  to  the  third. 

The  groups  of  simple  forms,  which  are  thus  associated  by  being  reducible  from 
the  same  axes,  constitute  what  is  called  by  crystal lographers  a  system  of  crys- 
tallization. Thus  the  octohedron,  the  cube,  and  the  rhombic  dodecahedron,  are 
three  forms  of  what  is  called  the  octohedral  or  regular  system.  Such  forms  are 
associated  not  merely  by  the  similarity  of  their  axis,  but  are  connected  still  more 
intimately  by  the  remarkable  fact,  that  any  substance  which;>iii  crystallizing 
assumes  one  form  of  a  system,  may,  and  frequently  does,  assume  other  forms 


ON  CRYSTALLIZATION.  449 

belonging  to  that  system.  Examples  of  this  may  be  seen  in  the  well-known  salt 
alum,  and  in  the  black  oxide  of  iron,  the  magnetic  ore  of  mineralogists;  the 
former  generally  crystallizing  in  the  octohedron  (fig.  1),  but  it  may  also  be 
obtained  in  the  form  of  the  cube  (fig.  2) ;  and  the  magnetic  iron  ore  is  found  not 
only  in  the  form  of  octohedrons  aitd  cubes,  but  likewise  in  that  of  the  rhombic 
dodecahedron  (fig.  3).  But,  what  is  still  more  remarkable,  the  same  substance 
is  not  only  capable  of  assuming  different  forms  of  the  same  system,  but  during 
the  act  of  crystallization  the  flices  of  two,  three,  four,  and  in  some  cases  even 
more,  of  these  forms  are  simultaneously  developed,  whereby  compound  crystals 
of  the  greatest  diversity  of  form  and  appearance  are  produced.  Thus,  in  the 
crystallization  of  alum  either  the  cube  or  octohedron  may  be  formed,  but  it  is  by 
far  more  common  that  the  faces  of  both  be  produced,  giving  rise  to  the  com- 
pound crystal  represented  in  1^.  4,  where  the  faces  of  the  cube  appear  truncating 
the  angles  of  the  octohedron.  Another  form  frequently  observed  in  alum  is 
represented  by  fig.  5,  where  in  addition  to  the  octohedron  the  faces  of  the  rhom- 
bic dodecahedron  are  also  developed  ;  and  as  these  are  twelve  in  number,  and 
correspond  in  situation  to  the  twelve  edges  of  the  octohedron,  their  develope- 
ment  removes,  or  as  it  is  technically  expressed,  truncates  the  twelve  edges  of 
the  latter  form.  Fig.  6  represents  a  combination  of  all  three  forms.  Similar 
and  still  more  complicated  combinations  are  observed  on  magnetic  iron  ore.    H 

The  importance  of  a  knowledge  of  all  the  simple  forms  of  a  system,  as  heit^ 
those  in  which  the  same  substance  may  occur,  and  which  alone  can  give  rise  to 
compound  crystals,  for  simple  forms  of  different  systems  are  never  combined, 
will  be  felt  from  what  has  already  been  stated.  The  first  person  who  proved  the 
existence  of  a  mathematical  connection  between  them  was  the  celebrated  crys- 
tallographer  Haiiy  ;  but  it  is  to  Weiss,  Professor  of  Mineralogy  in  Berlin,  that 
we  are  indebted  for  the  distinction  of  the  system  of  crystallization, — a  discovery 
which  justly  entitles  him  to  the  honour  of  being  the  founder  of  modern  crystal- 
lography. He  has  shown  that  all  crystalline  forms  maybe  brought  under  one 
of  the  six  following  systems,  which  may  be  conveniently  distinguished  as, 

1.  The  octohedral,  or  regular  system  of  crystallization. 

2.  The  square  prismatic  ditto  ditto. 

3.  The  right  prismatic  ditto  ditto. 

4.  The  oblique  ditto  ditto. 

5.  The  doubly  oblique  ditto  ditto. 

6.  The  rhombohedral  system   ditto  ditto. 

The  Octohedral  System. — This  system  is  characterized  by  the  three  equal  and 
rectangular  axes,  which  have  already  been  described.  Let  them  be  distinguished 
as  the  axes  a,  6,  and  c  ,•  and,  for  the  convenience  of  reference,  let  us  consider 
that  the  figure  be  brought  into  such  a  position-  that  two  of  them,  a  and  6,  be 
horizontal,  and  c  vertical.  The  figs.  1,  2,  and  3  are  drawn  under  this  supposi- 
tion. The  law  of  crystalline  symmetry  is  such,  that  if  a  face  of  a  crystal  be 
observed  to  bear  a  certain  relation  to  one  of  the  axes  a,  other  faces  must  fulfil 
the  same  condition  to  the  equal  axes  b  and  c.  Thus,  if  a  plane  be  seen  to  pass 
through  the  extremity  of  a,  or  be  parallel  to  it,  other  planes  must  pass  through 
the  extremity  of  b  and  c,  or  be  parallel  to  them.  Owing  to  the  perfect  sym- 
metry in  the  different  parts  of  the  crystal,  this  group  is  frequently  called  the 
regular  system  of  crystallization. 

It  consists  of  but  few  simple  forms,  the  number  being  necessarily  limited  to 

31 


I 


450  ^^  CRYSTALLIZATION. 

the  number  of  different  ways  in  which  a  plane  can  intersect  the  three  axes. 
These,  it  will  be  seen,  are  only  seven  : — 

1.  The  plane  may  cut  each  at  an  equal  distance  from  the  centre.     The  crj'stal 
the  faces  of  which  obey  this  law  is  the  octohedron,  figf.  1. 

2.  The  plane  may  cut  two  axes  at  an  equaX  and  the  third  at  a  greater  distance 
from  the  centre.     The  resulting  form  is  called  the  triakisoctohedron. 

3.  The  plane  may  cut  two  axes  at  an  equal,  and   the  third  at  a  less  distance 
from  the  centre.     The  resulting  form  is  the  ikosTtetrahedron. 

4.  The  plane  may  cut  ail  three  axes  unequally.    The  form  is  the  herakisocto- 
hedron. 

6.  The  plane  may  cut  two  axes  at  unequal  distances  from  the  centre,  and  be 
parallel  to  the  third.     The  resulting  crystal  is  the  tetrakishexahedron. 

6.  The  plane  may  cut  two  axes  in  points  equally  distant  from  the  centre,  and 
be  parallel  to  the  third.     The  form  is  the  rhombic  dodecahedron,  fig.  3. 

7.  The  plane  may  cut  one  axis,  and  be  parallel  to  the  other  two.    This  law 
gives  rise  to  the  cube  or  hexahedron,  fig.  2. 

Of  these  forms,  I,  6,  and  7  are  of  frequent  occurrence;  but  the  others  are 
usually  found  only  in  combination,  when  their  faces  are  generally  small,  and 
appear  symmetrically  arranged  around  the  angles  and  on  the  edges  of  the  former. 
Hence,  in  most  compound  crystals  of  this  system,  the  faces  either  of  the  octohe- 
dron  cube  or  rhombic  dodecahedron  may  be  readily  recognized  ;  find  as  these 
'  Suffice  to  fix  the  position  of  the  crystalline  axes,  they  serve  as  a  guide  to  deter- 
mine the  forms  of  the  combination.  Their  prevalence  presents  also  a  remarkable 
instance  of  the  tendency  to  simplicity  which  may  be  observed  in  all  the  processes 
of  nature.  This  is  not  only  seen  in  the  greater  simplicity  of  exterior  form,  but 
in  the  more  definite  nature  of  the  laws  by  which  the  faces  of  these  three  crystals 
are  determined  ;  for  while  a  plane  has  but  one  position  in  which  it  can  satisfy 
the  laws  1,  6,  and  7,  an  unlimited  number  of  planes  may  be  found  to  satisfy  the 
Mjonditions  expressed  by  2,  3,  4,  and  5.  Thus,  for  example,  there  is  but  one 
way  in  which  a  plane  can  satisfy  the  law  1 ;  while  there  are  as  many  ways  of 
satisfying  the  law  4,  as  there  are  of  taking  three  lines  which  shall  be  unequal. 
Hence  it  follows  that  there  can  be  but  one  octohedron,  while  the  number  of  hera- 
kisoctohedrons  is  unlimited,  and  the  fhces  of  two  different  ones  have  been 
observed  on  the  same  crystals.  The  latter  observation  also  applies  to  the  forms 
produced  according  to  the  laws  2,  3,  and  5:  but  the  number  of  varieties  which 
have  been  observed  is  very  limited,  and  the  relative  lengths  of  the  unequal  axes 
may  be  expressed,  almost  without  an  exception,  by  the  numbers  1,  ^,  |,  |, 
and  l 

It  is  frequently  observed  in  crystals  of  this  system,  that  one-'half  of  the  faces 

of  the  crystals  are  much  more  developed  than  the  other.     This  may  be  seen   in 

Fig.  7.  figure   7,  a  crystal  of  the  red   oxide  of  copper,  where 

'^4fjkff  "K       four  out  of  the   eight  faces   of  the  octohedron  have 

'  ^J  \\  increased,  and  the  other  four  proportionally  diminished. 

\^\  j/^     I  The   faces  which   increase,  as    well   as    those    which 

\      \  /^        I    diminish,  always  form  two  similar  and  symmetrically 

\  ^v-  /     arranged  groups,  the  increasing  faces  or  groups  of  faces 

N.        /\^^ I       touching  each  ofher  at  the  angular  points  of  the  crystal. 

\^'        \      y        Thus,    in  the    octohedron,  the    four   alternating   faces 
\y  which  do  not  intersect  in  edges,  but  merely  touch  each 


% 


ON  CRYSTALLIZATION. 


451 


Fig.  8. 


other  in  the  angular  points,  increase,  as  represented 
in  figure  7,  and  by  increasing  till  they  form  a  per- 
fect figure,  give  rise  to  the  well  known  crystal  the 
tetrahedron,  fig.  8.  These  forms  are  called  hemie- 
dral,  as  denoting  their  origin  :  hence  the  tetrahedron 
is  commonly  known  as  the  hemi-octohedron. 
Each  of  the  simple  forms  of  this  system,  with  the 
exception  of  the  cube  and  rhombic  dodecahedron, 
gives  rise  to  hemihedral  crystals :  the  exception 
evidently  results  from  the  impossibility  of  dividing 
the  faces  of  the  cube  and  rhombic  dodecahedron 
into  two  groups,  which  fulfil  tiie  necessary  condi- 
tions. 

The  Square  Prismatic  System. — The  forms  of  this  system  are,  like  those  of 
the  preceding,  characterized  by  three  axes,  which 
intersect  each  other  at  right  angles;  but  they  differ 
from  them  by  two  only  out  of  the  three  being  equal. 
Let  the  third,  which  may  be  either  greater  or  less 
than  the  two  equal  axes  be  called  c,  and  let  it  be 
placed  in  a  vertical  position.  The  octohedron 
formed  by  joining  the  extremities  of  these  axes,  is 
either  longer  or  shorter  in  the  direction  of  the  axis 
c  than  in  that  of  its  horizontal  axes,  as  is  seen  in  figure  9.     From  this  it  follows 


Fig.  9. 


Fig.  10. 


Fig.  11. 


that  these  octohedrons  may  be 
compared  to  a  double  four-sided 
pyramid  constructed  on  either  side 
of  a  square  base.  The  parts  of 
the  crystal  about  this  base  are 
therefore  similar  to  each  other,  but 
differ  from  those  about  its  upper 
or  lower  extremity ;  and  as  this 
observation  applies  equally  to  all 
forms  of  this  system,  it  is  the  cha- 
racter by  which  the  system  is  best 
distinguished.  This  difference  is 
owing  to  the  inequality  of  the  ver- 
tical axis,  which  causes  the  rela- 
tions of  the  faces  to  it  to  be  unconnected  with  those  they  bear  to  the  two  hori- 
zontal axes.  Hence  it  is  common  to  find  the  lateral  edges  truncated  without 
those  connected  with  the  extremities  of  the  crystal  being  affected,  wliereby  a 
square  prism  terminated  by  four-sided  pyramids,  as  represented  in  figure  10, 
is  produced.  The  same  may  occur  on  the  lateral  angles  as  well  as  edges,  as 
in  figure  11.  In  other  cases,  the  terminal  edges  and  angles  are  modified,  but 
always  in  a  different  manner  from  the  lateral. 

The  Right  Prismatic  System. — The  crystals  of  this  system  are  like  the  pre- 
ceding, characterized  by  three  rectangular  axes,  and  are  distinguished  from 
both  by  no  two  of  these  axes  being  equal.  Its  forms  are  therefore  not  only 
distinguished  by  a  difference  in  the  lateral  and  terminal  parts,  but  are  still 
her  marked  by  the  difference  between  the  front  and  back  of  the  crystal,  as 


r 


452 


ON  CRYSTALLIZATION. 


Fig.  12. 


Fig.  13. 


r^'~^^ 

— i"--- ~j| 

1 

V 

1// 

Fig.  14. 


compared  with  its  sides.  Thus 
in  figures  12,  13,  and  14,  which 
represent  three  of  the  common 
forms  of  sulphur,  the  different 
magnitude  in  the  parts  of  the 
crystals  about  each  axis  is  per- 
ceptible, and  sufficiently  marks 
the  different  crystalline  values 
of  the  three  axes.  But  this  is 
still  better  pointed  out  by  the 
three  different  and  independent 
modifications  of  the  rhombic  oc- 
tohedron,  which  forms  the  basis 
of  all  three  crystals. 

The  Oblique  Prismatic  Syt- 
tern. — ^The  crystals  of  this 
system,  of  which  an  example 
may  be  seen  in  sulphate  of 
the  protoxide  of  iron,  figure 
15,  differ  from  those  of  the 
right  prismatic  system  by  the 
front  and  back  parts  being 
dissimilar.  This  difference 
is  owing  to  two  of  the  axes 
intersecting  each  other  ob- 
liquely, while  the  third  still  remains  perpendicular  to  both. 

The  Doubly  Oblique  System. — This  system  is  readily  recog- 
nized by  the  complete  absence  of  all  symmetry  in  its  crystal- 
line forms.  This  results  from  all  three  axes  intersecting 
each  other  obliquely  ;  owing  to  which  the  left  and  right  sides, 
as  well  as  the  back  and  front,  are  of  diflferent  crystalline 
values.  From  this  it  follows  that  no  two  faces  are  connected 
except  those  which  are  parallel,  and  all  symmetry  of  form 
disappears,  as  observed  in  fig.  16,  which  represents  a  crystal 
of  the  sulphate  or  the  oxide  of  copper. 

The  Rhombohedral  System, — The  forms  of  this  system  of 

crystallization  are,  like  the  octohedral,  characterized  by  three  equal  and  similar 

Fig.  17.  axes ;  but  these  axes  intersect  each  other  at  equal,  but  not  at 

right  angles.     Its  most  simple  form  is  the  rhombohedron,  fig. 

17,  which  is  bound  by  six  equal  and  similar  rhombic  faces.    The 

/  axes  are  obtained  by  joining  the  centre  of  the  opposite  faces, 

J  Although  the  faces  of  the  rhombohedron  are  equal,  two  only  of 

its  angles,  marked  a,  are  regular,  being  formed  by  the  meeting 

of  three  equal  edges,  while  the  other  six  are  irregular.     The 

line  joining  a  a  is  called  the  principal  axis  of  the  rhombohedron,  the  angles  a 

the  terminal,  and  b  the  lateral  angles  of  the  rhombohedron. 

The  form  which  most  commonly  occurs  associated  with  the  rhombohedron  is 
a  hexagonal  prism,  fig.  18,  two  of  which  are  observed,  the  one  truncating  the 
six  angles,  the  other  the  lines  joining  these  angles,  the  faces  of  the  prism 


|S, 

Fig. 

— Ts 
1 

16. 

\1 

! 

V. 

i 

#^ 


ON  CRYSTALLIZATION.  45^ 

being;  in  both  cases  parallel  to  the  rhombohedral  axes  aa.     The  terminal  angles 
a  are  frequently  truncated  by  terminal  planes.  p-     jg 

The  different  forms  of  the  system  may  be  advantageously  ^-^r- 
studied  on  crystals  of  quartz  and  calcareous  spar.  ^M«. 

Besides  the  distinction  arising  from  external  form,  minerals  ' 
are  further  distinguished  by  differences  in  the  mechanical  con- 
nection of  their  particles,  peculiarities  which  mineralogists 
designate  by  the  name  of  structure.  The  structure  of  a  mineral  arises  from  its 
particles  adhering  at  some  parts  less  tenaciously  than  at  others,  and  conse- 
quently yielding  to  force  in  one  direction  more  readily  than  in  another.  Struc- 
ture is  sometimes  visible  by  holding  a  mineral  between  the  eye  and  the  light ; 
but  in  general  it  is  brought  into  view  by  effecting  the  actual  separation  of 
parts  by  mechanical  means. 

The  structure  of  minerals  may  be  regular  or  irregular.  It  is  regular  when  the 
separation  takes  place  in  such  a  manner,  that  the  detached  surfaces  are  smooth 
and  even  like  the  planes  of  a  crystal ;  and  it  is  irregular,  when  the  new  surface 
does  not  possess  this  character. 

A  mineral  which  possesses  a  regular  structure  is  said  to  be  cleavahle,  or  to 
admit  of  cleavage  ;  the  surfaces  exposed  by  splitting  or  cleaving  a  mineral  are 
termed  the /aces  of  cleavage;  and  the  direction  in  which  it  may  be  cleaved  is 
called  the  direction  of  cleavage.  Sometimes  a  mineral  is  cleavable  only  in  one 
direction,  and  is  then  said  to  have  a  single  cleavage.  Others  may  be  cleaved  in 
two,  three,  four,  or  more  directions,  and  are  said  to  have  a  double,  treble,  fourfold 
cleavage,  and  so  on,  according  to  their  number. 

Minerals  that  are  cleavable  in  more  than  two  directions  may,  by  the  removal 
of  layers  parallel  to  the  planes  of  their  cleavage,  be  often  made  to  assume  regu- 
lar forms,  though  they  may  originally  have  possessed  a  different  figure.  Calca- 
reous spar,  for  example,  occurs  in  rhombohedrons  of  different  kinds,  in  hexagonal 
prisms,  in  six-sided  pyramids,  and  in  various  combinations  of  these  forms ;  but 
it  has  three  sets  of  cleavage,  which  are  so  inclined  to  each  other  as  to  constitute 
a  rhombohedron  of  invariable  dimensions,  and  into  that  form  every  crystal  of 
calcareous  spar  may  be  reduced.  Lead  glance  possesses  a  treble  cleavage,  the 
planes  of  which  are  at  right  angles  to  each  other;  and  hence  it  is  always  con- 
vertible by  cleavage  into  the  cube.  The  cleavages  of  fluor-spar  are  fourfold,  and 
in  a  direction  parallel  to  the  planes  of  the  regular  octohedron,  into  which  form 
every  cube  of  fluor-spar  may  be  converted. 

Since  the  forms  enumerated  as  belonging  to  the  octohedral  system  of  crystalli- 
zation are  possessed  of  fixed  invariable  dimensions,  it  is  obvious  that  minerals, 
or  other  crystallized  bodies  included  in  that  system,  must  often  in  their  primary 
forms  be  identical  with  each  other.  In  the  other  systems  of  crystallization  this 
identity  is  not  necessary,  because  the  dimensions  of  their  forms  are  variable. 
Thus  octohedrons  with  a  square  base  may  be  distinguished  by  the  relative 
length  of  their  axis,  some  being  flat  and  others  acute.  Rhombic  octohedrons 
may  be  distinguished  from  each  other  by  the  relative  length  of  their  axis,  and 
the  angles  of  their  base.  By  Haiiy  it  was  regarded  as  an  axiom  in  crystallo- 
graphy, that  minerals  not  belonging  to  the  octohedral  system  are  characterized 
by  their  form  ;  that  though  two  minerals  may  in  form  be  analogous,  each  for 
instance  being  a  rhombic  prism,  the  dimensions  of  those  prisms  are  different. 
Identity  of  form  in  crystals  not  included  in  the  octohedral  system  was  thought  to 
indicate  identity  of  composition.     But  in  the  year  1819  a  discovery,  extremely 


454  ON  CRYSTALLIZATION. 

important  both  to  miheralogry  and  chemistry,  was  made  by  Mitscherlich  of  TBerlin, 
relative  to  the  connection  between  the  crystalline  form  and  composition  of  bodies. 
It  appears  from  his  researches,*  that  certain  substances  have  the  property  of 
assuming  the  same  crystalline  form,  and  may  be  substituted  for  each  other  in 
combination  without  affecting  the  external  character  of  the  compound.  Thus 
minerals  having  the  crystallization  and  structure  of  garnet,  and  which  from  their 
appearance  were  believed  to  be  such,  have  been  found  on  analysis  to  contain  dif- 
ferent ingredients.  Crystals  possessed  of  the  form  and  aspect  of  alum  may  be 
made  with  sulphates  of  potassa  and  peroxide  of  iron,  without  a  particle  of  alumi- 
nous earth ;  and  a  crystal  composed  of  selenic  acid  and  soda  will  have  a  perfect 
resemblance  to  Glauber's  salts.  The  axiom  of  Hauy,  therefore,  requires  an 
essential  modification. 

To  the  new  branch  of  science  laid  open  by  the  discovery  of  Mitscherlich, 
the  term  isomorphism  (from  woj  equal,  and  (io^fpri  form)  is  applied  ;  and  those 
substances  which  assume  the  same  figure  are  said  to  be  isomorphmcs.  Of  these 
isomorphous  bodies  several  distinct  groups  have  been  described  by  Mitscherlich. 
One  of  the  most  instructive  of  these  includes  the  salts  of  arsenic  and  phosphoric 
acid.  Thus,  the  neutral  phosphate  and  biphosphate  of  soda  have  exactly  the 
same  form  as  the  arseniate  and  binarseniate  of  soda ;  phosphate  and  biphosphate 
of  ammonia  correspond  to  arseniate  and  binarseniate  of  ammonia;  and  the 
biphosphate  and  binarseniate  of  potassa  have  the  same  form.  Each  arseniate 
has  a  corresponding  phosphate,  possessed  of  the  same  form,  possessing  the 
same  number  of  eq.  of  acid,  alkali,  and  water  of  crystallization,  and  differing  in 
fact  in  nothing,  except  that  one  series  contains  arsenic  and  the  other  an  equiva- 
lent quantity  of  phosphorus.  A  second  remarkable  group  contains  the  salts  of 
sulphuric,  selenic,  chromic,  and  manganic  acids.  The  salts  of  baryta,  strontia, 
and  oxide  of  lead,  constitute  a  third  group ;  and  a  fourth  consists  of  lime,  mag- 
nesia, and  the  protoxides  of  manganese,  iron,  cobalt,  nickel,  zinc,  qnd  copper. 
A  fifth  includes  alumina,  peroxide  of  iron,  and  the  green  oxide  of  chromium; 
and  a  sixth  group  includes  the  salts  of  permanganic  and  perchloric  acids.  In 
comj)aring  together  isomorphous  bodies  of  the  same  group,  identity  of  form  is 
not  to  be  expected  unless  there  is  similarity  of  composition.  A  neutral  phos- 
phate does  not  correspond  to  a  binarseniate,  nor  a  biphosphate  to  a  neutral  arse- 
niate ;  an  anhydrous  sulphate-  is  not  comparable  to  a  hydrated  seleniate  of  the 
same  base ;  nor  is  sulphate  of  protoxide  of  iron,  with  6  eq.  of  water,  isomor- 
phous with  sulphate  of  protoxide  of  manganese  with  5  eq.  In  all  such  instances, 
if  chemical  composition  differ,  crystalline  form  is  also  different. 

The  following  table  contains  the  principal  groups  of  isomorphous  substances 
at  present  observed  by  chemists :  a  more  extended  one,  partly  theoretical,  has 
been  drawn  up  by  Professor  Johnston,  of  Durham,  in  his  Report  on  Chemistry 
to  the  British  Association  : — 


Silver Ag. 

Gold Au. 

2. 

Arsenious  Acid       .        ,         .  AS2O3 

in  its  unusual  form. 

Seaquioxide  of  Antimony       .  SbjOg. 


3. 
Alumina  ....        AljOg. 

Peroxide  of  Iron    .        .        .        FejOj. 

4. 

Sails  of 
Phosphoric  Acid      .         .         .         Pi^s- 


Arsenic  Acid  .         .        .        AS2O5. 

•  Annates  de  Ch.  et  de  Physique,  vol.  xiv.  172,  xix.  350,  and  xxiv.  264  and  355. 


ON  CRYSTALLIZATION. 


455 


5. 

Strontia 

SrO. 

Salts  of 

Lime  (in  Arragonite)     . 

.        CaO. 

Sulphuric  Acid 

. 

. 

SO3. 

Protoxide  of  Lead 

PbO. 

Selenic  Acid 

, 

. 

SeOg. 

Chromic  Acid 
Manganic  Acid 

• 

• 

CrOg. 
MnOg. 

10. 
Salts  of 
Lime     .... 

.        CaO. 

6. 

Magnesia 

.        MgO. 

Salts  of 

Protoxide  of  Iron 

FeO. 

Perchloric  Acid 

. 

. 

CIA. 

Manganese 

MnO. 

Permanganic  Acid 

. 

MngOy. 

Zinc 

ZnO. 

7. 

Nickel      . 

NiO. 

Rnlts  nf 

Cobalt 

CoO. 

OdilS   OI 

Potassa 
Ammonia  with  1 

eq.  of  water 

KO. 
H4NO. 

Copper    .        .        CuO. 

Lead  in  Plumbo-) 

1  •                  /  PbO. 
calcite              5 

Salts  of 
Soda 
Oxide  of  Silver 

8. 

•        • 

NaO. 
Ago. 

11. 

Salts  of 
Alumina       .... 
Peroxide  of  Iron 

AI2O3. 
Fe,03. 

9. 

Oxide  of  Chromium 

CrA. 

Salts  of 

Sesquioxide  of  Manganese 

MnA 

Baryta  . 

. 

. 

BaO. 

The  facts  above  mentioned  afford  indubitable  proof  that  the  form  of  crystals 
is  materially  dependent  on  their  atomic  constitution  ;  and  they  at  first  induced 
Mitscherlich  to  suspect  that  crystalline  form  is  determined  solely  by  the  number 
and  arrangement  of  atoms,  quite  independently  of  their  nature.  Subsequent 
observation,  however,  induced  him  to  abandon  this  view ;  and  his  opinion  now 
appears  to  be,  that  certain  elements,  which  are  themselves  isomorphous,  when 
combined  in  the  same  manner  with  the  same  substance,  communicate  the  same 
form.  Similarly  constituted  salts  of  arsenic  and  phosphoric  acid  yield  crystals 
of  the  same  figure,  because  the  acids,  it  is  thought,  are  themselves  isomorphous ; 
and  as  the  atomic  constitution  of  these  acids  is  similar,  each  containing  the 
same  number  of  atoms  of  oxygen  united  with  the  same  number  of  atoms  of  the 
other  ingredient,  it  is  inferred  that  phosphorus  is  isomorphous  with  arsenic.  In 
like  manner  it  is  believed  that  selenic  acid  must  be  isomorphous  with  sulphuric 
acid,  and  selenium  with  sulphur;  and  the  same  identity  of  form  is  ascribed  to 
all  those  oxides  above  enumerated,  the  salts  of  which  are  isomorphous.  The 
accuracy  of  this  ingenious  view  has  not  yet  been  put  to  the  test  of  extensive 
observation,  because  the  crystalline  forms  of  the  substances  in  question  are  for 
the  most  part  unknown.  But  our  knowledge,  so  far  as  it  goes,  is  favourable ; 
for  peroxide  of  iron  and  alumina,  the  salts  of  which  possess  the  same  form,  are 
themselves  isomorphous.  It  may  hence  be  inferred  as  probable,  that  isomorphous 
compounds  in  general  arise  from  isomorphous  elements  uniting  in  the  same 
manner  with  the  same  substance. 

Isomorphous  substances  have  often  very  close  points  of  resemblance,  quite 
independently  of  form.  Thus,  arsenic  and  phosphorus  have  the  same  odour, 
they  both  form  gaseous  compounds  with  hydrogen,  they  differ  from  nearly  all 
other  bodies  in  their  mode  of  combining  with  oxygen,  and  yet  agree  with  one 
another,  and  their  salts  are  disposed  to  combine  with  the  same  quantity  of  water 
of  crystallization.     A  similar  analogy  subsists  between  seleryum  and  sulphur, 


45(5  ON  CRYSr ALLIZATION. 

both  being  fusible,  volatile,  and  combustible  in  nearly  the  same  degree,  forming 
with  hydrogen  colourless  gases  which  are  similar  in  odour  and  in  their  chemical 
relations,  and  giving  rise  to  analogous  compounds  with  oxygen.  The  characters 
of  sulphuric  and  selenic  acids  in  particular  are  very  similar ;  and  the  salts  of 
these  acids  are  equally  allied.  Sulphate  of  soda,  for  example,  has  the  unusual 
property  of  being  less  soluble  in  water  at  212°  than  at  100°,  and  the  very  same 
peculiarity  is  observable  in  seleniate  of  soda.  The  same  intimacy  of  relatioa 
exists  between  baryta  and  strontia,  between  lime  and  magnesia,  and  between 
cobalt  and  nickel. 

Ifiomorphous  substances,  owing  doubtless  to  the  various  points  of  resemblance 
"mhich  have  just  been  traced,  crystallize  together  with  great  readiness,  and  are 
separated  from  each  other  with  difficulty.  Daubeny  has  remarked  that  a  weak 
solution  of  lime,  which  in  pure  water  would  be  instantly  indicated  by  oxalate  of 
ammonia,  is  very  sluggishly  affected  by  that  test  when  much  sulphate  of  mag- 
nesia is  present;  and  I  find  that  chloride  of  manganese  cannot  be  purified  from 
lime  by  oxalate  of  ammonia.  A  mixture  of  the  sulphates  of  the  protoxides  of 
copper  and  iron  yields  crystals  which,  have  the  same  quantity  of  water  of  crys- 
tallization (6  equivalents),  and  the  same  form,  as  green  vitriol,  though  they  may 
contain  a  large  quantity  of  copper.  The  sulphates  of  the  protoxides  of  zinc  and 
copper,  of  copper  and  magnesium,  of  copper  and  nickel,  of  zinc  and  manganese, 
and  of  magnesium  and  manganese,  crystalliza  together,  contain  6  equivalents  of 
water,  and  have  the  same  form  as  green  vitriol,  without  containing  a  particle  of 
iron.  These  mixed  salts  may  be  crystallized  over  and  over  again  without  the 
ingredients  being  separated  from  each  other,  just  as  it  is  extremely  difficult  to 
purify  alum  from  peroxide  of  iron,  with  which  alumina  is  isomorphous.  In  these 
instances  the  isomorphous  salts  do  not  occur  in  definite  proportions:  they  are  not 
chemically  united  as  double  salts,  but  merely  crystallize  together. 

The  same  intermixture  of  isomorphous  substances  which  takes  place  in  artifi- 
cial salts  is  found  to  occur  in  minerals,  and  affords  a  luminous  explanation  of  the 
great  variety  both  in  the  kind  and  proportion  of  substances  which  may  coexist  in 
a  mineral  species,  without  its  external  character  being  thereby  essentially  affected. 
Thus,  garnet  is  a  double  silicate  of  alumina  and  lime,  expressed  by  the  formula 
Al^O^-f-SiO^)  -j-  3(CaO  -+-  SiO^) ,  but  in  garnet,  as  in  alum,  the  alumina  may 
be  replaced  by  peroxide  of  iron,  yielding  the  compound  (Fe20^-f-Si02)-h(3CaO 
-+-vSiO^),  or  they  may  be  both  present  in  any  proportion,  provided  that  their  sum 
is  equivalent  to  either  singly.  So,  while  peroxide  of  iron  displaces  the  alumina, 
the  lime  may  be  exchanged  for  protoxide  of  iron ;  and  a  mineral  would  result, 
(Fe20^-f-Si02)-+-(3FeO  +  Si03),  which  contains  neither  alumina  nor  lime, 
though  it  has  still  the  form  of  garnet.  Instead  of  protoxide  of  iron,  the  lime  may 
be  replaced  by  magnesia,  protoxide  of  manganese,  or  any  other  isomorphous  base; 
or  any  equivalent  quantity  of  some  or  all  of  these  may  take  the  place  of  the  lime, 
without  the  crystallographic  character  being  destroyed.  In  like  manner  epidote 
is  a  double  silicate  of  alumina  and  lime,  expressed  by  (Al  O  -j-  SiO  )-|-(CaO' 
-f-  SiO  ) ;  and  here  again  varieties  of  epidote  are  to  be  expecU^d,  in  which  alumina 
and  lime  are  replaced  partially  or  wholly  by  an  equivalent  quantity  of  isomor- 
phous bases. 

The  discovery  of  Mitscherlich,  while  it  accounts  for  difference  of  composition 
in  the  same  mineral,  and  serves  as  a  caution  to  mineralogists  against  too  exclu- 
sive reliance  on  crystallographic  character,  is  in  several  other  respects  of  deep 
interest  to  the  chemist,     it  lends  to  lay  «pen  new  pAths  of  research  by  unfolding 


ON  CRYSTALLIZATION.  457 

analosfies  which  would  not  otherwise  have  been  perceived. — ^The  tendency  of  iso- 
morphous  bodies  to  crystallize  together  accounts  for  the  difficulty  of  purifying 
mixtures  of  isoraorphous  salts  by  crystallization. — The  same  property  sets  the 
chemist  on  his  gfuard  against  the  occurrence  of  isomorphous  substances  in  crys- 
tallized minerals.  The  native  phosphates,  for  example,  frequently  contain  arsenic 
acid,  and  conversely  the  native  arseniates  phosphoric  acid,  without  the  form  of 
the  crystals  being  thereby  affected  in  the  slightest  degree. — It  is  a  useful  guide 
in  discovering  the  atomic  constitution  of  compounds.  All  chemists  are  agreed, 
from  the  composition  of  the  oxides  of  iron,  and  from  the  compounds  which  this 
metal  forms  with  other  bodies,  that  the  peroxide  consists  of  two  atoms  of  iron 
and  three  atoms  of  oxygen ;  and  therefore  it  is  inferred  that  alumina,  which  is 
isomorphous  with  peroxide  of  iron,  has  a  similar  constitution.  The  green  oxide 
and  acid  of  chromium,  the  oxygen  of  which  is  as  1  to  2,  afford  a  still  better  illus- 
tration. As  the  chromates  and  sulphates  are  isomorphous,  it  was  inferred  that 
chromic,  like  sulphuric,  acid  was  composed  of  one  atom  of  the  combustible  to 
three  atoms  of  oxygen.  On  this  presumption  it  follows  that  the  green  oxide, 
containing  half  as  much  oxygen  as  the  acid,  must  contain  two  atoms  of  chromium 
to  three  atoms  of  oxygen;  and  agreeably  to  this  inference  it  is  found  that  the 
green  oxide  is  isomorphous  with  alumina  and  peroxide  of  iron. — ^The  phenomena 
presented  by  isomorphous  bodies  afford  a  powerful  argument  in  favour  of  the 
atomic  theory.  The  only  mode  of  satisfactorily  accounting  for  the  striking  iden- 
tity of  crystalline  form  observable,  first,  between  two  substances,  and,  secondly, 
between  all  their  compounds  which  have  an  exactly  similar  composition,  is  by 
supposing  them  to  consist  of  ultimate  particles  possessed  of  the  same  figure,  and 
arranged  in  precisely  the  same  order.  Hence  it  appears,  that,  in  accounting  for 
the  connection  between  form  and  composition,  it  is  necessary  to  employ  the  very 
same  theory,  by  which  alone  the  laws  of  chemical  union  can  be  adequately  ex- 
plained. 

It  has  been  objected  to  some  of  the  facts  adduced  in  favour  of  isomorphism, 
that  the  forms  of  substances  considered  isomorphous  are  sometimes  approximate 
rather  than  identical.  The  primary  form  of  sulphate  of  strontia  is  a  rhombic 
prism  very  similar  to  that  of  sulphate  of  baryta ;  but  on  measuring  the  inclina- 
tion of  corresponding  sides  in  each  prism,  the  difference  is  found  to  exceed  two 
(degrees  ;  and  similar  differences  are  observable  in  the  rhombohedron  of  the  car- 
bonates of  lime  and  protoxide  of  iron.  This  has  induced  Professor  Miller  of 
Cambridge  to  indicate  this  approximation  by  the  term  plesiomorphism  {rCKYjotog, 
near) ;  and  it  has  been  brought  forward  in  a  clever  essay  by  Brooke,  as  an  argu- 
ment against  the  whole  doctrine  of  isomorphism,  an  essay  which  has  received 
an  able  reply  from  the  pen  of  Whewell.  (Phil.  Mag.  and  An.  N.  S.  x.  161  and' 
401.) 

In  one  of  the  essays  above  referred  to,  Mitscherlich  observed  that  biphosphate 
df  soda  is  capable  of  yielding  two  distinct  kinds  of  crystals,  which,  though  dif- 
ferent in  form,  in  composition  appear  to  be  identical.  The  more  uncommon  of 
the  two  forms  resembled  binarseniate  of  soda ;  but  the  more  usual  form  is  quite 
dissimilar.  He  has  since  discovered,  that  sulphur  is  capable  of  yielding  two 
distinct  kinds  of  crystals.  The  crystals  of  carbonate  of  lime  in  calcareous  spar 
and  in  arragonite  belong  to  different  systems  of  crystallization,  the  former  being 
*  rhombohedral,  and  the  latter  derived  from  a  rhombic  prism.  Arsenious  acid,  and 
probably  metallic  arsenic  also,  affords  an  instance  of  the  same  kind.  It  would 
thus  seem  that  elementary  and  compound  bodies  are  capable  of  assuming  two 


458  oxy.SALTS. 

distinct  crystalline  forms.  In  the  case  of  biphosphate  of  soda  an  explanation 
may  be  derived  from  the  experiments  of  Graham  on  metaphosphoric  acid ;  but 
the  fact  that  an  elementary  substance  is  susceptible  of  assuming  diflferent  forms 
is  wholly  unexplained. 

Mitscherlich  has  also  noticed  that  the  form  of  salts  is  sometimes  changed  by 
heat,  without  losing  their  solid  state.  This  change  was  first  noticed  in  sulphate 
of  magnesia,  and  also  in  the  sulphates  of  the  protoxides  of  zinc  and  iron.  It  ap- 
pears, in  these  instances  at  least,  to  be  owing  to  decomposition  of  the  hydrous 
salt  effected  by  increased  temperature ;  a  change  of  composition  which  is  accom- 
panied with  a  new  arrangement  in  the  molecules  of  the  compound. 


SECTION  I. 


CLASS  OF  SALTS,  ORDER  L 

OXY.SALTS. 

This  order  of  salts  includes  no  compound  the  acid  or  base  of  which  does  not 
contain  oxygen.  With  the  apparent  exception  of  the  ammoniacal  salts,  both  the 
acid  and  "base  of  the  salts  described  in  this  section  are  oxidized  bodies.  As  each 
acid,  with  few  exceptions,  is  capable  of  uniting  with  every  alkaline  base,  and 
frequently  in  two  or  more  proportions,  it  is  manifest  that  the  salts  must  consti- 
tute a  very  numerous  class  of  bodies.  It  is  necessary,  on  this  account  to  facili- 
tate the  study  of  them  as  much  as  possible  by  classification.  They  may  be  con- 
veniently arranged  by  placing  together  those  salts  which  contain  either  the  same 
salifiable  base  or  the  same  acid.  It  is  not  very  material  which  principle  of  ar- 
rangement is  adopted  ;  but  I  give  the  preference  to  the  latter,  because,  in  de- 
scribing the  individual  oxides,  I  have  already  mentioned  the  characteristic 
features  of  their  salts,  and  have  thus  anticipated  the  chief  advantage  that  arises 
from  the  former  mode  of  classification.  I  shall  therefore  divide  the  salts  into 
families,  placing  together  those  saline  combinations  which  consist  of  the  same 
acid  united  with  different  salifiable  bases.  The  salts  of  each  family,  in  conse- 
quence of  containing  the  same  acid,  possess  certain  characters  in  common  by 
which  they  may  all  be  distinguished;  and,  indeed,  the  description  of  many  salts, 
to  which  no  particular  interest  is  attached,  is  sufficiently  comprehended  in  that 
of  its  family,  and  may  therefore  be  omitted. 

All  the  powerful  alkaline  bases,  excepting  ammonia,  are  the  protoxides  of  an 
electro-positive  metal,  such  as  potassium,  barium,  or  iron  ;  so  that  if  M  represent 
an  eq.  of  any  one  of  those  metals,  M  -f-  O  or  MO  is  the  strongest  alkaline  base, 
and  often  the  only  one,  which  that  metal  can  form.  A  single  eq.  of  a  monobasic 
acid  neutralizes  MO,  forming  with  it  a  neutVal  salt.  Thus,  indicating  an  equiva- 
lent of  sulphuric  and  nitric  acid  by  the  signs  SO^and  NO^,  all  the  neutral  snlphates 
and  nitrates  of  protoxides  are  indicated  by  MO-f-SO^and  MO-fNO^.  There  is, 
therefore,  in  the  neutral  protosalts  of  each  family,  a  constant  ratio  in  the  oxygen  of 
the  base  and  acid,  resulting  from  the  composition  of  each  acid,  that  ratio  for  the  sul- 


OXY-SALTS.  iS^ 

pbates  being  as  1  to  3,  and  for  nitrates  as  I  to  5.  If  the  metal  M  of  a  neutral 
sulphate  pass  into  a  higher  grade  of  oxidation,  becoming  a  binoxide  MO^,  then 
will  that  binoxide  be  disposed  to  unite  with  2  eq.  of  acid,  and  form  a  bisalt, 
MO2+  280^,  in  which  the  oxygen  of  base  and  acid  is  still  as  1  to  3 ;  and  if  the 
metal  yield  a  sesquioxide,  M  O  ,  then  if  sufficient  acid  be  supplied,  the  resulting 
salt  will  consist  of  MO  -f  3S0^,  the  ratio  of  1  to  3  being  preserved.  This 
curious  law  relative  to  oxy-salts,  which  is  very  general,  was  first  noticed  by  Gay- 
Lussac  (Memoires  d'Arcueil,  ii.)  ;  and  Berzelius  has  found  it  to  hold  in  earthy 
minerals,  and  employed  it  as  a  guide  in  studying  their  composition. 

The  combination  of  salts  with  one  another  gives  rise  to  compounds  which  were 
formerly  called  triple  salts;  but  as  the  term  double  salt,  proposed  by  Berzelius, 
gives  a  more  correct  idea  of  their  nature  and  constitution,  it  will  always  be  em- 
ployed by  preference.  These  salts  may  be  composed  of  one  acid  and  two  bases, 
of  two  acids  and  one  base,  and  of  two  different  acids  and  two  different  bases. 
Most  of  the  double  salts  hitherto  examined  consist  of  the  same  acid  and  two  dif- 
ferent bases. 

The  difference  in  the  constitution  of  ammonia  and  that  of  all  other  bases  capa- 
ble of  uniting  with  ox-acids,  gives  great  interest  to  its  salts.  In  another  place, 
the  probable  existence  of  a  compound  radical  formed  of  1  eq.  of  nitrogen  and  4 
of  hydrogen,  and  called  by  Berzelius  ammonium,  was  pointed  out.  The  oxide' 
of  this  radical,  which  has  not  yet  been  obtained  in  an  uncombined  state,  he  con- 
siders as  the  basis  of  the  oxy-salts  of  ammonia.  This  view  is  not  supported  by 
analogy  alone,  but  is  based  on  the  remarkable  fact,  that  in  all  the  neutral  salts 
of  ammonia  the  quantity  of  water  necessary  to  convert  the  ammonia  into  oxide 
of  ammonium  is  always  present,  nor  can  it  be  removed  without  the  total  decom- 
position of  the  salt.  H.  Rose  has  indeed  succeeded  in  obtaining  anhydrous  com- 
pounds of  ammonia  with  the  ox-acids;  but  he  has  at  the  same  time  shown  that 
they  cannot  be  considered  as  salts,  for  although  containing  the  elements  for 
forming  an  anhydrous  and  neutral  salt  of  ammonia,  and  produced  by  direct 
combination,  neither  the  acid  nor  the  alkali  is  present  in  the  compound.  This 
he  has  proved  particularly  in  the  substance  formed  by  the  union  of  anhydrous- 
sulphuric  acid  with  ammonia  (An.  de  Ch.  et  Ph.  Ixii.  389).  Strong  evidence  in 
Its  favour  is  likewise  obtained  from  the  views  of  isomorphism.  It  has  been 
proved  by  Mitscherlich  that  in  all  the  crystallized  salts  of  potassa,  whether 
simple  or  double,  the  potassa  may  be  replaced  either  partially  or  completely  by 
an  equivalent  quantity  of  protohydrate  of  ammonia  without  any  change  in  the; 
form  of  the  crystal.  Ammonia  with  an  eq.  of  water  is  therefore  isomorphous 
with  potassa.  But  all  isomorphous  substances,  with  this  exception,  have  the 
same  chemical  constitution,  and  it  is  incompatible  with  the  theory  of  isomorphism 
to  suppose  one  alkali  to  be  isomorphous  with  the  hydrate  of  another.  But  that 
the  oxide  of  a  compound  radical  should  be  isomorphous  with  the  oxide  of  a, 
simple  metal  is  consistent  with — nay,  might  be  expected  from  their  known  analo^ 
gies. 

Another  view  of  the  constitution  of  the  oxy-salts  of  ammonia  has  recently  been 
proposed  by  Graham.  He  supposes  ammonia  not  to  be  a  base,  but  to  be  one  of 
a  class  of  bodies  which  he  calls  basic  adjuncts ;  a  term  used  to  denote  a  substance 
which,  without  being  a  base,  is  capable  of  entering  into  the  constitution  of  a  salt 
by  attaching  itself  to  other  bases.  Thus,  the  oxy-salts  of  ammonia  he  conceives 
to  be  salts  of  water,  to  the  base  of  which  ammonia  is  added  as  an  adjunct.  It 
is  scarcely  necessary  to  remark,  that  this  view  is  not  only  inconsistent  with  the 


4&k  SULPHATES. 

theory  of  isomorphism,  but  that  the  existence  of  adjunct  bases  is  hypothetical, 
and  arises  from  an  endeavour  to  support  another  hypothesis,  that  all  salts  are 
neutral  in  composition. 

SULPHATES. 

The  salts  of  sulphuric  acid  in  solution  may  be  detected  by  chloride  of  barium. 
A  white  precipitate,  sulphate  of  baryta,  invariably  subsides,  which  is  insoluble 
in  acids  and  alkalies;  a  character  by  which  the  presence  of  sulphuric  acid, 
whether  free  or  combined,  may  always  be  recognized.  An  insoluble  sulphate, 
such  as  sulphate  of  baryta  or  strontia,  may  be  detected  by  mixing  it,  in  fine 
powder,  with  three  times  its  weight  of  carbonate  of  potassa  or  soda,  and  exposing 
the  mixture  in  a  platinum  crucible  for  half  an  hour  to  a  red  heat.  Double  de- 
composition ensues;  and  on  digesting  the  residue  in  water,  filtering  the  solution, 
Deutrdlizing  the  free  alkali  by  pure  hydrochloric,  nitric,  or  acetic  acid,  and  adding 
chloride  of  barium,  the  insoluble  sulphate  of  that  base  is  precipitated. 

Several  sulphates  exist  in  nature,  but  the  only  ones  which  are  abundant  are 
the  sulphates  of  lime  and  baryta.  All  of  them  may  be  formed  by  the  action  of 
sulphuric  acid  on  the  metals  themselves,  on  the  metallic  oxides  or  their  carbon- 
ates, or  by  way  of  double  decomposition. 

The  solubility  of  the  sulphates  is  very  variable.  There  are  six  only  which 
may  be  regarded  as  really  insoluble;  namely,  the  sulphate  of  baryta,  and  of  the 
oxides  of  tin,  antimony,  bismuth,  lead,  and  mercury.  The  sparingly  soluble 
sulphates  are  those  of  strontia,  lime,  zirconia,  yttria,  and  oxide  of  silver.  All  the 
others  are  soluble  in  water. 

All  the  sulphates,  those  of  potassa,  soda,  lithia,  baryta,  strontia,  and  lime  ex- 
cepted, are  decomposed  by  a  white  heat.  One  part  of  the  sulphuric  acid  of  the 
decomposed  sulphate  escapes  unchanged,  and  another  portion  is  resolved  into  sul- 
phurous acid  and  oxygen.  Those  which  are  easily  decomposed  by  heat,  such  as 
sulphate  of  oxide  of  iron,  yield  the  largest  quantity  of  undecomposed  sulphuric 
acid. 

When  a  sulphate,  mixed  with  carbonaceous  matter,  is  ignited,  the  oxygen 
both  of  the  acid  and  of  the  oxide  unites  with  carbon,  carbonic  acid  is  disengaged, 
and  a  metallic  sulphuret  remains.  A  similar  change  is  produced  by  hydrogen 
gas  at  a  red  heat,  with  formation  of  water,  and  frequently  of  some  hydrosul- 
phuric  acid.  In  some  instances  the  hydrogen  entirely  deprives  the  metal  of  its 
sulphur. 

The  composition  of  neutral  protosulphates  is  expressed,  as  above  stated,  by  the 
formula  MO  +  SO^.  Consequently  the  acid  contains  three  times  as  much  oxy- 
gen as  the  base  ;  and  if  both  were  deprived  of  their  oxygen,  a  metallic  protosul- 
phuret  would  result,  as  indicated  by  the  formula  M  -\-  S. 

In  accordance  with  the  views  of  Graham  already  given,  the  sulphates  may  be 
divided  into  three  classes  ; — the  first  consisting  of  the  anhydrous  sulphates,  being 
such  as  can  exist  without  the  eq.  of  constitutional  water ;  the  second,  those  in 
which  the  constitutional  water  forms  an  essential  part ;  and  the  third  composed 
of  the  double  salts,  which  he  considers  as  produced  from  ihe  second  by  the  eq.  of 
constitutional  water  being  replaced  by  an  eq.  of  ^  sulphate  of  the  first  class.  If 
dilute  sulphuric  acid  be  exposed  in  an  open  dish  to  a  temperature  not  exceeding 
380°,  the  evaporation  proceeds  without  the  slightest  loss  of  acid  until  the  sp.  gr. 
is  raised  to  1'78,  when  it  ceases  entirely,  and  there  remains  a  definite  compound 
of  1  eq.  of  sulphuric  acid  and  2  eq.  of  water.   One  of  these  he  considers  as  basic. 


SULPHATES. 


461' 


the  other  as  constitutional  water,  the  acid  of  the  mentioned  strength  being  a  salt 
the  constitution  of  which  is  represented  by  the  formula  HO,  SO  ,  HO.  From^ 
it  any  one  of  the  three  classes  of  sulphates  may  be  formed,  the  eq.  of  basic  water 
being  readily  replaced  by  any  stronger  base,  while  the  eq.  of  constitutional 
water  can  only  be  removed  by  a  neutral  salt  producing  the  double  salts,  among 
which  the  bisulphates  must  also  be  included.  There  are,  however,  exceptions 
to  the  last  observation,  as  Graham  has  remarked  that  magnesia  and  its  class  of 
isomorphous  oxides  are  capable  of  acting  the  part  of  constitutional  water.  Al- 
though it  would  be  highly  advantageous  to  treat  of  the  sulphates  under  the  three 
classes  above  mentioned,  it  cannot  yet  be  attempted;  for  although  the  constitu- 
tional water  of  several  of  them  has  been  determined  by  Graham  in  his  valuable 
essay  already  quoted,  many  of  them  have  not  yet  been  examined  in  reference  to 
this  point.  The  following  table  represents  the  constitution  of  the  more  important, 
both  in  their  amorphous  and  crystallized  state : — 

Base.  Acid. 

47-15     1  eq.+  40-1 
94-3      2eq.-[-120-3 

1  eq.  of  water 

1  eq.-|-  80-2 


Names. 
Sulphate  of  Potassa 
Sesquisulph.  do. 

Do.  in  crystals  with  9  or 

Bisulph.  Potassa  .         .  47-15 

Do.  with  9  or  1  eq.  of  water 

Sulphate  of  Soda  .        .  31-3 

Do.  in  crystals  with  90  or  ] 

Bisulph.  Soda        .        .        .  31-3 

Do.  in  crystals  with  36  or 

Sulphate  of  Lithia         .         .  18 

Do.  in  crystals  with  9  or 

Sulph.  of  ox,  of  Ammonium  26-15 

Do.  in  crystals  with  9  or 

■  Sulphate  of  Baryta     .         .  76-7 

Do.         Strontia  .  51*8 

Do.        Lime      .        .  28-5 

Do.  as  Gypsum  with  18  or 

Sulphate  of  Magnesia        .  20*7 

Do.  in  crystals  with  54  or 

Sulphate  of  Alumina  •  51-4 

Do.  in  crystals  with  81  or 

Tersulph.  Alumina    .        .  51-4 


1  eq.-|-  40-1 

0  eq.  of  water  =:l6l-4 

1  eq.+  80  2    2  eq.=115-5 


Equiv.        FormulsB. 

1  eq.=  87-25     KOfSOg. 
3  eq.=214  6    2KO-f-3S03. 

=223-6 

2  eq.=127-35 

=106-35 
1  eq.=  71-4 


4  eq.  of  water 
1  eq.-{-  40-1 
1  eq.  of  water 
1  eq.-j-  40-1 
1  eq.  of  water 
1  eq.-j-  40- 1 
1  eq.4  40-1 

1  eq.-f-   40-1 

2  eq.  of  water 
1  eq.-f-  40-1 
-|-9  aq.  1  eq. 
6  eq.  of  water 
1  eq.-4-  40-1 
9  eq.  of  water 
1  eq.-j- 120-3 


=147-5 
1  eq.=  58-1 

=  67-1 
1  eq.=  66-25 

=  75-25 
1  eq.=ll6-8 
1  eq.=  91-9 
1  eq.^ss  68-6 

=  86-6 
1  eq. 


Do. 


in  crystals  with  162  or  18  eq.  of  water 


Sulph.  protox.  Manganese  35-7 

Do.  in  crystals  with    36  or 

Sulph.  protox.  Iron    .         .        36 

Do.  in  crystals  with     45  or 

Tersulph.  perox.  Iron        .        80 
Disulph.        do.  .        .       160 

Do.  as  a  hydrate  with  54  or 

Sulph.  protox.  Zinc  .        40-3 

Do.  in  crystals  with    54  or 

Sulph.  protox.  Nickel         .        37  5 


Do. 


in  crystals  ^yitb     54  or 


=123-8 
1  eq.=  91-5 
=172-5 
3eq.=l71-7 
=333-7 
1  eq.4-  40-1  1  eq. 
"1-9  aq.   1  eq.  =  848 

4  eq.  of  water  =120-8 
1  eq.-J-   401     1  eq. 

-f-9  aq.  1  eq.  =  85-1 

5  eq.  of  water  s=130-l 

1  eq.+  120-3     3  eq.=210-3 

2  eq.-f-   40-1     1  eq.=200-l 

6  eq.  of  water  =254-1 
1  eq.-j-  40-1      1  eq. 

-f-9  aq.  1  eq.  =  894 

6  eq.  of  water  =143*4 

1  eq.-+-  40-1      1  eq. 
-|-9  aq.  1  eq.  =  866 

6  eq.  of  water  =140-6 


KO-f-2S03. 

NaOfSOg. 

NaO-}-2S03. 

LO+SO3. 

H4Not303. 

BaO+SOg. 
SrO-j-SOg. 
CaO-f  SO3. 

MgO+S03HO. 

AI2O3+SO3. 

AI2O3-J-3SO3. 

MnOfSOgHO. 

FeO-f-SOgHO. 

Fe203-f-3S03. 
2Fe03fSO». 

ZnO+SOgHO. 

NiO-J-S03HO. 


SULPHATES. 


Names. 
Sulph.  protox.  Cobalt 


37-5      1 


Do.  In  crystals  with     49  or 

Tersulph.  Ox.  Chromium  80 

SuJp.  protox.  Copper  .        39-6 

Do.  in  crystals  with     37  or 

Disulphate         do.      .        .        79-2 
Sulp.  protox.  Mercury        .       210 
Subeulp.  perox.  do.  .       S72 

Bisulp.        do.  .        .      218 

Sulp.  ox.  Silver  .         .       116 


Acid. 
-  40-1     1  eq. 
■fB  aq.  1  eq. 
5  eq.  of  water 
1  eq.+120-3 

1  eq.-f  40-1 
-f-9  aq.  1  eq. 
4  eq.  of  water 

2  eq.-|-  401 
1  eq.-f-  40-1 
4eq.-f  120-3 
1  eq.-f  SO-2 
1  eq.4-  40- 1 


3  eq 
1  eq 


1  eq 
1  eq 
3  eq 

2  eq- 
1  eq. 


Equiv.        FormuliE. 
f 
=  86-6      C0CH-SO3HO. 
=131  6 
.=200-3      Cr208-|-3S08. 


=  88-7 
=r24-7 
=119-3 
=250-1 
=992-3 
=2982 
=156-1 


CuOfSOaHO. 

2CUO+SO3 
Hg()+S('3. 

4Hg02-|-3S(V 
Hg()2-|-2S()3. 
AgO-f-SO^. 


DOUBLE  SULPHATES. 


Sulphate   of  Soda    C  Sulphate  of  Soda 
and  Lime  (         do.         Lime 


60. 


Sulp.  of  Potassa  &   (  Sulph.  Potassa  87 

Magnesia  (     do.     Magnesia         60' 

Do,        with  54  or  6  eq.  of  water 
Sulp.   ox.   of  Am-    (  Sulp.  ox.  Ammonium  67 
monium  &  Mag.    (     do         Magnesia 
Do.         with  54  or  6  eq.  of  water 
Sulp.  of  Soda  and   |  Sulph.  Soda 
Magnesia  (     do.    Magnesia 

Do.         with  54  or  6  eq.  of  water 
Sulp.  of  Potassa  &   (  Sulph.  Potassa 
Alumina  (  Tersulph.  Alumina 

Do.        with  216  or  24  eq.  of  water 
Sulph.  of  Soda  &   J  Sulph.  Soda 
Alumina  (  Tersulph 

Do.        with  234  or  26  eq.  of  water     . 
Sulph.  ox.  Am.  &   (  Sulp.  ox.  Ammonium  57 
Alumina  (  Tersulph.  Alumina  171 

Do.        with  216  or  24  eq.  of  water     . 
Sulph.   Potassa  &    (  Sulph.  Potassa  87 

protox.  Mang.       (     do.  ox.  Mingan.       75 
Do.        with  54  or  6  eq.  of  water 
Sulph.  ox.  Am.  &   (  Sulph.  Ammwium      57 
protox.  Mang.       (     do.  ox.  Mang.  75 

Do.        with  54  or  6  eq.  of  water 


4  1  eq. 
6  1  eq. 
25  1  eq. 
8     1  eq. 


1  = 
1  = 


1  eq. 
1  eq. 


71 
Alumina  171 


4     1  eq 

8     1  eq 

25  1  eq. 
7     1  eq. 


4     1  eq. 
7     1  eq. 


25  1  eq. 

7  1  eq. 

25  1  eq. 

8  1  eq. 

25  1  eq. 
8     1  eq. 


:}= 


140-0    NaOjSOg  +  CaO.SOg. 

148.05  KO,S03-|-«MgO,S03. 

202-06 

127-05  H4NO,S03  +  MgO,S03. 

181-05 

132-2    NaOjSOg  -+-  MgOjSOg. 

186-2 


H 
}= 


474- P5 

243-1    NaOjSOa  f  AlgOajSSOa. 
477-1 

:  228-95  H4NO,S03-4-Al203,3S03. 
444-95 

163-05  K0,S03  +  MnO.SOj. 
217-05 

133-05  H4NO,S03  -f-  MnO,S03. 
196-06 


The  protoxides  of  iron,  zinc,  nickel,  and  cobalt  yield  with  potassa  and  ammo- 
nia double  salts  exactly  agreeing  in  form  and  composition  with  the  preceding 
double  salts  of  magnesia  and  oxide  of  manganese. 

Sulphate  of  Potassa. — This  salt  is  easily  prepared  artificially  by  neutralizing 
carbonate  of  potassa  with  sulphuric  acid;  and  it  is  procured  abundantly  by  neu- 
tralizing with  carbonate  of  potassa  the  residue  of  the  operation  for  preparing 
nitric  acid.  Its  taste  is  saline  and  bitter.  It  crystallizes  in  forms  belonging  to 
the  right  prismatic  system,  and  its  general  .form  closely  resembles  the  regular 
hexagonal  prism,  terminated  by  pyramids  with  six  sides  ;  the  size  of  which  is 
said  to  be  much  increased  by  the  presence  of  a  little  carbonate  of  potassa. 
According  to  Mitschcrlich  it  is  isomorphous  with  chromate  and  seleniate  of 
potassa.     (Pog.  Annalen,  xviii.  168.)    The  crystals  contain  no  water  of  crystal- 


SULPHATES.  y 


lization,  and  suffer  no  change  by  exposure  to  the  air.  They  decrepitate  when 
heated,  and  enter  into  fusion  at  a  red  heat.  They  require  16  times  their  weight 
of  water  at  60°,  and  five  of  boiling  water  for  solution. 

Bisnlphate  of  potassa  is  easily  formed  by  exposing  the  neutral  sulphate  with 
half  iis  weight  of  strong  sulphuric  acid  to  a  heat  just  below  redness,  in  a  plati- 
num crucible,  until  acid  fumes  cease  to  escape.  It  is  obtained  in  crystals  from 
a  concentrated  solution  at  high  temperatures,  as  in  the  cold  the  neutral  sulphates 
are  formed.  The  form  is  a  right  rhombic  prism,  which  is  in  general  so  flattened 
as  to  be  tabular.  According  to  Graham  they  contain  1  eq.  of  water,  which  he 
considers  to  be  basic ;  the  bisulphate  being  a  double  sulphate  of  water  and 
potassa.  The  anhydrous  bisulphate  has  been  prepared  by  Rose.  It  has  a  strong 
sour  taste,  and  reddens  litmus  paper.  It  is  much  more  soluble  than  the  neutral 
sulphate,  requiring  for  solution  only  twice  its  weight  of  water  at  60°,  and  less 
than  an  equal  weight  at  212°  F.  It  is  resolved  by  heat  into  sulphuric  acid  and 
the  neutral  sulphate. 

Phillips  has  described  a  sesquisulphate,  obtained  in  the  form  of  acicular  crys- 
tals like  asbestos,  from  the  residue  of  the  process  for  making  nitric  acid.  The 
conditions  for  insuring  its  production  have  not  been  determined.  (Phil.  Mag. 
and  Annals,  ii.  421.) 

Sulphate  of  Soda. — This  compound,  commonly  called  Glauber'' s  salt,  is  occa- 
sionally met  with  on  the  surface  of  the  earth,  and  is  frequently  contained  in 
mineral  springs.  It  may  be  made  by  the  direct  action  of  sulphuric  acid  on  car- 
bonate of  soda;  and  it  is  procured  in  large  quantity  as  a  residue  in  the  processes 
for  forming  hydrochloric  acid  and  chlorine. 

Sulphate  of  soda  has  a  cooling,  saline,  and  bitter  taste.  It  commonly  yields 
forms  belonging  to  the  right  prismatic  system,  and  containing  10  eq.  of  water  of 
crystallization,  the  whole  of  which  is  rapidly  lost  by  efflorescence  on  exposure 
to  the  air.  When  heated  they  readily  undergo  the  watery  fusion.  At  32°,  100 
parts  of  water  dissolve  12  parts  of  the  crystals,  48  parts  at  64*5°,  100  parts  at 
77°,  270  at  89-5°,  and  323  at  91-5°.  On  increasing  the  heat  beyond  this  point, 
a  portion  of  the  salt  is  deposited,  being  less  soluble  than  at  91*5°.  (Gay-Lus- 
sac.)  If  a  solution  saturated  at  91*5°  is  evaporated  at  a  higher  temperature,  the 
salt  is  deposited  in  opaque  anhydrous  prisms,  unconnected,  but  of  the  same  sys- 
tem as  the  hydrous  crystals.     Its  sp.  gr.  in  this  state  is  2*462.     (Haidinger.) 

Bisulphate  uf  Soda  may  be  formed  in  the  same  manner  as  the  analogous  salt 
of  potassa. 

Sulphate  of  Lithia. — This  salt  is  very  soluble  in  water,  fuses  by  heat  more 
readily  than  the  sulphates  of  the  other  alkalies,  and  crystallizes  in  flat  prisms, 
which  resemble  sulphate  of  soda  in  appearance,  but  do  not  effloresce  on  exposure 
to  the  air.     Its  taste  is  saline  without  being  bitter. 

Sulphate  of  Oxide  of  Ammonium. — This  salt  is  easily  prepared  by  neutralizing 
carbonate  of  ox.  of  ammonium  with  dilute  sulphuric  acid ;  and  it  is  contained 
in  considerable  quantity  in  the  soot  from  coal.  It  crystallizes  in  long  flattened 
six-sided  prisms.  It  dissolves  in  two  parts  of  water  at  60°,  and  in  an  equdl 
weight  of  boiling  water.  In  a  warm  dry  air  it  effloresces  and  loses  1  eq,  of  water. 
When  sharply  heated,  it  fuses,  and  is  decomposed,  yielding  nitrogen  gas,  water, 
and  sulphite  of  ox.  of  ammonium. 

The  anhydrous  compound  was  formed  by  Rose  by  conducting  dry  ammoniacal 
gas  into  a  glass  vessel  coated  by  a  thin  film  of  perfectly  anhydrous  sulphuric 
acid.     When  no  excess  of  acid  is  present,  it  undergoes  no  change  in  the  air,  and 


464  SULPHATES. 

is  soluble  without  change  in  water,  from  which  it  crystallizes  irregularly,  but  in 
forms  different  from  those  of  the  common  sulphate.  It  is  remarkable  that  the 
sulphuric  acid  is  only  partially  precipitated  by  chloride  of  barium  in  the  cold,  and 
no  precipitate  whatever  is  produced  by  chlorides  of  strontium  or  lime  until  heat 
is  applied,  and  even  then  the  action  is  imperfect.  Nor,  on  the  other  hand,  can 
the  ammonia  be  separated  by  the  chloride  of  platinum.  From  this  it  follows 
that  neither  the  sulphuric  acid  nor  the  ammonia  can  be  present  in  the  solution, 
although  their  elements  are  present  in  equivalent  proportions.  It  is  not  impro- 
bable it  may  be  an  amide,  and  formed  of  H^NSO^-f-  HO. 

Sulphate  of  Baryta. — Native  sulphate  of  baryta,  commonly  called  heavy  spar^ 
occurs  abundantly,  chiefly  massive,  but  sometimes  in  anhydrous  crystals,  the 
form  of  which  is  variable,  being  sometimes  prismatic  and  sometimes  tabular, 
deducible  from  a  right  rhombic  prism.  Its  density  is  about  4*4.  It  is  easily 
formed  artificially  by  double  decomposition.  This  salt  bears  an  intense  heat 
without  fusing  or  undergoing  any  other  change,  and  is  one  of  the  most  insoluble 
substances  with  which  chemists  are  acquainted.  It  is  sparingly  dissolved  by  hot 
and  concentrated  sulphuric  acid,  but  is  precipitated  by  the  addition  of  water. 

Sulphate  of  Strontia. — This  salt,  the  ce/es/ine  of  mineralogists,  is  less  abundant 
than  heavy  spar.  It  occurs  in  anhydrous  prismatic  crystals  of  peculiar  beauty 
in  Sicily,  and  is  isomorphous  with  the  sulphate  of  baryta.  Its  density  is  3*858. 
As  obtained  by  the  way  of  double  decomposition,  it  is  a  white  heavy  powder, 
very  similar  to  sulphate  of  baryta,  and  requires  about  3840  times  its  weight  of 
boiling  water  for  solution. 

Sulphate  of  Lime, — This  salt  is  easily  formed  by  mixing  in  solution  a  salt  of 
lime  with  any  soluble  sulphate.  It  occurs  abundantly  as  a  natural  production. 
The  mineral  called  anhydrite  is  anhydrous-sulphate  of  lime;  and  all  the  varieties 
of  gypsum  are  composed  of  the  same  salts,  united  with  water.  The  pure  crys- 
tallized specimens  of  gypsum  are  sometimes  called  selenite ,-  and  the  white  com- 
pact variety  is  employed  in  statuary  under  the  name  of  alabaster.  The  crystals 
of  anhydrite  belong  to  the  right  prismatic  system,  and  are  isomorphous  with  the 
sulphates  of  baryta  and  strontia,  while  the  forms  of  gypsum  are  oblique  pris- 
matic. The  latter,  which  are  by  far  the  more  general,  are  readily  recognized  by 
the  perfect  cleavage  plane  which  truncates  the  acute  angle  of  the  prism.  They 
contain  2  eq.  of  water,  one  only  of  which  is  considered  by  Graham  to  be  water 
of  crystallization,  the  other  being  constitutional.  The  former  is  readily  lost  by 
exposing  pounded  gypsum  to  a  temperature  of  212°  in  vacuo,  and  the  whole 
water  is  expelled  by  a  temperature  below  300°.  Thus  dried,  it  constitutes  the 
well-known  plaster  of  Parig,  which,  when  mixed  with  a  proper  proportion  of 
water,  rapidly  becomes  dry  and  solid,  owing  to  the  reproduction  of  gypsum.  It 
is  remarkable,  however,  that  gypsum  which  has  lost  only  I  eq.  of  water,  as  well 
as  that  which  is  dried  by  a  heat  exceeding  270°,  will  not  act  in  a  similar  manner. 
In  the  latter  case,  the  powder  is  a  perfect  anhydrite.     (Phil.  Mag.  vi.  417.) 

Sulphate  of  lime  has  hardly  any  taste.  It  is  considerably  more  soluble  than 
the  sulphate  of  baryta  or  strontia,  requiring  for  solution  about  500  parts  of  cold, 
and  450  of  boiling  water.  Owing  to  this  circumstance,  and  to  its  exisiitig  so 
abundantly  in  the  earth,  it  is  frequently  contained  in  spring  water,  to  which  it 
communicates  the  property  called  hardness.  When  freely  precipitated,  it  may 
be  dissolved  completely  by  dilute  nitric  acid.  It  is  commonly  believed  to  sus- 
tain a  white  heat  without  decomposition  ;  but  Thomson  states  that  it  parts  with 
some  of  its  acid  when  heated  to  redness. 


SULPHATES.  465 

Sulphate  of  Magnesia, — This  sulphate,  generally  known  by  the  name  of  Epsom 
salt,  is  frequently  contained  in  mineral  springs.  It  may  be  made  directly,  by 
neutralizing  dilute  sulphuric  acid  with  carbonate  of  magnesia  ;  but  it  is  procured 
for  the  purposes  of  commerce  by  the  action  of  dilute  sulphuric  acid  on  magnesian 
limestone,  native  carbonate  of  lime  and  magnesia. 

Sulphate  of  magnesia  has  a  saline,  bitter,  and  nauseous  taste.  It  crystallizes 
readily  in  small  quadrangular  prisms,  which  effloresce  slightly  in  a  dry  air.  It 
is  obtained  also  in  larger  crystals,  the  principal  form  in  which  is  a  right  rhombic 
prism,  the  angles  of  which  are  90°  30'  and  89°  30'. — (Brooke.)  Its  crystals  are 
soluble  in  an  equal  weight  of  water  at  60°,  and  in  three-fourths  of  their  weight 
of  boiling  water.  They  undergo  the  watery  fusion  when  heated  ;  and  the  anhy- 
drous salt  is  deprived  of  a  portion  of  its  acid  at  a  white  heat.  Dried  at  212°  it 
retains  2  eq.  of  water;  but  one  of  these  is  expelled  at  270°,  while  the  other  is 
retained  till  the  temperature  rises  to  460°. 

Sulphates  of  Alumina. — The  tersulphate  is  prepared  by  saturating  dilute  sul- 
phuric acid  with  hydrated  alumina,  and  evaporating.  It  crystallizes  with  diffi- 
culty in  thin  flexible  plates  of  a  pearly  lustre,  which  contain  18  eq.  of  water,  and 
require  twice  their  weight  of  water  for  solution.  Berzelius  says  it  occurs  native 
at  Milo  in  the  Grecian  Archipelago.     It  has  an  acid  reaction. 

The  hydrated  disulphate  is  known  to  mineralogists  under  the  name  of  alti- 
minite,  which  occurs  at  Halle,  on  the  river  Saal,  and  at  Newhaven  in  Sussex  ; 
and  Berzelius  says  the  same  compound  falls  when  ammonia  is  added  to  a  solu- 
tion of  the  tersulphate.  It  is  insoluble  in  water,  and  by  heat  is  first  rendered 
anhydrous,  and  then  its  acid  is  expelled,  leaving  pure  alumina.  The  composition 
given  in  the  table  is  from  an  analysis  of  aluminite  from  both  its  localities  by 
Stromeyer. 

Sulphate  of  Protoxide  of  Manganese. — This  salt  is  best  obtained  by  dissolving 
pure  carbonate  of  manganese  in  moderately  dilute  sulphuric  acid,  and  setting  the 
solution  aside  to  crystallize  by  spontaneous  evaporation.  The  crystals  are  trans- 
parent and  of  a  slight  rose  tint,  in  taste  resemble  Glauber's  salt,  and  belong  to 
the  doubly  oblique  prismatic  system.  It  is  insoluble  in  alcohol,  but  dissolves  in 
twice  and  a  half  its  weight  of  cold  water.  If  the  heat  is  gradually  applied,  it 
may  be  increased  to  redness  without  expelling  any  of  the  acid. 

Sulphates  of  the  Oxides  of  Iron. — Sulphate  of  the  protoxide,  commonly  called 
green  vitriol^  is  formed  by  the  action  of  dilute  sulphuric  acid  on  metallic  iron,  or 
by  exposing  protosulphurel  of  iron  in  fragments  to  the  combined  agency  of  air 
and  moisture.  The  salt  has  a  strong  styptic,  inky  taste.  When  perfectly  pure 
it  does  not  change  vegetable  blue  colours,  though  generally  stated  to  do  so,  the 
reddening  effect  being  only  produced  when  some  of  the  iron  passes  into  a  higher 
state  of  oxidation,  as  has  been  shown  by  Bonsdorff  (Pogg.  An.  xxxi.  81).  He 
finds  that  the  oxidation,  which  occurs  with  extreme  facility  in  a  perfectly  neutral 
solution,  is  completely  prevented  by  a  few  drops  of  sulphuric  acid  in  excess, 
and  the  resulting  crystals  have  a  distinctly  blue  colour.  The  common  green 
tint  is  consequently  a  delicate  test  of  the  presence  of  peroxide  of  iron.  The 
crystals  belong  to  the  oblique  prismatic  system,  and  contain  6  eq.  of  water,  one 
of  which  is  retained,  according  to  Graham,  till  the  temperature  rises  to  535°. 
By  operating  carefully  it  may  be  rendered  anhydrous  without  the  loss  of  acid. 
It  is  soluble  in  two  parts  of  cold  and  in  three-fourths  of  its  weight  of  boiling 
water.     This  salt  is  employed  in  the  manufacture  of  fuming  sulphuric  acid. 

The  tersulphate  of  the  peroxide  is  formed  by  mixing  with  a  solution  of  the 

32 


466  SULPHATES. 

protosulphate  exactly  half  as  much  sulphuric  acid  as  that  salt  contains,  and 
adding  to  the  mixture  in  a  boiling  state  successive  portions  of  nitric  acid  until 
nitrous  acid  fumes  cease  to  appear.  The  solution  is  then  evaporated  to  dryness 
to  expel  the  excess  of  nitric  acid,  and  the  teisulphate  remains  as  a  white  salt. 
After  being  strongly  heated,  it  dissolves  slowly  in  water ;  but  if  evaporated  at  a 
gentle  heat,  it  is  deliquescent,  and  very  soluble  in  water  and  alcohol,  but  insolu- 
ble in  strong  sulphuric  acid.  At  a  red  heat  it  gives  out  all  its  acid,  and  peroxide 
of  iron  is  all  left.  Its  solution  in  water  has  an  orange  colour,  which  is  yellow 
when  much  diluted. 

The  disulphate  of  the  peroxide  falls  as  a  hydrate  of  an  ochreous  colour,  when 
a  solution  of  the  protosulphate  is  kept  in  an  open  vessel. 

Sulphate  of  Oxide  of  Zinc. — This  salt,  frequently  called  white  vitriol,  is  the 
residue  of  the  process  for  forming  hydrogen  gas  by  the  action  of  dilute  sulphuric 
acid  on  metallic  zinc ;  but  it  is  also  made,  for  the  purposes  of  commerce,  by 
roasting  native  sulphuret  of  zinc.  It  crystallizes  by  spontaneous  evaporation  in 
transparent  flattened  four-sided  prisms  of  the  right  prismatic  system,  and  isomor- 
phous  with  Epsom  salts.  The  crystals  dissolve  in  two  parts  and  a  half  of  cold,  and 
are  still  more  soluble  in  boiling  water.  The  taste  of  this  salt  is  strongly  styptic. 
It  reddens  vegetable  blue  colours,  though  in  composition  it  is  strictly  a  neutral 
salt. 

Sulphate  of  Protoxide  (f  Nickel. — This  salt,  like  the  salts  of  nickel  in  general, 
is  of  a  green  colour,  and  crystallizes  from  its  solution  in  pure  water  in  right 
rhombic  prisms  exactly  similar  to  the  sulphates  of  zinc  and  magnesia.  If  an 
excess  of  sulphuric  acid  is  present,  the  crystals  are  square  prisms,  which,  accord- 
ing to  R.  Phillips  and  Cooper,  contain  rather  less  water  and  more  acid  than  the 
preceding :  though  the  difference  is  not  so  great  as  to  indicate  a  different  atomic 
constitution.  (Annals  of  Philosophy,  xxii.  439.)  Thomson  says  he  analyzed 
both  kinds,  and  found  their  composition  identical.  It  is  soluble  in  about  three 
times  its  weight  of  water  at  60°  F. 

Sulphate  of  Protoxide  of  Cobalt. — When  protoxide  of  cobalt  is  digested  in  dilute 
sulphuric  acid,  a  red  solution  is  formed,  which  by  evaporation  deposits  crystals 
of  the  same  colour.  Mitscherlich  has  shown  that  the  crystals  are  identical  in 
composition  with  sulphate  of  protoxide  of  iron  ;  and  Brooke's  measurements 
prove  these  salts  to  be  isomorphous.  (An.  of  Phil.  N.  S.  vi.  120.)  They  are 
insoluble  in  alcohol,  and  dissolve  in  about  24  parts  of  cold  water. 

Tersulphate  of  Oxide  (f  Chromium. — This  salt  may  be  fonned  by  saturating 
dilute  suljihuric  acid  with  hydrated  sesquioxide  of  chromium  ;  but  it  has  not  been 
obtained  in  crystals. 

Sulphates  of  the  Oxides  cf  0>pper. — Sulphate  of  the  red  oxide  of  copper  has  not 
been  obtained  in  a  separate  state.  The  sulphate  of  the  black,  or  protoxide,  blue 
vitriol,  employed  by  surgeons  as  an  escharotic  and  astringent,  may  be  prepared 
by  roasting  the  native  sulphuret;  but  it  is  more  generally  made  by  directly 
dissolving  the  protoxide  in  dilute  sulphuric  acid,  and  crystallizing  by  evapora- 
tion. This  salt  forms  crystals  of  a  blue  colour,  reddens  litnms  paper,  and  is 
soluble  in  about  four  of  cold,  and  in  two  parte  of  boiling  water.  The  crystals 
contain  6  eq.  of  water,  four  of  which  are  lost  at  212°  in  a  dry  air,  hut  the  fifth 
is  retained  till  the  temperature  exceeds  430°.  It  is  then  a  white  powder,  which 
combines  readily  with  water,  with  the  development  of  considerable  heat.  It  is 
isomorphous  with  sulphate  of  protoxide  of  manganese. 

When  pure  potassa  is  added  to  a  solution  of  the  sulphate  of  protoxide  of  cop- 


>i#' 

^'^' 


SULPHATES.  467 


per  in  a  quantity  insufficient  for  separating  the  whole  of  the  acid,  a  pale  bluish- 
green  precipitate,  the  disulphate,  is  thrown  down. 

Sulphate  of  protoxide  of  copper  and  ammonia  is  generated  by  dropping  pure 
ammonia  into  a  solution  of  the  sulphate,  until  the  sab-salt  at  first  thrown  down 
is  nearly  all  dissolved.  It  forms  a  dark  blue  solution,  from  which,  when  con- 
centrated, crystals  are  deposited  by  the  addition  of  alcohol.  It  may  be  formed 
also  by  rubbing  briskly  in  a  mortar  two  parts  of  crystallized  sulphate  of  protox- 
ide of  copper  with  three  parts  of  carbonate  of  ammonia,  until  the  mixture  acquires 
an  uniform  deep  blue  colour.  Carjjonic  acid  gas  is  disengaged  with  effervescence 
during  the  operation,  and  the  mass  becomes  moist,  owing  to  the  water  of  the 
blue  vitriol  being  set  free. 

This  compound,  which  is  the  ammoniuret  of  copper  of  the  pharmacopoeia,  con- 
tains sulphuric  acid,  protoxide  of  copper,  and  ammonia;  but  its  precise  nature 
has  not  been  determined  in  a  satisfactory  manner.  It  parts  gradually  with  am- 
monia by  exposure  to  the  air. 

Sulphates  of  the  Oxides  of  Mercury. — When  two  parts  gf  mercury  are  gently 
heated  in  three  parts  of  strong  sulphuric  acid,  so  as  to  cause  slow  effervescence, 
a  sulphate  of  the  protoxide  of  mercury  is  generated.  But  if  a  strong  heat  is  era- 
ployed  in  such  a  manner  as  to  excite  brisk  effervescence,  and  the  mixture  is 
brought  to  dryness,  a  bisulphate  of  the  peroxide  results,  both  being  anhydrous. 
(Donovan  in  An.  of  Phil,  xiv  )  When  this  bisulphate,  which  is  the  salt  em- 
ployed in  making  corrosive  sublimate,  is  thrown  into  hot  water,  decomposition 
ensues,  and  a  yellow  sub-salt,  forilnerly  called  turpeth  mineral,  subsides.  This 
salt  is  said  by  Phillips  to  consist  of  3  eq.  of  acid  and  4  of  the  peroxide.  The  hot 
water  retains  some  of  the  bisulphate  in  solution,  together  with  free  sulphuric 
acid. 

Sulphate  of  Oxide  of  Silver. — As  this  salt  is  rather  sparingly  soluble  in  water, 
it  may  be  formed  by  double  decomposition  from  concentrated  solutions  of  nitrate 
of  oxide  of  silver  and  sulphate  of  soda.  It  may  also  be  procured  by  dissolving 
silver  in  sulphuric  acid  which  contains  about  a  tenth  part  of  nitric  acid,  or  by 
boiling  silver  in  an  equal  weight  of  concentrated  sulphuric  acid.  It  requires 
about  80  times  its  weight  of  hot  water  for  solution^  and  the  greater  part  is  depo- 
sited in  small  needles  on  cooling.  By  slow  evaporation  from  a  solution  con- 
taining a  little  nitric  acid,  Mitscherlich  obtained  it  in  the  form  of  a  rhombic 
octohedron,  the  angles  of  which  are  almost  identicnl  with  that  of  anhydrous  sul- 
phate of  soda.     Seleniate  of  oxide  of  silver  is  isomorphous  with  the  sulphate. 

Sulphate  of  oxide  of  silver  forms  with  ammonia  a  double  salt,  which  crystal- 
lizes in  rectangular  prisms,  the  solid  angles  and  lateral  edges  of  which  are  com- 
monly replaced  by  tangent  planes.  It  consists  of  1  eq.  of  oxide  of  silver,  1  of 
acid,  and  2  of  ammonia  ;  and  it  is  formed  by  dissolving  sulphate  of  oxide  of  sil- 
ver in  a  hot  concentrated  solution  of  ammonia,  from  which  on  cooling  the  crystals 
are  deposited.  This  salt  is  isomorphous  with  a  double  chromate  and  seleniate 
of  oxide  of  silver  and  ammonia,  which  have  a  similar  constitution,  and  are  formed 
in  the  same  manner.     (Mitscherlich  in  An.  de  Ch.  et  Ph.  xxxviii.  62.) 

DOUBLE  SULPHATES. 

Sulphates  nf  Lime  and  Soda. — This  compound,  the  glauberite  of  mineralogists, 
occurs  in  very  flat  oblique  rhombic  prisms.  Berthier  prepared  it  by  fusing  toge- 
ther sulphate  of  lime  with  sulphate  of  soda  in  the  ratio  of  their  equivalents. 


468  DOUBLE  SULPHATES. 

Sulphate  of  soda  fused  in  similar  proportions  with  the  sulphates  of  magnesia, 
baryta,  and  oxide  of  lead,  gives  analogous  compounds.  In  these  instances  how- 
ever, the  affinity  is  so  feeble,  that  it  is  overcome  by  the  mere  action  of  water. 
(An.  de  Ch.  et  Ph.  xxxviii.  255.) 

Sulphate  of  Poiassa  and  Magnesia. —  On  mixing  solutions  of  these  salts  in 
atomic  proportion,  the  double  salt  is  formed  either  by  spontaneous  evaporation 
or  on  cooling  from  a  hot  rather  concentrated  solution.  The  crystals  are  pris- 
matic, and  of  a  complicated  form,  belonging  to  the  oblique  prismatic  system. 
(Brooke.)  A  similar  double  salt,  isomorphous  with  the  preceding,  is  formed  by 
substituting  ammonia  for  potassa.     Their  composition  is  given  in  the  table. 

Similar  pairs  of  double  salts  may  be  formed  with  the  protoxides  of  iron,  zinc, 
cobalt,  and  nickel.  These  salts  have  the  same  form  and  composition  as  the 
corresponding  salt  of  magnesia. 

Jlum. — This  well-known  substance  is  a  double  sulphate  of  potassa  and 
alumina,  which  crystallizes  with  great  facility  from  a  solution  containing  its 
elements.  It  is  prepared  in  this  country  from  alum-slate,  an  argillaceous  slaty 
rock  highly  charged  with  pyrites  :  on  roasting  this  rock,  the  sulphuret  of  iron  is 
oxidized,  the  resulting  sulphuric  acid  unites  with  alumina  and  potassa  present 
in  the  slate,  and  the  alum  is  dissolved  out  by  water.  By  frequent  crystalliza- 
tion it  is  purified  from  the  oxide  of  iron,  which  obstinately  adheres  to  it.  In 
Italy  it  is  prepared  from  alum-stone^  which  occurs  at  Tolfa  near  Rome,  and  in 
most  volcanic  districts,  being  formed  apparently  by  the  action  of  sulphurous  acid 
vapours  on  felspatic  rocks.  The  materials  of  the  alum  exist  in  the  stone  ready 
formed ;  and  they  are  extracted  by  gently  heating  the  rock,  exposing  it  for  a 
time  to  the  air,  and  lixiviaiion.  The  alum  from  this  source  has  been  long  prized, 
in  consequence  of  being  quite  free  from  iron.  In  both  of  these  processes  the 
alkali  contained  in  the  alum-rock  is  inadequate  for  uniting  with  the  sulphate  of 
alumina  which  is  obtained,  and  hence  a  salt  of  potassa  must  be  added. 

Alum  has  a  sweetish  astringent  taste,  and  reddens  litmus  paper.  It  is  soluble 
in  five  parts  of  water  at  60°,  and  in  little  more  than  its  own  weight  of  boiling 
water.  It  crystallizes  readily  in  octohedrons,  or  in  segments  of  the  octohedron, 
and  the  crystals  contain  24  eq.  or  almost  50  per  cent,  of  water  of  crystallization. 
On  being  exposed  to  heat,  they  froth  up  remarkably,  and  part  with  all  the  water, 
forming  anhydrous  alum,  the  alumen  uslum  of  the  pharmacopoeia.  At  a  full  red 
heat  the  alumina  is  deprived  of  its  acid. 

Alum  is  employed  in  the  formation  of  a  spontaneously  inflammable  mixture 
long  known  under  the  name  of  Homherg's  pyrophorus.  It  is  made  by  mixing 
equal  weights  of  alum  and  brown  suarar,  and  stirring  the  mass  over  the  fire  in  an 
iron  or  other  convenient  vessel  till  quite  dry  :  it  is  then  put  into  a  glass  tube  or 
bottle,  and  heated  to  moderate  redness  without  exposure  to  the  air,  until  inflam- 
mable gas  ceases  to  be  evolved.  A  more  convenient  mixture  is  made  with  three 
parts  of  lamp-black,  four  of  burned  alum,  and  eight  of  carbonate  of  potassa. 
When  the  pyrophorus  is  well  made,  it  speedily  becomes  hot  on  exposure  to  the 
air,  takes  fire,  and  burns  like  tinder;  but  the  experiment  frequently  fails  from 
the  difficulty  of  regulating  the  temperature. 

From  some  recent  experiments  by  Gay-Lussac,  it  appears  that  the  essential 
ingredient  of  Homberg's  pyrophorus  is  sulphuret  of  potassium  in  a  state  of  mi- 
nute division.  The  charcoal  and  alumina  act  only  by  being  mechanically  inter- 
posed between  its  particles;  but  when  the  mass  once  kindles,  the  charcoal  takes 
fire  and  continues  the  combustion.     He  finds  that  an  excellent  pyrophorus  is 


DOUBLE  SULPHATES.  469 

made  by  mixing-  27  parts  of  sulphate  of  potassa  with  15  parts  of  calcined  lamp- 
black, and  heating  the  mixture  to  redness  in  a  common  hessian  crucible,  of 
course  excluding  the  air  at  the  same  time.     (An.  de  Ch.  et.  Ph.  xxxvii.  415.) 

Alum,  having  exactly  the  same  form,  composition,  appearance,  and  taste,  as 
the  salt  just  described,  may  be  made  with  ammonia,  the  sulphate  of  which  re- 
places sulphate  of  potassa.  It  is  met  with  occasionally  as  a  natural  product,  and 
may  be  prepared  by  evaporating  a  solution  of  sulphate  of  ammonia  with  tersul- 
phate  of  alumina. 

A  soda  alum  may  also  be  prepared,  similar  in  form  and  composition  to  the 
preceding  alums,  except  that  it  contains  86  equivalents  of  water.  (Berzelius.) 
This  salt  is  disposed  to  effloresce  in  the  air. 

Iron  Mum. — By  mixing  sulphate  of  potassa  with  tersulphate  of  peroxide  of 
iron,  and  crystallizing  by  spontaneous  evaporation,  crystals  are  obtained  similar 
to  common  alum  in  form,  colour^  taste^  and  composition.  This  salt  has  often  a 
pink  tint,  but  is  sometimes  quite  colourless.  A  similar  double  salt,  quite  colour- 
less, may  be  made  with  ammonia  instead  of  potassa.  In  both  these  alums  the 
alumina  is  simply  replaced  by  an  equivalent  quantity  of  peroxide  of  iron. 

Chrome  Jlums. — The  tersulphate  of  oxide  of  chromium  forms  with  the  sul- 
phates of  potassa  and  ammonia  double  salts,  which  are  exactly  similar  in  form 
and  composition  to  the  preceding  varieties  of  alum.  They  appear  black  by 
reflected,  but  ruby-red  by  transmitted  light. 

Manganese  Alum. — Mitscherlich  obtained  this  salt  by  mixing  a  solution  of 
tersulphate  of  sesquioxide  of  manganese  with  sulphate  of  potassa,  and  evapo- 
rating to  the  consistence  of  syrup  by  a  very  gentle  heat.  On  cooling,  octohe- 
dral  crystals  of  a  brownish-violet  colour  were  deposited,  which  were  similar  in 
composition  to  common  alum.  The  tersulphate  used  for  the  purpose  is  prepared 
by  macerating  sesquioxide  of  manganese  in  very  fine  powder  with  strong  sul- 
phuric acid:  it  is  made  with  difliculty,  owing  to  the  indisposition  of  that  oxide 
to  unite  with  acids,  and  to  its  ready  conversion  by  heat  into  sulphate  of  the  pro- 
toxide. 

From  the  descriptions  of  the  salts  to  which  the  term  alum  has  been  applied, 
it  will  be  observed  that  they  are  characterized  by  two  common  properties :  they 
all  crystallize  in  the  octohedral  system,  and  they  are  all  constituted  as  repre- 
sented by  the  formula  RO.SO^  -f-  R203,3SOg  -f  24  aq.,  where  RO  represents  an 
eq.  of  potassa,  or  oxide  of  ammonium,  and  R^^,  any  of  the  isomorphous  oxides 
of  aluminium,  iron,  manganese,  and  chromium.  As  Berzelius  has  ably  remarked, 
the  formula  and  crystalline  form  serve  to  determine  the  genus  alum,  and  the 
oxidized  bases  its  species. 

Sulphate  of  Protoxide  of  Iron  and  Alumina. — This  salt,  which  has  recently 
been  formed  by  Klauer,  is  obtained  by  the  spontaneous  evaporation  of  a  mixture 
of  sulphate  of  protoxide  of  iron  and  tersulphate  of  alumina  in  eq.  proportions,  a 
large  excess  of  sulphuric  acid  being  present  (Lieb.  An.  xiv.  261).  The  salt  is  de- 
posited in  long  acicular  crystals,  the  constitution  of  which,  being  FeO,SO^  -f- 
Al20^,3S03  -f  24HO,is  similar  to  that  of  an  alum  ;  but  as  the  crystals  do  not  be- 
long to  the  octohedral  system,  it  has  been  improperly  described  as  one  of  that  class. 

A  compound,  exactly  analogous,  in  which  protoxide  of  manganese  is  substi- 
tuted for  protoxide  of  iron,  occurs  native  on  the  gold  coast  of  Africa,  in  beautiful 
silvery  fibres,  many  inches  long.  It  has  been  described  and  analyzed  by 
Apjohn,  who  found  its  formula  to  be  MnO,S03  +  A1^0^,3S03  -f-  24HO. 

A  similar  salt  of  magnesia  was  obtained  in  the  same  manner ;  and  it  is  exceed- 


470  DOUBLE  SULPHATES. 

inprly  probable  that  a  similar  compound  might  be  formed  with  the  isomorphons 
pxides  of  zinc,  copper,  nickel,  cobalt,  and  with  lime.  These,  in  their  turn, 
might  again  be  varied  by  substituting  for  the  alumina  the  sesquioxides  of  iron, 
manganese,  and  chromium. 

Anhydrous  Sulphates  wifh  Ammonia. — Rose  has  observed  that  some  sulphates 
possess  the  property  of  absorbing  ammonia,  and  of  forming  with  it  definite  com- 
pounds, which  differ  from  sulphates  of  ammonia  prepared  in  the  moist  way,  both 
by  containing  no  water  of  crystallization,  and  by  the  facility  with  which  the 
alkali  is  again  given  out.  They  are  formed  by  placing  the  anhydrous  sulphate 
in  a  glass  tube,  and  transmitting  over  it  at  common  temperatures  ammoniacal 
gas,  well  dried  by  fused  potassa,  as  long  as  any  increase  of  weight  is  observed  : 
some  sulphates  absorb  the  gas  very  rapidly  at  first,  and  with  disengagement  of 
heat;  but  the  absorption  afterwards  becomes  slow,  and  requires  a  day  or  two  in 
order  to  be  complete.  The  salts  most  remarkable  for  this  property  are  those 
which,  in  solution,  are  disposed  to  unite  with  ammonia.  Sulphate  of  protoxide 
of  copper  greedily  absorbs  ammonia,  and  acquires  a  deep  blue  colour  similar  to 
the  ammoniaret  of  copper,  prepared  with  moisture;  but  the  former  compound 
consists  of  2  eq.  of  sulphate  of  protoxide  of  copper  and  5  eq.  of  ammonia,  while 
the  latter  contains  1  eq.  of  sulphate  of  copper,  2  of  ammonia,  and  1  eq.  of  water. 
Sulphate  of  protoxide  of  cobalt,  as  well  as  that  of  nickel,  unites  with  3  eq.  of 
ammonia ;  that  of  zinc  with  2'5,  and  that  of  manganese  with  2  eq.  The  latter 
when  heated  loses  all  its  ammonia,  and  returns  to  its  original  condition ;  whereas 
most  of  the  other  ammoniaco-sulphates  suffer  partial  decomposition  at  the  same 
time.  Sulphate  of  oxide  of  silver  unites  with  1  eq.  of  ammonia ;  and  a  similar 
compound  was  prepared  by  C.  G.  Mitscherlich,  but  with  2  eq.  of  ammonia. 
With  most  of  the  other  anhydrous  sulphates  ammonia  refuses  to  unite. 

On  considering  the  nature  of  these  compounds,  one  is  at  first  disposed  to 
associate  them  with  double  salts,  supposing  the  acid  to  be  divided  between  the 
two  bases.  But  this  opinion  is  rendered  unlikely  by  the  large  quantity  of  com- 
bined ammonia,  by  the  facility  with  which  the  alkali  is  given  off,  and  by  the 
absence  of  water,  so  constantly  present  in  other  ammoniacal  sulphates.  Rose, 
with  much  plausibility,  compares  these  compounds  to  hydrates:  water  acts  as  a 
feeble  base  to  saline  compounds,  combining  with  some  in  one  or  more  propor- 
tions, and  not  at  all  with  others,  differing  greatly  in  the  ratio  in  which  it  com- 
bines with  different  salts,  and  being  abandoned  with  great  facility,  often  by  mere 
exposure  to  the  air.  The  same  features  characterize  the  combinations  of  ammo- 
nia with  the  anhydrous  sulphates.     (Pog.  Annalen,  xx.  149.) 

The  sulphates  are  not  the  only  salts  which  absorb  ammonia.  Rose  found  that 
the  nitrate  of  oxide  of  silver  unites  with  3  eq.  of  ammonia,  and  the  gas,  if 
freely  supplied,  is  at  first  absorbed  with  such  rapidity,  and  the  corresponding 
increase  of  temperature  is  so  great,  that  the  salt  enters  into  fusion.  Heat  expels 
the  ammonia  before  the  nitrate  of  oxide  of  silver  is  decomposed.  A  similar 
compound,  but  with  less  ammonia,  was  formed  by  C.  Mitscherlich. 

SULPHITES. 

The  salts  of  sulphurous  acid  have  not  hitherto  been  minutely  examined.  The 
sulphites  of  potassa,  soda,  and  ammonia,  which  are  made  by  neutralizing  those 
alkalies  with  sulphurous  acid,  are  soluble  in  water;  but  most  of  the  other  sul- 
phites, so  far  as  is  known,  are  of  sparing  solubility.     The  sulphites  of  baryta, 


NITRATES.  471 

fitrontia,  and  lime,  are  very  insoluble ;  and  consequently  the  soluble  salts  of  these 
earths  decompose  the  alkaline  sulphites. 

The  stronger  acids,  such  as  the  sulphuric,  hydrochloric,  phosphoric,  and  arse- 
nic acids,  decompose  all  the  sulphites  with  effervescence,  owing  to  the  escape  of 
sulphurous  acid,  which  may  easily  be  recognized  by  its  odour.  Nitric  acid,  by 
yielding  oxygen,  converts  the  sulphites  into  sulphates. 

When  the  sulphites  of  the  fixed  alkalies  and  alkaline  earths  are  strongly 
heated  in  close  vessels,  a  sulphate  is  generated,  and  a  portion  of  sulphur  sub-» 
limed.  In  open  vessels  at  a  high  temperature  they  absorb  oxygen,  and  are 
converted  into  sulphates ;  and  a  similar  change  takes  place  even  in  the  cold, 
especially  when  they  are  in  solution.  Gay-Lussac  has  remarked,  that  a  neu- 
tral sulphite  always  forms  a  neutral  sulphate  when  its  acid  is  oxidized ;  a  fact 
from  which  it  may  be  inferred,  that  neutral  sulphites  consist  of  1  eq.  of  the  acid 
and  1  eq.  of  the  base. 

The  hyposulphates  and  hyposulphites  are  of  such  little  practical  importance, 
that  it  is  unnecessary  to  describe  individual  salts :  their  general  character  has 
been  already  given.  For  a  particular  description  of  the  hyposulphates,  the 
reader  is  referred  to  an  essay  by  Heeren.     (An.  de  Ch.  et  Ph.  xl.  30.) 

NITRATES. 

The  nitrates  may  be  prepared  by  the  action  of  nitric  acid  on  metals,  on  the 
salifiable  bases  themselves,  or  on  carbonates.  As  nitric  acid  forms  soluble  salts 
with  all  alkaline  bases,  the  acid  of  the  nitrates  cannot  be  precipitated  by  any 
reagent.  They  are  readily  distinguished  from  other  salts,  however,  by  the  cha- 
racters already  described. 

All  the  nitrates  are  decomposed  without  exception  by  a  high  temperature  ;  but 
the  changes  which  ensue  are  modified  by  the  nature  of  the  oxide.  Nitrate  of 
oxide  of  palladium  is  decomposed  at  such  a  moderate  temperature,  that  a  great 
part  of  the  acid  passes  off  unchanged.  Nitrate  of  oxide  of  lead  requires  a  red 
heat,  by  which  it  is  resolved,  as  already  mentioned,  into  oxygen  and  nitrous 
acid.  In  some  instances  the  changes  are  more  complicated.  With  nitre,  for 
example,  nitrite  of  potassa  is  at  first  generated,  with  escape  of  oxygen  gas  :  as 
the  heat  increases,  the  nitrous  acid  is  resolved  into  binoxide  of  nitrogen  and 
oxygen,  the  former  of  which  remains  in  combination  with  potassa;  the  binoxide 
is  then  resolved  into  protoxide  of  nitrogen  and  oxygen,  the  former  being  retained 
by  the  alkali ;  and,  lastly,  nitrogen  gas  is  disengaged,  and  peroxide  of  potassium 
remains.  If  the  operation  is  performed  in  an  earthen  vessel,  the  peroxide  will 
be  more  or  less  decomposed,  in  consequence  of  the  affinity  of  the  earthy  sub>- 
stances  for  potassa.  The  preceding  facts  have  been  chiefly  collected  from  the 
observations  of  Phillips  and  Berzelius.  The  tendency  of  potassa  and  soda  to 
unite  with  protoxide  of  nitrogen  was  first  discovered  by  Davy ;  and  Hess  has 
lately  remarked  that  similar  compounds  are  obtained  with  soda,  baryta,  and  lime, 
as  well  as  potassa,  when  their  nitrates  are  heated  until  the  disengaged  gas  is 
found  to  extinguish  a  light. 

As  the  nitrates  are  easily  decomposed  by  heat  alone,  they  must  necessarily 
suffer  decomposition  by  the  united  agency  of  heat  and  combustible  matter.  The 
nitrates  on  this  account  are  much  employed  as  oxidizing  agents,  and  frequently 
act  with  greater  efficacy  even  than  nitro-hydrochloric  acid.  Thus  metallic  ti'ar 
Ilium,  which  resists  the  action  of  these  acids,  combines  with  oxygen  when  heated 


472 


NITRATES. 


with  nitre.  The  efficiency  of  this  salt,  which  is  the  nitrate  usually  employed  for 
the  purpose,  depends  not  only  on  the  affinity  of  the  combustible  for  oxygen,  but 
likewise  on  that  of  the  oxidized  body  for  potassa.  The  process  for  oxidizing 
substances  by  means  of  nitre  is  called  deflagration^  and  is  generally  performed 
by  mixing  the  inflammable  body  with  an  equal  weight  of  the  nitrate,  and  pro- 
jecting the  mixture  in  small  portions  at  a  time  into  a  red-hot  crucible. 

All  the  neutral  nitrates  of  the  fixed  alkalies  and  alkaline  earths,  together  with 
most  of  the  neutral  nitrates  of  the  common  metals,  are  composed  of  1  eq.  of 
nitric  acid,  and  1  eq.  of  a  protoxide.  Consequently,  the  oxygen  of  the  oxide 
and  acid  in  all  such  salts  must  be  in  the  ratio  of  1  to  5,  the  general  formula 
being  MO  f  NO^. 

The  only  nitrates  found  native  are  those  of  potassa,  soda,  lime,  and  magnesia. 

The  composition  of  the  principal  nitrates  is  exhibited  in  the  following  table : 


Names. 
Nitrate  of  Potassa 

Soda 

Oxide  of  Ammonium 
Nitrate  of  Baryta 
— — —   Strontia 


47-15 

31-3 

2615 

76-7 

51-8 


Acid. 
1  eq.-l- 54.15 
1  eq.  + 54-15 
1  eq.  -|-  54-15 
1  eq.  -f  54-15 
1  eq.  -|-  54-15 


Do.  in  prisms  with  45  or  6  eq.  of  water 
Nitrate  of  Lime  28-5        1  eq.  +  5415 
Magnesia  20-7        leq. -|-54-l5 
Protox.  Copper     39-6        leq. +5415 

Do,  in  prisms  with  63  or  7  eq.  of  water  ? 
Nitrate  of  protox.  Lead       111-6        1  eq.  -|-  54*  15 
Dinitrate  of  ditto  223-2        2  eq.  +  54-15 

Nitrate  of  protox.  Mercury  210  1  eq.  +  5415 

Do.  in  crystals  with  18  or  2  eq.  of  water 
Nitrate  of  perox.  Mercury  218  1  eq.  -|-  54-15 

Dinitrate  do.  436  2eq.-f54-15 

Nitrate  of  ox.  Silver  116  1  eq.  +54-15 


1  eq 
1  eq 
1  eq 
1  eq, 
1  eq, 

1  eq, 
1  eq 
1  eq, 

1  eq, 
1  eq. 
1  eq. 

1  eq, 
1  eq. 
1  eq. 


Equiv. 
=  101-3 
=  85-45 
,=  80-3 
=  130-85 
=  105-95 
=  160-95 
=  82-65 
=  74  85 
=  93-75 
=  156-75 
=  165-75 
=  277-35 
=  264-15 
=  282-15 
=  272-15 
=  490-15 
=  170-15 


Formulae. 

KO  +  NOg 

NaO-f- 


NO.. 


H4NO+NO5. 
BaO  f  NO5. 
SrO+NOg. 

CaO  +  NOg. 
MgO  +  NOj. 
CuO  -i  NOg. 

PbO  t  NO5, 
2PbO  +  NO5. 
HgO+NOj. 

Hg02  t  NO5. 
2Hg02  -j-  NO5. 
Ago  +  NOg. 


Nitrate  of  Potassa. — ^This  salt  is  generated  spontaneously  in  the  soil,  and  crys- 
tallizes upon  its  surface,  in  several  parts  of  the  world,  and  especially  in  the  East 
Indies,  whence  the  greater  part  of  the  nitre  used  in  Britain  is  derived.  In  some 
parts  of  the  Continent,  it  is  prepared  artifici-ally  from  a  mixture  of  common 
mould  or  porous  calcareous  earth  with  animal  and  vegetable  remains  containing 
nitrogen.  When  a  heap  of  these  materials,  preserved  moist  and  in  a  shady  situ- 
ation, is  moderately  exposed  to  the  air,  nitric  acid  is  gradually  generated,  and 
unites  with  the  potassa,  lime,  and  magnesia,  which  are  commonly  present  in  the 
mixture.  On  dissolving  these  salts  in  water,  and  precipitating  the  two  earths  by 
carbonate  of  potassa,  a  solution  is  formed,  which  yields  crystals  of  nitre  by 
evaporation.  The  nitric  acid  is  possibly  generated  under  these  circumstances 
by  the  nitrogen  of  the  organic  matters  combining  during  putrefaction  with  oxy- 
gen of  the  atmosphere,  a  change  which  must  be  attributed  to  the  affinity  of  oxy- 
gen for  nitrogen,  aided  by  that  of  nitric  acid  for  alkaline  bases.  The  nitre  made 
in  France  is  often  said  to  be  formed  by  this  process ;  but  the  greater  part  is  cer- 
tainly obtained  by  lixiviation  from  certain  kinds  of  plaster  of  old  houses,  when 
nitrate  of  lime  is  gradually  generated.  Liebig,  in  his  profound  work  on  the 
application  of  organic  chemistry  to  Agriculture  and  Physiology,  has  rendered  it 
highly  probable,  if  not  certain,  that  the  nitric  acid  is  formed  by  the  oxidation  of 


NITRATES.  473 

ammonia,  which  exists  in  the  atmosphere,  and  is  brought  by  absorption  in  con- 
tact with  organic  matters  in  a  state  of  slow  combustion  or  eremacausis.  Ammo- 
nia is  more  easily  oxidized  than  any  other  compound  of  nitrogen ;  probably 
because  it  contains  hydrogen,  the  oxidation  of  which  yields  water,  which  is 
essential  to  the  existence  of  nitric  acid.  Animal  matters  only  act  as  a  source  of 
ammonia,  and  nitric  acid  may  be  formed  where  the  decaying  organic  matter  con- 
tains no  nitrogen,  from  the  ammonia  present  in  the  atmosphere.  For  the  details 
of  his  argument  I  must  refer  to  Dr.  Playfair's  translation  of  the  above  work 
recently  (Sept.  1840)  published. 

Nitrate  of  potassa  is  a  colourless  salt,  which  crystallizes  readily  in  six-sided 
prisms.  Its  taste  is  saline,  accompanied  with  an  impression  of  coolness.  It 
requires  for  solution  seven  parts  of  water  at  60°,  and  its  own  weight  of  boiling 
water.  It  contains  no  water  of  crystallization,  but  its  crystals  are  never  quite 
free  from  water  lodged  mechanically  within  them.  At  616°  it  undergoes  the 
igneous  fusion,  and  like  all  the  nitrates,  is  decomposed  by  a  red  heat. 

Nitre  is  chiefly  employed  in  chemistry  as  an  oxidizing  agent,  and  in  the  for- 
mation of  nitric  acid.  Its  chief  use  in  the  arts  is  in  making  gunpowder,  which 
is  a  mixture  of  nitre,  charcoal,  and  sulphur.  In  the  East  Indies  it  is  employed 
for  the  preparation  of  cooling  mixtures  ;  an  ounce  of  powdered  nitre  dissolved  in 
five  ounces  of  water  reduces  its  temperature  by  fifteen  degrees.  It  possesses 
powerful  antiseptic  properties,  and  is  therefore  much  employed  in  the  preserva- 
tion of  meat  and  animal  matters  in  general. 

Nitrate  of  Soda. — This  salt  is  analogous  in  its  chemical  properties  to  the  pre- 
ceding compound.  It  sometimes  crystallizes  in  oblique  rhombic  prisms ;  but  it 
more  commonly  occurs  as  an  obtuse  rhombohedron.  (Brooke.)  It  is  plentifully 
found  in  the  soil  in  some  parts  of  India ;  and  at  Atacama  in  Peru  it  covers  large 
districts,  and  occurs  in  immense  quantity.  With  charcoal  and  sulphur  it  forms 
a  mixture  which  burns  much  slower  than  common  gunpowder,  and  therefore 
cannot  be  substituted  for  nitre  ;  but  it  may  be  advantageously  used  in  the  manu- 
facture both  of  sulphuric  and  nitric  acid.  It  is  disposed  to  deliquesce  in  the  air, 
and  is  soluble  in  twice  its  weight  of  cold  water,  and  still  more  freely  by  the  aid 
of  heat. 

Nitrate  of  Oxide  of  Ammonium, — It  may  be  formed  by  neutralizing  dilute 
nitric  acid  by  carbonate  of  ammonia,  and  evaporating  the  solution.  This  salt 
may  be  procured  in  three  different  states,  which  have  been  described  by  Davy. 
(Researches  concerning  the  nitrous  oxide.)  If  the  evaporation  is  conducted  at  a 
temperature  not  exceeding  100°,  the  salt  is  obtained  in  prismatic  crystals  iso- 
morphous  with  nitre.  If  the  solution  is  evaporated  at  212°,  fibrous  crystals  are 
procured  ;  and  if  the  heat  be  gradually  increased  to  300°,  it  forms  a  brittle  com- 
pact mass  on  cooling.  The  fibrous  and  compact  varieties  still  contain  water,  the 
former  8-2  per  cent,  and  the  latter  5*7.  All  these  varieties  deliquesce  in  a  moist 
air,  and  are  very  soluble  in  water. 

The  change  which  nitrate  of  ammonia  undergoes  at  a  temperature  varying 
between  400°  and  500°  has  already  been  explained.  When  heated  to  600°,  it 
explodes  with  violence,  being  resolved  into  water,  nitrous  acid,  binoxide  of 
nitrogen,  and  nitrogen.  The  fibrous  variety  was  found  by  Davy  to  yield  the 
largest  quantity  of  protoxide  of  nitrogen.  From  one  pound  of  this  salt  he  pro- 
cured nearly  three  cubic  feet  of  the  gas. 

Nitrate  of  Baryta. — This  salt  is  sometimes  used  as  a  reagent  and  for  pre- 
paring pure  bartya.    It  is  easily  prepared  by  digesting  the  native  carbonate, 


474  NITRATES. 

reduced  to  powder,  in  nitric  acid  diluted  with  8  or  10  times  its  weight  of  water 
The  salt  crystallizes  readily  by  evaporation  in  transparent  anhydrous  octohe- 
drons,  and  is  very  apt  to  decrepitate  by  heat  unless  previously  reduced  to 
powder.  It  requires  12  parts  of  water  at  60°  and  3  or  4  of  boiling  water  for 
solution,  but  is  insoluble  in  alcohol.  It  undergoes  the  igneous  fusion  in  the  fire 
before  being  decomposed. 

Nitrate  of  Stroniia. — This  salt  may  be  made  from  strontianite  in  the  same 
manner  as  the  foregoing  compound,  to  which  it  is  exceedingly  analogous.  It 
commonly  crystallizes  in  anhydrous  octohedrons  which  undergo  no  change  in  a 
moderately  dry  atmosphere,  and  are  insoluble  in  alcohol;  but  sometimes  it  con- 
tains 30  per  cent,  of  water  of  crystallization,  and  then  assumes  the  form  of  the 
oblique  prismatic  system. 

Nitrates  of  Lime  and  Magnesia. — These  salts  crystallize  in  hydrated  prisms 
when  their  solutions  are  concentrated  to  the  consistence  of  syrup,  but  the  quan- 
tity of  water  which  they  contain  is  not  ascertained.  They  deliquesce  rapidly  in 
the  air,  are  very  soluble  in  water,  and  are  dissolved  by  alcohol,  the  nitrate  of 
lime  more  freely  than  nitrate  of  magnesia. 

Nitrate  of  Protoxide  of  Copper. — This  salt  is  prepared  by  the  action  of  nitric 
acid  on  copper.  It  crystallizes,  though  with  some  difficulty,  in  prisms  of  a 
deep  blue  colour,  which  are  very  soluble  in  water  and  alcohol,  and  deliquesce 
on  exposure  to  the  air.  The  green  insoluble  subsalt,  procured  by  exposing  the 
neutral  nitrate  to  a  heat  of  400°,  or  by  dropping  an  alkali  into  a  solution  of  that 
fialt,  the  latter  being  in  excess,  is  a  trinitrate,  consisting  of  3  eq.  of  oxide  of 
copper,  1  eq.  of  acid,  and  1  eq.  of  water.  From  tiie  observations  of  Graham, 
the  neutral  salt  contains  3  eq.  of  constitutional  water,  and  therefore  may  be 
represented  by  the  formula  CuO,  NO^,  3H0  :  from  this  it  would  appear  that 
the  subsalt  is  similarly  constituted,  being  a  nitrate  of  water  with  3  eq.  of  con- 
stitutional oxide  of  copper.  It  is  on  this  supposition  represented  by  the  formula 
HO,  NO  ,  3CuO.  It  is  probable  that  the  nitrates  of  lime  and  magnesia  are 
similarly  constituted,  as  has  been  shown  to  be  the  case  with  nitric  acid  of  sp. 
gr.  1*42.     When  heated  to  redness  it  yields  pure  oxide  of  copper. 

Nitrate  of  Protoxide  of  Lead. — This  salt  is  formed  by  digesting  litharge  in 
dilute  nitric  acid,  and  crystallizes  readily  in  octohedrons,  which  are  anhydrous 
and  almost  always  opaque.  It  has  an  acid  reaction,  but  is  neutral  in  composi- 
tion. 

A  dinitrate  was  formed  by  Berzelius  by  adding  to  a  solution  of  the  neutral 
nitrate  a  quantity  of  pure  ammonia  insufficient  for  separating  the  whole  of  the 
acid. 

Nitrates  of  the  Oxides  of  Mercury. — The  protonitrate  is  conveniently  formed 
by  digesting  mercury  in  nitric  acid  diluted  with  three  or  four  parts  of  water, 
until  the  acid  is  saturated,  and  then  allowing  the  solution  to  evaporate  spontane- 
ously in  an  open  vessel.  The  solution  always  contains,  at  first,  some  nitrate  of 
the  peroxide;  but  if  metallic  mercury  is  left  in  the  liquid,  a  pure  protonitrate  is 
gradually  deposited.  The  salt  thus  formed  has  hitherto  been  regarded  as  the 
neutral  protonitrate;  but  according  to  the  analysis  of  M.  C.  Mitscherlich  (Pog. 
Annalen,  ix.  387),  it  is  a  subsalt,  in  which  the  protoxide  and  acid  are  in  the 
latio  of  208  to  36.  This  result,  however,  requires  confirmation.  The  neutral 
protonitrate  is  said  by  C.  Mitscherlich  to  be  obtained  in  crystals,  by  dissolving 
the  former  salt  in  pure  water  acidulated  with  nitric  acid,  and  evaporating  spon- 
taneously without  the  contact  of  metallic  mercury  or  uncombined  oxide.    These 


NITRITES.  475 

salts  dissolve  completly  in  water  slightly  acidulated  with  nitric  acid,  but  in  pure 
water  a  small  quantity  of  a  yellow  subsalt  is  generated. 

When  mercury  is  heated  in  an  excess  of  strong  nitric  acid,  it  is  dissolved 
with  brisk  effervescence,  owing  to  the  escape  of  binoxide  of  nitrogen,  and  trans- 
parent prismatic  crystals  of  the  pernitrate  are  deposited  as  the  solution  cools. 
"When  put  into  hot  water  it  is  resolved  into  a  soluble  salt,  the  composition  of 
which  is  unknown,  and  into  a  yellow  dinatrate  of  the  peroxide.  (An.  de  Ch, 
et  Phys.  xix.) 

Nitrate  of  Oxide  of  Silver. — Silver  is  readily  oxidized  and  dissolved  by  nitric 
acid  diluted  with  two  or  three  times  its  weight  of  water,  forming  a  solution 
which  yields  transparent  tabular  crystals  by  evaporation.  These  crystals,  which 
are  anhydrous,  undergo  the  igneous  fusion  at  426°,  and  yield  a  crystalline  mass 
in  cooling  ;  but  when  the  temperature  reaches  600°  or  700°,  complete  decom- 
position ensues,  the  acid  being  resolved  into  oxygen  and  nitrous  acid,  whil© 
metallic  silver  is  left.  When  liquefied  by  heat,  and  received  in  small  cylindrical 
moulds,  it  forms  the  lapis  infernalis  or  lunar  caustic^  employed  by  surgeons  as  a 
cautery.  The  nitric  acid  appears  to  be  the  agent  which  destroys  the  animal  tex- 
ture, and  the  black  stain  is  owing  to  the  separation  of  oxide  of  silver.  It  is 
sometimes  employed  for  giving  a  black  colour  to  the  hair,  and  is  the  basis  of  the 
indelible  ink  for  marking  linen. 

The  pure  nitrate,  whether  fused  or  in  crystals,  is  colourless  and  transparent, 
and  does  not  deliquesce  by  exposure  to  the  air ;  but  common  lunar  caustic  is 
dark  and  opaque,  and  dissolves  imperfectly  in  water,  owing  to  some  of  the 
nitrate  being  decomposed  during  its  preparation.  It  is  impure  also,  always  con- 
taining nitrate  of  protoxide  of  copper,  and  frequently  traces  of  gold.  The  pure 
salt  is  soluble  in  its  own  weight  of  cold,  and  in  half  its  weight  of  hot  water.  It 
dissolves  also  in  four  times  its  weight  of  alcohol.  Its  aqueous  solution,  if  pre- 
served in  clean  glass  vessels,  especially  with  the  addition  of  a  minute  quantity 
of  free  nitric  acid,  undergoes  little  or  no  change  even  in  the  direct  solar  rays ; 
but  when  exposed  to  light,  especially  to  sunshine,  in  contact  with  paper,  the 
skin,  or  any  organic  substance,  a  black  stain  is  quickly  produced,  owing  to  de- 
composition of  the  salt  and  reduction  of  its  oxide  to  the  metallic  state.  Thi$ 
change  is  so  constant,  that  nitrate  of  oxide  of  silver  constitutes  an  extremely 
delicate  test  of  the  presence  of  organic  matter,  and  has  been  properly  recom- 
mended as  such  by  Dr.  Davy.  Its  solution  is  always  kept  in  the  laboratory  as 
a  test  for  chlorine  and  hydrochloric  acid. 

Nitrate  of  oxide  of  silver,  even  after  fusion,  reddens  vegetable  colouring  mat- 
ters ;  but  it  is  quite  neutral  in  composition. 

NITRITES. 

Little  is  known  with  certainty  concerning  the  compounds  of  nitrous  acid  with 
alkaline  bases.  Nitrite  of  potassa  is  formed  by  heating  nitre  to  redness,  and  re- 
moving it  from  the  fire  before  the  decomposition  is  complete.  On  adding  a  strong 
acid  to  the  product,  red  fumes  of  nitrous  acid  are  disengaged,  a  character  which 
is  common  to  all  the  nitrites.  The  nitrite  of  soda,  baryta,  and  strontia,  may  be 
obtained  in  the  same  manner,  and  doubtless  several  others.  Two  nitrites  of 
oxide  of  lead  have  been  described  in  the  Annales  de  Chimie,  Ixxxiii.  by  Chevreul 
and  Berzelius.     It  is  possible,  however,  that  these  compounds  are  hyponitrites. 


476 


CHLORATES. 


The  salts  of  chloric  acid  are  very  analogous  to  the  nitrates.  As  the  chlorates 
of  the  alkalies,  alkaline  earths,  and  most  of  the  common  metals,  are  composed 
of  1  eq.  of  chloric  acid  and  1  eq.  of  a  protoxide,  MO  -f-  ClO^,  it  follows  that  the 
oxygen  of  the  latter  to  that  of  the  former  is  in  the  ratio  of  1  to  5.  The  chlo- 
rates are  decomposed  by  a  red  heat,  nearly  all  of  them  being  converted  into 
metallic  chlorides,  with  evolution  of  pure  oxygen  gas.  They  deflagrate  with  in- 
flammable substances  with  greater  violence  than  nitrates,  yielding  oxygen  with 
such  facility  that  an  explosion  is  produced  by  slight  causes.  Thus,  a  mixture  of 
sulphur  with  three  times  its  weight  of  chlorate  of  potassa  explodes  when  struck 
between  two  hard  surfaces.  With  charcoal  and  the  sulphurets  of  arsenic  and 
antimony,  this  salt  forms  similar  explosive  mixtures :  and  with  phosphorus  it 
detonates  violently  by  percussion.  One  of  the  mixtures,  employed  in  the  per- 
cussion locks  for  guns,  consists  of  sulphur  and  chlorate  of  potassa,  with  which 
a  little  charcoal  or  gunpowder  is  mixed ;  but  as  the  use  of  these  materials  is 
found  corrosive  to  the  lock,  fulminating  mercury  is  now  generally  preferred. 

All  the  chlorates  hitherto  examined  are  soluble  in  water,  excepting  the  chlo- 
rate of  protoxide  of  mercury,  which  is  of  sparing  solubility.  These  salts  are  dis- 
tinguished by  the  action  of  strong  hydrochloric  and  sulphuric  acids,  the  former 
of  which  occasions  the  disengagement  of  chlorine  and  protoxide  of  chlorine,  and 
the  latter  of  peroxide  of  chlorine. 

None  of  the  chlorates  are  found  native,  and  the  only  ones  that  require  particu- 
lar description  are  those  of  potassa  and  baryta. 

Chlorate  of  Potassa. — ^This  salt,  formerly  called  oxymuriate  or  hyper-oxymu- 
riaie  of  potash^  is  colourless  and  crystallizes  in  four  and  six-sided  scales  of  a 
pearly  lustre.  Its  forms  are  stated  by  Brooke  to  belong  to  the  oblique  prismatic 
system.  It  is  soluble  in  sixteen  tiroes  its  weight  of  water  at  60°,  and  in  two 
and  a  half  of  boiling  water.  It  is  quite  anhydrous,  and  when  exposed  to  a  tem- 
perature of  400°  or  500°  undergoes  the  igneous  fusion.  On  increasing  the  heat 
almost  to  redness,  effervescence  ensues,  and  pure  oxygen  gas  is  disengaged, 
phenomena  which  have  been  explained  in  the  section  on  oxygen.  It  can  bear  a 
heat  of  600°  without  decomposition. 

Chlorate  of  potassa  is  made  by  transmitting  chlorine  gas  through  a  concen- 
trated solution  of  pure  potassa,  until  the  alkali  is  completely  neutralized.  The 
solution  which,  after  being  boiled  for  a  few  minutes,  contains  nothing  but  chlo- 
ride of  potassium  and  chlorate  of  potassa,  is  gently  evaporated  till  a  pellicle 
forms  upon  its  surface,  and  is  then  allowed  to  cool.  The  greater  part  of  the 
chlorate  crystallizes,  while  the  chloride  remains  in  solution.  The  crystals,  after 
being  washed  with  cold  water,  may  be  purified  by  a  second  crystallization. 

Chlorate  of  Baryta  is  of  interest,  as  being  the  compound  employed  in  the  forma- 
tion of  chloric  acid;  and  the  readiest  mode  of  preparing  it  is  by  the  process  of 
Wheeler.  On  digesting  for  a  few  minutes  a  concentrated  solution  of  chlorate  of 
potassa  with  a  slight  excess  of  silicated  hydrofluoric  acid,  the  alkali  is  precipi- 
tated in  the  form  of  an  insoluble  double  fluoride  of  silicium  and  potassium,  while 
chloric  acid  remains  in  solution.  The  liquid  after  filtration  is  neutralized  by  car- 
bonate of  baryta,  which  throws  down  the  excess  of  silicated  hydrofluoric  acid, 
and  chlorate  of  baryta  is  left  in  solution.     By  evaporation  it  yields  prismatic 


CHLORITES.  477 

crystals,  which  require  for  solution  4  times  their  weight  of  cold,  and  a  still 
smaller  quantity  of  hot  water.  They  are  composed  of  76*7  parts  or  1  eq.  of 
baryta,  75*42  or  1  eq.  of  chloric  acid,  and  9  or  1  eq.  of  water. 

[Waechter  stales  that  light  is  evolved  during  the  crystallization  of  this  salt, 
and  that  it  communicates  to  the  flame  of  alcohol  an  intense  green  colour.  (Jour, 
fur  prakische  Chem.  i.  xxx.  p.  321.)] 

Perchlorates. — The  neutral  proto-salts  of  perchloric  acid  consist  of  1  eq.  of 
acid  and  base,  as  is  expressed  by  the  formula  MO  -}-  Cl^O^.  Most  of  these  salts 
are  deliquescent,  very  soluble  in  water,  and  soluble  in  alcohol  :  four  only  were 
found  by  Serullas  to  be  not  deliquescent, — the  perchlorates  of  potassa,  ammonia, 
protoxide  of  lead  and  protoxide  of  mercury.  When  heated  to  redness  they  yield 
oxygen  gas  and  metallic  chlorides  ;  and  they  are  distinguished  from  the  chlorates 
by  not  acquiring  a  yellow  tint  on  the  addition  of  hydrochloric  acid.  The  per- 
chlorate  of  potash  is  prepared  from  the  chlorate  by  the  action  of  heat  or  sulphuric 
or  nitric  acid,  as  already  mentioned.  It  is  the  most  insoluble  of  the  perchlorates, 
and  on  this  account  perchloric  acid  precipitates  potassa  from  its  salts,  being  a  test 
of  about  the  same  delicacy  as  tartaric  acid.  The  other  perchlorates  are  made  by 
neutralizing  the  base  with  perchloric  acid.  The  solubility  in  alcohol  of  the  per- 
chlorates of  baryta,  soda,  and  oxide  of  silver,  is  a  property  which  the  analytical 
chemist  may  avail  himself  of  in  analysis  for  the  separation  of  potassa  and  soda 
from  each  other. 

^HLORITES. 

The  alkaline  salts  of  chlorous  acid  are  readily  made,  as  mentioned  at  page  226, 
by  transmitting  a  current  of  chlorous  acid  gas  into  a  solution  of  the  pure  alkalies. 
All  that  have  as  yet  been  examined  are  soluble  in  water,  and  are  remarkable  for 
their  highly  bleaching  and  oxidizing  properties.  By  the  latter  properties  and 
the  evolution  of  chlorous  acid  on  the  addition  of  any  of  the  stronger  acids  their 
presence  is  readily  recognized. 

Hypochlorites. — The  hypochlorites  may  be  produced  by  the  action  of  chlorine 
gas  on  the  salifiable  bases.  The  most  important  of  them  is  the  hypochlorite  of 
lime,  the  well-known  bleaching  powder,  which  has  commonly  been  described 
as  the  oxymuriate  or  chloride  of  lime.  It  is  prepared  for  commercial  purposes 
by  exposing  thin  strata  of  recently  slaked  lime  in  fine  powder  to  an  atmosphere 
of  chlorine.  The  gas  is  absorbed  in  large  quantity,  and  the  chloride  of  calcium 
and  hypochlorite  of  lime  are  produced  in  equivalent  proportions. 

It  is  a  dry  white  powder,  which  smells  faintly  of  chlorine,  and  has  a  strong 
taste.  It  dissolves  partially  in  water,  and  the  solution  possesses  powerful  bleach- 
ing properties,  and  contains  both  chlorine  and  lime;  while  the  undissolved  por- 
tion is  hydrate  of  lime,  retaining  a  small  quantity  of  chlorine.  The  aqueous 
solution,  when  exposed  to  the  atmosphere,  is  gradually  decomposed  ;  chlorin^ 
is  set  free,  and  carbonate  of  lime  generated.  On  boiling  the  liquid,  chloride  of 
calcium,  and,  I  presume,  chlorate  of  lime  are  formed  ;  and  by  long  keeping,  the 
dry  chloride  appears  to  undergo  a  similar  change, — at  least  chloride  of  calcium 
is  produced  in  large  quantity.  It  is  also  decomposed  by  a  strong  heat :  at  first, 
chlorine  is  evolved  ;  but  pure  oxygen  is  afterwards  disengaged,  and  chloride  of 
calcium  remains  in  the  retort. 

The  composition  of  chloride  of  lime  was  first  carefully  investigated  by  Dalton,* 

*  Annals  of  Philosophy,  i.  15,  and  ii.  6. 


478  CHLORITES. 

and  it  has  since  been  analyzed  by  Thomson,*  WelteT,|  and  Ure.:i:  The  three 
fifst-mentioned  chemists  infer  from  their  researches  that  bleaching  powder  is  a 
hydrated  subchluride  or  dichloride  of  lime  in  which  one  equivalent  of  chlorine  is 
united  with  two  equivalents  of  lime.  They  are  also  of  opinion,  that  on  mixing 
this  dichloride  with  water,  the  chloride  is  dissolved,  and  one  equivalent  of  lime 
separated  as  an  insoluble  powder.  Dr.  Ure,  on  the  contrary,  denies  that  bleach- 
ing powder  is  a  dichloride,  and  maintains  that  the  elements  of  this  powder  do 
not  constitute  a  regular  atomic  combination.  He  found  that  the  quantity  of  chlo- 
rine absorbed  by  hydrate  of  lime  is  variable,  depending  not  only  on  the  pressure 
and  degree  of  exposure,  but  on  the  quantity  of  water  present.  From  these  ex- 
periments it  appears  that  the  commercial  bleaching  powder  is  essentially  a  hypo- 
chlorite with  single  equivalents  of  its  elements,  but  mixed  with  variable  quanti- 
ties of  hydrate  of  lime. 

CI  7 

According  to  Millon,  bleaching-powder  is  an  oxychloride  of  calcium,  Ca^   > 

^  CaO,  CIO  -|-  CaCl.    It  is  now  certain  that  even  if  hypochlorites  exist,  the 

bleaching  compounds  of  lime,  potash,  and  soda  contain  the  chlorides  of  these 

metals  as  an  essential  constituent,  according  to  the  second  of  the  above  formulae. 

But  according  to  the  view  of  Millon,  these  compounds  must  be  viewed  as  oxy- 

Chlorides,  corresponding  to  the  peroxides  of  the  metals,  in  which  part  of  the 

oxygen  is  replaced  by  chlorine.    The  peroxides  of  sodium  and  calcium  are  NaO^ 

CI  7  CI  7 

and  Ca02,  and  the  bleaching  compounds  are  Na      >  and    Ca      S  .      But   the 

peroxide  of  potassium  is  KO  ,  and  consequently  its  bleaching  compound  ought 

CI  7 
to  be  Kp.  2  C  In  point  of  fact,  it  contains  twice  as  much  chlorine  as  the  cor- 
responding compound  of  sodium,  which  renders  this  view  extremely  probable. 
Similar  oxychlorides  are  formed  by  adding  these  compounds  to  solutions  of  lead, 
iron,  and  copper ;  and  by  the  action  of  these  compounds  on  hydrochloric  acid, 
Millon  has  obtained  a  new  bleaching  compound,  perchloride  of  hydrogen,  HCl^ 
perfectly  analogous  to  peroxide  of  hydrogen,  which  is  the  type  of  the  class  of 
bodies  just  described,  as  well  as  of  the  supeivoxides  of  the  metals,  its  formula 

being  H  „  >  .    For  details  the  reader  is  referred  to  Millon^s  paper  in  the  Journal 

de  Pharmacie  for  September,  183!),  p.  595. 

Several  methods  have  been  proposed  for  estimating  the  value  of  different  spe- 
cimens of  bleaching  powder.  Perhaps  the  most  convenient  for  the  artist  is  that 
of  Welter,  which  consists  in  ascertaining  the  power  of  the  bleaching  liquid  to 
deprive  a  solution  of  indigo  of  known  strength  of  its  colour;  and  directions 
have  been  drawn  up  by  Gay-Lussac  for  enabling  manufacturers  to  employ  this 
method  with  accuracy.  (Annals  of  Philosophy,  xxiv.  218.)  For  analytical  pur- 
poses, the  best  method  is  to  decompose  chloride  of  lime,  confined  in  a  glass  tube 
over  mercury,  by  means  of  hydrochloric  acid.  Chloride  of  calcium  is  generated, 
and  the  chlorine  being  set  free,  its  quantity  may  easily  be  measured. 


*  An.  of  Pbil.  XV.  401.      t  Ann.  de  Ch,  et.  Ph.  vol.  viii.       X  Quarterly  Journal,  xiii.  1. 


479 

lODATES. 

From  the  close  analogy  in  the  composition  of  chloric  and  iodic  acids,  it  fol- 
lows that  the  general  character  of  the  iodates  must  he  similar  to  that  of  the  chlo- 
rates. Thus  in  all  neutral  protiodates  the  oxygen  contained  in  the  oxide  and 
acid  is  in  the  ratio  of  1  to  5.  They  form  deflagrating  mixtures  with  combustible 
matters ;  and  on  being  heated  to  low  redness,  oxygen  gas  is  disengaged  and  a 
metallic  iodide  remains.  As  the  affinity  of  iodine  for  metals  is  less  energetic 
than  that  of  chlorine,  many  of  the  iodates  part  with  iodine  as  well  as  oxygen 
when  heated,  especially  if  a  high  temperature  is  employed. 

The  iodates  are  easily  recognized  by  the  facility  with  which  their  acid  is 
decomposed  by  deoxidizing  agents.  Thus,  the  sulphurous,  phosphorous,  hydro- 
chloric, and  hydriodic  acids,  deprive  iodic  acid  of  its  oxygen,  and  set  iodine  at 
liberty.  Hydrosulphuric  acid  not  only  decomposes  the  acid  of  these  salts,  but 
occasions  the  formation  of  hydriodic  acid  by  yielding  hydrogen  to  the  iodine. 
Hence  an  iodate  of  potassa  may  be  converted  into  the  iodide  by  transmitting  a 
current  of  hydrosulphuric  acid  gas  through  its  solution.  None  of  the  iodates 
have  been  found  native.  They  are  all  of  very  sparing  solubility,  or  actually  inso- 
luble in  water,  excepting  the  iodates  of  the  alkalies. 

Iodate  of  Potassa. — This  salt  may  be  procured  by  adding  iodine  to  a  concen- 
trated hot  solution  of  pure  potassa,  until  the  alkali  is  completely  neutralized. 
The  liquid,  which  contains  an  iodate  and  iodide,  is  evaporated  to  dryness  by  a 
gentle  heat,  and  the  residue,  when  cold,  is  treated  by  repeated  portions  of  boiling 
alcohol.  The  iodate,  which  is  insoluble  in  that  menstruum,  is  left,  while  the 
iodide  of  potassium  is  dissolved.  A  better  process  has  been  recommended  by 
M.  Henry,  Jr.,  founded  on  the  property  which  iodide  of  potassium  possesses,  of 
absorbing  oxygen  while  in  the  act  of  escape  from  decomposing  chlorate  of 
potassa.  For  this  purpose  iodide  of  potassium  is  fused  in  a  capacious  hessian 
crucible,  and  when,  after  removal  from  the  fire,  it  is  yet  semi-fluid,  successive 
portions  of  pulverized  chlorate  of  potassa  are  projected  into  it,  stirring  well  after 
each  addition.  The  materials  froth  up  considerably,  and  when  the  action  is  over, 
a  white,  opaque,  cellular  mass  remains,  easily  separable  from  the  crucible  ;  tepid 
water  dissolves  out  the  chloride  of  potassium,  and  leaves  the  iodate.  Conve- 
nient proportions  are  one  part  of  iodide  of  potassium  and  rather  more  than  one 
and  a  half  of  chlorate  of  potassa.     (Journ.  de  Pharmacie,  July,  1832.) 

All  the  insoluble  iodates  may  be  procured  from  this  salt  by  double  decomposi- 
tion. Thus  iodate  of  baryta  may  be  formed  by  mixing  chloride  of  barium  with 
a  solution  of  iodate  of  potassa. 

A  biniodate  of  potassa  has  been  described  by  Serullas.  It  is  formed  by  incom- 
pletely neutralizing  a  hot  solution  of  chloride  of  iodine  with  potassa  or  its  car- 
bonate, and  setting  it  aside  to  cool.  A  peculiar  compound  of  chloride  of 
potassium  and  biniodate  of  potassa  falls ;  but  on  dissolving  this  substance,  fil- 
tering and  exposing  the  solution  to  a  temperature  of  77°,  the  biniodate  is  gra- 
dually deposited  in  right  rhombic  prisms  terminated  by  dihedral  summits.  It  is 
soluble  in  75  times  its  weight  of  water  at  59°. 

A  teriodate  may  be  formed  by  mixing  a  large  excess  of  sulphuric  acid  with  a 
moderately  dilute  solution  of  iodate  of  potassa.  On  evaporating  at  77°,  the  ter- 
iodate is  deposited  in  regular  rhomboidal  crystals,  which  require  25  times  their 
weight  of  water  at  60°  for  solution. 

Serullas  states  that  the  compound  of  chloride  of  potassium  and  biniodate  of 


480  PHOSPHATES. 

potassa,  above  mentioned,  maybe  formed  by  the  action  of  hydrochloric  acid  on 
iodate  of  potassa.  By  spontaneous  evaporation  it  is  obtained,  sometimes  in 
brilliant,  transparent,  elongated  prisms,  and  at  other  times  in  hexagonal  laminae  ; 
but  generally  it  crystallizes  in  right  quadrangular  prisms  with  their  lateral 
edges  truncated,  and  terminated  by  four-sided  summits.  (An.  de  Ch.  et  Ph. 
xliii.  113.) 

Bromates. — These  compounds  have  many  characters  in  common  with  the  chlo- 
rates and  iodates ;  but  hitherto  they  have  been  but  partially  examined. 

PHOSPHATES. 

In  studying  these  salts,  the  reader  must  bear  in  mind  that  there  are  three 
isomeric  modifications  of  the  same  acid,  which  have  been  described  under  the 
names  of  phosphoric^  pyrophosphoric^  and  metaphosphoric  acid ;  and  therefore  it 
will  be  necessary  to  have  three  corresponding  families  of  salts,  the  phosphates^ 
pyrophosphates^  and  meta phosphates.  This  distinction,  and  the  other  facts  lately 
recorded  by  Graham,  render  it  necessary  either  to  change  the  names  of  the  phos- 
phates, or  to  retain  their  old  names  in  opposition  to  the  principles  of  nomencla- 
ture. The  most  consistent  conduct  will  be  to  describe  each  salt  under  its 
scientific  name,  and  add  at  the  same  time  its  ordinary  one.  An  eq.  of  each  of 
the  three  acids,  is  a  compound  of  31*4  parts  or  2  eq.  of  phosphorus  +  40  parts 
or  5  eq.  of  oxygen  =  71*4,  expressed  by  the  formula  Pj^i*  ^^  ^o't^  a  salt  neu- 
tral in  composition,  1  eq.  of  an  alkaline  base  is  requisite;  and  in  the  case  of  any 
protoxide,  indicated  by  MO,  the  general  formula  will  be  MO  -1-  p20^.  If  2  eq. 
of  a  protoxide  are  united  with  one  of  the  acid,  we  have  a  disalt,  2M0  -|-  P^O^ ; 
and  if  3  eq.  of  a  base  combine  with  1  eq.  of  the  acid,  it  is  a  trisalt.  3M0  -+- 
P^O^.  It  seems  also  that  water  plays  the  part  of  an  alkaline  base  towards  each 
of  the  three  acids,  either  alone  or  conjointly  with  another  base:  the  salts  with 
such  compound  bases  can  scarcely  be  viewed  in  the  light  of  double  salts,  since 
the  two  bases  act  together  as  one  electro-positive  element. 

All  the  protophosphates  which  are  neutral  in  composition  are  soluble  in  water, 
and  redden  litmus  paper;  whence  they  are  commonly  called  superphosphates. 
The  triphosphates,  except  those  of  the  pure  alkalies,  are  either  sparingly  soluble 
or  insoluble  in  water  ;  but  they  are  all  dissolved  by  dilute  nitric  or  phosphoric  acid, 
being  converted  into  the  soluble  phosphates.  All  the  triphosphates  with  fixed 
and  strong  bases  bear  a  red  heat  without  change;  but  the  phosphates  and  diphos- 
phates, to  judge  from  experiments  on  the  soda  salts,  are  converted  into  meta- 
phosphates  and  pyrophosphates.  Most  of  tiie  phosphates  of  the  second  class  of 
metals  are  resolved  into  phosphurets  by  the  conjoint  agency  of  heat  and  com- 
bustible matter.  The  phosphates  of  the  alkalies  are  only  partially  decomposed 
under  these  circumstances,  and  the  phosphates  of  baryta,  strontia,  and  lime, 
undergo  no  change. 

The  presence  of  a  soluble  phosphate  may  be  distinguished  by  the  tests  already 
mentioned  for  phosphoric  acid.  The  insoluble  phosphates  are  decomposed  when 
boiled  with  a  strong  solution  of  carbonate  of  potassa  or  soda,  the  acid  uniting 
with  the  alkali  so  as  to  form  a  soluble  phosphate  :  the  earthy  phosphates,  indeed, 
are  decomposed  with  difficulty,  requiring  continued  ebullition,  and  should  pre- 
ferably be  fused  with  an  alkaline  carbonate,  like  an  insoluble  sulphate. 

Several  phosphates  are  met  with  in  nature,  such  as  those  of  lime,  alumina, 
and  the  oxides  of  manganese,  iron,,  uranium,  copper,  and  lead. 


•      PHOSPHATES.  481 

The  composition  of  the  principal  phosphates  is  given  in  the  following  table : 

Names.  Base.  Acid.  Equiv.  Formulae. 

Triphosphate  of  Soda  93-9     3  eq.     -j-  71-4  1  eq.=  165-3  3N0  -j-  P2O5. 

Do,         in  crystals  with  216  or  24  eq.  of  water  =  381-3 

Triphosph.  Soda  and  C Soda  62-6     2eq.)     ,      «,^    ,„„         ,^0      mu^n  xsn   1    n  n 

Basic  Water  Jwater        9        1  eq.J  +    ^^  ^  ^  ^^'^  ^^^      2NaO,HO+PA. 

Do.        in  crystals  with  216  or  24  eq.  of  water  =  359 

Do.  ...      135  or  15  eq.  of  water  =278 

n^nVB^^'^Watetlw^er      Vs'    Hi]  +  ''V^  I  ^-^nO-,    Na0.2H0  +  PA. 

Do.        in  crystals  with  18  or  2  eq.  of  water  =  138-7 

Triphosphate  of  Potassa  141-45  3  eq.    +   71-4  1  eq.  =  212-85  3K0+ P2O5. 

Triphosp.ofPotassa  (KO  94-3     2  eq.7     .     ^.   .   .  ,-.  ^     0K0  2H0-t.P0 

and  Basic  Water     ^HO  9        1  eq.5  ^^    /l4leq._l/4/     -is.u,x:tiu  +  FgUj. 

Add  Triphosphate     jpotassa     47-15  1  eq.j  _^   ,^.,  ^  ^^^^^ 35.55  j,0,2H0  +  PA- 

Triphosph.  of  Soda,  (Soda         31-3     1  eq.)    ,  «,  ^   ,  io-^ok  to-  o  tt  Tvrr*  tt/-.    . 

Oxide  Ammonium;)  Ox.  Am.  26-15  1  eq.(+  71-4  1  eq.  =  13785  NaO,H4NO,HO + 
and  Basic  Water      (Water        9        leq.)  ^2^5* 

Do.        in  crystals  with  72  or  8  eq.  of  water  =  209-85 

Triphos.  of  oxide  of  (Ox.  Am.  52-30  2  eq.)    ,     -...  .         _  .33.70  2H  NO  HO-UP  n 
Am.  &  Basic  Water  ^  Water        9        1  eq.  J  ^    /I  4  1  eq.  —  Id-J  7U  ^H4iNU,HU-f- P^. 


Acid  Triphosphate      (Ox.  Am 
ditto                          I  Water 

.  26-15 
18 

2rq:}+^^-4   1eq. 

=  1 15-55  H4NO,2HO-|-  P2O5. 

Bone  Phosphate  of  Lime 

228 

8  eq.     -1-214-2  3eq. 

=  442-2 

8CaO  -f.  3P2O5. 

Triphosphate  do. 

85-5 

3  eq.    4-  71-4  1  eq. 

=  156-9 

3CaO  -f-  PjOg. 

Triphos.  of  Lime  &    (Lime 
Basic  W^ater             (Water 

57 
9 

?q;}t  7..4,.q. 

=  127-4 

2CaO,2HO  -f  P^- 

Acid  Triphos.  do.       \^ll 

28-6 
18 

^q|+ "■*■■«.• 

:=  117-9 

CaO,2HO  -|-  PA- 

For  the  new  and  more  simple  views  of  the  constitution  of  the  phosphates, 
pyrophosphates,  and  metaphosphates,  which  are  becoming  prevalent,  the  reader 
is  referred  to  the  account  of  them  given  in  the  general  section  on  salts. 

The  triphosphate  of  baryta,  strontia,  protoxides  of  manganese,  iron,  copper, 
lead,  silver,  &c.  precisely  correspond  to  the  triphosphate  of  lime,  simply  substi- 
tuting 3  eq.  of  those  oxides.  These  oxides  in  like  manner  form  soluble  phos- 
phates analogous  in  composition  to  that  of  lime. 

Triphosphate  of  Soda. — This  salt,  described  by  Graham  as  the  siibsesquiphos- 
phate,  is  made  by  adding  pure  soda  to  a  solution  of  the  succeeding  compound 
until  the  liquid  feels  soapy  to  the  fingers,  an  excess  of  soda  not  being  injurious. 
The  liquid  is  then  evaporated  until  a  pellicle  appears,  and  the  crystals  which  form 
on  cooling  are  quickly  redissolved  in  water  and  recrystallized.  Though  the  crys- 
tals do  not  change  in  the  air,  the  solution  absorbs  carbonic  acid,  and  the  result- 
ing carbonate  of  soda  adheres  to  the  triphosphate. 

This  salt  crystallizes  in  colourless  six-sided  slender  prisms,  which  have  a 
strong  alkaline  taste  and  reaction,  require  5  times  their  weight  of  water  at  60°, 
and  still  less  of  hot  water,  for  solution,  and  at  170°  fuse  in  their  water  of  crys- 
tallization. They  may  be  exposed  to  a  red  heat  without  losing  the  characters  of 
a  phosphate.     The  feeblest  acids  deprive  the  salt  of  one-third  of  its  soda. 

When  this  salt  is  mixed  in  solution  with  nitrate  of  oxide  of  silver  in  excess, 
there  is  an  exact  interchange  of  elements,  such  that 

1  eq.  Triphosphate  of  Soda  3NO-}-P205    2      1  eq.  Triphosph.  of  Silver  3AgO-f-P20g' 
&  3  eq.  Nitrate  of  Silver       SCAgO-fNOg  1.     &  3  eq.  Nitrate  of  Soda      SCNaO-j-NOg. 

33 


482  PHOSPHATES.      • 

The  resulting  solution  is  therefore  quite  neutral.  The  triphosphate  of  oxide 
of  lead,  and  other  insoluble  triphosphates  may  be  prepared  in  like  manner. 

Triphosphate  of  Soda  and  Basic  Water. — This  salt  is  the  most  common  of  the 
phosphates,  being  manufactured  on  a  large  scale  by  neutralizing  with  carbonate 
of  soda  the  acid  phosphate  of  lime  procured  by  the  action  of  sulphuric  acid  on 
burned  bones.  It  is  generally  described  as  the  neutral  phosphate  of  soda,  and 
for  distinction's  sake  is  sometimes  termed  rhombic  phosphate,  from  its  crystals 
having  the  form  of  oblique  rhombic  prisms. 

This  salt  crystallizes  best  out  of  an  alkaline  solution;  but  however  prepared 
it  is  always  alkaline  to  test  paper,  and  requires  a  considerable  quantity  of  acid 
before  losing  its  alkalinity.  The  crystals  effloresce  on  exposure  to  the  air,  and 
require  4  times  their  weight  of  cold,  and  twice  their  weight  of  hot  water  for  solu- 
tion. It  often  contains  traces  of  sulphuric  acid,  from  which  it  may  be  purified 
by  repeated  solution  and  crystallization.  When  mixed  with  nitrate  of  oxide  of 
silver,  the  interchange  of  elements  is  such  that 

1  eq.  Rhombic  Phos.  2  NaO,  HCH-PgOg    2      1  eq.  Triphosph.  of  Silver  SAgO-j-PjOg. 
&  3  eq.  Nitrate  of  Silver  SCAgO-j-NOg)        £     &  2  eq.  Nitrate  of  Soda      2(NaO-f-N05. 

The  yellow  triphosphate  of  oxide  of  silver  falls  exactly  as  with  the  former  salt, 
but  1  eq.  of  nitric  acid  is  left  free  in  the  solution. 

When  a  solution  of  the  rhombic  phosphate  is  evaporated  at  a  temperature  of 
90°,  it  crystallizes  with  14  instead  of  24  equivalents  of  water,  and  the  crystals 
differ,  as  might  be  expected,  from  the  other  salt  in  fi[gure,  and  are  permanent  in 
the  air.  Both  salts  lose  their  basic  water  at  a  red  heat,  and  are  converted  into  a 
pyrophosphate. 

Acid  Triphosphate  of  Soda  and  Water. — This  salt,  commonly  called  hiphosphate 
of  soda  from  its  acid  reaction,  may  be  formed  by  adding  phosphoric  acid  to  a  solu- 
tion of  carbonate  of  soda,  or  to  either  of  the  preceding  phosphates,  until  it  ceases 
to  give  a  precipitate  with  chloride  of  barium.  Being  very  soluble  in  water,  the 
solution  must  be  concentrated  in  order  that  it  may  crystallize.  This  salt  is  capa- 
ble of  yielding  two  different  kinds  of  crystals  without  varying  its  composition. 
The  more  unusual  form,  isomorphous  with  binarseniate  of  soda,  is  a  right  rhombic 
prisra,  the  smaller  lateral  edge  of  which  is  78°  3(y,  terminated  by  pyramidal 
planes.  The  form  of  its  ordinary  crystals  is  a  right  rhombic  prism,  the  larger 
angle  of  which  is  93°  54'. 

The  crystals  of  this  salt  consist,  as  stated  at  page  481,  of  NaO,  2HO,p20^-f- 
2H0.  When  heated  to  212°,  the  water  of  crystallization  is  expelled,  and  the 
anhydrous  salt  remains,  still  yielding  a  yellow  precipitate  with  silver  when  neu- 
tralized by  ammonia;  but  if  exposed  to  a  heat  of  400°,  it  loses  half  its  basic 
water,  being  reduced  to  NaO,HO,P20^,  and  has  the  character  of  pyrophosphate 
of  soda.     At  a  red  heat  it  is  converted  into  metaphosphate  of  soda. 

Triphosphate  of  Potassa. — Graham  formed  this  salt  by  adding  caustic  potissa 
in  excess  to  a  solution  of  phosphoric  acid,  as  well  as  by  fusing  phosphoric  acid 
with  a  slight  excess  of  carbonate  of  potassa.  He  obtained  it  in  acicular  crystals, 
which  were  very  soluble  in  water,  but  not  deliquescent. 

Triphosphate  of  Potassa  a)id  Basic  Water. — This  salt  may  be  prepared  by  neu- 
tralizing the  superphosphate  of  lime  from  bones  with  carbonate  of  potassa.  It  is 
deliquescent,  and  has  not  been  obtained  in  regular  crystals. 

Acid  Triphosphate  of  Potassa  and  Basic  Water  may  be  formed  by  adding  phos- 
phoric acid  to  carbonate  of  potassa  until  the  liquid  ceases  to  give  a  precipitate 


PHOSPHATES.  483 

T^ith  chloride  of  banum,  and  setting  it  aside  to  crystallize.  The  crystals  belong 
to  the  square  prismatic  system,  and  they  usually  occur  in  square  prisms  termi- 
nated by  the  planes  of  an  octohedron.     They  are  acid  to  test  paper. 

When  this  compound  is  neutralized  by  carbonate  of  soda,  and  the  solution  set 
to  crystallize,  a  phosphate  of  soda  and  potassa  is  deposited  in  crystals,  the  form 
of  which  is  an  oblique  rhombic  prism,  which  frequently  occurs  without  modifi- 
cation. 

Tri'phosphate  (f  Soda  and  Oxide  of  Ammonia  and  B.asic  Water. — This  salt  is 
easily  prepared  by  mixing  together  1  eq.  of  hydrochlorate  of  ammonia  and  2  eq. 
of  the  rhombic  phosphate  of  soda,  each  being  previously  dissolved  in  a  small 
quantity  of  boiling  water.  As  the  liquid  cools,  prismatic  crystals  of  the  double 
phosphate  are  deposited,  while  chloride  of  sodium  remains  in  solution.  Their 
form  is  an  oblique  rhombic  prism.  This  salt  has  been  long  known  by  the  name 
of  microcosmic  salt.,  and  is  much  employed  as  a  flux  in  experiments  with  the  blow- 
pipe. When  heated  it  parts  with  its  water  and  ammonia,  and  a  very  fusible 
metaphosphate  of  soda  remains. 

Triphosphate  of  Ox.  Ammonium  and  Basic  Water. — This  salt  is  formed  by  add- 
ing ammonia  to  concentrated  phosphoric  acid  until  a  precipitate  appears.  On 
applying  }ieat,  the  precipitate  is  dissolved,  and  on  abandoning  the  solution  to 
itself,  the  neutral  salt  crystallizes.  The  form  of  the  crystals  is  an  oblique  rhombic 
prism,  the  smaller  angle  of  which  is  84°  SC/.  They  often  occur  in  rhombic 
prisms  with  diedral  summits.     (Mitscherlich.) 

The  acid  triphosphate  is  made  in  the  same  manner  as  the  preceding  triphos- 
phate of  potassa.  The  crystals  are  less  soluble  than  the  preceding  salt,  and 
undergo  no  change  on  exposure  to  the  air.  Their  form  is  an  octohedron  with  a 
square  base ;  but  the  right  square  prism,  terminated  by  the  faces  of  the  octohe- 
dron, is  the  most  frequent. 

Phosphates  of  Lime. — The  peculiar  compound  called  the  hone  phosphate^  exists 
in  bones  after  calcination,  and  falls  as  a  gelatinous  precipitate  on  pouring  chlo- 
ride of  calcium  into  a  solution  of  the  rhombic  phosphate  of  soda,  or  on  adding 
ammonia  to  a  solution  of  any  phosphate  of  lime  in  acids. 

Triphosphate  of  Lime  and  Basic  Water,  commonly  called  neutral  phosphate, 
falls  as  a  granular  precipitate,  consisting  of  fine  crystalline  particles,  when  the 
rhombic  phosphate  of  soda  is  added  in  solution  drop  by  drop  to  chloride  of  cal- 
cium in  excess.  The  residual  liquid  reddens  litmus,  owing  to  a  small  quantity 
of  triphosphate  of  lime  being  generated. 

Triphosphate  of  Lime  cannot  be  formed  by  precipitation,  but  occurs  in  hexago- 
nal prisms  in  the  mineral  called  apatite. 

Acid  Triphosphate  of  Lime  and  Basic  Water,  called  the  biphosphate  from  its 
acid  reaction,  is  formed  by  dissolving  either  of  the  preceding  salts  in  a  slight 
excess  of  phosphoric  acid.  The  compound  is  deliquescent,  very  soluble,  and 
crystallizes  with  great  difficulty.  It  exists  in  the  urine.  The  solution  formed 
by  the  action  of  sulphuric  acid  on  bones  is  probably  a  compound  of  lime  with  2 
or  more  eq.  of  phosphoric  acid,  being  really  a  superphosphate. 

Triphosphate  <f  Magnesia  and  Basic  Water. — It  is  formed  by  mixing  together 
hot  saturated  solutions  of  the  rhombic  phosphate  of  soda  and  sulphate  of  mag- 
nesia, and  separates  on  cooling  in  small  crystals  which  contain  13  eq.  of  water 
to  one  of  the  salt.  The  triphosphate  of  magnesia  is  principally  formed  when  the 
Bolutions  are  intermixed  in  the  cold.     These  salts  have  been  but  little  examined. 

The  phosphate  of  ammonia  and  magnesia  subsides  as  a  pulverulent  granular 


484  PYROPHOSPHATES. 

precipitate  from  neutral  or  alkaline  solutions,  containing  phosphoric  acid,  ammo- 
nia, and  magnesia.  It  is  readily  dissolved  by  acids,  and  is  sparingly  soluble  in 
pure  water,  especially  when  carbonic  acid  is  present:  but  it  is  insoluble  in  a  solu- 
tion of  most  neutral  salts,  such  as  hydrochlorate  of  ammonia.  It  constitutes  one 
variety  of  urinary  concretions.     According  to  Berzelius  it  consists  of 


Phosphoric  Acid 

71-4 

leq. 

P2O5. 

Magnesia 

41-4 

2eq. 

2MgO. 

Ammonia 

34-3 

2eq. 

2H^N. 

Water 

90 

10  eq. 

lOHO. 

The  mode  in  which  these  elements  are  arranged  is  unknown.  When  heated 
to  redness  it  loses  its  water  and  ammonia,  and  the  residue  is  diphosphate  of 
magnesia,  which  contains  36-67  per  cent,  of  pure  magnesia.  At  a  strong  red 
heat  it  fuses,  and  appears  when  cold  as  a  white  enamel. 

When  the  materials  for  forming  the  preceding  salt  are  mixed  while  hot,  small 
acicular  crystals  subside  on  cooling,  which  are  said  by  Berzelius  to  contain  less 
of  the  two  bases  than  the  other  salt. 

Phosphates  of  Protoxide  of  Lead. — The  triphosphate  is  precipitated  when  ace- 
tate of  oxide  of  lead  is  mixed  with  a  solution  of  the  rhombic  phosphate  of  soda, 
acetic  acid  being  set  free.  The  triphosphate  with  basic  water  is  best  formed  by 
adding  the  rhombic  phosphate  of  soda  gradually  to  a  hot  solution  of  chloride  of 
lead.  The  nitrate  should  not  be  used  for  the  purpose,  as  it  combines  with  the 
precipitate.  Both  these  phosphates  are  white,  and  are  frequently  formed  at  the 
same  time.  The  latter  fuses  readily  into  a  yellow  bead,  which  in  cooling 
acquires  crystalline  facettes. 

Triphosphate  of  Oxide  of  Silver. — ^This  compound  subsides,  of  a  characteristic 
yellow  colour,  when  the  rhombic  phosphate  of  soda  is  mixed  in  solution  with 
nitrate  of  oxide  of  silver,  nitric  acid  being  set  free  at  the  same  time.  It  is  apt 
to  retain  some  of  the  nitrate  in  combination.  This  salt  is  very  soluble  in  nitric 
and  phosphoric  acid,  forming  the  soluble  phosphate,  and  in  ammonia.  By  ex- 
posure to  light  it  is  speedily  blackened  ;  but  when  protected  from  this  agent,  it 
yields  on  drying  an  anhydrous  yellow  powder,  which  has  a  sp.  gr.  of  7-321 
(Stroraeyer).  Its  colour  changes  on  the  app'ication  of  heat  to  a  reddish-brown, 
but  its  original  tint  returns  on  cooling.  It  bears  a  red  heat  without  fusion  :  at  a 
white  heat  it  fuses,  and  if  kept  for  some  time  in  a  fused  state  a  portion  of  pyro- 
phosphate is  generated. 

PYROPHOSPHATES. 

The  discovery  of  these  salts  by  Clark  has  also  been  mentioned.  That  modifi- 
cation of  phosphoric  acid  termed  pyrophosphoric  acid,  is  procured  by  forcing  with 
the  aid  of  heat  phosphoric  acid  to  combine  with  2  eq.  either  of  water  or  some 
fixed  base.  The  only  pyrophosphates  which  have  as  yet  been  studied  are  those 
of  soda  and  oxide  of  silver.    These  salts  are  thus  constituted  : — 

Names.  Base.  Acid.  Equiv.  Formulae. 

DipyrophosphateofSoda    .    .    .    626    2  e(^lf-71-4  1  eq.=134'0  2NaO-}-P20s. 

Do  in  crystals  with  90  or  10  eq.  of  water  .       =224 

Acid  Dipyrophos.  Soda  c Soda         31-3)  ,  ^,  .  ,  ,,,  „  ^t  ^  rx^  .  t,  ^ 

and  Basic  Water         {water        9     ^  ^^-^^^'^  1  eq.=lll-7  Na0,H0+P^s 

Pyrophosphate  of  Soda       .    .     .     31-3     1  eq.+7I-4  1  eq. =102-7  NaOfP^O'. 

Dipyrophos.  Oxide  of  Silver    .     .232        2  eq.+71-4  1  eq.=303-4  2Ag0-|-P*0\ 


METAPHOSPHATES.  485 

Dipyrophosphate  of  Soda. — This  is  the  compound  first  prepared  by  Clark  from 
the  rhombic  phosphate,  by  expelling  its  basic  water.  "When  the  residual  mass 
is  dissolved  in  water  and  set  to  evaporate,  crystals  are  obtained,  having  the  out- 
line of  an  irregular  six-sided  prism,  derived  from  a  rhombic  prism.  These 
crystals  are  permanent  in  the  air,  much  less  soluble  in  water  than  the  original 
rhombic  phosphate,  and  guite  neutral  to  test  paper.  Ignited  with  carbonate  of 
soda,  a  phosphate  is  reproduced,  because  the  acid  is  forced  to  unite  with  3  eq. 
of  a  base. 

Dipyrophosphate  of  soda  is  permanent  both  in  crystals  and  in  solution  in  the 
cold  ;  but  by  long  boiling,  or  quickly  when  boiled  with  an  acid,  a  phosphate  is 
reproduced.  With  a  salt  of  lead  it  yields  a  white  dipyrophosphate  of  oxide  of 
lead  ;  and  on  washing  the  precipitate  and  decomposing  by  hydrosulphuric  acid 
gas,  a  solution  of  pyrophosphoric  acid  is  obtained,  which  again  forms  dipyro- 
phosphate of  soda  when  neutralized  with  soda. 

The  oxides  of  most  metals  of  the  second  class  yield  with  pyrophosphoric  acid 
insoluble  or  sparingly  soluble  salts,  which  may  be  prepared  by  double  decom- 
position with  dipyrophosphate  of  soda.  It  should  be  held  in  view,  however,  as 
Stromeyer  has  remarked,  that  most  of  these  salts  are  more  or  less  soluble  in  an 
excess  of  dipyrophosphate  of  soda;  and  that  some  of  them,  such  as  the  dipyro- 
phosphate of  the  oxides  of  lead,  copper,  nickel,  cobalt,  uranium,  bismuth,  man- 
ganese, and  mercury,  are  dissolved  by  it  with  great  facility. 

^cid  Dipyrophosphate  of  Soda  and  Water. — This  salt  is  formed  by  exposing, 
as  stated  at  page  482,  the  acid  triphosphate  to  a  heat  of  400°,  when  it  loses  one 
half  of  its  basic  water,  and  acquires  the  character  of  a  pyrophosphate.  This  salt 
dissolves  readily  in  water,  has  an  acid  reaction,  and  has  not  been  obtained  in 
crystals. 

Pyrophosphate  of  Soda. — When  the  preceding  salt,  NaOHO  -|-  PgO^*  is  heated 
to  600°  or  a  little  higher,  it  loses  its  basic  water,  and  yet  the  acid  does  not  lose 
the  character  of  pyrophosphoric  acid.  It  is  left,  therefore,  as  a  simple  pyrophos- 
phate of  soda,  NdO  -|-  P^O^.  On  adding  water  part  of  it  dissolves,  and  part  is 
left  as  an  insoluble  white  powder.  The  solution  is  quite  neutral  to  test  paper; 
but  on  adding  nitrate  of  oxide  of  silver,  the  dipyrophosphate  of  that  oxide  falls, 
and  free  nitric  acid  remains  in  solution.  The  soluble  and  insoluble  pyrophos- 
phate of  soda  appear  identical  in  composition,  and  the  former  at  a  heat^ust 
short  of  redness  may  be  wholly  converted  into  the  latter. 

Dipyrophosphate  of  Oxide  of  Silver. — This  salt  is  readily  formed  by  double 
decomposition  with  dipyrophosphate  of  soda  and  nitrate  of  oxide  of  silver,  the 
residual  liquid  being  quite  neutral  to  test  paper.  It  falls  as  a  snow-white  gra- 
nular precipitate,  which  fuses  readily  at  a  heat  short  of  incandescence  into  a 
dark  brown  liquid,  which  becomes  a  crystalline  enamel  on  cooling. 

METAPHOSPHATES. 

The  only  metaphosphates  which  have  yet  been  examined  are  those  of  soda, 
baryta,  and  oxide  of  silver,  which  are  thus  constituted  : — 

Names.  Base.  Acid.        Equiv.        Formulse. 

Metaphosphate  ofSoda        .  .  31-3     1  eq.+71'4     1  eq.=102'7     NaO+PzOg. 

Do.  Baryta     .  .  76-7     1  eq.-|-71-4     1  eq.=148-l     BaO-^VzO^. 

Do.  Ox.  Silver  .  116        1  eq.-t71-4     1  eq.=l87-4     AgO-f-PA- 

Submetaphos.  do.    .  .  348        3  eq.-}-142-8  2  eq.=490-8  3AgO+2P205. 


4p!|.  ARSENIATES, 

Metaphosphate  of  Soda. — When  the  pyrophosphate  or  acid  dipyrophosphate  of 
soda  is  healed  to  low  redness,  it  fuses,  and  on  cooling  becomes  a  transparent 
glass,  which  deliquesces  in  a  damp  air,  and  is  very  soluble.  The  solution  has 
a  feeble  acid  reaction.  When  mixed  with  nitrate  of  oxide  of  silver,  the  meta- 
phosphate of  that  oxide  falls  in  gelatinous  flakes,  wholly  unlike  the  pyrophos- 
phate, and  aggregates  together  as  a  soft  solid  when  heated  to  near  212°.  The 
metaphosphate  of  soda  does  not  change  by  keeping,  and  has  not  hitherto  been 
made  to  crystallize.  When  its  solution  is  evaporated,  and  kept  for  some  time 
at  400°,  it  is  reconverted  into  the  acid  dipyrophosphate  of  soda  and  basic  water. 
All  the  preceding  facts  are  drawn  from  Graham's  essay.  (Phil.  Trans.  1833, 
Part  ii.) 

Metaphosphate  of  Baryta  falls  in  gelatinous  flakes  on  adding  metaphosphate  of 
soda  to  a  solution  of  chloride  of  barium,  the  latter  being  in  excess  as  the  soda 
salt  dissolves  the  precipitate.  By  long-continued  boiling  metaphosphate  of  baryta 
is  at  length  dissolved,  and  at  the  same  time  converted  into  a  phosphate. 

The  metaphosphate  of  silver  is  obtained  by  precipitation,  as  above  stated. 
When  put,  while  moist,  into  boiling  water,  part  of  its  acid  is  removed,  and  the 
submetaphospbate  is  generated. 

ARSENIATES. 

Arsenic  acid  resembles  the  phosphoric  in  composition  and  in  many  of  its  pro- 
perties, but  as  far  as  is  yet  known  is  only  capable  of  forming  tribasic  salts. 
Those  which  contain  2  eq.  of  basic  water  are,  like  the  phosphates,  soluble  in 
water  and  redden  litmus,  whence  they  are  commonly  considered  as  bisalts.  If 
only  1  eq.  of  basic  water  be  present,  in  which  the  oxygen  of  the  alkaline  base 
and  acid  is  as  2  to  5,  the  salt  is  usually  termed  a  neutral  arseniate.  When  no 
basic  >jater  is  present,  the  salt  is  usually  described  as  a  subarseniate.  The  two 
last  series  of  salts,  except  those  with  the  alkalies,  are  of  sparing  solubility  in 
water :  but  they  are  dissolved  by  phosphoric  or  nitric  acid,  as  well  as  most  acids 
which  do  not  precipitate  the  base  of  the  salt. 

Many  of  the  arseniates  bear  a  red  heat  without  decomposition,  or  being  other- 
wist  modified  in  their  characters ;  but  they  are  all  decomposed  when  heated  to 
redness  along  with  charcoal,  metallic  arsenic  being  set  at  liberty.  The  arseniates 
of  the  fixed  alkalies  and  alkaline  earths  require  a  rather  high  temperature  for 
reduction;  while  the  arseniates  of  the  second  class  of  metals,  as  of  lead  and 
copper,  are  easily  reduced  in  a  glass  tube  by  moans  of  a  spirit-lamp  without 
danger  of  melting  the  glass.  Of  all  the  arseniates  that  of  oxide  of  lead  is  the 
most  insoluble. 

The  soluble  arseniates  are  easily  recognized  by  the  tests  described  in  the  sec- 
tion on  arsenic;  and  the  insoluble  arseniates,  when  boiled  in  a  strong  solution 
of  the  fixed  alkaline  carbonates,  are  deprived  of  their  acid,  which  may  then  be 
detected  in  the  usual  manner.  The  free  alkali,  however,  should  first  be  exactly 
neutralized  by  pure  nitric  acid. 

The  arseniates  of  lime,  and  of  the  oxides  of  nickel,  cobalt,  iron,  copper,  and 
lead,  are  natural  productions. 

The  composition  of  the  principal  arseniates  is  contained  in  the  following 
table :— 


ARSENIATES. 


487 


Names. 
Triarseniate  of  Soda  .        93-9 

Do.  in  crystals  with  216  or 

Triarsen.  Soda  CSoda       626 

and  Basic  Water      (Water      9 
Do.  in  crystals  with    216  or 

Do.  in  crystals  with    126  or 

Acid  Triarsen.  Soda     (Soda       31-3 

and  Basic  Water       (Water    18 
Do.  in  crystals  with    18   or 

Triarseniate  of  Potassa  141-45 

Triarsen.  of  Potassa     (Potassa  94-3 

and  Basic  Water       (Water      9 
Acid  Arsen.  of  Potas.  (Potassa  47*  15 

and  Basic  Water       (Water    18 
Triarseniate  of  Oxide    (  Ox.  Am.  52-30 
Am.  and  Basic  Water    (Water      9 
Acid  Triarsen.  of  Ox.  (Ox.  Am.  26-15 
Am.  and  Basic  Water  (Water     18 
Triarseniate  of  Baryta        .         230*1 
Triarseniate  do.     (Baryta  153*4 

with  Basic  Water     (Water       9 
Acid  Triarsen.  do 

with  Basic  Water 
Triarseniate  of  Lime 
Triarseniate         do. 

and  Basic  Water 
Acid  Triarsen.  do. 

and  Basic  Water 
Triarseniate  of  Ox.  Lead     . 
Triarseniate         do.     (Lead 

and  Basic  Water       (Water       9 
Triarseniate  of  Ox.  Silver      .     348 


Acid 

3eq.     +115-4 

24  eq.  of  water 

24  eq.  of  water 
14  eq.  of  water 


Equiv. 
:209-3 
:425-3 


Formulae. 
3Na+As205. 


1  eq.: 

1  eq.=187         2NaO,HO-t-As205. 


=403 
=313 


•I  +115-4  1  eq.=l64-7 


1  eq 

2  eq 

2  eq.  of  water 

3  eq.     +115-4 

115-4 
15-4 


(  Baryta 
(  Water 


(Li 
(W 


me 

Water 

Lime 

Water 


76-7 
18 

85-5 

57 
9 

28-5 

18 
334-8 
223-2 


2eq.)    . 
leq.J  T 


2el:}tll5-4 
3  eq.     -|- 115-4 

3  eq.     -|- 115-4 


2  :?:}+•>«■ 

3  eq.     +115-4 
3eq.    +115-4 


1  eq.: 
1  eq.= 

1  eq.= 

1  eq.= 

1  eq.= 
1  eq.= 
1  eq.= 

1  eq.= 
1  eq 
1  eq, 

1  eq 
1  eq. 
1  eq. 
1  eq. 


4  1  eq.= 


NaO,2HO+As205. 

;182-7 

:256-85  3KO+AS2O5. 

218-7    2KO,HO-i-A3205. 

162-55      KO,2HO+As205. 

176-7      2H4NO,HOtAsi05. 

=159-55    H4NO,2HO+As206. 
=345-5     SBaO+AszOg. 
=277-8     2BaO,HO+As205. 

=210-1      BaO,2HO+As206. 
=200-9     3Ca0+As.2O5. 
=181-4    2CaO,Ho-t-As205. 

161-9     CaO,2HO+As205. 
=450-2  3PbO+As205. 
:347-6  2PbO,HO+As206. 
463-4  3AgO+As206. 


Arseniates  of  Soda. — The  triarseniate  is  made  in  the  same  manner  as  triphos- 
phate of  soda,  with  which  it  is  isomorphous.  At  60°,  100  parts  of  water  dis- 
solve 28  of  the  crystals,  and  still  more  by  the  aid  of  heat.  At  186°  they  fuse 
in  their  water  of  crystallization. 

The  triarseniate  of  soda  and  basic  water  corresponds  precisely  in  form  and 
constitution  with  the  corresponding  phosphate,  and  like  it  parts  with  its  last  eq. 
of  water  at  a  red  heat ;  but  does  not,  on  losing  it,  receive  any  change  in  its 
characters.  It  is  efflorescent  and  alkaline  to  test  paper,  and  crystallizes  best  out 
of  an  alkaline  solution.  It  is  prepared  by  adding  soda  or  its  carbonate  in  slight 
excess  to  a  solution  of  arsenic  acid.  The  salt  with  14  eq.  of  water  coincides 
with  the  corresponding  phosphate. 

The  acid  triarseniate  of  soda  and  basic  water  is  prepared  like  the  correspond- 
ing phosphate. 

The  same  observation  applies  to  the  arseniates  of  potassa  and  ammonia,  each 
having  its  isomorphous  arseniate.  The  triarseniate  of  potassa  crystallizes  in 
needles  and  with  difficulty,  like  the  corresponding  phosph-ate.  The  arseniate  of 
potassa  may  be  formed  by  heating  nitre  to  redness  mixed  with  an  equal  weight 
of  arsenious  acid. 

The  compound  arseniate  of  potassa  and  soda  agrees  in  form  and  composition 
with  the  phosphate  of  those  bases. 

Arseniates  uf  Baryta. — The  triarseniate  is  best  prepared  by  gradually  adding  in 


488  ARSENITES. 

solution  triarseniate  of  soda  to  chloride  of  barium  in  excess,  and  falls  as  a  pul- 
verulent heavy  precipitate,  which  is  apt  to  contain  a  little  triarseniate  of  baryta 
and  basic  water  as  well  as  the  soda  salt,  and  should  therefore  be  well  washed 
with  boiling  water.  On  adding;  chloride  of  barium  to  an  excess  of  triarseniate 
of  soda,  the  latter  salt  always  falls  with  the  precipitate. 

To  prepare  the  triarseniate  of  baryta  and  basic  water  a  solution  of  the  rhombic 
triarseniate  of  soda  is  added  drop  by  drop  to  chloride  of  barium  in  solution,  when 
the  triarseniate  -soon  appears  in  white  crystalline  scales,  which  contain  3  eq.  of 
water.  On  reversing  the  process  by  adding  chloride  of  barium  to  the  arseniate, 
the  precipitate  is  a  mixture  of  the  triarseniate  of  baryta,  and  triarseniate  of 
baryta  and  water.  By  the  continued  action  of  hot  water  on  the  latter,  it  is  partly 
changed  into  the  acid  triarseniate  and  insoluble  triarseniate.  Tlie  acid  triarse- 
niate is  obtained  by  dissolving  either  of  the  two  former  salts,  in  a  moist  state,  by 
dilute  arsenic  acid. 

Triarseniates  of  Lime. — The  three  salts  analogous  to  those  of  baryta  are 
obtained  by  precisely  similar  processes.  The  triarseniate  of  lime  and  basic 
water  occurs  in  silky  acicular  crystals  as  a  rare  mineral  named  pharmacolite, 
which  contains  6  eq.  of  water  of  crystallization. 

TViarseniates  of  Protoxide  of  Lead. — The  triarseniate  is  formed  by  adding  in 
solution  acetate  of  oxide  of  lead  gradually  to  an  excess  of  triarseniate  of  soda. 
The  same  salt  falls  when  acetate  of  oxide  of  lead  and  the  rhombic  triarseniate  of 
soda  are  intermixed,  acetic  acid  being  set  free.  It  is  a  white  very  insoluble 
powder,  which  at  a  low  red  heat  acquires  a  yellow  tint,  which  it  loses  again  on 
cooling. 

The  triarseniate  with  basic  water  may  be  made  by  a  similar  process  as  for 
forming  the  corresponding  triphosphate,  and  is  a  white  insoluble,  easily  fusible 
powder. 

Triarseniate  of  Oxide  of  Silver. — This  salt  falls  as  a  brick-red  powder  when 
nitrate  of  oxide  of  silver  is  mixed  in  solution  with  triarseniate  of  soda  or  the 
rhombic  triarseniate,  in  the  latter  case  nitric  acid  being  set  free.  It  is  apt  to 
retain  some  of  the  nitrate,  which  cannot  be  removed  by  washing ;  a  property 
which  the  yellow  phosphate  of  oxide  of  silver  also  possesses. 

ARSENITES. 

These  salts  have  as  yet  been  but  little  examined.  The  arsenites  of  potassa, 
soda,  and  ammonia  may  be  prepared  by  acting  with  those  alkalies  on  arsenious 
acid  :  they  are  very  soluble  in  water,  have  an  alkaline  reaction,  and  have  not  been 
obtained  in  regular  crystals.  Most  of  the  other  arsenites  are  insoluble,  or  spar- 
ingly soluble,  in  pure  water;  but  they  are  dissolved  by  an  excess  of  their  own 
acid,  with  great  facility  by  nitric  acid,  and  by  most  other  acids  with  which  their 
bases  do  not  form  insoluble  compounds.  The  insoluble  arsenites  are  easily 
formed  by  double  decomposition. 

All  the  arsenites  are  decomposed  when  heated  in  close  vessels,  the  arsenious 
acid  being  either  dissipated  in  vapour,  or  converted,  with  disengagement  of  some 
metallic  arsenic,  into  arseniates.  Heated  -^Vith  charcoal  or  black-flux,  the  acid  is 
reduced  with  facility.     Formiate  of  soda  answers  still  better. 

The  soluble  arsenites,  if  quite  neutral,  are  characterized  by  forming  a  yellow 
arsenite  of  oxide  of  silver  when  mixed  with  the  nitrate  of  that  base,  and  a  crreen 
arsenite  of  protoxide  of  copper,  Scheele^s  green^  with  sulphate  of  that  oxide. 


CHROMATES.  489 

"When  acidulated  with  acetic  or  hydrochloric  acid,  hydrosulphuric  acid  causes 
the  formation  of  orpiment.  The  insoluble  arsenites  are  all  decomposed  when 
boiled  in  a  solution  of  carbonate  of  potassa  or  soda. 

The  arsenite  of  potassa  is  the  active  principle  of  Fowler's  arsenical  solution. 

CHROMATES. 

The  salts  of  chromic  acid  are  mostly  either  of  a  yellow  or  red  colour,  the  lat- 
ter tint  predominating  whenever  the  acid  is  in  excess.  The  chromates  of  oxides 
of  the  second  class  of  metals  are  decomposed  by  a  strong  red  heat,  by  which  the 
acid  is  resolved  into  the  green  oxide  of  chromium  and  oxygen  gas ;  but  the 
chromates  of  the  fixed  alkalies  sustain  a  very  high  temperature  without  decom- 
position. They  are  all  decomposed,  without  exception,  by  the  united  agency  of 
heat  and  combustible  matter.  The  neutral  chromates  of  protoxides  are  similar 
in  constitution  to  the  sulphates,  being  formed  of  1  eq.  of  the  base  and  1  of 
chromic  acid,  the  formula  being  MO  +  CrO^. 

The  chromates  are  in  general  sufficiently  distinguished  by  their  colour.  They 
may  be  known  chemically  by  the  following  character  : — On  boiling  a  chromate 
in  hydrochloric  acid  mixed  with  alcohol,  the  chromic  acid  is  at  first  set  free,  and 
is  then  decomposed,  a  green  solution  of  the  chloride  of  chromium  being  gene- 
rated. 

The  only  native  chromate  hitherto  discovered  is  the  red  dichromate  of  protox- 
ide of  lead  from  Siberia,  in  the  examination  of  which  Vauquelin  made  the  dis- 
covery of  chromium. 

Chromates  of  Potassa. — The  neutral  chromate  from  which  all  the  compounds  of 
chromium  are  directly  or  indirectly  prepared,  is  made  by  heating  to  redness  the 
native  oxide  of  chromium  and  iron,  commonly  called  chromate  of  iron,  with 
nitrate  of  potassa,  when  chromic  acid  is  generated,  and  unites  with  the  alkali  of 
the  nitre.  The  object  to  be  held  in  view  is  to  employ  so  small  a  proportion  of 
nitre,  that  the  whole  of  the  alkali  may  combine  with  chromic  acid,  and  consti- 
tute a  neutral  chromate,  which  is  easily  obtained  pure  by  solution  in  water  and 
crystallization.  For  this  purpose  the  chromate  of  iron  is  mixed  with  about  a 
fifth  of  its  weight  of  nitre,  and  exposed  to  a  strong  heat  for  a  considerable  time ; 
and  the  process  is  repeated  with  those  portions  of  the  ore  which  are  not  attacked 
in  the  first  operation.  It  is  deposited  from  its  solution  in  small  prismatic  anhy- 
drous crystals  of  a  lemon-yellow  colour,  which,  according  to  Brooke,  belong  to 
the  right  prismatic  system. 

Chromate  of  potassa  has  a  cool,  bitter,  and  disagreeable  taste.  It  is  soluble 
to  great  extent  in  boiling  water,  and  in  twice  its  weight  of  that  liquid  at  60° ; 
but  it  is  insoluble  in  alcohol.  It  has  an  alkaline  reaction,  and  on  this  account 
Tassaert*  regards  it  as  a  subsalt;  but  Thomson  has  proved  that  it  is  neutral  in 
composition,  consisting  of  52  parts  or  1  eq.  of  chromic  acid,  and  47*15  parts  or 
1  eq.  of  potassa. -j- 

Bichromate  of  potassa,  which  is  made  in  large  quantity  at  Glasgow  for  dye- 
ing, is  prepared  by  acidulating  the  neutral  chromate  with  sulphuric,  or  still  better 
with  acetic  acid,  and  allowing  the  solution  to  crystallize  by  spontaneous  evapo- 
ration. When  slowly  formed  it  is  deposited  in  four-sided  tabular  crystals,  the 
form  of  which  is  an  oblique  rhombic  prism.    They  have  an  exceedingly  rich  red 

*  An.  de  Ch.  et  Ph.  vol.  xxii.  t  Annals  of  Philosophy,  vol.  xvi. 


490  CHROMATES. 

colour,  are  anhydrous,  and  consist  of  1  eq.  of  the  allcali,  and  2  eq.  of  chromic 
acid.  (Thomson.)  They  are  sohible  in  about  ten  times  their  weight  of  water  at 
60°,  and  the  solution  reddens  litmus  paper. 

The  insoluble  salts  of  chromic  acid,  such  as  the  chromates  of  baryta  and 
oxides  of  zinc,  lead,  mercury,  and  silver,  are  prepared  by  mixing  the  soluble 
salts  of  those  bases  with  a  solution  of  chromate  of  potassa.  The  three  former 
are  yellow,  the  fourth  orange-red,  and  the  fifth  deep  red  or  purple.  The  yellow 
chmmate  of  lead,  which  consists  of  1  eq.  of  acid  and  1  eq.  of  oxide,  is  now 
extensively  used  as  a  pigment,  and  the  chromate  of  oxide  of  zinc  may  be  used 
for  the  same  purpose. 

A  dichromate,  composed  of  1  eq.  of  chromic  acid  and  2  eq.  of  protoxide  of 
lead,  may  be  formed  by  boiling  the  carbonate  of  that  oxide  with  excess  of  chro- 
mate of  potassa.  It  is  of  a  beautiful  red  colour,  and  has  been  recommended  by 
Badams  as  a  pigment.  (An.  of  Phil.  xxv.  .303.)  It  may  be  also  made  by  boil- 
ing the  neutral  chromate  with  ammonia  or  lime-water.  Liebig  and  Wohler  pre- 
pare it  by  fusing  nitre  at  a  low  red  heat,  and  adding  chromate  of  oxide  of  lead 
by  degrees  until  the  nitre  is  nearly  exhausted.  The  chromate  of  potassa  and 
nitre  are  then  removed  by  water,  and  the  dicromate  is  left  crystalline  in  texture, 
and  of  so  beautiful  a  tint  that  it  vies  with  cinnabar.     (Pog.  An.  xxi.  580.) 

Chromates  of  Silver. — When  a  soluble  salt  of  chromic  acid  is  added  to  a  solu- 
tion of  nitrate  of  silver,  a  deep  red-coloured  precipitate  is  obtained,  which  has 
usually  been  considered  as  the  neutral  chromate  of  silver.  But  it  has  recently 
been  proved  by  Warington  (Phil.  Mag.  xi.  489)  that  if  the  precipitation  be  made 
with  acid  solutions  a  bichromate  is  formed.  He  also  obtained  the  latter  salt  by 
the  direct  oxidation  of  metallic  silver  by  a  solution  of  bichromate  of  potassa 
acidulated  with  sulphuric  acid.  The  silver  is  oxidized  at  the  expense  of  a  part 
of  the  chromic  acid ;  while  another  part,  "by  uniting  with  the  resulting  oxide, 
forms  the  bichromate,  which  is  deposited  in  tabular  crystals  of  a  rich  crimson 
colour.  A  chrome  alum  is  at  the  same  time  formed,  and  the  oxidation  of  this 
silver  would  appear  to  be  induced  by  the  affinity  of  the  sulphuric  acid  for  the 
oxide  of  chromium. 

On  boiling  the  bichromate  in  distilled  water,  a  part  is  dissolved  and  separated 
as  the  solution  cools  in  beautiful  micaceous  crystals ;  but,  at  the  same  time,  a 
portion  of  the  salt  is  decomposed  into  chromic  acid  and  neutral  chromate  of 
silver.  As  thus  formed,  the  latter  is  of  a  dark  green  colour  :  it  is  crimson,  how- 
ever, by  transmitted  light,  and  yields  by  trituration  a  powder  similar  in  colour 
to  the  precipitated  chromate. 

Bichromate  of  Ch/oride  of  Potassium. — Peligothas  described  a  crystalline  com- 
pound in  which  chloride  of  potassium  acts  the  part  of  an  alkaline  base  in  relation 
to  chromic  acid.  It  is  prepared  from  bichromate  of  potassa  and  concentrated 
hydrochloric  acid  in  the  ratio  by  weight  of  about  3  to  4,  which  are  to  be  boiled 
together  for  some  time  in  a  rather  small  quantity  of  water;  and  it  is  deposited 
in  flat  quadrangular  prisms  of  the  same  colour  as  bichromate  of  potassa. 

In  this  process  there  is  a  mutual  interchange  between  the  elements  of  potassa 
and  hydrochloric  acid  ;   such  that 

2  eq.  Cliromic  acid     .        .        .        2Cr03    ^     2  eq.  Chromic  acid     .        .        .       2Cr03. 
1  eq.  Potassa      ....  KO       "S      1  eq.  Chlo.  of  Potassium     .         .         KCl. 

1  eq.  Hydrochloric  acid     .         .  HCl       '^     1  eq.  Water         ....         HO. 


BORATES.  491 

For  this  change  to  ensue  there  ought  to  be  a  certain  excess  of  hydrochloric 
acid,  and  yet  not  so  much  as  to  decompose  the  chromic  acid. 

This  salt  should  be  dried  on  bibulous  paper.  It  is  permanent  in  the  air.  In 
pure  water  it  is  decomposed,  the  materials  from  which  it  was  formed,  bichro- 
mate of  potassa  and  hydrochloric  acid,  being  reproduced  ;  but  it  may  be  dis- 
solved without  such  change  in  water  acidulated  by  hydrochloric  acid.  Peligot 
has  made  similar  bichromates  with  the  chlorides  of  sodium,  calcium,  and  mag- 
nesium, and  with  hydrochlorate  of  ammonia,  this  last  salt  being  exactly  similar 
in  appearance  to  the  bichromate  of  chloride  of  potassium.  (An.  de  Ch.  et  Ph. 
lii.  267.) 

BORATES. 

As  the  boracic  is  a  feeble  acid,  it  neutralizes  alkalies  imperfectly,  and  hence 
the  borates  of  soda,  potassa,  and  oxide  of  ammonium  have  always  an  alkaline 
reaction.  For  the  same  reason,  when  the  borates  are  digested  in  any  of  the 
more  powerful  acids,  such  as  the  sulphuric,  nitric,  or  hydrochloric,  the  boracic 
acid  is  separated  from  its  base.  This  does  not  happen,  however,  at  high  tem- 
peratures; for  boracic  rcid,  owing  to  its  fixed  nature,  decomposes  at  a  red  heat 
all  salts,  not  excepting  sulphates,  the  acid  of  which  is  volatile. 

The  borates  of  the  alkalies  are  soluble  in  water,  but  most  of  the  other  salts  of 
this  acid  are  of  sparing  solubility.  They  are  not  decomposed  by  heat,  and  the 
alkaline  and  earthy  borates  resist  the  action  of  heat  and  combustible  matter. 
They  are  remarkably  fusible  in  the  fire,  a  property  obviously  owing  to  the  great 
fusibility  of  boracic  acid  itself. 

The  borates  are  distinguished  by  the  following  character: — By  digesting  any 
borate  in  a  slight  excess  of  strong  sulphuric  acid,  evaporating  to  dryness,  and 
boiling  the  residue  in  strong  alcohol,  a  solution  is  formed  which  has  the  property 
of  burning  with  a  green  flame. 

Biborale  of  Soda. — This  salt,  the  only  borate  of  importance,  occurs  native  ia 
some  of  the  lakes  of  Thibet  and  Persia,  and  is  extracted  from  this  source  by 
evaporation.  It  is  imported  from  India  in  a  crude  state,  under  the  name  of  Tin" 
cal,  which,  after  being  purified,  constitutes  the  refined  borax  of  commerce.  It  is 
frequently  called  suh-horate  of  soda,  a  name  suggested  by  the  inconsistent  and 
unphilosophical  practice,  now  quite  inadmissible,  of  regulating  the  nomenclature 
of  salts  merely  by  their  action  on  vegetable  colouring  matter.  It  crystallizes  in 
prisms  of  the  oblique  system,  which  effloresce  on  exposure  to  the  air,  and  require 
twenty  parts  of  cold,  and  six  of  boiling  water,  for  solution.  When  exposed  to 
heat,  the  crystals  are  first  deprived  of  their  water  of  crystallization,  and  then 
fused,  forming  a  vitreous  transparent  substance  called  glass  of  borax.  The  crys- 
tals are  composed  of  69*8  parts  or  2  eq.  of  boracic  acid,  31*3  or  1  eq.  of  soda, 
and  90  or  10  eq.  of  water. 

The  chief  use  of  borax  is  as  a  flux,  and  for  the  preparation  of  boracic  acid. 
Biborate  of  magnesia  is  a  rare  natural  production,  which  is  known  to  mineralo- 
gists by  the  name  of  Boracile. 

A  new  biborate  of  soda,  which  contains  half  as  much  water  of  crystallization 
as  the  preceding,  has  been  lately  described  by  Buran.  It  is  harder  and  denser 
than  borax,  is  not  efflorescent,  and  crystallizes  in  regular  octohedrons.  It  is 
made  by  dissolving  borax  in  boiling  water  until  the  sp.  gr.  of  the  solution  is  at 
30°  or  32°  of  Beaume's  hydrometer :   the  solution  is  then  very  slowly  cooled ; 


492 


CARBONATES. 


and  when  the  temperature  descends  to  about  133°,  the  new  salt  is  deposited. 
It  is  found  to  be  more  convenient  for  the  use  of  jewellers  than  common  borax. 
(An.  de  Ch.  et  Ph.  xxxvii.  419.) 

The  neutral  borate  of  soda  hac  been  obtained  by  Berzelius  by  the  action  of 
boracic  acid  on  carbonate  of  soda  at  a  boiling  heat,  when  carbonic  acid  is 
evolved.  The  solution  on  cooling  yields  crystals  of  the  oblique  prismatic  sys- 
tem, and  containing  8  eq.  of  water.  Their  constitution  is  there  NaO,BaO^-|-8 
HO.  They  are  powerfully  alkaline,  and  on  exposure  to  the  air  readily  attract 
carbonic  acid,  forming  the  carbonate  and  biborate  of  soda.  He  also  obtained  the 
neutral  borate  of  potassa,  but  was  prevented  by  its  great  solubility  from  pro- 
curing it  in  crystals. 

CARBONATES. 

The  carbonates  are  distinguished  from  other  salts  by  being  decomposed  with 
effervescence,  owing  to  the  escape  of  carbonic  acid  gas,  by  nearly  all  the  acids ; 
and  all  of  them,  except  the  carbonates  of  potassa,  soda,  and  lithia,  may  be  de- 
prived of  their  acid  by  heat.  The  carbonates  of  baryta  and  strontia,  especially 
the  former,  require  an  intense  white  heat  for  decomposition ;  those  of  lime  and 
magnesia  are  reduced  to  the  caustic  state  by  a  full  red  heat;  and  the  other  car- 
bonates part  with  their  carbonic  acid  when  heated  to  dull  redness. 

All  the  carbonates,  except  those  of  potassa,  soda,  and  ammonia,  are  of  sparing 
solubility  in  pure  water;  but  all  of  them  are  more  or  less  soluble  in  an  excess  of 
carbonic  acid,  owing  doubtless  to  the  formation  of  supersalts. 

Several  of  the  carbonates  occur  native,  among  which  may  be  enumerated  the 
carbonates  of  soda,  baryta,  strontia,  lime,  magnesia,  and  the  protoxides  of  man- 
ganese, iron,  copper,  and  lead ;  together  with  some  double  carbonates,  such  as 
dolomite  or  the  double  carbonate  of  lime  and  magnesia,  and  baryto-calcite  or  the 
double  carbonate  of  baryta  and  lime. 

The  composition  of  the  principal  carbonates  is  stated  in  the  following 
table ; — 


Names.  Base.  Acid. 

Carbonate  of  Potassa       .        .        47-15        1  eq.+22-12 
Bicarbonate        do.  .        .        47-15         1  eq.-|-44-24 

Do.  in  crystals  with  9  or  1  eq.  of  water 

Carbonate  of  Soda  .        .        31-3  1  eq.-f-22-12 

Do.  in  crystals  with  90  or  10  eq.  of  water 

Do.  ...        63  or    7  eq.  of  water 

Bicarbonate  of  Soda         .        .        31-3  1  eq.-f44'24 

Do.  in  crystals  with  9  or  1  eq.  of  water 

Carbonate  of  Ammonia    .        .         17-15         1  eq.-|-22'12 
Bicarbonate     ditto  .        .         17  15         1  eq.-|-44-24 

Carbonate  of  Baryta         .        .        76-7  1  eq.-|-2212 

Strontia        .         .        51-8  1  eq.f  22-12 

Lime  .        .        28-5  1  eq.-|-22-12 

Magnesia      .        .        20-7  l.eq.-j-22-12 

Do.  in  crystals  with  27  or  3  eq.  of  water 

Carbonate  Protox.  of  Iron         .        36  1  eq.-j-22-12 

Dicarbonate  Protoi.  Copper    .        79-2  2  eq.-f-22-12 

Do.        in  malachite  with  9  or  1  eq.  of  water 
Carbonate  Protox.  Lead  .       111-6  1  eq.-|-22-12 


1  eq.= 

2  eq.= 

1  eq.= 


2  eq. 

1  eq. 

2  eq. 
1  eq. 
1  eq. 
1  eq. 
1  eq 

1  eq 
1  eq 

leq 


Equiv. 
=  69  27 
=  91-39 
=100-39 
53-42 
=143-42 
=116-42 
=  75-54 
=  84-54 
=  39-27 
=  61-39 
=  98-82 
=  73-92 
=  60-62 
,=  42-82 
=:  69-82 
,=  58-12 
,=101-32 
=110-32 
=133-72 


FormuljB. 
KO-l-COa. 
K0-|-2C0j. 

NaOfCO,. 


NaO-H2COg. 

H3N  +  CO2. 

H4N()t2C02. 

BaO-^-COg. 

SrO-fcOg. 

CaO-j-COa. 

MgOf  COj. 

FeO+COg. 
2Cu04-C0j. 


CARBONATES. 


493 


Names.                               Base.  Acid. 

Dicarbon.  Perox.  Mercury       .       436  2  eq.-j-22-12 

Double  Carbonates. 

Carbonate  of  Lime  (Carb.  Lime  .       .  5062 

and  Magnesia       (Carb.  Magnesia  .  42-82 

Carbon,  of  Baryta     (Carb.  Baryta        .  98  82 

and  Lime              (Carb.  Lime          .  6062 


Equiv.  Formulae. 

eq.=458-12     2ngO-|-C02. 


}  ^^-l  =  93-44  MgOjCOg+CaOjCOa. 
}  ^^'1  ==149-44  CaO,C02iBaO,C02. 


Carbonate  of  Poiassa. — This  salt  is  procured  in  an  impure  form  by  burning 
land  plants,  lixiviating  their  ashes,  and  evaporating  the  solution  to  dryness ;  a 
process  which  is  performed  on  a  large  scale  in  Russia  and  America.  The  car- 
bonate thus  obtained,  is  known  in  commerce  by  the  names  oi potash  ^nA  pe.arlask, 
and  is  much  employed  in  the  arts,  especially  in  the  formation  of  soap  and  the 
manufacture  of  glass.  When  derived  from  this  source  it  always  contains  other 
compounds,  such  as  sulphate  of  potassa  and  chloride  of  potassium  ;  and  there- 
fore, for  chemical  purposes,  it  should  be  prepared  from  cream  of  tartar.  On 
heating  this  salt  to  redness,  the  tartaric  acid  is  decomposed,  and  a  pure  carbonate 
of  potassa  mixed  with  charcoal  remains.  The  carbonate  is  then  dissolved  in 
water,  and,  after  filtration,  is  evaporated  to  dryness  in  a  capsule  of  platinum  or 
silver. 

Pure  carbonate  of  potassa  has  a  taste  strongly  alkaline,  is  slightly  caustic,  and 
communicates  a  green  tint  to  the  blue  colour  of  the  violet.  It  dissolves  in  less 
than  an  equal  weight  of  water  at  60°,  deliquesces  rapidly  on  exposure  to  the  air, 
and  crystallizes  with  much  difficulty  from  its  solution.  In  pure  alcohol  it  is 
insoluble.     It  fuses  at  a  full  red  heat,  but  undergoes  no  other  change. 

It  is   often  necessary,  for  commercial  purposes,  to  ascertain  the  value  of  dif- 
ferent samples  of  pearlash ;   that  is,  to  determine  the  quantity  of  real  carbonate 
of  potassa  contained  in  a  given  weight  of  impure  carbonate.     A  convenient  mode 
of  effecting  this  object  is  described  by  Faraday  in  his  excellent  work  on  Chemical 
Manipulation.     Into  a  tube  sealed  at  one  end,  91 
inches  long,  ^  of  an  inch  in  diameter,  and  as 
cylindrical  as  possible  in  its  whole  length,  pour 
1000  grains  of  water,  and  with  a  file  or  diamond 
mark  the  place  where  its  surface  reaches,  and 
divide  the  space  occupied  by  the  water  into  100 
equal  parts,  as  is  shown  in  the  annexed  wood- 
cut.    Opposite   to   the    numbers    23*44,  48-96, 
5463,  and  65,  draw  a  line,  and  at  the  first  write 
soda,  at  the  second  potassa,  at  the  third  carbon- 
ate of  soda,  and  at  the  fourth  carbonate  of  potassa. 
Then  prepare  a  dilute  acid  having  the  specific 
gravity  of  1*127  at  60°,  which  may  be  made  by 
mixing  one  measure  of  concentrated   sulphuric 
acid  with  four  measures  of  distilled  water.   This 
is  the  standard  acid  to  be  used  in  all  the  experi- 
ments, being  of  such  strength  that  when  poured 
into  the  tube  till  it  reaches  either  of  the  four 
marks  just  mentioned,  we  shall  obtain  the  exact 
quantity  necessary  for  neutralizing  100  grains  of 
the  alkali  written  opposite  to  it.     If,  when  the 
acid  reaches  the  word  carb.  potassa,  and  when,  consequently,  we  have  the  exact 


100 


Soda 


Potassa 
Carb.  Soda 


Carb.  Potassa      — 


5 

10 
15 
20 
25 
30 
35 
40 
45 
50 
55 
60 
65 
70 
75 
SO 
85 
90 
95 
100 


494  CARBONATES. 

quantity  which  will  neutralize  100  grains  of  that  carbonate,  pure  water  be  added 
until  it  reaches  1,  or  the  beginning  of  the  scale,  each  division  of  this  mixture 
will  neutralize  one  grain  of  carbonate  of  potassa.  All  that  is  now  required,  in 
order  to  ascertain  the  quantity  of  real  carbonate  in  any  specimen  of  pearlash,  is 
to  dissolve  100  grains  of  the  sample  in  warm  water,  filter  to  remove  all  the  in- 
soluble parts,  and  add  the  dilute  acid  in  successive  small  quantities,  until  by  the 
test  of  litmus  pap^,  the  solution  is  exactly  neutralized.  Each  division  of  the 
mixture  indicates  a  grain  of  pure  carbonate.  It  is  convenient,  in  conducting  this 
process,  to  set  aside  a  portion  of  the  alkaline  liquid,  in  order  to  neutralize  the 
acid,  in  case  it  should  at  first  be  added  too  freely.  To  this  instrument  the  term 
alkalimder  is  given,  a  name  obviously  derived  from  the  use  to  which  it  is  ap- 
plied. 

Bicarbonate  of  Potassa  is  made  by  transmitting  a  current  of  carbonic  acid  gas 
through  a  solution  of  the  carbonate;  or  by  evaporating  a  mixture  of  the  carbon- 
ates of  ammonia  and  potassa,  the  ammonia  being  dissipated  in  a  pure  state.  By 
slow  evaporation,  the  bicarbonate  is  deposited  from  the  liquid  in  hydrated  prisms 
with  eight  sides,  terminated  with  dihedral  summits. 

Bicarbonate  of  potassa,  though  far  milder  than  the  carbonate,  is  alkaline  both 
to  the  taste  and  to  test  paper.  It  does  not  deliquesce  on  exposure  to  the  air.  It 
requires  four  times  its  weight  of  water  at  60°  for  solution,  and  is  much  more 
soluble  at  212°  ;  at  this  temperature  it  has  been  stated  to  be  converted  into  sesqui- 
carbonate,  but  H.  Rose  has  shown  that,  though  gradually,  it  at  length  parts  with 
half  its  carbonic  acid.  The  escape  of  the  gas  he  finds  to  be  much  retarded  by 
pressure,  that  of  one  inch  of  mercury  making  a  difference ;  hence  the  loss  of  car- 
bonic acid  is  much  more  rapid  when  a  cold  solution  is  evaporated  in  vacuo,  both 
the  gas  and  aqueous  vapour  being  absorbed  by  quicklime  (Pog.  An.  xxxiv.  149). 
At  a  low  red  heat  it  is  converted  into  the  carbonate. 

Thomson,  in  his  "First  Principles,"  has  described  a  sesquicarbonate,  which 
was  discovered  by  Nimmo  of  Glasgow.  Its  crystals  contain  12  eq.  of  water,  as 
denoted  by  the  formula  2]K:0,3C02-hl2HO. 

Carbonate  of  Soda. — The  carbonate  of  commerce  is  obtained  by  lixiviating  the 
ashes  of  sea- weeds.  The  best  variety  is  known  by  the  name  of  barilla^  and  is 
derived  chiefly  fiom  the  salsola  soda  and  salicornia  herbacea.  A  very  inferior  kind, 
known  by  the  name  of  kelp,  is  prepared  from  sea-weeds  on  the  northern  shores 
of  Scotland.  The  purest  barilla,  however,  though  well  fitted  for  making  soap 
and  glass,  and  for  other  purposes  in  the  arts,  always  contains  the  sulphates  of 
potassa  and  soda,  and  the  chlorides  of  potassium  and  sodium.  A  purer  carbonate 
is  prepared  by  heating  a  mixture  of  sulphate  of  soda,  saw-dust,  and  lime,  in  a 
reverberatory  furnace.  By  the  action  of  carbonaceous  matter,  the  sul{)huric  acid 
is  decomposed  ;  its  sulphur  partly  uniting  with  calcium,  and  partly  being  dissi- 
pated in  the  form  of  sulphurous  acid,  while  the  carbonic  acid,  which  is  generated 
during  the  process,  unites  with  soda.  The  carbonate  of  soda  is  then  obtained  by 
lixiviation  and  crystallization.  It  is  difficult  to  obtain  this  salt  quite  free  from 
sulphuric  acid. 

It  crystallizes  in  rhombic  octohedrons,  the  acute  angles  of  which  are  generally 
truncated.  The  crystals  effloresce  on  exposure  to  the  air,  and,  when  heated,  dis- 
solve in  their  water  of  crystallization.  By  continued  heat  they  are  rendered 
anhydrous  without  loss  of  carbonic  acid.  They  dissolve  in  about  two  parts  of 
cold,  and  in  rather  less  than  their  weight  of  boiling  water,  and  the  solution  has 
a  strong  alkaline  taste  and  reaction.   The  crystals  commonly  found  in  commerce 


CARBONATES.  495 

contain  10  eq.  of  water;   but  when  formed  at  a  temperature  of  about  80°,  they 
retain  only  7  eq. 

The  purity  of  different  specimens  of  barilla,  or  other  carbonates  of  soda,  may 
be  obtained  by  means  of  the  alkalimeter  above  described. 

Bicarbonate  of  Soda. — This  salt  is  made  by  the  same  process  as  bicarbonate  of 
potassa,  and  is  deposited  in  hyd rated  crystalline  grains  by  evaporation.  Though 
still  alkaline  it  is  much  milder  than  the  carbonate,  and  far  less  soluble,  requiring 
about  ten  times  its  weight  of  water  at  60°  for  solution.  It  is  found  by  Rose  to 
undergo  the  same  changes  on  boiling  as  the  bicarbonate  of  potassa ;  it  is  con- 
verted into  the  carbonate  by  a  red  heat. 

Sesquicarhonale. — This  compound  occurs  native  on  the  banks  of  the  lakes  of 
soda  in  the  province  of  Sukena  in  Africa,  whence  it  is  exported  under  the  name 
of  Truna.  It  was  first  distinguished  from  the  two  other  carbonates  by  Phillips 
(Journal  of  Science,  vii.),  whose  analysis  corresponds  with  that  of  Klaproth.  Its 
formula  is  ^^?iO ,?>C0 ^-f  ^^O . 

Carbonate  of  Ammonia. — The  only  method  of  obtaining  the  substance  so  called 
is  by  mixing  perfectly  dry  carbonic  acid  and  ammoniacal  gases.  In  whatever 
proportion  the  two  gases  be  mixed,  they  unite  only  in  the  ratio  of  one  volume 
of  the  former  to  two  of  the  latter,  and  condense  into  a  white  light  powder.  This 
substance  therefore  contains  carbonic  acid  and  ammonia  in  equivalent  propor- 
tions, but  it  is  probable  that  the  elements  are  not  arranged  as  expressed  by  the 
name.  By  the  action  of  water  it  is  instantly  decomposed  into  ammonia  and  the 
sesquicarbonate. 

Bicarbonate  of  Oxide  of  Jmmonium. — This  salt  was  formed  by  Berthollet  by 
transmitting  a  current  of  carbonic  acid  gas  through  a  solution  of  the  common 
carbonate  of  ammonia  of  the  shops.  On  evaporating  the  liquid  by  a  gentle  heat, 
the  bicarbonate  is  deposited  in  small  prisms  of  the  right  rhombic  system,  which 
have  no  smell,  and  very  little  taste.  Berthollet  ascertained  that  it  contains 
twice  as  much  acid  as  the  carbonate.  It  cannot  exist  without  the  presence  of 
water,  of  which  it  contains  227  per  cent.  (Berzelius),  or  2  eq.  It  may  therefore 
be  considered  as  carbonate  of  basic  water  and  carbonate  of  oxide  of  ammonium, 
or  H0,C0^tH^xN0,C02. 

Sesquicarbonate  of  Oxide  of  Ammonium. — The  common  carbonate  of  ammonia 
of  the  shops,  sub-carbonas  ammoniac  of  the  pharmacopoeia,  is  different  from  both 
these  compounds.  It  is  prepared  by  heating  a  mixture  of  one  part  of  hydrochlo- 
rate  of  ammonia  with  one  part  and  a  half  of  carbonate  of  lime,  carefully  dried. 
Double  decomposition  ensues  during  the  process:  chloride  of  calcium  remains  in 
the  retort,  and  hydrated  sesquicarbonate  of  ammonia  is  sublimed.  The  carbonic 
acid  and  ammonia  are,  indeed,  in  proper  proportion  in  the  mixture  for  forming 
the  real  carbonate ;  but,  owing  to  the  presence  of  water  generated  by  the  combi- 
nation of  the  oxygen  of  the  lime  with  the  hydrogen  of  the  hydrochloric  acid, 
part  of  the  ammonia  is  disengaged  in  a  free  state. 

The  salt  thus  formed  consists,  according  to  the  analysis  of  Phillips,  lire,  and 
Thomson,  of  34*3  parts  or  2  eq.  of  ammonia,  66-36  parts  or  3  eq.  of  carbonic 
acid,  and  18  parts  or  2  eq.  of  water.  It  is  therefore  anhydrous  sesquicarbonate 
of  oxide  of  ammonium,  or  2H^NO-f-3C02.  When  recently  prepared,  it  is  hard, 
compact,  translucent,  of  a  crystalline  texture,  and  pungent  ammoniacal  odour;  but 
if  exposed  to  the  air,  it  loses  weight  rapidly  from  the  escape  of  pure  ammonia, 
and  becomes  an  opaque  brittle  mass,  which  is  the  bicarbonate.     The  results 


496  ^  CARBONATES. 

obtained  by  Rose,  who  has  lately  studied  the  carbonates  of  ammonia  with  care, 
will  be  given  in  the  or^nic  chemistry,  where  ammonia,  as  containing  a  com- 
pound radical,  is  more  properly  placed. 

Carbonate  of  Baryta  occurs  abundantly  in  the  lead  mines  of  the  north  of  Eng- 
land, where  it  was  discovered  by  Dr.  Withering,  and  has  hence  received  the 
name  of  Witherite.  It  may  be  prepared  by  way  of  double  decomposition,  by 
mixing  a  soluble  salt  of  baryta  with  any  of  the  alkaline  carbonates  or  bicarbon- 
ates.  It  is  anhydrous,  exceedingly  insoluble  in  distilled  water,  requiring  4300 
times  its  weight  of  water  at  60°,  and  2300  of  boiling  water  for  solution ;  but 
when  recently  precipitated,  it  is  dissolved  much  more  freely  by  a  solution  of  car- 
bonic acid.     It  is  highly  poisonous. 

Carbonate  of  Stroniia,  which  occurs  native  at  Strontian  in  Argyleshife,  and  is 
known  by  the  name  of  Strontianite,  may  be  prepared  in  the  same  manner  as  car- 
bonate of  baryta.  It  is  anhydrous,  and  very  insoluble  in  pure  water,  but  is  dis- 
solved by  an  excess  of  carbonic  acid. 

Carbonate  of  Lime, — This  salt  is  a  very  abundant  natural  production,  and  occurs 
under  a  great  variety  of  forms,  such  as  common  limestone,  chalk,  marble,  and 
Iceland  spar,  and  in  regular  anhydrous  crystals,  the  density  of  which  is  2'7.  It 
may  also  be  formed  by  preidpitation.  Though  sparingly  soluble  in  pure  water, 
it  is  dissolved  by  carbonic  acid  in  excess ;  and  hence  the  spring-water  of  lime- 
stone districts  always  contains  carbonate  of  lime,  which  is  deposited  when  the 
water  is  boiled. 

Daniell  noticed  that  an  aqueous  solution  of  sugar  and  lime  deposited  crystal- 
lized carbonate  of  lime  by  exposure  to  the  air.  Gay-Lussac  has  proved  that  the 
sugar  merely  acts  as  a  solvent,  presenting  lime  in  a  favourable  state  for  combin- 
ing with  the  carbonic  acid  of  the  atmosphere ;  and  that  all  the  lime  is  deposited 
in  acute  rhombohedrons,  which  contain  5  eq.  of  water  to  I  eq.  of  carbonate  of 
lime.  These  crystals  are  insoluble  and  remain  unchanged  in  cold  water;  but  in 
water  at  86°,  or  in  air,  they  lose  their  combined  water,  and  fall  to  powder.  When 
boiled  in  alcohol  they  retain  their  form,  but  lose  2  eq.  of  water  and  retain  3  eq. 
in  combination.     (An.  de  Ch.  et  Ph.  xlviii.  301.) 

Carbonate  of  Magnesia. — It  is  met  with  occasionally  in  rhombohedral  crystals, 
and  in  a  pulverulent  earthy  state,  but  more  commonly  as  a  compact  mineral  of  an 
earthy  fracture  called  Magnesite.  A  specimen  of  magnesite  from  the  East  Indies, 
where,  I  am  informed,  it  is  abundant,  has  been  analyzed  by  Henry,  who  found  it 
to  be  nearly  pure  anhydrous  carbonate  of  magnesia :  it  is  of  a  snow-white  colour, 
of  density  2*56,  and  so  hard  that  it  strikes  fire  with  steel.  (An.  of  Phil.  xvii. 
252.)  It  is  obtained  in  minute  transparent  hexagonal  prisms  with  3  eq.  of  water, 
when  a  solution  of  bicarbonate  of  magnesia  evaporates  spontaneously  in  an  open 
vessel.  The  crystals  lose  their  water  and  become  opaque  by  a  very  gentle  heat, 
and  even  in  a  dry  air  at  60°.  By  cold  water  they  are  decomposed,  yielding  a 
soluble  bicarbonate  and  an  insoluble  white  compound  of  hydrate  and  carbonate 
of  magnesia ;  and  hot  water  produces  the  same  change  with  disengagement  of 
carbonic  acid,  without  dissolving  any  magnesia.  The  formula  of  the  crystals  is 
MgO,C02+3IlO.  (Berzelius.)  Fritsche  obtained  in  the  same  way,  besides 
the  salt  of  Berzelius,  another  in  tabular'  crystals,  containing  5  at.  water,  MgO, 
CO  -f-  5H0.  When  heated,  it  loses  carbonic  acid,  and  leaves  a  new  compound, 
4(MgO,C02)  f  MgO,5HO. 

When  carbonate  of  potassa  is  added  in  excess  to  a  hot  solution  of  sulphate  of 


CARBONATES.  497 

magnesia,  a  white  precipitate  falls,  which  after  being  well  washed  has  been  long 
considered  as  pure  carbonate  of  magnesia ;  but  Berzelius  has  shown  that  it  con- 
sists of  the  following  ingredients  : — 

Magnesia  44-75  82-8    or  4  eq.  ^      Probable  formula  is 

Carbonic  Acid  35-77  66-36  or  3  eq.  V 

Water  19-48  36       or4eq.)      MgO,4H04-3MgO,C02. 


100-00  185-16  or  leq. 

This  compound  is  said  to  require  2493  parts  of  cold,  and  9000  of  hot  water 
for  solution.  It  is  freely  dissolved  by  a  solution  of  carbonic  acid,  bicarbonate  of 
magnesia  being  generated ;  but  on  allowing  the  solution  to  evaporate  sponta- 
neously, carbonic  acid  is  given  off,  and  crystals  of  the  hydrated  carbonate  above 
mentioned  are  obtained. 

Carbonate  of  Protoxide  of  Iron. — Carbonic  acid  does  not  form  a  definite  com- 
pound with  peroxide  of  iron,  but  with  the  protoxide  it  constitutes  a  salt  which  is 
an  abundant  natural  production,  occurring  sometimes  massive,  and  at  other  times 
crystallized  in  rhombohedrons.  This  protocarbonate  is  obtained  also  in  most  of 
the  chalybeate  mineral  waters,  being  held  in  solution  by  free  carbonic  acid ;  and 
it  may  be  formed  by  mixing  an  alkaline  carbonate  with  the  sulphate  of  protoxide 
of  iron.  When  prepared  by  precipitation  it  attracts  oxygen  rapidly  from  the 
atmosphere,  and  the  protoxide  of  iron,  passing  into  the  state  of  peroxide,  parts 
with  carbonic  acid.  For  this  reason,  the  carbonate  of  iron  of  the  pharmacopoeia 
is  of  a  red  colour,  and  consists  chiefly  of  the  peroxide. 

Bicarbonate  of  Protoxide  of  Cupper. — It  occurs  as  a  hydrate  in  the  beautiful 
green  mineral  called  malachite;  and  the  same  compound,  as  a  green  powder,  the 
mineral  green  of  painters,  may  be  obtained  by  precipitation  from  a  hot  solution 
of  sulphate  of  protoxide  of  copper  by  carbonate  of  soda  or  potassa.  When 
obtained  from  a  cold  solution,  it  falls  as  a  bulky  hydrate  of  a  greenish-blue 
colour,  which  contains  more  water  than  the  green  precipitate.  By  careful  drying 
its  water  may  be  expelled.  When  the  hydrate  is  boiled  for  a  long  time  in  water, 
it  loses  both  carbonic  acid  and  combined  water,  and  the  colour  changes  to  brown. 
The  rust  of  copper,  prepared  by  exposing  metallic  copper  to  air  and  moisture,  is 
a  hydrated  dicarbonate. 

The  blue-coloured  mineral,  called  blue  copper  ore,  appears  to  be  a  hydrate  and 
carbonate  of  the  protoxide  of  copper,  and  consists,  according  to  the  analysis  of 
Phillips,  of  (Quarterly  Journal  of  Science,  iv.) 

Protoxide  of  Copper        69  08  118    or3eq.)      Probable  formula  is 

Carbonic  Acid  2546  44-24    2  eq.  > 

Water  5  46  9         leq.)      CuO,HO  +  2CuO,Cu02. 


10000  171-24    1  eq. 

The  blue  pigment  called  verditen,  prepared  by  decomposing  nitrate  of  oxide  of 
copper  with  chalk,  has  a  similar  composition.     (Phillips.) 

Carbonate  of  Protoxide  of  Lead. — This  salt,  which  is  the  white  lead,  or  ceruse  of 
painters,  occurs  native  in  white  prismatic  crystals  derived  from  a  right  rhombic 
prism,  the  sp.  gravity  of  which  is  6*72.  It  is  obtained  as  a  white  pulverulent 
precipitate  by  mixing  solutions  of  an  alkaline  carbonate  with  acetate  of  protoxide 
of  lead ;  and  it  is  prepared  as  an  article  of  commerce  from  the  subacetate  by  a 
current  of  carbonic  acid,  by  exposing  metallic  lead  in  minute  division  to  air  and 
moisture,  and  by  the  action  on  thin  sheets  of  lead  of  the  vapour  of  vinegar,  by 
which  the  metal  is  both  oxidized  and  converted  into  a  carbonate. 

34 


498  CARBONATES* 

Dtcarbonate  of  Peroxide  of  Mercury. — When  a  solution  of  the  nitrate  of  per- 
oxide of  mercury  is  decomposed  by  carbonate  of  soda,  an  ochre-yellow  precipi- 
tate falls,  which  Phillips  finds  to  be  a  dicarbonate.  The  protoxide  appears  to 
form  no  compound  with  carbonic  acid ;  for  when  a  nitrate  of  that  oxide  is  decom- 
posed by  any  alkaline  carbonate,  the  precipitate  is  either  black  at  first  or  speedily 
becomes  so,  and  after  being  washed  is  quite  free  from  carbonic  acid. 

Double  Carbonates. — One  of  the  most  remarkable  of  these  is  the  double  car- 
bonate of  lime  and  magnesia,  which  constitutes  the  minerals  called  bitter-spar, 
pearl-spar,  and  dolomite.  The  two  former  occur  in  rhombohedrons  of  nearly  the 
same  dimensions  as  carbonate  of  lime.  The  latter  is  met  with  in  great  perfec- 
tion in  the  Alps,  and  there  usually  occurs  in  white  masses  of  a  granular  texture ; 
the  grains  often  cohere  loosely,  but  other  specimens  are  hard  and  compact,  and 
when  broken  present  the  crystalline  aspect  of  marble.  Its  density  is  2*884. 
Some  specimens  consist  of  the  two  constituent  carbonates  in  the  ratio  of  their 
eq.,  as  stated  in  the  table ;  but  the  ratio  of  the  ingredients,  as  may  be  expected, 
is  very  variable,  since  isomorphous  substances  crystallize  together  in  all  propor- 
tions. Carbonate  of  protoxide  of  manganese  is  often  associated  with  them. 
The  rock  called  magnesian  limestone  may  be  viewed  as  an  impure  earthy  variety  of 
dolomite. 

The  double  carbonate  of  baryta  and  lime  constitutes  the  mineral  called  baryto- 
ealcitej  which  Mr.  Children  found  to  contain  the  two  carbonates  in  atomic  pro- 
portion. 

Berthier  has  made  some  interesting  experiments  on  the  production  of  double 
carbonates  by  fusion.  Carbonate  of  soda,  when  fused  with  carbonate  of  baryta, 
strontia,  or  lime,  in  the  ratio  of  their  eq.,  yields  uniform  crystalline  compounds, 
which  have  all  the  appearance  of  being  definite.  An  eq.  of  dolomite  fuses  in 
like  manner  with  4  eq.  of  carbonate  of  soda.  Five  parts  of  carbonate  of  potassa 
and  four  of  carbonate  of  soda,  corresponding  to  an  eq.  of  each,  fuse  with  remark-* 
able  facility ;  and  this  mixture,  by  reason  of  its  fusibility,  may  be  advantageously 
employed  in  the  analysis  of  earthy  minerals. 

Compounds  similar  to  the  foregoing  may  be  generated  by  heating  sulphate  of 
aoda  with  carbonate  of  baryta,  strontia,  or  lime,  in  the  ratio  of  their  eq. ;  or  by 
employing  the  sulphate  of  these  bases  and  carbonate  of  soda.  In  like  manner 
carbonate  of  soda  fuses  with  chloride  of  barium  or  calcium ;  and  chloride  of 
sodium  with  carbonate  of  baryta  or  lime.     (An.  de  Ch.  et  Ph.  xxxviii.) 


SECTION  II. 


CLASS  OF  SALTS.    ORDER  IL 


HYDRO-SALTS. 


In  this  section  are  included  those  salts  only,  the  acid  or  base  of  which  is  a 
compound  containing  hydrogen  as  one  of  its  elements.  For  reasons  already  as- 
signed (page  286-7)  I  have  already  described  all  those  salts  which  were  for- 


AMMONIACAL  SALTS.  499 

merly  called  muriates  or  hydrochloraies  of  metallic  oxides  as  chlorides  of  metals, 
considering  that  in  general  the  neutralizing  power  of  hydrochloric  acid  is  not 
due  to  its  direct  combination  with  an  oxide,  but  to  chlorine  uniting  with  the 
metal  itself.  The  same  remark  applies  to  the  hydriodic  and  other  hydracids,  the 
salts  of  which  are  consequently  reduced  to  a  small  number.  The  only  salts, 
indeed,  which  are  included  in  this  section,  are  compounds  of  the  hydracids  with 
ammonia  and  phosphuretted  hydrogen.  Some  of  the  compounds  which  might, 
as  containing  an  hydracid,  be  comprehended  in  this  section,  may  with  greater 
propriety  be  placed  in  the  fourth,  seeing  that  in  them  the  hydracid  acts  rather  as 
a  base  or  electro-positive  ingredient  than  as  an  acid  or  electro-negative  substance. 
This  double  function,  which  chemists  have  long  recognized  in  certain  metallic 
oxides,  such  as  alumina  and  oxide  of  zinc,  appears  to  be  performed  even  by  so 
powerful  an  acid  as  the  hydrochloric.  Some  judicious  observations  on  this  sub- 
ject have  been  made  by  Professor  Kane  of  Dublin.  (Dublin  Journal  of  Science, 
i.  265.) 

The  compounds  of  ammonia  with  the  hydracids  maybe  described  as  chlorides 
of  the  hypothetical  radical  ammonium.  The  argument  for  doing  so  is  derived 
from  the  similarity  of  the  hydrochlorate  of  ammonia  to  the  chloride  of  potassium 
in  its  crystalline  form,  and  all  its  relations  to  other  chlorides.  But  the  argument 
does  not  apply  with  equal  force  in  both  cases ;  for  to  suppose  a  direct  compound 
of  ammonia  and  an  hydracid  is  perfectly  consistent  with  observation,  whereas 
the  existence  of  a  compound  of  ammonia  and  an  ox-acid  is  directly  opposed  to  it. 
In  the  former  case,  therefore,  we  have  two  ways  of  accounting  for  the  phenomena 
observed ;  in  the  latter  we  have  but  one,  and  that  one,  therefore,  though  hypo- 
thetical, must  be  adopted.  As  this  necessity  does  not  exist  in  the  compounds  of 
ammonia  with  the  hydracids,  they  are  treated  as  direct  binary  combinations  of 
their  constituents. 

Ammonia  unites  with  fluoride  of  boron,  bisulphuret  of  carbon,  and  some  other 
bi-elementary  compounds,  which  contain  neither  oxygen  nor  hydrogen,  consti- 
tuting saline  combinations,  which  are  included  in  this  section,  and  to  which,  con- 
sidering the  distinct  alkaline  character  of  ammonia,  the  ordinary  nomenclature  of 
salts  is  applicable. 

AMMONIACAL  SALTS. 

These  compounds  are  readily  recognized  by  the  addition  of  pure  potassa  or 
lime,  when  the  odour  of  ammonia  may  be  perceived.  Those  which  contain  a 
volatile  acid  may  in  general  be  sublimed  without  decomposition;  but  the  ammo- 
nia is  expelled  by  heat  from  those  acids  which  are  much  more  fixed  than  itself. 
The  most  important  of  these  salts  are  thus  constituted ; — 


Names. 

Base. 

Acid. 

Equiv.     Formulae. 

Hydrochlorate  of  Ammonia 

17-15 

1  eq.-|-  36-42 

1  eq.=  63  57     H3N+HCI. 

Hydriodate  do. 

1715 

1  eq.+127-3 

1  eq. =144-45     HgN-fHI. 

Hydrobromate  do. 

17-15 

1  eq.-h  79-4 

1  eq.=  96-55    HgNf  HBr. 

Hodrofluate  do. 

17-15 

1  eq.-H  19-68 

1  eq.=  36-83    HgN-f-HF. 

Hydrosulphate  do. 

17-15 

1  eq.4-  17-1 

1  eq.=  34-25    H3N4-HS. 

Trifluoborate  do. 

51-45 

3  eq.4-  66-94 

1  eq.==l  18-39  3H3N-+-BF3. 

Difluoborate  do. 

34-30 

2eq.+   66-94 

1  eq.=101-24  2H3N-I-BF3. 

Fluoborate  do. 

17-15 

1  eq.4-  66-94 

1  eq.=  84-09    HgN-f  BF3. 

Fluosilicate  do. 

1715 

1  eq.-l-  78-54 

1  eq.=  96-69    HaN+SiFa. 

CarbosuJphate  do. 

1715 

1  eq.+  38-32 

1  eq.=  55-47    HsN-hCS2. 

500  AMMONIACAL  SALTS. 

Hydrochlorate  of  Ammonia, — This  salt,  sal-ammoniac  of  commerce,  was  for- 
merly imported  from  Egypt,  where  it  is  procured  by  sublimation  from  the  soot 
of  camel's  dung ;  but  it  is  now  manufactured  in  Europe  by  several  processes. 
The  most  usual  is  to  decompose  sulphate  of  ammonia  by  the  chloride  either  of 
sodium  or  magnesium,  when  double  decomposition  ensues,  giving  rise  in  both 
cases  to  hydrochlorate  of  ammonia,  and  to  sulphate  of  soda  when  chloride  of 
sodium  is  used,  and  to  sulphate  of  magnesia  when  chloride  of  magnesium  is  em- 
ployed. The  sal-ammoniac  is  afterwards  obtained  in  a  pure  state  by  sublimation. 
The  method  now  generally  used  in  this  country  for  obtaining  sulphate  of  oxide 
of  ammonium  is,  to  decompose  with  sulphuric  acid  the  hydrosulphate  and  hydro- 
cyanate  of  ammonia  which  is  collected  in  the  manufacture  of  coal-gas  ;  but  it  may 
also  be  procured  either  by  lixiviating  the  soot  of  coal,  which  contains  sulphate  of 
oxide  of  ammonium  in  considerable  quantity,  or  by  digesting  with  gypsum  im- 
pure sesquicarbonate  of  oxide  of  ammonium,  procured  from  the  destructive  distil- 
lation of  bones  and  other  mineral  substances,  so  as  to  form  an  insoluble  carbonate 
of  lime  and  a  soluble  sulphate  of  oxide  of  ammonium. 

Hydrochlorate  of  ammonia  has  a  pungent  saline  taste,  a  density  of  1'45,  and  is 
tough  and  diflOicult  to  be  pulverized.  It  is  soluble  in  alcohol  and  water,  requiring 
for  solution  three  times  its  weight  of  water  at  60°,  and  an  equal  weight  at  212°. 
It  usually  crystallizes  from  its  solution  in  feathery  crystals,  but  sometimes  in 
cubes  or  octohedrons.  At  a  temperature  below  that  of  ignition  it  sublimes  with- 
out fusion  or  decomposition,  and  condenses  on  cool  surfaces  as  an  anhydrous  salt, 
which  absorbs  humidity  in  a  damp  atmosphere,  but  is  not  deliquescent.  It  is 
generated  by  the  direct  union  of  hydrochloric  and  ammoniacal  gases,  which  unite 
in  equal  volumes. 

Hydriodate  of  Ammonia, — It  is  formed  as  a  white  powder  by  the  direct  union 
in  equal  measures  of  hydriodic  and  ammoniacal  gases,  or  by  neutralizing  a  solu- 
tion of  hydriodic  acid  with  ammonia,  and  evaporating.  It  crystallizes  with  dif- 
ficulty in  anhydrous  cubes,  is  very  soluble  in  water,  and  deliquesces  in  a  moist 
atmosphere.  In  close  vessels  it  may  be  sublimed  without  change ;  but  it  suffers 
partial  decomposition  when  heated  in  the  open  air. 

"When  a  concentrated  solution  of  this  salt  is  digested  with  iodine,  a  brown  solu- 
tion is  obtained,  the  nature  of  which  is  not  understood. 

Hydrohromaie  of  Ammonia  is  a  white  anhydrous  salt,  which  may  be  formed  by 
similar  processes  as  the  hydriodate.  It  is  soluble  in  water  and  crystallizes  by 
evaporation  in  quadrilateral  prisms.  * 

Hydrofiuate  of  Ammonia It  is  prepared  by  mixing  one  part  of  sal-ammoniac 

with  2i  of  fluoride  of  sodium,  both  dry  and  in  fine  powder,  gently  heating  the 
mixture  in  a  platinum  vessel,  and  receiving  the  sublimed  salt  in  a  second  pla- 
tinum vessel,  the  temperature  of  which  is  not  allowed  to  exceed  212°.  Chloride 
of  sodium  is  generated,  and  hydrofiuate  of  ammonia  is  obtained  in  small  anhy- 
drous prismatic  crystals,  which  may  be  preserved  unchanged  in  the  air,  is  partly 
soluble  in  alcohol,  and  dissolves  readily  in  water.  At  an  elevated  temperature  it 
fuses  before  subliming.     It  acts  powerfully  on  glass  even  in  its  dry  state. 

When  this  salt  is  introduced  in  a  dry  state  into  ammoniacal  gas,  absorption 
ensues,  and  the  resulting  salt  appears  to  be  a  -dihydrofiuate  of  ammonia.  By 
sublimation  it  loses  ammonia  and  becomes  neutral.  An  acid  salt,  apparently  a 
bi-hydrofluate,  is  obtained  by  evaporating  the  aqueous  solution  of  the  neutral 
hydrofiuate,  ammonia  being  disengaged.     If  the  evaporation  take  place  at  100°, 


SALTS  OF  PHOSPHURETTED  HYDROGEN.  501 

it  separates  in  crystalline  grains,  which  redden  litmus,  and  deliquesce  rapidly  at 
common  temperatures. 

Hydrosulphate  of  Ammonia, — This  salt,  also  called  hydrosulphuret  of  ammonia, 
and  formerly  the  Fuming  Liquor  of  Boyle,  is  prepared  by  healing  a  mixture  of  one 
part  of  sulphur,  two  of  sal-ammoniac,  and  two  of  unslaked  lime.  The  changes 
which  ensue  have  been  explained  by  Gay-Lussac.  The  volatile  products  are  am- 
monia and  hydrosulphate  of  ammonia;  and  the  fixed  residue  consists  of  sulphate 
of  lime  with  chloride  and  sulphuret  of  calcium.  The  hydrosulphuric  acid  is 
formed  from  the  hydrogen  of  hydrochloric  acid  uniting  with  sulphur,  and  the 
oxygen  of  the  sulphuric  acid  is  derived  from  decomposed  lime,  the  calcium  of 
w^hich  is  divided  between  the  chlorine  of  the  hydrochloric  acid  and  sulphur. 
Hydrosulphate  of  ammonia  may  also  be  formed  by  the  direct  union  of  its  consti- 
tuent gases,  and  if  they  are  mixed  in  a  glass  globe  kept  cool  by  ice,  the  salt  is 
deposited  in  crystals.  It  is  much  used  as  a  reagent,  and  for  this  purpose  is 
usually  prepared  by  saturating  a  solution  of  ammonia  with  hydrosulphuric  acid 
gas,  or  by  precipitating  sulphuret  of  barium  with  carbonate  of  ammonia.  A  mix- 
ture of  sulphuret  of  barium,  water,  and  sal-ammoniac,  when  distilled,  also  yields 
this  compound.  It  is  frequently  called,  by  the  continental  chemists,  sulphuret  of 
ammonium,  and  has  all  the  characters  of  a  sulphuret. 

Fluohorates  of  Ammonia. — Fluoboric  acid  combines  with  three  times  and  with 
twice  its  volume  of  ammoniacal  gas,  forming  a  trifluoborate  and  difluoborate, 
which  are  liquid  at  common  temperatures.  The  neutral  fluoborate  is  formed  of 
equal  volumes  of  its  constituent  gases,  and  is  a  white  volatile  salt,  soluble  in 
water,  but  which  cannot  be  recovered  from  the  solution  ;  for  on  evaporation,  a 
subfluoborate  of  ammonia  is  expelled,  and  boracic  acid  is  left  in  solution.  The 
neutral  fluoborate  is  formed  by  heating  gently  either  of  the  subfluoborates. 

Fluosilicate  of  Ammonia. — Fluosilic  acid  and  ammoniacal  gases  unite  by 
volume  in  the  ratio  of  1  to  2,  forming  a  white  volatile  salt  which  is  decomposed 
by  water. 

Carbosulphaie  of  Ammonia. — When  dry  ammoniacal  gas  is  brought  into  con- 
tact with  bisulphuret  of  carbon,  direct  combination  ensues,  and  there  results  an 
uncrystalline  solid  mass  of  a  straw-yellow  colour,  which  may  be  sublimed  with- 
out decomposition.  By  contact  with  water  or  exposure  to  a  moist  air,  an  inter- 
change ensues  between  the  elements  of  water  and  bisulphuret  of  carbon,  giving 
rise  to  hydrosulphuric  and  carbonic  acids  ;  and  a  sulphur-salt  of  an  orange-yellow 
colour,  the  hydro-carbosulphuret  of  ammonia,  is  generated. 

Arsenio-per sulphate  of  Ammonia. — Berzelius  states  that  when  dry  persulphuret 
of  arsenic  is  exposed  to  ammoniacal  gas,  absorption  ensues,  and  a  yellowish- 
white  compound  results ;  but  the  elements  are  united  by  a  feeble  attraction,  and 
on  mere  exposure  to  the  air,  the  ammonia  escapes. 

SALTS  OF  PHOSPHURETTED  HYDROGEN. 

Rose  has  lately  called  the  attention  of  chemists  to  the  close  analogy  which 
exists  in  the  composition  of  ammonia  and  phosphuretted  hydrogen,  and  in  some 
of  their  properties.  The  latter  is  a  feeble  alkaline  base,  which  combines  with 
some  of  the  hydracids.  The  salt  best  known  is  the  hydriodate  of  phosphuretted 
hydrogen,  first  noticed  by  Gay-Lussac,  which  is  formed  of  137*3  parts  or  1  eq. 
of  acid  and  31*4  parts  or  1  eq.  of  base,  and  crystallizes  in  cubes.  The  crystals 
are  permanent  while  quite  dry  ;  but  with  water,  or  the  moisture  of  the  air,  they 


«02  SULPHUR.  SALTS. 

yield  a  solution  of  hydriodic  acid,  and  phosphuretted  hydrogen  gas  escapes. 
These  salts  are  all  decomposed  by  water,  and  exist  only  in  the  anhydrous  slate. 


SECTION  III. 


CLASS  OF  SALTS.    ORDER  IIL 


SULPHUR.SALTS. 

Thk  compounds  described  in  this  section  are  double  sulphurets,  just  as  the 
oxy-salts  in  general  are  double  oxides.  Their  resemblance  in  composition  to 
salts  is  perfect.  The  principal  sulphur-hoses  are  the  protosulphurets  of  potas- 
sium, sodium,  lithium,  barium,  strontium,  calcium,  and  magnesium,  and  hydro- 
sulphate  of  ammonia;  and  the  principal  sulphur-acids  are  the  sulphurets  of 
arsenic,  antimony,  tungsten,  molybdenum,  tellurium,  tin,  and  gold,  together 
with  hydrosulphuric  acid,  bisulphuret  of  carbon,  and  sulphuret  of  selenium. 
The  sulphur-salts  with  two  metals  are  so  constituted,  that  if  the  sulphur  in  each 
were  replaced  by  an  eq.  quantity  of  oxygen,  an  oxy-sait  would  result.  The 
analogy  between  oxy-salts  and  sulphur-salts  is  rendered  still  closer  by  the  cir- 
cumstance that  hydrosulphuric  and  hydrosulphocyanic  acids  have  the  character- 
istic properties  of  acidity,  and  unite  both  with  ammonia  and  with  sulphur-bases. 

The  sulphur-salts  may  be  divided  into  families,  characterized  by  containing 
the  same  sulphur-acid.  For  the  purpose  of  indicating  that  such  salts  are  double 
sulphurets,  as  well  as  to  distinguish  them  readily  from  other  kinds  of  salts,  I 
shall  construct  the  generic  ifame  of  each  family  from  the  sulphur  acid  terminated 
with  sulphuret.  Thus  the  salts  which  contain  persulphuret  of  arsenic  or  hydro- 
sulphuric acid  as  the  sulphur-acid  are  termed  arsenio-sulphurets  and  hydro-sul' 
phurets;  and  a  salt  composed  of  each  of  these  sulphur-acids  with  sulphuret  of 
potassium  is  termed  arsenio-sulphuret  and  hydro-sulphuret  of  sulphuret  of  potas- 
sium. For  the  sake  of  brevity  the  metal  of  the  base  may  alone  be  expressed,  it 
being  understood  that  the  positive  metal  in  a  sulphur-salt  enters  as  a  protosul- 
phuret  into  the  compound. 

HYDRO-SULPHURETS. 

The  sulphur-salts  contained  in  this  group  have  hydrosulphuric  acid  for  their 
electro-negative  ingredient.  Most  of  them  which  have  been  studied  are  soluble 
in  water,  and  may  be  obtained  in  crystals  by  evaporation.  They  are  decomposed 
by  exposure  to  the  air,  yielding  at  first  bisulphurets  of  the  metal,  and  then  a 
hyposulphite.  By  acids  the  hydrosulphuric  acid  is  expelled  with  effervescence. 
They  are  thus  constituted : — 

Name.  Sulphur.base.  Sulphur-acid.        Equiv.        Formulae. 

Hydro-sulphuret  of  Potassium         55-25         1  eq.-4-17-l         1  eq.s=  7235        KS-|-HS. 
Ditto  Sodium         .     40-4  leq.fl7l         1  eq.=  57-6  NaSfHS. 


HYDRO-SULPHURETS.  503 


Name. 

Sulphur-base. 

Sulphur 

-acid.        Equiv. 

Formulae. 

Ditto 

Lithium        .    26-1 

1  eq.-H17-l 

1  eq.=  43-2 

LS  +  HS. 

Ditto 

Barium         •     84-8 

1  eq.tl7-l 

1  eq.=10-19 

BaS-fHS. 

Ditto 

Strontium    .    59-9 

1  eq.+17-l 

1  eq.=  77-0 

SrS-HHS. 

Ditto 

Calcium       .     36'6 

1  eq.-|-171 

1  eq.=  53-7 

CaSfHS. 

Ditto 

Magnesium  .    28.8 

1  eq.+17-l 

1  eq.=i  45-9 

MgSf  HS. 

Hydro-sulphuret  of  Potassium. — This  salt  is  obtained  in  the  anhydrous  state  by 
introducing  anhydrous  carbonate  of  potassa  into  a  tubulated  retort,  transmitting 
through  it  a  current  of  hydrosulphuric  acid  gas,  and  heating  the  salt  to  low  red- 
pess.  The  mass  becomes  black,  fuses,  and  boils  from  the  escape  of  carbonic 
acid  gas  and  aqueous  vapour;  and  after  the  ebullition  has  ceased,  the  gas  is 
continued  to  be  transmitted,  until  the  retort  is  quite  cold.  The  resulting  anhy- 
drous hydro-sulphuret  of  potassium,  though  black  while  in  fusion,  is  white  when 
cold,  and  of  a  crystalline  texture;  but  if  air  had  not  been  perfectly  excluded,  it 
has  a  yellow  tint,  owing  to  the  presence  of  some  bisulphuret  of  potassium. 

The  same  salt  is  prepared  in  the  moist  way  by  introducing  a  solution  of  pure 
potassa,  free  from  carbonic  acid,  into  a  tubulated  retort,  expelling  atmospheric 
air  by  a  current  of  hydrogen  gas,  and  then  saturating  the  solution  with  hydro- 
sulphuric  acid.  At  first  the  potassa,  as  in  the  former  process,  interchanges 
elements  with  the  gas,  yielding  water  and  protosiilphuret  of  potassium :  after 
which  the  protosulphuret  unites  with  hydrosulphuric  acid.  The  solution  should 
be  evaporated  in  the  retort  to  the  consistence  of  syrup,  a  current  of  hydrogen 
gas  being  transmitted  through  the  apparatus  the  whole  time;  and  on  cooling 
the  salt  crystallizes  in  large  four  or  six-sided  prisms,  which  are  colourless  if  air 
was  perfectly  excluded.  The  crystals  contain  water  of  crystallization,  have  an 
acrid,  alkaline,  and  bitter  taste,  deliquesce  in  open  vessels,  and  dissolve  freely 
in  water  and  alcohol.  On  exposure  to  the  air  it  acquires  a  yellow  colour,  from 
the  formation  of  bisulphuret  of  potassium. 

Hydro-sulphuret  of  Sodium, — It  is  prepared  on  the  same  principles  as  the 
former  salt,  and  yields  by  evaporation  colourless  crystals.  When  a  hot  concen- 
trated solution  is  mixed  with  a  solution  of  hydrate  of  soda  also  concentrated,  the 
mixttire  on  cooling  deposits  four-sided  prisms,  which  are  protosulphuret  of 
sodium  with  water  of  crystallization.     The  interchange  of  elements  is  such  that 

1  eq.  Hydro-sulphuret  and  1  eq.  Soda    2      2  eq.  Sulphuret  and  1  eq.  water. 
NaS-f-HS  NaO  |,     2NaS  HO. 

Hydro-sulphuret  of  Lithium  may  be  prepared  in  the  same  way  as  the  two 
former  salts,  and  is  left  by  evaporation  as  a  crystalline  solid.  When  heated  in 
close  vessels  it  parts  with  its  water  of  crystallization,  and  like  the  two  former 
salts  retains  its  acid  even  at  a  red  heat. 

Hydro-sulphuret  of  Barium. — It  is  prepared  by  the  action  of  hydrosulphuric 
acid  on  a  solution  of  baryta  with  the  precautions  already  mentioned  for  exclud- 
ing atmospheric  air,  and  crystallizes  by  evaporation  in  four-sided  prisms,  which 
are  very  soluble  in  water,  but  dissolve  sparingly  in  alcohol.  The  crystals  part 
with  their  water  of  crystallization  when  heated,  and  at  a  commencing  red  heat 
give  out  hydrosulphuric  acid,  leaving  pure  sulphuret  of  barium. 

Hydro-sulphuret  of  Strontium  is  prepared  like  the  former  salt,  and  crystallizes 
in  large  radiated  prisms,  which  when  quite  dry  may  be  kept  several  days  ex- 


504  CARBO-SULPHURETS. 

posed  to  the  air  without  change.     When  heated  it  loses  its  water  and  acid,  and 
protosulphuret  of  strontium  as  a  white  powder  is  left. 

Hydro-sulphur ei  of  Calcium  is  formed  in  the  same  manner  as  the  preceding 
salts;  but  it  exists  only  in  solution;  for  on  attempting  to  crystallize  by  evapo- 
ration, hydrosulphuric  acid  is  driven  off,  and  the  sulphuret  of  calcium  in  prisms 
of  a  silky  lustre,  is  deposited.  The  hydro-sulphuret  of  magnesium  likewise 
exists  only  in  solution. 

CARBO-SULPHURETS. 
i;  ijtiiJfWii  '  jnoTi".^  ■ 

The  acid  of  these  Sulphtir-salts  is  bisulphuret  of  carbon  ;  'fen3'the  salts  them- 
selves are  thus  constituted  : — 

'  \ 

rt'.        Names.  Sulphur.        Sulphur-acid.  Equiv.  Formulae. 

Carbo-sulphuret  of  Potassium  65-25  1  eq.-f-38-32  1  eq.=  9357  KS+CSj. 

Ditto  Sodium       .        .        •         .    40-4  1  eq.-f-38-32  1  eq.=  78-72  NaS-j-CSj. 

Ditto  Lithium      .        .        .        .26-1  1  eq.-|- 38-32  1  eq.=  64-42  LS+CSg. 

Ditto  Hydrosulphate  of  Ammonia    34  25  1  eq.+38-32  1  eq.=  72.57  (HgN-j-HSH-CSj. 

Ditto  Barium        ....    84-8  1  eq.+38-32  I  eq.=123-l2  BaS-f-CSj. 

Ditto  Strontium  ....    59-9  1  eq.4-38-32  1  eq.=  98-22  SrS-j-CSj. 

Ditto  Calcium      ....    36  6  1  eq.+38-32  1  eq.=:  74-92  CaS-j-CSg. 

Ditto  Magnesium         .        .        .    28.8  1  eq.+3S-32  1  eq.=  67-12  MgS-j-CSg. 

Carho-sulphuret  of  Potassium. — On  agitating  bisulphuret  of  carbon  with  a 
strong  alcoholic  solution  of  protosHlphuret  of  potassium,  the  liquid  when  set  at 
rest  separates  into  three  layers,  the  lowest  of  which  is  carbo-sulphuret  of  potas- 
sium, and  is  of  the  consistence  of  syrup.  Another  process  is  to  digest  bisul- 
phuret of  carbon  at  86°  in  a  corked  bottle  full  of  a  strong  aqueous  solution  of 
protosulphuret  of  potassium,  until  the  latter  is  saturated.  A  concentrated  solu- 
tion of  this  salt  is  of  a  deep  orange,  almost  red,  colour;  and  when  evaporated  at 
86°  to  the  consistence  of  syrup,  a  deliquescent  yellow  crystalline  salt  is  depo- 
sited, which  is  sparingly  soluble  in  alcohol.  On  heating  It  to  150°  it  gives  off 
water  of  crystallization;  and  when  more  strongly  heated  it  is  resolved  into 
trisulphuret  of  potassium  and  charcoal. 

Carho-sulphuret  of  Sodium. — It  is  prepared  like  the  former  salt,  and  separates 
in  yellow  crystals  from  a  very  concentrated  solution.  It  is  deliquescent,  and 
dissolves  readily  in  alcohol  as  well  as  water. 

The  Carbo-sulphuret  of  Lithium  resembles  the  preceding  salt,  and  is  very  solu- 
ble in  water  and  alcohol.  Similar  carbo-sulphurets  are  obtained  by  the  action  of 
solutions  of  sulphuret  of  barium,  strontium,  and  calcium,  on  bisulphuret  of  car- 
bon :  the  solutions  are  of  an  orange  colour,  and  yield  crystalline  salts  by  evapo- 
ration. 

Carbo-sulphuret  of  Hydrosulphate  nf  Jlmmonia. — Zeise  prepares  this  salt  by 
filling  a  bottle  with  ten  measures  of  nearly  -absolute  alcohol  saturated  with  ammo- 
niacal  gas  and  one  measure  of  bisulphuret  of  carbon,  and  inserting  a  tight  cork. 
As  soon  as  the  liquid  has  acquired  a  yellowish-brown  colour,  the  bottle  is 
plunged  into  ice-cold  water,  when  the  carbo-sulphuret  is  deposited  either  in  yel- 
low penniform  crystals  or  as  a  crystalline  powder.  The  whole  is  thrown  upon  a 
linen  filter,  and  the  salt  after  being  washed,  first  with  absolute  alcohol  and  then 
with  etheri  is  dried  by  pressure  within  folds  of  bibulous  paper.  This  salt  is  very 
volatile,  passing  off  entirely  at  common  temperatures,  and  can  only  be  preserved 


ARSENIO-SULPHURETS. 


sdS 


in  well-corked  bottles.  Exposed  to  the  air  it  absorbs  humidity  and  acquires  a 
red  colour.  Its  solution  may  be  kept  unchanged  in  bottles  filled  with  it  and 
tightly  corked. 

The  carbo-sulphurets  of  barium,  strontium,  and  calcium  may  be  obtained  by 
acting  on  bisulphuret  of  carbon  with  a  solution  of  the  protosulphurets  of  those 
metals.  The  resulting  solutions  are  of  an  orange  or  brown  colour,  and  the  salts 
deposited  by  evaporation  are  of  a  citron-yellow  when  quite  dry.  The  carbo-sul- 
phuret  of  barium  is  of  sparing  solubility.  The  carbo-sulphuret  of  magnesium 
is  best  prepared  by  adding  sulphate  of  magnesia  to  a  solution  of  carbo-sulphuret 
of  barium.  Berzelius  has  also  prepared  several  carbo-sulphurets  of  the  metals 
of  the  second  class. 

ARSENIO-SULPHURETS. 

Berzelius  finds  that  each  of  the  three  sulphurets  of  arsenic  is  capable  of 
acting  as  a  sulphur-acid,  giving  rise  to  three  distinct  families  of  sulphur-salts, 
distinguishable  by  the  terms  arsenio-persulphurets,  arsenio-sesquisulphurets,  and 
arsenio'protosulphurets. 

Persulphuret  of  arsenic  is  a  very-powerful  sulphur-acid,  violently  displacing 
hydrosulphuric  acid  from  its  combinations  with  sulphur-bases,  even  at  common 
temperatures ;  and  when  digested  with  earthy  or  alkaline  carbonates,  it  expels 
carbonic  acid.  The  salts  of  this  sulphur-acid  may  be  prepared  by  several  differ- 
ent methods : — 

1.  By  digesting  the  persulphuret  of  arsenic  in  a  solution  of  a  sulphur-base, 
such  as  sulphuret  of  potassium  or  sodium,  until  it  is  saturated.  The  resulting 
soluble  arsenio-persulphuret  maybe  employed  to  prepare  insoluble  salts  of  the 
same  sulphur-acid  by  means  of  double  decomposition.  If  a  persulphuret  of 
potassium  is  used,  sulphur  is  deposited. 

2.  By  decomposing  a  hydrosulphuret  of  a  sulphur-base  with  persulphuret  of 
arsenic,  in  which  case  hydrosulphuric  gas  is  disengaged  with  effervescence. 

3.  By  decomposing  a  solution  of  an  arseniate  by  means  of  hydrosulphuric  acid 
or  hydrosulphate  of  ammonia. 

4.  By  dissolving  persulphuret  of  arsenic  in  a  solution  of  caustic  alkali,  such 
as  potassa ;  when  an  interchange  of  elements  between  portions  of  the  alkali  and 
persulphuret  ensues,  whereby  arsenic  acid  and  protosulphuret  of  potassium  are 
generated.     In  this  case 

I  eq.  Persulphuret  &  5  eq.  Potassa  2    1  eq.  Arsenic  Acid  &  5  eq.  Protosulphuret. 

AsjSg  5K0  -2  AsgOg  5KS. 

Two  salts  are  thus  generated  and  co-exist  in  the  solution,  namely,  arseniate  of 
potassa  and  arsenio-sulphuret  of  potassium.  Sirailai*  changes  invariably  occur 
when  sesquisulphuret  of  arsenic,  sesquisulphuret  of  antimony,  and  other  sul- 
phur-acids are  boiled  with  alkaline  solutions  ;  an  oxy-salt,  the  acid  of  which  is 
formed  of  oxygen  and  the  electro-negative  metal,  is  always  generated  ;  and  this 
salt,  if  soluble  in  water,  remains  together  with  the  sulphur-salt  in  solution.  An 
alkaline  carbonate  may  be  substituted  for  a  pure  alkali,  but  thei)  carbonic  acid  is 
expelled.  Th'ese  principles  are  concerned  in  the  production  of  kermes,  as  already 
explained. 

5.  The  last  method  which  requires  mention,  is  by  exposing  a  mixture  of  per^ 
sulphuret  of  arsenic  and  an  alkaline  carbonate  to  a  red  heat  in  a  covered  vessel. 


606  ARSENIO-SULPHURETS. 

Carbonic  acid  gas  is  disengaged  ;  and  an  interchange  of  elements,  similar  to  that 
just  explained,  takes  place  between  a  portion  of  the  alkali  and  the  sulphuret. 
The  fused  mass,  accordingly,  contains  an  arseniate  of  the  alkali,  as  well  as  a 
sulphur-salt.  This  tendency  to  the  formation  of  a  double  sulphuret  is  the  reason 
why,  in  decomposing  orpiment  by  black  flux,  the  whole  of  the  arsenic  is  never 
sublimed  ;  a  part  is  uniformly  retained  in  the  form  of  a  sulphur-salt,  the  arsenio- 
sesquisulphuret  of  sulphuret  of  potassium. 

Most  of  the  arsenio-persulphurets  of  the  second  class  of  metals  are  insoluble ; 
but  those  of  the  metals  of  the  alkalies  and  alkaline  earths  are  very  soluble  in 
water,  have  a  lemon-yellow  colour  in  the  anhydrous  state,  and  are  colourless 
when  combined  with  water  of  crystallization  or  in  solution.  When  exposed  to 
heat  in  close  vessels  they  give  off  sulphur,  and  an  arsenio-sesquisulphuret  is 
generated.  In  the  solid  state  they  are  very  permanent  in  the  air,  and  even  in 
solution  oxidation  takes  place  with  great  slowness.  When  decomposed  by  an 
acid,  persulphuret  of  arsenic  subsides,  hydrosulphuric  acid  gas  escapes,  and  a 
salt  of  the  alkali  is  generated.  Some  chemists  may  doubt  the  possibility  of  the 
arsenio-persulphurets  dissolving  as  such  in  water :  they  may  consider  the  arsenic 
and  the  metal  of  the  sulphur-base  to  be  united  with  oxygen,  and  all  the  sulphur 
with  hydrogen ;  but  this  supposition,  if  followed  out,  leads  into  such  complex 
and  improbable  modes  of  combination,  that  I  see  no  alternative  but  implicitly  to 
admit  the  views  here  adopted. 

The  following  table  exhibits  the  composition  of  the  principal  arsenio-persul- 
purets : — 

Names.  Sulph.-base.        Sulph -acid.        Equiv.  Formulae, 

"^^ou^ssium'"^^^*  "^^  }  ^^^•''^  3eq.+  165-9  1  eq.  «  321.66  3KS  f  As^Sg. 
Diarscpersulph.  do.  110-5  2  eq. -4- 155-9  leq.  =266-4  2KS -j- AsgSg. 
Arsenio-perBulph.  do.      65-25     1  eq.  +  155-9     leq.  =  21116     KS  f  AsgSg. 

Twarscpersulph.  of  )  ^^l^       3  eq.  +  155-9     1  eq.  =  277-1     3NaS  +  As^Sg. 
Sodium  )  ^    '  ^ 

Do.    in  crygtalB  with  270  or  30  eq.  of  water      =s  5471 

Diarse-pergulph.  of    )    g^.g      2  eq. -4- 1559     leq.  =  236-7    2Na8 -4- AajSj. 

Sodium  5  ^     ' 

Arsenio-peraulph.  do.      40-4      leq. -+-155-9     leq.  =  196-3      NaS -|- AsjSg. 

Triarse.-perHulph.  of  ) 

Hydroeulphate  of    S  102-75  3  eq.  +  155-9     1  eq.  =  268-65  3(HaN  4-  HS)  -H  AejSj. 

Ammonia  ) 

Diarse.-pcrsulph.  do.        68-6  2  eq.  +  155-9     leq.  =  224-4    2(H,N  +  HS) -{- As^Sg. 

Arsenio.persulph.  do.      34-25  1  eq.  -f  156-9     1  eq.  =  190- 16    (H3N  -+-  HS)  f  A4S5. 

Anenio-^pertulphureU  of  Potassium. — The  diarsenio-persiilphuret  is  best  ob- 
tained by  the  action  of  hydrosulphuric  acid  gas  on  the  diarseniate  of  potassa, 
and  yields  a  colourless  solution.  By  evaporation  in  vacuo  it  is  reduced  to  a  yel- 
lowish viscid  mass  which  dries  imperfectly,  but  when  exposed  for  some  time  to 
the  open  air  at  length  becomes  a  crystalline  mass  of  a  lemon-yellow  colour,  in 
which  rhomboidal  tables  are  perceptible.  When  this  salt  is  mixed  with  alcohol, 
it  is  resolved  into  the  triarsenio-persulphuret,  which  is  insoluble  in  the  alcohol, 
and  the  arsenio-persulphuret,  which  remains  in  solution.  The  latter  has  not 
been  obtained  in  the  solid  state.  The  former  is  deliquescent  and  very  soluble  in 
water;  but  when  its  solution  is  gently  evaporated,  the  residue  has  a  radiated 
crystalline  texture. 

Jirtenio-persulphurets  of  Sodium, — The  diartenio-persulphuret  is  formed  like 


MOLYBDO-SULPHURETS.  507 

the  corresponding  salt  of  potassium,  is  very  soluble  in  water,  and  by  evaporation 
yields  a  lemon-yellow  mass,  which  attracts  humidity  from  the  air.  On  mixing 
its  solution  with  alcohol  it  is  resolved  into  the  arsenio-persulphuret  and  triarsenio- 
persulphuret  of  sodium,  and  the  latter  falls  in  scaly  crystals  of  snowy  white- 
ness, which  may  be  collected  on  a  filter,  washed  with  alcohol,  and  dried  without 
change.  This  salt  by  solution  in  water  and  evaporation  may  be  obtained  in 
rhomboidal  tables  or  prisms  derived  from  a  rhombic  prism.  The  crystals  undergo 
no  change  in  the  air,  and  contain  30  eq.  of  water.  The  arsenio-persulphuret  has 
been  obtained  only  in  solution.  The  Arsenio-persulphureis  of  lithium  are  very 
analogous  to  those  of  sodium. 

Arsenio-persulphurets  of  hydrosulphate  of  Ammonia. — ^The  diarsenio-persulphuret 
is  obtained  as  a  colourless  solution  by  decomposing  with  hydrosulphuric  acid 
gas  a  solution  of  triarseniate  of  oxide  of  ammonium  and  basic  water.  By  spon- 
taneous evaporation  it  becomes  a  viscid  mass  of  a  reddish-yellow  colour,  and 
which  cannot  be  fully  dried  without  decomposition.  When  its  solution  is  mixed 
with  hydrosulphate  of  ammonia  and  agitated  with  hot  alcohol,  the  triarsenio-sul- 
phuret  is  deposited  in  colourless  prisms,  which,  after  being  well  washed  with 
alcohol  and  dried  on  bibulous  paper,  undergo  no  change  by  exposure  to  the  air. 
The  arsenio-persulphuret  remains  in  the  alcoholic  solution. 

Analogous  salts  may  be  similarly  prepared  with  barium,  strontium,  calcium, 
and  magnesium ;  and  insoluble  compounds  of  the  same  nature  may  be  formed  by 
way  of  double  decomposition  by  mixing  soluble  arsenio-persulphurets  with  oxy- 
salts  of  the  second  class  of  metals. 

The  salts  in  which  sesquisulphuret  of  arsenic  acts  as  an  acid,  resemble  those 
of  the  persulphuret  both  in  their  general  characters  and  mode  of  formation. 
Those  formed  with  the  protosulphuret  of  arsenic  cannot  be  made  in  the  moist 
way  by  direct  union  of  their  ingredients  ;  but  when  solutions  of  the  arsenio-ses- 
quisulphurets  are  evaporated,  spontaneous  decomposition  takes  place,  the  salts 
of  protosulphuret  of  arsenic  of  a  reddish-brown  colour  subsides,  while  arsenio- 
persulphurets  remain  in  solution. 

MOL  YBDO-  SULPHURETS. 

The  electro-negative  ingredient  of  these  salts  is  the  tersulphuret  of  molyb- 
denum, and  the  most  remarkable  of  them  is  the  molybdo-sulphuret  of  potassium, 
which  is  readily  formed  by'decomposing  with  hydrosulphuric  acid  gas  a  rather 
strong  solution  of  molybdate  of  potassa.  If  no  iron  is  present,  the  liquid  acquires 
a  beautiful  red  colour  like  the  solution  of  bichromate  of  potassa,  and  on  evapo- 
ration prismatic  crystals  with  four  and  eight  sides  are  deposited.  Berzelius  de- 
scribes this  compound  as  one  of  the  most  beautiful  which  chemistry  can  produce : 
the  crystals,  by  transmitted  light,  are  ruby-red,  and  their  surfaces,  while  moist 
with  the  solution  which  yielded  them,  shine  like  the  wings  of  certain  insects 
with  a  metallic  lustre  of  a  rich  green  tint.  The  crystals  are  anhydrous,  dissolve 
readily  in  water,  but  are  insoluble  in  alcohol.  On  the  addition  of  sulphuric  or 
any  of  the  stronger  acids,  a  salt  of  potassa  is  generated  with  escape  of  hydrosul- 
phuric acid,  and  precipitation  of  tersulphuret  of  molybdenum. 

Soluble  molybdo-sulphurets  of  sodium,  lithium,  and  ammonia  of  a  red  colour, 
may  be  obtained  by  a  process  similar  to  that  for  preparing  the  preceding  com- 
pound.   The  composition  of  these  salts  is  as  follows  : — 


508 

Names. 

Molybdo-sulphuret 

of  Potassium 
Molybdo-sulphuret 

of  Sodium 
Molybdo-sulphuret 

of  Lithium 
Molybdo-sulphuret 

of  Hydrosulphate 

of  Ammonia 


TUNGSTO-SULPHURETS.  ' 

Sulphur-bage.  Sulphur-acid.    Equiv.  Formulae. 

1  eq.-|-96-26  1  eq.==151-51  KS-j-MoSj.  * 

1  eq.  +  96-26  1  eq.=136-66  NaS+MoS,. 

1  eq.-t-96-26  1  eq.=122-36  LS-f-MoS,. 

34-25      1  eq. +96-26  1  eq.=130-51     (H3N-|-HS)4-MoS3. 


I  65-25 
\  40-4 
i26-l 


Similarly  constituted  soluble  salts  of  a  red  or  orange  colour  may  be  obtained 
by  boiling  solutions  of  sulphuret  of  barium,  strontium,  and  calcium,  with  an  ex- 
cess of  tersulphuret  of  molybdenum.  The  insoluble  molybdo-sulphurets  may  be 
prepared  from  the  former  by  way  of  double  decomposition. 

ANTIMONIO-  SULPHURETS. 

When  two  parts  of  carbonate  of  potassa  are  intimately  mixed  with  four  of  ses- 
quisulphuret  of  antimony  and  one  part  of  sulphur,  and  the  mixture  is  fused,  an 
antimonio-persulphuret  of  potassium  is  generated.  On  digesting  in  water,  a  sub- 
antimonio-persulphuret  is  dissolved,  and  is  deposited  by  gentle  evaporation  in 
large  colourless  tetrahedrons,  which  become  yellow  on  exposure  to  the  air.  The 
salts  which  this  sulphur-acid  forms  with  other  bases  have  not  been  examined. 

A  sulphur-salt  of  potassium,  in  which  sesquisulphuret  of  antimony  is  the  acid, 
remains  in  solution  after  the  kermes  is  deposited  (page  377),  and  may  be  ob- 
tained by  evaporation  in  vacuo  in  colourless  irregular  crystals  which  deliquesce 
rapidly  in  the  air. 


TUNGSTO-SULPHURETS. 

The  best  known  of  these  salts  is  that  of  potassium,  in  which  tersulphuret  of 
tungsten  is  combined  with  protosulphuret  of  potassium.  It  is  formed  when  a 
solution  of  tungstate  of  potassa  is  decomposed  by  hydrosulphuric  acid,  and  crys- 
tallizes by  evaporation  in  flat  quadrilateral  prisms,  which  are  anhydrous,  and  are 
of  a  pale  red  colour.  It  dissolves  sparingly  in  alcohol,  but  is  freely  soluble  in 
water,  yielding  an  orange-coloured  solution.  When  mixed  with  a  quantity  of 
acid  insufficient  for  entire  decomposition,  it  forms  a  bitungsto-sulphuret  of  a  brown 
colour. 

The  tungsto-sulphuret  of  potassium  unites  with  tungstate  of  potassa  as  a 
double  salt,  which  yields  a  yellow  solution,  and  crystallizes  in  rectangular  tables 
of  a  lemon-yellow  colour.  It  combines  also  with  nitrate  of  potassa,  and  the  re* 
suiting  double  salt  crystallizes  in  large  transparent  crystals  of  a  ruby-red  tint, 
and  when  heated  detonates  like  gunpowder. 

The  tungsto-sulphuret  of  sodium  is  prepared  from  tungstate  of  soda  by  hydro- 
sulphuric  acid,  and  crystallizes  with  difficulty  in  irregular  crystals  of  a  red  colour. 
It  deliquesces  in  the  air,  and  is  soluble  in  water  and  alcohol. 


509 


SECTION  IV. 


CLASS  OF  SALTS.    ORDER  IV. 


HALOID-SALTS. 


In  this  section  are  included  substances  composed  like  the  preceding  salts  of 
two  bi-elementary  compounds,  one  or  both  of  which  are  analogous  in  composi- 
tion to  sea-salt.  The  principal  groups  consist  of  double  chlorides,  double  iodides, 
and  double  fluorides.  In  these  the  haloid-bases  belong  usually  to  the  electro- 
positive metals,  and  the  haloid-acids  to  the  metals  which  are  electro-negative.  I 
shall  apply  to  them  the  same  principle  of  nomenclature  as  to  the  sulphur-salts. 

HYDRARGO-CHLORIDES. 

The  haloid-acid  of  this  family  is  bichloride  of  mercury,  which  reddens  litmus 
paper,  and  loses  the  property  when  a  haloid-base  is  present,  thus  bearing  a  close 
analogy  to  ordinary  acids.  Its  principal  salts  which  have  been  examined  are  thus 
constituted : — 

NamcF,  Basic  Chloride.        Bichlor.  Merc.       Equiv.        Formulae. 

^  Potass?um''^'°"*^^  "^^        }  ^^^'^^    ^  eq.4.273-84     1  eq.=422-98    2KCltHgCl2. 

Do.  in  rhombic  prisms  with  18  or  2  eq.  of  water        =440-98 
"  P^o'Sum  ^°"*^^  "^^  V   74-57     1  eq.-+-273-84     1  eq.=348-41     KCl+HgCla.      '      ' 

Do.  in  acicular  crystals  with  18  or  2  eq.  of  water       =366-41 

^  plussfum''^'''"*^^  °^        }    ''^■^^     ^  eq.+547-68    2  eq.=622-25    KClt2HgCl2. 
Do.  in  acicular  crystals  with  36  or  4  eq.  of  water       =668-25 

"dium^'**''^^''"'^^°^^°'     }    ^^''^^    leq.+273-84    1  eq.=333-66    NaCltHgClz. 

Do.  in  crystals  with  36  or  4  eq.  of  water  =:369-56 

Dihydrargo.chloride  of        )  j^^.j^     j  eq.t273-84     1  eq.=378-98  P^^'I+^p? 
hydrochio.  of  Ammonia    j  ^    •  -i  ^  ^     ^        -j-HgClj. 

Do.  in  flat  rhombic  prisms  with  18  or  2  eq.  of  water  =396-98 

The  preceding  salts,  except  the  last,  were  first  prepared  and  examined  by 
BonsdorfF  (An.  de  Ch.  et  Ph.  xliv.  189) ;  and  they  are  obtained  by  mixing  the 
ingredients  in  the  ratio  for  combining,  and  setting  aside  the  solution  to  crystal- 
lize. The  ammoniacal  salt  has  long  been  known  under  the  name  of  salt  of  alem- 
broth.  Bonsdorff  obtained  similar  compounds  with  the  chlorides  of  lithium, 
barium,  strontium,  calcium,  magnesium,  mang-anese,  iron,  cobalt,  nickel,  and 
copper.  Those  of  lithium,  calcium,  magnesium  and  zinc  are  deliquescent.  The 
hydrargo-chlorides  of  iron  and  manganese  are  isomorphous,  and  crystallize  in 
rhombic  prisms.  Hydrochloric  acid  combines  with  bichloride  of  mercury,  and 
yields  a  very  soluble  salt,  which  may  be  obtained  in  crystals  :  the  electro-posi- 


510  PLATINO:CHLORIDES. 

five  ingredient  is  here  probably  hydrochloric  acid,  and  as  such  will  be  considered 
as  chloride  of  hydrogen,  with  properties  analogous  to  the  chlorides  of  electro- 
positive metals. 

AURO-CHLORIDES.  ' 

These  salts,  the  electro-negative  ingredient  of  which  is  the  terchloride  of  gold, 
have  been  studied  by  Berzelius,  Johnston,  and  Bonsdorff.  They  are  prepared 
by  mixing  the  chlorides  in  atomic  proportions,  and  setting  aside  the  solution  to 
crystallize. 

Most  of  them  have  an  orange  or  yellow  colour,  and  consist  of  single  equiva- 
lents of  their  constituent  chlorides,  as  is  exemplified  by  the  composition  of  the 
three  following  salts  ; — 

Names.  Basic  Chlorides.  Terch.  Gold.     Eqiiiv.        Formulae. 

Auro-chloride  of  Potassium        74-67     1  eq.-|- 305-46     1  eq .=380-03     KCl-f-AuClj. 

Do.  in  prisms  with  45  or  5  eq.  of  water  =42503 

Ataro-chloride  of  Sodium  59-72     1  eq.-|- 305-46     1  eq.=365-18    NaCl+AuClj.' 

Do.  in  4-sided  prisms  with  36  or  4  eq.  of  water  =40M8 

^Xr^ror'AmSr       }'»«•'*    •e<,.  +  305.46    ,  e<,.=4,0.60  {'-"»"+««) 


AuCJ, 


Do.  in  acicular  crystals  with  36  or  4  eq.  of  water        =c446'6 


Jiur(hckloride  cf  Potassium. — This  salt  crystallizes  either  in  striated  prisms  or 
thin  hexagonal  tables,  which  effloresce  in  a  dry  air,  and  lose  all  their  water  at 
212°.  At  a  red  heat  the  terchloride  of  gold  is  decomposed,  leaving  chloride  of 
potassium  and  metallic  gold.     This  salt  is  soluble  both  in  water  and  alcohol. 

.Auro-chloride  of  Sodium  crystallizes  in  long  quadrilateral  prisms,  which  may 
be  exposed  to  the  air  without  change,  and  fuse  readily  in  their  water  of  crystal- 
lization.    The  auro-chloride  of  lithium  is  deliquescent. 

Aurorchloride  of  Hydrochlorate  of  Ammonia. — It  crystallizes  in  transparent 
needles  or  small  prisms,  which  become  opaque  by  exposure  to  the  air,  and  are 
soluble  in  water  and  alcohol. 

Auro-chloride  of  Hydrogen, — In  this  compound  hydrochloric  acid  is  probably 
the  positive  chloride.  It  crystallizes  readily  in  long  acicular  crystals  of  a  light 
yellow  colour  when  an  acid  solution  of  gold  is  cautiously  evaporated.  The  crys- 
tals undergo  no  change  in  dry  air,  but  in  a  moist  atmosphere  deliquesce  into  a 
yellow  liquid. 

Bonsdorff  has  prepared  the  auro-chlorides  of  barium,  strontium,  calcium,  mag- 
nesium, manganese,  zinc,  cadmium,  cobalt,  and  nickel.  Most  of  them  crystallize 
in  prisms  and  contain  water  of  crystallization. 

PLATINO-CHLORIDES. 

Both  the  protochloride  and  bichloride  of  platinum  act  as  haloid-acids.  Mag- 
nus prepared  the  platino-protochloride  of  potassium  by  mixing  chloride  of  potas- 
sium with  a  solution  of  protochloride  of  platinum  in  hydrochloric  acid.  It  crys- 
tallizes by  evaporation  in  red,  anhydrous,  four-sided  prisms,  which  are  insoluble 
in  alcohol,  but  dissolve  readily  in  water.  It  consists  of  single  equivalents  of  its 
constituent  chlorides. 

The  plalino-protochloride  of  sodium  may  also  be  prepared,  is  soluble  in  water 


PALLADIO-CHLORIDES.  511 

and  alcohol,  and  crystallizes  with  difficulty.  A  similar  salt  may  be  formed  with 
hydrochlorate  of  ammonia,  and  is  isomorphous  with  that  of  potassium,  which  it 
also  resembles  in  its  properties,  composition,  and  mode  of  preparation. 

The  solution  of  protochloride  of  platinum  in  hydrochloric  acid,  which  has  a 
deep  red  tint,  is  doubtless  a  double  chloride,  but  it  has  not  been  obtained  in 
crystals. 

The  principal  salts  of  bichloride  of  platinum  are  those  of  potassium,  sodium, 
and  ammonia,  which  are  thus  constituted  : — 

Names.  Basic  Chlorides.  Bichl.  of  Plat.       Equiv.        Formulae. 

Platino.bichloride  of  Po- )      ^^.^^     j        _^  jgg.g^  j        ^  g^^.gj  j^^l  +  PICI2. 

tassiura                              y                         ^     '  ^                                   t           z 

Sodium           59-72    1  eq.  +  169-64  leq.  =  229-36  NaCl -|- PlClg. 

Do.        in  prisms  with  54  or  6  eq.  of  water  ==  283-36 

Platino.bichloridfe   of  hy.)    j^^.j^     j  eq. -|.  169-64     leq.  =  274-78   { ^"^N  +  HCl)  + 
drochlorate  01  Ammonia^  ^     '  ^  (     PlCJj. 

P latino-bichloride  of  Potassium. — The  production  of  this  salt  by  mixing  its 
constituents  in  solution,  constitutes  one  of  the  best  tests  for  potassa.  It  is  com- 
monly obtained  as  a  powder,  of  a  pale  lemon-yellow  colour;  but  by  slow  evapo- 
ration it  yields  small  octohedrons  of  a  brilliant  lustre.  It  is  anhydrous,  insoluble 
in  alcohol,  and  is  sparingly  dissolved  by  cold,  but  more  freely  by  hot  water. 
Heated  to  redness  it  yields  chlorine,  and  the  residue  consists  of  platinum  and 
chloride  of  potassium. 

P latino-bichloride  of  Sodium. — This  salt  crystallizes  in  fine  transparent  prisms 
of  a  deep  yellow-colour,  which  are  soluble  in  water  and  alcohol.  When  gently 
heated  it  loses  its  water  of  crystallization,  and  becomes  a  pale  yellow  powder. 

P latino-bichloride  of  Hydrochlorate  of  Ammonia  falls  as  a  lemon-yellow  powder 
when  sal-ammoniac  is  mixed  with  a  strong  solution  of  bichloride  of  platinum. 
It  resembles  the  double  salt  of  potassium  in  its  properties  and  form,  crystallizing 
in  small  anhydrous  octohedrons  when  its  aqueous  solution  is  slowly  evaporated. 
This  salt  is  employed  in  the  preparation  of  platinum,  and  when  heated  to  red- 
ness leaves  that  metal  in  a  spongy  state. 

Bonsdorff  has  prepared  the  platino-bichlorides  of  barium,  strontium,  calcium, 
and  several  other  metals.  Most  of  them  crystallize  with  water  of  crystalliza- 
tion, and  have  a  yellow  or  orange  colour. 

TALLADIO-CHLORIDES. 

Both  of  the  chlorides  of  palladium  act  as  haloid-acids,  combining  with  many 
of  the  metallic  chlorides,  when  their  respective  solutions  are  mixed  and  evapo- 
rated. The  principal  ones  which  have  been  examined  are  those  with  potassium, 
sodium,  and  ammonia,  which  consist  of  single  equivalents  of  their  ingredients. 

The  palladio-protochloride  of  potassium  crystallizes  in  four-sided  prisms  of  a 
dirty  yellow  colour,  which  are  anhydrous,  insoluble  in  alcohol,  and  freely  soluble 
in  water.  The  corresponding  salt  bf  sodium  is  deliquescent  and  soluble  both  in 
water  and  alcohol.  That  of  hydrochlorate  of  ammonia  is  isomorphous  with  the 
salt  of  potassium,  which  it  resembles  in  its  other  properties. 

The  palladio-bichloride  of  potassium  is  obtained  by  evaporating  the  palladio- 
protochloride  with  nitro-hydrochloric  acid,  when  microscopic  crystals  of  a  cinna- 
bar-red colour  are  deposited  which  by  a  glass  are  found  to  be  regular  octohedrons. 


512  OXY-CHLORIDES. 


It  is  anhydrous,  insoluble  in  alcohol,  and  nearly  so  in  water.  When  heated,  or 
by  continued  ebullition,  it  is  reconverted  into  the  palladio-protochloride  of  potas- 
sium. The  corresponding  salt  of  hydrochlorate  of  ammonia  is  obtained  in  a 
similEir  manner,  and  resembles  the  former  in  form  and  other  properties. 

RHODIO-CHLORIDES. 

The  sesquichloride  of  rhodium  combines  with  the  chlorides  of  potassium  and 
sodium,  and  the  resulting  salts  are  thus  constituted  :— 

Names.  Basic  Chlor.    Sesquichl.  Rhod.    Equiv.      Formulae. 

Dirhodio-chloride  of  Potassium  41914    2  eq.  -f  210-66     1  eq.  =  359  80    2KC1  -f-  RjClg. 

Do.     in  four  sided  prisms  with  18  or  2  eq.  of  water  =:  377-8 

Trirhodio. chloride  of  Sodium     17916    3  eq.  -f  210-66     1  eq.  =  389  82    3NaCl  f  R2CI3. 

Do.    in  prisms  with  162  or  18  eq.  of  water  =  551-82. 

Dirhodio-chloride  of  Potassium. — It  is  obtained  by  mixing  the  respective  chlo- 
rides in  the  ratio  above  assigned,  and  crystallizes  in  four-sided  rectangular 
prisms,  which  are  of  a  deep  red  colour,  insoluble  in  alcohol,  and  contain  18 
parts  or  2  eq.  of  water  combined  with  359*8  parts  or  1  eq.  of  the  salt. 

Hydrochlorate  of  ammonia  yields  a  similar  double  salt,  analogous  in  its  pro- 
perties to  the  preceding. 

Trirhodio-chloride  of  Sodium. — ^This  salt  crystallizes  in  large  prismatic  crystals 
of  a  deep  red  colour,  which  lose  part  of  their  water  in  a  dry  air,  and  become 
covered  with  a  red  powder.    They  are  insoluble  in  alcohol. 

IRIDIO.CHLORIDES. 

The  chlorides  of  iridium  act  as  haloid-acids.  The  most  remarkable  of  its 
salts  is  the  iridio-bichloride  of  potassium,  which  in  form  and  properties  resem- 
bles the  platino-bichloride  of  potassium,  crystallizing  in  brilliant  octohedrons, 
but  of  a  black  colour,  which  are  sparingly  soluble  in  water.  Hydrochlorate  of 
ammonia  forms  with  it  a  similar  salt,  which  is  of  a  deep  cherry-red  colour. 

OSMIO.CHLORIDES. 

Berzelius  has  described  the  osmio-bichloride  of  potassium,  which  resembles 
in  form,  composition,  and  most  of  its  properties,  the  corresponding  salts  of  pla- 
tinum and  iridium.  It  is  insoluble  in  alcohol,  and  but  sparingly  dissolved  in 
water  ;  but  its  aqueous  solution,  when  gently  evaporated,  yields  octohedral  crys- 
tals of  a  deep  brown  colour. 

OXY-CHLORIDES. 

Chemists  are  acquainted  with  a  considerable  number  of  compounds  in  which 
a  metallic  oxide  is  united  with  a  chloride  either  of  the  same  metal,  which  is  the 
most  frequent,  or  of  some  other  chloride.  These  compounds  are  commonly 
termed  sub-muriates,  on  the  supposition  that  they  consist  of  hydrochloric  acid 
combined  with  two  or  more  eq.  of  an  oxide. 

Oxy-chlorides  of  Iron. — When  the  crystallized  protochloride  of  iron  ia  heated 
without  exposure  to  the  air,  the  last  portions  of  its  water  exchange  elements 


OXY.CHLORIDES.  51  ^ 

with  part  of  the  chloride  of  iron,  yielding^  hydrochloric  acid,  which  is  evolved, 
and  protoxide  of  iron.  On  raising  the  heat  so  as  to  expel  the  pure  chloride  of 
iron,  a  deep  green  oxy-chloride  in  scaly  crystals  remains.     (Berzelius.) 

The  ochreous  matter  which  falls  when  a  solution  of  the  protochloride  of  iron 
is  exposed  to  the  air,  is  hydrated  peroxide  of  iron  combined  with  some  perchlo- 
ride.  A  similar  hydrate  is  obtained  by  mixing  with  a  solution  of  the  perchloride 
of  iron  a  quantity  of  alkali  insufficient  for  complete  decomposition.  When  a 
solution  of  the  perchloride  is  evaporated  to  dryness  without  exposure  to  the  air, 
the  last  portions  of  water  exchange  elements  with  the  perchloride,  hydrochloric 
acid  is  disengaged,  and  after  subliming  the  pure  anhydrous  perchloride,  a  com- 
pound in  large,  brown,  shining  laminae  is  left,  which  consists  of  peroxide  and 
perchloride  of  iron.     (Berzelius.) 

Mr.  Phillips  has  described  a  soluble  oxy-chloride  which  appears  to  consist  of 
1  eq.  of  perchloride  of  iron  with  9  eq.  of  the  peroxide.  It  is  prepared  by 
digesting  hydrochloric  acid  with  the  required  proportion  of  the  moist  hydrated 
peroxide.  The  solution  is  of  a  brownish-red  colour,  and  a  precipitate  is  occa- 
sioned either  by  a  little  more  of  the  peroxide  or  a  little  acid,  indicating  the  for- 
mation of  other  oxy-chlorides  which  are  insoluble.  (Phil.  Mag.  and  An.  viii, 
406.) 

By  adding  bleaching-liquor  to  protonitrate  of  iron,  Millon  obtained  an  oxy- 
chloride,  corresponding  to  the  sesquioxide,  which  it  resembles  in  appearance.  Its 

formula  is 


Kil- 


Oxy-chlorides  of  Tin. — When  a  large  quantity  of  water  is  poured  on  crystal- 
lized protochloride  of  tin,  a  portion  of  water  and  protochloride  exchange  ele- 
ments, an  acid  solution  is  formed,  containing  the  double  chloride  of  tin  and 
hydrogen,  and  a  white  powder  subsides,  which  is  a  compound  of  the  protoxide 
and  protochloride  of  tin. 

Oxy-chloride  of  Chromium, — ^This  compound,  which  was  long  considered  as  the 
terchloride,  was  first  shown  to  be  an  oxy-chloride  by  Rose.  It  has  already  been 
mentioned  at  page  383. 

Oxy-chloride  of  Tungsten, — ^This  compound,  the  nature  of  which  was  first 
pointed  out  by  Rcse,  has  already  been  described  at  page  395. 

Oxy-chloride  of  Molybdenum. — Formerly  described  as  the  terchloride,  but 
shown  by  Rose  to  be  really  similar  in  constitution  to  the  two  preceding  com- 
pounds (page  393). 

Oxy-chloride  of  Antimony, — It  falls  as  a  white  curdy  precipitate  when  sesqui- 
chloride  of  antimony  is  thrown  into  water  (page  376),  and,  according  to  an  anal- 
ysis by  Phillips,  contains  7'8  per  cent,  of  chlorine. 

Oxy-chloride  of  Cerium, — This  compound  is  generated  by  heating  the  hydrated 
protochloride,  just  as  when  the  protochloride  of  iron  is  distilled. 

Oxy-chloride  of  Bismuth, — It  is  prepared  by  pouring  a  neutral  solution  of 
nitrate  of  oxide  of  bismuth  into  a  concentrated  solution  of  sea-salt;  and  a  similar 
compound,  but  with  more  oxide,  is  formed  when  a  dilute  solution  of  sea-salt  is 
used.    They  are  both  heavy  insoluble  powders  of  a  very  white  colour. 

Oxy-chloride  of  Copper. — This  compound  falls  as  a  green  hydrate  when  potassa 
is  added  to  a  solution  of  chloride  of  copper  in  quantity  insufficient  for  its  com- 
plete decomposition.  When  its  water  is  expelled,  it  becomes  of  a  liver-brown 
colour.  Berzelius  states  it  to  consist  of  1  eq.  of  the  chloride  and  3  en.  of  oxide 
of  copper.    It  is  used  as  a  pigment  under  the  name  of  Brunswick  green,  being 

35 


514  CHLORIDES  WITH  AMMONIA. 

prepared  for  that  purpose  by  exposing  metallic  copper  to  hydrochloric  acid  or  a 
Boliition  of  sal-ammoniac.  The  same  compound  is  generated  during  the  corro- 
sion of  copper  in  sea-\yater.     Millon,  by  the  process  above  mentioned,  obtained 

an  oxy-chloride  of  coppei,  Cu  p.  >  ,  which  seems  to  be  a  basic  compound. 

Oxy'chlorides  of  Lead. — A  compound  of  1  eq.  protochloride  to  2  eq.  of  protox- 
ide of  lead  has  been  found  as  a  colourless  mineral.  Another  oxy-chloride  with 
3  eq.  of  the  protoxide  is  prepared  by  adding  pure  ammonia  to  a  hot  solution  of 
chloride  of  lead.  It  falls  as  a  heavy  white  hydrate;  but  on  expelling  its  water 
by  heat»  it  acquires  a  pale  yelloW:  colour.  A  third  oxy-chloride  with  a  still 
larger  proportion  of  oxide  is  used  as  a  pigment  under  the  name  of  mineral  or 
patent  yellow;  and  it  is  prepared  by  the  action  of  moist  sea- salt  on  litharge,  by 
which  means  portions  of  the  protoxide  and  sea-salt  exchange  elements,  yielding 
soda  and  chloride  of  lead.  After  washing  away  the  alkali,  the  mixed  oxide  and 
chloride  are  dried  and  fused.  Millon  states  that  bleaching  liquor,  added  to 
nitrate  of  lead,  throws  down  a  white  precipitate,  which  soon  becomes  brown. 
These  colours  indicate   different   mechanical   states    of  the  same  compound, 

Pbp   >  ;  that  is  an  oxychloride,  corresponding  to  the  peroxide,  Pb„  y  . 

Oxy-chloride  of  Mercury. — This  compound  is  obtained  as  a  shining  crystalline 
powder,  of  a  brownish-black  colour,  when  peroxide  of  mercury  is  boiled  with  a 
solution  of  the  bichloride.     It  is  anhydrous,  and  consists  of  single  equivalents  of 

the  oxide  and  chloride.     Formula,  HgO^+HgCl   or  Hgp.  f  . 

Millon's  experiments  alluded  to  above,  and  in  the  section  on  the  hypochlorites, 
if  confirmed,  will  add  the  bleaching  compounds  to  the  order  of  oxy-chlorides ; 
and  render  it  probable  that  oxy-chlorides  in  general  are  not  compounds  of  oxides 
and  chlorides,  but  compounds  of  the  metal  with  oxygen  and  chlorine  correspond- 
ing to  the  peroxides  of  the  respective  metals. 

CHLORIDES  WITH  AMMONIA. 

Several  interesting  compounds  of  chlorides  with  ammonia  have  been  studied 
by  Persoz  and  Rose.  (An.  de  Ch.  et  Ph.  xliv.  315,  and  li.  5,  and  Pog.  Annalen, 
XX.  149.)  The  perchlorides  of  tin,  titanium,  antimony  and  iron,  and  the  oxy- 
chloride  of  chromium,  absorb  ammonia  at  common  temperatures  ;  and  most  of  the 
other  chlorides  absorb  it  when  gently  warmed.  The  chlorides  of  potassiimi, 
sodiuip,  and  barium,  do  not  absorb  ammonia;  while  those  of  strontium  and 
calcium  combine  with  4  eq.  of  the  alkali.  Chloride  of  copper  absorbs  3  eq. 
and  acquires  the  same  deep  blue  tint  as  the  ammoniaco-sulphate  of  copper. 
Chloride  of  nickel  unites  with  3,  and  chloride  of  cobalt  with  2  eq.  of  ammonia. 
Chloride  of  silver  takes  up  slowly  1  i  eq.  Calomel  absorbs  half  an  eq.  and  forms 
a  black  compound  ;  but  on  exposure  to  the  air  the  ammonia  flies  off,  and  pure 
white  calomel  remains.  Corrosive  sublimate,  by  the  aid  of  heat,  rapidly  absorbs 
half  an  eq.  of  ammonia,  and  forms  a  white  compound,  which  is  insoluble  in 
water,  and  bears  a  considerable  temperature  without  decomposition  :  the  white 
precipitate  of  pharmacy  is  probably  analogous  in  nature,  though  the  ratio  of  its 
ingredients  is  different.  Perchloride  of  titanium  combines  with  2  eq.  and  that 
of  tin  with  1.  The  bromides  and  iodides,  as  well  as  the  bicyanuret  of  mercury, 
absorb  ammonia  in  the  same  manner  as  the  chlorides.     Nearly  all  of  these  com- 


DOUBLE  IODIDES.  515 

pounds  depend  on  very  feeble  affinities.  Most  of  them  lose  their  ammonia  by- 
mere  exposure  to  the  air,  and  it  is  expelled  from  nearly  all  by  a  very  moderate 
heat .  in  some,  as  with  perchloiide  of  titanium,  heat  occasions  reactions  between 
the  chlorine  and  ammonia,  and  the  metal  is  insulated  ;  but  in  general  the  alkali 
is  simply  expelled,  and  the  chloride  returns  to  its  former  condition.  Though 
these  ammoniacal  chlorides  may  be  viewed  as  salts  ifi  which  a  metallic  chloride 
acts  as  an  acid,  they  appear  to  be  more  closely  allied  to  those  singular  compounds 
of  ammonia  with  the  oxy-salts  which  have  already  been  noticed.  To  this  re- 
mark some  of  them,  of  which  the  ammoniacal  chloride  of  mercury  is  an  instance, 
are  probably  exceptions,  and  are  rather,  as  Kane  has  shown,  to  be  viewed  as 
compounds  of  amide.  They  will  be  referred  to  in  this  form  in  the  organic 
chemistry. 

CHLORIDES  WITH  PHOSPHURETTED  HYDROGEN. 

The  analogy  which  Rose  has  traced  between  ammonia  and  phosphuretled  hy- 
drogen is  especially  remarkable  in  the  compounds  which  they  both  form  with 
metallic  chlorides.  He  has  examined  the  compounds  of  phosphuretted  hydrogen 
with  the  perchlorides  of  titanium,  tin,  antimony,  iron  and  alumina,  all  of  which 
correspond  to  ammoniacal  chlorides  of  similar  composition.  The  phosphuretted 
hydrogen  is  in  all  readily  displaced  by  water,  or  a  solution  of  ammonia.  Rose 
observed  that  the  resulting  compound  is  the  same  in  character  and  composition 
whichever  of  the  two  kinds  of  phosphuretted  hydrogen  were  used  in  its  prepara- 
tion. He  also  found  that  the  gas,  when  displaced  from  perchloride  of  titanium 
by  water,  does  not  inflame  spontaneously  ;  whereas,  if  displaced  by  a  solution 
of  potassa  or  its  carbonate,  by  carbonate  of  ammonia  or  hydrochloric  acid,  the 
gas  is  spontaneously  inflammable.  He  was  thus  able  to  disengage  at  will  either 
variety  of  phosphuretted  hydrogen  from  the  same  compound,  without  reference  to 
the  kind  which  had  been  used  in  its  preparation.  These  facts  first  led  Rose  to 
the  opinion  that  the  two  gases  of  phosphorus  and  hydrogen  must  be  identical  in 
composition. 

DOUBLE  IODIDES. 

These  compounds  have  not  as  yet  been  closely  studied ;  but  there  is  no  doubt 
that  the  iodides  are  capable  of  forming  with  each  other  an  extensive  series  of 
compounds.  BonsdorfF  obtained  the  hydrargo-biniodide  of  potassium  by  satu- 
rating a  strong  solution  of  iodide  of  potassium  with  biniodide  of  mercury  :  it  may 
also  be  forined  by  dissolving  corrosive  sublimate  in  a  solution  of  iodide  of  potas- 
sium, evaporating  to  dryness,  and  digesting  in  alcohol,  when  the  double  iodide 
is  dissolved,  and  chloride  of  potassium  is  left.  A  variety  of  double  iodides  have 
been  described  by  Boullay,  and  among  them  a  compound  of  biniodide  of  mercury 
and  hydriodic  acid.  (An.  de  Ch.  et  Ph.  xxxiv.)  In  general  the  double  hydrargo- 
biniodides  contain  single  equivalents  of  the  respective  iodides.  Liebig  obtained 
a  compound  of  the  bichloride  and  biniodide  of  mercury,  consisting  of  2  eq.  of 
the  former  to  1  eq.  of  the  latter,  as  indicated  by  the  formula  Hgl2-|-2HgCl2. 

Several  compounds  of  biniodide  of  platinum  with  other  iodides  have  been 
studied  by  Kane  and  Lassaigne.  (Dublin  Journal  of  Science,  i.  304,  and  An. 
de  Ch.et  Ph.  li.  125.)  The  compounds  at  present  known  are  thus  constituted: — 


516  DOUBLE  BROMIDES.— DOUBLE  FLUORIDES. 

Names.  Basic  lod.         Biniod.  Plat.  Equiv.     Formulae. 

Platino-biniodide  of  Potassium  165-45  I  eq.-|-351-4  1  eq.=516-85  KI-|-Pt  I2. 

Do.  of  Sodium       .        .         .  150-6  1  eq.-f  351  4  1  eq.=502-0  Nal-|-Pt  R 

Do.  of  Hydriodate  of  Ammonia  144-45  1  eq.-t-351-4  1  eq.=495-85  NHJ-j-Pt  Ij. 

Do.  of  Barium        ...  195  1  eq.-f- 351-4  1  eq. =546-4  Bal-j-Ptla. 

Do.  of  Zinc  .        .        .  158-6  1  eq.-j-351  4  1  eq.=510-0  ZnlfPtlj. 

Do.  of  Hydrogen  .        .  127-3  1  eq.f  351-4  1  eq.=478-7  HI-j-Ptl2. 

The  platino-biniodide  of  potassium  is  prepared  by  dig^esting  an  excess  of  bin- 
iodide  of  platinum  in  a  rather  concentrated  solution  of  iodide  of  potassium.  By 
spontaneous  evaporation  it  crystallizes  in  small  rectangular  plates  surmounted 
sometimes  with  a  four-sided  pyramid,  which  are  anhydrous,  unchanged  in  the 
air,  and  insoluble  in  alcohol.  The  colour  of  the  crystals  is  black  with  a  metallic 
lustre,  and  they  yield  a  deep  claret-coloured  solution  with  water.  The  biniodide 
of  platinum  appears  to  combine  also  with  the  iodide  of  platinum;  but  the  com- 
pound has  only  been  obtained  in  solution. 

The  platino-biniodides  of  sodium,  barium,  and  zinc  are  obtained  in  the  same 
manner  as  that  of  potassium,  crystallize  with  difficulty,  are  deliquescent  in  the 
air,  and  dissolve  in  water  and  alcohol.  The  ammoniacal  salt  is  analogous  in  its 
properties  to  that  of  potassium,  with  which  it  appears  also  to  be  isomorphous. 

Platino-hinivdide  of  Hydrogen. — ^This  compound  consists  of  hydriodic  acid 
and  biniodide  of  platinum,  in  which  the  former  is  regarded  as  the  electro-positive 
element.  It  is  prepared  by  acting  on  biniodide  of  platinum  with  a  cold  dilute 
solution  of  hydriodic  acid,  which  gradually  acquires  a  deep  claret  colour,  and  by 
evaporation  under  a  bell-jar  with  quicklime,  deposits  black  acicular  crystals. 
The  crystals  become  moist  by  exposure  to  the  air. 

Oxy-iodides, — The  principal  oxy-iodides  at  present  known  to  chemists  are 
those  formed  by  the  oxide  and  iodide  of  lead.  When  iodide  of  potassium 
is  mixed  with  acetate  of  oxide  of  lead  in  excess,  the  yellow  chloride  at  first 
formed  combfnes  with  oxide  of  lead  and  acquires  a  white  colour ;  and  the  same 
compound  is  obtained  directly  by  employing  a  subacetate.  Denot  finds  that 
there  are  three  oxy-iodides,  in  which  I  eq.  of  iodide  of  lead  is  united  with  1,  2, 
and  5  eq.  of  oxide  of  lead. 

DOUBLE  BROMIDES. 

These  compounds  have  not  yet  been  studied  ;  but  Bonsdorff  has  proved  the 
possibility  of  forming  compounds  similar  in  composition  and  properties  to  the 
double  chlorides.  He  obtained  the  hydrargo-bibromide  of  potassium  in  crystals, 
consisting  of  1  eq.  of  each  bromide  united  with  2  eq.  of  wa^er. 

DOUBLE  FLUORIDES. 

The  researches  of  Berzelius  have  led  to  the  formation  of  several  extensive 
families  of  double  fluorides,  in  which  the  fluorides  of  boron,  silicon,  titanium, 
and  of  other  electro-negative  metals  are  the  acids,  and  the  flourides  of  electro- 
positive metals  are  bases.  In  some  instances  hydrofluoric  acid  is  a  haloid-acid  ; 
but  more  commonly  it  acts  the  part  of  a  base. 

Hydro-JluoTides. — In  this  family  hydrofluoric  acid  is  combined  with  the  fluo- 
rides of  electro-positive  metals.  If  an  equivalent  of  any  electro-positive  metal  be 
indicated  by  M,  then  the  general  formula  for  this  family  is  MF  -|-  HF. 


BORO.FLUORIDES.  517 

The  hydro-fluoride  of  potassium  is  made  by  mixing  hydro-fluoric  acid  with  a 
solution  of  fluoride  of  potassium,  and  evaporating  by  a  gentle  heat  in  a  platinum 
capsule.  It  commonly  crystallizes  in  confused  laminae  ;  but  by  slow  evapora- 
tion in  square  tables  or  cubes,  which  are  anhydrous  and  dissolve  freely  in  pure 
water.  It  fuses  readily  when  heated,  and  loses  all  its  hydrofluoric  acid  at  a  low 
red  heat. 

The  hydro-fluoride  of  sodium  is  prepared  as  the  preceding  salt,  and  by  spon- 
taneous evaporation  yields  anhydrous  rhombohedral  crystals.  It  is  sparingly 
soluble  in  cold,  but  much  more  freely  in  hot  water.  The  hydrofluoride  of 
lithium  is  also  of  sparing  solubility.  The  fluorides  of  barium,  strontium,  cal- 
cium, and  magnesium  do  not  combine  with  hydrofluoric  acid. 

BORO.FLUORIDES. 

When  the  terfluoride  of  boron  (fluoboric  acid  gas)  is  acted  upon  by  water,  one 
out  of  every  four  eq.  of  the  gas  interchanges  elements  with  water,  giving  rise  to 
hydrofluoric  and  boracic  acids,  the  former  of  which  combines  as  a  haloid-base 
with  undecomposed  terfluoride  of  boron,  constituting  the  boro-hydrofluoric  acid, 
but  which  may  be  viewed  as  the  boro-Jluoride  of  hydrogen.  This  change  is  such 
that 

4  eq.  Terfluoride  of  Boron  4BF8  3  eq.  Terfluoride  of  Boron  3BFj. 

'^      3  eq.  Hydrofluoric  Acid  3HF. 

and  3  eq.  of  water  3H0     ^     and  1  eq.  Boracic  Acid  BO3. 

By  careful  concentration  and  cooling,  the  boracic  acid  separates  as  a  crystalline 
powder,  and  the  boro-fluoride  of  hydrogen  remains  in  solution.  It  is  strongly 
acid  to  test  paper,  and  its  composition  is  indicated  by  the  formula  HF-f-  BF^, 
being  an  eq.  of  each  fluoride.  On  adding  potassa  to  this  compound,  it  inter- 
changes elements  with  hydrofluoric  acid,  and  there  results  the  boro-fluoride  of 
potassium,  KF  -\-  BF  ,  the  hydrogen  being  simply  displaced  by  potassium. 
The  protoxides  of  most  other  metals  act  precisely  like  potassa,  and  therefore  the 
general  formula  of  these  compounds  is  MF  -f  BF  .  When  exposed  to  a  strong 
heat,  they  all  give  off"  terfluoride  of  boron,  and  a  metallic  fluoride  is  left. 

Boro-Jiuoride  of  Potassium. — It  is  prepared  by  dropping  boro-fluoride  of  hydro- 
gen drop  by  drop  into  a  solution  of  a  salt  of  potassa,  and  falls  as  a  gelatinous 
transparent  hydrate,  which  is  a  white  very  fine  powder  when  dried  It  has  a 
slightly  bitter  taste,  and  is  quite  neutral  to  test  paper,  is  very  sparingly  soluble 
in  alcohol  and  cold  water,  but  is  dissolved  freely  by  hot  water,  and  subsides  on 
cooling  in  small  brilliant  anhydrous  crystals.  At  a  strong  red  heat  it  gives  off 
the  terfluoride  of  boron,  and  fluoride  of  potassium  remains. 

The  horo-Jluoride  of  sodium  is  very  soluble  in  water,  and  is  therefore  best  ob- 
tained by  the  direct  action  of  boro-fluoride  of  hydrogen  on  fluoride  of  sodium.  It 
crystallizes  by  slow  evaporation  in  large  rectangular  prisms,  which  redden 
litmus  paper  strongly.  The  boro-fluoride  of  lithium  also  crystallizes  in  large 
prisms,  is  very  soluble  in  water,  and  deliquesces  in  the  air. 

The  horo-Jluoride  of  barium  is  prepared  by  adding  carbonate  of  baryta  to  boro- 
fluoride  of  hydrogen  till  it  ceases  to  be  dissolved,  avoiding  any  further  addition 
On  evaporating  to  the  consistence  of  a  syrup  long  acicular  crystals  form,  and  by 
keeping  the  solution  in  a  warm  place  it  yields  flat,  four-sided,  rectangular  prisms 


518  SILICO-FLUORIDES  — TITANO-FLUORIDES. 

h  is  acid  to  test  paper,  and  deliquescent.  The  boro-fllioride  of  calcium  and 
magnesium  may  be  prepared  in  a  similar  manner,  and  are  soluble  in  water. 
Lead  forms  a  soluble  boro-fluoride,  which  crystallizes  in  the  same  manner  as 
the  boro-fluoride  of  barium. 

SILICO-FLUORIDES. 

The  acid  solution,  called  silico-hydrnjlunric  acid  may  be  viewed  as  the  suhsesqui' 
ailico-Jluonde  of  hydrogen^  a  compound  of  157*16  parts  or  2  eq,  of  fluoride  of 
silicon  and  5904  or  3  eq.  of  fluoride  of  hydrogen  (hydrofluoric  acid),  as  indi- 
cated by  the  formula  3HF  +  2SiFg.  AVhen  the  solution  is  neutralized  with 
potassa,  the  alkali  interchanges  elements  with  the  fluoride  of  hydrogen,  water 
and  fluoride  of  potassium  are  generated,  and  the  latter  combines  with  the  fluoride 
of  silicon.  This  double  fluoride  consists,  therefore,  of  157-16  parts  or  2  eq.  of 
fluoride  of  silicon,  and  173*49  or  3  eq.  of  fluoride  of  potassium,  the  formula  of 
which  is  3KF  -}-  2SiF^.  A  similar  change  ensues  with  the  protoxides  of  most 
other  metals,  and  hence  the  general  formula  of  the  silico-fluorides  is  3MF  + 
2SiF^.  Oa  exposing  these  compounds  to  a  red  heat  fluoride  of  silicon  is  dis- 
engaged.        ,      .    , 

Silico-Jfiinrzde  nf  Potassium. — This  salt  falls  as  a  semi-transparent  jelly,  which, 
has  the  property  of  reflecting  the  colours  of  the  rainbow;  but  when  collected  on 
a  filter  and  dried,  it  becomes  a  dense  white  powder.  By  evaporating  a  saturated 
aqueous  solution,  it  separates  in  minul^  anhydrous  crystals.  It  is  sparingly 
soluble  in  hot  water*  and  still  less  so  in  cold  water. 

The  sili co-fluoride  of  sodium  resembles  the  former  salt,  but  is  much  more 
soluble  in  hot  water.  By  evaporation  it  is  obtained  in  minute  anhydrous  hexa- 
gonal prisms..  The  silico-fluoride  of  lithium  forms  similar  crystals,  but  is  more 
soluble  in  water. 

The  silico-fluoride  ff  barium  gradually  falls  in  microscopic  cr}'Stals,  which 
through  a  glass  appear  as  elongated  prisms,  when  chloride  of  barium  is  mixed 
with  the  silico-fluoride  of  hydrogen,  hydrochloric  acid  remaining  in  solution. 
This  salt  is  very  sparingly  soluble  in  water  whether  hot  or  cold. 

The  silico-fluorides  of  strontium,  calcium,  magnesium,  and  lead  are  best  pre- 
pared by  dissolving  their  respective  carbonates  in  silico-fluoride  of  hydrogen. 
The  salt  of  strontium  crystallizes  in  short  quadrilateral  prisms,  which  lose  their 
water  of  crystallization  at  a  gentle  heat  and  become  opaque.  For  complete  solu- 
bility in  water,  they  require  a  slight  excess  of  hydrofluoric  acid  to  be  present, 
and  then  they  dissolve  freely.  The  salt  of  calcium  crystallizes  in  regular  qua- 
drilateral prisms.  It  dissolves  readily  in  water  acidulated  with  hydrofluoric  or 
hydrochloric  acids,  but  is  decomposed  by  pure  water,  yielding  an  acid  soluble' 
salt,  and  an  insoluble  sub-salt.  The  salts  of  magnesium  and  lead  are  very 
aoluble,  and  leave  a  gummy  mass  by  evaporation. 

The  silico-fluorides  of  manganese,  iron,  zinc,  cobalt,  nickel,  and  copper  are 
soluble  in  water,  and  crystallize  in  similar  hexagonal  prisms,  probably  isomor- 
phous,  which  contain  respectively  1  eq.  of  the  silico-fluoride  and  7  eq.  of  water 
of  crystallrzation. 

TIT  ANO.  FLUORIDES. 

Hydrofluoric  acid  dissolves  titanic  acid,  and  forms  with  it  an  acid  solution 
which  may  be  viewed  as  the  litano-fluoride  of  hydrogen,  consisting  of  61-66 


OXY-FLUORIDES.  519 

parts  or  1  eq.  of  bifluoride  of  titanium,  and  19-68  or  1  eq.  of  fluoride  of  hydrogen, 
expressed  by  the  formula  HF  -j-  TiF^.  When  mixed  with  potassa,  water  and 
fluoride  of  potassium  are  generated,  and  the  titano-fluoride  of  potassium  results, 
the  formula  of  which  is  KF  -\-  TiF  .  By  substituting  most  other  protoxides  for 
potassa  similar  salts  may  he  prepared,  the  general  formula  being  MF  -f-  TiF  . 

Few  of  the  titano-fluorides  have  as  yet  been  studied.  That  of  potassium  crys- 
tallizes by  evaporation  in  scales  like  boracic  acid,  which  are  anhydrous,  and  but 
sparingly  soluble  in  cold  water.  The  titano-fluoride  of  sodium,  is  very  soluble, 
and  crystallizes  with  diflUculty. 

Similar  double  fluorides  may  be  formed,  in  which  the  fluorides  of  molybde- 
num, tellurium,  and  platinum  act  as  the  electro-negative  ingredients.  Few  of 
them,  however,  have  as  yet  been  studied.  Berzelius  has  prepared  the  alumino- 
fluorides  of  potassium  and  sodium,  and  the  zircono-fluoride  of  potassium.  He 
employed  the  latter  in  the  preparation  of  metallic  zirconium.  The  alumino- 
fluoride  of  sodium  is  found  in  nature  as  a  rare  mineral  called  cryolite. 

OXY-FLUORIDES. 

Several  fluorides  combine  with  oxides  in  the  same  manner  as  chlorides  and 
iodides.  An  oxy-fluoride  of  aluminium  is  prepared  as  an  insoluble  gelatinous 
hydrate  by  digesting  hydrate  of  alumina  in  a  solution  of  the  sesquifluoride  of 
aluminium.  This  oxy-fluoride,  combined  with  silicate  of  alumina,  constitutes 
the  topaz.  The  neutral  fluorides  of  cobalt,  nickel,  and  copper  are  decomposed 
by  hot  water,  being  resolved  into  soluble  hydro-fluorides,  and  insoluble  oxy- 
fluorides.,  Several  other  fluorides  doubtless  undergo  a  similar  change.  The  oxy- 
fluoride  of  lead  is  generated  either  by  digesting  fluoride  of  lead  in  solution  of 
ammonia,  or  by  fusing  together  the  fluoride  and  oxide  of  lead.  It  is  more  solu- 
ble than  the  fluoride,  and  the  solution  by  exposure  to  the  air  gives  a  precipitate 
of  carbonate  of  oxide  of  lead.  The  fluoride  of  lead  also  combines  by  fusion 
with  chloride  of  lead.  Fluoride  of  calcium  forms  a  very  fusible  compound  with 
sulphate  of  lime.  / 


PART    III. 
ORGANIC  CHEMISTRY- 


INTRODUCTORY. 


Organic  Chemistry  is  so  called  because  it  treats  of  the  substances  which 
form  the  structure  of  organized  beings,  and  of  their  products,  whether  animal  or 
vegetable.  It  has  long  been  known,  that  all  organized  structures,  as  well  as  all 
the  substances  formed  in  or  by  these,  are,  in  great  part,  composed  of  a  very 
limited  number  of  elements  ;  insomuch  that  a  large  proportion  of  them  may  be 
described  as  consisting,  almost  exclusively,  of  only  four  simple  substances, 
namely.  Carbon,  Hydrogen,  Oxygen,  and  Nitrogen, 

But  while  these  four  elements  undoubtedly  constitute  the  chief  part  of  all 
organized  tissues,  and  while  such  products  as  woody  fibre,  sugar,  starch,  gum, 
fat,  oils,  and  many  organic  acids,  contain  only  the  first  three,  that  is.  Carbon, 
Hydrogen  and  Oxygen,  we  must  not  forget  that  other  elements  occur  in  the 
organized  kingdoms  of  nature ;  some  of  them,  such  as  those  of  Phosphate  of 
Lime,  in  large  quantity;  and  all,  whether  they  occur  in  smaller  or  greater  pro- 
portien,  as  truly  essential  to  animal  and  vegetable  life,  as  the  four  elements  above 
mentioned,  the  predominance  of  which  characterizes  the  organic  world. 

Thus,  no  plant  can  grow,  or  form  cells,  or  even  fibre,  without  the  presence  of 
certain  mineral,  or  saline  compounds,  which  are  derived  from  the  soil,  and  which, 
when  the  plant  is  burned,  constitute  its  ashes.  These  are.  Potash,  Soda,  Lime, 
Magnesia,  with,  occasionally,  oxides  of  Iron  and  Manganese,  as  bases ;  and 
Silicic  Acid,  Phosphoric  Acid,  Sulphuric  Acid,  Chlorine  and  Fluorine,  as  acids 
and  acid-radicals. 

Again,  the  juices  of  all  plants,  and  more  especially  their  roots  and  seeds,  con- 
tain some  one  or  more  of  the  compounds  known  by  the  names  of  albumen, 
fibrine,  and  caseine.  Now  these  compounds  contain  small,  but  absolutely  essen- 
tial proportions  of  sulphur  and  phosphorus,  besides  earthy  and  alkaline  phos- 
phates. 

Lastly,  the  bones  of  animals  contain  not  only  phosphate  of  lime,  but  also 
phosphate  of  magnesia  and  fluoride  of  calcium,  both  in  considerable  quantity ; 
and  Iron  is  an  unfailing  constituent  of  blood. 


522  INTRODUCTORY. 

To  the  four  elements  first  mentioned,  as  constituting  the  chief  mass  of  organic 
substances,  we  must  therefore  add,  as  no  less  essential,  although  for  the  most 
part  in  smaller  proportion,  the  following  metalloids,  Chlorine,  Fluorine,  Sul- 
phur, Phosphorus,  and  Silicon;  and  the  following  metals,  Potassium,  Sodium, 
Calcium,  Magnesium,  Iron,  and  occasionally  Manganese. 

It  thus  appears  that  the  fourteen  or  fifteen  elements  which  constitute  the  chief 
mass  of  the  mineral  or  inorganic  world,  are  almost  the  same  which  occur  in 
organized  matter :  the  difference  being  chiefly  this,  that  in  inorganic  nature  the 
predominant  elements,  nearly  in  the  order,  of  their  abundance,  are.  Oxygen, 
Hydrogen,  Nitrogen,  Silicon,  Chlorine,  Sodium,  Aluminum,  Carbon,  and  Iron, 
after  which  follow  Potassium,  Calcium,  Magnesium,  Sulphur,  Phosphorus,  and 
Fluorine;  while  in  the  organic  department  the  order  is  nearly  as  follow's.  Car- 
bon, Oxygen,  Hydrogen,  Nitrogen,  Potassium,  Calcium,  Phosphorus,  Silicon, 
Sulphur,  Sodium,  Magnesium,  Chlorine,  Iron,  and  Fluorine.  Aluminum,  so 
very  aljundant  in  the  mineral  kingdom,  hardly  ever  occurs  in  organic  compounds, 
and  when  it  does  occur,  is  perhaps  accidental. 

The  above  considerations  are  sufllicient  to  show,  that  there  is  no  essential  dis- 
tinction to  be  made  between  organic  and  inorganic  Chemistry,  founded  on  the 
nature  of  the  elements  concerned.  ' 

Neither  is  there  any  such  distinction  to  be  pointed  out  in  regard  to  the  laws  of 
combination  and  decomposition  which  prevail  in  these  different  departments  of 
chemistry;  for  we  find  the  same  affinities  operating;  and  although  organized 
tissues,  and  their  products,  have,  in  gene.ral,  a  more  complicated  constitution 
than  inorganic  compounds,  containing  a  larger  number  of  equivalents  of  their 
elements,  and  consequently  having  much  higher  atomic  w-eights,  we  cannot  con- 
sider such  characters  as  forming  a  valid  ground  of  distinction. 
•  But  while  we  should  find  it  very  difficult,  if  not  impossible,  to  draw  the  line 
between  inorganic  and  organic  Chemistry  on  scientific  principles,  we  may  still 
recognize,  for  convenience  sake,  a  certain  distinction,  founded,  first,  on  the  ori- 
gin of  substances,  whether  animal  and  vegetable,  or  mineral ;  and  secondly,  on 
tlie  uniform  predominance  of  carbon  in  animal  and  vegetable  matter. 

In  reference  to  the  first  point,  it  is  to  be  observed,  that,  although  the  elements 
concerned  are  those  common  to  the  inorganic  and  organic  kingdoms,  the  com- 
pounds which  constitute  the  latter  are  formed  under  peculiar  circumstances,  such 
as,  for  the  most  part,  cannot  be  imitated  in  our  experiments. 

It  is  true  that  chemistry  has  succeeded,  in  some  cases,  in  forming  artificially 
certain  compounds  which  occur  as  products  of  organic  life,  such  as  Uroa,  For- 
mic Aoid,  and  Oil  of  Spiraea.  But,  in  the  first  place,  most,  if  not  all  of  these, 
require  for  their  production  the  aid  of  an  organic  product;  thus,  Formic  Acid  is 
produced  from  Starch,  Oil  of  Spiraea  from  Salleine ;  and  although  Urea  may  be 
obtained  from  Cyanic  Acid  and  Ammonia,  it  is  doubtful  if  either  Cyanogen  or 
Ammonia  can  be  obtained  except  from  organic  compounds,  directly  or  indirectly. 
Secondly,  it  is  particularly  to  be  noticed,  that  we  have  not  yet  succeeded  in  form- 
ing, artificially,  either  an  organized  tissue,  or  even  any  one  of  the  compounds 
(albumen,  &c.)  of  which  such  tissues  are  made.  Those  organic  compounds 
which  have  been  artificially  formed,  are  invariably  ;>r/>dMc/«  of  decomposition,  or, 
in  other  words,  the  excretions  or  secretions  of  organized  bodies;  and  are  far  less 
complex  in  their  constitution  than  organi-^ed  structures. 

From  these  facts  we  draw  the  conclusion,  that  certain  circumstances,  of  which 
the  most  important  is  the  vital  forccj  so  modify  the  play  of  affinities  in  organized 


'INTRODUCTORY.  V    52^ 

beings,  as  to  produce  the  compounds  usually  termed  organic,  which,  so  far  as 
they  are  capable  of  entering  into  the  composition  of  tissues,  cannot  be  imitated 
by  art. 

In  regard  to  the  second  peculiarity  of  organic  compounds,  namely,  the  pre- 
dominance of  carbon  in  their  composition,  we  observe  that,  as  this  carbon  is 
united  to  the  three  gasea,  Oxygen,  Hydrogen,  and  Nitrogen,  with  each  of  which 
it  forms  gaseous  compounds,  and  as,  further,  the  latter  elements,  among  them- 
selves, form  compounds,  such  as  water  and  ainmonia,  which  are  also  volatile,  so 
the  action  of  heat  on  organic  compounds  is  characteristic ;  producing  combusiion 
of  all,  save  the  ashes,  when  there  is  free  access  of  air ;  and  charring  them,  or, 
in  other  words,  causing  the  separation  of  part  of  their  carbon,  in  close  vessels^ 
while  the  greater  part  is  dissipated  in  the  form  of  volatile  products. 

Here,  then,  we  have  a  ready  test  of  organic  matter,  which  is  so  characteristic, 
that  we  might  almost  define  Organic  Chemistry  as  the  Chemistry  of  such  com- 
pounds as  are  charred  when  heated  to  redness  in  close  vessels.  There  ate  very 
few  substances,  indeed,  of  organic  origin,  which  do  not  exhibit  this  character. 

Organic  Chemistry  has  been  defined  as  the  Chemistry  of  Compound  Radicals  ; 
but,  although  we  must  admit  the  existence  of  many  such  radicals  in  Organic 
Chemistry,  we  cannot  adopt  this  definition  in  contradistinction  to  that  of  Inor- 
ganic Chemistry,  as  the  Chemistry  of  Simple  Rad'icals,  because  the  recent 
progress  of  science  has  led,  or  almost  compelled  us  to  admit  the  existence  of 
compound  radicals  in  Inorganic  Chemistry,  as  has  bee'n  explained  in  the  first 
Part  of  this  work.  , 

It  is,  perhaps,  worth  while  to  point  out,  that  all  the  organic  compound  radicals 
hitherto  established,  or  supposed  to  exist,  are  compounds  of  carbon,  if  we  except 
amidogen,  which  contains  only  hydrogen  and  nitrogen. 

It  is  also  proper  here  to  state,  that,  under  the  name  of  organic  compounds, 
many  substances  are  treated  of  which  do  not  occur  in  nature,  but  which  have 
been  obtained  by  subjecting  true  organic  products  to  various  influences  :  to  that, 
for  example,  of  heat,  as  in  what  is  called  the  destructive  distillation,  which 
yields  such  substances  as  naphtha,  naphthaline,  &c. ;  or  to  the  action  of  chlorine 
or  bromine,  of  sulphuric  or  nitric  acids,  of  alkalies,  &c„  by  all  which  means 
whole  series  of  new  compounds  are  obtained.  Lastly,  some  very  interesting  and 
important  compounds  are  included  under  the  term  organic,  which  arise  from  the 
addition  of  elements  not  naturally  occurring  in  the  organic  kingdom ;  as  for 
examj)le,  kakodyle  and  its  compounds,  which  contain  arsenic  as  an  essential 
constituent ;  and  the  very  singular  bases  in  which  platinum  is  added  to  the  usual 
elements  of  organic  alkalies.  -*^•-'• 

But  while,  as  has  just  been  stated,  compound  radicals  are  not  exclusively  cha- 
racteristic of  organic  chemistry,  we  may  still  derive  great  assistance  from  attend- 
ing to  the  compound  radicals  of  organic  chemistry.  For  while  we  admit  the 
existence  of  such  radicals  in  inorganic  chemistry,  along  with  simple  radicals,  we 
must  bear  in  mind  that  all  the  organic  radicals  as  yet  discovered  are  compound, 
and  many  of  them  exceedingly  complex,  containing  three  or  four  elements. 

It 'is  true  that  we  are  not  yet  acquainted  with  the  radicals  of  a  very  large  pro- 
portion of  organic  compounds ;  such  as  the  principal  organic  acids,  the  org-anic 
alkalies,  &c.  But  the  known  organic  radicals  furnish  us  with  the  means  of 
classifying  many  most  important  substances,  just  as  we  classify  the  compounds 
of  any  metalloid  or  of  any  metal  together.     As  to  those   groups  or  series  of 


BM 


COMPOUND  ORGANIC  RADICALS. 


organic  compounds,  the  radicals  of  which  are  not  yet  known,  we  can  only  class 
them  according  to  analogies  of  properties,  of  composition,  or  of  both. 

With  these  introductory  remarks,  we  shall  proceed  to  consider  the  known 
organic  compound  radicals,  and  their  derivatives. 

COMPOUND  ORGANIC  RADICALS. 

A  compound  radical  is  a  substance  which,  although  containing  two  or  more 
elements,  enters  into  combination  with  elementary  bodies  as  if '  it  were  itself 
elementary,  and  in  ordinary  circumstances  performs  exactly  the  part  of  an 
element. 

In  the  first  Part  of  this  work,  we  have  already  admitted  as  probable  the  exist 
ence  of  inorganic  compound  radicals,  such  as  SO  ,  the  radical  of  sulphuric  acid, 
and  NOg,  that  of  nitric  acid.  These  bodies  are,  in  their  relations  to  others, 
entirely  analogous  to  chlorine.  Thus  we  may  represent  the  acids  of  these  three 
radicals,  with  their  potassium  and  silver  salts  as  follows  : — 


(Chlorine 
Radicals  <     SO. 
(     NOe 

Acid. 

Potassium 
Salt. 

Silver  Salt. 

H+Cl 
H+SO4 
H  +  NOg 

KfCl 

K-I-SO4 

K-fNOe 

Ag+CI 
Ag  +  SO^ 
Ag  +  NOe 

-The  compound  inorganic  radicals,  SO^,  and  NO^,  therefore,  perform  exactly 
the  part  of  a  metalloid  of  the  group  of  chlorine. 

But  there  have  also  been  briefly  mentioned,  in  the  first  Part,  certain  compound  . 
organic  radicals,  which  not  only  exhibit,  in  their  relations,  characters  analogous 
to  those  of  chlorine,  but  actually  exist,  like  chlorine,  in  the  separate  state,  which 
is  not  the  case  with  SO^  and  NO^,  these  latter  being  only  known  in  combi- 
nation. 

The  organic  radicals  here  alluded  to  are  Cyanogen,  C^  N=Cy,  and  Mellone 
CgN^s=Me  (see  Part  II.,  p.  271).  They  may  be  comjJared  to  chlorine  exactly 
like  the  two  above  mentioned  inorganic  compound  radicals.    Thus, 


f  Chlorine  CI 
Radicals  ^  Cyanogen  Cy 
^Mellone  Me 

Acid. 

Potassium 
Salt. 

Silver  Salt. 

HH-Cl 
H-|-Me 

KtCl 
K-hMe 

As  +  CI 
Ag  +  Cy 
Ag+Me 

Cyanogen  and  Mellone  are,  therefore,  radicals  of  the  nature  of  the  chlorine 
group  of  metalloids.  The  bisulphuret  or  cyanogen,  or  sulphocyanogrn,  C^N 
S  =CyS  ,  although  it  contains  three  elements,  plays  the  same  part  as  chlorine 
or  cyanogen,  and  forms  with  hydrogen  the  acid  H  -f  CyS^,  and  with  potassium 
the  salt  K  +  CyS^. 

Some  compound  organic  radicals  appear  more  analogous  to  the  combustible 
group  of  metalloids,  that  is,  to  carbon,  sulphur,  or  phosphorus  ;  inasmuch  as 
they  form  acids  with  oxygen,  or  rather  with  the  elements  of  water  like  those 
metalloids,  and  are  besides  capable  of  entering  into  combination  with  chlorine, 
iodine,  &c.  Such  radicals  are  carbonic  oxide,  CO,  or  rather  an  isomeric  modi- 
fication of  it,  C^O^;  acetyle,  C^H^;  and  formyle,  C^H.     Each  of  these  may  be 


COMPOUND  ORGANIC  RADICALS. 


525 


viewed  as  the  radical  of  a  powerful  acid ;  for  C^O^  -j-  0=0^0^  is  dry  oxalic 
acid  ;  C^H  -f-  O^  is  dry  acetic  acid  ;  and  C2H  -|-  O^  is  dry  formic  acid.  Again, 
the  first  forms  with  chlorine  the  compound  C2O2  -f  Cl^,  called  phosgene  gas  or 
chlorocarbonic  acid,  while  the  two  others  yield  C^H^  -f  CI,  the  chloride  of 
acetyle,  and  CjH  -\-  Cl^  the  perchloride  of  formyle. 

Further,  there  are  organic  compound  radicals  which  play  the  part  of  metals, 
forming  salts  with  chlorine,  iodine,  sulphur,  cyanogen,  &c.,  and  yielding,  with 
oxygen,  compounds  possessing  basic  properties  analogous  to  those  of  metallic 
oxides.  Such  radicals  are  ethyle,  C^H^,  methyle,  C2H^,  and  kakodyle,  C^ 
HgASj. 


Radicals. 

Oxygen 
Compound. 

Chlorine 
Compound. 

Cyanogen 
Compound. 

Sulphur 
Compound. 

Ethyle  C4H5=Ae 
Methyle  C2H3=Mt 
Kakodyle  C4H6As2=Kd 

AeO 
MtO 
KdO 

AeCl 
MtCl 
KdCl 

AeCy 
MtCy 
KdCv 

AeS 
MtS 
KdS 

Lastly,  there  are  some  compound  organic  radicals,  which  partake  of  the  cha- 
racters of  the  two  last  groups,  forming,  like  the  acetyle  group,  acids  and  not 
bases  with  oxygen ;  but  yielding,  with  chlorine,  sulphur,  cyanogen,  &c.,  com- 
pounds analogous  to  those  formed  by  the  ethyle  group.  To  this  division  belong 
Benzoyle,  C  H^02=Bz;  Cinnamyle,  CjgHg02=Ci :  and  several  others.  Ben- 
zoyle  and  cinnamyle,  with  the  addition  of  oxygen  and  the  elements  of  water, 
produce  benzoic  acid,  BzO,HO,  and  cinnamic  acid,  CiO,HO.  This  group  is 
characterized  by  forming  with  hydrogen  certain  essential  oils.  Thus,  benzyle 
yields,  with  hydrogen,  the  essential  oil  of  bitter  almonds,  BzH ;  cinnamyle 
yields  the  oil  of  cinnamon,  CiH  ;  and  salicyle,  C  H^04=Sa,  another  radical  of 
this  group,  forms,  with  hydrogen,  the  oil  of  spiraea,  SaH. 

These  brief  statements  will  serve  to  show  that  there  are  different  kinds  or 
groups  of  compound  radicals,  just  as  there  are  of  simple  ones;  and  further,  that 
these  compound  radicals  exhibit  a  very  remarkable  tendency  to  combine  with 
simple  radicals,  and,  in  fact,  to  act  the  part  of  elementary  bodies.  And  let  us 
here  bear  in  mind  that  the  only  real  difference,  in  this  point  of  view,  between 
cyanogen  and  chlorine  is  this,  that  in  the  case  of  the  former  we  can  prove  the 
radical  to  be  compound,  while  we  cannot  as  yet  do  this  in  the  case  of  the  latter. 
But,  as  formerly  pointed  out,  we  call  chlorine,  and  indeed  all  other  elements 
simple,  only  because  we  have  not  been  able  to  show  them  to  be  compound; 
without  having  any  certainty  that  they  are  really  and  absolutely  simple.  If  we 
could  not  resolve  cyanogen  into  carbon  and  nitrogen,  we  should  be  compelled  to 
add  it  to  the  list  of  elements. 

But  although  compound  radicals  usually  act  towards  other  bodies  as  if  simple, 
and  consequently  combine  generally  with  simple  substances,  they  are  also 
capable  of  uniting  with  each  other.  In  fact,  this  is  but  another  proof  of  their 
close  resemblance  to  elementary  bodies  in  their  relations ;  for  as  simple  metals, 
such  as  potassium  and  silver,  unite  with  cyanogen  just  as  with  chlorine,  so  also 
such  compound  radicals  as  are  analogous  to  metals  can  combine  with  cyanogen, 
itself  a  compound  radical.  Thus  ethyle,  methyle,  benzoyle,  and  kakodyle  all 
combine  with  cyanogen,  yielding  compounds  formed  of  two  organic  radicals, 
one  playing  the  part  of  a  metalloid,  the  other  that  of  a  metal. 

Compounds  of  this  nature  furnish  the  very  best  proof  and  illustration  of  the 
advantages  which  we  derive  from  the  doctrine  of  compound  radicals,  acting  like 


526  COMPOUND  ORGANIC  RADICALS. 

elements,  whenever  we  are  justified  by  facts  in  adopting  and  applying  it.  Thus 
a  compound  has  been  formed  by  the  mutual  action  of  a  compound  of  kakqdyle 
and  a  compound  of  cyanogen,  the  analysis  of  which  proves  that  it  contains  car- 
bon, hydrogen,  nitrogen,  and  arsenic,  in  the  relative  proportions  indicated  by  the 
formula  C^H.NAs,.     What  view  are  we  to  take  of  such  a  formula'?  and  if  we 

0      0  '• 

look  on  the  compound  as  one  formed  of  these  four  elements  indiscriminately 
united,  how  are  we  to  retain  such  an  isolated  fact  in  the  memory  ?  But  if,  on 
the  other  hand,  we  view  it  as  the  cyanide'  of  kakodyle,  =  C^H^As^-f-  C^N,  or 
using  the  abbreviated  notation  appropriate  to  compound  ratiicals,  KdCy,  we  are 
at  once  enabled  to  retain  the  composition  and  chemical  relations  of  ihe  com- 
pound. Moreover,  when  we  find  that  the  radical,  Kd  (=C^HgAs^)  exists  in  a 
separate  form,  and  that  it  forms,  with  oxygen,  two  compounds,  KdO  and  KdO^; 
■with  chlorine,  KdCl ;  with  sulphur,  KdS  ;  and  that,  in  short,  it  plays  the  part 
of  a  metal  in  all  its  compounds,  and  may  in  fact  be  separated  from  some  of  these 
by  metals  having  stronger  afllnities  than  itself,  we  are  supplied  with  an  idea 
which  serves  to  connect  and  to  fix  all  these  any  many  more  analogous  facts  in 
the  memory. 

When  We  further  observe,  to  pursue  the  same  example,  that  the  cyanide  of 
kakodyle,  KdCy,  when  acted  on  by  hydrochloric  acid,  gives  rise  to  hydrocyanic 
acid  and  chloride  of  kakodyle;  and  that,  when  acted  on  by  potassa,  it  yields 
cyanide  of  potassium  and  oxide  of  kakodyle,  we  acquire  so  many  additional 
proofs  of  the  entire  analogy  between  simple  and  compound  radicals  in  their  rela- 
tions to  other  bodies.  For  the  two  changes  or  reactions  abovg-mentioned  are 
expressed  by  the  equations,  KdCy  -|-HC1  =KdCl  -f-  HCy;  and  KdCy  -f-  KO 
=  KdO  -|-  KCy ;  and  these  equations  are  exactly  similar  to  those  which  occur 
most  frequently  in  inorganic  chemistry. 

The  facts  already  ascertained  with  regard  to  those  compound  organic  radicals, 
whose  existence  has  been  either  established,  or  rendered  highly  probable,  entitle 
us  to  conclude  that  all  organic  compounds  contain  one  or  more  organic  radicals, 
combined  either  with  each  other,  or  with  elementary  radicals.  In  studying, 
therefore,  any  organic  product,  one  chief  object  is  to  determine  what  organic 
radical  or  radicals  it  contains,  since  the  knowledge  of  these  at  once  gives  us  a 
means  of  classification. 

Thus  alcohol,  on  the  theory  of  compound  radicals,  is  considered  as  the  hy- 
drated  oxide  of  ethyle  ;  ethyle  being  an  organic  radical,  C^H^.  So  that  alcohol, 
C4H  Or^  is  more  accurately  represented  as  (C^H^)  O  -(-  HO  ;  or,  if  we  represent 
ethyle,  C^H  ,  by  Ae,  Ahen  alcohol  becomes  AeO,HO,  hydrated  oxide  of  ethyle ; 
perfectly  analogous  to  KO,HO,  hydrated  oxide  of  potassium,  or  caustic  potash. 

Again,  benzoic  ether,  Cjj^Hjg04,  is  viewed  as  benzoate  of  oxide  of  ethyle,  C^ 
H  0  -f-  Cj^H  O  :  or,  more  briefly,  AeO  -|-  BzO.  Here  we  have  the  basic  oxide 
of  one  radical  united  with  the  acid  oxide  of  another. 

It  is  very  often  by  means  of  thus  tracing  the  different  organic  radicals,  that 
we  are  enabled  to  explain  the  very  numerous  cases  of  isomerism,  which  occur  in 
organic  chemistry.  Thus,  the  following  compounds  have  the  same  composition 
in  100  parts: — 

Aldehyde  .        .        .        C^H.Oj 

Acetic  Ether     .        .        .        CgHgO^ 
Butyric  Acid     .         .         .        CyflgO^ 

Now,  aldehyde  is  considered  to  be  the  hydrated  protoxide  of  acetyle,  (C^H^)  0 


COMPOUND  ORGANIC  RADICALS.  527 

+  HO  ;  or,  abbreviated,  AcO,HO.  Again,  acetic  ether  is  acetate  of  oxide  of 
elhule,  CjH^O  -f-  (^411^)  O, ;  or,  shortly,  AeO,AcO^;  the  dry  acetic  acid,  AcO^ 
=  (C^H2)  6^,  being  a  peroxid"e  of  the  same  radical,  acetyle,  (C4H^  =  Ac)  of 
which  aldehyde  is  the  protoxide.  Lastly,  butyric  acid  is  considered  (on  the 
older  view  of  acids,)  as  a  hydrated  acid,  a  compound  of  water  with  dry  butyric 
acid  :  thus  HO  -f-  C  H„0,.  It  is  true,  that  in  the  latter  case,  we  are  not  yet 
acquainted  with  the  true  radical  of  butyric  acid  ;  but,  we  cannot  doubt  that,  like 
acetic  acid,  it  does  contain  a  radical.  These  three  compounds,  therefore,  may 
now  be  represented  and  distinguished  as  follows : — 

Empirical  Formula.      Rational  Formula. 
Aldehyde  C4H4O2  =  (C4H3)  O  -j-  HO 

Acetic  Ether  C8Hg04  =  (C4H5)  O  +  (C4H3)  O3 

Butyric  Acid  CSH8O4  =  C8H7O3    +  HO 

Even  in  those  cases  in  which  the  composition  of  the  radical  is  not  known,  or 
not  known  with  certainty,  we  can  often  trace  the  radical  with  much  probability. 
Thus,  dry  oxalic  acid,  CO,  and  dry  mellitic  acid,  CO,  maybe  viewed  as  dif- 
ferent compounds  of  the  simple  radical  carbon,  the  latter  containing  just  twice 
the  proportion  of  carbon  to  the  same  quantity  of  oxygen  that  the  former  does. 
This  is  merely  stated  by  way  of  illustration;  for,  it  is  at  least  equally  probable 
that  the  true  radical  of  oxalic  acid  is  CO. 


But  in  the  following  four  acids  we  may  trace,  theoretically,  the  same  compound 
radical,  namelyf  formyle,  =  C  H,  in  combination  with  different  proportions  of 
oxygen.     Here  C  H  is  also  represented  by  Fo. 


.  Formic  Acid  (CjH)  +  O3  =  Fo  O3 

Succinic  Acid  C4H2O3  =  SCCgH)  "1-03  =  FojOg 

Malic  Acid  C4H2O4  =  2(C2H)  -|-  O4  =  FO2O4 

Racemic  Acid  C4H20g  =  2(C2H)  +  05  =  FOjOg 

These  relations,  although  as  yet  only  to  be  traced  in  the  formulae,  are  yet  not 
without  interest,  and  may,  at  all  events,  serve  to  aid  the  memory. 

In  like  manner,  it  may  be  observed,  that  the  following  acids  all  contain,  as 
hydrates,  4  eq.  of  oxygen ;  and  all  likewise  the  same  number  of  eqs.  of  carbon 
as  of  hydrogen. 


Acetic  Acid 

= 

C4   H4   O4 

Butyric  Acid 

= 

Cg   Hg   O4 

Valerianic  Acid 

= 

C,o  Hio  O4 

(Enanthic  Acid 

= 

Ci4  Hu  O4 

Laurie  Acid 

= 

C24  H24  O4 

Cocinic  Acid 

= 

C26  H26  O4 

Ethalic  Acid 

= 

C32  H32  O4 

Margaric  Acid 

= 

C34  H34  O4 

Here  we  may  suppose  the  radical  of  the  first  acid  to  have  been  changed  by 
the  successive  additions  of  4,  0,  10,  or  20  eqs.  of  carbon  and  hydrogen,  the 
oxygen  remaining  unchanged.  Or  we  may  as  readily  suppose  one  of  these  acids, 
by  losing  oxygen,  to  pass  into  another.  Thus  we  may  either  conceive  butyric 
acid  to  be  formed  from  acetic  acid  by  the  addition  of  C^H^;  or  acetic  acid  to 
give  rise  to  butyric  acid,  by  losing  half  its  oxygen;  for  2(C^H  O^)  =  C  H 


628  THEORY  OP  CHEMICAL  TYPES. 

When  compound  organic  radicals,  or  their  compounds,  are  subjected  to  pow- 
erful decomposing  agents,  they  tend  to  produce  new  and  less  complex  radicals. 
Thus,  when  alcohol,  the  hydrated  oxide  of  ethule,  is  oxidized,  it  gives  rise  to 
aldehyde  and  acetic  acid,  which  are  compounds  of  acetyls,  C^H^,  a  less  complex 
radical  than  ethyle,  C  H^.  Further,  when  organic  compounds  are  decomposed 
by  a  strong  heat,  they  tend  to  produce  compounds  of  simple  radicals,  such  as 
carbon  or  hydrogen,  or,  at  most,  of  the  least  complex  radicals,  such  as  cyan- 
ogen, C^N,  and  an^dogen,  NH^.  These  are  principles  of  very  general  appli- 
cation. 

It  may  here  be  observed,  that  while,  in  such  cases  as  the  supposed  conversion 
of  acetic  into  butyric  acid,  by  the  loss  of  half  its  oxygen,  the  change  is  from  a 
less  complex  to  a  more  complex  organic  compound,  and  while  we  can  hardly 
doubt  the  possibility  of  such  a  result,  yet  the  oxidation  of  a  compound  radical, 
that  is,  the  addition  of  oxygen,  appears  always  to  produce  less  complex  radicals 
or  compounds. 

It  is  often  urged,  as  an  argument  against  the  doctrine  of  compound  radicals, 
that  these  supposed  radicals  are  entirely  imaginary,  and  cannot  be  produced. 
Now,  it  is  true,  that  a  large  proportion  of  those,  whose  existence  is  best  attested, 
have  not  yet  been  obtained  in  the  uncombined  state ;  and'it  is  even  probable  that 
some  of  them  are  only  capable  of  existing,  or  rather  of  being  preserved,  when 
combined.  But  the  argument  founded  on  this  fact  has  no  cogency ;  for,  in  the 
first  place,  some  organic  radicals,  such  as  cyanogen  and  kakodyle,  are  well 
known  in  the  separate  state.  Now  cyanogen  and  kakodyle  are,  in  all  their  rela- 
tions, exactly  analogous,  the  former  to  chlorine,  the  latter  to  a  mJkl ;  and,  if  we 
■were  unable  to  demonstrate  their  compound  nature,  their  chemical  relations 
would  compel  us  to  classify  cyanogen  as  an  element  along  with  chlorine,  and 
kakodyle  along  with  the  metals ;  and  when  we  see  whole  series  of  organic  com- 
pounds, in  all  respects  analogous  to  those  of  cyanogen  and  kakodyle,  we  are 
entitled  logically  to  draw  the  conclusion  that  these  compounds  contain  similar 
compound  radicals,  even  although  we  cannot  isolate  them.  Secondly,  in  every 
chemical  theory  yet  broached,  many  substances  are  admitted  whose  existence 
cannot  be  directly  proved.  Thus,  the  so-called  anhydrous  organic  acids  are, 
almost  without  exception,  unknown  in  the  separate  state;  they  are  equally  ima- 
ginary with  the  radicals  whose  existence  is  doubted.  Nay,  many  inorganic  acids 
are  equally  hypothetical.  Anhydrous  nitric  acid  has  never  been  seen ;  and, 
although  there  are  reasons  for  doubting  its  existence,  yet  no  one  doubts  the 
Existence  of  hyposulphurous  acid,  which  yet  has  never  been  separated,  either  as 
a  hydrate,  or  in  the  anhydrous  state. 

We  conclude,  therefore,  that  organic  compound  radicals  "exist,  and  generally 
play  the  part  of  elements ;  and  we  shall  avail  ourselves  of  their  existence,  as  far 
as  it  is  established,  to  facilitate  the  study,  the  classification,  and  the  retention  in 
the  memory,  of  organic  compounds. 

THEORY  OF  CHEMICAL  TYPES.— DOCTRINE  OF  SUBSTITUTION. 

The  original  and  ingenious  researches  of  Laurent  have  led  to  the  adoption  of 
what  is  called  the  Theory  of  Types  and  the  Law  or  Doctrine  of  Substitution, 
which  have  been  supported,  and  in  a  great  measure  established,  by  Dumas  and 
other  distinguished  experimenters  of  the  French  school.  The  views  of  Laurent 
and  of  Dumas  were,  for  a  time,  vehemently  opposed  by  some  chemists,  especially 


THEORY  OF  CHEMICAL  TYPES.  529 

by  Berzelius  and  Liebig ;  but  although  they  have  in  some  points  been  modified 
and  restricted,  the  progress  of  discovery  has  gradually  led  to  their  general  recep- 
tion, so  that  recently  some  of  the  most  striking  illustrations  and  proofs  of  the 
law  of  substitution  have  been  discovered  by  Dr.  Hoffman,  assistant  to  Professor 
Liebig,  and  working  under  his  eye. 

As  the  subject,  therefore,  is  no  longer  purely  controversial,  it  would  be  wrong 
to  omit  it  from  an  elementary  work,  more  especially  as  the  doctrine  has  now 
taken  such  a  form  as  to  facilitate  very  much  the  study  of  organic  compounds  and 
of  their  metamorphoses. 

It  is  not  easy  to  define  a  chemical  type ;  but  in  inorganic  chemistry  we  may 
say,  for  example,  that  hydrochloric  acid,  HCl,  is  the  type  of  a  very  numerous 
class  of  acids,  the  character  of  which  is  that  they  contain  hydrogen  united  to  a 
salt  radical. 

If  for  chlorine  we  substitute  iodine,  bromine,  &c.,  or  even  cyanogen,  the  type 
remains  unchanged,  the  compound  is  still  an  acid,  analogous  to  that  which  was 
selected  as  the  type. 

Again,  common  salt,  NaCl,  is  the  type  of  a  very  large  series  of  salts,  in 
which  a  metal  is  united  with  a  salt  radical ;  and  if  we  substitute  potassium,  lead, 
or  silver  for  the  sodium,  the  type  is  unaltered ;  we  obtain  a  different  salt,  but 
still  a  salt  of  the  type  represented  by  NaOl. 

Here,  then,  we  have  the  simplest  types  and  the  most  obvious  cases  of  substi- 
tution; when  iodine  or  cyanogen  is  substituted  for  chlorine  in  the  acid  type;  or 
when  potassium,  lead,  or  silver  is  substituted  for  sodium  in  the  salt  type;  in 
both  cases  without  the  loss  of  the  type. 

Nriy  in  the  salt  type,  represented  by  NaCl,  we  may  not  only  replace  sodium 
by  other  metals,  but  we  may  also  substitute  iodine,  bromine,  &c.,  or  cyanogen  for 
the  chlorine,  and  still  the  type  will  remain  unchanged.  Iodide  of  sodium,  Nal, 
bromide  of  magnesium,  MgBr,  and  cyanide  of  silver,  AgCy,  are  all  as  good 
examples  of  the  salt  type  represented  by  NaCl,  as  common  salt  itself  is. 

It  has  been  proposed,  with  great  propriety,  by  Baudrimont,  to  employ  certain 
Greek  characters  as  symbols  in  representing  the  formulae  of  extensive  types  or 
of  types  in  general.  I  shall,  therefore,  express  the  above  salt  type  by  the  for- 
mula AX,  in  which  A  stands  for  any  metal  or  body  acting  as  a  metal,  and  x  for 
chlorine  or  any  other  radical  of  analogous  power,  such  as  cyanogen.  As  hydro- 
gen appears  to  stand  alone  in  the  power  of  forming  acids  with  bodies  of  the  type 
X,  the  acid  type  above  alluded  to  becomes,  in  its  most  general  form,  XH. 

But  while  it  is  very  easy  to  understand  the  extensive  substitutions  which  may 
be  effected  in  the  case  of  both  elements  of  the  type  AX,  yet  we  observe  that  in 
these  substitutions  the  electrical  character  of  the  elements  is  retained;  and  that 
as  A  is  the  positive,  and  X  is  the  negative  element,  so  they  are  only  replaced,  A 
by  positive  and  X  by  negative  elements  respectively. 

So  far  as  inorganic  chemistry  is  concerned,  the  study  of  types  would  serve 
generally  to  confirm  and  establish  the  electro-chemical  theory.  At  all  events,  we 
are  not  as  yet  acquainted  with  many  exceptions  to  it;  we  do  not  usually  find 
oxygen  or  chlorine  occupying  the  place  of  A  in  a  compound,  or  a  metal  playing 
the  part  of  X.  Even  in  inorganic  chemistry,  however,  there  are  some  examples 
of  such  interchanges.  Manganese  in  manganic  acid,  MnO^,  and  chromium  in 
chromic  acid,  CrO^,  obviously  represent  the  sulphur  in  sulphuric  acid ;  and  the 
manganese  in  hypermanganic  acid,  Mn^O^  represents  the  chlorine  in  perchloric 
acid,  ClOy ;  while,  in  its  other  compounds,  manganese  acts  as  a  metal. 

36 


^9  THEORY  OF  CHEMICAL  TYPES. 

But  the  researches  of  Laurent  and  Dumas  have  shown  that  in  organic  che- 
mistry the  substitution  of  one  element  for  another,  even  where  the  type  is 
retained,  is  not  limited  by  the  electrical  character  of  the  elements.  Thus,  in 
acetic  acid,  HO,  C^H^O^,  the  3  eq.  of  hydrogen  in  the  anhydrous  acid  may  be 
replaced  by  chlorine,  giving  rise  to  the  compound  HO,  C^Cl^O^,  in  which  the 
type  is  so  little  affected,  that  this  substance,  chloracetic  acid,  has  properties 
highly  analogous  to  those  of  acetic  acid.  Here  it  is  evident  that  the  chlorine 
performs  the  same  function  as  the  hydrogen,  which  it  replaces,  did ;  and  not,  as 
in  hydrochloric  acid,  an  opposite  function. 

Again,  in  aldehyde,  (C<H^)0  -f  HO,  the  3  eq.  of  hydrogen  in  the  radical  d 
H,  may  be  replaced  by  3  eq.  of  chlorine,  and  we  then  have  chloral,  (0^01^)0  + 
HO,  a  body  of  the  same  type  as  aldehyde. 

Such  cases  of  substitution  of  chlorine  (iodine,  bromine,  &c.,)  for  hydrogen, 
and  even  of  oxygen  for  hydrogen,  without  change  of  type,  are  very  frequent; 
and  it  is  this  kind  of  substitution,  so  adverse  to  the  electro-chemical  theory, 
which  is  included  in  the  theory  of  substitutions  of  Laurent.  Those  more  usual 
sutetitutions,  where  one  body  is  replaced  by  another  of  similar  electric  character, 
may  be  viewed  as  so  many  examples  of  the  doctrine  of  equivalents,  the  replacing 
body  being  equivalent  to  that  for  which  it  is  substituted,  on  the  electro-chemical 
theory. 

Adopting,  then,  the  views  of  Laurent,  we  are  compelled  to  admit  that  the  elec- 
tro-chemical theory  fails  when  applitJd  to  cases  of  substitution  of  chlorine  for 
hydrogen,  &c.,  where  the  type  remains  unaltered.  This  is  clearly  the  case  in 
acetic  and  chloracetic  acids ;  and  Hoffman  has  recently  shown  that  in  certain 
basic  organic  compounds  hydrogen  may  be  replaced  by  chlorine,  while  the  new 
compound  retains  the  basic  type  and  characters.  Aldehyde  and  chloral  furnish 
an  example  of  the  same,  in  a' body  neither  acid  nor  basic. 

Here,  then,  is  a  fact  of  very  general  occurrence,  which  not  only  proves  that 
the  electro-chemical  theory  of  combination  is  inapplicable,  at  all  events  in  many 
cases,  but  also  tends  to  establish  a  very  different  view  :  namely,  that  the  electric 
character  of  an  element  is  no  permanent  or  essential  property  ;  and  that  the  type 
or  character,  or  general  properties  of  a  compound,  depend,  not  on  the  nature^  but 
solely  on  the  arrangement  of  its  elementary  atoms ;  on  the  way  in  which  they 
are  grouped  to  form  the  compound  molecule. 

The  reader  will  remember  that,  in  the  section  on  Isomorphism,  the  principle 
was  laid  down  that  the  crystalline  form  of  certain  types  of  salts,  such  as  the 
alum  type,  as  well  as  many  other  properties  of  the  compounds  having  those 
types,  were  the  result  of  the  similar  grouping  of  analogous  elements.  We  now 
see  that,  according  to  the  law  of  substitution,  as  deduced  from  numerous  careful 
observations,  similarity  of  properties,  or  identity  of  type,  are  the  result  of  simi- 
larity of  grouping,  even  of  elements  not  analogous,  nay,  of  elements  electrically 
opposed  to  each  other.  It  is  evident,  therefore,  that  the  arrangement  of  the  ele- 
mentary molecules  to  form  the  compound  molecule  is  the  circumstance  on  which 
depend  almost  exclusively  the  properties  of  the  compound,  or  in  other  words,  the 
character  of  the  type. 

Substitution  may  be  either  complete  or  partial.  In  chloracetic  acid,  and  in 
chloral,  the  substitution  of  chlorine  for  the  hydrogen  of  the  radical  acetyle  C^  H^ 
is  complete.  But  when  ether  (C^  H^)  O  is  acted  on  by  chlorine,  the  substitu- 
tion takes  place  by  successive  steps,  one  equivalent  of  hydrogen  being  replaced 


THEORY  OF  CHEMICAL  TYPES.  531 

at  a  time,  after  the  oxygen  has  also  been  replaced  by  chlorine.    Thus  we  have, 
first — 

Ether  or  oxide  of  ethyle   =(C4H5)-i-0 
then,  chloride  orethyle=:(C4H5)-)-Cl 

then,  successively,  C4  ]r;/  +  Cl 

C4{a;tci 

and  lastly,  (C4Cl5)+Cl 

We  thus  obtain  the  series  of  compounds  here  indicated,  in  which  the  hydrogen 
is  gradually  replaced  by  chlorine,  until  at  last  we  obtain  the  compound  (C  CI  ) 
4-Cl=C4  Clo=2C2  CI3,  which  is  the  perchloride  of  carbon.  Most  of  these  com- 
pounds have  actually  been  obtained ;  and  it  is  obvious  that  they  may  all  be  re- 
ferred to  one  type.  Such  a  series  is  called  a  series  of  mechanical  examples  of 
the  type  in  question,  or  rather  of  subtypes  retaining  the  original  character  although 
modified. 

In  some  cases,  hydrogen  has  been  replaced  partly  by  chlorine  and  partly  by 
bromine.  Laurent  has  described  two  compounds  derived  from  naphthaline  by 
substitution,  the  empirical  formula  .for  boJ;h  of  which  is  the  following: — C  H 
Cl^  Br.  Yet  the  properties  of  these  two  compounds  are  quite  distinct,  and  it  is 
certain  that  this  difference  of  properties  must  depend  on  a  difference  in  the  ar- 
rangement of  the  elements.  Now,  in  the  formation  of  these  two  compounds  we 
have  a  very  beautiful  proof  of  the  existence  of  a  difference  in  the  arrangement :  for 
one  is  produced  when  chlorine  acts  on  the  compound  called  by  Laurent  bro- 
naphtese,  C^^HgEr^;  while  the  other  is  formed  when  bromine  is  made  to  act 
on  chlonaphtise,  C^^  H^  Cl^.  It  is  obvious  that  in  the  first  case  2  eq.  of  hydro- 
gen and  1  eq.  of  bromine  are  replaced  by  chlorine;  while  in  the  second,  1  eq.  of 
hydrogen  is  replaced  by  bromine.  While,  therefore,  all  four  compounds  may  be 
deduced  from  the  type  C^^  Hg,  and  while  both  the  bromine  and  chlorine  play  the 
part  of  hydrogen,  it  is  impossible  to  doubt  that  each  of  the  8  eq.  of  hydrogen 
has  its  special  place  in  the  compound  molecule  of  the  type,  and  that,  in  the  two 
empirically  identical  formulae  above  given,  the  1  eq.  of  bromine  does  not  replace 
the  same  eq.  of  hydrogen,  and  consequently  the  bromine  occupies  in  the  two 
compounds  different  positions.    The  same  remark  applies  to  the  3  eq.  of  chlorine. 

We  may  illustrate  our  meaning  as  follows: — Let  C  Hg  be  the  type,  and  let 
each  of  the  eqs.  of  hydrogen  have  a  number  attached  indicating  its  place  in  the 
typical  molecule.     We  shall  then  have 


Hj  Hg  H3  H4> 
H5  Hg  Hy  Hg) 


Now  if  we  represent  the  two  compounds  above  mentioned  in  the  following  man- 
ner, we  can  then  conceive  the  influence  of  arrangement  on  the  properties  of  two 
compounds  having  the  same  empirial  formula.     The  first  may  be 


and  the  second  may  be 


I  Hj  H2  H3  H^ 
CLClcCLBr, 


(H,  H2H3Br4> 
icij  Cle  CI7  Hj 


532  DECOMPOSITION  OF  ORGANIC  COMPOUNDS. 

It  is  only  on  this  principle  that  we  can  explain  the  facts  observed  by  Laurent; 
and  it  is  easy  to  see  that  the  above  type,  C^^  Hg,  will  admit  of  innumerable  modi- 
fications :  for  even  the  subtype  C^^  H^  Cl^  Br.  is  capable  of  yielding  many  more 
than  the  two  above  given;  and  the  change  of  I  eq.  produces  a  new  subtype, 
equally  fertile  in  new  forms. 

In  fact,  Laurent  has  actually  obtained,  as  will  be  shown  further  on,  a  very 
large  number  of  what  we  have  called  subtypes  from  the  type  C^^  Hs,  which  is 
naphthaline,  and  has  established  the  same  law  in  reference  to  many  other  types. 

The  preceding  observations  will,  I  trust,  be  found  sufficient  to  convey  a  clear 
general  notion  of  the  prevalent  doctrines  of  chemical  types  and  of  substitution, 
as  applied  to  organic  chemistry. 

THE  DECOMPOSITIONS  AND  METAMORPHOSES  OF  ORGANIC  COMPOUNDS. 

Organic  compounds,  whether  actual  organized  tissues,  unorganized  product^ 
of  animal  and  vegetable  life,  or  new  substances  artificially  produced,  are  gene- 
rally characterized  by  a  great  proneness  to  undergo  decomposition  or  metamor- 
phosis. This  instability  is  especially  marked  in  those  compounds  which  con- 
tain nitrogen,  not  only,  because,  containing  four  elements  (in  most  cases,  they 
are  exposed  to  more  numerous  causes  of  change  than  such  bodies  as  contain  only 
three  (carbon,  hydrogen,  and  oxygen),  but  also  because  nitrogen  is,  in  its  rela- 
tions to  those  three  elements,  the  most  remarkable  element  we  know.  Accord- 
ing to  the  circumstances  under  which  a  change  is  induced,  nitrogen  may  separate 
nncombined,  as  in  the  ultimate  analysis  of  organic  substances  by  combustion 
with  oxide  of  copper  or  chromate  of  lead  ;  or  it  may  combine  with  oxygen,  yield- 
ing nitric  acid,  as  in  nitrification  ;  or  with  carbon,  yielding  the  compound  radical 
cyanogen,  as  when  nitrogenized  organic  matter  is  ignited  with  carbonate  of 
potash ;  or  with  hydrogen,  yielding  ammonia,  as  when  nitrogenized  organic 
matter  is  ignited  with  hydrated  alkalies. 

It  is  easy  to  see,  therefore,  that  while  all  organic  matter  is  prone  to  change, 
this  is  especially  the  case  with  nitrogenized  compounds.  In  fact,  many  of  these 
compounds  cannot  be  kept  more  than  a  few  hours  without  the  commencement 
of  decomposition  or  metamorphosis,  in  the  shape  of  putrefaction  or  fermentation. 
This  kind  of  metamorphosis  will  be  separately  considered  hereafter :  in  the 
meantime  it  is  important  to  observe,  that  when  such  a  compound  has  entered  into 
a  state  of  decomposition,  it  acquires  the  properties  of  a  ferment,  that  is,  it  is 
capable  of  inducing  a  similar  metamorphosis  in  another  compound,  if  placed  in 
contact  with  it. 

The  true  explanation  of  this  fact  appears  to  be,  that  the  particles  or  molecules 
of  the  exciting  body  or  ferment,  being  in  a  condition  of  change,  and  therefore  in 
motion,  communicate  to  the  molecules  of  the  body  placed  in  contact  with  them 
an  amount  of  motion  sufficient  to  destroy  the  balance  of  the  existing  affinities; 
which  in  organic  compounds  is  easily  done,  the  "chemical  equilibrium  being  very 
unstable ;  and  thus  gives  rise  to  a  new  play  of  affinities  and  the  production  of 
new  compounds,  as  when  sugar  by  contact  with  yeast  is  resolved  into  alcohol 
and  carbonic  acid. 

But  in  addition  to  metamorphoses  of  the  kind  just  alluded  to,  which,  in  the 
various  ferments  at  least,  commence  spontaneously,  air  (at  all  events,  at  the 
commencement),  moisture,  and  a  certain  temperature  being  the  usual  conditions, 
organic  substances  undergo  very  well  marked  decompositions  when  exposed  to 


EREMACAUSIS  OF  ORGANIC  COMPOUNDS.  *  533 

the  action  of  heat  and  of  some  powerful  reagents;  and  it  seems  advisable  here 
to  give  also  a  general  account  of  such  decompositions,  as  they  admit  of  being 
classified  under  certain  heads  or  rules  generally  applicable. 

We  shall  here,  therefore,  briefly  describe  the  changes  produced  on  organic 
compounds  :  1,  by  oxidation ;  2,  by  the  action  of  acids  ;  3,  by  the  action  of  bases ; 
4,  by  the  action  of  heat  in  close  vessels,  or  the  destructive  distillation;  and  5, 
by  the  contact  of  ferments. 

1.  Oxidation:  a.  direct. — The  direct  oxidation  of  organic  compounds  takes  two 
distinct  forms.  The  first  is  the  familiar  one  of  combustion,  in  which  the  action 
of  the  atmospheric  oxygen  is  aided  by  a  high  temperature.  The  results  differ 
according  to  the  supply  of  oxygen.  If  there  be  an  excess  of  air,  or  of  oxygen, 
from  any  source,  the  whole  of  the  carbon  and  hydrogen  is  converted  into  carbonic 
acid  and  water,  which,  along  with  uncombined  nitrogen,  are  the  ultimate  pro- 
ducts of  the  action  of  oxygen  on  organic  matters.  But  if  the  supply  of  air  be 
deficient,  the  hydrogen  is  oxidized  in  preference  to  the  carbon,  which  is  depo- 
sited as  smoke,  soot,  or  lampblack. 

The  second  form  of  direct  oxidation  is  that  which  is  commonly  called  decay, 
but  which  Liebig  proposes  to  call  Eremacausis  (t.  e.  slow  combustion),  and 
which  takes  place  when  organic  matter  is  exposed  to  air  and  moisture.  In  dry 
air  it  does  not  occur. 

One  of  the  most  familiar  examples  of  this  kind  of  oxidation  is  that  decay  of 
wood  by  which  it  is  slowly  converted  into  a  dark  brown  powder — ulmine.  In 
this  process,  as  De  Saussure  has  shown,  the  wood  absorbs  oxygen,  and  produces 
an  equal  volume  of  carbonic  acid  along  with  water,  and  the  residue — ulmine.  As, 
in  combustion,  the  oxygen  combines  by  preference  with  hydrogen,  so  also  in 
eremacausis  there  is  every  reason  to  believe  that  the  absorbed  oxygen  combines 
with  the  hydrogen  of  the  wood,  and  that  an  equivalent  quantity  of  oxygen,  also 
derived  from  the  wood,  is  given  off  in  the  form  of  carbonic  acid.  Now,  since 
wood  may  be  represented  as  composed  of  carbon  and  the  elements  of  water,  and 
as  water  and  carbonic  acid  are  two  of  the  products  of  eremacausis,  it  might  be 
supposed  that  the  water  was  ready  formed  in  the  wood,  and  that  the  absorbed 
oxygen  had  combined  with  the  carbon.  But  it  has  been  shown  that,  in  presence 
of  hydrogen,  carbon  does  not  at  the  ordinary  temperature  combine  with  oxygen, 
for  which  its  affinity  is  less  powerful ;  and  besides,  in  the  decay  of  wood,  the 
proportion  of  carbon  in  the  residue  (the  ulmine)  is  constantly  greater  than  in  the 
wood.  Thus  oak  wood,  C  H  0  yields  in  one  stage  of  decay,  ulmine,  the 
composition  of  which  agrees  with  the  formula  C  H  O  ;  and  in  a  more  ad- 
vanced stage,  an  ulmine  of  the  formula  C  H  O  .  Here  we  see  that  for  every  * 
2  eqs.  of  hydrogen  oxidized  by  the  air,  1  eq.  of  carbon  and  2  eqs.  of  oxygen  have 
been  separated  ;  so  that  the  per  centage  of  carbon  in  the  residue  constantly  in- 
creases, and  the  final  result  of  eremacausis  would  be  a  residue  of  carbon;  were 
it  not  that,  as  the  proportion  of  carbon  in  the  ulmine  increases,  its  aflinity  for  the 
other  elements,  strengthened  by  its  mass,  becomes  too  powerful  to  be  overcome 
by  the  oxygen  of  the  air  without  the  aid  of  heat. 

Other  examples  of  eremacausis  are,  the  acetification  of  alcohol,  and  the  pro- 
cess of  nitrification  in  which  ammonia  undergoes  eremacausis.  These,  as  well 
as  other  instances,  will  be  considered  in  their  proper  place. 

Eremacausis  is  greatly  promoted  by  heat  and  by  the  presence  of  alkalies.     It 
is,  on  the  contrary,  arrested  or  retarded  by  cold,  dryness,  acids,  and   many  salts, ^ 
such  as  corrosive  sublimate,  which  has  been  used  to  prevent  the  decay  of  wood. 


$34  ACTION  OF  ACIDS  ON  ORGANIC  COMPOUNDS. 

There  is  one  circumstance  connected  with  eremacausis,  or  decay,  as  above 
described,  which  is  worthy  of  special  attention.  It  is,  that  a  substance,  in  a 
state  of  eremacausis,  if  placed  in  contact  with  another,  which  is  capable  of  un- 
dergoing this  change,  speedily  causes  the  latter  to  enter  into  the  same  condition 
of  change.  This  effect  of  contact  may  be  compared,  in  one  sense,  to  that  of  a 
body  in  combustion,  which  sets  fire  to  other  bodies ;  but  in  ordinary  combustion 
the  high  temperature  plays  an  important  part,  while  in  eremacausis  the  effect 
appears  to  be  due  to  the  communication  of  motion  from  the  particles  of  the  de- 
caying body  to  those  of  the  other  substance,  which  motion,  as  in  the  case  of  fer- 
mentation, overturns  the  existing  balance  of  affinities,  unstable  as  it  is  in  organic 
compounds,  and  gives  rise  to  the  formation  of  new  products. 

The  process  of  eremacausis,  or  slow  oxidation  in  the  atmosphere,  is  one  of 
very  great  practical  importance,  inasmuch  as,  by  this  means,  the  elements  of  dead 
organic  matter  are  made  to  assume  those  forms — namely,  the  forms  of  carbonic 
acid,  water,  and  ammonia — in  which  they  are  capable  of  contributing  to  the 
nutrition  of  new  or  growing  vegetables. 

A  peculiar  species  of  eremacausis  is  observed  in  the  case  of  the  simultaneous 
action  of  oxygen  and  ammonia  on  certain  colourless  vegetable  products,  which, 
absorbing  these  gases  greedily,  are  thus  converted  into  nitrogenized  compounds 
of  very  fine  blue  or  purple  colours.  Of  this  we  have  examples  in  orcine, 
erythrine,  and  phloridzine ;  and  there  is  good  reason  to  attribute  the  formation 
of  indigo,  from  a  juice  devoid  of  blue  colour,  to  an  action  of  this  kind,  since  both 
oxygen  and  amnionia  appear  to  be  necessary  to  its  production.  The  transforma- 
tion of  alloxantine  or  of  uramile  into  murexide  also  depends  on  the  simultaneous 
action  of  ammonia  and  oxygen. 

b.  Indirect  Oxidation.  The  indirect  oxidation  of  organic  compounds  may  be 
effected  in  a  variety  of  ways,  as.  for  example,  by  nitric  acid,  the  action  of  which 
we  shall  presently  describe  along  with  that  of  other  acids;  by  certain  salts,  as 
by  permanganate  of  potassa,  which  converts  sugar,  for  example,  into  oxalic  acid  ; 
or  by  the  employment  of  a  mixture  of  bichromate  of  potash  and  diluted  sulphuric 
acid,  by  which  means  salicine  may  be  made  to  yield  the  hyduret  of  salicyle  (oil 
of  spiraea)  :  or,  finally,  by  the  combined  action  of  heat  and  hydrated  alkalies,  as 
when  indigo,  heated  with  potash,  gives  rise  to  anthranilic  acid,  hydrogen  being 
given  off;  or  acetates,  heated  with  baryta,  yield  marsh  gas  and  carbonates. 

2.  .Action  of  Acids  on  Organic  Compounds.  This  action  is  very  various ;  the 
two  acids  most  frequently  employed  are  the  nitric  and  sulphuric  acids,  and,  as 
might  be  expected,  the  former  acts  more  as  an  oxidizing  agent  than  the  latter. 

When  sugar,  for  example,  is  heated  with  nitric  acid,  the  latter  loses  oxygen, 
for  nitrous  acid  is  given  off  in  enormous  quantity;  while  the  elements  of  the 
BUffar,  by  the  action  of  the  oxygen  are  made  to  combine  so  as  to  produce  com- 
pounds of  less  complex  radicals  than  that  of  sugar  probably  is.  Among  the  pro- 
ducts are  water,  carbonic  acid,  oxalic  acid,  and  saccharic  acid,  besides  others  not 
yet  investigated ;  but  the  three  first  sufficiently  show  the  tendency  of  oxidation 
to  promote  the  formation  of  less  complex  radicals. 

When  nitric  acid  acts  on  organic  matters,  there  is  generally  found  one  acid,  if 
not  more,  among  the  products,  and  in  this  way  a  large  number  of  acids  have  been 
discovered.  Examples  of  this  are,  mucic  acid  from  gum;  indigotic  and  car- 
bazotic  acids  from  indigo ;  margaric  acid  from  stearic  acid  ;  suberic  and  succinic 
PBcids  from  oily  acids,  besides  many  others.  It  frequently  happens  that  com- 
pounds, whether  acid  or  neutral,  formed  by  the  action  of  nitric  acid  on  organic 


ACTION  OF  BASES  ON  ORGANIC  COMPOUNDS.  535 

matter,  contain  hyponitrous  acid  as  a  constituent,  apparently  substituted  for  some 
element.  This  is  the  case  with  nitrobenzide  from  benzine,  and  with  nitronaph- 
thalase,  and  a  whole  series  of  compounds  discovered  by  Laurent  in  his  study  of 
the  action  of  nitric  acid  on  naphthaline.  The  carbazotic  or  nitropicric  acid  also 
appears  to  contain  a  compound  of  nitrogen  and  oxygen.  Some  organic  bases,  as 
morphia  and  brucia|  strike  a  deep  red  colour  with  nitric  acid. 

When  sulphuric  acid  is  made  to  act  on  organic  compounds,  it  chars  a  con* 
siderable  proportion  of  them  by  virtue  of  its  attraction  for  oxygen  and  hydrogen 
in  the  form  of  water.  But  in  many  cases  it  produces  very  different  effects.  Thus, 
by  boiling  with  sulphuric  acid  and  water,  starch  and  lignine  are  converted  into 
grape  sugar.  In  other  cases,  the  sulphuric  acid  seems  to  lose  so  much  oxygen 
as  to  produce  hyposulphuric  acid,  which  enters  into  combination  with  an  organic 
compound,  forming  a  new  acid,  as  when  sulphuric  acid  acts  on  naphthaline,  and 
forms  sulpho-naphthalic  acid ;  or  on  benzoic  acid,  forming  hyposulphobenzoic 
acid  ;  or  on  alcohol  under  certain  circumstances,  when  an  acid  is  produced  con- 
taining the  elements  of  hyposulphuric  acid  and  of  a  carbo-hydrogen.  In  other 
cases,  the  sulphuric  acid  combines  unchanged  with  the  organic  compound,  as  in 
sulphovinic  acid,  which  is  a  bisulphate  of  oxide  of  ethyle;  sulphomethylic  acid, 
and  others. 

Many  organic  compounds,  heated  with  excess  of  sulphuric  acid,  are  entirely 
decomposed,  yielding  water  which  combines  with  the  acid,  and  other  products 
which  are  disengaged.  Thus  oxalic  acid  is  resolved  into  water,  carbonic  acid, 
and  carbonic  oxide  ;  formic  acid  into  water  and  carbonic  oxide ;  alcohol  into  water, 
olefiant  gas,  and  other  products. 

Several  organic  compounds  are  dissolved  by  sulphuric  acid  with  the  production 
of  a  fine  red  or  purple  colour.  Salicine  strikes  a  red  colour  with  the  acid,  and 
cedriret,  one  of  the  constituents  of  tar,  dissolves  in  it  with  a  deep  blue  colour,  as 
does  also  naphthalase. 

Phosphoric  acid  may  be  employed  in  some  cases  to  remove  water  from  organic 
compounds,  as  it  does  not  char  them.  Like  sulphuric  acid,  it  forms  with  oxide 
of  ethyle  an  acid  salt,  known  as  phosphovinic  acid. 

Hydrochloric  acid  and  its  congeners  have  no  very  extensive  action  on  organic 
substances.  With  alcohol,  hydrochloric  acid  gas  yields  chloride  of  ethyle;  and 
a  current  of  this  gas,  passed  through  an  alcoholic  solution  of  a  fatty  acid,  gives 
rise  to  the  compound  of  the  fatty  acid  with  oxide  of  ethyle,  which  would  other- 
wise be  obtained  with  difficulty.  With  oil  of  turpentine,  oil  of  lemons,  and 
some  other  essential  oils  composed  of  carbon  and  hydrogen,  hydrochloric  acid 
gas  combines,  forming  solids  resembling  camphor.  '  Pyroxanthine,  a  substance 
contained  in  tar,  dissolves  in  strong  hydrochloric  acid  with  a  fine  and  deep  purple 
Colour. 

3.  Action  of  Bases  on  Organic  Compounds.  Hyd rated  bases  unite,  of  course, 
with  organic  acids ;  and  when  heated  with  neutral  substances,  they  generally  give 
rise  to  the  formation  of  acids,  such  as  acetic  and  oxalic  acids,  or  even  carbonic 
acid,  oxygen  being  taken  from  the  water  of  the  base,  and  hydrogen  being  disen- 
gaged, or,  (if  the  organic  body  contain  nitrogen,)  hydrogen  and  ammonia.  This 
property  of  hydrated  bases  is  employed  as  a  means  of  converting  all  the  nitro- 
gen of  organic  compounds  into  ammonia,  and  in  this  form  determining  its 
quantity. 

The  presence  of  bases  greatly  promotes  the  absorption  of  atmospheric  oxygen 


536  ACTION  OF  HEAT  ON  ORGANIC  COMPOUNDS. 

by  or^nic  substances.  This  is  the  reason  why  alkalies  assist  eTemacausis. 
The  same  effect  is  very  conspicuous  in  the  change  which  the  salts  of  aallic  acid 
(and  some  other  acids)  undergo  when  exposed  to  the  air.  A  solution  of  an  alka- 
line gallate  absorbs  oxygen  very  rapidly,  and  becomes  very  dark  in  colour,  being 
oxidized  in  a  far  shorter  time  than  if  the  acid  had  been  uncombined. 

4.  Action  of  Heat  on  Organic  Compounds  in  close  vessels.  This  action  is  known 
under  the  name  of  the  destructive  distillation.  It  must  be  considered  as  a  com- 
bustion with  a  very  limited  supply  of  oxygen,  that  namely  afforded  by  the  sub- 
stance itself.  A  very  great  variety  of  compounds  is  produced,  many  of  them 
very  interesting  and  useful.  The  destructive  distillation  may  be  considered  as  it 
affects  substances  containing  nitrogen,  and  substances  devoid  of  that  element. 
Many  products  are  common  to  both  cases,  but  many  also  are  confined  to  one 
case,  especially  to  that  of  nitrogenized  substances. 

The  destructive  distillation  of  non-nitrogenized  substances  has  been  chiefly 
studied  in  the  case  of  wood,  which,  when  heated  in  close  vessels,  yields  a  great 
variety  of  products :  some,  binary  compounds,  such  as  parafhne,  naphthaline, 
eupione,  water,  carbonic  oxide,  carbonic  acid,  marsh  gas,  and  olefiant  gas  :  others 
ternary,  such  as  acetic  acid,  C^H^O^ ;  hydrated  oxide  of  methyle  or  pyroxylic 
spirit,  (C^H^)  0,H0  ;  lignone,  xylite,  mesite,  and  other  volatile  etherial  liquids, 
composed  of  the  same  elements  as  pyroxylic  spirit,  and  very  similar  to  it  in  pro- 
perties ;  creosote ;  picamar ;  capnomore  ;  cedriret ;  pittacal,  and  p)rroxanthine, 
besides  many  others,  not  yet  properly  investigated. 

When  fatty  or  resinous  bodies  are  subjected  to  the  destructive  distillation, 
there  are  obtained,  besides  other  compounds,  two  solid  carbo-hydrogens  ;  chry- 
sene,  C^H,  and  pyrene,  C^^H^;  which  also  occur  among  the  products  of  the 
distillation  of  coal. 

This  latter  distillation  may  serve  as  an  example,  the  best  known,  of  the  action 
of  heat  on  nitrogenized  organic  bodies  ;  for  coal  contains  a  certain  although 
small  proportion  of  nitrogen.  The  products,  besides  creosote,  parafhne,  naph- 
thaline, and  probably  several  others  of  those  obtained  from  wood,  include  much 
ammonia,  hydrocyanic  acid:  some  peculiar  non-nitrogenized  acids,  as  carbolic 
acid,  Cj^H^  0,H0,  (a  remarkable  compound,  having  an  odour  resembling  that 
of  creosote,  and  yielding,  when  subjected  to  various  re-agents,  an  extensive 
series  of  new  compounds  [Runge,  Laurent]  ;)  rosolic  and  brunolic  acids ;  and 
two  very  remarkable  nitrogenized  bases,  containing  no  olxygen,  namely,  kyanol 
{aniline,  crystalline,)  C^^H^N,  and  leukol,  C^^^HgN;  besides  a  third,  not  yet 
fully  investigated,  pyrrol ;  finally,  paranaphthaline,  or  anthracene,  C  H  ,  and 
coal  tar  naphtha,  which  is  used  as  a  solvent  for  caoutchouc. 

The  distillation  of  animal  matter,  such  as  hoofs,  horns,  or  bones,  yields  analo- 
gous results,  but  is  characterized  by  the  very  large  amount  of  ammonia  which  is 
obtained,  animal  matter  being  richer  in  nitrogen  than  coal  is.  This  ammonia 
appears  as  carbonate,  which  salt  is  thus  manufactured,  and  hence  was  and  occa- 
sionally still  is,  called  salt  of  hartshorn. 

Many  organic  acids,  when  heated  in  close  vessels  to  a  certain  temperature, 
short  of  the  destructive  distillation,  undergo  a  remarkable  decomposition ;  car- 
bonic acid  is  given  off,  and  there  remains  a  new  acid,  which  is  called  a  pyro- 
genous  acid,  or  pyro-acid.  Thus  meconic  acid,  at  a  certain  temperature,  yields 
carbonic  acid  and  komenic  acid  :  while  komenicacid,  if  heated  in  its  turn,  yields 
carbonic  acid  and  pyromeconic  acid.     We  have  also  pyromucic,  pyrotartaric,  or 


FERMENTATION  OF  ORGANIC  COMPOUNDS.  537 

pyroracemic  and  pyrocitric  acids  ;  citric  acid  yielding  three  pyro-acids,  aconitic, 
(equisetic),  itaconic  and  citraconic  acids,  and  malic  acid  also  yielding  two,  maleic 
and  paramaleic  or  fumaric  acids. 

From  the  above  statements,  it  is  obvious,  that  the  action  of  heat  on  organic 
compounds  gives  rise  to  a  very  large  number  of  important  products,  of  which 
only  the  most  remarkable  have  been  named.  All  will  be  described  in  their  proper 
places. 

5.  Action  of  Ferments  on  Organic  Compounds.  Of  this  action  the  best  known 
and  most  important  example  is  the  fermentation  of  sugar,  by  which  it  is  resolved 
into  alcohol  and  carbonic  acid. 

The  circumstances  under  which  this  metamorphosis  occurs  are  these :  the 
sugar  must  be  dissolved,  the  solution  must  have  a  certain  temperature,  and  there 
must  be  present  a  ferment,  such  as  yeast  or  some  analogous  body.  In  the  juice 
of  the  grape  a  ferment,  the  fibrinous  or  caseous  constituent  of  the  juice  is  natu- 
rally present ;  and  Gay-Lussac  showed  that  the  contact  of  atmospherical  air  was 
necessary  to  commence  the  fermentation,  but  that  this  contact  with  the  atmos- 
phere might  be  only  for  a  vejy  brief  period,  after  which  air  was  no  longer  neces- 
sary. It  is  obvious  that  the  air  acts  by  inducing  a  state  of  change  in  the  ferment, 
for  if  any  ferment,  previously  exposed  to  the  air,  be  added  to  a  pure  solution  of 
sugar,  fermentation  will  take  place  without  the  mixture  being  exposed  to  the  air 
after  the  ferment  has  been  added. 

Berzelius  and  others  conceive  that  the  ferment  acts  by  contact  in  some  way  not 
very  clearly  defined,  by  catalysis,  as  it  is  called,  as  they  conceive  sulphuric  acid 
to  do  in  the  formation  of  ether  from  alcohol.  But  Liebig  has  proved  that  in  this 
latter  case  the  acid  first  combines  with  ether  (oxide  of  ethyle),  forming  sulpho- 
vinic  acid  (bisulphate  of  oxide  of  ethyle),  and  that  this  compound  at  a  tempera- 
ture rather  higher  than  that  at  which  it  is  formed,  is  decomposed  into  hydrated 
sulphuric  acid  and  ether  which  distils  over.  The  same  chemist  has  pointed  out 
many  other  instances  of  the  effect  of  contact,  even  in  inorganic  chemistry :  such 
as  the  action  of  oxide  of  silver  on  peroxide  of  hydrogen,  where  the  former  com- 
pound, by  contact  with  the  latter,  not  only  decomposes  it,  causing  oxygen  to  be 
rapidly  given  off,  but  is  i'self  decomposed,  losing  all  its  oxygen ;  the  solution 
in  nitric  acid  of  an  alloy  of  platinum  and  silver,  while  platinum  alone  is  insoluble 
in  that  acid ;  or  the  action  of  carbonate  of  silver  on  certain  organic  acids,  which 
cause  a  disengagement  of  carbonic  acid,  this  disengagement  being  attended  with 
a  partial  reduction  of  the  oxide  of  silver. 

These,  and  many  other,  more  familiar  cases,  particularly  those  where  a  com- 
pound is  decomposed  with  detonation  in  consequence  of  a  slight  touch,  or  gentle 
friction,  a  moderate  elevation  of  temperature,  or  the  contact  of  another  substance 
{e.  g.  chloride  of  nitrogen  with  oil)  all  tend,  according  to  Liebig,  to  establish 
the  doctrine  that  in  certain  compounds  the  balance  of  affinities  is  unstable,  and 
therefore  easily  overturned,  either  by  chemical  or  by  mechanical  influences.       ^ 

The  compounds  which  are  capable  of  fermentation  or  any  similar  metamor- 
phosis, are  all  of  them  bodies  in  which  such  an  unstable  equilibrium  exists : 
they  are  all,  in  point  of  fact,  easily  decomposed  by  many  different  agencies,  such 
as  heat,  acids,  bases,  oxygen,  chlorine,  &c.  &c.  Now,  we  can  offer  no  other 
explanation  of  these  facts  of  fermentation  than  this,  that  when  a  body  in  a  state 
of  progressive  change,  the  particles  of  which  are  consequently  in  a  state  of 
motion,  is  placed  in  contact  with  another  body,  the  particles  of  which  are  in  a 
state  of  unstable  equilibrium,  the  amount  of  motion  mechanically  communicated 


538  FERMENTATION  OF  ORGANIC  COMPOUNDS. 

to  the  particles  of  the  latter  from  those  of  the  former,  is  sufficient  to  overturn  the 
existing  equilibrium,  and  by  the  formation  of  a  new  compound  establish  a  new 
equilibrium  more  stable  under  the  given  circumstances. 

There  is  nothing  unphilosophical  in  this  explanation,  and  it  is  to  be  considered 
as  the  best  theory  of  fermentation  yet  attempted.  According  to  the  view  of 
Liebig,  a  ferment  is  merely  a  compound  in  a  state  of  decomposition,  capable  of 
setting  in  motion,  and  thereby  bringing  also  into  a  state  of  decomposition,  the 
particles  of  another  compound,  the  existence  of  which  depends  on  a  nice  balance 
of  affinities. 

On  the  other  hand  the  view  adopted  by  Berzelius,  according  to  which  fermen- 
tation, and  all  the  other  phenomena  of  chemical  change  produced  by  contact  are 
the  results  of  a  peculiar  unknown  force,  the  catalytic  force,  coming  into  action 
when  certain  bodies  are  placed  in  contact,  appears  unphilosophical,  as,  in  the 
first  place,  assuming  the  existence  of  a  new  force  where  known  forces  would 
suffice  to  explain  the  facts ;  and,  secondly,  as  furnishing  no  real  explanation, 
but  merely  acknowledging,  indirectly,  our  inability  to  off'erany  such  explanation. 
When  we  ascribe  an  effect  to  catalysis,  we  are  only  saying,  in  other  words,  that 
we  cannot  account  for  it ;  catalysis  is  thus  merely  a  convenient  term  for  all  that 
we  do  not  understand.  And  to  the  use  of  the  word  in  this  sense,  namely,  as  a 
name  for  the  agent  which  produces  certain  effects,  the  agent  itself  being  un- 
known, there  would  be  no  objection,  were  it  not  that  catalysis  has  been  employed 
to  account  for  phenomena  not  only  different  from  each  other,  but  actually  of  an 
opposite  kind.  For  example,  platinum,  in  causing  the  combination  of  oxygen 
and  hydrogen,  is  said  to  act  catalytically,  and  the  action  of  oxide  of  manganese, 
or  oxide  of  silver  in  decomposing  peroxide  of  hydrogen,  that  is,  in  causing  the 
separation  of  oxygen  and  hydrogen,  is  also  called  catalytic.  This  example 
proves  how  loosely  the  word  has  been  employed,  and  how  vague  are  the  views 
which  have  led  to  its  introduction. 

A  variety  of  important  and  interesting  processes  come  under  the  head  of  actions 
caused  by  ferments  ;  the  production  of  alcohol  from  sugar,  of  oil  of  bitter  almonds 
from  amygdaline,  and  of  lactic  acid  from  sugar  of  milk,  are  all  examples  of 
this ;  and  in  each  of  these  cases,  the  ferment  is  peculiar.  In  the  case  of  sugar 
it  is  yeast,  or  gluten  undergoing  eremacausis  and  putrefaction ;  in  the  case  of 
amygdaline  it  is  emulsine,  a  peculiar  modification  of  albumen  ;  and  in  the  case 
of  sugar  of  milk  it  is  caseine,  the  nitrogenized  constituent  of  the  milk. 

The  access  of  air  is  required  at  first  to  yield  oxygen  to  the  gluten,  &c.,  which 
then  entering  into  eremacausis,  or  if  air  be  excluded,  into  putrefaction,  are  capa- 
ble of  acting  as  ferments. 

In  the  actions  induced  by  ferments,  we  are  to  distinguish  those  in  which  some 
external  element  or  elements  are  added  to  those  of  the  compound,  which  cases 
resemble  ordinary  decompositions,  from  those  in  which  the  elements  of  the 
decomposed  body  merely  transpose  themselves,  producing  new  compounds.  The 
latter  are  properly  and  strictly  termed  metamorphoses.  Fermentations,  in  which 
oxygen  is  absorbed,  are  etamples  of  eremacausis,  and  it  has  already  been  men- 
tioned that  a  body  in  a  state  of  eremacausis  acts  on  other  bodies  as  an  excitant 
of  the  same  change,  that  is,  as  a  ferment. 

Indeed,  most  ferments,  whether  they  induce  eremacausis,  or  a  more  pure  meta- 
morphosis in  other  bodies,  are  themselves  in  a  state  of  eremacausis,  at  all  events 
in  the  commencement  of  the  change. 

The  subject  of  fermentation  and  ferments  will  be  hereafter  more  especially 


PUTREFACTION  OP  ORGANIC  COMPOUNDS.  539 

considered,  in  connexion  with  fermentescible  compounds :  here  the  subject  is 
merely  treated  in  a  general  way. 

Putrefaction,  under  ordinary  circumstances,  partakes  largely  of  eremacausis, 
and  differs  from  the  ordinary  kind  only  in  the  offensive  odour  of  some  of  the 
products,  chiefly  compounds  of  sulphur  and  phosphorus,  as  sulphuretted  and 
phosphuretted  hydrogen.  When  air  is  excluded,  putrefaction  goes  on,  provided 
moisture  be  present,  and  it  is  then  a  metamorphosis,  giving  rise,  in  the  case  of 
vegetable  matter  putrefying  under  water,  or  in  the  strata  of  mines,  to  gaseous 
products,  such  as  marsh  gas  and  olefiant  gas,  constituting  with  air  the  fire-damp, 
and  carbonic  acid,  which  is  the  choke-damp,  of  the  miner. 

Animal  matter,  in  a  state  of  putrefaction,  as  putrid  flesh,  blood,  cheese,  or 
wine  acts  as  a  ferment,  and  is  capable  of  causing  the  metamorphosis  of  sugar 
into  alcohol  and  carbonic  acid,  as  well  as  of  inducing  eremacausis,  and  also  pro- 
pagating a  putrefactive  decomposition  analogous  to  its  own.  Thus,  it  is  well- 
known  that  fresh  cheese,  if  inoculated  with  decaying  cheese,  soon  passes  into 
decay,  spreading  from  the  seat  of  the  inoculation. 

We  shall,  hereafter,  see  that  it  is  probable  that  some  poisons  and  miasmata  act 
as  ferments  on  the  blood.  The  singular  sausage  poison  of  Wurtemburg  is  animal 
matter  in  a  peculiar  state  of  decay,  and  does  not  contain  any  poisonous  compound, 
only  a  poisonous  state  or  condition ;  and  the  same  principle  may  hereafter  be 
found  to  furnish  the  true  explanation  of  contagions. 

Fermentation,  putrefaction,  and  eremacausis  are  all  promoted  by  the  same  cir- 
cumstances, and  arrested  by  the  same  influences.  Antiseptics  are  swbstances 
which  by  combining  with  the  ferment,  or  a  part  of  it,  or  even  with  the  body  to 
be  fermented,  prevent  the  continuance  either  of  the  decomposition  in  the  fer- 
ment, or  of  the  fermentation  itself.  Corrosive  sublimate  and  arsenic,  which  are 
powerful  antiseptics,  combine  with  animal  matter,  and  form  with  it  stable  com- 
pounds ;  creosote  combines  energetically  with  albumen,  &c.,  &c. 

In  fermentation,  properly  so  called,  the  elements  of  the  ferment  take  no  chem- 
ical share  in  the  metamorphosis  of  the  body  acted  on  by  the  mechanical  agency 
above  explained.  That  body  is  resolved  into  two  or  more  new  compounds  of 
less  complex  radicals.  The  elements  of  water  may  or  may  not  take  part  in  the 
change ;  when  they  do,  as  in  the  case  of  sugar,  the  weight  of  the  products,  in 
this  case  alcohol  and  carbonic  acid,  is  equal  to  thzj;  of  the  sugar,  plus  a  certain 
weight  of  water.  As,  when  the  water  is  passed  in  vapour  over  carbon  at  a  white 
heat,  the  carbon  is  shared  between  the  oxygen  and  hydrogen,  producing  carbonic 
acid  (or  oxide),  and  carburetted  hydrogen,  so  in  the  metamorphosis  of  sugar, 
and  other  analogous  cases,  we  have  on  the  one  hand  an  oxidized  compound,  (in 
the  case  of  sugar  represented  by  carbonic  acid),  and  on  the  other  a  compound  in 
which  part  of  the  carbon  is  united  to  all  the  hydrogen  (in  the  case  of  sugar,  the 
alcohol).  Similar  results  are  obtained  when  alcohol  or  acetic  acid  are  metamor- 
phosed by  heat,  and  this  may  be  viewed  as  a  general  character  of  the  metamor- 
phosis of  non-nitrogenized  bodies  :  namely,  that  the  carbon  is  divided  between 
the  oxygen  and  hydrogen. 

In  putrefaction,  again,  the  ferment  plays  a  chemical  part  in  the  change,  and 
two  or  more  compounds,  the  ferment  and  the  putrefying  body  or  bodies,  combine 
to  give  rise  to  new  compounds,  with  or  without  the  elements  of  water.  Putre- 
faction is  generally  the  characteristic  transformation  of  nitrogenized  compounds, 
and  the  very  great  tendency  of  such  compounds  to  undergo  transformations  is 
well  illustrated  by  the  spontaneous  metamorphosis  of  a  solution  of  cyanogen  in 


540  PUTREFACTION  OF  ORGANIC  COMPOUNDS. 

water.  Such  a  solution  contains  the  four  principal  elements  of  organic  bodies; 
and  its  transformations  may  be  said  to  be  the  only  case  of  putrefaction  which 
has  been  as  yet  carefully  studied. 

The  solution  after  a  time  becomes  brown  and  turbid,  and  deposits  a  dark 
matter,  containing  ammonia,  united  to  a  compound  formed  of  the  elements  of 
cyanogen  along  with  those  of  water.  This  matter  being  insoluble,  undergoes  no 
further  change.  Such  a  compound  might  arise  from  the  reaction  between  2  eq. 
cyanogen,  and  4  eq.  water :  thus,  SC^N  +  4H0  =  NH^  f  (C^HNO^)  ;  accord- 
ing to  some,  the  brown  matter  contains  no  ammonia,  and  is  C^N^HO  =  SC^N 
-t-  HO. 

Another  change  is  that  in  which  water  is  decomposed,  each  of  its  elements 
uniting  with  cyanogen,  and  producing  cyanic  and  hydrocyanic  acids  ;  thus : 
2H0  t  2C2N  ^(C^N,©  +  HO)  +  H,C2N. 

Another  metamorphosis  gives  rise  to  oxalic  acid  and  ammonia.  In  this  case, 
1  eq.  cyanogen  acts  on  3  eq.  water;  thus  ;   C^N  4-  3H0  =  NH  +  C^O^. 

But  cyanic  acid  cannot  exist  in  contact  with  water  and  other  acids  :  it  is 
instantly  metamorphosed  into  bicarbonate  of  ammonia  ;  thus  ;  C  NO  +  3H0  = 
NH3  +  2C0^. 

Towards  the  end  of  the  process,  when  ammonia  has  become  predominant,  the 
cyanic  acid  produced  undergoes  a  different  metamorphosis.  It  now  unites  with 
water  and  ammonia,  and  may  possibly  for  a  time  exist  as  hyd rated  cyanate  of 
ammonia ;  but  at  all  events  that  salt,  if  formed  at  all,  is  soon  transformed  into 
urea.     NH,4-0,N0  +H0  =C  H  N  O  =  urea. 

(5  2  2       4      2      2 

Again,  the  hydrocyanic  acid  gives  rise  to  another  brown  solid  body  containing 
cyanogen  or  paracyanogen  (possibly  mellone  also),, and  hydrogen;  and,  along 
with  this,  oxalic  acid,  urea,  and  carbonic  acid,  by  metamorphoses  already 
described. 

Lastly  the  hydrocyanic  acid  in  contact  with  water,  and  an  acid  or  an  alkali 
(here  oxalic  acid  or  ammonia),  undergoes  another  metamorphosis,  and  is  trans- 
formed into  formic  acid  and  ammonia ;  thus :  H,C  N  +  4H0  =  NH  -|-  C^HO  , 
HO. 

Thus  cyanogen,  a  binary  compound,  along  with  water,  another  binary  com- 
pound, gives  rise  to  no  less  than  eight  different  compounds ;  1st,  the  black 
compound,  containing  the  elements  of  cyanogen  and  those  of  water,  possibly 
C^HN^O:  2nd,  ammonia,  ^U^:  3rd,  cyanic  acid,  HOC^NO.  4th,  hydrocy- 
anic acid,  H,C  N.  5th,  oxalic  acid,  CO:  6th,  carbonic  acid  :  7th,  a  brown 
solid,  containing  cyanogen  (paracyanogen)  and  hydrogen :  8lh,  formic  acid, 
C^HOgiHO  :  and  in  addition  to  these,  three  bodies,  formed  by  the  combination 
of  two  of  the  above  eight,  and  containing  all  the  four  elements  ;  namely,  9th, 
oxalate  of  ammonia:  10th,  bicarbonate  of  ammonia:    Uth,  urea. 

This  striking  example  is  well  adapted  to  give  a  clear  idea  of  the  immense 
variety  attainable,  when,  instead  of  two  binary  compounds,  two  ternary  or  two 
quaternary  compounds,  along  with  water,  are  concerned;  and  of  the  slight 
modifications  of  external  circumstances  which  are  required  to  produce  results  so 
varied,  all  the  above  substances  being  produced  in  a  liquid  at  the  usual  tem- 
perature. 

It  is  hoped  (hat  the  above  sketch  of  the  doctrine  of  the  chemical  changes  and 
metamorphoses  of  organic  compounds  will  suffice  to  enable  the  student  to  follow 
the  individual  processes  and  reactions,  to  be  hereafter  mentioned,  which,  owing 
\o  our  limited  space,  we  must  treat  with  great  brevity.     We  shall  now  conclude 


ORGANIC  ACIDS.  541 

our  introductory  matter  by  some  general  observations  on  the  doctrines  now  held 
by  many  chemists  on  the  subject  of  the  organic  acids;  after  which  we  shall 
enter  on  the  study  of  the  known  organic  radicals. 

ORGANIC  ACIDS. 

The  acids  met  with  in  organic  chemistry  are  principally  compounds  of  carbon, 
hydrogen,  and  oxygen,  although  some  do  contain  also  nitrogen.  They  are  dis- 
tinguished from  inorganic  acids  by  their  high  atomic  weight,  and  by  the  action 
of  heat,  which  decomposes  them  all.  As,  in  many  of  them,  the  oxygen  they 
contain  is  a  multiple  by  a  whole  number  of  the  oxygen  of  the  bases  which  neu- 
tralize them,  so  they  are  viewed  as  oxygen  a^ids  by  those  who  consider  true 
sulphuric  acid  to  be  an  oxygen  acid,  SO^,  and  oil  of  vitriol  to  be  its  hydrate, 
HO,SO  .  In  the  case  of  acetic  acid,  for  example,  the  formula  of  which  is 
(C^Hg)  O^HO,  the  compound  (C^H^)  O^,  unknown  in  a  separate  form,  is  called 
dry  acetic  acid,  and  the  strong  acetic  acid  is  considered  as  its  hydrate;  and  the 
analogy  is  supposed  to  be  fortified  by  the  fact  that  dry  acetic  acid,  like  dry  sul- 
phuric acid,  contains  3  eq.  oxygen,  and  neutralizes  I  eq.  of  base,  MO,  containing 
I  eq.  of  oxygen. 

But  a  careful  study  of  the  organic  acids  leads  us  to  apply  to  them  the  same 
theory  which  we  have  already  adopted  for  the  inorganic  acids,  and  to  consider 
them  as  compounds  of  hydrogen,  with  compound  radicals,  usually  consisting  of 
carbon,  hydrogen,  and  oxygen.  On  this  view,  as  oil  of  vitriol  is  H,SO^,  the 
strongest  acetic  acid  is  H,  (C^H^)  0^.  It  is  true  that  this  radical,  (C^H^)  0^, 
does  not  exist,  or  is  not  known  in  the  separate  form ;  but  the  same  remark 
applies  to  dry  acetic  acid,  (C  H  )  O  ,  which  on  the  old  view  is  supposed  to  be 
combined  with  water,  for  it  also  is  unknown  in  the  separate  state. 

The  existence  of  compound  radicals  in  organic  acids  is  not  more  difficult  to 
imagine  than  that  of  SO^  the  compound  radical  of  sulphuric  acid,  for  (C  H  )0 
only  differs  from  it  in  containing  three  elements  instead  of  two  ;  indeed,  as  some 
ternary  organic  radicals  are  known  in  the  separate  form,  we  actually  derive  an 
argument  from  organic  acids  in  favour  of  the  existence  of  compound  radicals  in 
inorganic  acids.  Thus,  the  radical  or  organic  metal,  kakodyle,  forms  kakodylic 
acid. 

But  we  find,  among  organic  acids,  a  much  larger  proportion  which  are  bibasic, 
tribasic,  in  short  polybasic,  than  occurs  among  inorganic  acids.  Referring  to 
what  was  said  of  the  monobasic,  bibasic,  and  tribasic  phosphoric  acids,  it  will 
be  easily  understood  that  while  acetic  acid,  for  example,  is  monobasic,  tartaric 
acid,  malic  acid,  komenic  acid,  alloxanic  acid,  and  others  are  bibasic;  that  citric 
acid  and  mekonic  acid  are  tribasic,  and  that  saccharic  acid  is  quinquebaslc. 
And  as  the  three  modifications  of  phosphoric  acid  are  described  on  the  old 
view  as  monohydrated,  bihyd rated,  and  terhyd rated,  and  on  the  new  view,  as 
containing,  respectively,  1,  2,  and  3  eqs.  of  hydrogen,  replaceable  by  metals,  so 
tartaric  acid  may  be  either  C  H  O,  .2H0  or  C  H  0,„,H„;  malic  acid  may  be 

•^  8       4       10  o       4       12         JL  *^ 

CH  0,2^0   or  C„HO,  -H„;  and    so  on;   while   citric   acid   may  be  either 

o       4      o  8       4      10         2 

^12^5^11'^^^  or  Cj2H^Oj^,H3,  and  meconic  acid,  C^^H0jj,3H0,  or  C^^HO^^, 
H^;  and  lastly,  saccharic  acid  may  be  C^2H^Oj^,5HO  ;   or  ^^^P^^^^' 

In  such  polybasic  acids,  there  is  always  some  hydrogen  in  the  radical,  of 
which  it  is  a  constituent,  and  some  combined  with  the  radical,  and  replaceable 


^2  ORGANIC  RADICALS. 

by  its  equivalent  of  metals.  It  is  only  this  latter  hydrogen,  the  amount  of 
which  atTects  the  neutralizing  power  of  the  acid. 

Now,  among  the  phenomena  of  the  action  of  bases  on  organic  acids,  we  have 
gome  facts  which  seem  almost  to  demonstrate  the  existence  of  this  replaceable 
hydrogen,  as  such,  and  thus  to  establish  the  new  theory  of  acids.  Thus,  meconic 
acid,  which  is  tribasic,  forms,  like  tribasic  phosphoric  acid,  three  series  of  sails, 
in  which  1,2,  or  3  eqs.  of  hydrogen  are  replaced  by  metal.  But  while  the  meconic 
acid,  as  well  as  the  tribasic  phosphoric  acid,  readily  forms  with  the  oxide  of 
silver,  the  salt  in  which  all  the  hydrogen  is  replaced  by  silver ;  it  cannot  form, 
pr  forms  with  difficulty,  a  similar  salt  with  potash,  with  which  it  forms  very 
easily  salts  with  1  and  2  eqs.  of  metal,  and  2  or  1  eqs.  of  hydrogen.  Here  we 
have  the  apparent  contradiction  of  a  weak  base,  oxide  of  silver,  neutralizing  ihe 
?icid  easily  and  completely;  while  a  strong  base,  potash,  leaves  it  imperfectly 
neutralized.  This  cannot,  I  think,  be  accounted  for  on  the  old  view,  and  many 
similar  cases  might  be  mentioned.  On  the  new  view,  such  apparent  anomalies 
disappear:  for  since  the  neutralizing  depends  on  the  replacement  of  hydrogen  by 
a  metal,  it  is  evident  that  an  oxide  which  is  easily  reduced,  or  deprived  of  its 
oxygen  by  hydrogen,  like  oxide  of  silver,  will  most  easily  neutralize  acid,  while 
a  difficultly  reducible  oxide,  such  as  potash,  cannot  be  so  far  reduced  as  to  yield 
3  eqs.  of  metal,  so  as  to  form  the  neutral  salt. 

There  are  other  kinds  of  organic  acids  which  are  what  may  be  called  coupled 
acids  ;  that  is  to  say  they  contain  an  acid  coupled  with  another  body,  which  does 
not  neutralize  the  acid,  but  accompanies  it  in  all  its  combinations.  Thus,  in 
hyposulpho-haphthalic  acid,  C^^  H^  S^  0^,  HO,  we  have  hyposulphuric  acid  S^ 
0^,  coupled  with  naphthaline,  C^^  Hg,  and  the  coupled  acid  neutralizes  exactly 
as  much  base  as  the  hyposulphuric  acid  alone  would  do.  Again,  formobenzoilic 
acid  CjQ  H^  O^,  HO,  may  be  viewed  as  a  coupled  acid,  consisting  of  formic  acid 
Cg  HO^,  HO  and  oil  of  bitter  almonds  (hydurel  of  benzoyle)  C^^  H^  0^,  which 
neutralizes  just  as  much  base  as  the  formic  acid  alone.  Those  coupled  acids 
which  contain  hyposulphuric  acid,  as  is  often  the  case,  are  formed  by  the  action 
of  oil  of  vitriol,  or  of  anhydrous  sulphuric  acid,  on  organic  bodies,  when  2  eqs. 
of  acid,  losing  I  eq.  of  oxygen,  form  hyposulphuric  acid;  which  commonly  unites 
with  the  organic  matter  mitius  1  eq.  of  hydrogen,  that  hydrogen  having  couibined 
with  the  oxygen  derived  from  the  sulphuric  acid. 

ORGANIC  RADICALS. 

In  the' following  pages  we  shall  adopt  the  arrangement  of  Liebig,  which  has  the 
advantage  of  uniting  those  substances  which  are  naturally  allied  in  composition. 
It  proceeds,  in  the  first  place,  on  tlie  principle  of  describing,  under  each  known 
or  admitted  organic  radical,  all  the  compounds  derived  from  or  closely  connected 
with  it.  After  having  gone  through  these,  it  takes  up  the  consideration  of  the 
best  known  organic  acids,  including  the  oily  acids  ;  then  the  neutral  oils,  fat  and 
essential;  the  resins;  the  non-nitrogenous  colouring  matters,  bitter  and  extractive 
principles,  nitrogenized  colouring  matters, and  their  congeners;  the  organic  bases; 
starch;  gum;  woody  fibre;  destructive  distillation  of  wood,  of  lignite,  of  coal  ; 
nitrogenized  and  sulphurized  vegetable  principles,  albumen,  &c.,  the  modifica- 
tions of  these  in  the  animal  kingdom;  bile;  nervous  matter;  gastric  juice; 
saliva ;  excrements  ;  urine  ;  blood  ;  lymph,  &c.  And  the  whole  is  wound  up 
with  considerations  on  the  nutrition  of  plants  and  animals. 


AMIDE  dR  AMIDOGEN.  543 

This  arrangement  is  not  a  scientific  one,  and  in  the  present  state  of  our  know- 
ledoe  such  an  arrangement  is.  I  fear,  unattainable.  But  it  is  very  convenient, 
and,  by  judicious  groupinor,  very  much  facilitates  the  learning  and  the  retaining 
in  the  memory  of  the  immense  mass  of  facts  which  at  present  constitute  organic 
chemistry. 

We  proceed,  therefore,  to  consider  those  organic  radicals  which  are  admitted 
by  the  best  authorities,  .although  they  are  not  always  known  in  the  separate 
state.  The  first  compound  radicals  that  attract  our  attention  are  certain  binary 
ones,  already  mentioned  as  binary  compounds,  but  not  in  their  character  of  radi- 
cals, in  the  second  Part  of  this  work;  these  are  amide  or  amidogen,  cyanogen,  and 
carbonic  oxide. 

I.  Amide.    NHj=:Ad=16-19. 

Syn.  Jmtdngen. — It  has  already  been  mentioned  that  certain  compounds  exist, 
in  which  we  can  hardly  doubt  that  this  substance  is  present.  Thus,  potassium  or 
sodium,  heated  in  dry  ammoniacal  gas,  disengages  1  eq.  of  hydrogen,  forming  the 
compound  KNH  or  Na  NH  .  When  these  are  put  into  water,  potash  or  soda  is 
formed,  while  ammonia  is  set  free  :  K,NH  -|-HO=KO  -|-NH  .  Again,  when  oxa- 
late of  ammonia,  NH^,  HO,  C^O^  is  heated,  there  are  formed,  water  which  distils 
over,  and  the  compound  NH^C^O^  which  remains  behind :  thus,  NH^,HO,C202= 
2H0-I-NH  C  0  .  The  latter  compound  is  called  oxamide^  and  is  a  sparingly 
soluble  white  powder,  neutral  or  indifferent  in  itself,  but  yielding,  when  digested 
with  an  alkali  ammonia,  which  escapes,  and  oxalic  acid,  which  combines  with 
the  alkali.  Or  if  oxamide  be  heated  with  diluted  sulphuric  acid,  it  yields  am- 
monia which  combines  with  the  acid,  and  oxalic  acid  which  crystallizes  in  cool- 
ing.    In  both  cases  water  is  decomposed  :  thus  NH^  C^  0^  +  2H0  =  NH^,  HO 

Now  oxamide  is  interesting,  as  being  the  type  of  a  class  of  compounds,  all  of 
which,  when  heated  with  an  alkali  or  an  acid,  yield  ammonia  and  an  acid,  the 
ammonia  and  the  anhydrous  acid  together  containing  just  1  eq.  of  water  more 
than  the  compound  which,  with  the  aid  of  water,  has  yielded  them.  If  we  con- 
sider oxamide  as  NH^  "t"  ^2  ^2 »  ^^^^  *^'  ^®  composed  of  amide  (or  ammonia 
minus  hydrogen  NH  ),  and  the  radical  carbonic  oxide  (or  oxalic  acid  minus  oxy- 
gen C^O^),  then  all  its  congeners  are  likewise  compounds  of  amide,  on  the  one 
hand,  and  an  anhydrous  organic  acid,  minus  oxygen,  on  the  other.  On  this  view 
benzamide  is  benzoate  of  ammonia,  witims  water,  (NH^-f  C^^  H^  O^,  HO) — 2H0 
rsNH^-j-Cj^  H^  O  ;  or  it  is  amide  plus  benzoyle  (the  radical  of  benzoic  acid, 
C^^H^O^).  Therefore,  when  benzamide  is  acted  on  by  potash,  ammonia  is 
given  off,  and  benzoate  of  potash  is  left;  and  when  it  is  heated  with  an  acid,  a 
salt  of  that  acid  with  ammonia  is  obtained,  while  benzoic  acid  crystallizes. 
There  are  a  good  many  similar  compounds  which  are  called  amides,  and  are 
viewed  as  compounds  of  amide. 

It  is  obvious  that  the  distinctive  characters  of  amide,  which  is  not  known  in 
the  separate  form,  are  its  powerful  affinity  for  hydrogen,  and  its  equally  strong 
tendency  to  combine  with  radicals  which  have  a  very  great  affinity  for  oxygen, 
such  as  those  already  mentioned,  potassium,  sodium,  the  radical  C^  0^,  and  the 
radical  benzoyle. 

With  hydrogen  amide  forms  two  compounds,  ammonia,  Ad  H,  and  ammo- 


544  COMPOUNDS  OF  AMIDE. 

nium,  Ad  H^.  The  former  may  be  called,  in  this  view,  hydramide.  The  latter, 
as  has  been  already  explained,  is  considered  to  be  a  compound  metal. 

It  is  very  remarkable,  that  when  ammonia  or  hydramide  combines  with  an 
acid,  the  resulting  compound  is  not  a  salt,  unless  the  acid  contain  hydrogen. 
Thus,  hydramide,  with  dry  sulphuric  acid,  SO^,  forms  a  compound  which  is  not 
sulphate  of  ammonia,  and  is  not  a  salt  at  all.  But  if,  instead  of  SO^,  we  employ 
oil  of  vitriol,  HO,  SO^,  or  HO,  SO^,  sulphate  of  ammonia,  a  true  salt,  is  ob- 
tained. 

Here  we  may  conclude  that  Ad  H,  in  contact  with  H,  SO^,  takes  the  hydro- 
gen, forming  ammonium,  and  that  the  resulting  salt  is  composed  of  Ad  H^  -j- 
SO^;  that  is,  a  metal  combined  with  the  sulphuric  acid  radical,  just  as  sulphate 
of  potash  is  K,  SO^.  In  all  the  true  salts  of  ammonia,  therefore,  Ad  H  =  Am 
(Ammonium)  occupies  the  place  of  a  metal,  and  may  be  replaced  by  a  metal ; 
and  even  if  we  consider  sulphate  of  potash  to  be  KO,  SO^,  we  have  only  to  view 
the  sulphate  of  ammonia  as  NH^  0,  803=  Ad  H^  O,  803  =  Am  O,  SO3,  that  is, 
sulphate  of  oxide  of  ammonium. 

It  must  be  borne  in  mind,  however,  that  although  all  the  chemical  relations  of 
these  compounds  confirm  the  ammonium  theory,  yet  neither  ammonium  nor  its 
oxide  are  capablp  of  existing  uncombined ;  for  ammonium,  when  separated,  is 
resolved  into  ammonia  and  hydrogen ;  and  oxide  of  ammonium,  when  separated, 
assumes  the  forms  of  ammonia  and  water. 

Of  the  chief  compounds  of  amide,  ammonia  or  hydramide  has  been  previously 
described.  It  remains  for  us  to  direct  attention  to  this  substance  as  constantly 
present  in  the  atmosphere  in  minute  quantity,  from  whence  it  descends  in  the 
Tain,  being  an  absolutely  ^dispensable  agent  in  vegetation.  We  have  already 
seen  that  the  putrefaction  and  eremacausis  of  nitrogenized  compounds  yields  car- 
bonate of  ammonia  as  a  product.  Its  presence  in  the  air  is  therefore  certain,  d 
priori,  even  although  we  cannot  detect  it  until  it  is  condensed  and  accumulated 
in  rain.  It  is,  however,  absorbed  from  the  air  by  almost  all  minerals  and  soils, 
especially  aluminous  and  ferruginous  soils;  hence  a  trace  of  ammonia  is  often 
found  where  it  is  not  looked  for,  and  where  it  has  been  erroneously  believed  to 
have  been  formed  by  the  direct  union  of  hydrogen  and  nitrogen.  This  is  the 
true  explanation  of  the  very  remarkable  and  accurate  experiments  of  Faraday, 
which  have  lately  been  confirmed  by  Will  and  Varrentrapp. 

As  an  ingredient  of  manures,  ammonia  is  most  valuable.  Its  action  on  grow- 
ing vegetables  will  be  hereafter  explained. 

Ammonia  forms  a  large  number  of  compounds  with  the  oxides  of  metals,  the 
chlorides  of  metals,  of  sulphur  and  of  phosphorus,  and  finally  with  salts  in  gene- 
ral. These  belong  rather  to  inorganic  chemistry,  and  the  limited  size  of  this 
work  forbids  us  to  describe  them  in  detail. 

But  it  is  proper  here  briefly  to  noilhce  the  compounds  formed  by  amide  with 
metals,  inasmuch  as  amide  is  here  viewed  as  an  organic  radical,  and  some  of 
these  compounds  are  very  important  in  reference  to  organic  chemistry. 

Amide  then  forms  compounds  with  potassium,  sodium,  mercury,  copppr,  silver, 
and  platinum.  The  two  former  are  of  a>  greenish  olive  colour,  and  their  action 
on  water  has  been  described  above.  The  amide  or  amidide  of  mercury  HgAd, 
is  not  known  in  a  sepamte  state,  hut  forms  with  bichloride  of  mercury  the  salt 
called  white  precipitate,  HgAd-f-HffCl^. 

This  salt  is  prepared  by  adding  a  iimonia  to  a  solution  of  bichloride  of  mer- 


AMIDE  OF  PLATINUM.  545 

cury.  "When  boiled  with  potash,  it  yields  another  salt,  H^Ad  -f-  Hg'Cl2+  Hg 
Oj.  The  amidide  of  mercury  also  combines  with  the  basic  sulphate,  and  the 
basic  nitrates  of  the  same  metal,  forming^,  with  the  basic  protonitrate,  the  soluble 
mercury  of  Hahnemann. 

The  amidide  of  copper,  AdCu,  is  only  known  in  combination  with  the  hjrpo- 
_  sulphate  and  with  the  nitrate  of  ammonia. 

The  amidide  of  silver,  AgAd,  is  known  in  combination  with  the  nitrate,  sul- 
phate, seleniate  and  chromate  of  ammonia. 

But  it  is  the  amidide  of  platinum  which  oifers  the  greatest  interest,  as  it  gives 
rise  to  several  very  singular  compounds,  exhibiting  the  characters  of  very  pow- 
erful bases.  These  remarkable  substances  have  been  studied  by  Gros,  Reiset, 
and  very  recently  by  Peyrone,  but  are  yet  far  from  being  understood.  We  shall 
endeavour  briefly  to  state  what  is  known  of  them. 

When  bichloride  of  platinum,  PtCl^,  is  heated  for  some  time  to  nearly  the 
melting  point  of  tin,  it  loses  half  its  chlorine,  and  is  converted  into  protochlo- 
ride,  PtCl,  which  forms  a  powder  of  a  dirty  brownish  green  colour,  insoluble  in 
water.  By  continued  digestion  in  ammonia,  with  the  acid  of  heat,  the  protochlo- 
ride  is  first  changed  into  a  green  crystalline  compound,  which  finally  dissolves 
entirely,  forming  a  yellowish  solution,  which  on  evaporation  deposits  yellowish 
white  prismatic  crystals.  The  green  crystalline  compound,  discovered  by  Mag- 
nus, contains  the  elements  of  protochloride  of  platinum  and  those  of  ammonia, 
PtCl  NH  ;  the  yellowish  white  crystals,  discovered  by  Reiset,  contain  twice  as 
much  ammonia  and  the  elements  of  water,  PtCl,  2NH  -f-aq. 

These  two  compounds  are  very  remarkable ;  neither  of  them  contains  ammonia 
.as  such  ;  both  are  insoluble  in  hydrochloric  and  dilute  sulphuric  acids.  But  the 
green  compound  of  Magnus  dissolves  in  nitric  acid,  with  evolution  of  nitrous 
^  acid,  and  the  solution  on  cooling  deposits  white  crystalline  scales,  while  the 
liquid  contains  no  ammonia.  These  white  scales,  discovered  by  Gros,  are  the 
nitrate  of  a  new  base,  PtCl  N^H^O ;  which  may  be  derived  from  2  eq.  of  the 
insoluble  compound  of  Magnus,  Pt^Cl^N^H^,  by  the  loss  of  1  eq.  of  protochlo- 
ride of  platinum  and  the  addition  of  1  eq.  of  oxygen.  This  base  acts  exactly 
like  the  basic  oxide  of  a  metal,  or  like  oxide  of  ammonium,  NH  O,  combining 
with  acids  and  forming  neutral  salts.  It  not  only  forms  salts  with  nitric  and 
sulphuric  acids  and  the  like,  but  with  hydrochloric  acid  it  yields  a  heavy  crys- 
talline powder,  which  is  a  chloride,  bearing  the  same  relation  to  the  base  as 
chloride  of  ammonium,  NH^Cl  (sal  ammoniac)  does  to  oxide  of  ammonium. 
This  chloride,  therefore,  is  PtClN  H^Cl,  and  the  radical  of  the  oxide  or  base 
and  of  the  chloride,  will  bcPtClN^H^,  corresponding  to  ammonium,  NH^. 
Although  Gros  did  not  isolate  either  the  radical  or  its  oxide,  yet  from  the  cha- 
racters and  composition  of  its  salts,  there  can  be  no  doubt  of  its  existence.  If 
we  represent  this  radical,  PtClN^Hg  by  R,  then  we  have 

RO  =  oxide,  the  base  of  the  salts,  analogous  to  KO  or  NH^jO. 
RO  -J-  SOg  =  R  -|-  SO4  :=  sulphate,  analogous  to  K,S04 
RO  -\-  NO5  =  R  -j-  NOg  =  nitrate,  analogous  to  KjNOg 
RCl  =  chloride,  analogous  to  KCl  or  NH4,  CI 

The  soluble  crystalline  compound  of  Reiset,  PtClNgHg  -j-  aq.  when  heated  to 
212°,  becomes  anhydrous,  and  is  then  PtClNaHg,  that  is,  it  has  the  same  com- 
J)osition  as  the  radical  of  the  base  and  salts  of  Gros.     But  it  is  not  this  radical ; 

37 


546 


NEW  ORGANIC  BASES 


on  the  contrary,  it  is  the  chloride  of  a  different  radical,  PtN^H^,  and  its  true  for- 
mula is  PtN2H6 -h  CI. 

This  new  radical  is  also  perfectly  analogous  to  ammonium,  as  may  be  exhibited 
in  a  tabular  form  as  follows. 


Chlorine 
Compound. 

Sulphate. 

Nitrate. 

Double  Chloride 
with  Platinum. 

Ammoiiium  NH4  =  Am 
Radical  of)  p.^^  u  —  n' 
Reiset    JPtNeHe-R 

AmCl 
R'Cl 

AmS04 
R'S04 

AmNOg 
R'NOe 

AmCl  +  PtClj 
R'Cl  -H  PtCl.2 

In  the  case  of  ammonium,  we  cannot  isolate  the  oxide  AmO  =  NH  O,  as  it 
instantly  resolves  itself  into  ammonia  and  water,  NH  -|-  HO.  But  the  oxide 
of  Reiset's  platinum  radical,  R'O,  =  PtN^HeO,  or  rather  its  hydrate  PtN^HeO 
-+-  aq.  is  easily  obtained  from  the  sulphate  by  adding  just  so  much  baryta  as  will 
remove  the  sulphuric  acid,  and  evaporating  the  filtered  solution  in  vacuo,  when 
the  hydrated  oxide  crystrallizes  in  colourless  needles.  This  compound  is  strik- 
ingly analogous  to  hydrate  of  potash :  it  is  a  powerful  caustic,  attracts  carbonic 
-acid  from  the  air  as  strongly  as  potash,  and  exhibits  all  the  chemical  characters 
of  one  of  the  strongest  alkalies.  Few  compounds  are  so  remarkable  as  this 
base.     We  shall  call  it  the  base  a. 

This  singular  compound  may  be  viewed  as  containing  the  elements  of  pro- 
toxide of  platinum,  ammonia  and  water,  PtO,2NH  ,H0.  When  heated  to  212°, 
it  loses  its  water  and  half  its  ammonia,  leaving  a  compound  PtNH  O  or  PtO, 
NH  ,  which  appears  to  be  another  new  base,  6,  combining  with  acids  and  form- 
ing salts  which  detonate  when  heated.  This  last  compound,  when  heated  in  the 
air,  burns  like  tinder,  and  leaves  metallic  platinum.  It  is  the  oxide  of  a  third 
radical,  6,  =  PtNHg. 

With  hydrochloric  acid  the  base  a  of  Reiset  yields  water  and  the  original 
chlorine  compound,  thus  :  PtN,H„0  f  HCl  =  PtN,H„Cl  f  HO.  When  this 
chloride  is  heated  to  from  265°  to  290°,  it  loses  ammonia,  and  there  is  left  a 
yellow  powder  discovered  by  Peyrone,  which  dissolves  easily  in  hot  water,  and 
has  the  composition  of  the  green  insoluble  crystalline  compound  of  Magnus, 
PtClNH  ,  of  which  it  is  an  isomeric  modification.  Indeed,  the  compound  of 
Magnus,  (although  insoluble  in  hot  water,)  if  boiled  with  a  saturated  solution  of 
sulphate  or  nitrate  of  ammonia,  dissolves  and  is  deposited  on  cooling  in  yellow 
crystals.  The  yellow  ammoniated  protochloride  of  platinum  of  Peyrone  readily 
dissolves  in  ammonia,  and  the  solution  yields  fine  colourless  prisms  of  the  origi- 
nal chlorine  compound  of  Reiset,  but  apparently  not  containing  1  eq.  of  water  of 
crystallization,  which  is  said  to  be  present  in  the  white  scales  obtained  by  Reiset 
from  the  green  compound  of  Magnus. 

When  the  yellow  compound  of  Peyrone  is  acted  on  by  nitrate  of  silver,  it 
yields  chloride  of  silver,  and  two  new  compounds  containing  nitric  acid  and  pla- 
tinum, one  of  which  forms  yellow  octohedrons. 

If  the  sulphate  of  Reiset's  base,  PtN^H^  -|-  SO4  be  acted  on  by  iodide  of 
barium,  Bal,  there  is  formed  sulphate  of  baryta,  BaSO  ,  and  a  protoiodide  of 
Reiset's  radical,  o,  PtN^HcI.  This  iodide  is  soluble  and  crystallizable,  and 
when  boiled  with  water,  loses  ammonia,  while  a  new  iodine  compound  is  precipi- 


CONTAINING  PLATINUM. 


547 


tated,  PtNHJ,  corresponding  to  the  chlorine  compound  of  Peyrone  and  to  that 
of  Magnus,  both  of  which  are  PtNH^Cl. 

This  new  iodine  compound  seems  to  be  the  iodide  of  the  third  radical,  Z>,  Pt 
NH^ ;  for  when  acted  on  by  nitrate  or  sulphate  of  silver,  it  yields  iodide  of  sil- 
ver, and  a  nitrate  or  sulphate  of  this  new  radical  or  of  its  oxide,  PtNH  ,1  +  Ag, 
So^  =  PtNH3,SO^  +  AgI;  and  PtNH3,I  +  Ag,  NO^  =  PtNH^,  NO^  +  Agl. 
These  new  salts  may  of  course  be  represented  as  PtNHg,0  +  SO^,  and  PtNH^, 
O  -\-  NO^.  With  ammonia,  these  salts  yield  the  nitrate  and  sulphate  of  Reiset's 
base  a  ,•  and  with  hydrochloric  acid  they  yield  the  yellow  compound  of  Peyrone. 
This  would  indicate  that  the  latter  compound  is  PtNHg,Cl,  the  chloride  of  the 
radical  PlNH^,  while  the  green  salt  of  Magnus  may  be  the  ammoniated  protochlo- 
ride  of  platinum  PtCl  +  NH3,  or  probably  PtCl,NH3  +  aq. 

Here  we  have,  at  all  events,  three  very  remarkable  compounds,  which  contain 
platinum  and  the  elements  of  ammonia.  There  is,  first,  the  radical  b  last 
described,  PtNH^;  secondly,  the  radical  of  Reiset's  base,  a,  PtNiHg ;  and 
thirdly,  the  radicals  of  Gros's  base,  PtClNiHg. 

Now  we  have  given  the  history  of  these  compounds  somewhat  minutely, 
because  their  existence  throws  much  light  on  the  nature  of  a  numerous  and  im- 
portant class  of  bodies,  namely,  the  vegetable  bases  or  alkaloids. 

It  will  be  observed,  then,  that  the  three  new  radicals  above  described  all  con- 
tain nitrogen,  indeed,  all  contain  the  elements  of  ammonia,  and  are  in  their  che- 
mical relations  entirely  analogous  to  ammonium.     Thus  we  have 


Radical. 

Oxide. 

Chloride. 

Sulphate. 

Ammonium. 

Radical  of  ) 
Reiset'a  > 
base  b         ) 

Radical  of  S 
Reiset's  > 
base  a         ) 

Radical  of  ) 
Gros's  base) 

NH4 

PtNHg 

PtNjHe 
PtClN2H6 

NH*  +  0 
PtNHj  +  0 

PtN^Hg  +  O 
PtClNgHs+O 

NH4  +  CI 
PLNH3  +  CI 

PtNaHg  +  Cl 
PtClNjHe  +  Cl 

NH4  f  SO* 

PtNHg    f    SO4 

PtNaHfi  +  SO4 
PtClN2Hg+S04 

That  the  above  formulae  represent  in  some  respects  truly  the  relation  of  these 
new  bases  to  one  another,  is  rendered  probable  by  the  fact  that,  while  the  radical 
and  base  b  of  Reiset  differ  from  his  radical  and  base  a  by  containing  1  eq.  of 
ammonia  less,  and  these  last  from  those  of  Gros  by  containing  1  eq.  of  chlorine 
less,  we  can  actually  transform  the  salts  of  Reiset's  base  b  into  those  of  his  base 
fl,  by  the  addition  of  ammonia  ;  and  the  nitrate  of  Reiset's  base  a,  by  the  addi- 
tion of  chlorine,  yields  a  salt  having  the  properties  of  the  nitrate  of  Gros's  base. 

Now  we  have  seen  that  ammonium  may  be  viewed  as  a  compound  of  amide, 
as  NH2  +  H2  =  AdHi.  May  we  not  therefore  suppose  the  new  radicals  to  be 
also  compounds  of  amide  1     May  not  Reiset's  radical  b  be  ammonium,  in  which 

C  H 

1  eq.  of  hydrogen  has  been  replaced  by  1  eq.  of  platinum,  Ad  J  p.  ^         Again, 

just  as  we  have  seen  in  acids,  viewed  as  hydro jen  compounds,  analogous  ele- 
ments added  to  the  radical  without  affecting  the  neutralizing  power  of  the  acid, 
which  remains  the  same  as  long  as  the  replaceable  hydrogen  continues  unchanged, 
we  can  suppose  amide  to  be  a  basic  radical,  forming  with  hydrogen  the  base 
ammonia,  but  capable  of  taking  up  into  the  radical  analogous  elements  without 


548  CARBONIC  OXIDE  WITH  OXYGEN. 

aflfecting  the  basic  character  of  the  ammonia,  because  we  have  now  the  hydrogen 
compound  of  an  analogous,  but  more  complex,  basic  radical.  *  On  this  view, 
Reiset's  radical  b,  may  be  the  hydrogen  compound  of  a  basic  radical,  more  com- 
plex than  amide ;  in  fact,  amidide  of  platinum.  Its  formula  would  then  be  Ad 
Pt  -f  H,  and,  although  on  this  view  it  should  correspond  to  ammonia,  rather  than 
ammonium,  we  cannot  speak  positively,  as  this  is  the  least  known  of  the  three. 

The  other  two  radicals  may  be  readily  viewed  as  hydrogen  compounds  of 
complex  amidides,  as  ammonium  is  the  hydrogen  compound  of  amidide  of 
hydrogen. 

Amide,  NH^  =  Ad,  with  hydrogen,  forms  ammonia  AdH,  and  ammonium  Ad- 
H  -J-H.  In  like  manner,  in  the  radical  a  of  Reiset's  salts,  we  have  a  complex 
amide,  composed  of  amide  and  amidide  of  platinum.  Ad  +  PtAd  =  PtAd  , 
which,  with  1  eq.  hydrogen,  may  be  supposed  to  form  a  compound  analogous 
to  ammonia,  PtAd^,!!,  and  with  two  eq.  of  hydrogen,  actually  does  form  the 
radical  a  of  Reiset,  PiAd^H  -^  H,  exactly  analogous  to  ammonium.  So  the 
radical  of  Gros  may  be  derived  from  the  complex  amide  PtClAd  -|-  Ad  =  Pt- 
ClAdg,  which  may  form  PtClAd^  -\-  H  and  PtClAd^H  -f-  H,  the  latter  being  the 
actual  composition  of  the  radical  of  Gros,  corresponding  to  ammonium. 

It  may  also  be  mentioned,  that  just  as  we  may  view  ammoniacal  salts  as  con- 
taining ammonia  and  water  rather  than  ammonium  and  oxygen,  so,  the  base  b  of 
Reiset  may  be,  NH^  -j-  PtO,  analogous  to  NH^  -|-  HO  in  the  salts  of  ammonia. 
If  sulphate  of  ammonia  be  NHg,HO  -f-  SO^  the  sulphate  of  Reiset's  base  b  will 
then  be  NH^,PtO  -j-  SO^,  the  protoxide  of  platinum  here  playing  the  part  of 
water,  or  in  other  words,  platinum  playing  the  part  of  hydrogen,  a  substitution 
far  from  unnatural  or  improbable.     Again,  if  we  consider  the  ammoniaco-sulphate 


2NH  ^ 

of  copper  to  be    ^  o^  v  "^^  ^^3'  ^^^^  ^^^  sulphate  of  Reiset's  base  a  will  be 

>  -f-  SOg  where  platinum  replaces  copper,  also  a  not  improbable  substi- 


2NH3 
PtO 

tution.     Reiset  is  disposed  to  adopt  this  view. 

The  chloride  of  Gros's  radical,  PtClN  H^  -f-  CI,  may  be  viewed  as  a  com- 
pound of  bichloride  of  platinum  with  ammonia,  PtCl^  -f  2NH  ,  and  there  is 
even  reason  to  think  that  compounds  of  that  radical  may  be  obtained  from  the 
solution  of  bichloride  of  platinum  in  ammonia. 

From  the  above  remarks  it  will  appear  that  every  probable  view  which  can  be 
taken  of  these  very  interesting  bases  connects  them  with  amide,  ammonia,  or 
ammonium,  and  it  is  for  this  reason  that  they  have  been  treated  of  in  this  sec- 
tion. Many  pages  might  be  filled  with  details  concerning  them:  but  we  have 
here  only  indicated  those  points  which  will  help  to  elucidate  the  constitution  of 
the  vegetable  alkalies. 

That  important  class  of  compounds  not  only  contains  nitrogen,  as  an  essential 
element,  but  exhibits  the  same  analogy  with  ammonia  which  we  have  seen  to 
exist  in  the  compound  platinum  bases.  Moreover,  like  these  bases,  the  alka- 
loids do  not  contain  ammonia  as  such  ,•  and  the  probability  is  very  great  that  their 
constitution  is  analogous  to  that  of  the  bases  now  described. 

II.  Carbonic  Oxide  (as  a  Radical) ;  C2O2=28'106. 

Syn. :  Oralyle. — There  is  good  reason  to  believe  that  the  radical  of  oxalic 
acid  is  formed  of  2  eq.  of  carbonic  oxide.     It  has  long  been  known  that  carbonic 


OXALIC  ACID.  549 

oxide,  in  the  sun's  light,  combines  with  chlorine  to  form  phosgene  gas  or  chlo- 
Toearbonic  acid,  CO, CI  or  C)202,Cl2.  This  compound  may  be  viewed  as  the 
chloride  of  the  radical  C^O^,  or  as  carbonic  acid,  in  which  I  eq.  of  oxygen  is 

replaced  by  chlorine,  C  ^  p,  corresponding  to  C  <^  orCO^.  But  the  exist- 
ence of  this  radical  is  more  securely  inferred  from  the  combinations  it  forms 
with  oxygen,  potassium,  and  amide. 

CARBONIC  OXIDE  AND  OXYGEN. 
1.  Oxalic  Acid  (Cp^  0  +  HO,  or  C204,H=44-132. 

-  This  acid  occurs  in  nature,  generally  in  the  form  of  an  acid  oxalate  of  potash 
in  certain  vegetable  juices,  such  as  that  of  oxaiis  acetosella,  also  as  oxalate  of 
lime  in  many  lichens.  It  is  formed  artificially  by  the  action  of  nitric  acid  on 
sugar,  starch,  and  many  other  organic  compounds ;  also  by  the  action  of  hyper- 
manganate  of  potash  on  sugar,  &c. 

To  prepare  it,  one  part  of  pure  starch  is  gently  heated  with  8  parts  of  nitric 
acid,  sp.  gr.  1*20  or  1'25.  A  very  energetic  reaction  ensues,  and  much  nitrous 
acid  is  disengaged  ;  when  this  slackens,  heat  is  applied,  and  continued  till  no 
more  red  vapours  appear,  when  the  liquid,  if  sufficiently  evaporated,  deposits,  on 
cooling,  a  large  quantity  of  crystals  of  hydrated  oxalic  acid.  These  are  dried 
on  a  porous  tile,  to  remove  the  mother  liquor  which  contains  much  free  nitric 
acid,  saccharic  acid,  and  other  products.  The  dried  crystals  being  dissolved  in 
a  little  hot  water,  the  solution,  on  cooling,  deposits  pure  oxalic  acid  in  four- 
sided  prisms,  which  are  colourless,  very  acid,  very  soluble  in  hot  water,  mode- 
rately so  in  cold  water.  These  crystals  contain  3  eq.  of  water  of  crystallization, 
G ^0^,110  -}-  3  aq.  When  sharply  heated,  a  part  sublimes  as  dry  acid,  C^O^, 
HO.  Oxalic  acid  is  destroyed  by  heat  without  blackening,  which  seems  to ' 
distinguish  it  from  most  other  organic  acids. 

It  is  very  poisonous,  and  is  the  cause  of  many  fatal  accidents  from  its  simi-  ' 
larity  to  Epsom  salts,  from  which,  however,  it  is  easily  distinguished  by  its  very 
sour  taste.  The  best  antidote  is  prepared  chalk  administered  in  water,  which 
forms  the  insoluble  and  inert  oxalate  of  lime.  It  is  easily  detected  by  forming 
with  lime  water,  or  a  soluble  salt  of  lime,  if  no  free  acid  be  present,  the  very 
insoluble  oxalate  of  lime,  which  when  dried  and  heated  to  low  redness  is  con- 
verted, without  blackening,  into  carbonate  of  lime. 

When  oxalic  acid,  or  any  of  its  salts,  is  heated  with  oil  of  vitriol  in  excess,  a 
brisk  effervescence  takes  place,  and  the  gas  given  off  is  a  mixture  of  equal 
volumes  of  carbonic  acid  and  carbonic  oxide.  This  character  furnishes  another 
good  means  of  recognizing  oxalic  acid.  The  reaction  is  very  simple,  for  C^O^, 
ttO  t  H0,S03  =  ("^^3  +  ^^^)  +  ^O  +  ^^2-  '^^^  sulphuric  acid  seizes  the 
whole  of  the  water,  and  the  anhydrous  oxalic  acid,  C^O^,  cannot  exist  in  the 
separate  state. 

When  the  oxalates  of  certain  protoxides,  as  those  of  cobalt  and  nickel,  are 
heated  in  close  vessels,  the  metal  is  left;  carbonic  acid  being  given  off;  CoO, 
GgOg  =  Co  -}-  200  .  Other  oxalates,  as  that  of  manganese,  give  off  carbonic 
acid  and  carbonic  oxide,  leaving  the  protoxide  of  the  metal,  MnO,C20^  =  MnO 

-v-cotco^. 


550  OXAMIDE. 

Oxalic  acid  forms  salts  with  bases,  many  of  which  are  insoluble.    The  inso- 
lubility of  the  oxalate  of  lime  renders  oxalic  acid  useful  as  a  test  for  lime,  and  as 
a  means  of  separating  it,  and  determining  its  quantity,  in  analysis.     As  a  test, 
it  is  commonly  used  in  the  form  of  oxalate  of  ammonia.     It  can  only  delect  lime  j 
in  neutral  or  alkaline  fluids,  the  oxalate  of  lime  being  soluble  in  free  acids.  *l 

The  formation  of  oxalic  acid  by  the  action  of  oxidizing  agents  on  organic 
matters,  is  a  partial  oxidation  of  their  carbon ;  when  that  oxidation  is  complete, 
carbonic  acid  is  the  result.  The  action  of  nitric  acid  on  starch  or  sugar  is  com- 
plicated, and  not  so  well  understood  as  to  admit  of  being  expressed  in  the  form 
of  an  equation  ;  but  the  oxidation  of  sugar  by  permanganate  of  potash  is  very 
simple,  and  is  thus  represented,  Cj^H^^O^^  t  6  (K0,Mn20^)  =  6  (K0,C203) 
-I-  lOHO  ■+■  ISMnO^ ;  that  is,  1  eq.  of  anhydrous  sugar,  with  G  eq.  of  the  perman- 
ganate, produces  6  eq.  of  oxalate  of  patash,  10  eq.  of  water,  and  12  eq.  of  per- 
oxide of  manganese. 

The  most  important  oxalates  are  those  of  potash,  lime  and  ammonia.  There 
are  three  oxalates  of  potash;  th^  neutral  oxalate,  K0,C20^-+-  aq. ;  the  binoxa- 
late,  KO,C203  4-HO,C20^  +  2  aq. ;  and  the  qnadroxalate,  KOjC^Og-h  3  (HO, 
CgO^)  -\-  4  aq.  The  oxalate  of  lime  is  CaO,C203  +  2  aq.  The  oxalate  of 
silver  AgO,C  O  ,  detonates  when  heated,  yielding,  like  several  other  oxalates  of 
the  noble  metals,  carbonic  acid,  and  the  metal.  The  oxalate  of  ammonia,  NH^O, 
C  O  -|-aq.  is  much  used  as  a  test.  It  crystallizes  very  readily.  When  heated, 
it  gives  rise  to  a  very  remarkable  compound,  namely,  oxamide,  which  is  the  typo 
of  a  class.    We  shall  here  consider  it. 

Oxamide,  CjH^'SOf^Cp    -hNH2=44-296. 

When  oxalate  of  ammonia  is  heated  in  a  retort,  it  gives  rise  to  a  variety  of  pro- 
ducts, and  among  these,  to  a  white  crystalline  powder,  insoluble  in  cold  water, 
which  is  oxamide.  It  may  be  formed  far  more  abundantly  by  the  action  of 
ammonia  in  solution  on  oxalate  of  oxide  of  ethyle,  or  oxalic  ether.  (See  oxalate 
of  oxide  of  ethyle.) 

The  remarkable  character  of  oxamide  is,  that  while  itself  neutral,  and  certainly 
containing  neither  oxalic  acid  nor  ammonia,  it  is  easily  converted  into  oxalic  acid 
and  ammonia  by  boiling  it  either  with  strong  acids  or  strong  alkalies.  In  this 
reaction,  the  elements  of  1  eq.  of  water  are  shared  between  the  constituents  of 
oxamide,  that  is,  between  the  radical  CO  and  the  radical  amide,  NH  ;  for 
oxamide  is  nothing  more  than  oxalate  of  ammonia,  NH^0,C20g,  minus  2  eq.  of 
water,  or  NH2,C^02.  A  very  small  portion  of  an  acid,  for  example,  is  sufficient 
to  produce  this  eflTect  on  a  large  quantity  of  oxamide ;  for  if  the  acid  we  add  be 
neutralized  by  the  ammonia  produced,  a  corresponding  quantity  of  oxalic  acid 
is  set  free,  and  acts  as  any  other  acid  would  do.  A  minute  proportion  of  an 
acid,  therefore,  here,  appears  to  exert  its  influence  on  an  unlimited  portion  of 
oxamide,  but  this  is  only  in  appearance.  The  fact,  however,  that  the  presence 
of  a  little  oxalic  acid  enables  oxamide  to  decompose  water  and  to  produce  am- 
monia and  oxalic  acid,  is  very  important,  and  tends  to  throw  light  on  many 
similar  changes  in  the  organic  kingdom,  where  the  agency  is  not  so  apparent. 

But  oxamide  is  not  the  only  product  of  the  action  of  heat  on  oxalate  of  am- 
monia; for,  besides  carbonic  acid,  carbonic  oxide,  hydrocyanic  acid,  water, 
ammonia,  and  oxamide,  all  of  which  are  or  may  be  formed,  there  is  produced, 
when  the  heat  is  so  regulated  that  a  honey  yellow  residue  remains  in  the  retort. 


CARBONIC  ACID  AND  CHLORINE.  551 

a  new  acid,  called  oxamic  acid,  which  constitutes  that  residue.  It  is  mixed  with 
a  little  oxamide,  which  is,  however,  left  undissolved  by  hot  water,  in  which  the 
oxamic  acid  dissolves. 

Oxamic  acid  forms  soluble  and  crystallizable  salts  with  lime,  baryta,  ammo- 
nia and  oxide  of  silver.  Acids  precipitate  it  from  the  saturated  solution  of  its 
compound  with  ammonia,  as  a  white  sparingly  soluble  powder,  the  composition 
of  which  is  C  H  NO  -+-aq.  Although  an  acid,  this  compound  exhibits  all  the 
relations  of  a  compound  of  amide  or  amidogen,  being  converted  by  the  action  of 
alkalies  at  a  high  temperature  into  oxalic  acid  and  ammonia.  It  differs,  however, 
from  oxamide  in  yielding  2  eq.  oxalic  acid  and  1  eq.  ammonia ;  for  1  eq.  of 
oxamic  acid,  plus  3  eq.  of  water,  contains  the  elements  of  binoxalate  of  ammo- 
nia. C^O^,NH2+3HO=(HO,C203)  +  (NH^O,C203).  This  also  explains  its 
production ; — 

for  2  eq.  of  Oxalate  of  Ammonia  2  (NH4O,  C203)=C4H8N203 

when  acted  on  by  heat,  • 

Yield  1  eq.  ammonia  =    H3N 

3  eq.  water  =    Hj    O3 

1  eq.  anhydrous  oxamic  acid     =C4H2N  O5 


Together       .        .        .        C4H8N2O8 

Oxamic  acid  is  certainly  a  very  remarkable  compound,  being  an  acid  amidide, 
or  at  least  admitting  of  being  so  regarded,  C^0^,NH2.  There  are  a  few  other 
examples  of  acid  amidides,  and  we  shall  soon  come  to  one,  namely,  euchronic 
fictd,  which  is  highly  analogous  to  oxamic  acid  :  being  formed  by  the  action  of 
heat  on  mellitate  of  ammonia,  along  with  a  neutral  amidide^  paramide^  similar  to 
oxamide ;  and  as  oxamic  acid  yields  acid  oxalate,  so  euchronic  acid  yields  acid 
mellitate  of  ammonia  when  long  boiled  with  water.  Cyanic  acid  may  also  be  con- 
sidered as,  in  some  sense,  an  acid  amidide;  for  C^NOiHO  =  C^O^jNH  ;  and 
C202,NH-f-2HO=NH3,  200^;  or,  as  is  well  known,  cyanic  acid,  in  contact 
with  water,  produces  bicarbonate  of  ammonia. 

Oxamic  acid  may  further  be  viewed  as  a  coupled  oxalic  acid,  the  adjunct  in 
which  is  oxamide  :  for  C^O^NH^  is  equal  to  C203-}-C202,NH2.  Berzelius  adopts 
this  view,  and  is,  generally  speaking,  favourable  to  the  idea  of  coupled  acids. 

By  the  action  of  chlorocarbonic  acid  on  alcohol,  an  ether  is  formed,  which, 
with  ammonia,  yields  a  very  beautifully  crystallizable  compound,  long  known  as 
oxamethan,  which  is  nothing  else  than  oxamate  of  oxide  of  ethyle  (see  salts  of 
oxide  of  ethyle).  Its  composition  is  CgH^N0g=  (C^HJO  +  C^H^NO^.  A 
similar  compound  exists  with  oxide  of  raethyle,  and  was  formerly  called  oxame- 
thylan. 

2.  Carbonic  Acid.    C02=22. 

This  acid  has  been  already  described,  and  it  is  introduced  here  merely  because 
it  is  formed  by  the  complete  oxidation  of  carbonic  oxide ;  0^0^-1-02=2002. 

CARBONIC  ACID  AND  CHLORINE. 

Chlorocarbonic  Acid.     C  j^j  or  C04-Cl=49-5 

Syn.  Phosgene  gas.     When  equal  volumes  of  chlorine  and  carbonic  oxide  are 


5$Z  CROCONIC  ACID. 

mixed  and  exposed  to  the  snn's  rays,  they  combine  to  form  a  colourless  gas,  of 
a  pungent  disagreeable  smell,  which  acts  strongly  on  the  eyes.  Sp.  gr.  of  the  gas 
3*399.  When  dissolved  in  water  it  decomposes  it,  producing  carbonic  and  hy- 
diochloric  acids.  With  alcohol  and  pyroxilic  spirit  it  produces  very  remarkable 
compound  ethers,  to  be  hereafter  described. 

With  ammonia,  this  acid  forms  sal-ammoniac,  and  a  white  volatile  crystalline 
substance,  which  is  carbamide,  CO,NH  ,  produced  as  follows: — C0,Cl-t2NH 
=NH^,CltC0,NH2.  ' 

Under  the  influence  of  the  mineral  acids,  carbamide  yields  ammonia  and  car- 
bonic acid,  CO,NH2tHO=C02tNH3. 

The  chlorocarbonic  acid  may  be  considered  as  carbonic  acid  C  -j-  5  „    in 

which  half  the  oxygen  has  been  replaced  by  its  equivalent  of  chlorine,  C  + 
O 


\ 


CI. 


CARBONIC  OXIDE  WITH  POTASSIUM. 
Oxycarburet  of  Potassium  :    Rhodizonic  Acid. 

When  potassium  is  heated  in  carbonic  oxide  gas,  combination  takes  place,  and 
a  dark  olive  powder  is  formed,  composed  of  carbonic  oxide  and  potassium,  in  the 
proportion  of  C^O^-f-K^,  or  7CO-|-3K.  This  substance  is  formed  in  large  quan- 
tity in  the  preparation  of  potassium  from  carl)onate  of  potash  and  charcoal,  and 
is  the  source  of  great  loss  as  well  as  inconvenience.  No  such  compound  is 
formed  with  sodium,  for  which  reason  that  metal  may  be  more  cheaply  prepared 
than  potassium. 

The  oxycarburet  of  potassium,  if  heated  in  the  air,  takes  fire,  but  if  exposed 
to  moist  air,  or  placed  in  water,  it  is  converted  into  the  potash  salt  of  a  new  acid, 
rhodizonic  acid,  hydrogen  being  disengaged,  C^O  K  -|-3H0=C  0  ,3K0  -\-  H  , 
As  this  hydrogen,  however,  is  not  pure,  but  contains  carbon,  the  reaction  is  pro- 
bably more  complicated. 

All  the  salts  of  rhodizonic  acid  are  deep  red,  and  when  in  crystals,  reflect  a 
green  light.  The  rhodizonate  of  potash,  when  heated  in  solution  in  water,  un- 
dergoes'a  very  remaikable  change,  yielding  free  potash,  oxalate  of  potash  and 
croconate  of  potash,  the  latter  being  the  salt  of  another  new  acid  containing  the 
same  elements  as  rhodizonic  acid  in  different  proportions;  this  salt  is  C  O  ,K0 
orC^O^K.  The  composition  of  rhodizonate  of  potash  explains  this  reaction  per- 
fectly, for  C^O^t3KO=KOtKO,C^03tKO,C^O^. 

Croconic  A«id.    C504,HO  T  or  CjOgjH. 

This  acid  is  named  from  the  yellow  colour  of  its  salts.  It  is  obtained  from  the 
croconate  of  potash,  prepared  as  above,  by  the  action  of  fluosilicic  acid,  which 
separates  the  potash.  The  acid  is  yellow,  soluble  in  water  and  alcohol,  and  crys- 
tallizes easily.     All  its  salts  are  likewise  yellow. 

The  rhodizonic  acid,  C^0^,3H0,  may  be  viewed  as  a  tribasic  hydrogen  acid, 
C  OjQ,H^;  the  croconic  acid  may  also  be  viewed  both  as  a  hydrated  oxygen  acid, 
CjO^,HO,  and  as  a  hydrogen  acid,  C  0^,H.  In  Ibis  last  form  it  connects  itself 
with  carbonic  oxide,  as  it  may  be  SCO-fH.  The  same  remark  applies  to  another 
remarkable  acid,  containing  the  same  elements,  namely  tlie  mellitic  acid. 


ACTION  OF  HEAT  ON  MELLITATE  OF  AMMONIA.  553 

Mellitic  Acid.     C403,HO  or  C4O4H. 

This  acid  occurs,  combined  with  alumina,  in  a  very  rare  mineral,  probably  of 
organic  origin,  the  raellite  or  honey  stone.  The  acid  is  soluble,  very  sour,  and 
permanent,  not  being  altered  by  boiling  nitric  or  sulphuric  acids,  nor  by  a  heat 
of  nearly  580°.  The  general  formula  of  its  salts,  when  dried  at  212°,  is  MO,C^ 
O^H,  or  HO,C  O  M.  The  salt  of  silver,  however,  at  212°,  loses  I  eq.  of  water, 
and  is  left  as  C  O  ,AgO,  or  C  O  ,Ag.  According  to  the  latter  formula,  the 
radical  in  this  salt,  heated  to  212°,  is  a  form  of  carbonic  oxide,  C  0^=4C0. 

The  crystallized  acid  C^Og,HO,  or  C^O^H,  appears  to  unite  with  most  bases 
without  the  separation  of  water,  generally  observed  when  salts  are  formed.  And 
although  the  silver  salt  would  seem  to  contain  a  different  radical,  yet  it  yields, 
when  decomposed,  the  original  mellitic  acid. 

The  mellitate  of  silver  may  also  be  looked  on  as  oxalate  of  silver  AgOjCjOa, 
plus  2  eq.  of  carbon  in  the  acid  AgO,C403, 

The  mellitate  of  ammonia,  NH^0,C^H3,  when  heated  in  a  retort,  yields  several 
new  and  remarkable  products.  When  this  salt,  NH^,HO,C^O^=C^H^NO^  is 
heated  to  320°,  it  gives  off  ammonia  and  water,  and  there  remains  a  mixture  of 
two  new  compounds  ;  a  soluble  one  which  contains  euchronic  acid,  in  combina- 
tion with  ammonia,  and  an  insoluble  one  which  is  called  paramtde. 

Paramide  is  a  yellow  solid,  like  clay.  Its  most  remarkable  character  is  that, 
when  long  boiled  with  water,  it  is  converted  into  bimellitate  of  ammonia.  This 
is  the  character  of  an  amide,  hence  its  name.  The  composition  of  paramide  is 
CHNO^,  which  readily  explains,  both  its  formation,  and  its  conversion  into 
bimellitate  of  ammonia. 

If  from  bimellitate  of  ammonia,  NH40,C303,+HO,C403=C8H5N08 
we  subtract  4  eq.  of  water  H4   0^  <t 


there  will  remain  Paramide=C8H  NO4 

and  of  course,  when  reconverted  into  bimellitate  of  ammonia  by  long  boiling,  it 
merely  takes  up  again  these  4  eq.  of  water. 

The  soluble  compound,  euchronate  of  ammonia,  when  its  solution  is  acted  on 
by  hydrochloric  acid,  deposits  a  white  crystalline  powder,  which  is  euchronic 
acid,  Cj^gNOg,  2H0.     Its  formation  is  easily  explained,  for 

if  from  3  eq.  of  mellitate  of  ammonia=3(C4H4N04)=Ci2Hi2N30,3 
we  subtract  6  eq.  of  water  and  2  eq.  of  ammonia      =      HiaNgOg 


there  will  remain  anhydrous  euchronic  acid         =Ci2       N  Og 

We  can  now  see  that  the  action  of  heat  on  7  eq.  of  mellitate  of  ammonia  gives 
rise  to  the  following  substances  : — 


2  eq.  Paramide 

= 

C,6H2  N^Og 

1  eq,  Euchronic  Acid= 

C^      NOe 

4  eq.  Ammonia 

=: 

H,2N4 

14  eq.  Water 

H,4    0,4 

llitate  of  ammonia 

^28^28^7^28 

When  euchronic  acid  is  boiled  with  water,  it  is  dissolved  and  converted  into 
an  acid  mellitate  of  ammonia. 


554  CYANOGEN. 

1  eq.  Euchronic  Acid         =        Cy     NOg 
and  6  eq.  Water  =  Hg   Og 


Together  C^HgNO^ 


3  eq.  Mellitic  Acid  =        CjjHg   O^ 

and  1  eq.  Ammonia        =  H3N 


Together  CjjHgNOu 

Euchronic  acid  is  deoxidized  by  a  plate  of  zinc,  yielding  a  powder  of  a 'fine 
deep  blue  colour,  which  dissolves  in  ammonia  or  potash,  with  a  splendid  tint  of 
purple.  The  blue  powder  is  an  inferior  oxide  of  the  same  nitrogenized  radical, 
which,  combined  with  more  oxygen,  forms  euchronic  acid.  The  whole  subject 
of  mellitic  acid  and  euchronic  acid  is  most  interesting,  but  mellitic  acid  is  so 
rare  that  it  is  very  difficult  to  find  material  for  the  investigation.  As  mellitic 
acid,  like  succinic  acid,  is  of  organic  origin,  and  contains  only  1  eq.  of  hydrogen 
less,  and  1  eq.  of  oxygen  more  than  succinic  acid,  we  may  hope  to  be  enabled  to 
obtain  it  artificially. 

III.  Cyanogen.    C2N=Cy=26-23. 

This  very  important  compound  has  already  been  mentioned  as  a  compound  of 
carbon  and  nitrogen ;  but  we  have  now  to  consider  it  in  its  far  more  important 
character  of  a  compound  radical.  In  fact,  it  was  the  first  compound  radical  dis- 
covered, and  the  discovery  of  cyanogen  by  Gay-Lussac  has  proved  more  fertile 
in  results  than  any  other  discovery  yet  made  in  Organic  Chemistry.  As  cya- 
nogen acts  exactly  like  an  element,  we  shall  repiesent  it  by  the  symbol  Cy, 
rather  than  by  C^N ;  using  the  latter  only  where  the  elements  of  cyanogen,  and 
not  itself,  enter  into  changes  and  reactions. 

Cyanogen  is  formed  when  animal  matter  is  ignited  along  with  carbonate  of 
potash  in  close  or  covered  iron  vessels.  The  cyanogen  being  a  gas,  and  com- 
bustible, would  be  dissipated,  and  in  open  vessels  burned,  were  it  not  that  it 
enters  into  combination  with  potassium  derived  from  the  carbonate,  forming 
cyanide  of  potassium,  KCy,  a  salt  not  altered  by  a  red-heat  in  close  vessels.  As 
this  salt,  however,  is  decomposed  by  the  action  of  water,  yielding  carbonate  of 
potash  and  of  ammonia,  hydrogen  being  set  free,  (K,C2N  +  5HO  =  KO,C02  -f- 
NH^,HO,CO  -f  H),  it  is  necessary  to  convert  the  cyanide  of  potassium  into  a 
more  stable  compound.  This  is  effected  by  the  addition  of  iron,  or  of  sulphuret 
of  iron,  the  latter  of  which  is  formed  by  the  mutual  action  of  the  sulphate  of 
potash  (always  present  in  potashes),  carbon,  and  the  iron  of  the  vessel.  The 
iron,  or  its  sulphuret,  is  readily  dissolved  by  the  aqueous  solution  of  cyanide  of 
potassium,  yielding  cyanide  of  iron,  FeCy,  and  sulphuret  of  potassium  KS,  for 
KCy  -\-  FeS  =  FeCy -I- KS.  The  elements  of  the  cyanide  of  iron  then  form, 
with  cyanide  of  potassium,  the  very  permanent  double  cyanide,  well-known  as 
prussiate  of  potash,  properly  ferrocyanide  of  potassium,  which  forms  large  and 
pure,  transparent,  yellow  crystals.  From  this  compound,  all  the  other  com- 
pounds of  cyanogen,  and  cyanogen  itself,  are  prepared.  Its  empirical  formula  is 
FeCy,2KCy  -|-  3H0,  or  FeK^Cy^  -f-  3H0.  At  212°  it  loses  all  the  water,  and 
then  contains  only  iron,  potassium,  and  cyanogen  Fe  -f  K^-j-Cy^.  It  may  be 
conveniently  viewed  as  a  compound  of  cyanide  of  iron  with  cyanide  of  potas- 
sium ;  but  we  shall  see  hereafter  that  its  rational  formula  is  probably  very  dif- 


HYDROCYANIC  ACID. 


555 


ferent,  and  that  it  'is  a  compound  of  potassium  with  a  new  radical,  ferrocya- 
nogen. 

Cyanogen  gas  is  best  prepared  by  heating  dried  bicyanide  of  mercury,  when 
the  gas  is  given  off,  a  part  however,  assuming  the  solid  form,  and  remaining 
behind  as  a  black  matter,  paracyanogen,  isonicric  with  cyanogen ;  or  by  heating 
a  mixture  of  6  parts  dried  ferrocyanide  of  potassium,  and  9  parts  bichloride  of 
mercury,  when  chloride  of  potassium  is  formed  by  the  action  of  the  bichloride 
on  the  cyanide  of  potassium  of  the  ferrocyanide,  and  the  cyanide  of  mercury,  if 
formed,  is  at  once  decomposed  by  the  heat.  reCy,2KCy  -f-  }ioC]^=  FeCy, 
2KC1  -|-  Hg+  Cy^.  The  cyanide  of  iron  is  not  altered.  The  gas  may  be  col- 
lected over  mercury,  but  is  absorbed  by  water,  with  which  it  produces  the 
various  changes  which  have  been  minutely  explained  at  p.  540.  It  has  a 
very  pungent  and  peculiar  smell,  is  colourless  and  transparent ;  and  may  be 
liquefied  by  a  pressure  of  about  4  atmospheres.  It  is  combustible  and  bums 
with  a  beautiful  pink  or  purplish  flame. 

Cyanogen  forms  with  hydrogen  an  acid,  the  hydrocyanic,  HCy ;  with  oxygen 
and  the  elements  of  water,  three  acids,  CyO,HO  ;  Cy202,2HO  :  and  Cy^O^, 
3H0  ;  of  which  the  first  is  cyanic,  the  second  fulminic,  and  the  third  is  cyanuric 
acid.  With  chlorine,  &c.  it  combines  ;  with  sulphur  it  forms  a  new  radical 
CyS^,  sulphocyanogen ;  and  with  metals  it  forms  salts,  perfectly  analogous  with 
chlorides,  such  as  KCy,FeCy,AgCy,HgCy2,  &c.  In  short  it  plays  exactly  the 
part  of  a  simple  radical,  and  were  it  not  easily  decomposable,  we  should  at  once 
class  it  with  chlorine  as  an  element. 


TABLE   OF   COMPOUNDS. 

Hydrocyanic  Acid CyH, 

Cyanic  Acid 

CyO,HO. 

Urea                .... 

CyO,HO,NH3. 

Fulminic  Acid 

.        CyA,2H0. 

Cyanuric  Acid 

Cy303,3HO. 

Mellone           .... 

CysN. 

Chloride  of  Cyanogen,  {gaseous) 

.        CyCl. 

Chloride             "            (solid) 

.             CygCIg 

Bromide             « 

CyBr. 

Iodide                 " 

Cyl. 

Bisulphur^t        " 

.        CyS^. 

Cyanide  of  Potassium     . 

CyK.  fee,  &c. 

CYANOGEN  AND  HYDROGEN. 
Hydrocyanic  or  Prussic  Acid.    HCy  =  27*23 

This  acid  may  be  obtained  by  a  great  variety  of  processes  ;  but  the  easiest, 
most  economical,  and  most  certain,  is  to  act  on  the  ferrocyanide  of  potassium 
with  diluted  sulphuric  acid.  The  process  requires  to  be  slightly  modified, 
according  as  our  object  is  to  prepare  the  dry  or  anhydrous  acid,  or  the  diluted 
aqueous  solution  of  it  used  in  medicine. 

1.  Anhydrous  Acid. — To  prepare  this  acid,  15  parts  of  powdered  ferrocyanide 
are  to  be  distilled  at  a  gentle  heat  with  a  mixture  of  9  parts  of  oil  of  vitriol,  and 
9  of  water,  and  the  product  is  to  be  received  in  a  convenient  receiver  placed  in 
a  freezing  mixture,  and  containing  5  parts  of  chloride  of  calcium  in  small  lumps. 


556 


HYDROCYANIC  ACID. 


As  soon  as  liquid  enough  has  distilled  to  cover  the  chloride,  the  distillation  is 
stopped,  and  the  hydrocyanic  acid,  deprived  of  water  by  the  chloride  of  calcium, 
is  to  be  decanted  into  a  dry  and  well-stopped  bottle.  It  may  also  be  obtained  by 
distilling,  under  similar  circumstances,  cyanide  of  potassium  with  dilute  sul- 
phuric acid.  In  both  cases,  the  acid  is  formed  by  the  reaction  of  sulphuric  acid 
on  cyanide  of  potassium,  or  its  elements.  KCy -f- H,SO^  =  K,SO^+ HCy. 
Dry  hydrocyanic  acid  is  a  limpid  and  colourless  liquid,  of  sp.  gr.  0*6967  at  66° ; 
at  59°  it  becomes  a  fibrous  mass,  in  consequence  of  the  presence  of  a  trace  of 
water;  and  at  80°  it  boils;  the  density  of  its  vapour  is  0  9476.  It  is  inflam- 
mable, and  has  a  very  peculiar  and  disagreeable  smell  and  taste.  It  is  the  most 
energetic  poison  known,  one  drop  introduced  into  the  mouth  being  sufficient  to 
destroy  an  animal  of  considerable  size.  When  pure  it  is  soon  spontaneously 
decomposed,  depositing  a  dark  brown  solid  ;  a  trace  of  sulphuric  acid  causes  it 
to  keep  perfectly.  When  in  contact  with  the  strong  mineral  acids  and  water, 
it  is  decomposed,  being  converted  into  ammonia  and  formic  acid;  H,C2N4- 
4H0  =  NH3,H0  +  CJ^HOg. 

2.  Medicinal  or  diluted  Hydrocyanic  Acid. — This  may  be  prepared  by  simply 
diluting  the  anhydrous  acid  with  the  required  proportion  of  water,  adding,  for 
example,  97  grains  of  water  to  3  of  the  acid,  to  obtain  an  acid  of  3  per  cent. ; 
which  is  about  the  average  strength  used  in  medicine.  In  round  numbers,  to  1 
part,  hy  weighty  of  dry  acid,  32|  parts  of  water,  by  weight,  are  to  be  added;  or, 
to  1  volume  of  anhydrous  acid,  22|  volumes  of  water.  But  as  it  is  troublesome 
to  prepare  the  anhydrous  acid,  it  is  best  to  distil  2  parts  of  ferrocyanide,  with  I 
of  sulphuric  acid  and  2  of  water,  to  dryness  in  a  chloride  of  calcium  bath,  con- 
densing in  a  Liebig's  apparatus, 


in  the  receiver  of  which  2  more  parts  of  water  are  placed.  By  this  means  we 
obtain  4^  parts  of  an  acid,  not  anhydrous,  but  far  too  strong  for  use,  containing 
from  15  to  20  per  cent,  of  dry  acid.  Its  precise  strength  is  ascertained,  and  it 
is  reduced  to  the  standard  strength,  in  the  following  simple  manner : — 

Any  convenient  quantity,  say  50  or  100  grains,  is  weighed  out,  being  added 
to  a  counterpoised  vessel  containing  about  2  drachms  of  nitrate  of  silver,  dis- 
solved in  2  or  3  ounces  of  water.  Let  us  suppose  that  we  have  dropped  into 
this  vessel  70  grains  of  our  acid.  This  will  be  entirely  converted  into  cyanide 
of  silver,  but  we  make  sure  by  testing  with  a  drop  of  nitrate  of  silver.  The  prp- 
cipitate  is  then  collected  on  a  filter,  well  washed,  dried  at  212°  on  a  weighed 


HYDROCYANIC  ACID.  557 

filter,  and  the  increase  in  weight  of  the  filter  gives  the  weight  of  the  cyanide  of 
silver  formed.  Now  this  cyanide  is  formed  as  follows;  HCy  +  (AgO,NO  ) 
=  AgCy-h(HO,NO^.)  Therefore,  1  eq.  of  hydrocyanic  acid,  HCy  ==  27-23 
produces  1  eq.  cyanide  of  silver  AgCy  =  134-54  ;  or  1  grain  of  anhydrous  hydro- 
cyanic acid  will  yield  almost  exactly  5  grains  of  cyanide  of  silver;  for  2723: 
134  54:  :  1  :  4*94.  "We  may,  therefore,  safely  assume  that  the  weight  of  the 
cyanide  of  silver,  divided  by  5,  gives  the  weight  of  anhydrous  acid  present  with 
sufficient  accuracy  for  all  practical  purposes.  Now,  we  have  used  70  grains  of 
our  dilute  acid,  the  strength  of  which  we  wish  to  know.  Let  us  suppose  that 
our  filter  weighs,  when  empty,  20  grains,  and  with  the  cyanide  of  silver,  dried 
at  212°  till  it  ceases  to  lose  weight,  100  grains.  The  difference,  or  80  grains,  is 
the  weight  of  cyanide  of  silver  obtained  from  70  grains  of  our  acid.  Dividing 
this  by  5,  we  have  16  grains  as  the  weight  of  anhydrous  acid  contained  in  the 
70  grains,  and  consequently  combined  with  54  of  water. 
Now,  if  we  wish  to  state  the  per  centage  of  this  acid,  we  obtain  it  by  the  cal- 

16x100 
culation,  70  :  16  :  :  100  :  x,  and  x= — —  =22'85,  so  that  our  acid  con- 
tains 22*85  per  cent,  of  anhydrous  acid.  But  if  our  only  object  be  to  reduce  the 
acid  to  a  standard  strength,  say  that  of  3  per  cent.,  this  last  calculation  is  unne- 
cessary, and  we  can  proceed  as  follows :  acid  of  3  per  cent,  contains  3  grs.  of 
dry  acid  and  97  of  water;  therefore,  to  find  how   much  water  is  to  be  added  to  16 

97X16 

grs.  of  anhydrous  acid,  3  :  97  :  :  16  :  x,  and  x= =  517'3    grains    of 

o 

water,  which  must  be  added  to  16  grs.  of  anhydrous  acid,  to  bring  it  to  the 
same  strength.  But  our  70  grains  of  acid  contain  already,  with  the  16  of  anhy- 
drous acid,  54  grains  of  water,  consequently  we  have  only  to  add  to  these  70 
grains  5173  —  54  =  4633  grains  of  water,  and  the  same  quantity  of  water  for 
every  70  grains  of  the  same  acid.  Of  course,  it  is  easy  to  calculate  the  water 
necessary  for  1  or  more  ounces  of  the  acid,  when  we  have  once  found  it  for  any 
given  quantity.  I  have  here  supposed  70  grains,  but  with  50  or  100  the  calcu- 
tion  is  easier,  and  with  a  drachm  by  weight  (60  grains),  we  have  simple  data 
for  calculating  how  much  water  is  required  for  any  number  of  ounces  or  drachms 
of  acid. 

This  beautiful  and  simple  method  of  preparing  the  medicinal  hydrocyanic 
acid,  and  ascertaining  its  precise  strength,  has  been  minutely  described,  because 
of  its  practical  importance.  It  is  so  simple  an  operation,  that  any  one  may  very 
soon  learn  to  ascertain  the  strength  of  hydrocyanic  acid,  and  it  is  very  exact. 
Besides,  no  other  method  of  obtaining  a  medicinal  acid  of  uniform  strength 
ought  to  be  trusted  to ;  and  we  ought  never  to  attempt  to  obtain  the  acid  of  the 
standard  strength  by  distillation,  although  many  methods  are  given  for  this.  I 
have  never  seen  any  one  of  these  yield  twice  the  same  result ;  whereas  by  the 
above  method  we  can  prepare  acid  of  exactly  the  same  strength  any  number  of 
times,  and  the  acid  prepared  from  the  ferrocyanide,  by  sulphuric  acid,  keeps  per- 
fectly well.  Of  course,  when  we  have  added  the  calculated  quantity  of  water  to 
reduce  the  acid,  it  is  proper  to  ascertain  its  strength  once  more,  to  make  sure  that 
we  have  made  no  error  in  our  calculation.  If  it  be  acid  of  3  per  cent.,  it  will 
yield  15  grains  of  cyanide  of  silver  from  100  of  acid. 

There  are  two  other  methods  which  deserve  to  be  mentioned,  aS;  with  pure 
materials  and  careful  manipulation,  they  yield,  in  a  few  minutes,  a  standard  acid. 
The  first  is  that  of  Dr.  Clarke,  who  adds  to  1  eq.  cyanide  of  potassium  dissolved 


558  CYANOGEN  AND  OXYGEN. 

in  water,  2  eq.  tartaric  acid,  which  separates  the  potassium  as  cream  of  tartar, 
while  diluted  hydrocyanic  acid  remains  dissolved.  For  every  100  ^rs.  of  water, 
7^  grs.  of  cyanide  of  potassium  and  16^  of  crystallized  tartaric  acid,  are 
required.  This  is  an  excellent  extemporaneous  process,  if  we  have  pure  cyanide 
of  potassium,  but  that  salt  does  not  keep  well,  and  even  in  its  preparation  it  is 
apt  to  be  decomposed,  at  least,  partially.  It  is,  besides,  an  expensive  salt.  The 
other  is  the  process  of  Everett,  who  suspends  cyanide  of  silver  in  water,  and  adds 
an  equivalent  of  hydrochloric  acid.  AgCy  •+•  HCl  =  Ag CI  -f-  HCy.  This  is 
also  a  good  extemporaneous  process,  15  grs.  of  AgCy  being  used  for  every  100 
of  water,  and  4  grs.  of  dry  HCl,  that  is,  about  12  grs.  of  acid  sp.  gr.  1*21, 
being  added.  This  process  is  also  expensive,  although  the  silver  is  not  lost; 
but  the  chief  objection  is,  that  it  is  difficult  to  add  the  precise  amount  of  hydro- 
chloric acid  which  is  necessary,  and  that  an  excess  causes,  pro  tanio,  a  conversion 
of  the  hydrocyanic  acid  into  formic  acid  and  ammonia. 

The  medicinal  acid  has  the  smell  and  taste  of  the  anhydrous,  and  is  very  poi- 
sonous, the  average  dose  safe  for  an  adult  being  1  to  2  drops  in  a  glass  of  water. 
It  is  as  much  used  as  a  sedative  and  anodyne,  but,  unless  its  strength  and  dose 
be  perfectly  known,  it  is  a  dangerous  remedy.  Fatal  accidents  have  occurred 
from  prescriptions,  found,  after  experience,  to  act  favourably,  being  made  up  in 
another  place,  or  by  the  same  druggist  with  afresh  stock;  this  fresh  stock  being 
exactly  of  the  standard  strength,  while  the  previous  acid  had  lost  so  much  by 
keeping  that  the  dose  has  been  of  necessity  increased.  There,  danger  actually 
arose  from  a  too  weak  acid  being  used.  Hence  the  necessity  for  the  great  exact- 
ness, for  which  rules  are  given  above.  In  cases  of  poisoning  by  this  acid,  now 
unfortunately  of  very  frequent  occurrence,  there  is  seldom  time  to  administsr  an 
antidote;  but  when  life  is  not  extinct,  we  may  confidently  rely  on  the  antidotes 
we  possess.  The  best  is  the  administration  of  two  solutions,  one  of  mixed  sul- 
phate of  proto:^ide  and  peroxide  of  iron,  and  the  other  of  carbonate  of  potash,  as  , 
recommended  by  Messrs.  Smith,  Edinburgh,*  by  which  the  acid  still  in  the 
stomach  is  rendered  insoluble,  being  converted  into  Prussian  blue.  The  symp- 
toms already  produced  are  best  combated  by  ammonia  inspired  from  a  sponge, 
or  taken,  diluted,  internally,  and  by  other  diffusible  stimulants ;  also  by  the  cold 
affusion. 

Hydrocyanic  acid  is  very  easily  recognized  by  its  smell,  and  by  its  forming 
Prussian  blue  if  acted  on,  in  solution,  successively,  by  proto-persulphate  of  iron, 
by  potash,  and  by  an  excess  of  hydrochloric  acid.  The  first  two  tests  form  the 
Prussian  blue,  the  last,  dissolving  the  excess  of  oxide  of  iron,  brings  the  blue 
into  view.  Any  liquid,  suspected  to  contain  hydrocyanic  acid,  ought  first  to  be 
distilled  with  the  addition  of  a  little  dilute  sulphuric  acid,  and  the  tests  applied 
to  the  first  ounce  that  comes  over.  Nitrate  of  silver  produces  a  white  cloud  of 
cyanide  of  silver,  exactly  like  the  chloride  in  appearance. 

Hydrocyanic  acid,  with  metallic  oxides,  gives  rise  to  water  and  metallic  cyan- 
ides.    HCy4-M0  =  H0-+-MCy:  or  2HCy -hM02=  2H0  +  MCy^. 

CYANOGEN  AND  OXYGEN. 
1.  Cyanic  Acid.    CyO,HO  =  CyOg,H  =  43-26. 

A  monobasic  acid ;  is  formed  when  dry  cyanide  of  potassium  is  heated  in  the 

*  See  Lancet  for  1844,  vol.  ii.  p.  41. 


CYANIC  ACID  AND  CYANATES.  559 

air,  when  oxygen  is  absorbed,  and  cyanate  of  potash  is  produced.     KCy  +  O 
=  KO,CyO  or  K,Cy02. 

When  a  stronger  acid  is  added  to  this  salt,  the  cyanic  acid  is  set  free,  but  im- 
mediately decomposes  with  water,  producing  ammonia  which  unites  with  the 
strong  acid  used,  and  carbonic  acid  which  escapes  as  gas.  C  NO,H0  4-2HO 
=  NH  +2C0  .  The  carbonic  acid  carries  with  it  a  little  cyanic  acid,  which 
forms  dense  white  vapours,  and  has  a  pungent  acid  smell  like  that  of  strong 
acetic  acid.  Under  all  circumstances,  free  cyanic  acid,  in  contact  with  water,  is 
instantly  destroyed. 

It  may,  however,  be  obtained  in  the  anhydrous  state,  according  .to  the  formula 
CyO^  +  H,  or  as  monohydrated  acid,  if  viewed  as  CyO,HO,  by  distilling  cya- 
nuric  acid,  Cy^Og  -f-  H^,  or  Cy^O^  +  3H0.  This  acid  is  isomeric  with  cyanic 
acid,  and,  when  heated,  1  eq.  cyanuric  acid  splits  up  into  3  eq.  cyanic  acid, 
which  appears  in  the  receiver  as  a  volatile,  pungent,  very  corrosive  acid  liquid. 
This  acid  only  keeps  for  a  very  short  time,  even  in  the  freezing  mixture  in  which 
it  is  condensed.  If  removed  from  the  cold,  it  soon  becomes  turbid,  then  hot, 
boils  violently  and  with  violent  shocks,  and  is  converted  into  a  solid  dense  white 
body,  like  porcelain,  quite  insoluble  and  indifferent. 

This  is  Cyamelide,  another  isomeric  compound,  containing  the  same  elements 
in  the  same  proportions,  hut  differently  arranged,  possibly  C^O^+NH;  for  it 
yields,  under  the  influence  of  water  and  strong  acids,  carbonic  acid  and  ammonia, 
(C202,NH  +  2H0  =  200^  +  NH^)  just  as  cyanic  acid  does.  When  distilled, 
it  is  reconverted  into  cyanic  acid,  another  proof  that  it  is  isomeric  with  that  acid. 

CYANATES. 

The  salts  of  cyanic  acid  are  all  distinguished  by  the  action  on  them  of  strong 
acids,  which  cause  disengagement  of  carbonic  acid,  while  ammonia  may  now  be 
detected  in  the  liquid.  The  cyanates  of  potash,  ammonia,  &c.  are  soluble,  those 
of  lead,  silver,  &c.,  insoluble. 

Cyanate  of  Potash  is  best  formed  by  the  oxidation  of  Liebig's  cyanide  of  potas- 
sium,* which  may  easily  be  eflfected  by  adding  litharge  in  proper  quantity'to  the 
melted  salt,  KCy -j- 2PbO  =  K,Cy02-|-Pb2.  The  cooled  mass  is  powdered 
and  boiled  with  alcohol  of  80  per  cent.,  which  on  cooling  deposits  pure  crystals 
of  cyanate  of  potash,  very  similar  to  chlorate  of  potash.  Or  dried  ferrocyanide 
of  potassium,  mixed  with  half  its  weight  of  peroxide  of  manganese,  may  be 
gently  heated,  spread  out  on  an  iron  plate,  when  it  burns  like  tinder,  partly  at 
the  expense  of  the  oxide  of  manganese,  partly  in  the  oxygen  of  the  air.  It  is 
well  stirred  till  every  part  has  glowed,  and  the  cold  mass  is  treated  with  alcohol 
as  above. 

Cyanate  of  potash  must  be  kept  in  sealed  tubes,  for  in  phials  occasionally 
opened  it  is  soon  changed  into  bicarbonate  of  potash,  ammonia  being  given  off. 
K,C2N02+  3H0  =  (K0^2C02)  +  NH^ :  Triturated  with  dried  oxalic  acid,  this 
salt  yields  oxalate  of  potash  and  cyamelide.  When  acetic  acid  is  added  to  a 
concentrated  freshly  made  solution  of  cyanate  of  potash,  the  latter  being  Jn 
excess,  there  is  deposited  the  acid  cyanurate  of  potash, 

CyaOelH^orCysOal^gg 
*  The  formation  of  this  salt  will  be  described  below. 


560 


CYANATE  OF  AMMONIA. 


a.  basic.  "When  dry  ammonia  and  the  vapour  of  cyanic  acid  are  mixed,  they 
form  a  light  white  solid,  which  is  a  cyanate  of  ammonia,  containing  more  ammo- 
nia than  is  required  for  a  neutral  salt.  This  salt  gives  off  ammonia  when  treated 
with  alkalies,  and  cyanic  acid  when  treated  with  sulphuric  acid.  But  if  dis- 
solved in  water,  and  the  solution  digested  and  evaporated,  it  yields  crystals, 
which,  although  containing  the  elements  of  cyanic  acid,  ammonia,  and  water, 
exhibit  neither  of  these  characters  of  a  cyanate,  but  are  found  to  possess  all  the 
properties  of  urea^  a  product  of  the  animal  system. 

b.  anomalous  cyanate  of  ammonia,  or  urea,  C2H^N202  =  (C2N0,H0,NH  ). 
This  remarkable  compound  exists  in  large  proportion  in  healthy  urine,  and  is 
extracted  from  it  by  evaporating  at  about  200°  to  a  thin  syrup,  and  adding  about 
an  equal  volume  of  colourless  nitric  acid,  sp.  gr.  1*35,  quite  free  from  nitrous 
acid,  which  forms  a  very  copious  crystallization  of  nitrate  of  urea,  while  the 
colouring  matter  is  destroyed  with  brisk  effervescence.  If  cold  be  applied,  the 
colouring  matter  resists,  and  the  nitrate  is  then  very  dark  and  very  difficult  to 
purify  ;  cold  ought  therefore,  not  to  be  used,  and  the  nitrate  of  urea  is  deposited 
nearly  white,  having  only  a  clear  ygllow  tint.  It  is  dissolved  in  water,  after 
being  recrystallized,  and  neutralized  by  potash  or  baryta.  The  whole  is  then 
gently  evaporated  to  dryness,  after  separating  as  much  nitrate  of  potash  or  of 
baryta  as  possible,  and  the  dry  mass  digested  in  alcohol,  which  dissolves  only 

•the  urea,  and  by  spontaneous  evaporation  yields  it  in  large  transparent  prismatic 
crystals.  Should  these  not  be  colourless,  the  digestion  of  their  aqueous  solution 
with  a  little  permanganate  of  potash,  which  has  no  action  on  urea,  destroys  the 
colouring  matter  entirely.  Should  an  excess  of  that  salt  be  added,  a  few  drops 
of  alcohol  will  instantly 'destroy  it,  and  the  filtered  liquor  will  yield  snow-white 
crystals  of  urea. 

But  although  urea  may  thus  be  obtained  (or  by  the  action  of  oxalic  acid  on 
the  urine,  which  forms  a  sparingly  soluble  oxalate  of  urea)  in  any  quantity  from 
urine,  it  is  found  much  easier  to  prepare  it  artificially  from  cyanate  of  ammonia 
Liebig  reoommends  the  following  process,  which  I  have  found  to  succeed  per- 
fectly. 28  parts  of  dried  ferrocyanide  of  potassium,  and  14  of  peroxide  of  ma 
ganese  are  mixed  in  powder  and  calcined,  as  above  described,  on  a  flat  iron  plate 
at  a  very  low  red  heat,  sufficient  to  keep  up  the  glow  which  takes  place.  When 
this  is  over,  the  cold  mass,  powdered,  is  acted  on  by  a  moderate  quantity 
of  cold  water,  which  dissolves  the  cyanate  of  potash.  This  is  filtered  off,  and 
set  aside.  A  fresh  portion  of  cold  water  being  added  to  the  powder,  to  wash  it, 
is  also  filtered,  and  in  this  liquid  are  now  dissolved  20A  parts  of  sulphate  of 
ammonia,  and  the  solution  is  added  to  the  first  filtered  solution  of  the  cyanate. 
A  large  quantity  of  sulphate  of  potash  is  deposited,  which  is  strained  off,  and  the 
filtered  liquid  now  containing,  with  some  sulphate  of  potash,  all  the  cyanate  of 
ammonia,  is  evaporated  to  dryness,  during  which  process  the  cyanate  of  ammonia 
is  transformed  into  urea.  The  dry  mass  is  dige^ied  in  alcohol,  which  dissolves 
only  the  urea,  and  yields  it  from  the  first  chemically  pure  and  in  any  quantity  Jf 
the  operation  be  carefull3rperformed.  Urea  thus  obtained  is  far  cheaper  than 
that  extracted  from  urine. 

The  artificial  production  of  urea  from  cyanate  of  ammonia  was  discovered  by 
"Wohler.  It  was  the  first  example  of  an  organic  product  artificially  formed, 
although  many  other  cases  are  now  known. 


Dn 

m  M 
a.l 

4 


FULMINIC  ACID.  561 

Urea  forms  four-sided  prisms,  resembling  nitre  in  appearance,  and  also  in  their 
taste,  which  is  saline  and  cooling,  exactly  like  that  of  nitre.  It  is  soluble  both 
in  water  and  alcohol.  When  heated,  it  melts,  gives  off  much  ammonia,  and 
finally  solidifies,  being  in  a  great  measure  converted  into  ammonia  and  cyanuric 
acid. 

Urea  belongs  to  the  class  of  organic  bases,  for  it  forms  crystallizable  com* 
pounds  with  several  acids,  such  as  nitric,  oxalic,  and  acetic  acids. 

The  nitrate,  when  impure,  crystallizes  in  scales  of  a  high  lustre;  when  pure, 
it  forms  opaque  prisms,  or  a  crystalline  powder.  It  is  sparingly  soluble  in  cold 
water,  but  very  soluble  in  hot  water.     Formula,  (C,.H4N,02,HO»N05.) 

The  oxalate  forms  long  transparent  prisms,  very  sparingly  soluble.  Formula, 
(C,H,NA,H0,CA)=C,H5N,0s. 

The  acetate  I  have  obtained  as  a  mass  of  prismatic  crystals,  exceedingly  soluble 
in  water.     Formula,  probably  (C,H,N202,HO,C4Ha03)=C6HsN206. 

Although  urea  combines  with  pure  nitric  acid,  it  is  instantaneously  decomposed 
by  hyponitrous  acid,  yielding  ammonia,  water,  and  equal  volumes  of  carbonip 
acid  and  nitrogen  gases.  C^H.NAt  N03=NH3+HO+2CO,tN2.  Wheii 
acted  on  by  strong  acids,  or  alkalies,  with  the  aid  of  heat,  nrea  takes  up  the  ele<f 
ments  of  water,  and  forms  carbonate  of  ammonia,  C2H4N.202-t-2HO=3(NH3, 
CO2).  When  urine  is  left  in  contact  with  the  mucus  usually  suspended  in  it, 
the  mucus  entering  into  decomposition  excites  in  the  urea  such  a  reaction  with 
the  elements  of  water,  as  very  soon  to  convert  the  whole  urea  into  carbonate  of 
ammonia.  Hence  the  reason  why  urine  soon  becomes  alkaline,  evep  if  acid  when 
voided.  But  if  filtered  from  the  mucus  as  soon  as  passed,  it  keeps  unchanged, 
in  clean  vessels,  for  a  long  period. 

2.  FuLMiNic  Acid.     CvjOa,  2HO=Cy204,H2=86'5, 

A  bibasic  acid,  unknown  in  the  separate  form.  It  is  obtained  in  combination 
with  oxide  of  mercury,  or  oxide  of  silver,  by  treating  alcohol  with  the  nitrates 
of  these  metals,  and  free  nitric  acid.  A  violent  effervespence  takes  place,  dense 
white  vapours  are  disengaged,  and  a  crystalline  powder  is  deposited,  which  is 
fulminate  of  mercury  or  of  silver.  Both  detonate  powerfully  by  heat,  friction, 
or  percussion. 

In  the  above  reaction  there  are  first  formed,  on  the  one  hand,  hyponitrpus  acid  ; 
on  the  other,  aldehyde,  and  formic  and  oxalic  acids.  The  fulminic  acid  is  the 
result  of  a  reaction  between  oxide  of  ethyle  (ether)  and  hyponitrous  acid,  in  pre- 
sence of  oxide  of  mercury  or  oxide  of  silver.  2i!^0^-]-CJi^)0=C^N^O^-^5HO 
=Cy.^02,2HOf3HO. 

This  acid  cannot  be  isolated,  being  instantly  decomposed  when  deprived  of  a 
fixed  base.     It  forms  two  series  of  salts :   neutral,  with  2  eq.  of  fixed   base, 

C  HO 

Cy^O^,  2M0  ;  and  acid,  with  1  eq.  of  fixed  base  and  1  of  water  Cy^O^  <  ^^ 

It  also  forms  salts  with  1  eq.  of  two  different  bases,  of  which  one  is  always 
easily  reducible,  as  oxide  of  silver,  mercury  and  copper,  while  the  other  may 
be  diflicult  to  reduce,  such  as  baryta,  potash,  &c. 

The  fulminates  of  silver  and  mercury, -Cy^O^,  2 AgO,  and  Cy^O^,  2HgO,  are 

C  HO 

examples  of  the  firvSt  class.  The  acid  fulminate  of  zinc  Cy  0    <  „  ^     formerly 

22^  ZnU,  "^ 

supposed  to  be  the  fulminic  acid,  is  an  example  of  the  second  ;  and  the  double 

38 


5p3.  CYANURIC  ACID. 

fulminates  of  copper  and  silver,  and  of  potash  and  silver,  Cy  O    ^  .     ,.        and 

2    2^  AgU, 

Cy^  ^2    ;  A   O  ^^^  examples  of  the  third.     No  neutral  fulminates  exist  with 

2  eq.  of  a  difficultly  reducible  oxide,  such  as  potassa,  soda,  baryta,  &c.  ;  nor  do 
any  acid  fulminates  occur  with  such  bases.  These  very  remarkable  facts  evi- 
dently point  to  some  relation,  not  yet  understood,  between  the  oxygen  of  the 
base  in  a  salt  and  the  acid  of  that  salt.  Of  course  all  the  above  formulae  may  be 
written  according  to  the  theory  of  compound  radicals  and  hydrogen  acids. 

To  prepare  the  fulminate  of  mercury,  which  is  much  used  for  percussion  caps, 
1  part  of  mercury  is  dissolved  in  12  parts  of  nitric  acid,  sp.  gr.  1*36  ;  11  parts  of 
alcohol  at  80  per  cent,  are  added,  and  the  whole  is  warmed.  A  brisk  reaction 
soon  ensues,  very  thick  white  vapours  are  given  off,  and  the  salt  is  deposited  in 
crystalline  grains,  mixed  with  a  little  metallic  mercury.  This  salt  explodes  by 
friction,  by  percussion,  or  by  heat,  and  it  is  a  dangerous  product,  exploding  oc- 
casionally without  apparent  cause.  An  explosion  of  this  nature,  not  long  since, 
destroyed  the  distinguished  chemist,  Mr.  Hennell,  who  was  preparing  a  large 
quantity  in  the  open  air.  The  fulminate  of  silver  is  prepared  in  the  same  way, 
only  with  10  parts  of  nitric  acid  and  20  of  alcohol.  Caustic  alkalies  precipitate 
from  its  solution  half  the  silver,  forming  double  fulminates  ;  and  chlorides  also 
only  precipitate  half  the  silver.  Nitric  acid,  added  to  the  solution,  causes  a  de- 
posit of  acid  fulmipate  of  silver, 

CyA{^S  "CyA{Ag 

Hydrochloric  acid  added  to  fulminate  of  silver,  gives  rise  to  water,  chloride 
of  silver,  hydrocyanic  acid,  and  a  new  acid,  chlorohydrocyanic  acid  C2NC1;„H2. 
Thus— T 

C4N8O2.  ^AgCH-7HCl=4HO  +  2AgCl+C2NH+C2NC]5,Hj. 

3.  Cyai^uric  Acid.    CygOg,  3HO=Cy30e,H3=126-75. 

A  tribasic  acid  discovered  among  the  products  of  the  distillation  of  uric  acid. 
It  is  formed  when  solid  chloride  of  cyanogen  CyaCla  acts  on  water :  CyaClj-f- 
6HO=3H01-t-Cy306,H3.  It  is  also  formed  when  urea  is  heated  so  as  to  expel 
its  ammonia.  According  to  what  has  been  stated  of  the  composition  of  urea,  it 
ought  to  yield  cyanic  acid  when  deprived  of  its  ammonia ;  but  at  that  tempera- 
ture 3  eq.  of  cyanic  acid,  3CyO,HO,  coalesce  to  form  1  eq.  of  cyanuric  acid, 
Cy303,3HO,.  Whep,  again,  acetic  acid  is  added  to  cyanate  of  potash,  in  quan- 
tity insufficient  to  decompose  the  whole,  there  is  deposited  a  salt  which  is  an 

C  KO 
acid  cyan^rate  of  potash,  Cy^Og  j  ^^^ 

Finally,  cyanuric  acid  is  obtained  by  dissolving  melame,  ammeline,  ammelide 
and  melamine  (see  those  substances)  in  sulphuric  acid,  and  diluting  and  healing 
the  solution,  until  it  yields  no  precipitate  with  ammonia.  On  evaporation  and 
cooling,  the  acid  forms  prismatic  crystals,  which  are  Cy^02,3HOf  4  aq.  When 
dissolved  in  hot  nitric  or  hydrochloric  acid,  it  is  deposited,  on  cooling,  in  anhy- 
drous octahedrons.  When  it  has  been  prepared  by  heating  urea,  it  is  purified 
by  dissolving  it  in  oil  of  vitriol,  and  adding  nitric  acid,  drop  by  drop,  till  the 


CYAMELIDE.  5^, 

colonr  is  entirely  destroyed.  An  equal  bulk  of  water  is  then  added,  and  on  cool- 
ing, pure  cyanuric  acid  is  obtained  in  crystals. 

Cvanuric  acid  has  a  weak  acid  taste,  and  is  sparingly  soluble  in  cold  water, 
more  soluble  in  hot  wat«r.  Unlike  cyanic  and  fulminic  acids,  it  is  very  perma-; 
nent  in  the  uncombined  state.  When  heated  in  close  vessels,  it  is  entirely  vola- 
tilized in  the  form  of  cyanic  acid,  of  which  3  eq.  are  exactly  equal  to  1  eq.  of 
cyanuric  acid. 

As  cyanuric  acid  is  formed  when  urea  (cyanate  of  ammonia)  is  decomposed 
by  heat,  and  when  cyanate  of  potass  is  acted  on  by  acetic  acid,  and  as  cyanuric 
acid,  when  heated,  is  resolved  into  cyanic  acid,  we  have  every  reason  to  think 
that  in  the  former  cases,  3  eqs.  of  cyanic  acid  coalesce  to  form  one  of  cyanuric 
acid,  and  that,  in  the  latter  case,  1  eq.  of  cyanuric  acid  is  broken  up  into  3  eqs. 
of  cyanic  acid.     3(CyO,HO)=Cy303,3HO. 

Like  other  tribasic  acids,  cyanuric  acid  forms  three  series  of  salts,  according 
to  the  formulae  : — 

Salt  with  1  eq.  of     Salt  with  2  eq,  of     Salt  with  3  eq.  of 
Hydrated  Acid.  fixed  base.  fixed  base.  fixed  base. 

CygO^SHO  CyaOg^^^g  ^JyA  {^HO  CygOg,  3M0 

The  salts  with  1  and  2  eqs.  of  fixed  base  are  acid ;  that  with  3  eqs.  is  neutral. 
With  potash  and  other  similar  oxides,  only  the  two  acid  salts  zuce  known  i  with 
oxide  of  silver,  the  salts  with  2  and  3  eqs.  of  oxide,  ,  ^ 

The  three  fallowing  salts,  namely,  i 

Cyanate  of  Silver.  Fulminate  of  Silver.  Cyanurate  of  Silver; 

CyO^AgOj  Cy202,2AgO;.  CygOg,  3AgO. 

have  exactly  the  same  composition  in  100  parts ;  and  yet  they  are  in  properties 
entirely  dissimilar;  this  can  only  be  accounted  for  by  some  such  difference  in 
their  formulse,  as  is  exhibited  above.  The  aci<ls  of  these  salts  are  all  mutually 
convertible :  for  when  fulminate  of  silver  is  decomposed  by  a  salt  of  ammonia, 
the  fulminate  of  ammonia  is  transformed,  like  the  cyanate,  into  urea;  urea  when 
heated  yields  cyanuric  acid  ;  and  cyanuric  acid  when  distilled  is  transformed  into 
cyanic  acid.  All  these  circumstances  favour  the  belief  that  all  three  are  com- 
pounds of  cyanogen,  and  that  they  differ  in  the  absolute  number  of  equivalents 
of  their  elements. 

Cyamelide ;  Cgpa  +  NH  ? 

But  this  is  not  the  end  of  these  transformations :  for  when  cyanic  acid  is  left 
to  itself  it  becomes  turbid  and  hot,  and  is  soon  converted  with  great  heat,  into 
an  opaque  white  solid  body,  cyanielide,  which  has  no  acid  properties  ;  and  which 
is  also  obtained  as  a  white  insoluble  powder,  when  fused  cyanate  of  potash  is 
triturated  with  dried  oxalic  acid,  in  which  case  oxalate  of  potash  is  formed,  and 
the  cyanic  acid,  at  the  moment  of  being  set  free,  is  transformed  into  cyamelide. 
Cyamelide  is  neutral  and  insoluble  in  water  and  acids.  It  dissolves  in  aqua 
potassae,  ammonia  being  evolved,  and  the  solution  yields  cyanurate  of  potash. 
Heated  by  itself  it  yields  cyanic  acid,  which  again  passes  into  cyamelide  ;  and 
when  heated  with  strong  sulphuric  acid  it  forms  sulphate  of  ammonia,  while  car- 
bonic acid  escapes ;  this  action  is  identical  with  that  which  occurs  when  cyanic 
acid  is  acted  on  by  water  and  by  acids.  All  these  observations  prove  that  cyame- 


564  CYANOGEN  AND  CHLORINE. 

lide  is  another  isomeric  modification  of  cyanic,  fulminic,  or  cyanuric  acid.  Its 
probable  formula  is  C^O^  +  NH,  and  this,  with  2  eqs.  HO,  yields  bicarbonate 
of  ammonia,  just  as  cyanic  acid,  the  formula  of  which  is  the  same,  does.  The 
action  of  potash  is  probably  this.     4(C202NH)  +  3H0  +  4K0  =  Cg^f30g, 

^  -|-2K0,C0  4- NH  ;  that  is:  4  eqs.  cyamelide,  3  eqs.  water,  and  4 

eqs.  potash,  yield  1  eq.  cyanurate  of  potash,  2  eqs.  carbonate  of  potash,  and  1 
eq.  ammonia. 

The  three  oxygen  acids  of  cyanogen  may  be  fitly  compared  with  the  three 
phosphoric  acids ;  and  as  we  have  hitherto  made  use  of  the  older  view  of  these 
acids,  that  which  makes  them  hydrated  oxygen  acid,  we  shall,  in  this  compari- 
son, adopt  the  other  theory,  and  speak  of  them  as  hydrogen  acids. 


Monobasic. 

Bibasic. 

Tribasic. 

Acids  of  Cyanogen 

.        Cy02  +  H 

CyA  +  Hj 

CyaOe  +  H' 

Acids  of  Phosphorus 

.        P^Oe  t  H 

P2O7   +H2 

V,0,  +H3 

In  the  cyanic  acids,  both  the  radical  and  the  replaceable  hydrogen  being  doubled 
and  trebled,  the  capacity  of  saturation  increases  in  the  same  ratio.  In  the  phos- 
phoric acids,  the  capacity  of  saturation  also  increases  with  the  replaceable  hydro- 
gen, but  a  great  addition  to  the  radical  has  no  corresponding  effect  in  increasing 
either  the  replaceable  hydrogen  or  the  neutralizing  power.  Thus,  if  to  tribasic 
phosphoric  acid  P  O^  -f  H,  we  add  2  eqs.  of  P^O  =  P^O^^  we  obtain  PgOj^-j- 
H  =3(P  O  -f-H);  that  is,  the  acid  becomes  monobasic,  but  the  quantity  of 
base  neutralized  is  the  same  after  that  addition  as  before.  Notwithstanding  this 
difference,  however,  the  analogy  between  the  monobasic,  bibasic,  and  tribasic 
acids  of  cyanogen  and  phosphorus,  as  well  as  that  between  their  salts,  is  most 
interesting  and  worthy  of  attention.  As  we  believe  that  the  phosphoric  acids 
contain  three  different  radicals,  P„0^,P„0  .  and  P„0„,  so  we  may  admit  that  the 

'       2     6'     2     7'  2     8'  -^ 

three  cyanic  acids  have  each  a  distinct  radical ;  only  in  this  case  the  three  radi- 
cals are  alike  in  composition,  and  differ  in  their  relative  weight :  the  first  being 
C^NssCy;  the  second  C^N2=Cy^;  and  the  third  CgN3  =  Cy3;  or,  in  other 
words,  these  radicals  are  three  different  cyanogens.  The  relations  of  chlorine 
to  cyanogen  countenance  this  idea. 

CYANOGEN  AND  NITROGEN. 

Mellone  =  Cy^N  =  CjN*  =  Me  =  93. 

Cyanogen,  when  it  combines  with  nitrogen  in  the  proportion  of  3  eq.  Cy  to  1 
eq.  N  =  CgN  ,  produces  a  very  remarkable  compound,  discovered  by  Liebig, 
and  called  mellone,  which  being  itself  a  well  marked  compound  radical,  will  be 
described  as  such,  and  not  as  a  compound  of  cyanogen  and  nitrogen. 

^  CYANOGEN  AND  CHLORINE. 

Cyanogen  forms  two  chlorides :  one  gaseous,  but  compressible,  obtained  by 
the  action  of  chlorine  gas  on  dry  hydrocyanic  acid  ;  the  other  solid,  formed  by  a 
spontaneous  transformation  of  the  former  when  kept  in  the  liquid  form  in  sealed 
tubes.  Both  are  volatile  and  both  contain  cyanogen  and  chlorine,  equivalent  for 
equivalent.  But  the  vapour  of  the  solid  chloride  is  three  times  denser  than  that 
of  the  other ;  and,  moreover,  the  solid  chloride,  in  contact  with  water,  produces 


CYANOGEN  AND  METALS.  565 

hydrochloric  and  cyarmric  acids :  while  the  gaseous  chloride,  under  the  same 
circumstances,  gives  rise  to  hydrochloric  acid,  and  cyanic  acid,  the  latter  with 
water,  at  once  passing  into  bicarbonate  of  ammonia,  so  that  the  final  result  is 
sal  ammoniac  and  carbonic  acid. 

These  considerations  prove  that  the  two  chlorides  are  isomeric  :  that  the  first 
or  gaseous  chloride  is  CyCl ;  and  that  the  solid  chloride  is  Cy  CI  ,  and  is  formed 
by  the  junction  of  3  eq.  of  the  other;  and  we  are  consequently  justified  in  ex- 
tending this  view  to  cyanic  and  cyanuric  acids,  and  in  supposing  the  vapour  of 
the  latter  to  be  three  times  more  condensed  than  the  vapour  of  cyanic  acid  :  and 
the  cyanogen  of  cyanuric  acid  to  be  the  cyanogen  of  the  solid  chloride,  and  three 
times  denser  than  ordinary  cyanogen. 

CYANOGEN  WITH  BROMINE  AND  IODINE. 

With  these  elements  cyanogen  readily  combines  when  cyanide  of  mercury  is 
distilled  with  bromine  or  iodine.  The  bromide  and  iodide  are  both  volatile,  and 
crystallizable,  pungent  and  poisonous. 

To  judge  by  the  density  of  their  vapours,  these  compounds  are  CyBr  and  Cyl, 
corresponding  to  the  liquid  chloride,  which  is  also  very  pungent  and  irritating  to 
the  eyes. 

CYANOGEN  AND  SULPHUR. 
Bisulphuret  of  Cyanogen.    CySg  =  68-5. 

When  sulphocyanide  of  potassium,  (see  that  salt)  is  acted  on  by  chlorine  or 
by  dilute  nitric  acid,  there  is  obtained  an  orange-yellow  powder,  which  contains 
sulphur  and  cyanogen,  and  which  is  supposed  by  some  to  be  bisulphuret  of 
cyanogen,  by  others  to  contain  hydrogen.  This  question  will  be  considered 
hereafter,  for  whether  this  be  so  or  not,  there  is  a  compound,  possibly  that  com- 
pound of  sulphur  and  cyanogen,  which  acts  as  a  radical,  and  is  hence  called 
sulphocyanogen.  It  will  be  described  separately,  since  it  is  far  more  important 
as  a  radical  than  as  a  compound  of  cyanogen. 

CYANOGEN  AND  METALS. 

With  metals,  cyanogen  forms  compounds  which  in  many  cases  are  analogous 
to  the  chlorides  of  the  same  metal.  When  the  metal  is  easily  reducible,  such 
a?  silver,  mercury  or  palladium,  the  cyanide  is  formed  by  the  action  of  hydro- 
cvanic  acid  on  the  oxide,  or  its  salts  :  MO  +  HCy  =  HO  -\-  MCy.  In  the  case 
of  difficultly  reducible  metals,  such  as  potassium,  hydrocyanic  acid  seems  to 
coiubine  with  the  oxide,  not  being  able  to  reduce  it,  until  another  cyanide  is 
added,  which  tends  to  form  a  double  cyanide. 

Cyanide  of  Potassium^  =  KCy  is  best  formed  by  heating  to  whiteness  in  close 
vessels  the  ferrocyanide  of  potassium,  a  salt  which  may  be  viewed  as  containing 
cyanide  of  iron  and  cyanide  of  potassium.  The  former  is  converted  into  inso- 
luble carburet  of  iron  ;  the  latter  remains  unchanged,  and  may  be  mechanically 
picked  out,  or  dissolved  by  hot  alcohol  of  60  p.  c,  which  deposits  it  on  cooling. 
Or,  an  alcoholic  solution  of  pure  and  dry  hydrocyanic  acid  is  added  to  an  alco- 
holic solution  of  potash ;  or,  lastly,  the  vapours  of  hydrocyanic  acid,  formed  on 
the  process  given  at  p.  556,  are  conducted  into  an  alcoholic  solution  of  potassa, 
kept  cool,  when  the  salt  is  deposited. 


666  CYANOGEN  OF  METALS. 

It  is  white,  and  crystal) izable  in  cubes.  It  has  no  smell  when  pure,  but  when 
exposed  to  moist  air,  smells  of  hydrocyanic  acid.  It  is  very  poisonous.  When 
heated  it  fuses  easily,  and  is  not  altered  by  heat  irf  close  vessels.  Heated  in  the 
air  it  absorbs  oxygen  and  is  converted  into  cyanate  of  potash  KCy  -|-  0  ==  KO. 
CyO.  It  is  very  soluble  and  deliquescent,  and  its  solution,  attracting  carbonic 
acid  from  the  air,  gives  off  hydrocyanic  acid  :  hence  its  smell. 

Cyanide  of  Sodium  is  analogous  to  the  preceding  salt. 

Cyanide  of  Zinc^  ZnCy  is  obtained  by  adding  hydrocyanic  acid  to  acetate  of 
zinc.     It  is  a  snow-white  insoluble  powder,  which  is  used  in  medicine. 

Cyanide  of  Iron. — Protocyanide  of  iron,  FeCy,  has  not  been  isolated.  There 
appears  to  exist  a  percyanide,  also  not  yet  isolated,  Fe  Gy  ;  and,  according  to 
Pelouze,  there  may  be  obtained  an  intermediate  cyanide,  Fe.Cy  ,  analogous  to 
the  magnetic  oxide  of  iron,  as  a  green  powder. 

'But  although  the  cyanides  of  iron  are  little  known,  there  are  some  very  im- 
portant compounds,  especially  those  of  two  radicals,  which  contain  those 
•elements,  namely,  cyanogen  and  iron,  along  with  hydrogen  and  with  metals. 
These  will  be  described  after  we  have  gone  over  the  simple  cyanides  of  the 
metals. 

Cyanide  of  Cobalt,  CoCy,  is  obtained  as  a  brownish-white  precipitate,  by  add- 
ing hydrocyanic  acid  to  the  acetate  of  cobalt.  Cobalt  also  forms  compounds 
analogous  to  those  of  iron  above  alluded  to,  with  cyanogen,  &c. 

Bicyanide  of  Mercury,  HgCy  ,  is  easily  obtained  by  dissolving  red  oxide  of 
mercury  in  very  dilute  hydrocj'^anic  acid,  till  the  smell  of  the  acid  is  destroyed. 
The  liquid,  rendered  neutral,  if  necessary,  by  a  few  drops  of  hydrocyanic  acid, 
yields  fine  crystals,  on  evaporation  and  cooling.  Or  it  may  be  made  by  the  action 
of  three  parts  of  persulphate  of  mercury  on  two  of  ferrocyanide  of  potassium 
dissolved  in  fifteen  of  hot  water^  which  is  boiled  and  filtered,  and  the  filtered 
liquid  on  cooling  deposits  the  bicyanide. 

It  forms  regular  prismatic  crystals,  permanent  in  the  air,  of  a  horrible  metallic 
taste,  soluble  in  water  and  alcohol.  It  is  used  for  making  cyanogen,  also  to 
prepare  hydrocyanic  acid  by  one  process,  and  to  yield  the  bromide  and  iodide  of 
cyanogen. 

Cyanide  of  Silver,  AgCy. — Formed  by  the  action  of  hydrocyanic  acid  or 
cyanide  of  potassium  on  nitrate  of  silver.  It  is  exactly  similar  to  the  chloride, 
white,  curdy,  insoluble  in  water  or  acids,  soluble  in  ammonia.  It  is  decomposed 
by  hydrochloric  acid,  yielding  hydrocyanic  acid. 

Cyanide  of  Palladium^  PdCy. — The  affinity  of  cyanogen  for  palladium  is  mo»t 
powerful,  and  hydrocyanic  acid,  or  a  soluble  cyanide,  when  added  to  a  sv^lt  of 
oxide  of  palladium,  precipitate  the  cyanide  as  a  grey  powder.  This  property 
fierves  for  separating  palladium  from  other  metals. 

Cyanides  (f  Gold. — The  protocyanide,  AuCy,  is  formed  by  adding  cyanide  of 
potassium  in  excess  to  protochloride  of  gold,  till  a  clear  solution  is  formed,  and 
then  adding  hydrochloric  acid,  which  precipitates  the  protocyanide  as  a  bright- 
-yellow  powder,  very  permanent,  and  soluble  in  cyanide  of  potassium. 

The  tercyanido,  AnCy^,  is  formed  by  \\\e  action  of  cyanide  of  potassium  on 
terchloride  of  gold,  and  appears  as  whitish-yellow  precipitate,  soluble  in  cyanide 
•of  potassium,  insoluble  in  acids. 


567 


DOUBLE  CYANIDES  OF  THE  METALS. 

The  insoluble  metallic  cyanides,  such  as  those  of  iron,  cobalt,  copper,  silver, 
gold,  platinum,  and  others,  dissolve  readily  in  cyanide  of  potassium,  or  sodium, 
forming  crystal lizable  double  cyanides,  which  are  not  affected  by  soluble  carbo- 
nates nor  by  chlorides,  but  are  generally  decomposed  by  acids,  which  precipitate 
the  insoluble  cyanide.  If  these  double  cyanides,  which  may  be  2KCy +  mCy 
(mCy  being  an  insoluble  metallic  cyanide)  are  added  to  the  solution  of  the  oxide 
of  another  metal  forming  also  an  insoluble  cyanide,  this  latter  metal  takes  the 
place  of  the  potassium,  and  a  new  double  insoluble  cyanide  is  the  result.  Thus 
(2  KCy  f  mCy)  +  2M0  =  2K0  +  (2MCy  f  mCy).  (Here  m  may  be  iron 
and  M  copper  or  lead.)  Now,  as  these  double  cyanides,  thus  precipitated,  are 
of  various  and  often  characteristic  colours,  the  ferrocy^nide  of  potassium,  2KCy 
H-FeCy,  is  extensively  used  as  a  test  for  metals. 

The  protocyanide  of  iron,  the  percyanide  of  iron,  the  percyanide  of  cobalt,  and 
perhaps  some  others,  not  only  form  double  salts  with  the  elements  of  cyanide  of 
potassium,  but  also  produce  very  remarkable  acids,  by  combining  with  the  ele- 
ments of  hydrocyanic  acid,  that  is,  with  hydrogen  replacing  the  potassium  of  the 
double  salt.  Thus  ferrocyanic  acid  is  2HCy  -f-  FeCy,  and  so  on.  In  these 
compounds  the  hji^drocyanic  acid  is  no  longer  poisonous,  and  it  is  therefore  highly 
probable  that  these  acids,  and  their  corresponding  salts,  really  c«ntain  new  and 
very  peculiar  radicals.  The  assumption  of  these  radicals  will  alone  enable  us  to 
classify  or  remember  these  compounds. 

IV,    Ferrocyanogen.    Cj-gFe  =  Cfy  ==  105-87. 

We  assume,  then,  the  existence  of  this  radical  as  the  basis  of  ferrocyanide  of 
potassium,  or  prussiate  of  potash.  It  is  bibasic,  combining  with  2  eq.  of 
hydrogen  or  of  metals.  The  following  formula;  expresses  the  composition  of 
ferrocyanic  acid,  and  of  ferrocyanide  of  potassium,  &c. 

Ferrocyanic  Acid  =Cry,H2    =   CvgFejHj   ==  2HCy-f-FeCy. 
Ferrocyanide  of  Potassium  =Cty,K2    =  Cy3Fe,K2    =  2KCy -|- FeCy. 
Iron            =  3Cfy,Fe4  =  3Cy3Fe,Fe4  =  9Cy  +  7Fe. 

It  will  be  seen,  by  the  two  first  compounds,  that  we  may  consider  them  either 
as  compounds  of  the  radical  Cfy  with  hydrogen  or  metals,  or  as  double  cyanides. 
In  the  third,  which  is  the  formulas  of  Prussian  blue,  we  see  that  the  iron  exists 
in  two  different  states,  in  one  of  which  it  cannot  be  detected  by  the  usual  tests. 
That  form  is  the  radical  Cfy,  which  exists  also  in  the  two  preceding  compounds. 

Ferrocyanic  Acid.    Cfy,H2=  107-87. 

This  very  interesting  compound  is  obtained  by  mixing  a  cold  saturated  solu- 
tion of  ferrocyanide  of  potassium  with  one  quarter  its  volume  of  strong  hydro- 
chloric acid,  and,  agitating  the  mixture  with  half  its  bulk  of  pure  ether,  the  ether 
rises  to  the  surface,  carrying  with  it,  suspended,  a  white  crystalline  substance, 
which  when  washed  with  ether  and  dried,  is  ferrocyanic  acid.  It  is  soluble  in 
water  and  alcohol,  has  a  decidedly  acid  taste  and  reaction,  and  decomposes  the 
alkaline  carbonates,  forming,  with  carbonate  of  potash,  the  ferrocyanide  of  potas- 
sium.   The  production  of  this  compound   by  the  action  of  hydrochloric  acid  on 


568  FERROCYANIDE  OF  POTASSIUM. 

ferrocyanide  of  potassium  is  very  easily  explained.  CfyJC^  +  SHClss  Cfy,Hj 
-H2KC1. 

Although  this  compound  may  be  represented  as  a  combination  of  cyanide  of 
iron  with  hydrocyanic  acid,  FeCy  +  2HCy,  there  is  every  reason  to  believe  that 
it  contains  no  hydrocyanic  acid,  as  such.  For  not  only  is  it  far  more  strongly 
acid,  (and  protocyanide  of  iron  cannot  be  supposed  to  give  acid  properties  to 
hydrocyanic  acid,)  but  it  is  totally  destitute  of  all  poisonous  properties,  for  both 
it  and  its  salts  may  be  taken  internally  without  further  effect  than  the  laxative 
action  common  to  most  neutral  salts. 

Ferrocyanic  acid,  being  bibasic,  forms  two  kinds  of  salts  :  in  the  first  the  2 
eq.  of  hydrogen  are  replaced  by  2  eq.  of  potassium,  sodium,  &c. ;  &c.,  in  the 
second,  they  are  replaced  by  equivalents  of  two  different  metals:  such  as  potas- 
sium and  barium.     An  example  of  the  first  class  is,  Cfy  -f  K^;  of  the  second, 

C  K 

Cfy  j  u  .  Of  all  these  compounds,  by  far  the  most  important  is  the  ferrocya- 
nide of  potassium,  or  prussiate  of  potash,  from  which  all  the  compounds  of  cya- 
nogen may  be  prepared,  and  which  is  manufactured  on  the  large  scale,  being  also 
used  in  the  arts. 

Ferrocyanide  of  Potassium.  Syn.  Prussiate  of  Potash.  Anhydrous,  CfyK^, 
184-17.  Crystallized,  it  is  Cfy,K2  +  3H0  =  21 1-2.-— This  valuable  salt  is  pre- 
pared by  fusing  animal  matter,  such  as  dried  blood,  hoofs,  hair,  horns,  &c.,  or 
the  animal  chahrcoal  remaining  after  such  matters  have  been  distilled  to  obtain 
carbonate  of  ammonia,  with  potashes  or  pearlash,  in  iron  vessels,  as  long  as  gas 
is  disengaged.  The  melted  mass  is  then  withdrawn  from  the  fire,  and  when 
cold,  lixiviated  with  water,  the  solution  digested  with  the  insoluble  part,  filtered 
and  evaporated,  when  it  deposits,  on  cooling,  yellow  crystals;  which  by  a 
second  solution  and  crystallization  become  quite  pure. 

The  essential  points  of  this  process  are,  first,  the  presence  of  as  much  nitrogen 
as  possible  in  the  animal  matter:  hence  fresh,  dried  uncalcined  animal  matter  is 
far  preferable  to  animal  charcoal :  secondly,  the  presence  of  metallic  iron  or  sul- 
phuret  of  iron :  the  former  is  either  directly  derived  from  the  vessels,  which  are 
rapidly  corroded,  or  added  as  filings;  the  latter  is  formed  from  the  iron  of  the 
vessels  by  the  action  of  bisulphuret  of  potassium,  which  arises  from  the  decora- 
position,  by  charcoal  at  a  red  heat,  of  the  sulphate  of  potash  contained  in  the 
potashes  or  pearlash;  hence  pure  carbonate  of  potash  is  not  adapted  to  this  pro- 
cess. Thirdly,  the  exclusion  of  the  air  as  far  as  possible,  in  order  to  prevent 
the  oxidation  and  destruction  of  the  cyanide  of  potassium  formed. 

The  explanation  of  the  process  is  very  simple  and  beautiful,  and  we  are 
indebted  for  it  to  the  researches  of  Liebig.  When  animal  matter  is  heated  along 
with  potash,  cyanogen  is  formed,  and  combining  with  the  potassium  (set  free  at 
the  same  time  by  ihe  action  of  carbon  on  potash)  produces  cyanide  of  potassium, 
a  salt  which  is  not  decomposed  by  a  red  heat  in  closed  vessels.  At  the  same 
time,  metallic  iron  and  sulphuret  of  iron  are  present  in  the  mixture,  but  not  a 
trace  of  the  ferrocyanide,  previous  to  the  action  of  water,  for  the  very  obvious 
reason,  that  the  ferrocyanide  is  decomposed  by  a  red  heat,  into  cyanide  of  potas- 
sium and  carburet  of  iron,  nitrogen  being  disengaged. 

If  the  cooled  mass  be  now  digested  in  water,  the  cyanide  of  potassium  dis- 
solves, either  the  metallic  iron  with  disengagement  of  hydrogen,  or  the  sul- 
phuret of  iron,  and  the  filtered  liquid  now  contains  the  ferrocyanide. 

Direct  experiments  have  shown  that  cyanide  of  potassium  dissolves  either 


FERROCYANIDE  OF  IRON.  569 

iron,  oxide  of  iron,  or  sulphuret  of  iron,  producing  the  ferrocyanide ;  3KCy  + 
Fe  +  HO  =  (2KCy  f  FeCy)  -\-  KO  +  H.  Or,  3KCy  +  FeS  =  (2KCy  + 
FeCy)  -f-  KS.  And  it  has  also  been  shown  by  Liebior  that  if  the  fused  mass 
be  lixiviated  with  alcohol,  the  residue,  when  treated  with  water,  yields  no  fer- 
rocyanide, while  the  alcohol  contains  none,  but  only  cyanide  of  potassium. 

Taking  these  facts  into  consideration,  perhaps  the  best  method  would  be  to 
use  pure  carbonate  of  potash,  free  from  sulphate,  by  which  means  no  sulphuret 
of  potassium  would  be  formed,  and  the  iron  vessels  would  not  suffer  as  they  now 
do.  The  cyanide  of  potassium,  being  dissolved  in  water  and  filtered,  should 
then  be  placed  in  contact  with  iron  turnings  in  flat  open  vessels,  when,  the  third 
part  of  the  potassium  being  oxidized  by  the  air,  the  iron  is  rapidly  dissolved, 
and  a  quantity  of  ferrocyanide  obtained  equal  to  that  indicated  by  the  cyanide 
of  potassium  present. 

The  ferrocyanide  of  potassium  forms  large  honey-yellow,  transparent,  flat, 
quadrangular  prisms,  derived  from  a  rhombic  octahedron.  It  is  very  soluble  in 
water,  and  forms  precipitates  in  almost  all  metallic  solutions,  many  of  which 
are  characteristic.  Thus,  w^ith  solutions  of  zinc  and  lead,  it  gives  a  white  pre- 
cipitate, with  those  of  copper  a  chesnut  brown,  with  those  of  peroxide  of  iron  a 
deep  blue,  with  protoxide  of  iron  a  pale  blue,  with  those  of  barium  and  calcium 
whitish-yellow  crystalline  precipitates.    The  lead  precipitate  is  pfy.Pb^;  that 

of  copper  CfyjCu^;  those  of  barium  and  calcium  Cfy  ^  „  and  Cfy  >  ^    ;  and 

that    of  zinc,  2Cfy  f  5  ^"a  +  6  aq.  =  Cfy,Zn2  t  Cfy  ^  |.°  +  6  aq.    That  of 

C  Fe  C  Fg 

protoxide  of  iron  is  2Cfy  j  j-  ^  =  CfyjFe^  +  Cfy  j      .     All  of  these  formulae 

are  easily  referred  to  the  general  formula  of  the  ferrocyanides,  CfyjM^. 

Ferrocyanide  of  Iron, — But  the  most  remarkable  of  all  these  compounds  is  that 
formed  with  persalts  of  iron,  namely  prussian  blue.  It  is  produced  when  ferro- 
cyanide of  potassium  comes  in  contact  with  perchloride,  or  any  salt  of  peroxide 
of  iron.  Now  as  ferrocyanogen  is  a  bibasic  radical,  1  eq.  of  it  corresponds  to  2 
eq.  of  potassium,  hydrogen,  oxygen,  chlorine,  &c.;  and  as  perchloride  of  iron, 
Fe^Cl^,  contains  3  eq.  of  chlorine,  1|  eq.  of  ferrocyanide  of  potassium  will  be 
required  to  decompose  1  eq.  of  it,  or,  to  avoid  fractions,  3  eq.  of  ferrocyanide 
Cfy^Kg=  3Cfy,K2,  are  required  for  2  eq.  perchloride  of  iron,  Fe^Cl^  =  2Yef)\^, 
The  result  is,  Cfy  K  +  Fe  CI  =  6KCi -j-  Cfy  Fe  :  and  this  last  is  the  true 

,  -  •'36'  46  '  ■'34 

lorraula  of  prussian  blue,  although,  from  its  tendency  to  combine  both  with  fer- 
rocyanide of  potassium  and  with  oxide  of  iron,  its  analysis  offers  great  difficul- 
ties. The  formula  Cfy  Fe  or  Fe  Cfy  shows  that  prussian  blue  corresponds  to 
peroxide  and  perchloride  (sesquioxide  and  sesquichloride)  of  iron,  Fe  O  and  Fe 
Cl^,  for  Cfy  being  bibasic  is  equivalent  to  CI  or  O  ,  and  consequently  Fe^Cy^ 
is  equivalent  to  Fe  CI  or  Fe  O^,  that  is,  to  2Fe„Cl  and  2Fe^0,.  It  must  be 
admitted  to  be  a  very  strong  argument  in  favour  of  the  existence  of  ferrocya- 
nogen, as  a  bibasic  radical,  according  to  the  theory  of  Liebig,  that  prussian  blue, 
on  all  other  theories  the  most  complex  and  anomalous  compound  in  the  whole 
range  of  chemistry,  becomes  quite  normal  and  one  of  a  series. 

Ferrocyanide  of  potassium  is  employed  to  yield  cyanogen  and  all  its  compounds. 
We  have  already  seen  how  cyanogen,  hydrocyanic  acid,  cyanide  of  potassium, 
cyanate  of  potash,  urea,  cyanic  and  cyanuric  acids,  and  ferrocyanic  acid  are  ob- 
tained from  it.     Cyanide  of  potassium,  for  testing,  and  to  be  used  as  a  flux  and 


570  COBALTOCYANOGEN. 

in  analysis,  is  best  prepared,  according  to  Liebig,  by  heating  8  parts  of  the  dry 
ferrocyanide  with  3  of  pure  carbonate  of  potash  in  an  iron  vessel  till  the  fused 
mass  is  colourless.  It  is  then  poured  off  from  the  sponge  of  reduced  iron,  and 
kepi  in  well-stoppered  bottles.  This  very  useful  preparation,  known  as  Liebig's 
cyanide  of  potassium,  is  not  quite  pure,  containing  a  little  cyanate  of  potash  : 
but  this  does  not  interfere  with  its  use.  But  another  very  remarkable  compound 
is  produced  by  the  action  of  a  current  of  chlorine  gas  on  the  solution  of  ferro- 
cyanide, if  transmitted  until  the  solution  ceases  to  produce  prussian  blue  with 
perchloride  of  iron,  yielding  only  a  brownish-green  colour,  but  no  precipitate. 
The  liquid  now  gives,  on  evaporation,  beautiful  deep  hyacinth  red  crystals  of  a 
new  salt,  the  ferridcyanide  of  potassium,  discovered  by  Gmelin.  This  salt  con- 
tains a  new  radical,  ferridcyanogen. 

V.  Ferridcyanogen,    Cy6Fe2=Cfdy=211-74. 

This  radical  has  not  yet  been  isolated.  It  is  formed  by  the  coalescence  of  2 
eq.  of  ferrocyanogen,  and  is  tribasic.  It  forms  an  acid  with  hydrogen,  and  salts 
with  metals. 

Ferridcyanic  Acid.    (2Cfyf  H3)=Cfdy,H3=214-74. 

This  acid  is  obtained  from  the  lead  salt  Cfdy,Pb  ,  by  the  action  of  sulphuric 
acid.  It  is  soluble  in  water,  and  by  the  action  of  sulphuretted  hydrogen,  is  con- 
verted into  ferrocyanic  acid:  2Cfy,H^-f-HS=2f Cfy,H2)-|-S.  With  bases  it 
forms  salts  ;  as  with  potash  the  ferridcyanide  of  potassium. 

Ferridcyanide  of  Potassium.  Syn.  Red  prussiate  of  potash.  Its  preparation 
has  been  described  above.  Its  formula  is  2Cfy-|-K  =Cfdy,K  ;  and  it  is  quiie 
anhydrous.  Like  the  yellow  prussiate,  it  forms  precipitates  with  most  metallic 
solutions,  many  of  which  are  characteristic.  With  salts  of  peroxide  or  with  per- 
chloride of  iron,  it  only  strikes  a  brown  or  green  colour,  but  with  protochloride 
or  salts  of  protoxide,  it  forms  prussian  blue.  As  the  radical  is  tribasic,  1  eq.  of 
it  ought  to  be  equivalent  to  3  eq.  of  oxygen,  chlorine,  &c.,  and  if  we  suppose 
the  potassium  in  the  ferridcyanide  replaced  by  its  equivalent  of  iron,  we  should 
have  Cfdy,Fe^=Fe^Cy^;  for  K3Cfy2t3FeO=Fe3Cfy2-|-3KO ;  and  Yof^y^^ 
Fe  Cy  .  But,  instead  of  this  compound,  there  is  formed  prussian  blue,  the  same 
we  have  above  described  as  being  formed  by  the  action  of  yellow  prussiate  or 
peroxide  of  iron.  In  fact,  when  the  red  prussiate  is  added  to  a  solution  of  a  salt 
of  protoxide,  or  to  protochloride  of  iron,  yellow  prussiate  is  formed  along  with 
Prussian  blue  and  a  salt  of  potash.  Bearing  in  mind,  as  in  all  the  above  expla- 
nations, that  1  eq.  ferridcyanogen  Cfdy  is  equal  to  2  eq.  ferrocyanogen  Cfy,  and 
that,  consequently,  the  led  prussiate,  Cfdy,K^  may  be  equally  well  represented 
as  2Cfy,K3,  then  \tre  have  2(2Cfy,K3)  + 4(FeO,S03)=(3CfytFe^t (Cfy, KJ+ 
4(KO,S03). 

The  ferridcyanide  of  potassium  may  be  viewed  as  ferrocyanide  of  potassium, 
plus  a  certain  amount  of  ferrocyanogen;  2(Cfdy,K3)=3(Cfy,K2)-4-Cfy. 

With  salts  of  lead,  ferridcyanide  of  potassium  forms  the  ferridcyanide  of  lead, 
Cfdy,Pb3. 

VI.  COBALTOCYANOGEN.    Cy6Co2=Cky=2 16-52. 

Not  yet  isolated,  but  known  in  combination  with  hydrogen,  potassium,  &c.  It 
is  analogous  to  ferridcyanogen  in  constitution,  and  like  it,  is  tribasic. 

Cobaltocyanic  add  CkyH3=219'52. — Obtained  by  the  action  of  sulphuric  acid 


PLATINOCYANOGEN.  571 

on  cobaltocyanide  of  lead  Cky,Pbg.    It  forms  silky  filaments,  which  are  deli- 
quescent and  strongly  acid.  \ 

Cohallocyanide  of  Potassium^  Cky,K. — Is  obtained  by  acting-  on  a  salt  of  oxide 
of  cobalt  with  solution  of  cyanide  of  potassium  and  hydrocyanic  acid,  when  hy- 
drogen is  given  off  and  the  new  salt  is  obtained  in  crystals.  The  protocyanide  of 
cobalt,  precipitated  on  the  first  addition  of  cyanide  of  potassium,  redissolves  in  an 
excess  of  that  salt,  forming  a  compound,  2CoCy4-KCy,  or  2CoCy-j-3KCy.  At  all 
events  there  is  enough  of  cyanide  of  potassium  present  to  form  the  latter  compound. 
The  hydrocyanic  acid,  being  now  added,  yields  1  eq.  of  cyanogen,  converting  the 
2  eq.  of  protocyanide  into  1  eq.  of  sesquicyanide  of  cobalt,  while  hydrogen  is 
given  off:  2CoCy+HCy=Co2Cy^-j-H.  Lastly,  the  sesquicyanide  Co^Cy^,  with 
the  3  eq.  of  cyanide  of  potassium,  3KCy,  produces  the  cobaltocyanide  of  potas- 
sium, Cy  Co  +K  =Cky,K  .  The  crystals  are  isomorphous  with  those  of  the 
red  prussiate  of  potash  ;  they  are  yellow,  soluble  ;  their  solution  is  not  altered 
by  acids,  and  gives,  in  solution  of  protoxide  of  cobalt,  a  beautiful  rose-coloured 
precipitate,  analogous  probably  to  prussian  blue;  possibly,  however,  it  may  be 
Cky,Co^.  It  precipitates  many  other  metallic  solutions,  such  as  those  of  lead 
and  silver. 

Cobaltocyanide  of  potassium  is  a  singularly  permanent  salt,  resisting  the  action 
of  the  strongest  acids ;  which  is,  in  itself,  a  sufficient  proof  that  it  cannot  con- 
tain cyanide  of  potassium  as  such.  With  the  salts  of  nickel  it  forms  a  green 
precipitate,  Cky,Ni  ,  which  is  insoluble  in  boiling  dilute  acids.  This  property 
has  been  applied  by  Liebig  to  the  separation  of  cobalt  from  nickel  in  analysis. 
All  other  metals  being  removed,  an  excess  of  potash  is  first  added,  and  then  hy- 
drocyanic acid  till  the  precipitate  at  first  formed  is  dissolved,  and  the  whole  is 
then  boiled.  Hydrochloric  acid  is  now  added,  and  if  no  nickel  be  present,  it 
produces  no  change,  because  it  has  no  action  on  cobaltocyanide  of  potassium. 
But  if  nickel  be  present  (of  course  by  this  time  as  cyanide)  it  is  converted  into 
chloride,  and  this  is  instantly  precipitated  by  the  cobaltocyanide  of  potassium  as 
cobaltocyanide  of  nickel.  Should  there  be  more  cobalt  than  nickel  present,  the 
whole  nickel  is  precipitated,  and  the  precipitate,  acted  on  by  potash,  leaves  the 
nickel  as  peroxide,  while  the  cobalt  is  dissolved  as  cobaltocyanide,  and  may  be 
determined  along  with  the  portion  not  precipitated  for  want  of  nickel.  If,  on  the 
^other  hand,  there  be  more  nickel  than  cobalt,  all  the  cobalt  is  contained  in  the 

reen  precipitate  of  cobaltocyanide  of  nickel,  and  may  be  dissolved  by  potash, 

id  its  quantity  determined,  while  the  nickel  left  by  the  potash  as  peroxide  may 
Se  added  to  that  left  in  the  liquid  for  want  of  cobalt.     Such  is  an  outline  of  this 

jry  beautiful  and  refined  method,  which  gives  most  accurate  results. 

VII.    CHROMOcvANOGENr    CygCr2=Cry. 

This  radical  is  little  known.     It  is  analogous  to  the  two  preceding,  forming 
^ith  hydrogen  an  acid,  Cry,H  ,  and  with  potassium  a  yellow  crystallizable  salt, 
IryjK^,  which  precipitates  metallic  solutions. 

VIII.    PLATINOCYANOGEN.    PtCy2=Cpy=151-38. 

This  radical  is  not  known  in  the  separate  state.  It  forms  with  hydrogen  a 
w/ystallizable  acid  of  a  gold  or  copper  colour  and  metallic  lustre,  Cpy,!!^,  which 
is  very  soluble  and  deliquescent.  This  acid  is  powerful,  decomposes  the  car- 
'  lonates,  and  produces  platinocyanides,     Platinocyanide  of  potassium,  Cpy,K2, 


I 


572  IRIDIOCYANOGEN. 

is  obtained  by  heating  sponay  platinum  to  low  redness  with  dried  ferrocyanide 
of  potassium,  and  lixiviating  with  water;  or  by  dissolving  protochloride  of  pla- 
tinum in  hot  solution  of  cyanide  of  potassium.  It  forms  crystals  yellow  and 
metallic  by  transmitted,  blue  by  reflected  light.  By  the  action  of  this  salt  on 
protonitrate  of  mercury,  a  cobalt-blue  precipitate  is  formed,  which,  when  heated 
in  the  fluid,  becomes  white,  and  is  then  pure  platinocyanide  of  mercury,  Cpy, 
Hg(1)  This  salt,  acted  on  by  sulphuretted  hydrogen,  yields  the  platinocyanic 
acid.  A  solution  of  platinocyanide  of  potassium  acted  on  by  chlorine,  yields 
beautiful  copper-like  crystals  of  a  new  salt,  which  is  either  a  double  cyanide, 
2K0y-j-Pt2Cy^4-  5H0;  or  the  potassium  salt  of  a  new  radical,  Pt-Cy  ,K  + 
6H0.  (Knop.) 

The  platinocyanides  of  barium,  strontium,  and  calcium,  are  easily  obtained  by 
the  action  of  platinocyanic  acid  on  these  bases,  and  crystallize  readily  in  beau- 
tiful greenish  yellow  colour,  or  in  some  cases  green  and  red  with  metallic  lustre. 

IX.  IRIDIOCYANOGEN.    Cy3lr=Ciy. 

This  radical  has  not  been  isolated — it  forms  with  hydrogen,  iridiocyanic  acid 
Cy^lT,U^,  which  is  obtained  by  the  action  of  sulphuretted  hydrogen  on  iridiocy-. 
anide  of  lead  Cy  Ir,  Pb  . 

Iridiocyanide  of  Potassium,  Cy^Ir,K  ,  is  obtained  by  the  action  of  protochloride 
of  iridium  on  cyanide  of  potassium.  It  forms  colourless  crystals ;  its  solution 
gives,  with  salts  of  peroxide  of  iron,  a  deep  indigo  colour. 

There  appears  to  be  a  series  of  similar  compounds  formed  by  cyanide  of  pal- 
ladium. The  palladiocyanide  of  potassium  corresponds  to  the  platinocyanide, 
and  its  formula  is  Cy  PdK. 

There  is  also  reason  to  believe  that  manganese  forms  a  manganocyanogen, 
corresponding  to  ferridcyanogen,  Cy^Mn^ssCmy.  The  manganocyanide  of  potas- 
sium is  probably  Cy^Mn^+K  =Cmy,C  . 

From  what  has  been  stated  in  the  preceding  pages,  it  will  be  seen  that  cyano- 
gen has  a  very  great  tendency  to  form  cyanides  containing  2  or  3  metals,  and 
likewise  cyanides  containing  one  of  these  metals  and  hydrogen  in  the  place  of 
the  other.  As  these  latter  compounds  are  very  powerful  acids,  we  are  naturally 
led  to  consider  them  as  hydrogen  acids,  in  which  the  hydrogen  is  combined  with 
radicals.  This  view  has  been  adopted  above,  and  we  have  seen  reason  to  admit 
the  following  radicals : — 

Platinocyanogen  Cpy   =  CyjPt 

Palladiocyanogen  Cpdy  =  CyjPd 

Ferrocyanogen  Cfy    ssCygFe 

Iridiocyanogen  Ciy    =  Cy^Ir 

Ferridcyanogen  =  Cfdy  srsCygF^ 

Cobaltocyanogen  =:  Cky  =  CygCoj 

Chromocyanogen  =  Cry    =  CygCrj 

Manganocyanogen  =s  Cmy  =CygMnj 

It  will  be  observed  that  there  are  three  different  formulae  among  these  radicals, 
namely,  Cy^M ;  Cy^,M;  and  Cy^M^;  the  first  monobasic,  the  second  bibasic, 
the  third  tribaeic.  No  other  view  can  at  present  be  given  of  these  compounds, 
of  their  acids,  and  of  their  salts,  which  is  at  once  so  satisfactory,  so  consistent. 


SULPHOCYANOGEN.  573 

and  so  advantageous  for  the  learner,  as  being  adapted  to  assist  the  memory.  It 
is  true  that  the  acids  may  be  viewed  as  compounds  of  cyanide  of  a  metal  with 
cyanide  of  hydrogen  (hydrocyanic  acid),  and  their  salts  as  compounds  of  two 
metallic  cyanides.  Thus,  ferrocyanic  acid,  Cy^Fe-f-H^,  may  be  said  to  be  2H 
Cy  -\-  FeCy,  and  ferrocyanide  of  potassium,  2KCy  +  FeCy.  Again,  ferrid- 
cyanic  acid  may  be  3HCy+ Fe^Cy^  and  its  potassium  salt  3KCy -|- Fe  Cy  ; 
while  platinocyanic  acid  and  its  potassium  salt  may  be  HCy  +  PtCy  and  KCy 
+  PtCy. 

But  the  strong  acid  properties  and  inert  nature  of  these  acids,  and  the  remark- 
able permanence,  both  of  the  acids  and  of  the  salts,  are  entirely  inconsistent 
with  the  presence  of  so  weak  an  acid  and  so  frightful  a  poison  as  hydrocyanic 
acid,  or  of  bodies  so  easily  decomposed  as  hydrocyanic  acid  and  cyanide  of 
potassium.  Besides,  there  are  numerous  double  cyanides,  such  as  KCy,ZnCy; 
KCy,CdCy  ;  KCy,Cu2Cy,  &c.  &c.  &c.,  which  act  as  such  ;  being  easily  decom- 
posed, and  exhibiting  no  indications  of  containing  radicals  like  those  above 
described.  We  shall  therefore  not  dwell  on  any  other  view,  and  merely  allude 
here  to  the  true  double  cyanides,  as  belonging  more  to  the  history  of  the  metals, 
and  less  to  that  of  the  organic  radicals. 

PARACYANOGEN. 

As  an  appendix  to  the  metallic  cyanides,  we  may  here  mention  this  compound, 
which  is  left  behind  as  a  dark-brown  powder,  when  cyanide  of  mercury  is  heated 
in  a  retort.  As  cyanogen  and  mercury  alone  are  given  off,  we  should  expect  the 
salt  to  be  dissipated  by  heat  entirely  ;  but  this  not  being  the  case,  it  is  evident 
that  the  residue,  if  it  contain  no  mercury,  must  have  the  same  composition  as 
cyanogen,  and  be,  in  short,  an  isomeric  modification  of  it — a  solid  cyanogen. 
Again,  when  cyanide  of  silver  is  heated,  it  gives  off  part  of  its  cyanogen ;  it 
then  glows,  and,  if  soon  removed  from  the  fire,  yields  a  peculiar  residue,  which 
is  only  partly  dissolved  by  nitric  acid.  The  insoluble  residue  appears  to  contain 
silver  and  cyanogen  in  the  proportion  AgCy  ,  and  it  is  probable  that  the  cya- 
nogen here  is  in  the  solid  modification,  of  which  1  eq.  is  supposed  to  be  formed 
by  3  eq.  of  cyanogen. 

Whether,  therefore,  we  admit  paracyanogen  as  a  separate  radical  or  not,  the 
two  residues  just  mentioned  contain  carbon  and  nitrogen  in  the  proportions  to 
form  cyanogen.  It  is  also  possible  that  some  such  compound  may  exist  in 
cast  iron  and  steel,  which  appear  to  contain  nitrogen  as  well  as  carbon. 

In  treating  of  mellone,  we  shall  see  that  doubts>  may  be  entertained  of  the 
existence  of  paracyanogen,  and  that  the  proportions  of  carbonic  acid  and  nitro- 
gen gases  obtained  in  analyzing  the  supposed  paracyanogen  may  be  derived  from 
a  mixture  of  mellone  and  carbon. 


CYANOGEN  AND  SULPHUR. 

X.     SuLPHocYANOGEN.    CySj  =  Csy. 

Syn.  Bisulphuret  of  Cyanogen. — When  ferrocyanide  of  potassium  is  heated 
with  sulphur,  there  is  formed  a  new  salt,  the  formula  of  which  is  CyS  -f-  K. 
This  is  sulphocyanide  of  potassium,  which  appears  to  contain  the  radical  CyS  , 
or  Csy.  We  cannot  say  that  this  radical  is  known  in  the  free  state,  but  by  the 
action  of  chlorine  on  sulphocyanide  of  potassium  there  is  formed  a  bright  orange 


574  SULPHOCYANIDE  OF  POTASSIUM. 

powder,  which  contains  sulphocyanogen,  mixed  with  some  other  bodies.  Like 
the  preceding  radicals,  sulphocyanogen,  with  hydrogen,  forms  a  peculiar  acid, 
the  sulphocyanic  or  hydrosulphocyanic  acid. 
^  Hydrosulphocyanic  Acid — CyS,H  =  CsyH — is  obtained  bypassing  sulphur- 
etted hydrogen  gas  through  sulphocyanide  of  lead,  Csy,Pb,  suspended  in  water. 
Tiie  solution  thus  formed  is  highly  acid,  and  has  the  odour  of  acetic  acid.  It 
strikes  a  blood-red  colour  with  salts  of  peroxide  of  iron,  and  this  property  is 
found  in  all  soluble  sulphocyanides.  The  formula  of  this  acid  corresponds  to 
that  of  cyanic  acid,  CyO^,H ;  and  it  may  be  viewed  as  cyanic  acid,  the  oxygen 
of  which  has  been  replaced  by  sulphur.  With  metallic  oxides,  it  forms  the  sul- 
phocyanides of  the  metals  ;  C^^^.n  -f  MO  =  CyS^M  +  HO. 

Sulphocyanide  of  Potassium — CyS2,K=  Csy,K.  The  best  process  for  obtain- 
ing this  salt  is  to  melt  at  a  gentle  heat  (only  raised  at  the  end  to  low  redness) 
46  parts  of  dried  ferrocyanide  of  potassium,  32  of  sulphur,  and  17  of  pure  car- 
bonate of  potash.  The  mass  when  cold  is  boiled  with  water,  and  the  solution, 
being  filtered  and  evaporated,  deposits  striated  prismatic  crystals  of  the  salt, 
yery  similar  in  appearance,  and  in  taste  also,  to  nitre. 

If  not  quite  pure,  it  is  purified  by  solution  in  alcohol  and  recrystallization.  In 
this  process,  the  whole  cyanogen  of  the  ferrocyanide  is  first  converted  into  cya- 
nide of  potassium,  and  then,  by  the  taking  up  of  sulphur,  into  sulphocyanide ; 
while  the  iron  is  converted  into  sulphuret.  As  1  eq.  ferrocyanide  contains  3  eq, 
of  cyanogen  and  2  of  potassium,  1  eq.  of  carbonate  of  pota«h  is  added,  and  the 
3  eq.  of  cyanide  of  potassium  thus  obtained  take  up  6  eq.  of  sulphur  to  form  the 
new  salt.     3KCy  +  8^  =  3(CyS2,K). 

Sulphocyanide  of  potassium  causes  precipitates  in  some  metallic  solutions, 
but  as  many  metallic  sulphocyanides  are  soluble,  the  greater  number  of  metals 
are  not  precipitated  by  this  salt.  With  salts  of  peroxide  of  iron  it  strikes  an 
intense  blood-red  colour,  but  causes  no  precipitate.  With  acetate  of  lead  it 
gives  yellow  crystals,  and  with  subacetate  a  white  precipitate,  and  with  salts  of 
suboxide  of  copper  also  an  insoluble  white  subsulphocyanide  of  copper.  Sul- 
phocyanide of  silver  is  precipitated  as  a  curdy  white  solid,  when  sulphocyanide 
of  potassium  is  added  to  nitrate  of  silver.  The  other  sulphocyanides  are  soluble. 

When   sulphocyanic  a(yd    is  set  free  from  its  salts,  by  diluted  acids,  and 

exposed  to  heat,  it  is  resolved,  with  the  aid  of  the  element*  of  water,  into  car- 

'  CS   1 

bpnic  aqid,  bisulphuret  of  carbon,  and  ammonia.  C^NS^,!!  +  l^p^=z       2  C  ^ 

2  ■* 

NH  .     Compare  this  with  the  spontaneous  decomposition  of  cyanic  acid  when 

CO  ) 

set  free  from  its  salts  :  C^NO^,!!  t  H^O^  ==  qq^  f  t  NH3.     This  shows  that 

the  view  which  considers  sulphocyanic  acid  as  cyanic  acid,  the  oxygen  of  which 
has  been  replaced  by  sulphur,  is  confirmed  by  the  similarity  in  the  decomposi- 
tion of  these  two  acids ;  which,  in  this  point  of  view,  may  be  said  to  belong  to 
the  same  type. 

When  sulphocyanide  of  potassium  is  mixed  with  6  or  8  volumes  of  strong 
hydrochloric  acid,  hydrocyanic  acid  is  given  off,  and  a  new  crystalline  acid  is 
deposited,  which  contains  more  sulphur,  and  may  be  called  (hydro)  persulpho- 
cyanic  acid.  3(CyS  ,M),  that  is  3  eq.  of  sulphocyanic  acid  lose  (.'yH,  1  eq.  of 
hydrocyanic  acid,  and  there  remain  2  eq.  of  the  compound  CyS^.H,  or  persul- 
phocyanic  acid.  The  formula  of  its  ssalts  is  CySg,M.  When  the  acid  is  dis- 
solved in  ammonia,  it  soon  deposits  sulphur,  and   the  liquid   retains  a  mw 


MELLONE.  575 

compound  Cy  S  ,H2  (=  2CyS^,H  — S)  combined  with  ammonia  :    on  adding  an 
acid,  persulphocyanic  is   reproduced  and    deposited,  wiiile  sulphocyanic  acid 

remains  in  the  solution:  Cy^S^,li^=   ;  C  S^'h 

When  solution  of  sulphocyanide  of  potassium  is  acted  on  by  chlorine,  or  by 
nitric  acid,  a  bright  orange-yellow  powder  is  deposited,  which  was  long-  supposed 
to  be  sulphocyanogen;  but  it  now  appears  to  be  a  compound  or  mixture  of  vSul- 
phocyanogen,  sulphocyanic  acid,  and  water,  in  the  proportions  SCyS^-f-  CyS^, 
H  t  HO  =  CgN3Sg  +  (C2NS^,H)  +  HO  =  CgN^S^H^O.  This  yellow  com"- 
pound  undergoes  a  very  remarkable  change  when  heated  :  it  gives  off  bisulphuret 
of  carbon,  sulphur,  and  a  little  persulphocyanic  acid,  and  there  is  left  in  the 
retort  a  grayish  yellow  powder,  containing  no  sulphur,  oxygen,  nor  hydrogen, 
and  not  decomposed  by  a  low  red  heat.  By  a  strong  red  heat  it  is  dissipated, 
yielding  a  mixture  of  3  vol.  cyanogen  to  1  vol.  nitrogen. 

This  residue  may  be  viewed  as  a  cyanide  of  nitrogen  NCy^  =  C^N^,  and  as 
it  plays  the  part  of  a  radical,  analogous  to  cyanogen,  it  is  called  mellone,  and 
has  the  symbol  Me.  Its  production  from  sulphocyanogen  is  easily  explained : 
4(C2NS2)  =  aCS^  +  S^  +  CgN^.  If  the  orange-yellow  compound  which  yields 
it  be  thrown  into  melted  sulphocyanide  of  j)otassium  the  mellone  actually  seizes 
the  potassium,  expelling  the  sulphocyanogen,  which  is  resolved  into  bisulphuret 
of  carbon,  sulphur,  cyanogen,  and  nitrogen,  all  of  which  escape  with  efferves- 
cence. This  is  because  mellone  is  not  only  a  powerful  radical,  but  also  capable 
of  resisting  a  strong  heat. 

XI.    Mellone.    Me  =  C6N4  =  92-94. 

The  preparation  of  this  radical  by  the  action  of  heat  on  impure  sulphocyanogen, 
has  been  described  above.  It  may  also  be  obtained  by  heating  to  low  redness 
the  sulphocyanide  of  ammonium,  as  will  be  explained  below.  It  appears  as  a 
grayish-yellow  powder,  which  is  capable  of  combining  directly  with  potassium 
when  heated  with  it,  and  of  decomposing  sulphocyanide  of  potassium,  as  before- 
mentioned.  In  both  cases  it  forms  a  fusible,  soluble,  crystallizable  salt,  mel- 
lonide  of  potassium.  When  to  the  solution  of  this  salt  an  acid  is  added,  it 
causes  a  white  gelatinous  precipitate,  which  is  an  acid,  sparingly  soluble  in 

ater,  the  hydromellonic  acid. 

TABLE  OF  COMPOUNDS. 

Hydromellonic  Acid        .        .        .  CgN4,H 

Melam 2C6N4  +  CNH3 

Melamine C6N4 -f- SNHg 

Ammeline C6N4 -f- NHg  +  2H0 

Ammelide 2C8N4  -f  NH3  -f  6H0 

Hydromellonic  Acid — MeH  =  C  N  ,H — is  best  formed  by  mixing  a  hot  solu- 
tion of  mellonide  of  potassium  with  strong  hydrochloric  acid^  when,  on  cooling, 
hydromellonic  acid  is  deposited  as  a  snow-white  powder.  It  is  somewhat  solu- 
ble in  hot  water,  sparingly  so  in  cold  ;  it  is  a  strong  acid,  and  with  acetate  of 
potash,  produces  mellonide  of  potassium,  displacing  the  acetic  acid.  If,  how- 
ever, a  saturated  hot  solution  of  the  mellonide  be  mixed  with  acetic  acid,  half 
the  potash  is  removed,  and  on  cooling,  crystals  of  an  acid  salt  are  deposited, 
which,  in  the  case  of  a  hydrogen  acid,  is  very  unusual.    It  is  possible,  however, 


■ 


* 


576  SULPHOCYANIDE  OF  AMMONIUM. 

that  hydromellonic  acid  may  be  bibasic,  which  would  account  for  the  fact  of  its 
forming  an  acid  salt. 

Mellonide  of  Potassium. — Me,K  =  C  N  ,K — occurs  as  an  accidental  product 
in  the  making  of  sulphocyanide  of  potassium.  It  is  best  obtained  by  fusing  at  a 
low  red  heat,  in  a  covered  iron  crucible,  dried  ferrocyanide  of  potassium,  with 
about  half  its  weight  of  sulphur,  and  adding,  towards  the  end  of  the  fusion, 
about  5  per  cent,  of  dried  carbonate  of  potash.  The  cooled  mass  is  boiled  with 
water,  and  the  filtered  solution  concentrated,  till,  on  cooling,  it  forms  a  semi- 
solid mass  of  minute  needles,  which  are  purified  from  sulphocyanide  by  washing 
with  alcohol,  in  which  the  mellonide  is  insoluble.  The  mellonide  may  also  be 
obtained  by  adding  mellone  to  fused  sulphocyanide  of  potassium,  when,  by  the 
decomposition  of  the  sulphocyanogen,  an  additional  quantity  of  mellone  is 
formed.  In  the  first  process,  also,  a  portion  of  mellone  is  formed  by  the  action 
of  heat  on  the  sulphocyanide  of  iron,  produced  at  the  commencement  of  the 
fusion;  and  this  mellone  acts,  as  in  the  second  process,  on  the  sulphocyanide 
of  potassium,  giving  rise,  in  so  doing,  to  an  additional  amount  of  mellone: 
hence,  the  advantage  of  adding  some  carbonate  of  potash,  to  prevent  any  loss  of 
mellone.  Finally,  mellonide  of  potassium  may  also  be  prepared  by  adding  2 
parts  of  dry  subsuiphocyanide  of  coppe/  to  3  of  fused  sulphocyanide  of  potassium. 

Mellonide  of  potassium  is  soluble  in  water,  insoluble  in  alcohol.  It  has  a 
bitter  taste,  and  its  crystals  contain  5  eq.  of  water,  of  which  4  eqs.  are  expelled 
at  212°.  When  acted  on  by  hydrochloric  acid,  it  yields  hydromellonic  acid; 
when,  by  acetic  acid,  it  gives  the  acid  salt  above-mentioned.  By  the  action  of 
mellonide  of  potassium  on  the  salts  of  baryta,  strontia,  lime  or  magnesia,  the 
mellonides  of  barium,  &c.  are  obtained  as  sparingly  soluble  salts,  which  crystal- 
lize in  fine  needles. 

By  boiling  mellonide  of  potassium  with  excess  of  potash,  ammonia  is  given 
off,  and  a  new  salt  is  formed.  This  decomposed  by  acetic  acid,  yields  a  white 
crystalline  precipitate,  containing  no  potash,  probably  a  new  acid.  When  dilute 
solution  of  mellonide  of  potassium  is  acted  on  by  strong  hydrochloric  acid,  and 
boiled  till  the  hydromellonic  acid  is  re-dissolved,  the  liquid,  on  cooling,  deposits 
cyanuric  acid,  and  contains  sal  ammoniac.  Hydromellonic  acid  Cy  NH,  with  3 
eq.  of  water  H^O^,  and  1  eq.  oxygen,  yields  dry  cyanuric  acid,  Cy^O^,  and  oxide 
of  ammonium,  NH^O.  The  equivalent  of  oxygen  is  probably  derived  from  the 
atmosphere;  but  this  decomposition,  as  well  as  the  preceding,  requires  minute 
investigation. 

PRODUCTS  OF  THE  DISTILLATION  OF  SULPHOCYANIDE  OF  AMMONIA. 

As  an  appendix  to  sulphocyanogen  and  its  derivative  mellone,  we  may  con- 
sider the  remarkable  results  of  the  action  of  heat  on  sulphocyanide  of  ammo- 
nium, NH^,C^NS^. 

When  this  salt  is  heated  in  a  retort,  there  are  given  off  as  gases  or  vapours, 
bisulphuret  of  carbon,  ammonia,  and  sulphuretted  hydrogen,  the  two  latter  partly 
combined  as  sulphuret  of  ammonium: 

4  eq.  Sulphocyanide  of  Ammonium  .        .  =  Cg  N^  Sg  Hig 

may  yield 

2  eq.  Bisulphuret  of  Carbon        .        .        .        .  =  Cj        S^ 

4  eq.  Ammonia =        N4        H,j 

4  eq.  Sulphuretted  Hydrogen      .        .        .        .  =  S4  H^ 

1  eq.  Mellone =  Cg  N4 

Cg    Ng    Sg    H,« 


MELAMINE,  AMMELINE,  AMMELIDE.  577 

Such  is,  in  fact,  the  result  of  the  action  of  a  strong  heat  on  the  salt,  mellone 
alone  remaining  in  the  retort.  But  if  a  more  moderate  heat  be  employed,  a  gray 
residue  is  left,  containing  the  elements  of  mellone  with  those  of  ammonia.  If 
this  crude  residue  be  dissolved  in  boiling  potash,  and  the  solution  quickly 
filtered,  there  is  deposited,  on  cooling,  a  heavy  white  powder,  which  is  the  chief 
product  of  the  distillation  of  the  sulphocyanide,  in  a  state  of  purity.  It  has  been 
called  Melam,  and  its  formula  is  C^  N,  H„=  ^C.N^  -j-  3NH,,  or  3  eq.  mellone 
and  3  eq.  ammonia. 

When  the  crude  melam  is  acted  on  by  oil  of  vitriol  it  dissolves  with  the  aid 

of  a  gentle  heat,  and  if  water  be  added,  and  the  whole  boiled  till  the  addition  of 

carbonate    of  ammonia  causes   no   further  precipitate,  the  liquid,   on    cooling, 

deposits  a  large  quantity  of  cyanuric  acid,  and  is  found  to  contain  sulphate  of 

ammonia.     Now,  as  mellone,  by  the  action  of  acids  or  alkalies,  yields  cyanuric 

acid  and  ammonia,  it  is  easy  to  see  that  melam  should  do  the  same,  C    N   H  ; 

that  is,  melam  is  equal  to  2  eq.  mellone  C^^^^,  and  3  eq.  ammonia  N  H  ;  and 

if  we  represent  mellone  by  ^:^^^  melam  will  be  2  Cy  N  -f-  3NH  .     Now  let 

us  add  12  eq.  of  water,  and  2Cy3N  t  H^^^^^  =  2  (Cy30g,H3)  +  2NH3.  and 

adding  the  3  eq.  of  ammonia  already  present  in  melam,  we  have  2  eq.  hydrated 

cyanuric  acid,  2  CCygOQ,!!^),  and  5  eq.  ammonia,  SNH^,  as  the  final   results 

from  1  eq.  melam  and  12  eq.  water,  under  the  influence  of  acids  and  heat. 

When  melam  is  acted  on  by  boiling  with  potash,  a  series  of  new  compounds 

is  obtained.     The   first  is  melamine^  which  is  deposited  in   crystals  when  the 

alkaline  solution  cools.     Melamine  contains  no  oxygen,  but  is  an  artificial  organic 

base,  neutralizing  acids,  and  forming  salts'.     Its  formula  is  C^N  H  =  C  N    + 
..  00064' 

N^H^;  that  is,  it  contains  the  elements  of  1  eq.  mellone,  and  2  eq.  ammonia. 

The  second  new  body  is  obtained  as  a  white  powder,  when  the  alkaline  solu- 
tion which  has  deposited  melamine,  is  supersaturated  with  acetic  acid.  It  is 
called  ammeline,  and  is  also  a  base,  although  weaker  than  melamine.  Its  for- 
mula is  CgN^HX)^  =  CgN^  t  NH3  +  2H0,  or  1  eq.  mellone,  1  eq.  ammonia, 
and  2  eq.  water.     It  forms  a  crystallizable  salt  with  nitric  acid. 

It  may  here  be  observed,  that  melam,  C^^N^Hg,  with  2  eq.  water,  H^O^,  con- 
lins  the  elements  of  I  eq.  melamine,  C^N^H.,  and  1  eq.  ammeline,  C  N  H  0  . 

!•  'oot)  »  '6552 

When  either  melamine  or^immeline  is  dissolved  in  strong  sulphuric  acid,  or 
melam  in  nitric  acjd,  and  the   solution  mixed  first  with  two  vol    of  water,  and 

Ken  with  four  of  alcohol,  a  white  powder  is  obtained,  resembling  ammeline, 
It  having  the  formula  Cj^N^HgOg  =  ^C^N^H-  NH3  +  6H0,  or  2  eq.  mellone, 
eq.  ammonia,  and  6  eq.  water.  It  is  called  ammelide,  and  has  rather  the  cha- 
cters  of  an  acid  than  of  a  base. 

Melamine,  by  the  action  of  hydrochloric  acid,  aided  by  heat,  is  transformed 
into  ammeline,  giving  off  ammonia,  while  water  is  taken  up.     C  N  H    -|-  H  0 
=  C,N,H.O^,  and  C^N.H^O^  -  NH,  =  C^N,H,0^. 

Melam  also,  when  treated  in  the  same  way,  yields  ammeline  and  ammonia. 
=f  (C '/hT^  =  C..N„H„0^;  and  C^,N„H„0,  _  NH,  =  C.^N„H„0, 

All  these  substances  may  be  resolved,  by  the  action  of  acids,  into  cyanuric 
id  and  ammonia.     It  appears  that  they  are  all,  that  is,  melam,  melamine,  and 

ammeline,  first  converted  into  ammelide,  and  that  ammelide  is  the  source  of  the 

cyanuric  acid  and  ammonia. 

It  is  obvious  that  they  are  all  closely  related   to  each  other,  and  to  cyanuric 

acid.     That  they  are  also  related  to  mellone  is  probable,  because  when  heated 

39 


m- 


*5t8 


••••"RELATIONS  OF  MEL  AMINE,  &c. 


they  leave  a  yellow  residue,  which  is  converted  by  a  stronger  heat  into  cya- 
nogen and  nitrogen;  which,  in  short,  is  mellone.  All  these  compounds  may  be 
represented  as  tribasic  cyanurate  of  ammonia,  minus  water,  or  water  and  am- 
monia.    Thus, 


1  eq.  anhydrous  cyanurate  of  ammonia,  CygOjjSNHs 
Minus  3  eq.  water  .... 


Yields  1  eq.  melamine    . 

1  eq.  anhydrous  cyanurate  of  ammonia 
Minus  1  eq.  water         =  HO)  ^^  q 

•'      1  eq.  ammonia  ssHgNJ  "^     ^ 

Yields  1  eq.ammeline     . 

2  eq.  anhydrous  cyanurate  of  ammonia 
Minus  1  eq.  ammonia  =  NHg     ) 

'♦      6  eq.  water       =     HeOeJ 

Yields  1  eq.  melam 
2  eq.  anhydrous  cyanurate  of  ammonia 
Minus  3  eq.  ammonia    . 


Yield  1  eq.  ammelide 


=  CeN6H9  03 
=  Ha  03 

=  Cg  Ne  He 
=  Ce  Ne  Hg  O3 

=      N    H4O 

=  C6  N5  H5  O2 
=  C,2N,2H,806 

=  N       HgOg 

=  C,.2N,,H9 

=  C,2N,2H,806 

=  N3    Hg 

=:C^N,H9  0« 


When  the  mass  remaining  in  the  retort  in  whicR  urea  is  heated,  atid  formerly 
believed  to  be  cyanuric  acid  or  cyanurate  of  ammonia,  is  acted  on  by  acids,  it 
yields  cyanuric  acid,  and  ammonia  is  found  in  the  solution ;  but  if  it  be  boiled 
with  water,  an  insoluble  snow-white  powder  is  obtained,  which  agrees  with 
ammelide  in  almost  all  its  properties.  Its  formula,  however,  is  C  N  H  0  ,  and 
it  ipay  also  be  derived  from  cyanurate  of  ammonia,  as  follows : — 


1  eq.  anhydrous  tribasic  cyanurate  of  ammonia)    r  IV  H  O 


Cy303,3NH, 
Minus  2  eq.  ammonia 


and 
Plus  1  eq,  water 


=      N2H6 


=  C6N4H3O3 
=  HO 


Yields  1  eq.  of  the  new  product  frofti  urea  =  CeN4H404 


This  product,  therefore,  is  intermediate  between  ammelide  and  cyanuric  acid. 

To  be  transformed  into  hydrated  cyanuric  acid  it  has  only  to  lose  I  eq.  arin- 
monia,  and  to  gain  3  eq.  water.  Its  formation  from  urea  is  very  easily  under- 
stood ;  for  4  eq.  urea,  minus  3  eq.  carbonic  acid  and  4  eq.  ammonia,  will  give 
this  compound : — 


4  eq.  urea  ..... 

Minus  2  eq.  carbonic  acid  C2O4  ) 

*'      4  eq.  ammonia  N4H,2J 

1  eq,  of  the  new  compound 


CgNsH.sOg 

=  C2N4H,2(}4 

C6N4H4  04 


In  order  to  render  still  more  obvious  the  relation  of  these  compounds,  melam 
excepted,  to  cyanuric  acid  and  among  each  other,  let  us  express  the  hypotheti- 
cal compounds  NH  by  M^,  M,  therefore,  standing  for  i  eq.  NH.  We  then 
have— 


TO  CYANURIC  ACID.  579 

Melamine,  CgNeHg  ....  =Cy3  Mg  -f  H3 
Ammeline,  CeNgHgOa  .        .        .        =Cyj  |^4  f  Hj 

Ammelide,  C6N4jH4i03  .  .  .  r^Cyj  |^3  f  H, 
The  new  compound  from  urea,  C6N4H4O4  =Cya  ^  2  _j_  jj^ 
And  cyanuric  acid  ....        =Cy3     O5  -|-  H3 

Here  we  see  the  change  in  properties  accompanying  the  gradual  substitution 
of  M  for  0.  At  one  end  of  the  series  is  melamine,  a  base,  containing  no  oxy- 
gen ;  at  the  other  cyanuric  acid,  a  highly  oxygenized  acid ;  while  ammeline  is  a 
weak  base,  and  the  remaining  two  are  neutral,  or  have  a  tendency,  but  a  very 
slight  one,  to  acid  properties. 

Before  quitting  these  compounds,  it  is  proper  to  point  out  that  as  sulphocyanic 
acid  corresponds  to  cyanic  acid,  sulphur  being  substituted  for  oxygen,  so  sulpho- 
cyanide  of  ammonium  corresponds  precisely  in  the  same  way  to  urea  ;  for  urea 
is  C^N^H^O^,  and  sulphocyanide  of  ammonium  is  (see  above)  C^N^H^S^.  That 
this  analogy  is  not  imaginary  we  have  seen  in  the  similarity  of  the  action  of  heat 
on  both. 

In  the  case  of  urea,  4  eq.        ...».»        ssiCgNijHjgOj 
yield  2  eq.  carbonic  acid,  €2,04  >  r  tm  tr   n 

and     4  eq.  ammonia,  N4H,^{  *        *         •        =^2^^4«i2^4 

Leaving  1  eq.  of  the  new  body        ....        =CgN4H4  O4 

In  the  case  of  sulphocyanide  of  ammoniutn,  4  eq,  ,        ssrCgNgHigSg 

yield  2  eq.  bisulphure 
and     4  eq.  ammonia, 


yield  2  eq.  bisulphuret  of  carbon,  C2S4  •  ) 


Leaving  1  eq.  mellone-j-4  eq.  sulphuretted  hydrogen     ^  =aCgN4-j-H4S4  .4 

The  analogy  only  fails  here  in  the  iaot,  that  the  elements  CgN^H^S^,  instead 
of  uniting,  as  C^N^H^O^  do,  to  form   one  compound,  are  resolved  into  two, 

I^fcnamely,  raellone  and  sulphuretted  hydrogen.  Of  course  the  substance  from  urea 
^^may  be  viewed  as  compound  of  1  eq.  mellone  and  4  of  water  ;  and  it  may  pos- 
sibly hereafter  be  resolved  into  those  subs.tances. 
1^^^  When  mellone  is  boiled  with  nitric  acid  a  new  acid  is  formed,  ci^stallizing 
^^in  octohedrons,  which,  when  redissolved  in  water,  form  pearly  scales.  Liebig, 
who  alone  has  studied  it,  found  its  formula  and  all  its  reactions  exactly  like 
those  of  cyanuric  acid,  and  called  it  cyanilic  acid  ;  I  eq.  mellone  and  6  eq.  water, 
C  N  -j-HgOg,  are  equal  to  1  eq.  cyanilic  (or  cyanuric)  acid,  and  1  eq.  ammonia 
(C  N  Og,Hgi-NHg.)  Further  experiments  are  required  to  establish  cyanilic  acid 
as  an  independent  acid. 

Having  now  concluded  our  sketch  of  the  compounds  derived  fVom  that  of  sul- 
phur and  cyanogen,  it  only  remains  to  mention,  that  cyanogen  forms  one  or  two 
compounds  with  sulphuretted  hydrogen,  and  that  sulphocyanic  acid  forms  a  com- 
pound with  the  same  gas.  These  compounds,  however,  are  as  yet  too  little 
known  to  permit  of  their  being  clearly  laid  down. 


I 
I 


Cyanogen  does  not  form  any  compound  of  importance  with  phosphorus  or  the 
remaining  metalloids.     But  there  is  a  very  interesting  and  important  series  of 


P^^  URIC  ACID.  M-r 

compounds,  in  which  we  may  .conceive,  with  some  probability,  a  radical  to 
exist,  formed  of  the  elements  of  cyanogen  and  those  of  oxalyle,  or  carbonic 
oxide,  C^O  .  This  is  the  series  of  compounds  derived  from  uric  acid,  and 
consequently,  closely  connected  with  urea,  which  we  have  seen  to  be  derived 
from  cyanate  of  ammonia,  and,  through  cyanic  acid,  from  cyanuric  acid,  which 
connects  it  again  with  mellone,  melam,  and  sulphocyanogen. 

We  shall  first  briefly  describe  uric  acid  itself,  as  the  starting  point  of  an  ex- 
tensive series  of  products.  The  radical  supposed  to  exist  in  these  compounds 
will  be  better  understood  if  described  after  we  have  become  acquainted  with 
them. 

CYANOGEN  WITH  CARBONIC  OXIDE. 

XII.  Urylb. 

1.  Uric  Acip.    C,oN4H406=CH,N4H905f  HO. 

Syn.  Urilie  Mid.^—LitMc  ./^ctW.— Occurs  in  small  quantity  in  the  healthy  tirine 
of  man  and  quadrupeds,  and  in  much  larger  quantity  in  the  urine  of  birds, 
whether  carnivorous  or  herbivorous,  as  in  the  pigeon  and  hawk  tribes.  In  the 
urine  of  birds  it  forms  the  white  part,  in  the  form  of  urate  of  ammonia,  and  it  is 
still  found  as  such  in  guano — a  substance  produced  by  the  long-continued  action 
of  the  air  on  the  urine  (or  excrement,  for  they  are  voided  together)  of  sea-fowl. 
The  only  excrement  of  serpents,  as,  for  example,  of  the  boa  constrictor,  is  a  white 
semi-solid  mass,  which  soon  dries,  and  is  pure  urate  of  ammonia.  In  serpents, 
which  are  all  carnivorous,  it  is  very  remarkable  that  the  whole  excreta  (except 
occasionally  haif  and  feathers,  which  pass  undigested),  should  take  the  form  of 
urate  of  ammonia^.  In  diseased  urine,  uric  acid  is  often  deposited  on  cooling,  and 
generally  of  a  reddisl4,colour ;  it  also  constitutes  the  most  frequent  form  of  gravel 
and  of  calculus,  when  deposited  within  the  bladder.  Urate  of  soda  is  found  in 
the  chalk  stones  of  gouty  patients ;  and  it  is  well  known  that  gout  is  a  disease 
closely  allied  to  calculus  of  this  kind. 

It  is  best  obtained  from  the  excrement  (or  urine)  of  the  boa,  which   is  pow- 

.Jered,  and  dissolved  in  40  parte  of  boiling  water  by  the  gradual  addition  of 
caustic  potash,  till  the  liquid  is  decidedly  alkaline.  The  uric  acid  forms  urate 
of  potash,  which  dissolves^  while  the  ammonia  escapes.  The  hot  liquid,  being 
filtered  to  separate  impurities  (and  with  the  above  proportion  of  water  it  filters 
rapidly,  while  with  less  it  crystallizes  on  the  filter  and  chokes ^it  up),  is  mixed 

.with  a  decided  excess  of  hydrochloric  acid,  when  the  uric  acid  is  set  free,  and 
being  insoluble,  is  deposited,  at  first  as  a  very  bulky  gelatinous  hydnte,  which 
in  a  few  minutes  spontaneously  loses  water  and  shrinks  into  a  crystalline  heavy 
precipitate.  This  is  well  washed  with  cold  water  and  dried  in  the  air,  when  it 
forms  a  shining  powder,  composed  of  distinct  but  minute  crystals.   If  made  from 

.  a  cold  saturated  solution  of  urate  of  potassa,  the  crystals  are  much  larger,  but 
contain  17*6  per  cent. ;  in  this  case  4  eq.  of  water  are  expelled  at  212°,  leaving 

.  the  same  substance  as  that  precipitated  from  a  hot  solution,  which,  when  dried 
in  the  air,  loses  no  weight  at  212°.  The  latter  is  CjgN^H^O^H-HOr=Urf  HO ; 
the  large  crystals  are  a  hydrate,  Ur,H0-f-4  aq. 

If  pure  white  fragments  of  the  urine  of  the  boa  have  been  used,  the  above 
simple  process  yields  uric  acid  chemically  pure,  even  when  the  solution  in  potash 
has  had  a  decided  yellow  colour.  This  uric  acid  is  snow  white,  and  is  entirely  dis- 


URIC  ACID.  581 

sipated  by  heat,  leaving  no  trace  of  ashes.  But  if  the  boa's  urine  have  been 
impure,  or  if  calculi  have  been  employed  to  yield  uric  acid,  in  both  of  which 
cases  the  alkaline  solution  is  brown,  often  very  dark,  and  yields  a  coloured  uric 
acid,  or  again  if  we  wish  to  extract  uric  acid  from  guano,  we  must  first  purify 
the  urate  of  potash  by  evaporating  the  alkaline  solution  till  it  crystallizes  in  a 
mass,  or  passing  carbonic  acid  through  it  to  neutralize  the  free  potash,  when  the 
urate  of  potash  is  deposited,  and  is  washed  on  a  filter  with  cold  water,  in  which 
it  is  very  sparingly  soluble,  till  it  is  quite  white.  It  is  then  dissolved  in  boiling 
water,  and  decomposed  by  hydrochloric  acid  as  before.  I  have  described  thus 
minutely  the  preparation  of  pure  and  colourless  uric  acid,  because  none  of  the 
very  interesting  products  derived  from  it  can  be  obtained  if  we  employ  uric  acid 
with  even  a  very  slight  tinge  of  colour.  The  presence  of  a  mere  trace  of  the 
colouring  matter  of  urine  I  have  found  to  exert  a  most  remarkable  influence  on  the 
oxidation  of  uric  acid  by  nitric  acid,  an  influence  which  I  can  only  compare  to 
that  of  a  ferment  in  causing  a  peculiar  decomposition  to  take  place. 

Uric  acid  requires  15000  parts  of  cold  and  nearly  2000  of  hot  water  for  solu- 
tion, and  its  solution  reddens  litmus.  It  forms  salts  with  bases,  especially  with 
the  alkalies  and  alkaline  earths,  all  of  which  are  insoluble  or  sparingly  soluble. 
Urate  of  potash,  the  most  soluble  of  them,  requires  85  parts  of  boiling  water, 
but  less  if  free  potash  be  added.  The  urate  of  soda  is  still  less  soluble,  requiring 
124  parts  of  hot  water.  The  urate  of  ammonia,  a  frequent  form  of  calculus,  is 
very  sparingly  soluble,  requiring  243  parts  of  hot  and  1727  of  cold  water.  These 
are  the  only  urates  of  any  importance. 

PRODUCTS  OF  THE  OXIDATION  OF  URIC  ACID. 

Uric  acid  is  very  permanent  under  ordinary  circumstances,  but  is  readily  oxi- 
dized by  powerful  oxidizing  agents,  such  as  peroxide  of  lead,  peroxide  of  man- 
ganese, permanganate  of  potash,  and  nitric  acid. 

1.  Oxidation  nf  uric  acid  by  peroxide  of  lead.  If  uric  acid  be  mixed  with 
twenty  parts  of  boiling  water,  and  peroxide  of  lead  added  in  small  portions  to 
the  liquid  k<»pt  boiling,  the  brown  colour  of  the  oxide  disappears,  and  a  heavy 
white  powder  is  formed.  When  we  have  added  about  two  parts  of  the  oxide  for 
one  of  uric  acid,  or,  at  all  events,  when  the  oxide  begins  not  to  lose  its  brown 
colour,  the  hot  liquid  is  to  be  filtered,  and  on  cooling  it  deposits  a  number  of 
hard  brilliant  white  crystals,  of  which  more  are  obtained  on  evaporation.  The 
mother  liquid  at  last  crystallizes  in  a  mass  of  very  soluble  prismatic  crystals. 
These  last  are  pure  urea  ;  the  first  crystals  are  Allantoine,  and  the  powder  is 
oxalate  of  lead,  mixed  with  a  little  carbonate,  and  with  the  excess  of  peroxide. 
Hence,  the  products  of  this  oxidation  are.  Urea,  Allantoine,  and  Oxalic  Acid. 
After  describing  allantoine,  we  shall  be  able  to  explain  the  reaction. 

Allantoine.— C^^P^.-^^YTi,  Allantoic  Acid.—T\\\^  body  was  first  observed 
in  the  allantoic  fluid  of  the  fetal  calf,  which  is,  in  fact,  the  urine  of  the  fetal 
animal.  When  this  fluid  is  evaporated,  it  deposits  crystals  of  allantoine,  for- 
merly called  allantoic  acid,  which,  however,  is  not  an  acid.  Its  occurrence  in 
the  allantoic  fluid,  that  is,  as  an  ingredient  in  urine;  and  its  artificial  production 
from  uric  acid  by  a  process  of  oxidation,  are  facts  of  very  great  interest  when 
viewed  in  connection.  It  is  best  obtained  from  uric  acid,  as  above  described.  It 
is  a  very  indifferent,  or  neutral  substance,  and  forms  few  compounds;  only  one, 


I 


6l^  ALLOXAN* 

with  oxide  of  silver,  has  been  described,  the  formula  of  which  is  C^N^HjO^-f 
AgO=&  eq.  allantoine,  minus  1  eq.  water,  and  plus  1  eq.  oxide  of  silver. 

When  boiled  with  alkalies,  it  is  resolved  into  ammonia  which  escapes,  and 
oxalic  acid  which  combines  with  the  alkali.  In  fact,  both  allantoine,  C^N^  -f- 
H^Og,  and  oxalate  of  ammonia,  C^O^  -f  NH^,  may  be  represented  as  formed  of 
cyanog^en  and  water,  and  it  is  obvious  that  the  addition  of  3  eq.  of  water,  to 
1  eq.  of  allantoine  gives  C^N^  +  H^O^  =  2(C2NH303). 

We  can  now  explain  the  formation  of  allantoine. 

1  eq.  Uric  acid =C,oN4H40« 

Plus  2  eq.  oxygen  (from  .2  eq,.  PbO^)        =03) 

and  3  eq.  water      ".        .        .        H3O3J    "*"«   ""  "'"^ 


Together 

Are  equal  to  1  eq.  urea   . 

2  eq.  oxalic  acid 
1  eq.  allantoine   , 


=  C,  N2H3O, 


Together 
Or  in  the  form  of  an  equation, 

C,oN4H406  +  O2  +  H3O3  =  C2N2H4O2  -f-  2C2O3  -4-  C4X2H3O3 

That  allantoine  is  closcjly  related  to  uric  acid  and  urea  further  appears  from 
the  fact,  that  1  eq.  uric  acid,  1  eq.  urea,  ajid  1  eq.  water,  added  together,  are 
exactly  equal  to  the  sum  of  3  eq.  allantoine.  C^^N^H^Og-l-  C^N^H  O^  +  HO 
=  C,A««0,  =  3(C^N,H303). 

2.  Oxidation  of  uric  actd  hy  peroxide  of  mans;anese.  This  is  performed  much 
as  the  preceding,  and  there  appear  to  be  produced  compounds,  partly  the  same  as 
those  from  peroxide  of  lead,  partly  different.  Of  the  latter,  one  at  least  is  crys- 
tallizable,  but  has  not  been  sufficiently  examined.  The  subject  requires  investi- 
gation.'   vtin    w     \)\-  r.  ')'  • 

3.  By  p&rrhttngandte: cf  potash.  In  this  oxidation  also,  some  products  appear, 
■which  are  obtained  by  peroxide  of  lead  ;  such  as  urea,  and,  in  some  forms  of 
the  experiment  at  all  events,  oxalic  acid  ;  but  I  have  also  observed  the  formation 
of  a  new  acid,  containing  nitrogen,  the  precise  nature  and  composition  of  which 
is  not  yet  ascertained. 

4.  By  nitric  acid.  This  mode  of  oxidation  of  uric  acid  has  been  minutely 
studied  by  Liebig  and  Wohler,  and  they  have  shown  that  it  yields  a  very  large 
number  of  new  and  important  products,  among  which  is  again  found  orea,  and 
also,  under  certain  circumstances,  oxalic  acid.  The  changes  are  best  traced 
when  colourless  nitric  acid  of  a  moderate  concentration,  of  sp.  gr.  1*3  or  1*25 
for  example,  is  employed. 

1.  Moxan.  When  uric  acid  is  added,  in  small  portions,  to  this  acid,  it  is 
dissolved  with  a  gentle  and  uniform  effervescence',  due  to  the  escape  of  pure 
carbonic  acid  and  nitrogen  gases,  without  any  trace  of  the  red  vapours  of  nitrous 
acid.  Heat  is  also  developed,  so  that  no  external  heat  is  required,  and  it  may 
even  be  necessary  to  moderate  the  rea{3lion  by  placing  the  vessel  in  cold  water. 
If  too  much  uric  acid  be  added  at  once,  or  if  the  mixture  be  allowed  to  get  too 
hot,  a  violent  reaction  ensues,  accompanied  by  copious  red  fumes,  after  which 
the  experiment  cannot  succeed,  and  must  be  recommenced  with  fresh  materials. 
The  presence  of  a  trace  of  the  colouring  matter  of  the  urine  infallibly  causes 


ALLOXAN— ITS  METAMORPHOSES.  583 

this  violent  reaction,  even  with  a  much  weaker  nitric  acid,  and  thus  prevents  us 
from  obtaining  the  desired  result,  even  to  a  small  extent.  In  all  these  cases,  the 
whole  seems  to  be  converted  into  oxalate  and  carbonate  of  ammonia.  When  the 
operation  is  properly  managed,  and  a  little  practice  makes  it  quite  easy,  there 
appear,  in  the  warm  liquid,  after  a  certain  quantity  of  uric  acid  has  been  dis- 
solved, granular  crystals  of  the  new  compound,  alloxan.  If  a  little  more  uric 
acid  be  added,  it  is  still  dissolved,  and  when  the  warm  liquid  (at  about  120°) 
contains  a  good  many  crystals,  it  is  allowed  to  cool,  when  the  quantity  of  crys- 
tals greatly  increases.  They  are  now  thrown  on  a  filter  stopped  with  asbestus, 
and  when  they  have  drained,  the  acid  liquor  still  in  their  pores  is  displaced  by  a 
little  ice-cold  water,  which  is  added  till  the  droppings  altogether,  with  the 
liquid  first  filtered,  have  exactly  the  original  bulk  of  liquid.  (This  liquid  is 
again  treated  as  before  with  uric  acid,  the  crystals  again  collected  and  washed 
"with  a  little  cold  water,  and  this  operation  may  be  repeated  always  four,  occa- 
sionally five  times,  with  the  same  acid,  yielding  five  crops  of  crystals,  and  pre- 
serving the  mother  liquor,  of  which  hereafter.)  The  crystals  are  now  dissolved 
on  the  funnel  with  water  at  120°,  and  the  filtered  solution  evaporated  at  that  or 
even  a  lower  temperature,  till,  on  being  set  aside,  it  deposits  large  transparent 
crystals  of  hydrated  alloxan,  which  are  chemically  pure.  The  mother  liquid  of 
these  crystals,  being  gently  evaporated,  yields  more,  and  the  final  mother  liquid, 
which  is  now  rather  acid,  from  nitric  acid,  is  added  to  the  original  acid  mother 
Uquor,  to  be  used  for  other  purposes.  By  the  above  process,  I  have  constantly 
obtained,  without  difficulty,  upwards  of  90  parts  of  hydrated  alloxan,  quite  pure, 
from  100  of  uric  acid,  besides  what  remains  in  the  mother  liquid,  and  cannot  be 
extracted  in  that  form.  \^ 

The  crystals  of  hydrated  alloxan,  when  heated  to  212°  lose  about  27  per  cent... 
of  water,  =  6  eq.     The  dry  or  anhydrous  alloxan,  wfiich  may  also  be  obtained 
in  crystals  when  a  saturated  solution  is  evaporated  in  a  warm  place,  is  composed 
of  C^N^H  0,  .  which  explains  its  formation  from  uric  acid ;  for  C,  N  H  O.  -f-  0„ 

o       ^       4       10  *  10       4      '4      0  * 

-It  H^O^  =  Cj^N2H^Ojg  +  €2N2H^02:  that  is,  uric  acid,  ;)/ws  2  eq.  oxygen  and 
4  eq.  water,  yields  1  eq.  alloxan  and  1  eq.  urea. 

The  urea,  when  formed,  is  in  contact  with  hyponitrous  acid  (derived  from 
nitric  acid  by  the  separation  of  2  eq.  oxygen),  and  is  immediately  decomposed 
by  it,  yielding  oxide  of  ammonium,  which  combines  with  some  free  nitric  acid, 
carbonic  acid,  and  nitrogen,  which  two  last  escape  as  gases,  C2^2^4^2  "^  "^^3 
=F  NH^,0  *f-  2CO2  -[-  Nj.  At  the  end  of  the  operation,  therefore,  the  acid  liquid, 
which  has  deposited  crystals  of  alloxan,  contains  nothing  but  alloxan,  nitrate  of 
ammonia,  and  free  nitric  acid.  We  may  therefore  express  the  final  result  as 
follows :  C^^N^H^O^  f  2CH0,N0^)  +  2H0  =  C^N^H^O^^  +  (NH^0,N03)  ±  , 
2C0^+N^. 

Alloxan  is  very  soluble  in  water,  also  in  alcohol.  Its  solution  stains  the  skin 
pink,  and  gives  to  it  a  heavy  sickly  odour.  Its  taste  is  peculiar  and  almost  acid- 
ulous; but,  although  it  reddens  litmus,  it  has  not  the  chemical  characters  of  an 
acid.  It  is  a  very  remarkable  substance,  from  the  numerous  transformations 
which  it  undergoes,  when  subjected  to  the  action  of  different  re-agents. 

By  the  action  of  soluble  fixed  alkalies,  it  is  converted  into  a  powerful  acid, 
alloxanic  acid  ;  by  the  action  of  ammonia  it  yields  another  acid,  mykomelinic 
a^id ;  boiled  with  peroxide  of  lead,  it  is  converted  into  area  and  carbonic  acid; 
by  boiling  with  nitric  acid  it  is  changed  into  a  new  and  powerful  acid,  parahanic 
acid ;  by  the  action  of  sulphuretted  hydrogen  and  other  deoxidizing  agents,  it 


584  ALLOXANIC  AND  MESOXALIC  ACIDS. 

yields  a  new  compound  alloxantine  ;  with  hydrosulphuret  of  ammonia  it  gives  a 
new  salt  called  dialuraie  of  amm(mia ,-  with  sulphurous  acid  it  combines,  form- 
iiiff  a  compouTid  acid,  alloxano-snlphurous  acid  :  and  with  sulphite  of  ammonia  it 
forms  another  new  salt  called  Ihionurate  of  ammonia.  Such  are  the  compounds 
formed  by  the  direct  action  of  re-agents  on  alloxan ;  but  many  others  are  pro- 
duced by  the  action  of  re-agents  on  these,  singly  or  jointly.  Thus,  when  alloxan 
or  alloxantine  are  both  present  in  a  hot  solution,  ammonia  causes  the  develope- 
ment  of  a  deep  purple  cblour,  and  the  deposition,  on  cooling,  of  the  gold  green 
crystals  of  murexide ;  acids  acting  on  thionurate  of  ammonia  produce  ihionuric 
acid^  uramile,  and  uramilic  acid,-  acids  acting  on  murexide,  produce  murexan  ; 
acids  acting  on  dialurate  of  ammonia  separate  dialuric  add;  ammonia,  acting  on 
parabanic  acid,  converts  it  into  a  new  acid,  oxaluric  acid ;  and  by  the  action  of 
heat  on  alloxanate  of  baryta  another  new  acid,  mesoxalfc  acid^  is  produced.  We 
shall  endeavour  briefly  to  trace  the  formation  and  the  relations  of  these  remark- 
able products. 

2.  Mloxanic  Jcid.  Its  formula  ^^N^H^Og  -\-  2H0.  It  is  therefore  isomeric 
with  alloxan,  and  differs  from  it  in  this,  that  2  eq.  water  have  become  basic,  and 
replaceable  by  metallic  oxides.  It  is  a  bibasic  acid.  It  is  formed  when  solution 
of  alloxan  is  mixed  with  barytic  water,  as  long  as  the  white  precipitate  first 
formed  redissolves  with  a  gentle  heat.  When  it  begins  to  be  permanent,  a  drop 
or  two  of  alloxan  is  added  to  clear  all  up  ;  and  on  cooling,  alloxanate  of  baryta 
is  deposited  in  small  white  crystals.  From  this  salt  the  acid  is  obtained  by  add- 
ing sulphuric  acid,  so  as  to  separate  all  the  baryta.  The  acid  solution  on  evapo- 
rating yields  crystals  of  alloxanic  acid.  The  acid,  when  neutralized  by  ammonia, 
forms,  with  nitrate  of  silver,  a  white  precipitate,  which,  when  boiled,  becomes 
yellow,  and  is  reduced  with  effervescence.  When  the  solutions  of  its  salts, 
with  baryta,  lime,  and  strontia,  are  boiled,  they  become  turbid,  depositing  car- 
bonates, while  urea  and  a  mesoxalate  remain  dissolved.  The  formula  of  the 
alloxanates  is,  CgN2H20g,2MO  +  aq. 

3.  Mesoxalic  Jcid.  Obtained,  in  combination  with  baryta,  by  boiling  allox- 
anate of  baryta;  or  combined  with  oxide  of  lead,  by  adding  alloxan  in  solution, 
to  a  boiling  solution  of  acetate  of  lead.  The  baryta  salt  is  pale  yellow,  and 
sparingly  soluble ;    the  lead  salt  white  and  insoluble.     The  former   is    ^^fi^^ 

^   „  ^   the  latter  C^O^,2PbO.    The  acid  may  be  obtained  from  either  of  tliese 

salts;  it  crystallizes,  is  very  sour,  and  is  probably  bibasic,  and  has,  also  proba- 
bly, the  formula  C  O  ,2H0.  In  that  case,  the  anhydrous  acid  is  very  remarkable 
as  a  new  compound  of  carbon  and  oxygen,  of  the  same  class  as  mellitic  and 
oxalic  acids  ;  hence  the  name.  It  is  characterized  by  forming,  when  neutralized 
by  ammonia  with  nitrate  of  silver,  a  yellow  precipitate,  which,  when  heated,  is 
reduced  with  brisk  effervescence.  This  is  evidently  the  cause  of  the  reaction  of 
alloxanic  acid,  above  mentioned,  with  nitrate  of  silver.  Mesoxalic  acid  deserves 
and  requires  a  very  careful  investigation.  Its  formation  from  alloxan  or  allox- 
anic acid,  if  its  formula  be  C^O^,  is  very  easily  explained :  for  1  eq.  alloxan, 
minus  1  eq.  urea,  gives  2  eq.  mesoxalic  acid.    CgN^H^O^^j —  ^2-^2^4^2^^  ^6^8 

4.  Mykmnelinic  Acid.  C  N  HO.    Is  formed  when  ammonia  acts  on  solution 

8      4      5      5 

of  alloxan ;  when  a  yellowish  gelatinous  precipitate  of  mykonielinate  of  ammo- 
nia soon  appears.  This,  boiled  with  dilute  sulphuric  acid  yields  a  similar  yel- 
lowish precipitate,  which,  when  dry,  forms  a  powder  sparingly  soluble  in  cold, 


I 


PARABANIC,  OXALURIC  AND  THIONURIC  ACIDS.  585 

more  readily  in  hot,  water.  It  is  decidedly  acid.  It  is  formed  of  the  acid  hy 
the  reaction  of  2  en.  of  ammonia  on  1  eq.  alloxan.     C^N^H  O,^  -f-  2NH-  =  C 

*  3       2       4      10  <j  o 

N^H^O^  -|-  5H0.  It  would  appear  to  differ  from  allantoine,  only  by  1  eq.  of 
water ;  for  eq.  of  allantoine  are  CgN^H^Og. 

5.  Parabanic  acid.     C^N„0  +2H0.     Is  formed  when  alloxan  or  uric  acid  is 

o      2      4' 

heated  with  an  excess  of  nitric  acid,  and  the  solution  concentrated  until  on  cool- 
ing it  forms  a  soft  crystalline  mass.  This  is  dried  on  a  tile,  and  the  dry  crystals 
are  purified  by  solution  in  hot  water,  filtration,  and  redVystallization.  A  larg^e 
quantity  of  parabanic  acid  may  easily  be  obtained  from  the  acid  mother  liquors 
of  alloxan.  When  pure,  the  acid  is  beautifully  white  and  crystallized,  very  acid, 
and  very  soluble.  It  is  characterized  by  its  great  permanence  in  the  free  state, 
for  it  may  be  boiled  with  nitric  acid,  as  its  preparation  shows,  and  at  the  same 
time  by  its  extreme  proneness  to  change  in  contact  with  bases.  Thus,  if  neu- 
tralized with  ammonia  in  the  warm  solution,  it  deposits,  on  cooling,  a  crystallized 
salt,  which  is  oxalurate  of  ammonia.  The  same  change  takes  place  with  all 
bases  except  oxide  of  silver,  so  that  the  parabanate  of  silver  is  the  only  salt  of 
this  very  powerful  and  remarkable  acid  which  can  be  obtained.  To  he  converted 
into  oxal uric  acid,  parabanic  acid  only  requires  3  eq.  of  water.  The  production 
of  parabanic  acid  is  very  simple.  1.  From  uiic  acid.  C^^N^H^Og-f-O^-j-H^O^ 
=  ^2^2^,0,  +  200^  +  C^N^0^,2H0.  2.  From  alloxan.  C^N^H^O^^  +  0^  = 
2C02+2HO  +  CgN20^,2HO. 

6.  Oxalurie  acid.  CgN^HgO^-f-HO.  Formed  by  the  action  of  bases  on  para- 
banic acid.     C.N  O^  -|-  KO  f  3H0=C  N  H  O  ,K0,     The  acid  is  obtained  by 

024'  '  023     7'  ■' 

adding  dilute  sulphuric  acid  to  a  hot  saturated  solution  of  oxalurate  of  ammonia, 
prepared  by  the  action  of  ammonia  on  parabanic  acid.  On  cooling,  the  oxalurie 
acid  is  deposited  as  a  heavy  white  powder.  When  long  boiled  in  water,  it  is 
decomposed  into  oxalate  of  urea  and  free  oxalic  acid.  In  fact,  it  contains  the 
elements  of  2  eq.  oxalic  acid  and  1  eq.  urea.  2C  O  +C  N  H p,=C  N  H  O  , 
HO.  It  IS  also  characterized  by  forming  with  oxide  of  silver  a  white  salt,  which 
dissolves  in  hot  water,  and  crystallizes  beautifully  on  cooling. 

The  oxalurate  of  ammonia^  NH^O-j-CgN^H^O^,  is  formed  whenever  a  solution 
of  alloxan,  or  alloxantine  in  water,  or  of  uric  acid  in  nitric  acid,  is  evaporated 
with  excess  of  ammonia,  and  where  colouring  matter  is  present,  as  when  ammo- 

:a  is  made  to  act  on  the  acid  in  the  mother  liquors  of  alloxan,  the  oxalurate  is 
often  deposited  in  radiated  hemispherical  concretions,  which  sometimes  attain  the 
size  of  an  inch  or  two  in  diameter,  and  are  very  hard.  When  declorized  by  ani- 
mal charcoal,  it  forms  small,  soft,  flexible  needles.  I  have  found  that  this  salt, 
when  exposed  to  heat  in  a  retort,  yields  ammonia,  hydrocyanic  acid,  and  much 
oxamide,  besides  water,  and  perhaps  other  products,  while  a  dark  residue  is 
left. 

7.  Thionuric  Acid,  0^^^^^p^^^{C^^^p^.'2^0^)^<2YiO,  is  formed  when 
sulphite  of  ammonia,  with  excess  of  base,  is  added  to  solution  of  alloxan,  and 
the  whole  boiled  for  a  few  minutes,  or  until  crystals  appear  in  the  hot  liquid. 
On  cooling  it  forms  a  semi-solid  mass,  from  the  separation  of  a  large  quantity  of 
thionurate  of  ammonia  in  beautiful  silvery  crystals,  which  are  to  be  washed  with 
cold  water,  and  dried  on  a  tile.  From  this  salt  thionurate  of  lead  is  prepared, 
and  this,  being  decomposed  by  sulphuric  acid,  yields  thionuric  acid.  The  acid 
is  crystallizable,  but  very  soluble.  It  is  bibasic,  and  contains  the  elements  of  1 
eq.  alloxan,  1  eq.  ammonia,  and  2  eq.  sulphurous  acid,  not,  however,  as  such, 
for  the  elements  of  2  eq,  water  have  assumed  the  basic  form. 


586  URAMILIC  ACID.— ALLOXANTINE. 

Its  most  striking  character  is,  that  when  its  solution  is  heated  it  becomes  turbid 
from  the  deposition  of  a  new  compound,  uramile,  and  in  the  liquid  sulphuric 
acid  may  now  be  found,  which  was  not  previously  present.  CgNgH^Og-j-SSO^ 
^CgN^H^0g-j-2S0^;  so  that  the  sulphurous  acid  obtains  oxygen  from  the  rest 
of  the  acid,  and  becomes  sulphuric  acid,  leaving  uramile,  C^N^H^Og. 

Thionurate  of  Jmmonia,  (CgN^H ^0^,2802) -|-2NH^O-|-2aq.  is  formed  as  above 
described.  When  its  solution  is  mixed  with  1  eq.  of  hydrochloric  acid,  half  the 
ammonia  is  removed,  and  by  evaporation  we  obtain  acid  thionurate  cf  ammonia 
in  minute  silky  needles.  But  when  the  hot  solCtion  of  thionurate  of  ammonia 
is  mixed  with  an  excess  of  acid,  the  thionuric  acid  is  set  free  and  instantly 
decomposed,  uramile  being  deposited.     Little  is  known  of  the  other  thionurates. 

8.  Uramile;   C  N,H  O^;  its  formation  has  been  described  above.     It  occurs 

•   1  o      3      5     o 

either  as  a  crystalline  powder,  or  in  dendritic  or  feathery  crystallizations,  of  very 
beautiful  aspect.  It  dissolves  in  ammonia  and  potash,  and  the  solution  absorbs 
oxygen ;  becoming  purple,  and  depositing  green  crystals  of  murexide,  or  of 
potassium-murexide.  When  boiled  with  peroxide  of  mercury,  and  a  very  little 
ammonia,  it  is  also  converted  into  murexide.  Boiled  with  caustic  potash,  or 
with  dilute  acids,  it  is  said  to  yidd  uramilic  acid.  Nitric  acid  reconverts  it  into 
alloxan. 

9.  Uramilic  Mid.  Obtained,  by  Liebig  and  Wohler,  by  evaporating  acid  thi- 
onurate of  ammonia,  or  uramile,  with  dilute  sulphuric  acid;  also,  it  is  said,  by 
boiling  uramile  with  potash.  It  appeared  to  these  chemists  as  fine  prisms,  very 
soluble  in  water,  and  its  analysis  indicated  the  formula  CJ^^N^Hj^^O^^ ;  which 
might  be  derived  from  2  eq.  uramile  by  the  loss  of  1  eq.  ammonia,  and  the  addi- 
tion of  3  eq*  water.  2(CgN3H^Og)  +  2H0— NH3=CjgN^HjpOj^.  But  this  acid 
has  not  been  again  obtained,  and  its  existence  is  still  doubtful. 

10.  Moxantine ;  C  N  H  O  ;  obtained  in  large  quantity  by  diluting  the  acid 
mother  liquid  of  alloxan  with  3  or  4  parts  of  water,  and  passing  a  current  of  sul- 
phuretted hydrogen  through  it.  In  a  short  time  sulphur  is  deposited,  and  then 
white  crystals  of  alloxantine.  When  a  large  quantity  has  formed,  it  is  collected 
with  the  sulphur,  on  a  filter,  washed  with  a  little  cold  water,  and  the  filter  with 
its  contents  then  boiled  with  a  large  quantity  of  water.  The  solution  filtered 
while  hot,  and  with  the  addition  of  a  few  drops  of  hydrochloric  acid,  deposits, 
on  cooling,  a  large  crop  of  pure  crystals  of  alloxantine.  The  acid  liquid,  filtered 
from  the  first  deposit,  often,  on  standing  a  day  or  two,  deposits  a  large  additional 
quantity  of  alloxantine.  This  always  happens,  if  too  much  sulphuretted  hydro- 
gen has  been  used  ;  for  that  converts  the  alloxantine  partially  into  dialuric  acid, 
which  is  more  soluble,  but  by  absorbing  oxygen  from  the  air  is  reconverted  into 
alloxantine,  and  thus  deposited.  Imi^  jIh.W;  . 

Alloxantine  may  also  be  obtained  by  deoxidizing  a  pure  solution  of  alloxan, 
either  by  sulphuretted  hydrogen,  or  by  other  deoxidizing  agents  ;  or  by  heating  a 
solution  of  alloxan  to  the  boiling  point,  either  by  itself  or  with  the  addition  of 
dilute  mineral  acids,  when  alloxantine  is  formed  and  deposited  on  cooling.  But 
the  process  above  given  for  converting  into  alloxantine  the  alloxan  of  the  acid 
mother  liquor,  which  cannot  be  purified  by  crystallization,  is  so  productive,  and 
yields  alloxantine  so  pure,  that,  if  we  have  to  prepare  alloxan,  we  need  never  be 
at  a  loss  for  alloxantine. 

The  formation  of  alloxantine  from  alloxan  by  sulphuretted  hydrogen  is  easily 
explain.ed,  for  these  compounds  only  differ  by  1  eq.  hydrogen,  which  the  alloxan 
takes  from  sulphuretted  hydrogen.     Oxidizing  agents,  by  converting  this  hydro- 


ALLOXANTINE.— DIALURIC  ACID.  587 

gen  into  water,  readily  reconvert  alloxantine  into  alloxan.     C  N  H  0    +  0  = 
HOf  C.N^H^O,„. 

Alloxantine  forms  white,  hard,  brilliant  crystals,  which  never  exceed  a  certain 
small  size.  It  is  very  sparingly  soluble  in  cold  water,  much  more  so  in  hot 
water.  Its  solution  is  characterized  by  giving  with  solution  of  baryta  a  deep 
violet  precipitate,  which  with  excess  of  baryta,  changes  to  white;  and  by  in- 
stantly reducing  nitrate  of  silver,  forming  a  black  powder  of  silver,  the  alloxan- 
tine passing  into  alloxan,  or  oxaluric  acid.  The  crystals  of  alloxantine,  heated 
to  300°,  lose  3  eq.  of  water. 

In  the  preparation  of  alloxan,  it  is  necessary,  as  has  been  stated,  to  be  very 
careful  that  the  first  solution  of  the  crystals  formed  in  the  nitric  acid  should  not 
be  heated  too  strongly,  because,  as  this  solution  contains  free  nitric  acid,  allox- 
antine is  formed  at  a  certain  temperature ;  and,  besides,  even  a  pure  solution  of 
alloxan,  if  boiled,  is  partly  converted  into  alloxantine.  The  action  of  diluted 
nitric  and  other  mineral  acids  on  alloxan  is  to  produce,  from  2  eq.  alloxan,  1  eq. 
alloxantine,  3  eq.  oxalic  acid,  1  eq.  ammonia,  and  1  eq.  cyanic  acid,  the  latter, 
with  3  eq.  water,  producing  bicarbonate  of  ammonia.  When  solution  of  alloxan 
is  boiled  alone,  it  is  converted  into  alloxantine,  parabanic  acid,  and  carbonic  acid. 
3(C  AH4O  J=(C,N,H,0,„)  t  C^N,H,0,+ 2C0,. 

In  all  these,  or  in  similar  cases,  the  presence  and  the  relative  proportion  of 
alloxantine  contained  in  alloxan  at  any  period,  may  be  judged  of  by  the  colour 
of  the  precipitate  formed  in  baryta.  If  pure  white,  no  alloxantine  is  present:  if 
slightly  pink,  it  is  present  in  small  quantity ;  if  deep  violet,  all,  or  nearly  all,  the 
alloxan  has  been  converted  into  alloxantine. 

It  is  when  both  alloxan  and  alloxaBtine  are  present,  that  the  addition  of  am- 
monia produces  the  deep  purple  colour,  and  the  green  crystals,  of  murexide. 
"When  ammonia  acts  on  alloxantine  alone,  it  gives  rise  to  uramile,  and,  finally, 
to  oxalurate  of  ammonia. 

The  most  remarkable  change  which  alloxantine  undergoes  is  that  caused  by 
the  further  action  of  sulphuretted  hydrogen.  If  that  gas  be  passed  through  a  hot  • 
solution  of  alloxantine  sulphur  is  precipitated,  and  an  acid  liquid  is  obtained, 
which,  if  neutralized  by  carbonate  of  ammonia,  forms  a  salt  in  soft  white  silky 
crystals,  the  dialurate  of -ammonia.  Alloxantine,  by  the  action  of  hydrogen, 
which  removes  1  eq.  oxygen,  is  converted  into  dialuric  acid. 

11.  Dialuric  Mid.  C^^p^-\-nO=C^f{p^.  Produced  by  the  action  of 
sulphuretted  hydrogen  on  alloxantine.    C  N  H  O,  +HS=S-f  2H04-C  N  H  O  . 

T»i  1-  •  ..  ^"25      10  8248 

It  IS  best  obtained,  in  combination  with  ammonia,  by  adding  a  slight  excess  of 
hydrosulphuret  of  ammonia  to  a  solution  of  alloxan  or  alloxantine,  when  a  copious 
crystalline  precipitate  appears.  This,  when  boiled,  dissolves  in  the  liquid,  and 
on  cooling  is  deposited  in  minute  silky  prisms,  which  are  white,  but  in  drying 
become  pink,  or  even  deep  red.  They  should  be  washed  on  the  filter,  first  with 
diluted  hydrosulphuret  of  ammonia,  then  with  alcohol,  to  which  a  little  hydro- 
sulphuret has  been  added  ;  and  lastly,  with  pure  alcohol ;  and  dried  by  pressure 
in  blotting  paper,  and  in  the  vacuum  of  the  air-pump.  They  may  thus  be  ob-* 
tained  white,  or  very  nearly  so;  and  when  once  quite  dry  they  are  permanent.  . 
When  this  salt  is  dissolved  in  hot  and  moderately  strong  hydrochloric  acid,  crys- 
tals of  dialuric  acid  are  deposited  on  cooling.  These  crystals  resemble  some- 
what those  of  alloxantine,  but  are  larger,  and  not  so  brilliant.  Their  solution, 
and  the  crystals  themselves  under  water,  absorb  oxygen,  and  are  soon  changed 


i 


588  MUREXIDE.     ' 

into  alloxantine,  from  which  dialuric  acid  only  differs  by  1  eq.  oxygen,  and  1 
eq.  water. 

Dialuric  acid  is  a  powerful  acid.  Its  salts  are  insoluble  or  sparingly  soluble, 
and  only  permanent  in  the  dry  state.  The  dialurate  of  ammonia,  above  de- 
scribed, is  the  most  interesting. 

12.  Murexide.  Syn.  Purpurate  of  ammonia.  Formed,  as  already  mentioned, 
when  ammonia  acts  on  a  solution  containing  both  alloxan  and  alloxantine,  which 
explains  its  production  when  ammonia  is  added  to  the  solution  of  uric  acid  in 
dilute  nitric  acid,  after  evaporation  to  a  certain  extent:  also,  when  uramile  or 
murexan  is  boiled,  with  red  oxide  of  mercury  or  oxide  of  silver,  in  water,  with 
a  few  drops  of  ammonia,  or  when  uramile  or  murexan  is  dissolved  in  ammonia 
and  exposed  to  the  atmosphere;  and  in  a  great  variety  of  circumstances  from  all 
the  preceding  compounds,  or  nearly  all  of  them. 

On  the  small  scale,  4  grains  of  alloxantine  and  7  grains  of  hydrated  alloxan, 
are  dissolved  together  in  ^  oz.  by  measure  of  water  by  boiling,  and  the  hot  solu- 
tion added  to  ^  oz.  by  measure  of  a  saturated  or  nearly  saturated  solution  of 
carbonate  of  ammonia,  the  latter  being  cold.  This  mixture  has  exactly  the 
proper  temperature  for  the  formation  of  murexide ;  and  it  does  not,  owing  to  its 
small  bulk,  remain  too  long  hot.  It  instantly  becomes  intensely  purple,  while 
carbonic  acid  is  expelled  ;  and  as  soon  as  it  begins  to  cool,  the  beautiful  green 
and  metallic-looking  crystals  of  murexide  appear.  As  soon  as  the  liquid  is  cold, 
these  may  be  collected,  washed  with  a  little  cold  water,  and  dried  on  filtering- 
paper.  I  have  obtained  them,  by  the  above  process,  and  on  this  small  scale,  of 
from  2  to  3  lines  in  length.  When  made  with  larger  quantities,  the  crystals  are 
always  smaller,  owing,  probably,  to  some  effect  of  the  slower  cooling  of  the 
larger  mass  of  liquid,  as  continued  heat  is  not  favourable  to  their  formation.  If 
we  do  not  care  about  having  the  finest  crystals,  we  may  prepare  murexide  in 
large  quantity  by  adding  solution  of  alloxan  to  a  boiling  solution  of  alloxantine, 
and  cautiously  adding  cold  solution  of  carbonate  of  ammonia,  till  the  mixture  has 
become  nearly  black,  and  the  green  crystals  begin  to  appear.  The  vessel  being 
removed  from  the  fire,  deposits  a  very  large  quantity  of  murexide.  In  these  pro- 
cesses, the  residual  liquid  is  still  coloured,  and  is  alkaline  from  excess  of  am- 
monia: if  kept,  it  loses  the  red  colour,  becomes  yellowish,  and  if  evaporated, 
yields  much  alloxanate  of  ammonia  in  crystals. 

Murexide  is  one  of  the  most  beautiful  products  of  chemistry ;  the  crystals  are 
metallic  green  by  reflected  light,  like  the  cantharides  fly  or  the  gold  beetle,  and 
deep  red  by  transmitted  light.  Their  solution  is  deep  purplish  red,  and  they 
dissolve  in  potash  with  the  most  splendid  purplish  blue  colour  that  can  be  ima- 
gined; this,  however,  soon  disappears.  When  their  solution  is  acted  on  by  a 
dilute  mineral  acid,  ft  is  decolorized,  and  deposits  a  shining  scaly  crystalline 
powder,  of  a  pale  yellow  colour,  which  is  murexan.  The  same  compound  is 
obtained  when  acids  are  added  to  the  solution  of  murexide  in  potash,  after  the 
purple  tint  has  disappeared  on  digestion  in  a  gentle  heat. 

The  composition  of  murexide  is  uncertain,  and  there  are  different  views  of  its 
constitution.  According  to  some  it  is  a  salt  of  ammonia;  and  this  view  is  sup- 
ported by  the  fact  that,  with  salts  of  baryta  and  oxides  of  lead  and  silver,  it 
yields  purple  salts,  which,  according  to  Fritzsche,  contain  the  same  acid  that  in 
murexide  is  combined  with  ammonia,  and  which  may  be  called  purpuric  acid. 
But  murexide  is  not  a  compound  of  ammonia  with  the  purpuric  acid  of  Pmut, 
for  when  that  body  (murexan)  is  dissolved  in  ammonia,  it  only  forms  nyirexide 


MUREXAN— URYLE.  589 

by  absorbing  oxygen  from  the  air,  and  yields  other  compounds  at  the  same  time. 
Again,  the  action  of  sulphuretted  hydrogen  is  inconsistent  with  the  view  of 
murexide  being  a  salt  of  ammonia,  and  in  many  of  its  relations  it  more  resembles 
a  neutral  body — such  as  a  compound  of  amide.  Its  products  of  decomposition 
are  very  numerous,  and  altogether  the  subject  is  one  of  much  difficulty.  Possibly 
there  may  be  two  substances  similar  in  appearance,  but  distinct  in  constitution; 
one  a  salt  of  ammonia,  the  other  an  indifferent  body,  or  an  amidide.  The  great 
discrepancy  in  the  results  of  analysis,  is  obtained  by  Liebig  and  Wohler  on  the 
one  hand,  and  Fritzsche  on  the  other,  as  well  as  some  differences  in  the  proper- 
ties ascribed  to  it  by  different  chemists,  lead  to  some  such  conclusion.  The 
formula  considered  by  Liebig  and  Wohler  the  most  probable,  all  things  consi- 
dered, but  not  established,  is  C^^^^^H^Og;  another,  somewhat  less  probable,  is 
C  „N„H,  O,  .     Both  of  these  will  enable  us  to  account  for  its  production  in  dif- 

20      8       10      14  '^ 

ferent  circumstances.  The  formula  of  Fritzsche,  which  agrees  with  his  analysis, 
is  CjgN^HgOjj  =  NH3  -j-  C^^Nflp^^.  The  salt  formed  with  nitrate  of  silver 
is,  Cie^jH^O  -f-  AgO,  which  would  exhibit  the  unusual  phenomenon  of  am- 
monia, instead  of  oxide  of  ammonium,  being  replaced  by  oxide  of  silver;  and 
the  baryta  compound  is  ^jgN^H^O^^  -j-  HO  -j-  BaO.  Admitting  the  formulae 
of  Fritzsche  for  the  silver  and  barium  compounds  to  be  correct,  these  are  not 
demonstrated  to  be  salts  of  purpuric  acid :  but  besides  this,  his  formula  for  mu- 
rexide does  not  enable  us  to  explain  its  production  in  any  case.  In  these  circum- 
stances, we  shall  not  attempt  to  explain  the  formation  of  murexide,  further  than 
to  point  out,  that  it  appears  to  require  the  presence  of  a  compound  intermediate 
between  alloxan  and  alloxantine  (the  former  losing  oxygen,  the  latter  gaining  it), 
and  of  ammonia;  and  that  it  is  not  the  only  product. 

13.  Murexan.  Syn.  Purpuric  Acid.  C^N^H^O^  ?  Formed  by  the  action  of 
acids  on  murexide,  but  along  with  several  other  products.  It  appears  as  a 
shining  powder,  composed  of  scales,  generally  pale  yellow,  sometimes  pale 
brown,  never  quite  white.  It  is  insoluble  in  water  or  nearly  so,  but  the  liquid 
filtered  from  it  has  always  a  peculiar  opalescent  aspect  and  play  of  colours.  It 
dissolves  in  potash  and  ammonia,  and  the  solutions  become  purple,  by  absorbing 
rapidly  oxygen  from  the  air,  and  finally  deposit  green  crystals.  When  boiled 
with  peroxide  of  mercury,  water,  and  a  little  ammonia,  it  yields  murexide.  It 
dissolves  in  oil  of  vitriol,  and  is  precipitated  unchanged  by  water.  In  all  these 
characters,  except  in  its  external  aspect,  it  coincides  entirely  with  uraraile,  and 
it  is  not  impossible  that  it  may  be  hereafter  found  to  be  uramile,  disguised  by  the 
presence  of  a  foreign  substance.  For  the  present,  however,  its  analysis  compels 
us  to  distinguish  it  from  uramile. 

Having  now  described  the  numerous  products  of  the  oxidation  of  uric  acid  by 
nitric  acid,  we  are  prepared  .to  understand  the  nature  of  the  radical  supposed  to 
be  common  to  most  of  these  compounds. 


Urvle.    Ul.  =  CgN^a^  =  4C0  +  2G2N. 

Syn.    Cyanoxalic  Acid.      This  radical  is  unknown  in  the  separate  form.     It 
jfjcontains  the  elements  of  four  eq.  carbonic  oxide  or  2  eq.  oxalyle  (C  O  ),  and  2 
iq.  cyanogen.     Hence  the  name  cyanoxalic  acid.     Assuming  it  to  exist,  we  have 
le  following  series. 


690  XANTHIC  AND  CYSTIC  OXYDES— BENZOYLE. 


Rational  formulae. 

Names. 

Empirical  fonnuls. 

Ul  -J-  1  eq.  urea 

=  Uric  acid 

^  C,oN4     H4  Oe 

Ul  +  0  4-  5H0 

=  Alloxantine 

=  C8N2      H5OW 

Ul  -f-  Oj  -f  4H0 

=  Alloxan 

==  Cg  Nj      H4  010 

Ul  t  4H0 

=  Dialuric  acid 

=  Cg  Ng     H4  Og 

Ul  +  NH3  +  2H0 

=  Uramile 

=  C8N3      HgOe 

Ul  +  a  +  4H0  H-  NH9> 
+  2S0,                \ 

=  Thionuric  acid 

^CgNsHA^Sg 

The  ready  conversion  of  these  compounds  one  into  another  is  a  strong  argu- 
ment for  the  existence  of  the  radical  Uryle.  But  the  rational  formulae  above 
given  do  not  represent  what  we  suppose  to  be  the  actual  arrang-ement;  they  only 
point  out  by  what  simple  means,  as  the  addition  or  removal  of  oxygen,  or  am- 
monia, or  water,  the  elements  of  the  new  compounds  might  be  supplied.  The 
other  derivatives  of  uric  acid  are  probably  compounds  of  different  radicals:  thus, 
parabanic  and  oxaluric  acids  each  contain  only  6  eq.  of  carbon,  and  cannot  there- 
fore be  compounds  of  uryle. 

APPENDIX  TO  URIC  ACID. 

1.  Uric  or  Xanthic  oxide.  This  is  a  very  rare  ingredient  of  irri nary  calculi. 
Its  formula  is  CJ^N^H^O^,  which,  taken  double,  differs  from  uric  acid  only  by  2 
eq.  oxygen.  Hence  its  name  of  uric  oxide.  It  is  soluble  in  potash  and  preci- 
pitated by  acids  as  a  white  powder.  It  dissolves  in  nitric  acid,  and  the  solution 
evaporated  to  dryness  leaves  a  yellow  residue;  hence  the  name  of  xanthic  oxide. 
It  is  said  to  occur  in  small  quantities  in  some  kinds  of  guano. 

2.  Cystic  oxide.  CgNH^O  S  .  Another  very  rare  form  of  calculus.  It  dis- 
solves both  in  acids  and  alkalies,  and  has  the  characters  of  an  organic  base, 
forming  crystalline  compounds  with  acids.  It  is  remarkable  from  the  large 
quantity  of  sulphur  it  contains. 

XIII.    Benzotle.    Bz  =  C^HgOj. 

This  is  the  radical  of  Benzoic  Acid,  of  oil  of  bitter  almonds,  and  of  an  exten- 
sive series  of  compounds.  The  radical  is  not  yet  known  with  certainty  in  the 
separate  form,  although  a  compound  exists,  having  the  same  composition.  (See 
Benzile.)  We  shall  describe  first  the  benzoic  acid,  and  afterwards  the  other 
compounds  derived  from,  or  connected  with  it. 

TABLE  OF  COMPOUNDS, 

Benzoic  acid  ....  C'*H»03,H0  =  B70,H0 

Hyduret  of  Benzoyle         .  .  .  .  s=:  Bz,H 

=  BzCl  4.  HCl 
=  BzAd 

=  Fo3,BzHfHO 

Benzoate  of  Ilyduret  of  Benzoyle             .            .  =  BzO,HO  -j-  2BrH 

Hippuric  acid =  C'«NH80^  -|-  HO. 

1.    Benzoic  Acid.    CnHjOa.HO  =  BzO,HO,  or  BzOjjH. 

This  acid  is  found  in  gum  benzoin,  mixed  with  some  resins;  and  it  also 
occurs  in  the  urine  of  herbivorous  animals,  under  certain  circumstances.  It  is 
also  formed  by  the  oxidation  of  the  oil  of  bitter  almonds.  It  may  be  obtained 
from  benzoin  by  sublimation,  the  powdered  gum  being  gently  heated  on  an  iron 


Chloride  " 

Benzamide 
Formobenzoilic  acid 


m 


t 


BENZOIC  ACID— HYDURET  OF  BENZOYLE.  591 

plate  forming  the  bottom  of  a  broad  and  short  cylinder,  the  top  of  which  is 
covered  with  bibulous  paper  pasted  tightly  down  to  the  sides,  while  another 
cylinder  slides  over  the  upper  end  of  the  first,  to  prevent  the  escape  of  the  acid. 
The  vapours  of  the  acid,  which  is  very  volatile,  pass  through  the  paper,  and 
forming  crystals,  are  there  retained,  falling  on  its  upper  surface.  The  following 
method,  however,  is  far  more  productive,  as  in  the  process  of  sublimation  some 
of  the  acid  is  always  decomposed.  Benzoin  is  dissolved  in  strong  alcohol,  and 
to  the  hot  solution  there  is  added  hydrochloric  acid  in  quantity  sufficient  to  pre- 
cipitate the  resin:  the  whole  is  then  distilled.  The  benzoic  acid  passes  over 
under  the  form  of  benzoic  ether  (benzoate  of  oxide  of  ethyle) ;  and  when  the 
greater  part  of  the  liquid  has  been  distilled  off,  water  is  added  to  the  residue, 
and  distilled  as  long  as  any  other  passes  over  with  it.  When  this  ceases,  the 
hot  water  remaining  in  the  retort  is  filtered,  and  on  cooling  deposits  part  of  the 
benzoic  acid  in  crystals.  The  benzoic  ether  and  all  the  distilled  liquors  are  now 
treated  with  caustic  potash,  until  all  the  ether  is  decomposed,  and  the  solution, 
now  containing  benzoate  of  potash,  is  heated  to  boiling,  and  supersaturated  with 
hydrochloric  acid.  On  cooling  it  deposits  the  benzoic  acid  in  crystals.  By  this 
means  the  whole  benzoic  acid  of  the  benzoin  is  obtained. 

Benzoic  acid  forms  fine  light  prismatic  crystals,  or  flexible  pearly  scales. 
When  pure,  it  has  no  smell,  but  by  heat  it  acquires  the  odour  of  benzoin  or  of 
vanilla,  and  as  commonly  prepared  it  has  a  very  pleasant  odour  derived  from  the 
presence  of  some  foreign  compound  which  accompanies  the  acid,  and  is  not 
easily  separated  from  it.  It  is  very  fusible  and  volatile,  and  its  vapours  are  very 
irritating,  provoking  cough.  It  is  inflammable,  burning  with  smoke.  It  is  spar- 
ingly soluble  in  cold  water,more  so  in  boiling  water ;  it  dissolves  also  in  alcohol 
and  ether. 

With  bases  it  forms  salts,  many  of  which  are  crystallizable.  Their  general 
formula  is  BzO,MO,  or  BzO^,!^.  When  the  alkaline  and  earthy  benzonates  are 
heated  in  close  vessels,  they  yield  carbonates,  while  new  products  distil  over, 
such  as  benzone,  benzole,  naphthaline,  &c.  The  benzonate  of  peroxide  of  iron, 
3BzO  -f  Fe^O^,  has  a  reddish  white  colour,  and  is  insoluble.  Benzoic  acid,  in 
the  form  of  benzoate  of  ammonia,  is  therefore,  sometimes  used  as  a  means  of 
separating  peroxide  of  iron  from  some  other  bases.  But  its  use  requires  many 
precautions,  and  it  is  quite  inapplicable  if  alumina,  glucina,  yttria,  or  zirconia 
be  present.  Benzoate  of  silver,  BzO,AgO,  is  sparingly  soluble,  and  when  formed 
in  hot  solutions  crystallizes  on  cooling. 


2.    Hyduret  of  Benzoyle.    CjiHeOgSs:  BzH. 


Syn.  Essential  oil  of  bitter  almonds.  When  bitter  almonds,  after  being  mace- 
rated with  water  for  a  day  or  two,  are  distilled  with  the  water,  there  is  obtained 
a  fragrant  oily  liquid,  heavier  than  water,  which  contains,  besides  hyduret  of 
benzoyle,  benzoic  acid,  hydrocyanic  acid,  and  benzoine,  a  solid  compound  iso- 
meric with  the  hyduret  of  benzoyle.  To  purify  it,  this  oily  liquid  is  distilled 
along  with  a  mixture  of  protochloride  of  iron  and  slaked  lime,  which  retain  the 

ttwo  acids,  and  the  benzoine  remaining  behind,  the  pure  hyduret  passes  over. 
It  is  a  colourless  transparent  liquid,  of  a  high  refractive  power.  It  has  a  pecu- 
liar and  very  powerful  smell,  and  it  is  on  this  account  that  the  crude  oil  is  so 
much  used  in  perfumery.  Its  odour  has  been  compared  to  that  of  hydrocyanic 
acid,  but  this  has  arisen  from  the  fact  that  the  crude  oil  contains  both  ;  for  on 
comparing  the  two,  no  similarity  can  be  perceived.     It  ought,  however,  to  be 


592  FORMOBENZOILIC  ACID. 

borne  in  mind  that  the  commercial  oil  is  highly  poisonous,  not  only  because  it 
contains  hydrocyanic  acid,  but  because  the  hyduret  of  benzoyle  is  poisonous. 
Hydiiret  of  benzoyle  boils  at  356°. 

When  exposed  to  the  air,  it  absorbs  2  eq.  of  oxyoren,  and  is  converted  into 
pure  crystallized  benzoic  acid.  BzH  -f  O  =BzO,HO.  Heated  with  caustic 
potash  in  close  vessels,  it  yields  benzoate  of  potash  and  hydrogen  gas  which  is 
disengaged.  KO,HO  -f  BzH  =  KO,BzO  -f  H.  It  is  still  more  easily  con- 
verted into  benzoate  of  potash  by  an  alcoholic  solution  of  potash  ;  the  alcohol 
here  swims  above  the  salt,  and  holds  in  solution  an  oily  matter  not  yet  examined. 
When  hyduret  of  benzoyle  is  mixed  with  a  little  hydrocyanic  acid,  and  placed 
in  contact  with  aqua  potassae,  lime  water,  or  baryta  water,  it  is  gradually  con- 
verted into  the  solid  crystalline  compound,  isomeric  with  itself,  which  is  called 
benzoyne.  When  mixed  with  aqua  ammoniae,  and  gently  heated,  it  produces  a 
new  compound,  hydrobenzamide.  With  chlorine  and  bromine,  if  dry,  it  yields 
chloride  and  bromide  of  benzoyle,  with  hydrochloric  and  hydrobiomic  acids;  if 
water  be  present,  benzoic  acid  is  likewise  fqrmed,  part  of  which  combines  with 
some  unchanged  Jiyduret  of  benzoyle. 

3.  Chloride  of  benzoyle^  formed  by  the  action  of  dry  chlorine  on  the  hyduret, 
is  a  colourless  liquid,  of  a  strong  disagreeable  odour.  It  is  formed  as  follows  ; 
BzH  f  01^=  BzCl  -f-  H  CI.  With  the  alkalies  it  yields  benzoate  of  the  alkali, 
and  chloride  of  the  metal :  BzCl  f  2K0  =  KO,BzO  f  KCl.  With  dry  ammo- 
nia it  yields  henzamide ;  with  alcohol  it  produces  benzoic  ether  and  hydrochloric 
acid.  AeO,HO  f  BzCl  =  AeO,BzO  +  HCl.  When  acted  on  by  metallic  bro- 
mides, iodides,  sulphurets,  or  cyanides,  it  produces  metallic  chlorides,  and  bro- 
mide, iodide,  sulphuret  or  cyanide  of  benzoyle.  The  bromide  if  benzoyle  is  a 
crystalline  solid,  in  other  respects  analogous  to  the  chloride.  The  iodide  and 
sulphuret  of  benzoyle  are  also  crystallizable  :  the  cyanide  is  a  liquid  having  an 
,  odour  like  that  of  ciiinamon. 

4.    Benzamide.    C,4NH70j  =  Cj4H50j -j- NH,=  B^Ad. 

J,  This  compound  is  formed  when  dry  ammonia  acts  on  chloride  of  henzoylJB, 
iBzCl-f-  NH^,!!  =  Bz,NH2 -f-  HCl:  also  when  hippuric  acid  (which  see),  is 
boiled  with  peroxide  of  lead.  When  prepared  from  the  chloride,  it  is  accompa- 
nied by  sal  ammoniac,  formed  by  the  hydrochloric  acid  produced,  with  the  excess 
of  ammonia.  This  is  removed  by  cold  Water ;  and  the  benzamide,  being  dis- 
solved in  hot  water,  crystallizes  on  cooling.  It  forms  fine  soft  needles  or  pearly 
scales,  very  fusible  and  volatile.  Like  other  amidides,  it  yields  ammonia  when 
boiled  with  alkalies,  while  a  benzoate  is  formed. 

5.    FormobenzoilicAcid.{%^^^^-l^^j;;3"«^2+n0  =  FoO3, 

This  compound  is  obtained  by  adding  to  distilled  water  some  crude  oil  of  bit- 
ter almonds,  which  always  contains  hydrocyanic  acid  (see  amygdaline,)  and 
evaporating  to  dryness  along  with  some  hydrochloric  acid.  From  the  dry  mass, 
ether  dissolves  the  new  acid,  which  it  deposits  as  a  crystalline  powder  by  eva- 
poration. In  this  process,  the  hydrocyanic  acid,  under  the  influence  of  hydro- 
chloric acid,  is  converted,  along  with  the  elements  of  water,  into  formic  acid 
and  ammonia.  The  latter  combines  with  the  hydrocyanic  acid,  the  former  with 
the  hyduret  of  benzoile,  yielding  formobenzoilic  acid.  With  bases,  this  acid 
forms   salts,  in  which  the  quantity  of  base  neutralized  is  exactly  that  which 


COMPOUNDS  OF  BENZOYLE.  593 

would  be  neutralized  by  the  formic  acid  alone.  Their  formula  is  MO  -f-  FoO, , 
BzH  ;  by  which  it  is  seen  that  the  hyduret  of  benzoyle  has  entered  into  the 
radical  of  the  acid,  without  altering  its  power  of  saturation ;  and  perhaps  the 
rational  formula  of  the  acid  ought  rather  to  be,  (FoO  ,BzH)  -J-  H;  and  that  of 
the  salts,  (FoO^,BzH)  -|-  M ;  which  exhibits  this  view  still  more  clearly. 

6.     Benzoate  of  Hyduret  of  Benzoyle.     C^a^gOig  =  BzO,HO  -J-  2BzH. 

This  compound  is  formed  when  moist  chlorine  is  passed  through  the  oil  of 
bitter  almonds.  Hydrated  benzoic  aid  is  formed,  which  unites  with  the  un- 
changed hyduret.  The  action  of  moist  chlorine  in  producing  hydrated  benzoic 
acid  is  as  follows :  BzH  f  2H0  f  ^1^  =  2HC1  f  BzO,HO.  The  new  com- 
pound is  crystalline,  insoluble  in  water,  soluble  in  alcohol  and  ether.  It  is  vola- 
tile without  decomposition.  An  alcoholic  solution  of  potash  dissolves  it,  and 
converts  it  into  benzoate  of  potash. 

7.    Hippuric  Acid,    CigNHgOg -j- HO. 

This  acid  is  found  in  very  considerable  quantity  in  the  urine  of  herbvivorous 
animals,  such  as  the  horse  and  cow,  more  especially  when  stall-fed.  It  has  also 
been  lately  discovered  by  Liebig  in  human  urine.  It  is  easily  obtained  by  eva- 
porating gently  to  a  small  bulk  the  fresh  urine  of  the  horse  or  cow,  and  acidu- 
lating with  hydrochloric  acid.  On  standing,  the  liquid  deposits  brown  crystals 
of  hippiiric  acid,  which  may  be  decolorized  by  a  little  bleaching  liquor  and 
hydrochloric  acid. 

The  pure  acid  forms  pretty  large  semi-opaque  four-sided  prisms,  sparingly 
soluble  in  cold  water,  very  soluble  in  hot  water  and  in  alcohol.  When  heated, 
it  melts,  and  gives  off  benzoic  acid,  benzoate  of  ammonia,  and  an  oily  matter, 
which  has  a  very  fragrant  odour  like  that  of  the  tonka  bean.  By  nitric  acid  it 
is  converted  into  benzoic  acid.  Heated  with  peroxide  of  manganese  and  sul- 
phuric acid,  it  yields  ammonia,  carbonic  acid,  and  benzoic  acid  ;  boiled  with  per- 
oxide of  lead,  it  yields  benzamide  and  carbonic  acid. 

"VN(ith  bases  it  forms  salts,  most  of  which  are  soluble  and  crystallizable. 

Hippuric  acid  may  be  viewed  in  two  ways ;  first,  as  a  compound  of  benzamide 

ith  an  acid,  C  HO  (fumaric  or  aconitic  acid?);  secondly,  as  composed  of 
hyduret  of  benzoyle,  hydrocyanic  acid,  and  formic  acid.  Either  view  readily 
accounts  for  its  easy  decomposition  into  benzoic  acid  and  other  products.  As  an 
ingredient  of  the  urine,  this  acid  is  important;  and  we  shall  hereafter  see  that 
benzoic  acid,  taken  into  the  system,  appears  in  the  urine  as  hippuric  acid. 

PRODUCTS  OF  THE  DECOMPOSITION  OF  THE  COMPOUNDS  OF  BENZOYLE. 

1.     Hyposulphobenzoic  Acid.    C,4H403  -j-  S2O5+  2H0. 

A  bibasic  acid.  Formed  when  anhydrous  sulphuric  acid  acts  on  crystallized 
benzoic  acid.  C^^H^03,H0  +  2SO3  =  C^^H^O^  +  S^O^  +  2H0.  The  acid  is 
soluble  and  crystallizable,  and  forms  with  "baryta  a  soluble  and  crystallizable 
salt,  from  which  the  acid  may  be  obtained  by  the  action  of  sulphuric  acid.  It 
forms  two  series  of  salts,  one  with  2  eq.  of  fixed  base,  the  other  with  1  eq.  of 
fixed  base  and  1  eq.  of  water. 

2.    Bromobenzoic  Acid.    CjgHgBrOg -f- 2H0. 

A  bibasic  acid.    When  the  vapour  of  bromine  is  allowed  to  act  on  benzoate 

40 


594  COMPOUNDS  DERIVED  FROM  BENZOYLE. 

of  silver  at  the  ordinary  temperature,  there  is  produced  this  acid,  along  with  bro- 
mide of  silver  and  hydrobromic  acid.  2  eq.  of  benzoate  of  silver  and  4  eq.  of 
bromine  yield  1  eq.  bromobenzoic  acid,  1  eq.  hydrobromic  acid,  and  2  eq.  bro- 
mide of  silver.  2(C^^H^03AgO)  f  ^^^  =  C^aH^BrO^  +  HBr  +  2AgBr.  Ether 
dissolves  the  acid  and  deposits  it  on  evaporation,  in  a  confused  mass  of  crystals, 
very  sparingly  soluble  in  water.  When  the  acid  crystallizes,  it  takes  up  2  eq. 
of  water.  With  bases  it  forms  salts,  which  are  generally  soluble  and  crystal- 
lizable.     Their  general  formula  is  C^U^BtO^,2MO, 

3.    Benzole.    CjjHj. 

Syn.  Benzine,  Benzene.  Phene, — Occurs  in  the  volatile  liquids  condensed 
from  oil  gas ;  but  is  best  obtained  in  a  state  of  purity  by  distilling  I  part  of 
crystallized  benzoic  acid  with  3  of  slaked  lime.  It  is  a  limpid,  colourless  liquid, 
of  an  agreeable  etherial  odour.  Its  sp.  gr.  is  0-85 ;  it  boils  at  186°,  and  at  32°  it 
becomes  solid.  It  is  insoluble  in  water,  soluble  in  alcohol  and  ether.  In  its 
formation,  1  eq.  of  benzoic  acid  yields  2  eq.  carbonic  acid  and  1  eq.  benzole,  the 
carbonic  acid  uniting  with  the  lime.     C^jH^O^,HO  =  ^^^(,  +  ^^^2* 

4.  Sulphobenzide.  C)  H  SO  .  When  anhydrous  sulphuric  acid  acts  on  ben- 
zole, a  viscid  mass  is  formed,  from  which,  by  the  addition  of  water,  is  separated 
a  new  compound,  which  may  be  dissolved  and  crystallized  by  means  of  ether. 
^12^6  +  ^^3  =  HO  +  ^la^jiSO^.  Sulphobenzide  is  quite  neutral.  5.  Bypo- 
gulphobenzidic  Add. — This  acid  is  found  in  the  liquid  from  which  the  preceding 
compound  has  been  deposited.  Its  formula  is  ^^^^^^J^^  "f  HO.  It  may  be 
viewed  as  formed  by  the  action  of  2  eq.  of  dry  sulphuric  acid  on  1  eq.  of  ben- 
zole, C,  H. -}- 2S0,  =  C,  H -S  O -HO;  or  as  formed  by  the  combination  of 
sulphobenzide  with  oil  of  vitriol ;  ^^2^5*802  -f-  HO,SOg.  Either  view  readily 
explains  its  formation.  The  acid  is  best  obtained  pure  from  its  salt  with  oxide 
of  copper  (which  crystallizes  very  easily),  by  the  action  of  sulphuretted  hydro- 
gen. It  is  very  soluble,  and  may  be  crystallized.  It  has  a  very  acid  taste,  and 
neutralizes  bases,  forming  crystallizable  salts.  6.  Nitrobenzide.  C^H^NO^. — 
Formed  when  benzole  is  dissolved  to  saturation  in  fuming  nitric  acid,  and  water 
added  to  the  hot  solution.  On  cooling,  the  nitrobenzide  falls  to  the  bottom  as  a 
heavy  oil.  It  is,  at  60°,  a  yellow  liquid,  very  sweet  to  the  taste,  with  an  odour 
like  that  of  cinnamon ;  it  boils  at  434°,  and  solidifies  at  37°.  Its  sp.  gr.  is 
1*20^.  It  is  insoluble  in  water,  soluble  in  alcohol  and  ether.  It  is  formed  from 
1  eq.  benzole  and  1  eq.  nitric  acid.  C^^H^  -f  N0^=  HO  +  C^H^,NO^.  7. 
Jizobenzide.  C^^U^N. — This  compound  is  formed  when  an  alcoholic  solution  of 
nitrobenzide  is  distilled  with  dry  hydrate  of  potash.  After  the  alcohol  has  dis- 
tilled, the  azobenzide  volatilizes,  forming  large  red  crystals,  fusible  at  150°, 
boiling  at  380°.  The  production  of  this  compound  is  not  yet  explained  ;  and  its 
formula  requires  confirmation.  8.  Chloride  of  henzoh.  C  H  CI  . — Formed 
when  chlorine  gas  and  benzole  are  exposed  to  the  sun's  rays.  It  is  a  colourless 
crystalline  solid.  9.  Chlorobenzine.  ^la^^CJ^* — Obtained  by  distilling  the 
preceding  compound  with  hydrate  of  lime,  as  a  colourless  oily  liquid. — Bromine 
forms  with  benzole  analogous  compounds. 

10.    Benzone.    C13H5O. 

One  of  the  products  of  the  distillation  of  neutral  benzoate  of  lime.     When 
purified  from  benzole  and  naphthaline,  it  is  an  oily  viscid  colourless  liquid,  hea- 


BENZOTNK.    BENZILE.  595 

vier  than  water.     It  differs  from  1  eq.  of  anhydrous  benzoic  acid  by  1  eq.  of 
carbonic  acid,     C^Jip^  =  ^13^5^  +  CO^, 

11.    Hydrobenzamide.    C42H18N2. 

When  1  vol.  hyduret  of  benzoyle  and  20  vol.  of  strong  aqua  ammoniae  are 
exposed  in  an  hermetically  sealed  vessel  to  a  temperatare  of  from  105°  to  120°, 
it  is  converted  after  a  time  into  a  crystalline  mass,  which  is  to  be  washed  with 
ether.  The  residue  dissolved  in  alcohol,  yields,  by  spontaneous  evaporation,  regu- 
lar crystals  of  hydrobenzamide.  In  its  formation,  3  eq.  hyduret  of  benzole,  and  2 
eq.  ammonia,  produce  1  eq.  hydrobenzamide  and  G  eq.  water.  ^(C  H  O  )  -|-  2NH 
=  C^HjgN^  -f  6H0.  If,  in  preparing  this  substance,  we  employ  the  crude  oil  of 
bitter  almonds,  we  obtain  a  yellow  resinous  mass,  which  is  a  mixture  of  hydro- 
benzamide^ benzhydramide,  azobenzoyle,  and  azotide  of  benzoyle,  all  of  them  dis- 
covered by  Laurent.  12.  Benzhydramide  is  isomeric  with  hydrobenzamide,  but 
is  not  converted,  like  the  former,  into  hyduret  of  benzoyle,  and  sal-ammoniac  by 
the  action  of  hydrochloric  acid.  13.  Azobenzoyle.  C  H  N  ,  is  much  less  solu- 
ble in  alcohol  than  the  preceding.  It  is  derived,  from  benzoyle  as  follows : — 
3(C^^H^0J  +  2NH3=  C^^Hj^N^  +  6H0.  14.  Azoiide  of  benzoyle,  C^^H^N,  is 
quite  insoluble  in  boiling  alcohol.  It  may  be  derived  from  anhydrous  benzoic 
acid  as  follows  :  C^^H^03  +  NH3  =  C^^H^N  -f  3H0. 

15.     Benzimide.    C28NHi,04. 

According  to  Laurent,  this  compound  is  found  in  the  crude  oil  of  bitter  almonds. 
It  is  crystallizable,  and  appears  to  be  decomposed  by  acids  into  benzoic  acid  and 
ammonia.  It  may  be  derived  from  anhydrous  bibenzoate  of  ammonia  by  the 
separation  of  2  eq.  water.  C^gH^^Og  +  NH^  =  C^gH^^NO^  t  2H0.  But  this 
is  not  probable.  A  compound  precisely  similar  is  obtained  when  an  alcoholic 
solution  of  potash  is  added  to  a  mixture  of  hyduret  of  benzoyle  and  strong 
hydrocyanic  acid ;  but  this  compound  yields  with  acids  ammonia  and  hyduret  of 
benzoyle. 


I 


16.  Benzoine.    Cj^HgO^. 

Isomeric  with  hyduret  of  benzoyle.  It  is  formed  when  an  alcoholic  solution 
f  potash  or  sulphuret,  or  cyanide  of  potassium,  act  on  the  crude  oil  of  bitter 
Imonds,  containing  hydrocyanic  acfd.  It  separates  in  a  congeries  of  small  crys- 
Is,  insoluble  in  water,  soluble  in  alcohol.  It  may  be  volatilized  without  change. 
Sulphuric  acid  dissolves  it  with  a  violet  colour.  Hydrate  of  potash,  melted  with 
it,  forms  benzoate  of  potash,  with  disengagement  of  hydrogen.  It  dissolves  with 
a  violet  colour  in  a  hot  alcoholic  solution  of  potash,  and  is  converted  by  boiling 
with  it  into  benzilic  acid.  When  its  vapour  is  passed  through  a  red-hot  tube,  it 
is  converted  into  hyduret  of  benzoyle,  or  at  least  into  an  oil  smelling  like  that 
compound,  and  passing  into  benzoic  acid  on  exposure  to  the  air.  By  the  action 
of  chlorine  it  loses  hydrogen,  and  is  converted  into  Benzile,  a  compound  having 
the  composition  of  the  radical  benzoyle. 

The  action  of  hydrocyanic  acid  in  promoting  the  formation  of  benzoine  is  not 
yet  explained  ;  but  it  is  certain  that  from  pure  hyduret  of  benzoyle  we  cannot 
procure  it,  while  the  addition  of  hydrocyanic  acid  ensures  its  formation. 

17.  Hydrobenzoinamide. 

Syn.  Benzoniamide,     Isomeric  with  hydrobenzamide.     It  is  formed  by  ex- 


596  COMPOUNDS  DERIVED  FROM  BENZOYLE. 

posing  a  mixture  of  benzoine  and  ammonia  to  a  moderate  heat ;  and  appears  as 
a  white  tasteless  powder,  volatile  without  decomposition. 

18.    Benzile.    CUH5O2. 

Syn.  Benzoyle.  It  is  formed  by  the  action  of  chlorine  gas  on  melted  ben- 
zoine. When  cold  the  mass  is  boiled  with  alcohol,  which  on  cooling  deposits 
benzile  in  crystals  which  are  yellow  six-sided  prisms ;  insoluble  in  water,  solu- 
ble in  alcohol  and  ether,  melting  at  195°  and  volatile  without  decomposition.  An 
alcoholic  solution  of  potash  dissolves  it  with  a  violet  colour,  and  converts  it  into 
benzilic  acid. 

19.    Benzilic  Acid.    CagH'iOg+HO. 

Formed  when  benzile  is  dissolved  in  a  hot  alcoholic  solution  of  potash,  and 
boiled  until  the  violet  colour  at  first  produced  has  disappeared,  and  is  no  longer 
restored  by  a  fresh  portion  of  potash.  To  the  boiling  solution  of  benzilale  of 
potash  hydrochloric  acid  is  added  in  excess,  and  on  cooling  the  benzilic  acid  is 
deposited  in  colourless  brilliant  crystals,  fusible  at  248°,  not  volatile,  but  yield- 
ing, when  heated,  benzoic  acid,  and  purple  vapours.  Sulphuric  acid  dissolves 
it  with  a  bright  crimson  colour.  Its  formation  is  explained  as  follows  : — 2  eq. 
of  benzile  take  up  2  eq.  of  water,  one  of  which  is  incorporated  in  the  acid ; 
while  the  other  is  replaceable  by  bases.  ^G^^p^)  -f  2H0  =  C^gHi.O^  -h 
HO.  Benzilate  of  potash  forms  large  transparent  crystals,  soluble  in  water  and 
alcohol. 

20.  Jzohenzoide. — <^84Hg2N5  *?  Obtained  by  adding  ammonia  to  the  oil  pro- 
duced when  bitter  almonds  are  distilled  per  descensum,  and  dissolving  away  by 
means  of  ether  all  other  products.  A  white  powder,  decomposed  by  heat.  Its 
formula  is  doubtful. 

21-  Cyanobenztle.  Formed  when  an  alcoholic  solution  of  benzile  is  warmed 
with  I  of  its  volume  of  concentrated  hydrocyanic  acid.  It  is  deposited  in  large 
transparent  crystals,  the  composition  of  which  is  not  yet  known. 

21.    Hyduret  of  Sulphobenzoyle.    Ci^HjSjjH. 

One  vol.  of  crude  essence  of  bitter  almonds  is  dissolved  in  8  or  10  of  alcohol, 
and  gradually  mixed  with  one  vol.  of  hydrosulphuret  of  ammonia.  After  a  time, 
the  mixture  deposits  a  fine  white  powder,  formed  of  grains  smaller  than  those  of 
Btarch,  which  give  to  the  fingers  a  very  persistent  odour  of  garlic.  It  is  insolu- 
ble in  water  and  alcohol.  Ether  liquefies  it,  but  a  few  drops  of  alcohol  restore 
its  solid  form.  It  may  be  considered  as  the  hyduret  of  a  new  radical,  in  which 
the  oxygen  of  benzoyle  has  been  replaced  by  sulphur.  When  heated,  it  melts, 
and  if  now  allowed  to  cool,  forms  first  a  transparent  plastic  mass,  and  afterwards 
a  brittle  glass.    If  kept  melted  for  some  time,  it  crystallizes,  but  is  now  altered, 

22.    Stilbene.    CmUn. 

When  the  preceding  compound  is  strongly  heated,  it  gives  off  a  large  quan- 
tity of  sulphuretted  hydrogen,  and  a  little  of  a  liquid,  apparently  bisulphuret  of 
carbon.  ContiniAng  the  heat,  there  distil  over,  first  a  substance  crystallizing  in 
pearly  scales,  stilbene ;  and  later,  a  compound  crystallizing  in  needles,  called  by 
Laurent,  the  discoverer,  sulphessale.  To  obtain  the  stilbene  pure,  the  first  crys- 
tals are  dissolved  in  boiling  alcohol,  which  leaves  undissolved  the  other  body, 


BROMIDE  OF  BENZOYLS.  597 

and  on  cooling  deposits  stilbene  in  tables.  These  being-  dissolved  in  hot  ether, 
form,  by  slow  evaporation,  remarkably  fine  crystals,  with  the  pearly  lustre  of 
stilbite,  hence  the  name.  It  is  fusible  and  volatile,  and  combines  with  chlorine 
and  bromine.  Nitric  acid  decomposes  it,  giving  rise  to  several  new  products. 
Strong  chromic  acid  attacks  it  with  violence,  and  reproduces  hyduret  of  benzoyle.    ^ 

Chloride  of  stilbene  is  formed  when  chlorine  is  passed  through  melted  stilbene. 

It  appears  in  two  isomeric  modifications,  a  and  5,  both  of  which  have  the  for- 
mula C  H^^'^U'  ^^^  crystallize  in  different  forms.  By  the  action  of  a  boiling 
alcoholic  solution  of  potash,  each  loses  1  eq.  of  hydrochloric  acid  (or  its  ele- 
ments), and  thus  they  produce  two  isomeric  modifications  of  a  new  compound  C^^ 

\  „ii  which  Laurent  calls  Chlostilbase ;  and  in  which  1  eq.  of  hydrogen  of 

stilbene  is  replaced  by  chlorine.  One  of  these  is  called  Chlostilbase  a,  the  other 
Chlostilbase  h.  Both  are  oily  liquids,  but  they  are  distinguished  by  the  action 
of  bromine,  which  combines  with  both,  producing  again  two  isomeric  com- 
pounds, both  crystallizable,  but  in  entirely  diflferent  forms.    Their  formulae  are, 

Along  with  chloride  of  stilbene  is  formed  another  compound,  chloride  of  chlo- 
stilbase, analogous  to  these  bromides  of  chlostilbase.  It  is  a  crystallizable  solid  : 

formula,     C^g^^f+^V 

Bromide  combines  with  stilbene,  forming  the  bromide  of  stilbene,  C^gH^^'^  V 
which  is  a  white  powder. 

When  stilbene  is  boiled  with  nitric  acid,  it  forms  several  compounds  not  yet 
fully  examined.  Among  these  are  Nitrostilbase,  Nitrostilbese,  and  Nitrostilbie 
I         acid.     The  latter,  according  to  Laurent,  is  ^as^yNO^^. 

23.  Hyduret  of  Sulphnzohenzoyle,  (C^^H^S|N^)  H,  is  generally  formed  along 
with  hyduret  of  sulphobenzoyle.  It  seems  to  be  hyduret  of  benzoyle,  in  which 
the  2  eq.  oxygen  of  the  benzoyle  are  replaced  partly  by  sulphur,  partly  by  nitro- 
gen. Besides  these  compounds  Laurent  has  described  a  hydrosulphuret  of  azo- 
benzoyle,  with  the  strange  formula  Cj^HgSN|.     Ought  it  not  rather  to  be  C^^H^ 

»'         SN1 
By  the  action  of  ammonia  on  the  crude  essence,  he  has  obtained  two  other 
compounds,  Jzobenzoidine,  C^^HgN^(l)  ;  ?Lr\d  ^zobenzoilide,  isomeric  with  it; 
also  two  which  he  calls  hyduret  of  azobenzoyline  and  hyduret  of  benzoyline,  the 

•  former  C,  H.N^  :  the  latter  isomeric  with  the  crude  essence. 
All  these  compounds  are  interesting,  but  the  most  recent  researches  of  Laurent 
go  to  prove  that  the  formula  of  the  last-named  compound  should  be  trebled,  C^^ 
H^^N^,  and  that  it  is  a  base,  which  he  calls  amarine, 

24.  Nitrobenzoic  Acid.    C14H4NO7HO. 

Formed  when  nitric  acid  acts  on  benzoic  acid.  It  is  a  crystalline  volatile 
acid,  and  contains  the  elements  of  benzoic  acid,  in  which  I  eq.  hyponitric  or 
nitrous  acid  has  been  substituted  for  1  eq.  hydrogen.     C^^H^O^ — H-|-NO^=C^^ 

s  kjU  ^^ ;  and  the  basic  water  of  the  benzoic  acid  unites  with  the  new  acid 
^  JNO     -* 

as  with  the  old.  *• 


598  AMYGDALINE. 

25.  Bromide  of  Benzole.    Ci2H6Br6. 

This  compound  is  formed  as  a  white  insoluble  powder,  when  bromine  acts  on 
benzole.     An  alcoholic  solution  of  potash  removes  hydrobromic  acid  (or  its  ele- 

ments),  and  causes  the  separation  of  a  white  crystalline  body,  ^j,  ^  "R^  '    which 

3 

Laurent  calls  hromohenzinise  ,•  and  which  is  formed  by  substitution  of  bromine  for 
half  the  hydrogen  of  benzole.    The  bromide  of  benzole  may,  therefore,  be  C^ 

26.  Hydrocyanate  of  benzmne.  ^.gN  H^  O  ,  is  formed  as  a  light  crystalline 
matter,  when  oil  of  bitter  almonds  is  mixed  with  one-fourth  its  volume  of  dry 
hydrocyanic  acid,  and  warmed  with  its  own  volume  of  aqua  potassae,  sp.  gr.  1*25, 
diluted  with  six  parts  of  alcohol.  I(  arises  from  the  action  of  3  eq.  hyduret  of 
benzoyle  and  2  eq. hydrocyanic  acid:  KC  Bfi^)-\-2{CJSiB)-{-  C^^'N^U^p^-{- 
2H0. 

27.  Hydrocyanate  of  henzile,  Cj^H^O^  +  C^NH  =  C^gNHgO^,  is  formed  by 
direct  combination  when  a  hot  alcoholic  solution  of  benzile  is  mixed  with  an  equal 
bulk  of  anhydrous  hydrocyanic  acid.     It  forms  large  colourless  crystals. 

APPENDIX  T©  BENZOYLE. 
1.  Amygdaline.    C4(jNH27022 

Is  found  in  bitter  almonds,  in  the  leaves  of  the  cherry  laurel,  and  probably  in 
the  kernels  of  all  the  bitter  species  of  amygdalus  and  prunus  as  the  peach  and 
plum.  To  obtain  it,  bitter  almonds  are  pounded  and  forcibly  pressed  between 
warm  iron  plates  to  remove  the  fat  oil  (oil  of  almonds).  The  marc  or  residue  is 
boiled  with  alcohol  of  94  per  cent.,  and  the  tinctures  distilled  off  in  the  water- 
bath  to  the  consistence  of  syrup.  This  liquid,  which  contains  amygdaline  and 
sugar,  is  diluted  with  water,  mixed  with  yeast,  and  set  aside.  When  the  fer- 
mentation is  over,  the  whole  is  filtered  and  again  evaporated  to  a  syrup,  which 
being  mixed  with  a  large  excess  of  cold  alcohol  (of  94  per  cent.)  deposits  the 
amygdaline  as  a  white  crystalline  powder.  .  This  is  pressed  in  folds  of  bibulous 
paper,  and  finally  purified  by  repeated  crystallization  from  boiling  alcohol.  It 
forms  crystalline  scales,  very  soluble  in  water,  very  sparingly  soluble  in  cold 
alcohol,  but  more  soluble  in  hot  alcohol.  It  has  a  bitter  taste.  When  heated  it 
emits  an  odour  like  that  of  May  blossom,  and  leaves  a  bulky  coal. 

When  distilled  with  nitric  acid,  or  other  oxidizing  agents,  it  is  resolved  into 
ammonia,  hyduret  of  benzoyle,  benzoic  acid,  formic  acid,  and  carbonic  acid. 
Caustic  alkalies  convert  it  into  ammonia  and  amygdalinic  acid  ;  permanganate  of 
potash  converts  it  into  cyanate  and  benzoate  of  potash. 

2.  Amygdalinic  Acid.    C^oHjgOji-j-HO. 

Prepared  by  boiling  amygdaline  with  baryta  as  long  as  ammonia  is  given  oflf, 
and  then  removing  the  baryta  from  the  soluble  amygdalinate  of  that  base  by  sul- 
phuric acid.  By  evaporation  it  yields  a  transparent  amorphous  mass,  which  has 
a  very  pleasant  acid  taste.  Nitric  acid,  and  other  oxidizing  agents,  convert  it 
into  hyduret  of  benzoyle,  with  formic  and  benzoic  acid.  Its  salts  are  almost  all 
soluble :  their  formula  is  ^'^qH^O^j-HMO. 


THEORY  OF  COMPOUNDS  OF  BENZOYLE.  599 

3.  Distilled  Water  of  Bitter  Almonds. 

Expressed  bitter  almonds  are  made  into  a  thin  cream  with  water,  and  this  dis- 
tilled in  the  heat  of  a  chloride  of  calcium  bath,  till  a  quantity  of  water  has  passed 
over  equal  in  weight  to  the  almonds  before  being  pressed.  The  distilled  water 
is  milky  from  suspended  oil  of  bitter  almonds,  and  smells  both  of  hyduret  of 
benzoyle  and  of  hydrocyanic  acid.  When  freshly  prepared,  it  contains  little 
more  than  1  grain  of  hydrocyanic  acid  per  ounce ;  but  its  strength  diminishes  by 
keeping,  and  as  it  is  difficult  to  obtain  it  of  uniform  strength  even  when  fresh,  it 
is  not  a  good  form  of  administering  hydrocyanic  acid.  It  is  remarkable,  that 
nitrate  of  silver  does  not  detect  the  hydrocyanic  acid,  unless  ammonia  is  added 
with  the  nitrate,  and  after  a  time  neutralized  by  nitric  acid.  It  is  used  in  medi- 
cine, especially  on  the  Continent,  and  is  poisonous. 

4.  Laurel  Water. 

Obtained  by  distilling  two  parts  of  fresh  leaves  of  prunus  laurocerasus  with  water 
till  three  parts  have  passed  over.  It  exactly  resembles  the  preceding  water,  and 
is  equally  uncertain,  and  equally  poisonous. 

THEORY  OF  THE   FORMATION  OF  HYDURET  OF  BENZOYLE   FROM   BITTER 

ALMONDS. 

Bitter  almonds  contain,  like  sweet  almonds,  a  large  qntntity  of  an  albuminous 
or  caseous  matter,  called  emulsine  or  synaptase,  along  with  abundance  of  a  mild 
fat  oil,  the  oil  of  almonds,  very  similar  to  olive  oil.  But  in  addition  to  these, 
the  bitter  almonds  contain  4  or  5  per  cent,  of  amygdaline,  which  is  not  present 
in  sweet  almonds. 

Now,  if  the  amygdaline  be  removed  by  boiling  alcohol,  the  residue,  when  dis- 
tilled with  water,  docs  not  yield  a  trace  of  the  volatile  oil  of  bitter  almonds. 
Again,  if  the  residue  of  the  bitter  almonds,  after  the  fat  oil  has  been  pressed 
out,  be  heated  to  such  a  point  as  to  coagulate  the  emulsine,  before  water  is  added, 
the  distillation  also  yields  no  volatile  oil,  even  although  the  amygdaline  be  present. 

These  facts  prove  that  the  production  of  the  volatile  oil  of  bitter  almonds  de- 
pends on  the  presence,  first,  of  amygdaline,  secondly  of  soluble  emulsine;  and 
■that  is  the  result  of  the  mutual  action  of  these  bodies  on  each  other.  This  is 
farther  demonstrated  by  the  fact  that  if  amygdaline  be  placed  in  contact  with  the 
emulsine  or  synaptase  of  sweet  almondSfand  water,  distillation  of  the  mixture  now 
yields  the  oil  abundantly. 

When  the  solution  of  10  parts  of  amygdaline  in  100  of  water  is  added  to  a 
solution  of  1  part  of  synaptase  in  10  of  water,  mutual  decomposition  at  once 
takes  place  :  the  liquid  acquires  the  odour  of  hyduret  of  benzoyle  and  of  hydro- 
cyanic acid,  and  when  distilled,  yields  the  crude  oil  of  bitter  almonds,  which  is 
a  mixture  of  these  two  compounds.  The  residue  of  the  distillation  contains  sugar 
in  such  quantity,  that  it  is  probable  the  elements  of  the  synaptase  have  contri- 
buted to  form  it ;  and  when  this  sugar  is  destroyed  by  fermentation,  a  fixed  acid 
is  found.  If  the  synaptase  has  been  coagulated,  it  has  not  the  slightest  action 
on  amygdaline. 

When  the  expressed  bitter  almonds  are  moistened  with  water,  the  v6ry  same 
reaction  occurs;  and  if  enough  water  be  present  to  dissolve  the  oil  as  it  is 
formed,  the  whole  amygdaline  disappears  in  a  short  time.     But  if  the  expressed 


600  THEORY  OF  COMPOUNDS  OF  BENZOYLE. 

almonds  be  thrown  into  boiling  water,  the  synaptase  coagulates,  and  can  then 
produce  no  change  in  the  amygdaline.  To  obtain  the  full  proportion  of  oil,  1 
part  of  expressed  almonds  should  be  macerated  for  24  hours  with  20  parts  of 
water  at  about  102°,  and  then  distilled. 

100  parts  of  araygdaline  produce  47  of  crude  oil,  and  these  47  parts  of  crude 
oil  contain  almost  exactly  6  of  anhydrous  hydrocyanic  acid  ;  so  that  17  grains  of 
amygdaline,  dissolved  in  1  oz.  of  emulsion  of  sweet  almonds,  yields  a  mixture 
containing  1  grain  of  dry  hydrocyanic  acid,  and  consequently  of  the  same 
strength  as  the  distilled  water  professes  to  be.  This  mixture  has,  besides,  the 
advantage  of  containing  the  hyduret  of  benzoyle  present  in  the  distilled  water, 
to  which  is  perhaps  owing  the  superiority  of  the  distilled  water  of  bitter  almonds 
on  laurel  leaves  over  mere  diluted  hydrocyanic  acid,  a  superiority  which,  ac- 
cording to  the  Continental  physicians,  is  very  decided  and  obvious.  The  above 
simple  recipe,  given  by  Liebig  and  Wohler,  is  admirably  adapted  for  extempo- 
raneous use,  and  the  mixture  ought  never  to  be  made  in  larger  quantity  at  a 
time,  as,  like  the  distilled  water,  it  alters  by  keeping. 

In  the  above  remarkable  decomposition,  we  have  a  very  beautiful  example  of 
a  metamorphosis  in  which  the  elements  of  two  bodies  take  a  share;  but  as  the 
whole  of  the  products  are  not  yet  exactly  known,  and  even  the  composition  of 
the  emulsine  or  synaptase  is  uncertain,  we  cannot  explain  the  whole  change  with 
precision.  We  know,  however,  that  from  1  eq.  amygdaline,  C^NH^^O^^,  the 
following  compounds  may  be  derived : — 

1  eq.  hydrocyanic  acid Cj  NH 

2  eq.  hyduret  of  benzoyle         .        .        .        .        Cjg    H,204 
k  eq.  sugar .        Cg     Hg  O5 

2  eq.  formic  acid C4      Hj  Og 

7  eq.  water H7  O7 

1  eq.  amygdaline C^^N  H27O22 

Also,  1  eq.  araygdalinic  acid,  C^^H^^O^,  may  yield 

3  eq.  formic  acid Cg  Hg  O9 

2  eq.  hyduret  of  benzoyle         ....        Cj^Hij  O4 

i  eq.  sugar Cg  H5  O5 

6  eq.  water        ...,.•..  Hg  Og 

1  eq.  amygdalinic  acid ^ao^^^%\ 

Now,  we  can  trace  all  these  products  among  the  results  of  this  transformation; 
and  it  is  probable,  not  only  that  there  is  more  sugar  than  can  be  accounted  for 
by  the  amygdaline,  but  also  that  other  products,  not  yet  known,  are  formed  :  as, 
for  example,  the  fixed,  acid  above  alluded  to.  The  emulsine  or  synaptase, 
which  produces  this  remarkable  change  in  amygdaline,  in  which  it  itself  partici- 
pates, contains  nitrogen,  is  soluble  in  water,  coagulable  by  heat,  and  in  sliort 
very  analogous  both  to  albumen  and  caseine,  along  with  which  we  shall  again 
notice  it.     In  the  almond  it  appears  to  be  accompanied  by  albumen. 

We  have  seen,  above,  that  the  assumption  of  the  existence  of  the  radical  ben- 
zoyle brings  a  number  of  compounds  into  a  more  easily  understood  form,  and 
very  materially  aids  the  memory  by  enabling  us  to  classify  these  compounds  as 
analogous  to  others  better  known.     Other  views  may  be  taken  of  this  series  of 


HYDURET  OF  SALICYLE.  601 

compounds:  for  example,  according  to  Dumas,  hyduret  of  benzoyle  may  be 
represented  as  a  compound  of  benzoic  acid  with  a  earbo-hydrogen :  SC^^H^O^-j- 
(C  H  )  H  :  benzoic  acid  being  the  teroxide  and  the  carbo-hydrogen  the  terhy- 
dur'et  of  the  body,  C„H,:  for  2  (C^^H,)  O^  +(C,^H^)  H3=C^^H,,0,  =  3  (C,^ 
HgO  )  =  3BzH.  The  same  view  might  be  extended  to  some  of  the  other  com- 
pounds of  benzoyle,  but  it  is  complex,  and  cannot  well  be  applied  to  benzamide, 
hydrobenzamide,  and  several  others.  Again,  according  to  Mitscherlich,  benzoic 
acid  is  0  H  -\-  2C0  ;  that  is,  benzole  plus  2  eq.  carbonic  acid;  while  a  dry 
benzoate  would  contain,  united  to  the  base,  the  hypothetical  body  benzide^  ^12^5' 
and  the  equally  hypothetical  anhydrous  oxalic  acid,  C  O^.  These  views  appear 
both  to  be  in  all  respects  inferior  to  that  which  we  have  adopted,  and  which 
must  be  retained,  until  a  better  shall  be  proposed. 

XIV.  Salicyle.    C14H5O4  =  Sa. 

This  is  the  hypothetical  radical  of  a  remarkable  series  of  compounds;  and,  as 
such,  belongs  to  the  same  group  as  benzoyle.  Its  most  interesting  compound  is 
the  hyduret  of  salicyle,  which  we  shall  therefore  first  consider. 

TABLE   OF   COMPOUNDS. 

Hyduret  of  Salicyle C^Hg  O4,    H 

Salicyhc  acid (C^Hg  O4)     0,H0 

Chlorosalicylic  acid Cj^H-  O^,     CI 

Nitrosalicylic  acid Cj^Hg  O4,     NO^ 

Salicine C42H220,6-j-6HO 

Phloridzine C^sHjaOig-f-BHO 

1.  Hyduret  of  Salicyle.    Ci^HgO^.H  =  SaH. 

Stn^  Salicylous  acid.  This  compound  is  found  as  the  chief  ingredient  in  the 
essence  of  meadowsweet,  that  is  the  essential  oil  obtained  by  distilling  the 
^^flowers  of  spirsea  ulmaria  with  water.  It  is  probable  that,  like  the  essence  of 
^^■Ktter  almonds,  it  is  formed  by  the  metamorphosis  of  a  compound  or  compounds 
^^fcresent  in  the  flowers.  The  crude  essence  is  distilled  with  aqua  potassse,  which 
^^■fombines  with  the  hyduret,  and  an  oil  distils  over  which  seems  to  be  a  carbo- 
hydrogen.  The  salt  of  potash  being  now  redistilled  with  a  slight  excess  of 
dilute  sulphuric  acid,  yields  the  pure  hyduret  of  salicyle. 

It  may  also  be  obtained  by  distilling  one  part  of  salicine,  one  part  of  bichro- 
mate of  potash,  two  and  a  half  of  oil  of  vitriol,  and  twenty  of  water,  together. 
The  salicine  is  dissolved  in  part  of  the  water,  and  the  acid  diluted  with  the  rest. 
The  mixture  is  then  made  in  a  retort,  and  after  the  effervescence  which  takes 
place  is  over,  the  whole  is  distilled,  and  yields  the  hyduret,  to  the  amount  of 
one-fourth  of  the  salicine  employed. 

Hyduret  of  salicyle  is  an  oily  colourless  liquid  having  a  fragrant  aromatic 
odour,  and  a  burning  taste.  Its  sp.  gr.  is  1*1731,  and  it  boils  about  380°.  With 
chlorine  and  bromine  it  forms  new  compounds.  With  bases  it  forms  salicylurets, 
water  being  separated.  HSa  -f-  MO  =  HO  +  MSa,  so  that  it  has  the  cha- 
racters of  an  acid. 

Salicyluret  of  ammonium.  Sa,NH  ,  is  formed  when  concentrated  ammonia  is 
poured  upon  hyduret  of  salicyle.  It  is  a  yellow  solid,  having  a  faint  odour  of 
roses.     When  moist,  this  salt  is  decomposed  spontaneously,  becoming  black. 


602  SALICYLIC  ACID. 

and  giving  off  ammonia  and  an  odour  like  that  of  roses.  With  dry  ammoniacal 
gas,  hydiiret  of  salicyle  forms  the  compound  3SaH  -f  SNH^. 

Salici/limide,  C^^-^'^^^gOg,  is  formed  when  caustic  ammonia  is  added,  drop  by 
drop,  to  a  solution  of  1  vol.  hyduret  of  salicyle  in  3  vol.  alcohol,  and  the  small 
yellow  crystals  which  first  formed  are  dissolved  by  a  gentle  heat.  On  standing, 
salicyliraide  appears  in  the  form  of  golden  yellow  brilliant  prisms.  It  is  formed 
from  3  eq.  hyduret  of  salicyle  and  2  eq.  of  ammonia,  by  the  separation  of  6  eq. 
water,  3  (C^^Ufi^)  +  2NH3  —  6H0  =  O^^N^U^fi^.  As  it  is  no  longer 
soluble  in  the  liquid  from  which  it  was  first  deposited,  it  is  probable  that  the 
yellow  salt  first  formed,  which  dissolved  in  the  alcohol  by  aid  of  a  gentle  heat, 
was  salicyluret  of  ammonium,  which  by  excess  of  ammonia,  was  converted  into 
salicylimide. 

The  salts  of  the  hyduret  of  salicyle  or  hydrosalicylic  acid,  are  constituted,  for 
the  most  part,  according  to  the  formula  SaM.  The  potassium  salt,  SaK,  when 
exposed  to  the  air  in  a  moist  state,  becomes  first  green,  then  black.  When  the 
change  is  complete,  water  dissolves  acetate  of  potash,  and  leaves  a  black  matter, 
melanic  acid,  ^10^4^5*  ^  ^q*  ^f  salicyluret  of  potassium,  2  eq.  water,  and  3  eq. 
oxygen,  contain  the  elements  of  1  eq.  acetate  of  potash,  and  1  eq.  melanic  acid, 
C,  H  O  .K  +  2H0  +  O,  =  C  H,0  .K  +  C,  H  O..  Melanic  acid  combines 
With  bases. 

2.  Salicylic  Acid.    (CJ4H5O4)  0,H0  =  SaO,HO  =  SaOgH. 

Formed  when  hyduret  of  salicyle  is  heated  with  hydrate  of  potash  till  the  mass 
loses  its  brown  colour.  Hydrogen  is  given  off,  and  salicylate  of  potash  is 
formed.  Hydrochloric  acid,  added  to  the  solution  of  this  salt,  causes  the  deposi- 
tion of  crystals  of  salicylic  acid. 

The  same  acid  is  formed  when  coumarine,  the  stearoptene  or  camphor  of  the 
tonka  bean,  is  acted  on  by  caustic  potash.  Moreover  the  essential  oil  of  winter- 
green,  or  Gaultheria  procumhens,  appears,  by  the  researches  of  Cahours  and  Ger- 
hard, to  be  the  salicylate  of  oxyde  of  methyle. 

Salicylic  acid  crystallizes  in  tufts  of  slender  prisms,  very  like  benzoic  acid. 
It  may  be  sublimed  without  decomposition.  The  formation  of  this  acid  from 
hyduret  of  salicyle  is  very  simple:  Cj^H^O^,H  t  KO,HO  =  Cj^H^O^,KO  f 
H^.  When  the  salicylate  of  potash  is  decomposed  by  an  acid,  the  salicylic 
acid  takes  up  1  eq.  of  basic  water,  and  separates  as  Cj^H^O^,HO,  or  Cj^H^Og,H. 
The  decompositions  of  this  acid  are  very  interesting,  connecting  it  with  several 
other  series  of  organic  compounds. 

When  it  is  acted  on  by  nitric  acid,  it  is  first  converted  into  indigotic  acid,  or 
anilic  acid,  Cj^H^NOg,HO,  along  with  other  products;  and  by  the  continued 
action  of  nitric  acid,  there  is  finally  produced  the  remarkably  bitter  acid,  called 
carbazotic,  or  nitropicric  acid,  Cj2H2NgOj^,HO.  Both  these  acids  are  formed 
from  indigo  by  the  action  of  nitric  acid. 

When  salicylic  acid  is  distilled  with  caustic  baryta,  it  yields  carbonate  of 
baryta,  and  a  heavy  oily  liquid,  which  is  the  acid  known  as  carbolic  acid 
(Runge),  and  hydrate  of  phenyle  (Laurent),  the  formula  of  which  is  C^^p^=^ 
Cj2H^,0,H0.  The  production  of  carbolic  acid  from  salicylic  acid  is  easily 
understood:  it  is  in  fact  analogous  to  that  of  benzine  from  benzoic  acid.  ^14^, 
0^,H0  -|-  2BaO  =  2  (BaCCO^)  +  ^x^fi^'  ^^  ^^^  action  with  baryta  is  so 
violent  as  to  destroy  a  great  part  of  tlie  acid,  it  is  found  better  to  heat  rapidly 


COMPOUNDS  DERIVED  FROM  SALICYLE.  603 

salicylic  acid  mixed  with  powdered  glass,  when  it  is  resolved  into  carbolic  and 
carbonic  acids. 

Now  it  is  very  remarkable,  that  carbolic  acid,  which  is  one  of  the  chief  in- 
gredients of  the  oil  of  coal  tar,  a  product,  therefore,  of  the  destructive  distillation, 
is  also  converted  by  the  action  of  nitric  acid  into  nitropicric  acid.  This  would 
indicate  that  when  salicylic  acid  is  acted  on  by  nitric  acid,  it  yields,  first,  some 
compound  containing  the  same  radical  as  carbolic  and  nitropicric  acid,  and  that 
this  is  further  oxidized  into  the  latter  acid.  We  shall  hereafter  see  that  the  pro- 
bable radical  of  carbolic  acid  is  pltene,  C^O^,  from  which,  by  substitution  and 
oxidation,  carbolic  and  nitropicric  acids,  and  a  whole  series  of  compounds,  may 
be  formed. 

On  the  whole,  from  its  relation  to  hyduret  of  salicyle  and  to  salicine  (from 
which  it  may  also  be  formed  by  the  action  of  caustic  potash),  from  its  analogy 
in  formation,  constitution,  and  properties  to  benzoic  acid,  from  its  occurrence  in 
nature  in  the  first  compound  of  methyle  not  artificially  produced,  and  from  its 
ready  convertibility  into  indigotic  acid,  carbolic  acid,  and  nitropicric  acid,  sali- 
cylic acid  is  a  compound  of  very  great  interest. 

The  salts  of  salicylic  acid  have  the  general  formula  C  H  O  ,M0  or  C^^H^Og, 
M.  The  salicylate  of  oxide  of  methyle  ^^0^,0  -\-  C^^H^O^,  occurs  in  the  essen- 
tial oil  of  Gaultheria  procumbens,  and  is  much  used  in  perfumery.  It  gives  rise 
to  a  number  of  remarkable  products,  when  subjected  to  the  action  of  nitric  acid, 
chlorine,  bromine,  alkalies,  &c. ;  but  all  these  things  will  be  treated  of  in  their 
proper  places. 

3.  Chlorosalicylic  Acid.      Cu  H5  J^f  or  C14  H5  O4,  CI. 

When  dry  chlorine  is  made  to  act  on  dry  hyduret  of  salicyle,  this  compound 
is  formed,  along  with  hydrochloric  acid ;  it  crystallizes  readily,  and  may  be  sub- 
limed unchanged.  Its  formation  is  entirely  analogous  to  that  of  chloride  of 
benzoyle,  and  it  might  be  viewed  as  chloride  of  salicyle,  C^^  H^  O^,  CI  =  Sa 
CI.  But  its  properties  are  those  of  an  acid,  and  hence  we  are  compelled  to  con- 
sider it  as  salicylic  acid,  C^^  H^  O^,  in  which  1  eq.  oxygen  has  been  replaced 
by  I  eq.  chlorine,  the  type  remaining  unchanged.      Hence  after  this  substitution, 

it  is  still  an  acid,  and  its  true  formula  is  C     H^  ^  ^4  an  acid  of  the  type  of  an- 


.^^dr( 


drous  salicylic  acid. 

ith  ammonia,  it  forms  a  new  compound,  chlorosalicylimide.  As  in  the  action 
ammonia  on  hyduret  of  salicyle,  so  in  this  case  2  eq.  ammonia  act  on  3  of  the 
acid,  and  6  of  water  are  separated.  The  formula  of  chlorosalicylimide,  which  is 
a  yellow,  insoluble  solid,  is  C^^  ^u  ^2  ^\  ^6^  ^^r  3  (C^^  H^  CI  OJ  +  2  NH3 
=  6  HO  +  C^2  Hj5  CI3  N^  Og.  It  is,  in  fact,  salicylimide  in  which  3  eq.  chlo- 
rine have  been  substituted  for  3  eq.  hydrogen. 
With  bromine  and  iodine,  hyduret  of  salicyle  yields  the  two  analogous  compounds 

bromosalicylic  acid,  and  iodosalicylic  acid ;  C^^  H^   <  ^-^and  C^^  H^  >  ,4* 

4.  Nitrosalicylic  Acid,  C14  H5  NOs^Cu  H5  J^tq  . 
lis  acid  is  formed  by  the  action  of  nitric  acid  on  hydur§t  of  salicyle.    It 


604  PHLORIDZINE. 

fonns  yellow  prisms,  and  with  bases,  yields  yellow  detonating  salts.  Ammonia 
colours  it  blood-red,  and  perehloride  of  iron  cherry-red.  It  would  appear,  ac- 
cording to  the  above  formula,  derived  from  the  analysis  of  Piria,  to  bp  salicylic 
acid,  in  which  1  eq.  nitrous  (hyponitric)  acid  is  substituted  for  1  eq.  oxygen. 
But  its  characters,  and  those  of  its  salts,  are  such  as  to  lead  to  the  suspicion  that 
it  is  identical  with  the  nitrophenesic  acid  of  Laurent  (derived  from  carbolic  acid 
by  the  action  of  nitric  acid),  the  formula  of  which  is  Cj^H^N^Og,  HO.  The 
subject  requires  further  investigation.  It  is  not  improbable  that  this  acid  may 
ultimately  be  found  identical  with  indigotic  acid,  Cj^H^NOg,  HO. 

APPENDIX  TO  SALICYLE. 
6.  Salicine.    C42H29O22  =  C42H23O16  -f  6H0. 

This  compound  occurs  in  the  bark  of  all  such  willows  as  are  bitter,  such  as 
Salix  helix,  S.  amygdalina,  &c.  It  is  extracted  by  boiling  with  water,  decoloriz- 
ing the  decoction  with  litharge,  removing  the  lead  dissolved  by  sulphuric  acid 
and  sulphuret  of  barium,  and  evaporating  to  a  syrup.  The  salicine  crystallizes 
on  standing,  in  fine  scales  of  a  silky  lustre,  which  have  a  very  pure  bitter  taste, 
and  are  highly  febrifuge.  It  is  neutral,  soluble  in  water  and  alcohol,  insoluble 
in  ether.  Oil  of  vitriol  colours  it  blood-red.  When  a  mixture  of  acetate  of  lead 
with  ammonia  is  added  to  a  solution  of  salicine,  there  is  formed  a  precipitate, 
which  appears  to  be  C^^H^jO^g  -f-  6PbO.  Distilled  with  bichromate  of  potash 
and  sulphuric,  it  yields  formic  and  carbonic  acids,  hyduret  of  salicyle,  and  a 
resinous  matter. 

Saliretine,  C^Hj^O^-f-  HO.  When  salicine  is  boiled  with  diluted  sulphuric 
or  hydrochloric  acid,  it  deposits  a  yellowish  white  powder,  which  has  the  cha- 
racters of  a  resin.  This  is  saliretine.  It  is  insoluble  in  water  and  ammonia, 
soluble  in  alcohol.  Oil  of  vitriol  colours  it  blood-red ;  heated  with  nitric  acid,  it 
yields  nitropicric  acid.  Its  formation  is  accompanied  by  the  production  or  sepa- 
ration of  grape  sugar.  In  fact,  salicine,  plus  1  eq.  hydrogen,  contains  the  ele- 
ments of  saliretine  and  of  grape  sugar.  C  H  0  -f  H  =  C  H^^O  ,  HO  -f-  C 
H„0„. 

Chlorosalicine,  When  chlorine  is  made  to  act  on  a  solution  of  salicine,  there 
is  obtained  a  powder,  C5  H  Cl^O  .  This  is  chlorosalicine,  which  is  salicine, 
having  4  eq.  of  chlorine  substituted  for  4  eq.  hydrogen.  If  heat  be  applied 
during  the  operation,  a  red  liquid  is  formed,  which  is  C^H^gCl^Oj^.  It  appears 
to  be  formed  from  salicine,  minus  4  eq.  water,  ^421^250^^,  by  the  substitution  of 
7  eq.  chlorine  for  7  eq.  hydrogen. 

Rutiline  is  the  name-  given  to  the  red  compound  formed  by  the  action  of  oil  of 
vitriol  on  salicine.  When  pure  it  is  of  a  deep  reddish-brown  colour ;  acids 
change  it  to  a  bright  red,  alkalies  to  a  deep  violet. 

6.  Phloridzine.    C4aH2»Oi4  =  C42H23O18  +  6H0. 

This  is  a  substance,  very  analogous  to  salicine,  which  occurs  in  the  bark  of 
the  roots  of  the  apple,  pear,  plum,  &c.  It  is  extracted  in  the  same  way  as  sali- 
cine, and  resembles  it  much ;  forming  small  scales,  soluble  in  hot  water,  and  in 
alcohol,  very  bitter  and  powerfully  febrifuge.  It  may  be  viewed  as  salicine, 
phis  2  eq.  oxygen,  or  as  a  higher  oxide  of  the  same  radical.  When  boiled  with 
dilute  sulphuric  acid,  it  yields  a  resinous  compound,  phloretine,  analogous  to  sali- 


CINNAMIC  ACID.  605 

retine,  along  with  grape  sugar.  Phloretine  is  C^H^.O^^  =  Cg^N^^Og,  HO  ;  and 
C  H  O  -\-^^fliP^4— ^4^29^24'  According  to  Stas,  however,  Phloretine 
is  C  H  O  ,  or  double  or  quadruple  of  this.  The  compound  of  phloretine  with 
oxide  of  lead  he  found  to  be  C^^^^O,,  2PbO  ;  which  would  indicate,  for  hydrated 
phloretine,  C^^H^03,  2H0  =  C^^H^O^,  HO  =  C^^H^O^. 

By  the  action  of  nitric  acid  on  phloridzine,  there  is  formed  a  puce-coloured 
acid,  nitrophloretic  acid,  which,  according  to  Piria,  is  C^H^^NO^;  according 
to  Stas,  C^H^^NO^^. 

Phhridzeine.  C  H  gN  0  .  When  moist  phloridzine  is  exposed  to  air  and 
ammonia,  it  is  transformed  into  a  deep  red  compound,  which  dissolves  in  am- 
monia, and  may  be  precipitated  by  acids.  It  is  equal  to  phloridzine,  plus  8  eq. 
oxygen  and  2  eq.  ammonia.  When  dissolved  in  ammonia,  and  dried  in  vacuo, 
it  leaves  a  purple  mass,  with  coppery  lustre,  which  communicates  to  water  a 
splendid  blue  colour.  This  is  a  compound  of  phloridzeine  and  1  eq.  ammonia. 
The  formation  of  this  blue  pigment  is  a  very  good  example  of  that  kind  of  erema- 
causis  with  the  aid  of  ammonia,  by  which  indigo,  litmus,  orchil,  &c.  are  pro- 
duced from  colourless  bodies, 

XV.   CiNNAMYLE.     CgHsOzs^Cl. 

The  radical  of  essence  of  cinnamon,  but  unknown  in  a  separate  form. 

TABLE  OF  COMPOUNDS. 

Hyduret  of  Cinnamyle,  .  .  .  CigHgOz,  H. 

Cinnamic  Acid,  ....        C18H8O4 

1.  Hyduret  of  Cinnamyle.    CiH  =  CigHgOz,  H. 

This  is  the  purified  essence,  or  oil  of  cinnamon.  The  oil  of  commerce  con- 
tains, besides,  cinnamic  acid  and  two  resins,  all  of  which  have  been  produced 
from  the  original  oil,  C^^Hj^O^  by  the  additions  to  3  eq.  of  it,  of  8  eq.  oxygen. 
3  (C^H^^O^)  +  03=  C^^Ufi^  (cinnamic  acid  t  C^H^O  (a  resin) ;  +  C3^H^^ 
©^  (another  reain),  -|-  5H0.    With  less  oxygen,  hyduret  of  cinnamyle,  C^^HgO^, 

R'b  formed,  along  with  the  resins,  so  that  the  oil  of  commerce  contains,  besides 
be  original  oil,  all  the  compounds  above  mentioned. 
'  The  hyduret  of  cinnamyle,  CiH,  is  a  fragrant  oil.  It  forms,  with  nitric  acid, 
I  crystalline  compound,  CiH  -f-  NO^,  which,  when  mixed  with  water  is  resolved 
nto  its  constituents,  hyduret  of  cinnamyle  and  nitric  acid.  When  the  hyduret 
is  exposed  to  the  air,  it  absorbs  oxygen,  producing  cinnamic  acid,  CiO,  HO  = 
C„H303,  HO. 

The  fresh  oil  of  cinnamon  is,  as  has  been  stated,  C^H^^O^.  With  6  eq.  oxy- 
gen from  the  air,  it  yields  hyduret  of  cinnamyle  and  the  two  resins :  with  2  eq. 
more,  the  hyduret  passes  into  cinnamic  acid.  With  oil  of  vitriol,  3  eq.  of  the 
fresh  oil  =  C^H^O^,  lose  3  eq.  water,  and  form  two  resins,  one  =  C^H^O  ; 
the  other  C^H  ^O  .  With  hydrochloric  acid,  it  yields  an  oil  and  two  resins;  one, 
C   HO;  the  other  C    HO. 

2.  Cinnamic  Acid.    CsH'O^  +  HO  =  CiO,  HO. 

Formed  by  exposing  oil  of  cinnamon  to  the  air.     It  is  most  easily  obtained  by 

dissolving  the  oil  of  balsam  of  Peru  in  an  alcoholic  solution  of  potash,  evapo- 

ting  to  dryness,  dissolving  in  hot  water,  and  adding  to  the  solution  of  cinna- 


f 


606  BALSAM  OF  PERU. 

mate  of  potash  an  excess  of  hydrochloric  acid.  It  crystall-'ze?  very  readily,  and 
may  be  sublimed.  By  the  action  of  nitric  acid,  cinnamic  rcid  is  converted  into 
hyduret  of  benzoyle,  and  into  an  acid  very  similar  to  benzoic  acid,  if  not  iden- 
tical with  it.  When  cinnamic  acid  is  added  to  cold  nitric  rcid,  it  forms  an  acid, 
CjgH„NOg  =  CjgHgO^— H  +  NO^;  that  is,  cinnamic  acid,  in  which  1  eq.  of 

C  H 

nitrons  acid  is  substituted  for  1  of  hydrogen ;  C^^    <  ^^    0  ,  HO.   This  is  niiro- 

cinnamic  acid.  Its  salts  detonate  when  heated.  With  oxide  of  ethyle,  it  forms 
a  cry  stall  izable  ether,  AeO,  C^gHgNO^. 

When  oil  of  cinnamon  is  acted  on  by  nitric  acid  with  the  aid  of  heat,  it  yields 
benzoic  and  nitrobenzoic  acids.     By  the  action  of  chlorine,  oil  of  cinnamon  is 

converted  into  several  new  products,  one  of  which  is  chlarocinnose^  C     ^  ^-.1  ^ 

C  ci^o^. 

It  is  hyduret  of  cinnamyle  in  which  4  eq.  of  chlorine  are  substituted  for  4  eq.  of 
hydrogen. 

Balsam  of  Peru  contains  compounds  connected  with  cinnamyle.  The  principal 
is  an  oil,  cinnameine,  which,  when  boiled  with  alkalies,  yields  cinnamic  acid  and 
a  neutral  oily  body,  peruvine,  ^18^12^2*  Cinnamine,  heated  with  dry  potassa, 
yields  hydrogen  gas  and  pure  cinnamate  of  potassa.  When  exposed  to  cold,  cin- 
nameine  deposits  crystals,  which  have  the  same  composition  as  hyduret  of  cin- 
namyle, and  are  therefore  an  isomeric  modification,  analogous  to  benzoine. 

According  to  Richter,  balsam  of  Peru  contains  two  distinct  oils,  myroxiline^ 
insoluble  in  alcohol,  myrinspermine^  soluble  in  alcohol.  With  an  alcoholic  solu- 
tion of  potassa,  myriospermine  yields  an  acid  resembling  cinnamic  acid,  but  dif- 
ferent from  it,  myriospermic  acid.  Balsam  of  Tolu  resembles  Balsam  of  Peru  in 
its  constituents.    These  substances  require  further  investigation. 

In  the  preceding  pages  we  have  considered  a  large  number  of  compound  radi- 
cals, constituting  chiefly  the  group  of  radicals  analogous  in  their  relations  to 
chlorine  :  namely,  cyanogen  ;  ferrocyanogen  and  its  numerous  congeners  ;  sul- 
phocyanogen  ;  and  mellone.  We  have  only  described  one  radical,  amide,  whicn 
has  a  tendency  to  produce  basic  compounds,  such  as  ammonia,  ammonium,  and 
the  platinised  basest  and  one,  carbonic  oxide  or  oxalyle,  the  chief  tendency  of 
which  is  to  form  acid  compounds,  such  as  oxalic,  carbonic,  rhodizonic,  croconic, 
and  mellitic  acids.  Finally,  we  have  studied  three :  namely,  benzoyle,  salicyle, 
and  cinnamyle,  whose  characteristic  is  to  form  essences  or  fragrant  volatile  com- 
pounds with  hydrogen,  acids  with  oxygen,  and  peculiar  compounds  with  chlo- 
rine, iodine,  &c.  This  last  group  would  appear  to  have  a  strong  tendency  to 
form  acid  compounds :  for  not  only  is  an  acid  formed  by  the  union  of  salicyle 
and  oxygen,  but  the  hyduret  of  salicyle  is  a  decidod  acid,  forming  salicylous 
acid,  C  H  0  ,H0,  isomeric  with  benzoic  acid;  instead  of  hyduret  of  salicyle, 
C  H  O  .  Further,  the  chloride,  bromide,  and  iodide  of  salicyle,  although 
they  contain  salicyle, /)/u»  those  elements,  are  all  strong  acids,  and  appear  to  be 
in  fact  salicylic  acid  with  1  eq.  of  chlorine,  &c.  substituted  for  1  eq.  of  hydro- 
gen. It  is  evident  that  this  group  of  radicals,  so  well  characterized  by  their 
hydrogen  compounds,  does  not  correspond  exactly  to  any  simple  radical,  but  has 
characters  common  to  different  groups  of  elementary  radicals,  being,  however, 
analogous  in  more  points  to  carbon,  sulphur,  and  phosphorus  than  to  any  other 
elements.     In  studying  the  decomposition  of  the  compounds  of  salicyle,  we  have 


ETHYLE.  607 

met  with  the  very  remaikable  fact  of  the  production  from  that  radical  of  a  series 
of  compounds  :  namely,  anilic  acid,  nitropicric  acid,  carbonic  acid,  &c.,  probably 
derivatives  of  a  totally  different  radical,  phenyle  ;  which  radical  is  also  met  with 
in  numerous  other  decompositions,  and  especially  in  the  decomposition  of  indigo 
by  nitric  acid,  by  alkalies,  and  by  heat,  and  in  the  destructive  distillation  of  coal. 
This  is  an  important  consideration,  as  evel^y  day's  experience  tends  to  identify 
with  each  other  the  products  of  decomposition  of  different  and  apparently  quite 
unconnected  organic  compounds,  even  in  cases  where  these  products  have  been 
described  as  different.  Another  very  important  fact  which  has  come  under  our 
notice  is  the  occurrence  of  salicylate  of  oxide  ofmethyle  as  the  chief  ingredient 
in  the  oil  of  Gaultheria.  Not  only  is  the  occurrence  of  salicylic  acid  interesting, 
since  this  acid  was  only  known  before  as  an  artificial  product,  but  the  existence, 
in  this  oil,  of  oxide  of  methyle,  hitherto  only  known  as  a  product  of  destructive 
distillation,  goes  far  to  confirm  the  theory  which  admits  this  radical,  methyle, 
and  others  similar  to  it.  All  the  properties  of  the  oil  of  Gaultheria  entirely  agree 
with  the  doctrine  of  its  containing  two  radicals,  methyle  and  salicyle,  the  former 
oxidized,  as  a  base;  the  latter,  also  oxidized,  as  an  acid. 

We  now  proceed  to  consider  that  group  of  radicals  to  which  methyle  belongs, 
and  which  are  analogous,  in  their  relations,  to  metals,  more  than  to  any  other 
class  of  elements ;  forming,  like  metals,  bases  with  oxygen.  This  group  con- 
tains Eihyle,  Methyle,  Amyle,  Glyceryle,  Cetyle,  and  Cacodyle;  besides  several 
radicals,  derived  from  the  decomposition  of  these :  as,  Acetyle  from  Ethyle,  and 
Formyle  from  Methyle.  These  latter,  however,  belong  to  that  group  which  are 
analogous  to  the  combustible  metalloids,  and  form  acids  with  oxygen,  instead  of 
bases,  like  the  radicals  from  which  they  are  derived,  and  in  connection  with 
which  they  shall  be  described. 

XVI.  Ethyle.    C^HgrsAe. 

Unknown  hitherto  in  a  separate  form ;  but  very  well  known  as  anhydrous 
oxide,  or  ether,  and  hydrated  oxide,  or  alcohol.     These  compounds  have  not  yet 

een  found  as  natural  products  of  vegetable  life,  although  it  is  probable  that  the 
grance  of  certain  fruits,  such  as  pine-apples,  melons,  apples,  is  derived  from 

ompounds  of  ethyle.  The  compounds  of  ethyle,  especially  alcohol,  are,  how- 
ever, very  abundantly  produced  by  the  fermentation  of  saccharine  vegetable 
juices,  such  as  that  of  the  grape.  The  alcoholic  or  vinous  fermentation  of  sugar 
is  a  metamorphosis,  induced  in  the  sugar  by  contact  with  yeast  or  ferment,  which 
is  gluten  or  fibrine  in  a  state  of  decomposition.  In  this  metamorphosis,  the  par- 
ticles of  the  ferment  only  act  in  communicating  mechanical  motion  to  those  of 
the  sugar;  they  do  not  join  the  elements  of  the  sugar  in  producing  new  com- 
pounds, but  are  decomposed  separately  ;  while  the  elements  of  the  sugar,  plus  a 
small  proportion  of  the  elements  of  water,  form  two  compounds,  alcohol  and  car- 
bonic acid.     Cj^HjjOjj+HO=2(C^H^,0-f-HO)t4C02. 

TABLE   OF    COMPOUNDS. 

Oxide  of  Ethyle C4H5  0 

Hydrate  Oxide  of  Ethyle  C4H5  0,HO; 

Chloride  <«  « C^li^.Cl, 

Bromide  «<  « C4H5,Br 

Iodide  «  « C4H5,I 

Sulphuret  «  «c C4H5,S 

Mercaptaa        «  «« CiHgjS+HS. 


^08  OXIDE  OF  ETHYLE. 

*     1.  Oxide  of  Ethyle.    AeO=C4H5,0. 

Syn.  Ether,  Sulphuric  Ether. — This  compound  is  obtained  from  alcohol,  its 
hydrate,  by  heating  it  gently  along  with  sulphuric  or  phosphoric  acid,  which  re- 
moves the  water,  or  at  all  events  causes  the  separation  of  the  ether  from  the 
water.  The  best  process  is  as  follows :  5  parts  of  alcohol,  of  at  least  90  per 
cent.,  are  mixed  with  9  of  sulphuric  acid,  and  the  mixture  introduced  into  a 
retort,  where  it  is  rapidly  heated  to  the  boiling  point,  and  kept  at  that  point, 
while  by  means  of  a  bent  tube  passing  through  the  cork  which  stops  the  tubulure 
of  the  retort,  and  furnished  with  a  stop-cock,  fresh  alcohol  is  allowed  to  enter 
the  retort  so  as  to  keep  the  liquid  constantly  at  the  original  level,  flowing  in  ex- 
actly as  fast  as  the  ether,  &c.  distils  over.  The  products  are  condensed  in  a 
powerful  refrigeratory,  such  as  Liebig's,  figured  at  p.  556 ;  they  consist  chiefly 
of  ether,  with  water  in  such  proportion  as  would  convert  the  ether  into  alcohol ; 
and  a  very  little  alcohol,  sometimes  none  at  all.  The  operation  may  be  advan- 
tageously continued  until  31  parts  of  alcohol,  at  90  per  cent.,  have  flowed  into 
the  retort,  and  of  course  an  equal  volume  of  ether  and  water  has  distilled  over. 

This  process,  as  to  its  final  result,  may  be  thus  expressed.  AeO,H04-2(HO, 
S03)=2HO,S03+HO-t-AeO.  That  is,  the  action  of  heat  and  of  oil  of  vitriol 
has  caused  the  separation  of  the  ether  and  the  water,  which,  together,  constitute 
alcohol.  And  it  is  to  this  view  of  the  change,  which  he  considers  one  of  decom- 
position by  contact,  that  Berzelius  applies  his  theory  of  a  catalytic  force.  But 
in  reality,  the  process  consists  of  two  stages  :  the  first  is  the  formation  of  bisul- 
phate  of  oxide  of  ethyle  (sulphovinic  acid)  AeO,HO,2S03;  and  the  second  is 
the  decomposition  of  this  by  heat  into  AeO  and  HO,2S03.  The  bisulphate  is 
formed  when  a  mixture  of  2  eq.  oil  of  vitriol,  1  eq.  alcohol,  and  from  1  to  3  eq. 
of  water,  is  heated  to  about  285° ;  and  at  almost  precisely  the  same  temperature, 
the  bisulphate  is  decomposed,  especially  if  the  liquid  be  kept  in  steady  ebulli- 
tion. Now,  the  bisulphate  contains  anhydrous  sulphuric  acid,  ether,  and  water, 
SSO^-j-AeO-j-HO  ;  and  when  decomposed  the  sulphuric  acid  seizes  the  water, 
thus  preventing  the  ether  from  uniting  with  it  to  reproduce  alcohol.  The  ether, 
therefore,  distils  over;  but  as,  when  the  bisulphate  was  formed,  ether,  AeO,  dis- 
placed water,  HO,  from  half  the  oil  of  vitriol,  so  now,  when  the  bisulphate  is 
decomposed,  and  while  its  water  is  retained  by  the  2  eq.  of  anhydrous  acid,  the 
vapours  of  ether  traverse  a  liquid  containing  oil  of  vitriol  diluted,  both  with  the 
water  displaced  from  the  other  part  of  it  by  the  ether,  and  with  the  water  of  the 
alcohol  (which  at  90  per  cent,  amounts  to  2  eq.  for  1  of  ether,  one  combined 
with  the  ether  to  form  the  alcohol,  the  other  serving  to  dilute  it).  Now,  a  sul- 
phuric acid,  thus  far  diluted,  and  heated  to  a  temperature  even  short  of  285°, 
gives  off  water,  and  therefore  the  vapour  of  ether  in  passing  through  this  acid, 
becomes  saturated  with  the  vapour  of  water,  without  combining  with  it,  and  thus 
ether  and  water  distil  over  together.  At  the  surface  of  the  boiling,  or  effervescing 
liquid,  however,  the  ether  produced  by  the  decomposition  of  the  bisulphate  is 
brought  into  contact  with  water  in  the  nascent  state,  also  derived  from  that  de- 
composition, and  in  this  planner,  according  to  Liebig,  a  little  alcohol  is  repro- 
duced, and  distils  over  with  the  ether,  the  ether  being  produced  in  the  body  of 
the  liquid,  the  alcohol  only  at  the  surface.  It  is  certain  that  a  little  alcohol  gene- 
rally accompanies  the  ether,  even  in  the  most  successful  operation ;  but  it  is  not 
easy  to  see  how,  according  to  the  above  explanation,  the  sulphuric  acid  which, 
in  the  bcdy  of  the  liquid,  is  able  to  prevent  the  ether  from  combining  with  water, 


HYDRATE  OF  OXIDE  OF  ETHYLE.  609 

should  fail  to  do  so  al  the  surface.  The  ether  and  water,  it  would  appear,  are 
equally  in  the  nascent  state  in  both  situations.  While,  therefore,  we  admit 
Liebig's  very  beautiful  explanation  of  the  facts  connected  with  the  production 
of  ether,  we  cannot  feel  the  same  certainty  in  regard  to  his  explanatir)n  of  the 
simultaneous  occurrence  of  alcohol.  It  will  now  be  seen  how  little  necessity 
there  is  for  resorting  to  the  mysterious  agency  of  catalysis  ;  for  the  change  is  not 
one  due  to  contact  alone,  but,  on  the  contrary,  one  depending  on  strong  affinities 
very  nicely  balanced,  and  influenced  to  a  very  great  extent  by  the  degree  of  heat 
employed.  The  idea  that  the  contact  of  oil  of  vitriol  caused  the  ether  and  water 
of  alcohol  to  separate,  arose  from  the  circumstance  that  the  formation  of  the 
bisulphate  of  ethyle  takes  place  at  a  temperature  quite  close  to  that  at  which  it 
is  decomposed,  and  that  the  formation  of  the  bisulphate  in  this  process  had  been 
overlooked. 

The  crude  ether  is  mixed  with  an  alcoholic  solution  of  potash,  so  as  to  render 
it  alkaline,  and  distilled  in  the  vapour-bath,  as  long  as  the  sp.  gr.  of  the  product 
does  not  exceed  0*735  at  80°.  The  ether  is  then  digested  for  a  few  days  with 
chloride  of  calcium,  or  quicklime,  and  rectified  once  more  with  one  of  these  sub- 
stances. When  pure,  oxide  of  ethyle  is  a  colourless,  very  mobile,  highly  refract- 
ing liquid,  of  sp.  gr.  0-725  at  60°.  It  is  very  volatile,  boiling  at  76°,  and  pro- 
ducing intense  cold  by  its  evaporation.  It  has  a  pungent,  cooling,  aromatic 
taste  ;  and  a  penetrating,  agreeable  odour.  It  is  very  combustible,  and  its  vapour 
is  apt  to  form  dangerous  explosive  mixtures  with  air.  When  oxidized  slowly, 
it  yields  aldehyde,  aldehydic  acid,  acetic  and  formic  acids. 

Ether  is  used  in  medicine  as  a  diffusible  stimulant,  and  in  chemistry  as  a 
solvent,  especially  of  organic  matters  :  such  as  fats,  fat  oils,  essential  oils, 
resins,  some  acids,  and  some  bases. 

In  its  relations  to  other  bodies  it  exhibits  the  characters  of  a  base,  neutraliz- 
ing acids,  and  forming  compounds  which  are  subject  to  the  laws  of  double 
decomposition,  like  salts  of  inorganic  bases.  These  salts  of  oxide  of  ethyle 
are,  commonly,  ethereal  liquids  ;  many  of  them  crystallizing  at  low  tempera- 
tures, and  a  good  many  being  solid  and  crystalline  at  ordinary  temperatures. 
They  are  often  called  ethers,  with  the  name  of  the  acid ;  as  acetic  ether,  ben- 
zoic ether,  &c.  Those  ethers  which  contain  organic  acids  are  for  the  most  part 
fragrant.  The  formula  for  the  salts  of  oxide  of  ethyle  corresponds  to  that  for 
the  salts  of  potash,  &c.  Thus,  as  KO,A.  represents  acetate,  and  KO,Bz  benzoate 
of  potash,  so  AeO,A  or  AeO,Ac02,  and  AeO,Bz  or  AeO,BzO  represent  the  ace- 
tate and  benzoate  of  oxide  of  ethyle. 

The  analogy  between  ether  and  metallic  protoxides  is  further  shown  in  the 
action  of  both  on  hydrochloric  acid  and  its  congeners  ;  for  while  KO,  with  HCl 
yields  HO  and  KCl;  so  AeO  +  HCl  =  HO  +  AeCl :  that  is,  ether,  with 
hydrochloric  acid,  yields  water  and  chloride  of  ethyle.  The  same  is  true  of  the 
bromide,  iodide,  &c.,  and  by  proper  means  both  the  cyanide  of  ethyle,  AeCy, 
and  the  sulphuret  of  ethyle,  AeS,  may  be  obtained.  In  short,  we  cannot  better 
connect  and  classify  the  numerous  facts  now  known  in  regard  to  ether,  than  by 
adopting  the  view  which  considers  it  as  the  basic  oxide  of  ethyle,  a  compound 
radical,  very  analogous  to  a  metal. 

2.  Hydrate  of  oxide  of  ethyle.  AeO,HO  =  C^H^O,HO.  Syn.  Alcohol.  This 
compound  is  formed  when  ether  and  water  meet  in  the  nascent  state,  as  we  shall 
see  occurs  when  some  of  the  acid  salts  of  ethyle  are  heated,  or  otherwise  decom- 

41 


t 


610  HYDRATED  OXIDE  OF  ETHYLE. 

posed.  But,  practically,  it  is  produced  entirely  from  sugar  by  fermentation.  The 
juice  of  the  grape,  or  any  other  saccharine  juice,  or  an  infusion  of  malt,  when 
exposed  to  the  air  for  a  short  time,  and  then  from  a  temperature  of  from  40°  to 
85°,  soon  enters  into  fermentation,  and  a  large  quantity  of  carbonic  acid  is  given 
off,  while  the  sugar  totally  disappears,  and  alcohol  is  found  in  its  place.  A  pure 
solution  of  sugar  in  water  does' not  ferment,  but  on  the  addition  of  yeast  it  does 
so.  The  juice  of  the  grape  and  the  infusion  of  malt  both  contain,  besides  sugar, 
some  body  which  plays  the  part  of  yeast,  or  ferment.  Tliis  is,  in  the  grape 
juice,  fibrine,  and  in  the  malt,  gluten,  both  of  which  readily  enter  into  putrefac- 
tion when  exposed  to  air  and  moisture,  and  being  in  this  state,  their  particles  in 
motion,  this  motion  is  communicated  to  the  particles  of  sugar,  and  the  existing 
equilibrium  of  affinities  being  thereby  disturbed,  new  compounds  are  formed,  in 
this  case  alcohol  and  carbonic  acid.  The  subject  of  fermentation  will  be  after- 
wards fully  discussed :  in  the  mean  time,  it  is  to  be  observed  that  any  similar 
substance,  in  a  state  of  putrefaction,  will  induce  the  fermentation  of  sugar ;  as, 
for  example,  putrefying  flesh,  blood,  milk,  cheese,  white  of  egg,  urine,  &c.  &c., 
and  that  none  of  these  ferments  contributes  to  the  production  of  the  alcohol,  or 
carbonic  acid,  but  yield  ammonia  and  other  products.  Crystallized  cane  sugar, 
CjgHjjOjj,  requires  the  elements  of  1  eq.  of  water  to  yield  2  eq.  alcohol  C^U^^ 
O^  ^nd  4  eq.  carbonic  acid  4C02  =  C^O^;  and  grape  sugar,  Cj^Hj^Oj^,  pro- 
duces, besides  the  alcohol  and  carbonic  acid,  2  eq.  of  water.  Thus  we  have 
^i2^rPn  +  HO  =2(C^H,0^)  -+-400^;  and  C^H^^O^,  =  2(C^H,0^)  +  4C0^ 
+  2H0. 

From  the  fermented  liquid,  which,  in  the  case  of  the  grape  juice,  is  wine,  in 
that  of  malt,  beer,  ale,  or  wort,  the  alcohol  is  separated  by  distillation,  and  being 
more  volatile  than  water,  it  predominates  in  the  first  portions  distilled.  These 
constitute,  when  from  wine,  brandy ;  when  from  a  fermented  infusion  of  malt, 
whiskey ;  and  when  from  fermented  solution  of  molasses,  rum.  In  these  forms 
it  still  contains  30,  40,  or  more  per  cent,  of  water,  and  a  little  volatile  odoriferous 
oil.  It  is  again  rectified,  and  the  first  portions  distilled  are  colourless,  and  go 
by  the  name  of  spirits  of  wine.  After  another  rectification  they  are  called  rec- 
tified spirits  of  wine.  They  now  contain  only  alcohol,  with  from  10  to  20  per 
cent  of  water,  which  is  removed  by  digesting  the  spirit  with  quicklime,  and  dis- 
tilling: or  by  rectifying  over  dried  carbonate  of  potash,  or  chloride  of  calcium.  J 

Pure  or  absolute  alcohol  is  a  colourless,  mobile  fluid  of  sp.  gr.  0'795  at  60®, 
.and  boiling  at  173°.  It  has  a  burning  taste,  and  a  pleasant  fruity  smell.  Rec- 
tified spirit  of  wine,  that  of  90  per  cent,  is  very  similar  to  it,  having  the  sp.  gr. 
0*825  to  0'836 ;  ordinary  spirit  of  wine,  at  70  per  cent.,  has  the  sp.  gr.  0-880. 
Pure  alcohol  has  never  been  frozen.  It  is  very  combustible,  and  produces,  in 
burning,  a  very  intense  heat.  Hence  spirit  of  wine  is  much  used  for  lamps  for 
chemical  purposes.  Alcohol  has  a  strong  attraction  for  water,  and  on  this  account 
acts  as  an  antiseptic,  preserving  animal  and  vegetable  substances  from  putrefac- 
tion. The  strength  of  alcohol  is  ascertained  by  its  specific  gravity  ;  and  all  che- 
mical works  contain  tables  of  the  relation  between  the  density  of  the  spirit  and 
the  per  centage. 

Alcohol  is  a  powerful  diffusible  stimulant,  and  has  intoxicating  properties.  It 
is  much  used  as  a  solvent,  for  many,  indeed  most  vegetable  acids  and  bases,  for 
volatile  oils,  for  resins,  and  for  many  salts,  even  inorganic.  Most  deliquescent 
salts  are  soluble  in  alcohol,  as  are  the  caustic  alkalies  and  iodine.    Acids  act  on 


CHLORIDE  OF  ETHYLE.    MERCAPTAN.  611 

alcohol,  producing  the  compound  ethers.  Solutions  made  with  proof  spirit  (a 
mixture  of  equal  vflumes  of  rectified  spirit  of  wine  and  of  water,  sp.  gr.  0*960), 
are  called  tinctures. 

3.  Chloride  of  ethyle,  AeCl  =  C^H^,C1,  is  prepared  by  saturating  alcohol  with 
hydrochloric  acid  gas,  and  distilling  the  mixture  in  the  vapour-bath,  collecting 
the  product  in  a  well  cooled  receiver.  It  is  formed  as  follows  :  AeO,HO  H-  HCl 
=  AeCl  -f-  2H0.  It  is  dried  by  digestion  with  chloride  of  calcium.  It  is  a 
colourless  liquid,  sp.  gr.  0-874,  boiling  at  52°,  of  an  aromatic  odour,  slightly 
alliaceous.  When  exposed  to  the  combined  action  of  chlorine  and  the  sun's 
rays,  it  yields  by  substitution  a  whole  series  of  chlorinized  ethers,  of  which 
series  one  extremity  is  ether  (C^H^)O  ;  and  the  other,  perchloride  of  carbon 
(C^C1^)C1  =  2C  CI  .  With  an  alcoholic  solution  of  protosulphuret  of  potas- 
sium KS,  it  gives  chloride  of  potassium  and  sulphuret  of  ethyle.  AeCl  -f-  KS 
=  AeS  +  KCl.  With  hydrosulphuret  of  sulphuret  of  potassium,  it  yields  mer- 
ca/?/an,  which  is  alcohol,  in  which  all  the  oxygen  has  been  replaced  by  sulphur. 
AeCl  +  KS,HS  =  KCl  +  AeS,HS  ;  the  latter,  mercaptan,  being  analogous  to 
AeO,HO. 

4.  Bromide  of  ethyle^  formed  by  distilling  bromine  with  alcohol  and  phos- 
phorus. These  are  first  formed,  when  the  materials  are  mixed,  phosphorous  and 
hydrobromic  acids,  and  the  latter  when  heated  with  the  alcohol,  decomposes  it, 
yielding  AeBr,  which  resembles  the  chloride. 

5.  Iodide  of  eihyle^  Ael,  formed  by  a  similar  process,  is  analogous  to  the  two 
preceding  compounds. 

6.  Sulphuret  of  ethyle^  AeS,  is  prepared,  as  above  stated,  from  the  chloride  by 
sulphuret  of  potassium.  It  is  a  colourless  liquid,  boiling  at  167°,  of  a  strong 
offensive  alliaceous  smell. 

7.  Hydrosulphuret  of  sulphuret  of  ethyle  or  mercaptan,  AeS,HS  =  C^H^S^  or 
C^H^,S  -f-  HS.  This  very  remarkable  compound  is  formed  when  a  solution  of 
sulphate  of  lime  and  ethyle  (sulphovinate  of  lime)  of  sp.  gr.  1-28,  is  distilled 
with  its  own  bulk  of  a  solution  of  potash  of  the  same  density,  previously  satu- 
rated with  sulphuretted  hydrogen,  and  converted  into  KS,HS.  The  volatile  pro- 
duct, after  digesting  it  with  a  little  oxide  of  mercury  and  chloride  of  calcium,  to 
remove  sulphuretted  hydrogen  and  water,  is  mercaptan.  Its  formation  is  thus 
explained :  (CaO,S03  +  AeOSOg)  +  KS,HS  =  CaO,S03  t  K0,S03  +  AeS, 
HS.  Pure  mercaptan  is  a  colourless  liquid,  very  mobile,  boiling  at  97°,  of  sp. 
gr.  0-842.  It  has  a  most  penetrating  and  offensive  odour  of  onions,  as  it  were 
concentrated,  which  adheres  obstinately  to  the  hair  or  clothes,  so  that  it  is  most 
unpleasant  to  experiment  upon.  As  above  mentioned,  it  is  formed  from  alcohol 
by  substitution  of  sulphur  for  oxygen ;  and  as  alcohol  is  tho  hydrate  of  oxide  of 
ethyle,  AeO,HO,  mercaptan  is  the  hydrosulphuret  of  the  sulphuret  of  ethyle, 
AeS,HS.     The  sulphuret  of  ethyle,  AeS,  corresponds  to  the  oxide,  ether,  AeO. 

Mercaptan  acts  strongly  on  some  metallic  oxides,  especially  those  of  the  noble 
metals,  such  as  mercury,  gold,  platinum,  Itc.  The  metal  takes  the  place  of  the 
hydrogen  of  the  sulphuretted  hydrogen  in  mercaptan;  thus  MO  -|-  (AeS,HS) 
=  HO  -f-  (AeS, MS).  The  red  oxide  of  mercury  is  acted  on  by  mercaptan,  and 
converted  into  a  white  crystalline  compound,  called  the  mercaptide  of  mercury ; 
oxide  of  gold  forms  a  gelatinous  white  mercaptide ;  and  oxide  of  lead  yields 
lemon  yellow  crystals  of  mercaptide  of  lead,  AeS,PbS. 

Mercaptan  may  also  be  viewed  as  H  +  AeS^,  in  which  case  the  above  metallic 
compounds  will  have  the  general  formula  M  -f-  AeS^*  Here  the  supposed  radical, 


i 


iQJjJ  SALTS  OF  OXIDE  OF  ETHYLB.  ?    ■ 

the  mercaptum  of  Zeise,  is  bisulphuret  of  eihyle ;  so  that  on  either  view  mercap- 
tan  is  connected  with  ethyle.  • 

Zeise  has  described,  under  the  name  of  thialic  oil  or  ether,  another  very  fetid 
compound,  which  seems  to  be  AeS  ,  or  persulphuret  of  ethyle. 

Seleniuret  and  cyanide  of  ethyle  are  both  volatile  alliaceous  offensive  liquids, 
formed  when  sulphate  of  ethyle  and  potassa  is  distilled  with  seleniuret  or  cya- 
nide of  potassium.  Sulphocyanide  of  potassium,  alcohol  and  sulphuric  acid, 
when  dissolved  together,  yield  a  most  offensive  volatile  liquid,  supposed  to  be, 
or  at  all  events  to  contain,  sulphocyanide  of  ethyle.  It  will  be  observed  that  all 
these  compounds  of  sulphur  with  ethyle  and  similar  bodies  are  characterized  by 
odours  resembling  that  of  garlic,  but  so  intense  and  penetrating  as  to  be  insup- 
portable. This  character  is  observed  in  all  volatile  organic  compounds  of  sul- 
phur, whether  artificial,  as  the  above,  or  natural,  as  oils  of  garlic,  assafoetida, 
horseradish,  &c. 

7.  Salts  of  Oxide  of  Ethyle. 

Oxide  of  ethyle  forms  both  neutral  and  acid  salts.  The  neutral  salts  are  not 
at  ordinary  temperatures  decomposed  by  other  salts,  like  inorganic  saline  com- 
pounds. Thus  an  alcoholic  solution  of  chloride  of  calcium  does  not  cause  any 
precipitate  in  an  alcohol  solution  of  oxalate  of  oxide  of  ethyle  or  oxalic  ether. 
But  they  are  easily  decomposed  by  contact  with  hydrated  alkalies,  the  acid 
uniting  with  the  alkali,  while  the  oxide  of  ethyle  separates  as  hydrate,  that  is, 
as  alcohol.  Thus  oxalic  ether  C  0  ,AeO,  with  hydrate  of  potash,  KO,HO, 
yields  oxalate  of  potash  KO,C  O  ,  and  hydrate  of  oxide  of  ethyle,  AeO,HO. 

Oxide  of  ethyle  has  a  very  great  tendency  to  form  double  salts,  in  which  there 
are  2  eq.  of  the  acid,  1  eq.  of  a  basic,  and  1  eq.  oxide  of  ethyle.  In  these  salts, 
the  acid,  as  in  the  neutral  salts  cannot  be  detected  by  the  usual  tests;  and  indeed 
they  may  be  viewed  as  simple  salts,  containing  a  compound  acid,  of  which  oxide 
of  ethyle  is  a  constituent  united  to  the  inorganic  base.  Thus  the  double  sul- 
phate of  ethyle  and  potash,  KO,SO  -\-  AeO,SO  ,  may  be  viewed  as  sulphovi- 
nate  of  potash,  KO  +  AeO,2SO  ;  and  sulphovinic  acid  is,  on  this  view,  when 
separated,  HO  -f  AeO,2S03. 

The  acid  salts  of  ethyle  are  on  one  view  double  salts,  as,  for  example,  the 
double  sulphate  formed  of  sulphate  of  ethyle,  AeOjSO^,  with  sulphate  of  water, 
HO,SO^.  On  the  other  view,  they  are  compound  or  coupled  acids,  and  the 
above  example  becomes,  as  mentioned  in  the  last  paragraph,  sulphovinic  acid, 
HO  +  (AeO,2SO  ),  the  hydrate  of  a  compound  of  anhydrous  sulphuric  acid 
with  ether.  These  acid  salts  are  decomposed,  by  boiling  with  water,  into 
alcohol  which  distils  over,  and  hydrated  acids  which  remain  behind.  When 
distilled  with  the  salts  of  volatile  acids,  they  yield  the  ethers  of  those  acids : 
formiate  and  acetate  of  ethyle  may  be  thus  obtained.  When  an  acid  salt  of 
ethyle  is  heated  with  acids  not  volatile,  it  often  happens  that  the  ethers  of  these 
acids  are  obtained  :  this  is  the  case  with  the  fatty  acids  and  with  some  others. 

TABLE  or  SALTS  OF  THE  OXIDE  OF  ETHYLE. 


Acid  sulphate  of  the  oxide  of  Ethyls 
Acid  phosphate  **  "     . 

Nitrate  "  "     • 

Hyponifrite  "  "    • 

Carbonate  «  "     . 


HOjSOg  f  AeOSOj 

P205,AeO,2HO 

AeOjNOg 

AeO.NO, 

AeOjCO, 


OXIDE  OF  ETHYLE  WITH  NITRIC  ACID. 


613 


Double  carbonate  of  ethyle  and 

potash 

K0,C02  +  AeO.COa 

Oxalate  of  oxide  of  ethyle 

AeOjCgOg 

Oxamate        "            '« 

AeO,C203  +  M,CP2- 

Sulphocarbonate  and  water      . 

AeO,HO,2CS2 

Bicyanurate  of  oxide  of  Ethyle 

.    CygOajSAeO,  +  CyaOsjSHO  f  3Aq 

Benzoate              "              " 

AeO,BzO 

Hippurate             "              " 

AeO,  -f  CigNHgOg 

Salicylate             «              " 

.        .        AeO  t  C,,HA 

8.  ^cid  sulphate  of  oxide  of  ethyle,  VLO,^0^  +  AeSO^,  is  also  called  sulpho' 
vinic  acid,  HO  +  (AeO,2SO  ).  Sulphuric  acid  forms  no  neutral  compound 
with  oxide  of  ethyle.  The  acid  salt  is  formed  when  the  vapour  of  ether  is  con- 
ducted into  oil  of  vitriol,  or  when  oil  of  vitriol  is  mixed  with  alcohol  and  heated 
to  a  certain  point.  To  obtain  it  pure,  the  doubl^  sulphate  of  ethyle  and  baryta 
(sulphovinate  of  baryta)  in  solution,  is  decomposed  by  sulphuric  acid,  and  the 
filtered  liquid  is  a  solution  in  water  of  the  acid  sulphate.  It  has  a  very  sour 
taste,  and  cannot  be  concentrated  by  evaporation,  whether  at  the  ordinary  tem- 
perature or  with  the  aid  of  heat,  without  being  decomposed  into  alcohol  and 
sulphurip  acid.  It  forms,  with  most  bases,  crystallizable  double  salts,  which 
are  all  soluble,  so  that,  for  example,  the  addition  of  baryta  causes  no  precipitate 
if  the  acid  be  pure.  As  the  acid  sulphate  itself  is  called  sulphovinic  acid,  so 
these  double  salts  are  called  sulphovinates.  It  is  because  all  these  salts  are 
soluble,  that  the  usual  tgsts  cannot  detect  the  sulphuric  acid  they  contain. 
When,  however,  their  solutions  are  boiled  with  a  little  hydrochloric  acid,  alcohol 
is  given  off,  and  then  the  sulphuric  acid  may  be  detected  as  usual.  All  these 
salts  are  decomposed  by  heat,  yielding,  according  to  the  temperature,  double 
sulphate  of  ethyle  and  etherole,  alcohol,  sulphurous  acid,  olefiant  gas,  and  a  sul- 
phate as  residue,  mixed  with  charcoal.  When  heated  with  hydrated  alkalies, 
they  yield  sulphates  and  alcohol.  The  double  sulphate  of  ethyle  and  potash  crys- 
tallizes in  shining  scales,  which  are  the  anhydrous  salt,  KO,SOg  +  AeO,SOj. 
The  baryta  salt  contains  2  eq.  of  water  of  crystallization,  and  forms  beautiful 
tabular  crystals,  as  do  also  the  salt  of  lime,  and  the  salt  of  lead,  both  of  which 
likewise  contain  2  eq.  of  water.  These  three  salts  are  all  composed  according 
to  the  formula,  MO,SO   f  AeCSO^  -f-  2  eq. 

C  AeO 

9.  Jcid  phosphate  of  oxide  of  ethyle,  or  phosphovinic  acid,  ^fi^  <  2H0     ^^ 

formed  in  the  same  way  as  sulphovinic  acid,  and  obtained  pure  from  the  double 
AeO 


salt  of  baryta,  P„0 


2    5  )  2BaO 


+  12H0. 


It  is  a  tolerably  permanent  acid,  de- 
composed only  by  a  high  'temperature.  With  bases  it  forms  double  salts,  in 
which  the  2  eq.  water  of  the  acid  are  replaced  by  2  eq.  of  a  protoxide.  The 
baryta  salt,  the  formula  of  which  is  given  above,  crystallizes  in  pearly  scales. 


» 


OXIDE  OF  ETHYLE  WITH  NITRIC  ACID. 


10.  Nitrate  of  Oxide  of  Ethyle.    AeOjNOg 


When  2  fluid  ounces  of  alcohol,  and  1  fluid  ounce  of  pure  nitric  acid,  of  sp. 
gr.  1*4,  are  distilled  together,  with  the  addition  of  10  or  20  grains  of  urea,  to 
destroy  any  nitrous  or  hyponitrous  acid,  the  distillation  proceeds  calmly  and 
smoothly,  and  the  distilled  liquor  contains  water,  alcohol,  and  nitrate  of  ethyle, 


614  SALTS  OF  OXIDE  OF  ETHYLE. 

which  partly  separates,  towards  the  end  of  the  process,  as  a  heavy  oily  stratum, 
and  is  more  completely  separated  by  the  addition  of  water.  It  is  a  colourless 
liquid,  of  sp.  gr.  1*112;  which  boils  at  185°,  and  is  inflammable,  burning  with 
a  bright  white  flame.  It  is  quite  insoluble  in  water,  but  very  soluble  in  alco- 
hol; and  it  possesses  a  pleasant  smell  and  a  sweet  taste.  An  alcoholic  solution 
of  potash  converts  it  into  alcohol  and  pure  nitrate  of  potash. 

11.  Hyponitrite  ofOxideofEthyle.    AeOjNO,. 

SvN.  Nitrous  ether. — Nitric  ether*  This  is  best  prepared  in  a  state  of  purity 
when  a  current  of  hyponitrous  acid  vapours,  derived  from  starch  and  nitric  acid, 
is  passed  through  weak  alcohol,  the  product  being  condensed  in  Liebig's  refri- 
geratory. The  ether  is  washed  with  water,  and  dried  by  means  of  chloride  of 
calcium.  The  whole  apparatus  must  be  kept  cool,  otherwise  the  action  is  too 
violent,  and  the  results  very  complex.  When  nitrous  ether  is  made  by  the 
usual  processes,  in  which  ordinary  nitric  acid  is  mixed  with  alcohol,  the  product 
always  contains  a  large  proportion  of  aldehyde,  and  in  fact  very  little  of  the  true 
ether.  The  action  in  this  case  is  as  follows,  2  (C^HgO^)  -|-  NO^  =  C^H^O, 
HO  (aldehyde),  -f  3H0  +  (C^H^,0  -f-  NO3).  The  pure  hyponi'trous  ether, 
prepared  by  Liebig's  process,  given  above,  is  a  pale  yellow  liquid,  boiling  at 
62°,  of  sp.  gr.  0*947.  It  has  a  very  agreeable  odour  of  rennet-apples.  With 
an  alcoholic  solution  of  potash,  it  yields  alcohol,  and  pure  hyponitrite  of  potash. 
The  sweet  spirit  of  nitre  or  spiriius  aetheris  nitrosi  of  the»pharmacop(Eia,  is  a  solu- 
tion of  the  impure  hyponitrous  ether  in  alcohol. 

12.  Carbonate  of  Oxide  of  Ethyle.    AeOjCOj. 

Syn.  Carbonic  ether.  When  oxalic  ether  is  acted  on  by  potassium,  there  are 
formed  several  products,  one  of  which  is  this  ether.  When  pure,  it  is  an  aro- 
matic liquid,  of  sp.  gr.  0-975,  boiling  at  260°.  An  alcoholic  solution  of  potash 
converts  it  into  alcohol  and  carbonate  of  potash.  Chlorine  acts  on  it,  forming 
products  to  be  described  when  we  treat  of  the  action  of  chlorine  on  ethers 
generally. 

13.  Double  carbonate  of  elhyle  and  potassa,  KO,CO  +  AeO,CO  ,  is  formed 
when  dry  carbonic  acid  gas  is  passed  through  an  alcoholic  solution  of  fused 
potash.  A  saline  mass  is  obtained,  from  which,  after  washing  with  ether, 
alcohol  dissolves  the  double  salt,  leaving  carbonate  and  bicarbonate  of  potash. 
The  double  salt  forms  pearly  scales,  which  are  decomposed  by  water  into  alcohol 
and  bicarbonate  of  potash. 

14.  Oxalate  of  oxide  of  ethyle.  keO.Cfi^. — Syn.  Oxalic  Ether. — This 
ether  is  formed  by  distilling  4  parts  of  superoxalate  of  potash,  5  of  oil  of  vitriol 
and  4  of  alcohol  at  90  p.  c,  mixing  the  product  with  4  times  its  bulk  of  wat^r, 
and  washing  with  water  the  ether  which  separates,  until  all  free  acid  is  removed. 
The  ether  is  then  rectined.  It  is  a  colourless  liquid,  of  sp.  gr.  1*093,  boiling  at 
364°.  It  has  an  aromatic  smell.  If  pure,  it  may  be  kept  under  water:  but  if  a 
trace  of  alcohol  or  of  oxalic  acid  be  present,  it  is  soon  resolved  into  oxalic  acid 
and  alcohol  when  in  contact  with  water.  Fixed  alkalies  cause  the  same  change. 
When  an  excess  of  ammonia  is  added  to  it,  oxamide  is  formed  :  where  the  ether 
is  in  excess,  there  is  formed  a  substance  in  beautiful  pearly  tables,  formerly 
called  oxamethane,  but  now  proved  to  be  oxamate  of  ethyle.  These  two  reac- 
tions are  easily  explained.     In  the  first  case,  AeO,C20^  -f-  NH^  =  (AeO,HO) 


SALTS  OF  OXIDE  OF  ETHYLE.  615 

=  (C2^2'^^^2)*  ^"  ^^®  second,  half  the  ether  undergoes  the  above  change, 
and  the  other  half  combines  with  the  oxamide  formed.     AeO.C  0,+  CO  ,NH„ 

'23'  22'  3 

=  AeO,C  NH^O^.  Chlorine  acts  on  oxalic  ether,  giving  rise  to  products  whicb 
will  be  hereafter  described  along  with  the  results  of  the  action  of  chlorine  on 
other  ethers. 

When  to  an  alcoholic  solution  of  oxalic  ether  there  is  added  enough  of  an 
alcoholic  solution  of  potassa  or  soda  to  decompose  the  half  of  the  ether,  double 
salts  are  obtained,  of  the  formula  M0,C20^  +  AeO,C20g.  When  the  alcoholic 
solution  of  the  double  oxalate  of  ethyle  and  potash  is  treated  by  fluosilicic  acid, 
there  is  obtained  the  acid  oxalate  of  ethyle,  UO,C^O^  -f-  AeOjC^O^,  which  is  often 
called  oxalomnic  acid.  The  salt  of  potash,  K0,C20^  -f-  (AeOjC^O^)  (oxalovinafe 
(f  potash)  forms  crystalline  scales;  soluble  in  alcohol.  The  oxalovinate  of  baryta 
is  extremely  soluble,  and  may  be  used  to  furnish  the  other  oxalovinates,  by  act- 
ing with  it  on  the  soluble  sulphates  of  different  bases. 

15.  Oxamate  of  oxide  of  ethyle,  CgNH^O  =  AeO,C^NH20^  =  keO,Qp^  -\- 
Ad,C^02,  is  formed,  as  above  stated,  when  ammonia  is  cautiously  added  to  an 
alcoholic  solution  of  oxalic  ether,  until  a  white  powder  (oxamide)  begins 
to  appear.  The  liquid  now  yields  fine  pearly  tabular  crystals,  formerly  called 
oxamethane.  It  now  appears  to  be  oxamate  of  ethyle,  but  may  also  be  viewed 
as  oxalate  of  ethyle,  plus  oxamj^e.  By  an  excess  of  ammonia,  it  is  converted 
into  alcohol  and  oxamide.  The  action  of  ammonia  on  oxalic  ether  has  been 
explained  above. 

16.  Sulphocarhonate  of  ethyle  and  water.  AeO,HO,2CS2. — When  bisulphuret 
of  carbon  is  added  to  a  strong  alcoholic  solution  of  potash  a  salt  is  obtained,  in 
colourless  or  yellow  needles,  which  is  a  double  sulphocarhonate  of  ethyle  and 
potash,  K0,CS2  +  AeO,CS  .  When  this  salt  is  acted  on  by  diluted  sulphuric 
or  hydrochloric  acid,  there  is  obtained  a  heavy  oily  liquid.  This  is  the  acid 
compound  in  question,  HO,CS  -\-  AeO,CS2,  formerly  called  xanthic  acid,  from 
the  yellow  colour  of  its  salts.  With  bases  it  gives  rise  to  double  salts,  like  that 
of  potash  just  mentioned;  which  were  called  xanthates.  The  salt  of  protoxide 
(suboxide)  of  copper  is  lemon  yellow. 

17.  Bicyanurate  of  oxide  of  ethyU,  (Cy303,3AeO  +  Cy303,3HO)  +  3  aq. :  is 
formed  when  the  vapours  of  hydrated  cyanic  acid  are  brought  in  contact  with  a 
mixture  of  ether  and  alcohol.  It  appears  in  the  form  of  prismatic  brilliant  crys- 
tals, easily  purified  from  cyamelide  by  boiling  alcohol  or  even  water,  which  dis- 
solve it  and  deposit  it  on  cooling. 

18.  Benzoate  of  oxide  of  ethyle^  or  benzoic  ether,  AeO,BzO,  is  best  formed  by 
distilling  4  parts  of  alcohol,  2  of  benzoic  acid,  and  1  of  strong  hydrochloric  acid. 
The  ether  distils  over  with  alcohol,  from  which  water  separates  it.  When  pure, 
it  is  an  oily,  colourless  liquid,  of  a  faint  agreeable  aromatic  odour,  and  an  acrid, 
spicy  taste.  Its  sp.  gr.  is  1*054,  and  it  boils  at  about  410°.  Chlorine  decom- 
poses it,  giving  rise  to  several  products,  probably  by  substitution. 

19.  Hippurate  of  oxide  of  ethyle,  or  hippuric  ether,  C^H^,0  -f-  C^gNH^O^,  is 
formed  by  passing  a  current  of  hydrochloric  acid  gas  through  a  solution  of  hip- 
puric acid  in  alcohol,  and  heating  the  mixture  for  some  time  near  to  its  boiling 
point.  The  addition  of  water  separates  a  thick,  heavy  oil,  which  when  purified 
from  alcohol  and  hydrochloric  acid,  and  placed  in  vacuo,  along  with  sulphuric 
acid,  forms  a  solid  crystalline  mass,  composed  of  silky  needles.  It  is  decom- 
posed, like  other  ethers,  by  alkalies,  arid  by  boiling  with  water. 

20.  Salicylate  of  oxide  of  ethyle,  C^H^,0  -j-  C^^H^O^,  is  obtained  by  distilling 


616  COMPOUNDS  OF  ETHYLE. 

2  parts  of  alcohol,  IJ  of  salicylic  acid,  and  I  of  sulphuric  acid.  When  purified 
from  alcohol,  acid,  and  water,  it  is  a  colourless  oily  fluid,  having  a  sweet  smell 
like  that  of  the  corresponding  compound  of  methyle,  which  occurs  naturally  in 
the  oil  of  Gaultheria  procumbens.  It  is  heavier  than  water,  and  boils  at  437°, 
Like  the  oil  of  Gaultheria,  it  plays  the  part  of  an  acid,  forming  w^ith  bases 
crystallized  soluble  salts.  "When  exposed  to  a  high  temperature  with  caustic 
baryta,  it  yields  carbonic  acid,  and  an  oil  analogous  to  that  obtained  from  the 
methyle  compound,  probably  C^gH^O^.  When  fuming  nitric  acid  is  added  drop 
by  drop  to  the  salicylic  ether,  it  dissolves  it  with  a  deep  red  colour:  water  now 
separates  an  oil,  which  soon  concretes  into  a  solid  mass,  which  when  dissolved 
in  hot  alcohol,  yields  on  cooling,  yellow  silky  needles.  These  are  indigntate  or 
anilate  of  oxide  of  eihyle^  C^H^,0  -f-  C^^NH^O^.  By  the  further  action  of  nitric 
acid,  carbazotic  or  nitropicric  acid  is  obtained.  The  indigotic  ether  dissolves  in 
potash  and  soda,  apparently  like  the  salicylic  ether,  playing  the  part  of  an  acid. 
Indigotic  ether  does  not  dissolve  in  ammonia  :  left  in  contact  within  close  ves- 
sels, it  finally  disappears :  alcohol  is  reproduced,  and  there  is  formed  a  new 
product,  anilarnide,  ^i.N  H^O^j,  which,  when  pure,  forms  brilliant  yellow  crys- 
tals. W^hen  boiled  with  potash,  anilamide  yields  anilate  (indigotate)  of  potash, 
and  gives  off  ammonia ;  for,  Cj^^N^HgOg  +  2H0  =  NH3  f  Cj^H^NOg,HO. 
Bromine  acts  on  salicylic  ether,  producing  two  compounds:  monobromuretted 

C  H  * 

salicylic  ether,  Cj^HgErOg  =  C^  j  ^^o  +  C^^H^O^:  and  bibromuretted  sali- 
cylic ether,  C^^U^Bip^  "^  ^4  1  Br  ^  "*"  ^14^5^5*  '^^®  ^°"°®^  crystallizes  in 
fine  needles:  the  latter  in  large  pearly  scales,  which,  when  melted,  form  on  cool- 
ing a  most  beautiful  crystallization,  formed  of  large  and  perfect  cubes,  like  those 
of  bismuth. 


COMPOUNDS  OF  ETHYLE  OF  UNCERTAIN  CONSTITUTION. 

1.  Chloro-carbonic  ether,  CgH^ClO^  =  C^H^,0  +  C^  5  p|  ?  Formed  when  ab- 
solute alcohol  is  placed  in  contact  with  chloro-carbonic  acid  gas.  It  appears  as 
an  oily  liquid,  of  sp.  gr.  1'133,  boiling  at  200°.  It  is  formed  as  follows :  2  eq. 
of  chloro-carbonic  acid  and  1  of  alcohol,  losing  1  eq.  hydrochloric  acid,  yield  I 
eq.  of  the  new  ether.     C^O^Cl^  f  C^H^O^  =  HCl  +  CgH^ClO^.     It  may  be 

viewed  as  a  compound  of  oxide  of  ethyle,  with  a  peculiar  acid  C    ^   ^?;    or   as 

carbonic  ether  C^H^O^,  ^/ms  1  eq.  chloro-carbonic  acid,  C  j  /-,,• 

.2.  Urethane,  CgH^NO^,  is  formed  by  the  action  of  ammonia  on  the  preceding 
compound,  along  with  sal  ammoniac,  from  which  it  is  separated  by  being  sub- 
limed, or  rather  distilled,  when  it  passes  over  at  a  gentle  heat,  as  a  liquid  which 
crystallizes  omcooling.  It  is  very  soluble  in  water  and  alcohol,  and  yields  very 
large  crystals.     It  may  be  viewed  as  chlorocarbonic  ether,  in  which  amide,  NH 

has  been  substituted  for  the  chlorine  :  C  H  .0  -+-  C„  ^   -  3  _  .      It   is   formed 

4    5'  2  ^  NHj 

as  follows :  €gH^C10^  +  2NH3  =  (NH3,HC1)  t  C^H^NO^.  It  may  also  be 
viewed  as  formed  of  2  eq.  carbonic  ether  and  I  eq.  urea  :  for  2(C  H^O^)  -f  (C^ 
N^H^O^)  =  2CCgHyN0^).     Finally,  it  has  the  composition  of  dry  lactate  of 


TRANSFORMATIONS  OF  ETHYLE.  617 

ammonia,  NH^  +  CgH^O^,  or  rather  a  compound  of  ammonia  with  sublimed 
lactic  acid.  * 

METAMORPHOSES  OF  THE  COMPOUNDS  OF  ETHYLE. 

When  ether  or  alcohol  is  passed  in  vapour  through  a  red  hot  tube,  it  yields 
aldehyde,  water,  defiant  gas,  and  marsh  gas,  3(C^H^0)  =  C^H^O^+HO + 
^^2^2  H-  C^H^  :  or  2(C^H^0)  =  C^H^O^  +  C^H^  +  C^H^.  By  the'  action  of 
chloride  of  zinc  on  alcohol,  there  are  formed  water,  and  two  liquid  carbo-hydro- 
gens,  CgH^and  C^^H^,  together  C^gH^g,  that  is,  defiant  gas,  or  an  isomeric  modi- 
fication of  it.  Now  ether  and  alcohol  both  contain  the  elements  of  water  and  of 
defiant  gas;  for  alcohol  is  C  HO   =2H0  +  C  H   :  and  ether  is  C  H0  = 

402  44  45 

HO  +  C  H^. 

4      4 

In  the  manufacture  of  ether  there  occur  two  liquids,  one  of  which  is  called 
oil  of  wine,  which  is  C^gH^^,  or  very  nearly  the  proportions  of  defiant  gas, 
according  to  the  only  analysis  we  have.  The  other  is  called  the  sweet  or  heavy 
oil  of  wine,  and  is  a  compound  of  sulphuric  acid  with  ether,  and  a  body  having 
the  same  composition  in  100  parts  as  defiant  gas.  Sweet  oil  of  wine  is  SSO^ 
-f-  AeO  -f-  C^H^ ;  and  as  this  body,  C^H^,  is  called  etherole,  the  compound  is 
named  the  double  sulphate  of  oxide  of  ethyle  and  of  etherole.  This  latter  is 
produced,  along  with  sulphovinic  acid,  from  the  reaction  of  4  eq.  dry  sulphuric 
acid  and  3  eq.  ether,  4SO3  +  3AeO  =  (2SO3, AeO,HO)  -\-  (2S03,AeO,C^H J. 
The  same  compound  is  formed  when  sulphovinate  of  lime  is  heated,  but  is 
accompanied  by  alcohol,  sulphurous  acid,  defiant  gas,  and  a  residue  of  sulphate 
of  lime  and  charcoal,  2(CaO,AeO,2S03)  =  (2S03,AeO,C^HJ  + HO  +  2(CaO, 
SO3) ;  and  again,  2(CaO,AeO,2SO  )  =  2(CaO,S03)  f  280^  t  GUfi^-^  C^H^ 
H-C^  +  2H0. 

The  sweet  oil  of  wine  is  an  oily  liquid,  quite  neutral.  It  boils  at  536°,  and 
has  the  sp.  gr.  1-133.  When  heated  with  water  it  gives  off  etherole  as  an  inso- 
luble oil,  while  the  liquid  contains  pure  sulphovinic  acid.  When  the  etherole 
thus  separated  is  exposed  to  cold,  it  deposits  crystals  of  etherine,  a  compound 
isomeric  with  etherole  and  with  olefiant  gas. 

I  ETHIONIC,  ISETHIONIC,  METHIONIC  AND  ALTHIONIC  ACIDS. 


m 


These  acids  are  formed  by  the  action  of  sulphuric  acid  on  ether  and  alcohol 
under  various  circumstances.     When  anhydrous  acid,  SO3  acts  on  alcohol,  or 

hen  olefiant  gas  is  absorbed  by  that  dry  acid,  there  is  formed  a  compound,  28^3 
-t-  C^H^,  in  crystals,  which,  when  put  into  cold  water,  produce  ethionic  acid, 
2803,0  jH^O.  When  this  solution  is  heated,  2  eq.  of  sulphuric  acid  and  1  of 
alcohol  separate  from  one  half,  and  there  is  formed  from  the  other  half  isethionie 
acid,  2S03,C^H^O,  or  rather  §20^,0^11^02.  Ethionate  of  baryta,  formed  by 
adding  baryta  to  the  acid  before  boiling,  is  2S03,C^H^O,BaO.  From  it  all  the , 
other  ethionates  may  be  made.  The  salts  of  isethionie  acid,  like  those  of  ethi- 
onic acid,  have  the  same  composition  in  100  parts  as  the  sulphovinates ;  but  as 
they  contain  hyposulphuric  acid,  their  formula  is  S^0^,C^H^02  -f-  MO.  They 
crystallize  with  remarkable  facility.  Wheji,  in  acting  on  ether  with  anhydrous 
sulphuric  acid,  the  mixture  gets  too  hot,  there  is  formed  a  new  acid,  methionic 
acid,  the  baryta  salt  of  which  is  S^C^HgO^/BaO,  or  8^0^,0211302  +  BaO.  This 
acid  apparently  bears  the  same  relation  to  oxide  of  methyle,  C2H30,as  isethionie 
does  to  ether,  C^H^O.  When  oil  of  vitriol  in  great  excess,  is  heated  with  alcohol, 


618  ACETYLE.    ALDEHYDE. 

defiant  gas  is  given  off,  and  the  residue  is  found  to  contain  an  acid,  the  salts  of 
which  have  the  very  same  composition  as  the  sulphovinates,  hut  differ  in  crys- 
talline form.  This  acid  is  called  althionic  acid.  It  is  highly  probable  that  the 
althionates  are  mixtures  or  compounds  of  sulphovinates  with  isethionates,  just  as 
the  salts  of  ethionic  acid  appear  to  contain  sulphovinates  and  isethionates  or 
compounds  isomeric  with  these.  The  two  compounds  which  seem  to  be  distinct 
and  independent  are  sulphovinic  acid,  (AeO,HO,2SO^)  and  isethionic  acid,  iso- 
meric with  it,  but  probably  arranged  as  (HOjAeO^iS^O^)  ;  the  salts  of  the  for- 
mer being  strictly  double  sulphates  of  ethyleand  bases,  (M0,S02+  AeO,S02) ; 
and  those  of  the  latter  being  MO  -\-  [keO^^^^^'  Whatever  explanation  may 
be  given  of  the  fact,  it  is  a  fact,  that  the  ethionic  and  althionic  acids  and  their 
salts  have  the  same  empirical  composition  as  these  two  acids  and  their  salts,  at 
least  according  to  the  best  analyses  we  have. 

PRODUCTS  OF  THE  OXIDATION  OF  ETHYLE  AND  ITS  DERIVATIVES. 

The  oxidation  of  alcohol  and  of  ether  may  be  effected  in  a  great  variety  of 
ways,  and  the  products  are  rather  numerous,  varying  according  to  the  amount  of 
oxygen  taken  up.  Thus  we  have,  first  aldehyde,  then  acetic  acid,  formic  acid, 
oxalic  acid,  and  finally  carbonic  acid  and  water.  The  first  effect  of  oxidation  is 
to  destroy  the  radical  ethyle,  giving  rise  to  a  new  and  less  complex  radical, 
acefyle  =  C^H^.  Afterwards  we  obtain  compounds  of  the  still  less  complex 
radical,  formyle,  ==  C  H  ,  and  lastly,  compounds  of  the  simple  radicals  carbon 
and  hydrogen. 

We  shall  here  consider,  first,  the  radical  acetyls  and  its  compounds :  bearing 
in  mind  that  while  derived  from  the  basic  radical  ethyle,  acetyle  has  no  basic 
characters  whatever,  but  is,  on  the  contrary,  a  most  distinctly  acidifiable  radical. 

TABLE  OF  PRODUCTS. 

Acetyle C^HgSsAc 

Hydrated  Oxide  of  Acetyle  (Aldehyde)      .  (C4H3)0,  -|-  HO 

Acetal C4H3,0  +  C4H50-HHO 

Acetylous  Acid (C4H3)02,HO 

Acetic  Acid C^Ha.Og  -|-  HO 

XVII.  Acetyle.  •  C^^=^kc. 

A.cetyle  is  unknown  in  a  separate  form,  but  is  easily  obtained  in  the  form  of  a 
hydrated  protoxide,  or  aldehyde^  and  hydrated  peroxide,  or  acetic  acid. 

1.  Hydrated  Oxide  of  Acetyle,  or  Aldehyde.    (C^Hg)  0,  HO.  =  AcO,  HO. 

Aldehyde  is  formed  when  ether  or  alcohol  is  passed  through  a  red-hot  tube, 
or  when  ether  or  alcohol  are  oxidized  by  nitric  acid,  or  by  chlorine,  &c.  In 
these  cases  it  is  not  pure;  but  it  may  be  obtained  quite  pure  by  distilling  2  parts 
of  the  compound  of  aldehyde  and  ammonia  dissolved  in  2  parts  of  water,  along 
with  a  mixture  of  3  parts  of  oil  of  vitriol  and  4  of  water,  and  rectifying  at  a  tem- 
perature of  about  60°,  over  chloride  of  calcium. 

It  is  a  clear,  colourless  liquid,  of  a  peculiar  and  powerful  etherial  odour,  of  sp. 
gr.  0*79  at  65°,  and  boiling  at  70°.  It  mixes  in  all  proportions  with  water, 
alcohol,  and  ether,  and  is  neutral  and  inflammable.  In  contact  with  the  atmos- 
phere it  rapidly  absorbs  oxygen,  passing  into  hydrated  acetic  acid  :  for  C^H^^O 


ACETAL.  619 

+   HO,  with  0  .  at  once  produce  C  H.O,  +  HO  ;  or  AcO,HO  +  O^  =  AcO,, 
HO. 

When  heated  with  caustic  potash  it  is  rapidly  converted  into  the  brown  matter  . 
called  resin  of  aldehyde.  If  gently  heated  with  oxide  of  silver  and  water,  part 
of  the  oxide  is  reduced  without  effervescence,  coating  the  glass  tube  with  a 
bright  surface  of  silver,  while  the  water  is  found  to  contain  a  salt  of  silver,  the 
acid  of  which  contains  less  oxygen  than  acetic  acid  :  this  is  aldehydic  qr  lampic 
acid,  CJifi^,UO,  or  Ac02,H0.  The  solution  of  aldehydate  of  silver,  if  filtered 
and  heated  to  boiling,  again  deposits  metallic  silver,  while  the  aldehydic  acid  be- 
comes acetic. 

When  long  kept,  even  in  sealed  tubes,  aldehyde  is  transformed  into  two  iso- 
meric modifications,  namely,  metaldehyde,  a  hard  crystalline,  inodorous  solid ; 
and  elaldehyde,  which  is  liquid. 

Aldehijdite  of  ammonia.  C^H^,0  +  NH^  -f-  HO.  Aldehyde  has  no  basic  cha- 
racters, and  rather  exhibits  a  tendency  to  the  acid  character,  in  combining  with 
ammonia,  as  it  does  directly,  to  form  a  crystallized  compound.  To  prepare  it, 
as  the  substance  from  which  aldehyde  is  obtained,  6  parts  of  oil  of  vitriol,  4  of 
water,  4  of  alcohol,  and  6  of  peroxide  of  manganese,  in  fine  powder,  are  distilled 
together.  The  crude  product  is  twice  rectified  over  chloride  of  calcium ;  it  is 
now  aldehyde,  containing  a  little  water,  alcohol,  and  acetic  and  formic  ethers ; 
and  this  liquid,  when  mixed  with  ether,  and  saturated  with  ammoniacal  gas, 
yields  crystals  of  the  new  compound,  which  are  washed  with  ether.  These 
crystals  become  brown  on  being  kept,  even  in  close  vessels,  and  acquire  the 
smell  of  burnt  feathers.  They  dissolve  in  water  and  alcohol,  but  hardly  in  ether. 
Nitrate  of  silver  forms,  in  the  concentrated  solution,  a  precipitate,  insoluble  in 
alcohol,  which,  when  heated,  is  reduced. 

2.  Acetal.    CgHgOj  =  C4H3,0  +  C^  H.jO  +  HO  =  AcO  +  AeO  +  HO. 

It  is  formed  by  the  action  of  the  oxygen  of  the  air  on  the  vapours  of  alcohol, 
under  the  influence  of  the  black  powder  of  platinum.  It  is  a  colourless  very 
mobile  liquid,  sp.  gr.  0-825,  boiling  at  203°.  It  might,  according  to  its  compo-' 
sition,  be  a  compound  of  3  eq.  oxide  of  ethyle,  and  1  eq.  acetic  acid ;  for  3 
(C^H^,0)f  C^H^O^  =  CjgHjgOg=  2(CgHg03).  But  the  action  of  potash,  which 
forms  resin  of  aldehyde,  and  of  oil  of  vitriol,  which  blackens  and  thickens  it  as 
it  does  aldehyde,  indicate  pretty  certainly  the  presence  of  aldehyde ;  and  we 
therefore  prefer  the  formula  above  given,  which  makes  acetal  a  compound  of 
aldehyde  and  oxide  of  ethyle. 

The  resin  of  aldehyde,  formed  by  the  action  of  potash  on  aldehyde  is  little 
known.  Elaldehyde,  an  isomeric  form  of  aldehyde,  which  is  liquid  at  ordinary 
temperatures,  but  solid  at  32°,  has  a  formula  exactly  triple  that  of  aldehyde, 
^12^12^6*  Metaldehyde^  the  other  isomeric  modification,  which,  like  the  pre- 
ceding, spontaneously  forms  in  aldehyde,  when  kept,  has  no  doubt  a  similar  rela- 
tion in  its  formula  to  that  of  aldehyde ;  but  its  precise  formula  is  not  yet  known. 
The  density  of  its  vapour  would  settle  the  point.  It  forms  very  hard  prisms, 
which  sublime  at  248°  without  melting.  It  is  worthy  of  notice  that  aldehyde, 
like  the  corresponding  chlorine  compound,  formed  by  substitution,  cA/ora/,  C^Cl  O 
-f  HO,  undergoes  very  easily,  and  even  spontaneously,  these  very  singular  me- 
tamorphoses. This  indicates  a  relation  in  the  constitution  of  these  bodies,  which 
cannot  be  overlooked. 


h%Q  ACETIC  ACID. 

3.  Acetylous  Acid.    (CjH3)02,HO  =  AcOajHO. 

Syn.  Aldehydic  acid.  Lampic  acid.  It  has  already  been  stated  that  this  acid 
is  obtained  in  combination  with  oxide  of  silver,  when  aldehyde  is  gently  heated 
with  excess  of  that  oxide  in  water.  The  solution,  when  the  silver  has  been 
separated  by  sulphuretted  hydrogen,  contains  the  acetylous  acid  very  diluted. 
It  is  very  easily  decomposed,  especially  by  heat,  into  acetic  acid  and  a  brown 
resin,  like  that  of  aldehyde.  When  the  acetylite  or  aldehydate  of  silver  is  decom- 
posed by  baryta,  so  as  to  precipitate  all  the  oxide  of  silver,  and  the  acetylite  of 
baryta  is  now  heated  with  the  precipitated  oxide  of  silver,  the  metal  is  reduced, 
and  acetate  of  baryta  is  now  found  in  the  solution.  This  demonstrates  the  rela- 
tion of  acetylous  to  acetic  acid  ;  for  BaO,Ac02  -\-  AgO  =  BaO,Ac03  +  ^^'  '^^^^^ 
acid  is  one  chief  ingredient  of  the  acid  produced  by  the  slow  combustion  of  ether 
in  the  lamp  with  a  spiral  of  platinum  wire  on  the  wick,  the  platinum  continuing 
red-hot,  but  no  flame  appearing,  and  which  acid  is  called  lampic  acid. 

Aldehyde  is  a  constant  ingredient  of  the  nitrous  ether  of  the  pharmacopoeias. 

4.  Acetic  Acid.    C^HgjOa  -f-  HO  =  AcOgjHO. 

Syn.  Acetylic  acid. — Pyroligneous  acid. — Vinegar. — This  important  acid  is 
formed  in  two  principal  ways  :  first,  by  the  oxidation  of  alcohol :  and,  secondly, 
by  the  destructive  distillation  of  wood.  Wine,  beer,  and  other  fermented  liquors, 
if  exposed  to  the  air,  under  certain  circumstances,  undergo  what  is  erroneously 
termed  the  acetous  fermentation  ;  that  is,  they  attract  oxygen  from  the  air,  under- 
go eremacausis  of  the  alcohol  they  contain,  and,  after  a  time,  contain  no  alcohol, 
but  in  its  place  acetic  acid  ;  they  are,  in  fact,  converted  into  vinegar.  The  ulti- 
mate change  is  very  simple  :  CJifi^-\-0=i  C^H30^,3HO,  =  Ac03,H0  -+-  2  aq. 
But  we  have  already  seen  that  there  are  intermediate  steps  in  the  process.  The 
first  effect  of  the  oxygen  is  to  remove  from  the  alcohol,  or  rather  from  the  ethyle 
in  it,  2  eq.  of  hydrogen,  thus  leaving  the  radical  acetyle,  C  H^,  in  the  place 
of  the  ethyle  (C^H^)0,HO  +  02=(C^H3)0,H04-2  aq.  In  this  stage,  alcohol 
is  simply  converted  into  aldehyde,  while  2  eq.  of  water  are  formed.  In  the 
next  stage,  the  hydrated  protoxide  of  acetyle  (the  aldehyde),  or  rather  the  radi- 
cal C^H^,  takes  up  two  additional  equivalents  of  water,  and  thereby  becomes 
acetic  or  acetylic  acid  (C^H3,)0,HOt02=(C^H3)03,HO. 

Such  being  the  action  of  the  oxygen  of  the  air  on  alcohol,  it  is  obvious  that 
the  process  of  acetification  is  no  fermentation,  but  a  case  of  eremacausis  or  slow 
combustion.  But,  as  was  formerly  explained,  the  state  of  eremacausis  is  induced 
by  contact  of  a  body  in  that  state  or  even  in  the  state  of  fermentation  or  putre- 
faction, and  the  presence  of  a  ferment  is  required  to  commence  the  process  of 
eremacausis  of  alcohol.  Pure  alcohol,  exposed  to  air  alone,  is  not  acetified  :  but 
if  its  vapour,  mixed  with  air,  come  in  contact  with  platinum  powder,  eremacausis 
is  induced.  Hence,  if  alcohol  be  placed  in  a  flat  basin  under  a  bell  jar,  beside 
a- small  flat  dish  containing  platinum  black,  the  bell  jar  is,  in  a  few  seconds, 
filled  with  the  pungent  smell  of  aldehyde ;  and  in  an  hour  or  two,  the  acetifica- 
tion is  nearly  complete.  Here  the  platinum,  by  virtue  of  its  singular  power  of 
causing  gases  or  vapours  to  unite  on  its  surface,  acts  as  a  ferment,  or,  as  it  may 
be  called,  an  excitant,  inducing  the  slow  combustion,  and  acting  as  a  carrier  of 
oxygen  from  the  air  to  the  alcohol. 

In  wine  or  beer,  there  is  present  an  actual  ferment  in  the  shape  of  gluten  or 
fibrin,  at  least  in  all  cases  where  the  vinous  fermentation  has  not  decomposed 


HYDRATED  ACETIC  ACID.  621 

the  whole  of  the  ferment.  In  these  cases,  exposure  to  the  air  for  a  short  time 
causes  the  decomposition  of  the  gluten,  &c.  to  recommence ;  and  this  state  of 
decomposition,  heing  mechanically  communicated  in  the  shape  of  motion  to  the 
particles  of  alcohol,  slow  combustion  commences,  and  continues  till  every  trace 
of  alcohol  has  been  acetified,  when  the  process  is  arrested  for  want  of  fuel,  that 
is,  of  alcohol.  Where,  in  the  fermentation  of  wine  (as  sherry),  or  of  beer  (as 
Bavarian  beer),  all  ferment  has  been  destroyed  or  removed,  these  liquors  do  not 
become  sour  when  exposed  to  air :  and  if  we  wish  to  acetify  them,  we  mnst  add 
yeast  or  some  other  ferment.  So,  also,  when  we  wisli  to  make  strong  vinegar 
by  the  acetification  of  brandy  or  of  whiskey,  we  have  to  add  a  ferment,  such  as 
yeast,  and  expose  the  mixture  to  a  certain  temperature  in  open  vats.  By  carefully 
attending  to  all  these  principles,  the  process  of  acetification  may  be  very  much 
abridged.  The  following  is  the  rapid  process  now  followed  on  the  Continent. 
There  is  made  a  mixture  of  1  part  of  alcohol  at  80  p.  c,  4  to  6  parts  of  water, 
and  yo^oo  °^^  ferment  such  as  vinegar,  honey,  or  must  of  beer.  A  large,  high 
barrel  is  packed  with  twigs  or  shavings  of  beech,  previously  soaked  in  strong 
vinegar ;  and  holes  are  drilled  in  the  middle  and  upper  part  of  the  barrel  to  admit 
a  free  circulation  of  air.  The  mixture  is  now  warmed  to  from  75°  to  80°,  and 
made  to  trickle  slowly  upon  the  shavings  and  through  the  barrel,  thus  exposing 
an  immense  surface  to  the  air.  The  temperature  rises  rapidly  to  95°  or  105°,  and 
if  a  proper  supply  of  air  be  given,  continues  at  that  point  during  the  operation. 
When  the  mixture  has  been  three  or  four  times  passed  through  the  barrel,  it  is 
found  perfectly  acetified :  this  may  take  place  in  from  24  to  36  hours.  Should 
the  supply  of  fresh  air,  that  is,  of  oxygen,  be  deficient,  much  aldehyde  is  pro- 
t  duced,  which,  from  its  volatility,  is  carried  off  as  vapour  and  lost.  This  was 
K  long  a  source  of  great  loss  to  the  makers,  and  the  cause  could  not  be  traced,  until 
B^  Liebig,  by  the  discovery  of  aldehyde,  explained  it,  and  showed  how  to  avoid  the 
B^  loss,  by  giving  a  due  supply  of  air.  The  manufacturer  now  obtains,  as  nearly 
K  *  as  can  be  expected,  the  theoretical  quantity  of  vinegar  from  his  spirits.  Any 
^  aromatic  substance,  or  essential  oil,  or  even  a  trace  of  wood  vinegar  (contami- 
nated with  kreosote,  &c.)  will  arrest  the  progress  of  acetification. 

The  peculiar  pleasant  smell  of  good  vinegar,  in  addition  to  that  of  pure  dilutedr. 
acetic  acid,  is  owing  to  the  presence  of  acetic  ether.  Distilled  vinegar  is  a  tol- 
erably pure  but  weak  acetic  acid ;  but  to  obtain  acetic  acid  pure  and  strong,  we 
must  have  recourse  to  the  salts  of  acetic  acid,  which,  when  distilled  with  mode- 
rately strong  sulphuric  acid,  yield  pure  acetic  acid,  mixed  with  more  or  less  " 
water. 

The  pyroligneous  acid  is  contaminated  with  pyroxylic  spirit  and  with  oil  of  tar. 
When  combined  with  soda,  lime,  or  oxide  of  lead,  these  salts  may  be  easily 
purified  by  crystallization,  and  by  heating  them  so  far  as  to  expel  or  destroy  the 
oily  impurities.  The  pure  salts,  distilled  with  sulphuric  acid,  yield  acetic  acid, 
identical  with  that  from  true  vinegar. 

Hydrated  acetic  acid^  radical  vinegar,  or  crystallizahle  acetic  acid,  AcO  ,H0,  is 
obtained  by  distilling  3  parts  of  dry  powdered  acetate  of  soda  with  9*7  of  oil  of 
vitriol,  as  pure  and  concentrated  as  possible:  |  of  the  acid  distils  over  by  the 
heat  spontaneously  developed  in  the  mixture;  a  gentle  heat  expels  the  rest.  The 
product  is  rectified  and  exposed  to  a  cold  of  23°  or  24°,  when  crystals  of  the 
hydrate  are  formed  in  a  weaker  liquid.  The  crystals  are  allowed  to  drain,  and 
then  melted,  and  again  exposed  to  cold.  The  crystals  of  this  second  operation 
are  generally  free  from  all  superfluous  water.    At  temperatures  below  60°j  Jiy- 


622  SALTS  OF  ACETIC  ACID. 

drated  acetic  acid  is  solid,  at  62°  or  63°  it  melts,  forming  a  liquid  which  some- 
times continues  liquid  at  a  much  lower  temperature,  and  then  crystallizes  from 
some  very  trifling  cause.  The  sp.  gr.  of  the  liquid  is  1*063;  it  boils  at  248°; 
has  a  pungent,  peculiar,  but  agreeable  smell,  and  a  burning  acid  taste.  It  raises 
a  blister  on  the  skin,  and  soon  produces  a  painful  sore,  like  a  mineral  acid.  It 
is  miscible  in  all  proportions  with  water,  alcohol,  and  ether.  It  dissolves  cam- 
phor and  essential  oils,  and  the  aromatic  vinegar  is  a  solution  of  camphor  with  a 
little  oil  of  lemons  and  bergamot,  &c.  Strong  acetic  acid,  in  this  form,  is  used 
as  a  diffusible  stimulant,  applied  to  the  nostril  in  faintness  or  sickness.  It  may 
be  used,  also,  externally  as  a  very  powerful  rubefacient  and  epispastic.  The 
hydrated  acid  is  combustible.  It  is  decomposed  by  anhydrous  sulphuric  acid, 
yielding  a  new  acid,  sulphacetic  acid:  also  by  chlorine,  yielding  by  substitution 
chloracetic  acid.  The  vapour  of  acetic  acid,  passed  through  a  red-hot  tube,  yields 
carbonic  acid  and  acetone,  C^H^O  :  the  same  transformation  occurs  when  acetic 
acid  is  heated  with  bases. 

The  salts  of  acetic  acid  are,  almost  without  exception,  soluble  in  water  :  the 
acetates  of  silver  and  protoxide  of  mercury  are  sparingly  soluble.  The  formula 
for  the  neutral  acetate  is  yiO^G^jd^  or  M,C^H20^.  There  are  hardly  any 
acid  salts ;  but  a  considerable  number  of  basic  salts,  as  basic  acetates  of  lead 
and  copper. 

Acetate  of  oxide  of  ethyh  or  acetic  ether ^  AeO,  AcO^,  is  easily  prepared  by  dis- 
tilling 10  parts  of  acetate  of  soda,  16  of  oil  of  vitriol,  and  6  of  alcohol.  The 
product  is  rectified  over  lime  and  chloride  of  calcium.  It  may  also  be  obtained 
by  distilling  any  sulphovinate  with  strong  acetic  acid.  In  either  case,  acetic 
acid  is  brought  in  contact  with  nascent  ether,  and  combines  with  it.  Acetic  ether 
is  a  colourless  liquid  of  a  refreshing  odour,  very  combustible.  It  boils  at  165°; 
its  sp.  gr.  is  0-89.  It  is  easily  decomposed  by  alkalies,  yielding  an  acetate  and 
alcohol.  Acids  also  decompose  it.  It  is  always  present,  in  small  quantity,  in 
"wine  vinegar,  which  owes  its  flavour  to  this  compound. 

Acetate  of  ammonia.  There  is  a  well-known  febrifuge  and  diaphoretic  remedy 
called  the  spirit  of  Mindererus^  which  is  a  diluted  solution  of  acetate  of  ammonia, 
formed  by  neutralizing  distilled  wine  vinegar  with  carbonate  of  ammonia.  A 
more  uniform  preparation,  although  stronger  than  that  usually  employed  here,  is 
made  by  neutralizing  6  parts  of  aqua  ammoniac,  sp.  gr.  0*96,  with  strong  acetic 
acid,  and  adding  enough  water  to  make  up  24  parts.  This,  being  uniform,  can 
easily  be  reduced  if  desirable.  There  is  an  acid  acetate  of  ammonia,  which 
forms  deliquescent  needles.  Acetate  of  potash,  KO,AcO  ,  is  obtained  as  a  fibrous 
crystalline  mass,  very  deliquescent,  which  has  a  warm  saline  taste.  It  is  much 
used  as  a  diuretic.  When  heated  with  arsenious  acid,  it  yields  oxide  of  caco- 
dyle ;  a  substance  of  most  remarkable  composition  and  characters,  C^HgAs2,0. 
Acetate  of  soda  NaO,AcO  -j-6  aq.  is  formed  from  pyroligneous  acid,  and  is  the 
form  in  which  the  acid  is  brought  in  order  to  be  purified  from  oil  of  tar.  The 
Bait  is  melted  at  a  moderate  heat,  and  roasted,  then  redissolved,  filtered  through 
charcoal,  evaporated,  again  melted,  and  so  on,  until  it  becomes  snow-white.  10 
parts  of  the  crystals  of  the  salt  after  the  first  fusion,  while  still  slightly  coloured, 
being  distilled  with  6  of  oil  of  vitriol,  yield  what  is  called  wood  vinegar,  suffi- 
ciently pure  for  use,  but  requiring  7  waters  to  reduce  it  to  the  average  strength 
of  wine  vinegar.  Acetates  of  baryta,  strontia  and  lime  all  crystallize  readily. 
The  first  is  used  as  a  test ;  the  last  in  the  manufacture  of  acetic  acid  and  all  other 
acetates  from  pyroligneous  acid.     Acetate  of  alumina,  Al^O^,  3AcO^,  prepared  by 


SALTS  OF  ACETIC  ACID.  623 

mixing  solutions  of  alum  and  acetate  of  lead  (or  of  baryta)  is  reiy  soluble.  It 
is  much  used  in  the  above  form,  containing  sulphate  of  potash,  as  a  most  valua- 
ble mordant  in  dyeing  and  calico  printing.  When  heated  it  deposits  an  insoluble 
basic  salt,  which  adheres  tenaciously  to  the  cloth,  and  afterwards  combines 
firmly  with  the  colouring  matter.  The  pure  acetate  of  alumina,  formed  from 
sulphate  of  alumina  and  acetate  of  baryta,  is  not  so  decomposed  by  heat,  but  re- 
quires the  presence  of  a  neutral  salt.  Acetate  of  manganese^  MnOjAcO^,  formed 
by  acting  on  sulphate  of  manganese  by  acetate  of  lime,  is  much  used  in  calico 
printing,  as  it  gives  with  bleaching  liquor  a  rich  bronze  brown.  Acetate  of  zinc, 
ZnO,AcO  ,H-3  aq.  is  used  in  medicine  and  pharmacy.  Acetate  of  protoxide  of 
iron,  FeO,AcO  ,  is  used  as  a  mordant.  Acetate  cf  peroxide  of  iron,  Fe^O^jSAcO^, 
is  formed  by  precipitating  acetate  of  lead  with  persulphate  of  iron.  It  has  the 
same  valuable  properties  as  acetate  of  alumina,  depositing  a  basic  salt,  when 
heated  with  neutral  salts,  and  is  much  prized  as  a  mordant.  Acetate  of  lead ,-  a. 
neutral,  Syn.  Sugar  of  lead ,-  is  best  prepared  by  dissolving  litharge  in  acetic 
acid,  and  crystallizing.  It  has  a  sweet  astringent  taste,  and  is  much  used  as  an 
astringent  and  styptic  in  diarrhcea,  dysentery,  and  various  haemorrhages.  It  is 
poisonous,  especially  where  it  forms  carbonate  :  it  ought  therefore  never  to  be 
given  without  abundance  of  vinegar  being  taken  by  the  patient.  The  crystals 
are  PbO,Ac0^4-3  aq.  b.  sesquibasic,  3PbO+2AcCg  soluble  pearly  scales,  c.  tri- 
basic  or  subacetate  of  lead  is  formed  in  crystals  by  mixing  1  vol.  of  aqua  ammoniae 
with  5  of  a  cold  saturated  solution  of  the  neutral  salt,  and  setting  it  aside.  It 
forms  long  needles.  The  solution,  or  Goulard's  extract,  is  made  by  digesting  7 
parts  of  litharge  with  6  of  sugar  of  lead  and  30  of  water,  till  the  oxide,  which 
is  not  dissolved,  has  become  white.  It  is  much  used  as  a  lotion,  and  to  precipi- 
tate gum,  organic  acids,  albumen,  caseine,  extractive  matter,  &c.  from  organic 
mixtures  and  solutions.  Its  formula  is  3PbO  +  AcO^.  d.  sexbasic,  formed  by 
adding  the  last  or  any  of  the  previous  acetates  of  lead  to  an  excess  of  ammonia. 
It  forms  a  crystalline  powder  very  sparingly  soluble,  which  is  6PbO-f  AcO^.  It 
usually  exists  in  white  lead,  along  with  carbonate  of  lead. 

Acetate  of  copper,  a.  neutral ,-  appears  in  two  forms :  as  dark  green  oblique 
rhombic  prisms,  becoming  opaque  in  air:  CuO,AcO^=5  aq  :  and  as  dark  blue 
transparent  crystals  of  great  beauty,  CuO,Ac02  -j-  5  aq.  These  latter,  heated 
to  86°,  lose  4  eq.  of  water,  and  fall  to  a  powder  of  the  green  salt.  b.  bibasic  or 
verdigris,  2CuO-l- AcO^fG  aq.=CuO,AcO^,  5  aq.-J-CuO,HO.  Verdigris  is  pre- 
pared by  a  tedious  process,  and  is  seldom  pure,  containing  usually  different 
basic  acetates,  c.  sesquibasic,  3CuO,2AcO  +  6  aq.  d.  tribasic,  6CuO,2AcOg  -[- 
3  aq.  The  two  last  occur  in  the  verdigris  of  commerce.  All  these  salts  are  poi- 
sonous. 

Schweinfurt  or  Vienna  green  is  a  double  salt,  formed  of  acetate  and  arsenite  of 
copper;  CuO,AcO^-|-3(As20g.CuO)  is  formed  when  10  parts  of  verdigris,  sus- 
pended in  water,  are  left  to  digest  for  24  hours,  after  mixing  them  with  a  hot 
solution  of  8  parts  of  arsenious  acid  in  100  of  water.  A  dirty  green  precipitate 
first  appears,  which  on  standing  changes  to  a  most  beautiful  green,  much  used 
as  a  paint. 

Acetate  of  protoxide  of  mercury  is  obtained  in  sparingly  soluble  silvery  scales  by 
adding  acetate  of  potash  to  protonitrate  of  mercury,  both  hot.  It  blackens  when 
exposed  to  light.     It  is  used  in  medicine,  especially  on  the  Continent. 

^Acetate  of  silver,  AgO,AcO  ,  very  much  resembles  the  preceding  salt.  It  is 
occasionally  used  as  a  test.    It  is  very  sparingly  soluble. 


624 


ACTION  OF  CHLORINE,  BROMINE,  ETC.,  ON  ETHYLE,  ACETYLE,  AND 
THEIR  DERIVATIVES. 

1.  Oxide  of  Ethyle  and  Chlorine. 

When  dry  chlorine  is  made  to  act  on  ether,  with  the  aid  of  the  sun's  rays, 
there  are  produced  several  compounds.     Tiie  first  is  a  heavy,  oily  liquid,  oxy- 

chloride  of  acetyle,  C^H^  <  p.  ;  which  is  dry  acetic  acid  with  2  eq.  of  oxygen 

^       2 
replaced  by  2  eq.  of  chlorine.     With  water,  it  forms  acetic  and  hydrochloric 

acids.  When  the  action  is  pursued,  there  is  obtained  a  compound  C  CI  O,  which 
is  ether,  in  which  all  the  hydrogen  is  replaced  by  chlorine.  The  first  compound 
may  be  connected  with  this  one  by  being  viewed  as  ether  in  which  hydrogen  is 

C  H 

partially  replaced  by  chlorine,  C^  j  c\^'     ^^^^^^J  there  is  obtained  a  crystal- 

lizable  solid  compound,  C^Cl^,  which  may  be  represented  as  C^Cl  ,C1,  showing 
that  the  oxygen  of  ether  is  also  here  replaced  by  chlorine.  This  last  body  is 
chloride  of  carbon,  C^Cl^,  for  0^01^=20^01^.  Besides  these  compounds  there 
are  others  formed  at  the  same  time,  more  difficult  to  separate,  and  which  are 
doubtless  the  intermediate  links  of  the  chain  of  substitutions,  beginning  with 
ether,  0^H^,0,  and  ending  with  chloride  of  carbon,  0^01^,01.  The  other  mem- 
bers of  the  series  which  are  more  easily  obtained  by  the  action  of  chlorine  on 
chloride  of  ethyle,  (see  below,  p.  625),  are  0^H^,01,  chloride  of  ethyle:   0 

5^4  01:   C    5^3    CI:  C    5^2    ci :   C    5  ^^   CI;   and  as   the  compound 

C^Cl^O  is  formed,  it  is  probable  that  there  is  another  series,  beginning  with 
ether,  and  ending  with  0^01^,0,  in  which  the  oxygen  remains  unchanged.  The 
above  are  not  all  cases  of  substitution  with  preservation  of  the  type ;  for  the 

C  H  CO 

compound   C^  j  p|  O,  may  very  likely  be  C^H^  j  p      belonging  to   the  type 

of  acetic  acid,  rather  than  that  of  ether.  These  compounds  are  as  yet  but  little 
known:  it  is  obvious  that  the  simultaneous  occurrence  of  so  many  similar  com- 
pounds must  render  the  study  of  them  exceedingly  complicated  and  difficult. 

The   body    C^H^  <  p.      or  oxychloride  of  acetyle,  when  acted  on  by  sulphu- 

retted  hydrogen,  yields  two  new  compounds,  in  which  its  chlorine  is  partially 
or  entirely  replaced  by  sulphur.     Both  are  crystalline:  one,  the  oxysulphuret  of 

acetyle,  C^H^  <  (^    forms  large  colourless  prisms :  the  other,  oxychlorosulphuret 

V.      2 

of  acetyle,  C^H^  J  -^j  forms  yellow  tabular  crystals. 

2.  Salts  of  Oxide  of  Ethyle  with  Chlorine. 

When  chlorine  acts  on  these  salts  or  ethers,  their  oxide  of  ethyle  is  acted  on 
as  if  separate,  but  in  many  cases  the  acids  remain  combined  with  the  new  chlo- 
rinized  compounds:  or  the  acids  also  are  acted  on, and  the  products  derived  from 
them  combine  with  those  derived  from  the  ether. 

jlcelic  ether  yields  a  compound  C^U^C\fi^,  which  may  be  viewed  as  C^H^ 


ACTION  OF  CHLORINE  ON  ETHERS.  625 

5        +  C  H  0  ,  that  is,  acetate  of  the  oxychloride  of  acetyle.     When  the  cora- 

pound  is  further  exposed  to  the  action  of  chlorine  at  a  high  temperature,  it  yields 
a  series  of  compounds,  in  which  its  hydrogen  is  gradually  replaced  by  chlorine, 
till  the  compound  CgClgO^  is  left,  which  is  called  perchloruretted  acetic  ether. 
Acetic  ether  is  C  H  0  ;  and  we  have  the  acetate  of  oxychloride  of  acetyle  C 

I  c,;  0/-   'hen  C,  I  »^^  0,  :  C3  ;  «^^  0,  :  C,  [  ^3^  0,  :  C,  J  «.^  O,    :  C. 

C  H 

^  p    0  :  and  C  CI  O  .    The  two  last  can  be  obtained  with  certainty  pure :  the 

C  H 

others,    after   C^  j      e  o^,  are  so  mixed  that  it  is  very  difficult  to  obtain  them 

pure  enough  for  analysis. 

When  benzoic  ether,  AeO,BzO,  is  acted  on  by  chlorine,  it  loses  2  eq.  hydro- 
gen, and  1  eq.  oxygen,  and  takes  up  3  eq.  chlorine,  producing  a  compound  which 
may  be  viewed  as  containing  chloride  of  benzoyle  and  oxychloride  of  acetyle, 

BzCI  t  C  H   5^,   =  C   H  CI  O  . 

4      3   /  Cl  18      8       3     3 

Oxalic  ether,  exposed  to  the  action  of  chlorine  under  the  influence  of  the  direct 
rays  of  the  sun,  loses  all  its  hydrogen,  which  is  replaced  by  chlorine.  (C  H^) 
0,0^0^,  thus  becomes  (C^Cl^)  OjC^O^.  The  latter  is  called  chloroxalic  ether. 
It  is  a  crystallizable  solid,  fusible  at  288°.  Dry  ammonia  acts  on  it  as  on  oxalic 
ether,  producing  chloroxamethane,  a  crystalline  compound  analogous  to  oxame- 
thane.  It  was  formerly  stated  that  oxamethane,  C^H  NOg,  has  the  composition 
of  oxamate  of  oxide  of  ethyle  (C^H^)  O  -j-  C^H^NO^;  or  of  oxalic  ether  plus 
oxamide  (C^H^)  0,C^O^-{-^Yi^,C^^,  In  like  manner,  chloroxamethane  repre- 
sents chloroxalic  ether  plus  oxamide:  (C^CIJ  0,C^0^  -f  NH^iC^O^  =  C^H^ 
CI  NOg.  When  chloroxamethane  is  left  in  contact  with  ammonia,  it  takes  up  2 
eq.  of  water,  and  forms  a  new  salt,  chloroxalovinate  of  ammonia,  C^Cl  0,NH 
0,20^0^,  which  is  deliquescent.  From  the  corresponding  salt  of  soda  the  chlo- 
roxalovinic  acid  may  be  obtained,  which  may  of  course  be  viewed  as  an  acid 
oxalate  of  the  compound  C^Cl^O.  Its  formula  is  C^Cl^CC^O^  -f-  HOjC^Og. 
By  the  action  of  alcohol  on  chloroxalic  ether,  there  is  formed  a  neutral  oil,  C  CL 
O  ,  which  contains  the  elements  of  anhydrous  chloroxalovinic  acid,  C  CI  0, 
2(3^0^;  and  when  dissolved  in  potash,  yields  chloroxalovinate  of  potash. 

Carbonic  ether,  by  the  action  of  chlorine,  yields  two  products:  1st.  Bichloru- 

retted  carbonic  ether,  C^  \  ^3  0,C02=  C^H^Clj^O^;  and  2nd.  Perchloruretted 

carbonic  ether,  C^Cl^OjCO^  =  CJ^Cl  O  .  The  former  is  an  oily  liquid ;  the 
latter  crystallizable. 

Chloride  of  ethyle  (C^H^  CI,  when  acted  on  by  chlorine,  yields  a  very  remark- 
able series  of  products,  in  which  the  hydrogen  is  gradually  replaced  by  chlorine, 
as  mentioned  at  p.  624,  to  which  I  refer  for  the  formulae.     I  shall  only  here 

C  H 

mention,  that  the  compound  there  represented  as  C^  <  ^^  CI,  =  C^H  CI  ,  cor- 
responds to  aldehyde,  and  is,  therefore,  probably  (C^H^)  Cl-|-  HCl,  jus*'as  alde- 

C  H 

hyde  is  (C^H^),  O  -|-  HO.     In  like  manner,  the  compound  C^  j-^3  ,  CI  =  C 

2 

HjClg,  corresponds  to  dry  acetic  acid,  C^H^O^.    The  action  of  potash  on  these 

42 


626  CHLORAL.  CHLORACETIC  ACID. 

two  compounds  confirms  this  view,  according  to  which  they  are  protochloride 
and  perchloride  of  acetyle. 

When  alcohol^  the  hydrated  oxide  of  ethyle,  is  subjected  to  the  long-continued 
action  of  chlorine,  aided  by  the  sun's  rays,  there  is  formed,  after  a  very  tedious 
operation,  a  remarkable  compound  called  chloral^  the  empirical  formula  of  which 
is  C  HCl  O  ^  C  CI  0  -f-  HO.  This  compound  represents  aldehyde  or  hydrated 
oxide  of  acetyle,  in  which  the  hydrogen  of  the  acetyle  has  been  replaced  by 
chlorine.  It  is  an  oily  liquid,  boiling  at  199°,  of  sp.  gr.  1*502.  Like  aldehyde, 
chloral,  when  kept,  is  spontaneously  converted  into  an  insoluble  solid  compound 
which  has  the  same  composition  as  chloral  itself.  In  contact  with  water,  chloral 
is  soon  converted  into  a  solid  hydrate,  which  dissolves  in  a  larger  quantity  of 
water.  It  contains  1  eq.  chloral  and  2  eq.  water.  When  heated  with  caustic 
alkalies,  chloral  produces  formiate  of  the  alkali  and  perchloride  of  formyle,  C 
HCI3O2  t  HO,KO  =  (C^H)  03,K0  -I-  (C^H)  Cl^.  The  perchloride  of  for- 
myle, in  contact  with  the  alkali,  is  partly  decomposed,  yielding  chloride  of  the 
metal. 

Pure  Acetic  Acid^  when  acted  on  by  chlorine  and  the  sun's  rays,  is  converted 
into  a  crystallizable  acid,  the  chloracetic  acid,  C  CI  O  ,H0.  As  acetic  acid 
may  be  considered  to  be  aldehyde  pltis  2  eq.  oxygen,  or  hydrated  peroxide  of 
acetyle,  so  chloracetic  acid  is  chloral  plus  2  eq.  oxygen,  or  hydrated  peroxide  of 
C  CI  ,  which  may  be  called  chloraceiyle.  Chloracetic  acid  forms  tabular  crys- 
tals, fusible  at  113°,  boiling  at  390°.  The  density  of  the  liquefied  acid  at  113<^ 
is  1*6 17.  When  heated  with  excess  of  potash,  it  yields  first  carbonic  acid  and 
perchloride  of  formyle,  C^Cl303,HO  +  2K0  =  2  (KCCO^)  t  C^HCl^.  The 
perchloride  of  formyle  is  partly  converted  by  another  portion  of  potash,  into 
formiate  of  potash  and  chloride  of  potassium,  C^HCl^  -|-  4K0  =  3KC1  -f-  KO, 
C,H03. 

With  bases,  chloracetic  acid  forms  salts  which  are  very  analogous  to  the  ace- 
tates; and  it  is  very  important  here  to  observe,  that  both  in  chloral  and  chlora- 
cetic acid,  the  substitution  of  chlorine  for  all  the  hydrogen  of  the  radical 
(acetyle)  of  aldehyde  and  acetic  acid,  has  not  affected  the  general  chemical  cha- 
racters of  the  compounds;  that,  in  other  words,  the  original  type  has  been 
retained.  We  have  also  seen,  in  the  preceding  pages,  among  the  products  of  the 
action  of  chlorine  on  oxide  of  ethyle  and  on  the  salts  of  oxide  of  ethyle,  that 
oxide  of  ethyle,  C^H^O,  is  converted  into  oxide  of  chlorethyle,  C  CI  0,  without 
the  type  being  altered:  the  oxide  of  chlorethyle  forming  with  the  acids  previ- 
ously combined  with  oxide  of  ethyle,  compounds  perfectly  analogous  to  the 
ethers  from  which  they  are  obtained. 

The  sulpkuret  of  ethyle  is  readily  acted  on  by  chlorine,  and  yields  a  yellow  oily 
liquid,  of  sp.  gr.  1*673,  boiling  at  320°,  of  a  most  fetid  odour,  the  formula  of 

C  H 

which  is  C^  j  p.  S.     Here  4  eq.  of  hydrogen  of   the  compound,  C^H^S,  are 

replaced  by  chlorine. 

Heavy  muriatic  ether  is  an  oily  liquid,  formed  by  the  action  of  moist  chlorine 
on  alcohol.  It  is  obviously  a  mixture,  and  probably  contains  aldehyde,  chloride 
of  ethyle,  chloral,  and  products  intermediate  between  aldehyde  and  chloral. 

Bromal.  C^Br^O,!!^  This  compound,  analogous  to  chloral,  is  formed  by 
the  action  of  bromine  on  alcohol.  It  forms  a  hydrate  with  3  eq.  water.  By 
caustic  alkalies  it  is  resolved  into  formic  acid,  which  combines  with  the  alkali, 
and  perbromide  of  formyle. 


COMPOUNDS  DERIVED  FROM  ALCOHOL.  6Q7 

Iodine  does  not,  so  far  as  is  known,  produce  a  compound  corresponding  to 
chloral  and  bromal;  but  a  solution  of  iodine  in  alcohol,  treated  with  an  alcoholic 
solution  of  potash,  yields  formiate  of  potash  and  periodide  of  formyle,  CJil. 

By  the  action  of  chlorine  on  alcohol,  holding  in  lolution  hydrocyanic  acid  or 
a  metallic  cyanide,  there  is  produced  a  crystalline  compound,  the  empirical  for- 
mula of  which  appears  to  be  C^gH^^N.Cl^Og.  This  is  equal  to  3  eq.  aldehyde, 
2  eq.  chloride  of  cyanogen,  and  2  eq.  water;  but  the  true  nature  of  this  com- 
pound is  unknown. 

3.  Compounds  derived  from  Alcohol,  but  of  uncertain  constitution. 

Olejlant  Gas.  Syn.  Hyduret  of  Acetyle.  C^H^  =  C^H3,C1  =  AcH.  This 
well-known  compound  is  generally  present  in  coal  gas,  oil  gas,  and  in  general, 
in  all  gaseous  mixtures  produced  by  the  action  of  heat  on  organic  substances. 
It  is  best  obtained  pure  by  heating  1  part  of  alcohol  with  6  or  7  of  oil  of  vitriol. 
There  is  produced  some  ether,  then  sweet  oil  of  wine,  and  lastly,  a  mixture  of 
sulphurous  acid  and  defiant  gases.  By  passing  the  gas  through  milk  of  lime, 
the  sulphurous  acid  is  removed,  and  by  then  passing  it  through  oil  of  vitriol,  the 
ether,  alcohol,  and  water  which  may  be  present,  are  likewise  separated.  Pure 
defiant  gas  has  been  already  described  (see  p.  261,  Part  II.);  here  we  shall 
attend  to  its  combinations.  It  is  absorbed  by  anhydrous  sulphuric  acid,  forming 
the  crystalline  compound  formerly  mentioned,  2S0  -f-  C  H  ,  which,  in  contact 
with  water,  produces  ethionic  acid.  When  mixed  with  its  own  volume  of  chlo- 
rine, both  gases  are  condensed  into  a  liquid,  the  composition  of  which  is  C  H 
Cl^.  This  is  the  oily  compound,  from  which  the  gas  was  called  olefiant  gas: 
the  oil  is  often  called  the  oil  of  the  Dutch  chemists ;  having  been  discovered  by 
an  association  of  chemists  in  Holland. 

When  mixed  with  2  vol.  of  chlorine,  and  set  fire  to,  the  whole  of  the  carbon 
of  the  gas  is  deposited  in  the  solid  form  or  as  smoke,  while  all  the  hydrogen 
forms  hydrochloric  acid,  C  H^  f  Cl    =  4HC1  f  C  . 

The  oil  of  olefiant  gas,  or  of  the  Dutch  chemists,  C  H^,C1  ,  may  be  viewed 
as  composed  of  hydrochloric  acid,  and  a  chloride  of  acetyle:  HCl  -f-  C  H  CI. 
When  acted  on  by  an  alcohol  solution  of  potassa,  chloride  of  potassium  and  water 
are  formed,  and  a  new  compound  separates,  which  is'the  protochloride  of  acetyle, 
C^H^Cl.  It  is  gaseous  at  ordinary  temperatures,  has  an  alliaceous  smell  and 
burns,  like  all  similar  chlorinized  compounds,  with  a  dark  red  flame  edged  with 
green.     \Ki  0°  it  condenses  into  a  liquid. 

When  this  protochloride  of  acetyle  is  acted  on  by  perchloride  of  antimony,  it 
yields,  among  other  products,  a  liquid,  boiling  at  240°,  which  is  C  H  CI  ,  and 
therefore  has  the  same  composition  as  perchloride  of  acetyle,  formerly  men- 
tioned. But  the  action  of  potash  dissolved  in  alcohol,  proves  that  these  two 
compounds  are  distinct,  and  that  the  one  now  under  consideration  is  C^H^Cl^  -f- 
HCl.  At  all  events,  it  yields  chloride  of  potassium,  water,  and  a  very  volatile 
liquid,  0^\{^C\^  =  'ii[Cji{,Q\),  or  in  other  words,  protochloride  of  formyle. 

By  continuing  the  action  of  chlorine  there  is  obtained  a  compound  C^H  CI 
=  C^HCl^  -j-  HCl ;  which,  with  potash,  yields  the  body  C^HCl^ ;  and  the  final 
result  of  this  action  is  the  protochloride  of  carbon,   C  CI   =4CC1;  which, 
however,  unites  with  chlorine  to  produce  the  sesquichloride,  C^Cl^H-  Cl2=  C^ 
CL  =  2C  CI. 


^1^  BICHLORIDE  OF  PLATINUM. 

The  perchlortde  of  acetyle  has  been  already  mentioned  as  a  product  of  the  action 
of  chlorine  on  ether:  it  is  C^H^Cl2  =  AcCL. 

The  oil  of  olejiant  gas^  C  H^Cl^,  which  may  be  considered  the  hydrochlorate 
of  chloride  of  acetyle,  C^H^,C1  -j-  HCl,  is  best  prepared  by  passing  olefiant  gas 
into  perchloride  of  antimony,  as  long  as  it  is  absorbed.  The  mixture,  if  dis- 
tilled, yields  the  oil  in  question.  It  is  purified  by  alternate  distillation  with  water 
and  sulphuric  acid,  and  finally  drying  it  with  chloride  of  calcium.  It  is  a  very 
mobile  liquid,  of  a  pleasant  etherial  smell,  and  a  very  sweet  taste ;  it  boils  at 
180°,  is  insoluble  in  water,  soluble  in  alcohol  and  ether. 

'  When  subjected  to  the  action  of  chlorine,  it  yields  hydrochloric  acid,  and  pro- 
ducts rich  in  chlorine.  Among  these  are,  the  hydrochlorate  of  chloride  of  for- 
myle,  C^HCl  f  HCl,  which  distils  at  240^  and  the  bichloride  of  formyle,  C^ 
H,C1  ,  which  distils  at  275°.  This  last  is  finally  converted  into  sesquichloride 
of  carbon ;  for  C2H,Cl2  +  Cl^  =  Cfi\^  +  HCl. 

Chloreiheral  is  the  name  given  by  D'Arcet  to  a  compound  formed  by  the  action 
of  chlorine  on  olefiant  gas,  containing  both  alcohol  and  ether.  Its  empirical  for- 
mula is  C  H  CIO ;  so  that  it  may  be  aldehyde,  plus  oil  of  olefiant  gas ;  C  H  O, 
HO  +  C^H3C1,HC1  =  2(C^H^C10);  or  oxychloride  of  acetyle,  plu»  oxide  of 

ethyle:  C^H^  5  CI  "^  C^H^O  =  2(C^H^C10).    The  true  nature  of  this  com- 

pound  is  unknown. 

Bromine  forms,  with  olefiant  gas,  a  liquid  compound  analogous  to  the  oil  of 
olefiant  gas.  Its  formula  is  C^^^^r  -\-  HBr.  Iodine  forms,  with  olefiant  gas, 
a  solid  compound,  which  would  appear  to  be  C^H^,!!  + 1^  rather  than  C^H^,!  -|- 
HI. 

Anhydrous  sulphuric  acid  absorbs  olefiant  gas,  producing  a  white  crystalline 
solid,  2S0  +  C  H  H^;  which,  when  dissolved  in  water,  forms  with  1  eq.  of 
water,  ethionic  acid,  2SO3-I-  O^H^O  =  C^H^O^  f  S^O^.  The  original  crystal- 
line compound  has  been  called  sulphacetylic  acid. 

4.    Action  of  bichloride  of  platinum  on  Alcohol. 

This  action  is  very  complex,  yielding  aldehyde,  chloride  of  ethyle,  chloride  of 
acetyle,  and  other  volatile  compounds,  along  with  a  salt,  composed  of  chloride 
of  platinum  and  chloride  oC  acetyle.  It  is  possible  that  3  eq.  of  oxide  of  ethyle, 
with  4  eq.  of  bichloride  of  platinum,  may  yield  1  eq.  aldehyde,  1  eq.  water,  4  eq. 
hydrochloric  acid,  and  2  eq,  of  the  new  salt.  3(C^H^0)  +  4PtCl2=  CH3O, 
HO  +  HO  t  4HC1 1  2(C^H3C1  f  Pt^Cl).  Zeise  considers  the  salt  to  be  C^H^ 
-I-  2PtCl,  which  formula  differs  from  the  preceding  in  containing  1  eq.  hydrogen 
more.  Malaguti  supposes  it  to  be  C^H30  -f  2PtCl ;  but  Zeise  has  shown  that 
it  contains  no  oxygen.  It  does  not  crystallize,  but  forms  a  gummy  mass,  spon- 
taneously decomposing  when  kept. 

When  a  solution  of  bichloride  of  platinum  in  alcohol  is  digested  with  a  little 
hydrochloric  acid,  and  chloride  of  potassium,  the  alcohol  distilled  off,  and  the 
residue  neutralized  by  carbonate  of  potash,  a  yellow  crystallizable  salt  is  ob- 
tained, which  contains  the  preceding  compound,  plus  1  eq.  chloride  of  potas- 
sium, C  H  CI  -f  Pt  CI  -I-  KCl.  Similar  double  salts  are  formed  with  chloride 
of  sodium  and  chloride  of  ammonium. 

These  double  salts  form  with  ammonia  a  yellow  precipitate,  which  is  C^H^CI, 
PtCl  +  NH3. 


COMPOUNDS  OF  MESITYLE.  629 

5.     Action  of  heat  on  acetic  acid  and  the  acetates. 

Acetone.  Syn.  Pyroacetic  Spirit.  Mesitic  Alcohol.  Formula  C  H  O.  Is  formed 
when  acetic  acid  is  passed  through  a  tube  heated  to  low  redness,  along  with  car- 
bonic acid,  carbonic  oxide,  and  carburetted  hydrogen :  also  when  the  acetate  of 
an  alkali  or  alkaline  earth  is  exposed  to  heat,  when  a  carbonate  is  left,  and  ace- 
tone distils  over.  It  is  best  prepared  by  distilling  a  mixture  of  2  parts  of  crys- 
tallized acetate  of  lead,  and  1  part  quicklime.  Its  formation  is  easily  explained ; 
for  anhydrous  acetic  acid,  C^H^O^  contains  the  elements  of  1  eq.  carbonic  acid, 
and  1  eq.  acetone.  ^fiP2~^^2  ~^  ^3^3^'  Acetone  is  also  formed  in  the 
distillation  of  sugar,  of  citric  acid,  of  tartaric  acid,  &c.  It  is  purified  by  recti- 
fication, until  its  boiling  point  becomes  constant  at  100°.  It  is  a  clear  and 
colourless  liquid,  of  sp.  gr.  0'7921,  and  has  a  peculiar  smell  and  a  pungent  taste. 
It  is  miscible  with  water,  alcohol,  and  ether,  in  all  proportions ;  and  is  sepa- 
rated from  water  by  the  addition  of  caustic  potassa,  chloride  of  calcium,  or  other 
salts  insoluble  in  acetone. 

Heated  with  hydrochlorite  of  lime,  it  is  converted  into  carbonic  acid  and  per- 
chloride  of  formyle.  When  prepared  by  the  distillation  of  acetates,  acetone  is 
accompanied  by  an  oily  liquid  C^^H^O. 

Acetone  contains,  in  3  eq.,  the  elements  of  1  eq.  carbonic  ether  and  1  eq.  ole- 
fiant  gas  (hyduret  of  acetyle).  C^H^0,C03  +  C^H3,H  =  CgHgO^  =  3(C3H^ 
0) ;  or,  in  4  eq. ;  we  have  the  elements  of  1  eq.  acetic  ether,  and  1  eq.  hyduret 
of  acetyle  :  C^H^O,C^H303  +  C^H3,H  =  C^2H^^0^  =  4(C3H30).  -  Kane  con- 
siders acetone  to  be  C^llfi^=  C^Up,RO;  that  is,  the  hydrated  oxide  of  a 
radical  CgH^,  which  he  calls  mesityle.  In  this  view,  acetone  is  analogous  to 
alcohol,  and  CgH,0,  the  oxide  of  mesityle,  to  ether.  But  although  Kane  has 
obtained  this  compound  C^H  O,  and  also  another  C  H  CI,  his  chloride  of  mesi- 
tyle, and  although  he  has  likewise  formed  double  salts  containing  sulphuric  acid 
and  the  elements  C^H^O,  yet  the  analogy  is  far  from  being  established.  It  has 
not  yet  been  found  possible  to  reproduce  acetone,  the  alcohol,  from  the  supposed 
ether  of  the  series,  as  we  can  reproduce  alcohol  from  the  salts  of  oxide  of  ethyle. 
Moreover,  in  these  double  salts,  the  body  C  H  O,  does  not  act  as  a  base,  but  is 
only  coupled  with  the  acid,  as  naphthaline  in  sulphonaphthalic  acid.  We  shall 
not,  therefore,  enter  into  minute  details  of  the  theoretical  views  alluded  to.  It  is 
sufficient  to  enumerate  the  supposed  radical  mesityle,  C^H^ :  its  oxide  CgH^O, 
oxide  of  mesityle;  its  hydrated  oxide,  CgH^O,HO  (acetone);  the  chloride  and 
iodide  of  mesityle,  CgH^Cl  and  CgH^I ;  the  acid  sulphate  of  oxide  of  mesityle, 
CgH^O,HO,2S03  (sulphomesitylic  acid)  ;  the  double  salts  of  this  sulphate,  the 
formula  of  which  is  CgH^O,HO,2MO,2S03 ;  and  a  compound  discovered  by 
Zeise,  containing  oxide  of  mesityle  with  chloride  of  platinum,  CgH^O,PtCl. 

The  action  of  nitric  acid  on  acetone  gives  rise  to  a  new  product :  nitrite  of 
oxide  of  pteleyle,  C^H  0,N03;  phosphoric  acid  appears  to  form  a  compound  acid 
with  acetone;  and  when  phosphorus,  iodine,  and  acetone  are  distilled  together, 
another  acid  is  obtained,  which  appears  to  contain  hypophosphorous  acid. 

When  chlorine  acts  on  acetone,  it  produces  a  liquid,  CgH^Cl^O^,  which  is 
called  mesitic  chloral. 

Mesitylene,  C^H^.  This  compound  is  obtained  when  acetone  is  distilled  with 
fuming  sulphuric  acid.  It  is  an  oily  liquid,  boiling  about  300°.  Acetone  2(0^ 
H3O)  =  CgH^  -I-  2 HO  ;  and  this  explains  its  production. 

When  mesitylene  is  acted  on  by  nitric  acid,  it  yields  a  liquid  C  H  0  ,  called 


630  KAKODYLE. 

by  Kane  mesitic  aldehyde.  But  when  chlorine  is  passed  through  mesitylene,  a 
evystalline  solid  is  obtained,  containing  a  new  radical,  pteleyle,  combined  with 
chlorine.  C^H^ -}- Cl^  =  CgH^Cl  f  HCl.  The  compound  CgH^Cl,  is  the  chlo- 
ride of  the  supposed  new  radical  pteleyle,  C  H  .  Kane  has  described  a  com- 
pound in  yellow  scales,  which  he  considers  to  be  iodide  of  pteleyle.  It  is  very 
desirable  that  the  whole  of  the  compounds  derived  from  acetone  should  be  again 
carefully  examined,  since  their  true  constitution  cannot  be  considered  as  estab- 
lished. 

COMPOUNDS  CONTAINING  ARSENIC,  DERIVED  FROM  ACETYLE. 

When  acetate  of  potash  is  heated  along  with  aisenious  acid,  a  very  remark- 
able liquid  is  obtained,  which  is  the  oxide  of  a  new  radical.  This  liquid,  which 
is  spontaneously  inflammable,  and  has  a  most  offensive  alliaceous  smell,  has 
been  long  known  in  an  impure  state,  under  the  names  of  the  liquor  of  Cadet, 
and  akarsine.  Bunsen,  by  a  long  series  of  the  most  profound  and  persevering 
researches,  established  its  true  character  as  the  oxide  of  the  radical  kakodyle. 
He  has  even  succeeded  in  obtaining  the  radical  itself  in  the  separate  state,  and 
in  establishing  the  most  perfect  analogy  between  that  radical  and  a  metal,  in  all 
its  chemical  relations. 

XVIII.    Kakodtle.    C^HgAsjissKd. 

The  radical  is  best  obtained  from  the  chloride  of  kakodyle,  KdCl,  by  the 
action  of  zinc  at  212°.  Chloride  of  zinc  is  formed,  and  kakodyle  is  set  free. 
It  is  rectified  in  an  apparatus  filled  with  carbonic  acid  gas,  to  prevent  decompo- 
sition. It  is  a  clear  liquid,  refracting  light  strongly.  When  cooled,  it  crystal- 
lizes in  large  square  prisms,  and  acquires,  when  pure,  the  appearance  of  ice.  Its 
smell  is  insupportably  offensive,  and  its  vapour  is  highly  poisonous.  The  two 
latter  characters  belong  to  all  the  compounds  of  kakodyle,  with  hardly  an  excep- 
tion. Kakodyle  is  spontaneously  inflammable  in  the  air :  a  rod  moistened  with 
it  instantly  takes  fire  when  exposed  to  the  air.  It  forms  two  distinct  oxides : 
the  protoxide  KdO  (alkarsine),  and  kakodyle  acid,  KdOg. 

TABLE  OF  COMPOUNDS. 

Protoxide  of  Kakodyle C^iQks^,0=:KAO 

Kakoflylic  Acid =  KdOg 

Chloride  of  Kakodyle KdCl 

Protoxide  of  Kakodyle.    C^^ks^fi  =  KdO. 

Syn.  Alkarsine,  This  is  the  chief  ingredient  of  the  liquor  of  Cadet ;  it  is 
purified  by  repeated  rectifications  in  an  atmosphere  of  carbonic  acid,  and  is, 
when  pure,  a  limpid  etherial  liquid,  refracting  light  powerfully  ;  it  boils  at  about 
300°,  and  at — 9°  it  crystallizes  in  white  scales  of  a  satiny  lustre.  Its  smell  is 
most  offensive,  and  its  taste  very  nauseous.  If  placed  on  the  skin,  it  causes  vio- 
lent itching,  and  if  taken  internally  it  is  a  most  energetic  poison.  It  is  sparingly 
soluble  in  water,  more  soluble  in  alcohol  and  ether.  Like  kakodyle,  it  takes  fire 
when  exposed  to  the  air.  When  left  under  water,  it  gradually  disappears,  being 
for  the  most  part  converted  into  kakodylic  acid.  The  production  of  oxide  of 
kakodyle  is  very  simple  :  2  eq.  dry  acetic  acid  and  1  eq.  arsenious  acid  yield 
4  eq.  carbonic  acid  and  1  eq.  oxide  of  kakodyle.  'ii{CJi{p^  -{•  As^O^=^  ^CO^ 
+  C,H,A8,0. 


COMPOUNDS  OF  KAKOPLATYLE.  631 

Kakodylic  Acid.     Kd03=C^H6As2,03. 

Syn.  Akargene.  Formed  by  the  gradual  oxidation  of  the  protoxide,  under 
water.  It  forms  oblique  four-sided  prisms,  brittle,  and  of  a  glassy  lustre.  They 
have  no  smell,  and  are  soluble  in  water  and  alcohol.  Its  salts  do  not  crystallize. 
Many  reducing  agents  convert  it  into  the  protoxide  by  removing  2  eq.  of  oxygen. 
It  is  not  in  the  least  poisonous. 

There  appears  to  be  an  intermediate  oxide  KdO^;  but  it  has  not  been  obtained 
in  a  state  of  purity. 

Chloride  of  Kakodyle^  KdCl=C^HgAs  ,C1  =KdCl,  is  obtained  by  heating  a 
compound  of  oxide  of  kakodyle  and  corrosive  sublimate  along  with  hydrochloric 
acid:  KdO,HgCl^+HCl-f-KdCl+HOf  HgOl^.  It  is  a  volatile  horribly  fetid 
liquid,  the  vapour  of  which  attacks  strongly  the  lining  membrane  of  the  nose, 
and  provokes  a  flow  of  tears.  When  exposed  to  the  air  it  deposits  crystals  of  an 
oxychloride  of  kakodyle  KdO-|-3KdCl.  The  iodide,  bromide,  and  fluoride  of 
kakodyle  are  in  all  points  analogous  to  the  chloride;  and  form,  when  exposed  to 
the  air,  oxyiodide,  oxybromide,  &c. 

Sulphur  forms  with  kakodyle  three  compounds;  the  protosiilphuref,  KdS,  is 
obtained  by  distilling  chloride  of  kakodyle  with  hydrosulphuret  of  barium : 
KdCl  t  BaS,  HS  =  KdS  f  BaCl  f  HS.  It  is  a  clear,  volatile,  very  fetid 
liquid,  heavier  than  water.  It  dissolves  sulphur,  forming  the  bisu/phuret  KdS  , 
which  is  a  very  permanent  compound.  The  persulphuret^  •^^^''^3'  ^^  ^  sulphur 
acid,  and  forms  sulphur  salts  which  are  very  permanent,  with  the  sulphurets  of 
highly  basic  metals.  The  sulphur  salt  of  kakodyle  and  lead,  PbS,KdS  crystal- 
lizes beautifully. 

Cyanide  of  Kakodyle,  KdCy=C^HgAs2,C^^N,  is  formed  by  distilling  bicya- 
nide  of  mercury  with  water  and  oxide  of  kakodyle.  When  pure  it  forms  large 
brilliant  crystals,  very  fusible  and  volatile.  The  vapour  of  this  compound  is  so 
poisonous  as  to  be  in  the  highest  degree  dangerous  to  the  experimenter. 

COMPOUNDS  OF  KAKODYLE  CONTAINING  PLATINUM. 

Chloride  of  Kakoplafyk,  C  H  As  PtO  ,CI.  This  compound  is  formed  when 
an  alcoholic  solution  of  bichloride  of  platinum  is  added  to  a  similar  solution  of 
chloride  of  kakodyle,  when  a  reddish  brown  precipitate  is  formed,  which,  being 
boiled  with  water,  gives  a  solution  from  which,  on  cooling,  needles  of  the  new 
compound  are  deposited.  Bromide  of  kakoplatyle  and  iodide  of  kakoplatyle  may 
be  formed  from  the  chloride,  and  are  analogous  to  it.  The  former  appears  in 
large  yellow  crystals,  the  latter  in  golden  micaceous  scales. 

When  the  chloride  is  acted  on  by  sulphate  of  silver,  there  is  obtained,  along 
with  chloride  of  silver,  the  sulphate  of  the  oxide  of  kakoplatyle,  C^H^As^PtO^, 
SO^.     It  forms  white  crystalline  grains. 

The  radical  of  these  singular  compounds,  kakoplatyle,  may  be  represented  as» 
composed  of  protoxide  of  platinum,  water,  and  kakodyle  ;  PtO,HO,C  HgAs^.  We 
have,  therefore,  the  following  series,  which,  like  those  derived  from  the  bases 
containing  platinum  formerly  described,  throws  much  light  on  the  nature  of  the 
vegetable  bases. 

Radical,  Kakoplatyle  .  .  PtO-f-Kd  ssC^HgAsgPtO. 

Chloride  of  do.,  anhydrous  .  .       PtO,Kd+Cl 

Chloride,  hydrated  .  .  PtO,Kd+Cl+HO 

Chloride,  ammoniated  .  .        PtO,Kd4-Cl-|-NH3 

Oxide,  hydrated  .  .  PtO,Kd+0  +H0 

Sulphate,  hydrated        .  .  .       (PtO,Kd-J-0,HO)+S03. 


632  CANE  SUGAR. 

It  is  to  be  particularly  borne  in  mind  that  this  radical,  whose  basic  character 
is  quite  obvious,  contains  two  metals,  arsenic  and  platinum,  quite  foreign,  in 
general,  to  organic  compounds. 

The  existence  of  kakodyle  itself,  and  the  perfect  analogy  which  may  be  traced 
between  it  and  the  simple  metals,  in  their  relations  to  all  other  substances,  ren- 
der the  results  of  the  researches  of  Bunsen,  which  have  been  so  very  briefly  de- 
scribed in  this  work,  of  the  very  highest  importance  to  the  theory  of  organic 
compounds,  and  especially  to  that  of  compound  radicals. 

APPENDIX  TO  ETHYLE  AND  ACETYLE.— SUGAR. 

Sugar,  as  the  substance  from  which  alcohol  and  all  the  compounds  of  ethyle 
are  exclusively  obtained,  comes  properly  to  be  considered  here  as  an  appendix  to 
these  compounds.  There  are  several  kinds  of  sugar,  capable  of  undergoing  fer- 
mentation and  of  producing  alcohol.  These  are,  cane  sugar ;  grape  sugar ;  (sugar 
of  starch  ;  of  honey ;  diabetic  sugar;)  sugar  of  milk;  and  uncrystallizable  sugar. 
The  sugar  of  mushrooms  has  been  found  to  be  mannite,  which  is  not  fermentes- 
cible. 

VABIETIE8  OF  SUGAR. 

Cane  Sugar  ....  C,2H909+2HO 

Grape  Sugar  (Starch  Sugar)  .  ,  Cj2H,40j4 

Sugar  of  Milk  (lactine)  .  .  .     C24H24O24 

Sugar  of  Mushrooms  .  .  .  CjjHjsOjs 

1.  Cane  sugar^  C  H^jO^+gHO,  occurs  in  great  abundance  in  the  sugar  cane, 
the  beet  root,  the  maple,  besides  many  other  vegetables.  It  is  extracted  from 
the  juice  of  these  plants  by  crystallization,  the  evaporation  being  conducted  at  as 
low  a  temperature  as  possible.  It  crystallizes  with  great  facility,  either  in  small 
grains  by  rapid  cooling  of  a  strong  syrup,  as  in  loaf  sugar;  or  in  large  distinct 
crystals  by  a  slow  process,  as  in  sugar  candy.  The  above  formula  represents 
the  composition  of  pure  crystallized  sugar. 

Sugar  forms  large  transparent  hard  crystals,  which  melt  at  302°,  or  according 
to  Peligot  at  356°,  forming  a  viscid  liquid,  which  on  cooling  forms  a  transparent 
amorphous  mass,  barley  sugar.  This,  when  kept,  gradually  becomes  crystalline, 
opaque  and  friable.  About  420°  sugar  is  converted  into  caramel,  losing  3  eq.  of 
water. 

Sugar  dissolves  in  -J  of  its  weight  of  cold,  and  in  any  quantity  of  boiling 
water ;  a  solution  saturated  at  230°  becomes  a  solid  crystalline  mass  on  cooling 
(tablet)  :  a  solution  saturated  in  the  cold  is  viscid,  and  is  called  syrup.  Syrup, 
when  long  boiled,  loses  the  property  of  crystallizing.  The  crystallization  of 
sugar  from  syrup  is  also  prevented  by  the  addition  of  ^^j  of  oxalic,  citric,  or  malic 
acids.  When  boiled  with  diluted  sulphuric  acid,  cane  sugar  is  converted  into 
grape  sugar.  With  strong  sulphuric  acid  it  produces  a  dark  brown  liquid,  con- 
taining a  new  acid,  sulphosaccharic  acid.  Nitric  acid  converts  it  into  saccharic 
acid,  oxalic  acid,  and  carbonic  acid. 

When  boiled  with  very  diluted  sulphuric  acid,  sugar  absorbs  oxygen  from  the 
air,  and  produces  formic  acid,  and  a  brown  matter  identical  with  ulmine,  formed 
by  the  decay  of  wood.  Sugar  prevents  the  precipitation  of  many  metallic  solu- 
tions by  alkalies;  and  when  mixed  with  oxide  of  copper  and  potash,  the  oxide 
of  copper  is  dissolved,  forming  a  purple  solution,  which  on  hc'^iinr'  deposits  red 


GRAPE  SUGAR.  633 

suboxide  of  copper.  It  reduces  partially  the  oxides  of  many  metals,  when  boiled 
with  their  solutions. 

Sugar  forms  crystallizable  compounds  with  the  alkalies,  oxide  of  lead,  and 
chloride  of  sodium.  When  in  contact  with  the  lining  membrane  of  the  stomach 
of  a  calf,  or  with  the  caseine  of  milk,  sugar  is  transformed  into  lactic  acid. 

Sugar,  if  taken  along  with  nitrogenized  food,  may  be  called  nutritious :  it 
would  appear,  however,  to  act  chiefly  in  contributing  to  the  support  of  respira- 
tion, and  thus  keeping  up  the  animal  heat.  An  animal,  confined  to  sugar  as 
food,  soon  dies  from  want  of  nitrogen,  with  the  symptoms  of  starvation. 

When  a  solution  of  sugar  is  examined  by  polarized  light,  it  gives  rise  to  a 
series  of  rings  of  the  prismatic  colours,  when  the  plane  of  polarization  is  made 
to  rotate  from  left  to  right. 


SUGAR  WITH  BASES  AND  SALTS. 


CaO. 
HO  ' 


With  lime  sugar  forms  a  sparingly  soluble  compound,  C^^HgOg  -f-   ^ 

With  baryta,  it  forms  a  crystallizable  compound,  C  H  Qq  ^  tt/-|  •  With  ox- 
ide of  lead  it  yields  an  insoluble  compound,  C^H  0  ,2PbO;  and  with  common 
salt  it  yields  a  crystalline  compound,  SC^^HgOg  +  r  ^^J  pi 

2.  Grape  Sugar.  Syn.  Glucose.  Diabetic  Sugar.  Starch  Sugar,  C  H  O  . 
This  sugar  occurs  in  the  juice  of  many  fruits,  and  is  besides  a  product  of  the 
metamorphoses  of  starch,  cane  sugar,  woody  fibre,  sugar  of  milk,  &c.,  when 
boiled  with  diluted  acids.  It  may  also  be  obtained  from  starch  by  the  action  of 
infusion  of  malt,  or  of  diastase.  It  occurs  in  the  urine  of  those  affected  with 
diabetes  mellitus.     The  crystals  which  form  in  honey  are  likewise  grape  sugar. 

It  is  best  extracted  from  dried  grapes,  or  honey,  and  is  also  prepared  on  the 
large  scale  from  starch.  1  part  of  starch  is  boiled  with  4  of  water,  and  from 
T^o  *o  tV  "^  sulphuric  acid,  during  36  or  40  hours ;  or  an  infusion  of  malt  is 
added  to  jelly  of  starch,  which  soon  becomes  liquid,  and,  in  a  few  hours  is  con- 
verted into  sugar.  When  acid  is  used,  it  is  neutralized  by  chalk,  the  solution  of 
sugar  filtered,  and  evaporated  to  a  syrup,  or,  if  required,  to  a  dry  mass.  In  this 
process,  starch,  ^^^^^^0^^,  takes  up  4  eq.  of  water,  and  produces  grape  sugar, 
C^^Hj^Oj^  ;  so  that  100  parts  of  pure  starch  yield,  or  ought  to  yield,  122  of  grape 
sugar.  The  same  explanation,  only  varying  the  quantity  of  w^ater,  applies  to 
the  conversion  into  grape  sugar  of  cane  sugar,  ^^f^^fi^^'t  woody  fibre,  Cj^HgO^; 
and  sugar  of  milk  C  H  0  ,  these  compounds  requiring  3,  6,  and  2  eq.  of  water 
respectively  to  form  grape  sugar. 

The  action  of  infusion  of  malt  is  not  explained :  all  that  we  know  is,  that  this 
infusion,  or  a  solution  of  diastase,  a  substance  contained  in  it,  do  actually  cause 
starch  to  take  the  form  of  grape  sugar.  It  is  probable  that  the  diastase  is  in  a 
state  of  decomposition,  and  may  act  as  a  ferment.  The  action  of  the  acid  would 
seem  to  be  equally  obscure ;  but  there  is  some  reason  to  think  that  there  is  first 
formed,  as  in  the  case  of  ether,  a  coupled  acid,  or  acid  salt,  which,  like  sulpho- 
vinic  acid,  is  decomposed  by  boiling.  According  to  De  Saussure,  sulphuric  acid 
and  starch  actually  form  a  crystallizable  compound. 

Grape  sugar  crystallizes  from  alcohol  in  square  tables  or  cubes;  a  concentrated 
syrup  of  it  yields  only  a  mass  formed  of  crystalline  grains.    It  is  much  less 


634  COMPOUNDS  DERIVED  FROM  SUGAR. 

soluble,  requiring  1^  part  of  cold  water,  and  less  sweet  to  the  taste  than  cane 
sugar:  in  fact  1  part  of  cane  sugar  sweetens  as  much  as  2^  of  grape  sugar.  It 
is  much  more  soluble  in  cold  alcohol  than  cane  sugar.  At  212°  grape  sugar  loses 

2  eq.  of  water;  when  heated  beyond  284°  it  becomes  caramel.  Hot  water  dis- 
solves any  quantity  of  grape  sugar,  but  the  syrup  is  not  so  nearly  viscid  as  that 
of  cane  sugar.  Solution  of  grape  sugar  exhibits  the  prismatic  rays  with  polarized 
light  when  the  plane  of  polarization  is  rotated  from  right  to  left,  the  colours  being 
less  brilliant.  Now,  as  cane  sugar,  when  fermenting,  becomes  first  grape  sugar, 
the  coloured  rings  at  first  shown  by  it  when  the  plane  of  polarization  rotated 
from  left  to  right  disappear  during  fermentation;  but  reappear  when  rotation  is 
made  from  right  to  left. 

Grape  sugar  is  easily  distinguished  from  cane  sugar  by  the  action  of  acids  and 
bases.  Strong  sulphuric  acid  dissolves  without  charring  it,  forming  sulphosac- 
charic  acid;  and  the  alkalies  or  alkaline  earths,  which  do  not  decompose  cane 
sugar  unless  very  concentrated,  rapidly  convert  grape  sugar  into  a  brown  matter. 
Peroxide  of  lead  converts  it,  at  212°,  into  basic  formiate  of  lead,  carbonate  of 
lead,  and  water. 

With  baryta  and  lime,  and  oxide  of  lead,  grape  sugar  forms  compounds  which 
it  is  difficult  to  obtain  pure.  That  with  baryta  appears  to  contain  3  eq.  baryta 
for  2  eq.  of  sugar,  and  as  the  baryta  replaces  water  in  such  compounds,  it  is  pro- 

bably  C2^H^^O^^,3BaO  =  C^H^^O^^  ^  3^^^.      The  compound  with  lime  ap- 

pears  to  be  C,  H,  0,„,2CaO ;  and  that  with  lead,  C,  H^  0„,3PbO.     If  we  sup- 

^  12      12     12  '  '        12      11     11  * 

pose  the  dry  grape  sugar  to  be  C^H^^O^j,  and  to  combine  with  3  eq.  water  and 

3  eq.  base,  then  we  should  have 

Crystallized  grape  sugar         .,.'...        Cj2H,iOj,+    3H0 

Compound  With  baryta {c;2H;;o;|+     3Ba0 

^'"'s Ci2H,i0,i+  J   pjQ 

-: oxide  of  lead ^u^iPu'f'     ^^^^ 

But  the  compound  which  grape  sugar  forms  with  common  salt,  and  which 
crystallizes  very  readily,  does  not  agree  exactly  with  this  view.  ..The  crystals 
are  2{C^^}i^fi^)-\-NaC\-\-2UO  ;  and  at  212°  they  lose  the  two  equivalents  of 
water. 

The  sulphosaccharic  acid,  above  mentioned,  as  being  formed  when  grape 
sugar  is  acted  on  by  oil  of  vitriol,  has  not  been  fully  examined.  It  forms  a  solu- 
ble salt  with  baryta. 

With  organic  acids  grape  sugar  forms  compounds,  the  sugar  in  which  cannot 
be  brought  to  crystallize.  Hence  organic  acids  in  vegetable  juices  act  injuriously 
by  first  converting  cane  sugar  into  grape  sugar,  and  then  forming  with  it  uncrys- 
tallizable  compounds. 

When  siigar  is  boiled  with  hydrochloric  acid,  it  yields  different  brown  pro- 
ducts, according  to  the  strength  of  the  acid.  With  equal  parts  of  acid  and  water, 
it  yields  a  body,  ^a^Wj^O  :  with  a  weaker  acid,  two  brown  compounds  ;  a  solu- 
ble one,  C^^Hj_jOj2,  and  an  insoluble  one,  C^pH^gO^^.  When  boiled  with  diluted 
sulphuric  acid,  two  substances  are  formed,  which  are  nearly  hlack  ;  one,  sacchul- 
mine,  insoluble,  and  the  other  sacchulmic  acid,  soluble  in  ammonia.  The  latter 
"C„H„0„. 


ACTION  OF  NITRIC  ACID  ON  SUGAR.  635 

When  boiled  with  alkalies,  cane  sugar  is  first  converted  into  grape  sugar,  and 
then  into  formic  acid,  the  two  new  acids,  the  glucic  acid  and  the  melassic  acid. 
Glucic  acid  is  very  soluble,  and  its  formula  is  either  C^^Hj^0^^,6H0,  or  C^^Hg 
0  ,3H0.  It  is  chiefly  formed  before  the  application  of  heat,  which  converts  it 
into  melassic  acid.  This  latter  acid  is  formed  from  sugar  by  the  joint  action  of 
heat  and  alkalies.  It  has  a  very  dark  colour,  and  when  separated  by  hydrochlo- 
ric acid,  appears  as  a  black  flocculent  deposit.     Its  formula  is  C    HO   (]). 

Caramel,  the  black  matter  formed  by  heating  sugar  to  about  400°,  has  the 
formula  of  anhydrous  cane  sugar,  C  H  O  .  It  dissolves  readily  in  water  form- 
ing a  solution  like  sepia,  which  is  tasteless  when  pure.  The  caramel  of  com- 
merce contains  a  good  deal  of  undecomposed  sugar. 

When  sugar  is  distilled  with  3  parts  of  lime,  it  yields  a  liquid  which  is  a 
mixture  of  acetone  and  metacetone.  Metacetone  is  a  colourless  liquid,  of  an 
agreeable  odour,  boiling  at  183°,  and  insoluble  in  water.  Its  formula  is  CgH^O ; 
and  it  may  be  considered  as  2  eq.  acetone  C  H  O  ,  minus  I  eq.  w^ater. 

1  eq.  of  anhydrous  sugar CjjHgOg 

Contains — 1  eq.  acetone  C3  H3O 

1  eq.  metacetone Cg  H5O 

3  eq.  carbonic  acid  .         .         .         .  C3       Og 

1  eq.  water HO 

Together CjjHgOg 

The  formation  of  these  products  is  therefore  easily  accounted  for. 

When  sugar  is  heated  with  hydrate  of  potassa,  several  products  are  formed,  but 
among  them  is  an  acid,  C^H^O^,HO,  which  is  metacetonic  acid,  evidently  de- 
rived from  metacetone  by  oxidation  at  the  expense  of  the  hydrate.  It  is  very 
similar  to  acetic  acid. 

ACTION  OF  NITRIC  ACID  ON  SUGAR. 

Saccharic  Jcid,  C^^H^^OjjSHO  ?,  or  CgH^O^,HO,  is  one  of  the  products  of  the 
action  of  diluted  nitric  acid  on  cane  or  grape  sugar.  When  stronger  acid  is  used, 
oxalic  and  carbonic  acids  are  the  chief  products.  When  sugar  has  been  heated 
with  2  parts  of  nitric  acid  and  10  of  water,  the  acid  liquid  gives,  with  basic  ace- 
tate of  lead,  an  insoluble  saccharate  of  lead,  which  is  decomposed  by  sulphuret- 
ted hydrogen,  and  the  acid  solution  so  far  neutralized  with  potassa  th^at  on 
evaporation  it  yields  crystals  of  the  acid  saccharate  of  potash.  This  salt  is  puri- 
fied, again  converted  into  saccharate  of  lead,  and  again  the  lead  salt  is  decom- 
posed by  sulphuretted  hydrogen.  The  acid  this  time  is  pure.  It  crystallizes 
with  difficulty. 

This  acid  has  been  supposed  to  be  quintibasic,  and  to  form  5  series  of  salts,  but 
the  latest  researches  of  Heintz  lead  to  the  conclusion  that  it  is  either  C  H  O^.HO, 

0      4     7 

or  C^HgOj^,2HO.  Owing  to  the  very  discordant  results  of  different  experi- 
menters, we  shall  not  here  enter  into  details  which  are  uncertain.  Saccharic  acid 
forms  a  crystallizable  acid  salt  with  potassa,  and  definite  salts  with  many  other 
bases.  It  is  isomeric  with  mucic  acid :  for  Cj2HgOj^,2HO  is  the  probable  form- 
ula of  mucic  acid. 


636  MUCIC  ACID. 

The  saccharate  of  silver,  when  gently  heated  under  water,  is  decomposed,  the 
silver  being  reduced  ;  and  as  this  occurs  without  effervescence,  the  reduced  metal 
adheres  to  the  glass,  and  forms  a  bright  mirror  surface.  The  other  saccharates 
are  only  interesting  in  respect  to  their  composition.  On  the  whole,  saccharic 
acid  is  a  compound  of  high  theoretical  interest,  and  the  formation  of  two  iso- 
meric acids,  saccharic  and  mucic,  by  the  action  of  nitric  acid  on  cane  and  grape 
sugar  on  the  one  hand,  and  on  sugar  of  milk  on  the  other,  is  a  fact  which  may 
hereafter  lead  to  a  knowledge  of  the  true  constitution  of  the  different  kinds  of 
sugar. 

Notwithstanding  the  fact  that  cane  sugar  is  easily  converted  into  grape  sugar, 
and  that  the  formulae  differ  only  by  3  eq.  water,  it  is  evident  that  these  two  kinds 
of  sugar  differ  more  than  if  they  were  merely  different  kinds  of  hydrates  of  the 
same  compound.  Strong  mineral  acids  instantly  decompose  cane  sugar,  but  have 
little  action  on  grape  sugar;  while  alkalies,  which  combine  with  cane  sugar  to 
form  crystalline  compounds,  rapidly  convert  grape  sugar  into  dark  compounds, 
glucic  and  melassic  acids.  And  although  both  sugars  agree  in  undergoing  the 
same  (vinous)  fermentation,  yet  it  is  most  probable  that  cane  sugar,  before  fer- 
menting, becomes  grape  sugar. 

When  vegetable  juices  containing  cane  sugar  are  evaporated,  the  presence  of 
organic  acids  causes  its  conversion  into  grape  sugar;  and  when  lime  is  added,  to 
clarify  the  juice,  the  action  of  the  lime  on  grape  sugar  when  evaporated,  produces 
glucic  and  melassic  acids;  in  other  words,  renders  much  sugar  dark  and  uncrys- 
tallizable,  converting  it  into  molasses.  A  great  part  of  the  loss  owing  to  this 
cause  has  of  late  years  been  avoided  by  carefully  neutralizing  with  sulphuric 
acid  as  soon  as  the  lime  has  effected  the  clarification. 

3.  Sugar  of  milk,  or  laciine,  ^34^^g'^j^g-\'^^^=^  24^24^  24'^^  obtained  by  eva- 
porating clarified  whey  till  it  crystallizes.  When  pure  it  forms  hard  white  crys- 
tals, soluble  in  5  or  6  parts  of  cold  and  2^  of  hot  water.  The  taste  of  the 
crystals  is  feeble,  but  a  concentrated  solution  tastes  very  sweet.  It  is  insoluble 
in  ether  and  alcohol.  It  stands  between  cane  sugar  and  grape  sugar  in  compo- 
sition; for  while  cane  sugar  is  Cj^Hj^O^^,  and  grape  sugar  ^^2^14^14'  lactine  is 
C„,H„  0„,  =  2(C   H,  0,J.     By  boiling  with  diluted  acids  it  is  converted  into 

242424^1212     12'  •'^ 

grape  sugar.  By  the  action  of  nitric  acid  it  yields  mucic  or  saccholactic  acid.  It 
combines  with  ammonia  and  with  oxide  of  lead.  Its  presence  prevents  the  pre- 
cipitation of  many  metallic  solutions.  Sugar  of  milk  is  susceptible  of  the  vinous 
fermentation,  and  it  is  well  known  that  some  nations  prepare  an  intoxicating 
liquor  from  milk  by  fermentation.  There  is  reason  to  think  that  previous  to  fer- 
mentation, it  is  like  cane  sugar  converted  into  grape  sugar  ;  and  at  all  events 
milk  does  not  ferment  until  an  acid  has  been  formed  in  it,  which  acid  converts 
lactine  into  grape  sugar. 

Sugar  of  milk  forms  two  compounds  with  oxide  of  lead:  first,  neutral,  C^H^^ 
Oj^,5PbO  :  second  basic,  C24HjgO^^,I0PbO. 

Mucic  Acid,  ^12^8^14"'"^^^'  '^  formed  when  diluted  nitric  acid  acts  on  sugar 
of  milk,  gum,  or  mannite.  It  is  a  white  crystalline  powder,  of  a  feebly  acid 
taste,  soluble  in  6  parts  of  boiling  water,  which  deposits  nearly  the  whole  on 
cooling.  Its  solution  when  long  heated  and  evaporated,  yields  the  modijied  mucic 
acid.  Mucic  acid  dissolves  in  oil  of  vitriol  with  a  crimson  colour.  When  heated 
it  blackens,  and  yields  among  other  products,  pyromucic  acid. 

Mucic  acid  is  bi basic,  and  forms  two  series  of  salts,  one  with  2  eq.  fixed  base, 


VINOUS  OR  ALCOHOLIC  FERMENTATION.  637 

the  other  with  1  eq.  fixed  base,  and  1  eq.  water.  These  salts  have  little  interest. 
The  mucaie  of  oxide  of  ethyle^  or  mucic  ether,  crystallizes  in  four-sided  prisms, 
soluble  in  hot  water.  When  boiled  with  a  base,  it  yields  alcohol,  and  mucate 
of  the  base.     Its  formula  is  C^HgOj^-fSAeO. 

Modified  mucic  acid  is  more  soluble  in  water,  soluble  in  alcohol,  from  which 
solution  it  is  deposited  in  square  tables.  Its  aqueous  solution,  saturated  at  the 
boiling  point,  deposits  on  cooling  ordinary  mucic  acid.  Its  salts  are  more  soluble 
than  the  mucates,  but  the  acid  in  them  easily  passes  into  the  ordinary  acid.  It 
is  probable  that  the  modified  acid  contains  1  eq.  of  water  more  than  the  other. 

Pyromucic  acid,  C  HO  -[-  HO,  is  formed  by  the  dry  distillation  of  mucic 
acid.  1  eq.  of  mucic  acid,  C^^^^^O^^,  contains  the  elements  of  1  eq.  pyromucic 
acid,  CjpH^Og,  6  eq.  water,  H^O^;  and  2  eq.  carbonic  acid,  CgO^.  Pyromucic  acid 
forms  brilliant  white  scales,  fusible  at  266°,  and  volatilizes  completely  at  a  tem- 
perature somewhat  higher.  It  is  soluble  in  water  and  alcohol.  Its  salts  are 
not  important.  Pyromucate  of  oxide  of  ethyle,  C^^H^O^,  AeO,  is  a  solid  crystaili- 
zable  compound,  fusible  at  93°,  volatile  at  410°.  Chlorine  acts  on  this  ether,  form- 
ing a  new  compound,  C    H^^Cl  0  ,  the  constitution  of  which  is  quite  uncertain. 

4.  Sugar  of  mushrooms,  Wiggers  obtained  from  ergot  of  rye  a  saccharine 
compound,  crystallizing  in  transparent  rhombic  prisms,  soluble  in  water  and 
alcohol,  and  susceptible  of  the  vinous  fermentation.  An  analysis  of  this  sugar 
gave  the  formula  C^^H^jO^g,  that  is,  grape  sugar,  minus  1  eq.  water.  This  may 
be  a  distinct  kind  of  sugar  ;  but  the  mushroom  sugar  of  Braconnot  is  mannite  or 
manna  sugar. 

We  have  seen  that  starch  and  woody  fibre  may  be  converted  into  grape  sugar 
by  boiling  with  dilute  sulphuric  acid  :  in  like  manner,  salicine  and  phloridzine, 
boiled  with  the  same  acid,  yield  saliretine  and  phloretine,  in  each  case  along 
with  grape  sugar.  But  the  action  of  the  infusion  of  malt,  is  still  more  singular; 
we  have  seen  that  starch  by  contact  with  infusion  of  malt  is  rapidly  converted 
into  grape  sugar.  This  action  is  ascribed  to  the  presence  of  diastase,  a  nitro- 
genized  body  which  exists  in  malt,  and  which,  while  it  causes  the  conversion  of 
starch  into  sugar,  itself  disappears.  The  action  is  not  fully  understood,  but 
there  is  no  doubt  that  when  seeds  germinate,  the  starch  they  contain  is  in  this 
manner  rendered  soluble,  and  conveyed,  as  sugar,  to  all  parts  of  the  plant,  there 
to  be  converted  into  woody  fibre  by  a  process  the  inverse  of  that  by  which  woody 
fibre  is  converted  into  sugar.  This  latter  is  seen  in  the  ripening  of  fleshy  fruits, 
where  a  quantity  of  cellular  matter  (lignine)  disappears,  and  the  proportion  of 
sugar  very  much  increases. 

VINOUS  OR  ALCOHOLIC  FERMENTATION. 

This  name  is  given  to  that  change  by  which  sugar  is  resolved  into  alcohol  and 
carbonic  acid,  by  contact  with  a  ferment.  The  sugar  must  be  dissolved  in  water, 
and  the  solution  must  be  exposed  to  a  temperature  or  from  40°  to  86°.  If  a  fer- 
ment, such  as  yeast,  be  added,  the  sugar  soon  disappears,  carbonic  acid  is  given 
off  in  large  quantity,  and  the  liquid  is  found  to  contain  alcohol,  which  may  be 
separated  by  distillation.  Now,  grape  sugar,  C^^H^^O^^,  contains  the  elements 
of  2  eq.  alcohol,  4  eq.  carbonic  acid,  and  2  eq.  water,  2  (C^H^O^)  -f-  400^  -f- 
2H0 ;  and,  by  very  exact  experiments  it  has  been  proved  that  100  parts  of  grape 
sugar  yield  only  47*12  of  alcohol,  44*84  of  carbonic  acid,  together  91*96  parts, 


VISCOUS  FERMENTATION. 

the  loss,  9*04  parts  being  the  2  eq.  of  water  separated.  On  the  other  hand, 
cane  sugar,  C^^H^O^j,  requires  the  addition  of  1  eq.  of  water  to  yield  2  eq. 
alcohol,  and  4  eq.  carbonic  acid,  =  2  (C^H^O^)  -f  ^CO^;  and  here  also  experi- 
ment has  demonstrated,  that  100  parts  of  cane  sugar  yields  53*727  parts  of  alco- 
hol and  51-298  of  carbonic  acid,  together  105*025;  the  increase,  or  5-025  parts 
being  due  to  the  1  eq.  of  water  taken  up  to  form  dry  grape  sugar,  C  H  O  , 
into  which  cane  sugar  "is  converted  befoi^  it  undergoes  fermentation.  These 
facts  prove  that  the  ferment  takes  no  direct  part  in  the  reaction,  but  only  acts  by- 
inducing  a  state  of  change. 

A  considerable  number  of  substances,  if  in  a  state  of  decomposition,  act  as 
ferments  on  a  solution  of  sugar:  among  these  are,  besides  yeast,  vegetable 
gluten,  albumen,  caseine  or  fibrine,  and  the  corresponding  animal  substances} 
also  animal  matter  generally,  if  in  a  state  of  putrefaction. 

The  only  explanation  we  can  give  is  that  the  particles  of  these  bodies,  being 
in  a  state  of  decomposition,  are  in  motion,  and  by  communicating,  mechanically, 
an  impulse  or  motion  to  the  particles  of  the  sugar,  destroy  the  balance  of  affinities 
to  which  the  existence  of  sugar  is  owing;  and  thus  give  rise  to  a  new  balance 
or  equilibrium,  mord  stable  under  the  given  circumstances.  The  elementary  par- 
ticles of  the  sugar  being  disturbed  in  their  previous  arrangement,  group  them- 
selves according  to  their  individual  affinities,  and  while  the  carbpn  forms,  on  one 
side,  a  compound  containing  all  the  hydrogen  (alcohol),  it  yields  on  the  other,  a 
compound  containing  the  greater  part  of  the  oxygen  (carbonic  acid). 

When  a  natural  juice,  as  that  of  the  grape,  ferments,  some  of  the  various  sub- 
stances it  contains  undergo  a  decomposition,  probably  of  an  analogous  kind, 
giving  rise  to  other  new  products,  which  are  important  in  regard  to  the  flavour 
of  the  liquid  (wine,  beer,  or  spirits),  produced  in  the  fermentation.  Thus  all 
wine  contains  cenanthic  ether ;  potato  spirit  contains  the  oil  of  potato  spirit 
(fusel  oel.  German) :  grain  spirit  contain  a  similar  oil.  It  is  not  improbable,  that 
besides  the  vinous  fermentation  which  takes  place  in  the  greater  part  of  the 
sugar,  a  peculiar  reaction  occurs,  between  a  portion  of  the  sugar  and  the  ferment 
(or  some  other  nitrogenized  compound  present),  the  result  of  which  is  the  pro- 
duction of  these  peculiar  oily  liquids.  The  bouquet,  or  so  much  prized  flavour 
of  the  finer  wines,  is  doubtless  owing  to  some  etherial  compound  produced  in  a 
similar  way,  but  the  origin,  properties,  and  composition  of  which  are  as  yet  alto- 
gether unknown.  It  may  be  mentioned  here,  however,  that  cenanthic  ether, 
which  is  the  cause  of  that  peculiar  smell  which  belongs  to  all  wine,  and  is  so 
marked  that  we  can  at  once  tell,  after  many  weeks  or  months,  that  an  empty- 
bottle  has  formerly  contained  wine,  is  a  compound  of  oxide  of  ethyle  with  a 
fatty  acid ;  and  the  oil  of  potato  spirit  is  a  compound  analogous  to  alcohol ;  the 
hydrated  oxide  of  a  radical  amy/c,  Cj^H^j. 

VISCOUS  FERMENTATION. 

When  certain  saccharine  juices,  such  as  those  of  beet-root,  carrots,  onions,  &c. 
are  exposed  to  a  temperature  of  from  86°  to  104°,  a  peculiar  fermentation  takes 
place.  The  sugar  disappears,  but  instead  of  alcohol  and  carbonic  acid,  there  are 
obtained  mannite  lactic  acid,  and  a  mucilaginous  substance,  having  the  composi- 
tion of  gum;  this  latter  renders  the  liquid  ropy, and  viscid, hence  the  name  given 
to  the  process. 


MANNITE.    LACTIC  ACID.  639 

The  composition  of  mannite  is Cg  H^  Og 

Thai  of  lactic  acid  is Cg  H^  O5 

Together  C,2Hj20ji 

It  is  evident,  therefore,  that  1  eq.  of  dry  grape  sugar,  ^^2^^2^^2^  losing  1  eq, 
oxygen,  might  give  rise  to  mannite  and  lactic  acid.  The  gum  has  the  same 
composition  as  sugar,  so  that  we  are  led  to  believe  that  the  nitrogenized  consti- 
tuents of  the  juice  are  acted  on  by  the  sugar,  from  which  they  obtain  oxygen; 
and  that  these  compounds  are  themselves  decomposed  by  the  oxygen,  mannite, 
and  lactic  acid,  which  are  very  permanent,  being  produced  from  the  suoar. 

This  peculiar  fermentation  is  produced  when  cheese  is  added  to  a  solution  of 
sugar,  and  the  whole  kept  at  a  proper  temperature. 

Mannite  C.H  0^  occurs  as  the  chief  ingredient  of  manna.  It  is  also  found  in 
certain  juices,  in  mushrooms,  in  roots,  such  as  that  of  celery,  and  is  formed 
artificially  as  above  described.  It  is  easily  purified  by  solution  in  alcohol  and 
crystallization.  It  forms,  when  crystallized  in  water,  large  prisms,  of  a  weak 
sweet  taste.  It  is  not  susceptible  of  the  vinous  fermentation.  Nitric  acid  and 
permaganate  of  potassa  act  on  it  as  on  sugar.  Concentrated  arsenic  acid  gives 
it  a  brick  red  colour. 

Lactia  Jidd^  C^H^O^  \  HO,  so  called  because  it  occurs  in  sour  milk,  is  also 
formed  abundantly,  as  above  described,  in  a  peculiar  fermentation  of  certain  sac- 
charine juices  at  a  high  temperature.  In  milk  it  is  derived  from  the  sugar  of 
milk  ;  and  by  neutralizing  sour  milk  with  carbonate  of  soda,  adding  sugar  of 
milk,  allowing  it  again  to  become  acid,  again  neutralizing,  and  so  on  in  succes- 
sion, as  long  as  the  caseine  causes  the  peculiar  change  to  take  place,  it  may  be 
obtained  in  large  quantity.  A  still  easier  process  is  to  dissolve  14  parts  of  cane 
sugar  in  60  of  water,  and  to  add  4  of  moist  cheese  and  a  sufficient  quantity  of 
prepared  chalk.  The  mixture  being  kept  some  time  at  from  77°  to  86°  F.  will 
at  last  become  quite  thick  with  crystals  of  lactate  of  lime.  If  the  action  of  the 
caseous  ferment  be  pushed  further,  and  at  a  higher  temperature,  the  lactate  of 
lime  is  not  obtained,  but  in  Its  place  hutyrate  of  lime  in  large  quantity.  See 
Butyric  acid.  The  above  quantities  will  yield  about  13  parts  of  lactate  after  it 
has  been  purified  by  crystallization;  besides  from  1|  to  2  parts  of  mannite.  The 
acid  of  sour  crout  is  lactic  acid,  and  by  boiling  the  juice  of  sour  crout  with  chalk 
or  carbonate  of  zinc,  lactate  of  zinc  or  of  lime  may  be  obtained. 

From  the  lactate  of  lime,  lactic  acid  may  he  obtained  by  the  action  of  oxalic 
acid,  which  removes  the  lime  as  oxalate.  The  filtered  solution  is  lactic  acid, 
which  is  concentrated  by  evaporation,  and  purified  by  solution  in  ether.  From 
the  lactate  of  soda,  lactate  of  zinc  may  he  obtained  by  adding  chloride  of  zinc  to 
the  hot  saturated  solution;  on  cooling,  lactate  of  zinc,  being  sparingly  soluble  in 
cold  water,  crystallizes.  This  salt,  acted  on  by  barytic  water,  yields  lactate  of 
baryta,  from  which  sulphuric  acid  removes  the  baryta,  and  the  filtered  liquid  is 
pure  diluted  lactic  acid. 

In  its  most  concentrated  form,  hydrated  lactic  acid  is  a  syrupy  liquid  of  a  very 
strong  but  pleasant  acid  taste.  Its  sp.  gr.  is  1'215.  Its  formula  CgH^O^  -j-  HO 
=  CgHgOg.  It  is  therefore  polymeric  with  dry  grape  sugar  and  with  gum ;  both 
of  which  are  C  H  O  .  At  482°  the  hydrate  is  decomposed,  and  yields  a  sofid 
crystalline  sublimate,  C  H  O  ,  which  has  been  called  anhydrous  lactic  acid,  or 
sublimed  lactic  acid.  This  compound  dissolves  readily  in  hot  water,  and  the 
solution  if  evaporated  yields  the  original  hydrate  CgH^O^  =  C^H^O^  -j-  2H0, 


640  HYDRATED  OXIDE  OF  METHYLE. 

But  when  the  acid  is  neutralized  by  bases,  only  one  of  the  2  eq.  of  water  taken 
up  by  the  sublimed  acid  is  replaced  by  a  base;  and  consequently  we  cannot 
look  on  the  sublimed  acid  as  the  true  anhydrous  acid.  The  anhydrous  acid,  as 
it  exists  in  the  lactates,  is  CgH^O  ;  and  the  sublimed  acid  is  not  lactic  acid,  but 
is  converted  into  lactic  acid  when  boiled  with  water. 

The  general  formula  for  the  lactates  is  CgH^O^,MO.  The  lactates  of  the  alka- 
lies are  very  soluble  and  deliquescent :  that  of  lime  is  less  soluble  in  cold  water 
and  crystallizes  readily.  The  lactate  of  zinc  is  sparingly  soluble  in  cold  water, 
and  is  hence  well  adapted  for  the  extraction  and  purification  of  the  acid. 

XIX.    Methyle.    C2H3  =  Mt. 

This  is  the  hypothetical  radical  of  a  numerous  series  of  compounds,  entirely 
analogous  to  those  of  ethyle.  There  is  the  oxide  nf  methyle,  MtO,  analogous  to 
oxide  of  ethyle ;  and  the  hydrated  oxide  of  methyle  MtO, HO,  analogous  to  alco- 
hol. This  last  is  the  compound  from  which  all  the  others  are  obtained.  The 
extraordinary  analogy  between  ethyle  and  methyle  will  enable  us  to  describe  the 
compounds  of  the  latter  very  briefly. 

TABLE  OF  COMPOUNDS. 

Hydrated  Oxide  of  Methyle CgHgOjHO 

Oxide  of  Methyle iS^^^O 

Chloride  of  Methyle .  CjHgjCl 

Iodide  of  Methyle CgHg,! 

Sulphuret  of  Methyle CgHgjS 

1.    Hydrated  Oxide  of  Methyle.    MtO,HO. 

Syn.  Pyroxilic  Spirit.  This  compound  is  one  of  the  chief  products  of  the 
destructive  distillation  of  wood,  and  is  found  in  the  watery  portion,  along  with 
acetic  acid,  acetone,  acetate  of  oxide  of  methyle,  and  several  other  etherial  liquids, 
besides  portions  of  the  oily  matter  of  the  tar  dissolved  in  them. 

By  rectification  with  chloride  of  calcium,  the  pyroxilic  spirit,  which  combines 
with  that  salt,  is  separated  from  several  other  liquids  which  distil  over  in  the 
heat  of  the  vapour  bath.  The  residue^  if  mixed  with  its  own  bulk  of  water,  and 
again  heated  in  the  vapour  bath,  now  gives  oif  the  pyroxilic  spirit,  which  is  still 
mixed  with  water.  It  is  purified  by  rectification  with  quicklime,  which  also 
destroys  any  acetate  of  methyle  that  may  be  present. 

Pure  hydrated  oxide  of  methyle  is  a  liquid  very  similar  to  alcohol,  having  the 
same  density,  and  the  same  degree  of  inflammability.  Its  odour  is  peculiar  and 
etherial.     It  boils  at  about  140°  or  150°. 

When  heated  with  peroxide  of  manganese,  water,  and  sulphuric  acid,  it  yields 
various  products,  among  which  the  chief  are, /ormic  acid  and  formomethylal.  It 
is  decomposed  by  nitric  acid,  yielding  oxalic  acid,  and  by  chlorine,  yielding  new 
products.  It  dissolves  resins,  and  is  used  in  making  varnishes.  It  forms,  with 
baryta  a  crystalline  compound  BaO  -f  MtO,HO  ;  and  with  chloride  of  calcium, 
another  crystalline  body  in  large  hexagonal  tables,  CaCl  -j-  2(MtO,HO). 

By  the  action  of  platinum  powder,  pyroxilic  spirit  is  oxidized  into  formic  acid, 
which  bears  the  same  relation  to  it  that  acetic  acid  does  to  alcohol, 

2.    Oxide  of  Methyle.    MtO  =  (C2H3)0. 
This  compound  is  obtained,  like  ether  (^xide  of  ethyle),  when  the  preceding 


§      SALTS  OF  OXIDE  OP  METHYLE.  641 

compound  is  distilled  with  its  own  volume  of  oil  of  vitriol ;  it  escapes  as  an 
inflammable  gas.  Like  oxide  of  ethyle,  it  is  a  base  and  neutralizes  acids.  It 
even  forms  a  neutral  sulphate,  which  oxide  of  ethyle  cannot  do.  It  is  worthy 
of  notice,  that  oxide  of  methyle  is  polymeric  with  alcohol;  for  C  H,0  =  2(C 
H^O) :  so  that  these  two  bodies  have  the  same  composition,  in  100  parts  ;  that 
is,  the  same  relative  proportions  of  the  same  element,  but  a  very  different  abso- 
lute amount :  the  equivalent  of  alcohol  being  twice  as  heavy  as  tbat  of  oxide  of 
methyle.  The  constitution  of  these  compounds,  moreover,  is  different,  for  one 
is  a  hydrate,  C^H^O  -f-  HO  ;  while  the  other  is  an  anhydrous  oxide,  C^H  O. 

3.  Chloride  of  methyle^  C^^^CX  =  MtCl,  is  a  gas,  of  an  ethereal  smell,  in- 
flammable, of  sp.  gr.  ri737.  It  is  formed  by  the  action  of  sulphuric  acid  and 
chloride  of  sodium  on  pyroxilic  spirit.  By  the  action  of  chlorine,  aided  by  the 
sun's  rays,  it  yields  several  new  compounds  containing  chlorine. 

4.  Iodide  of  methyle^  ^2^3'^  ^^  ^^^'  ^^  obtained  by  distilling  12  parts  of 
pyroxilic  spirit,  8  of  iodine,  and  1  of  phosphorus.  It  is  a  liquid,  boiling  between 
102^  and  122*^.     The  fluoride  and  cyanide  of  methyle  are  analogous  liquids. 

5.  Sulphuret  of  methyle,  0^11^,8=  MtS,  is  best  formed  by  the  action  of  a  cur- 
rent of  chloride  of  methyle  on  sulphuret  of  potassium  dissolved  in  alcohol. 
MtCl  -f-  KS  =  MtS  -f-  KCl.  It  is  a  mobile  liquid,  of  a  very  offensive  alliaceous 
odour,  boiling  at  104°.  Its  sp.  gr.  in  the  liquid  form  is  0845 ;  in  the  form  of 
vapour,  it  is  2*115.  With  chlorine,  it  gives  rise  to  several  new  compounds.  The 
hydrosulphuret  of  sulphuret  of  methyle  (corresponding  to  mercaptan)  I  obtained 
by  distilling  the  double  sulphate  of  methyle  and  potassa  with  the  hydrosulphuret 
of  potassium.  (KO,MtO,2S03)  t  HS,KS  =  2(KO,S03)  -f-  HS,MtS.  Its  for- 
mula is  HSjMtS  =  0^112,8  4-  HS.  It  is  a  colourless  liquid,  lighter  than  water, 
which  boils  at  70°,  and  acts  on  the  oxides  of  mercury  and  lead  exactly  as  mer-^ 
captan  does.  Its  odour  is  most  offensive,  resembling  that  of  leeks  highly  con- 
centrated. 

SALTS  OF  OXIDE  OF  METHYLE. 

1.  Neutral  Sulphate.  MtO,SOg,  is  obtained  when  pyroxilic  spirit  is  distilled 
with  a  large  excess  of  sulphuric  acid.  It  forms  an  oily  liquid,  of  a  slightly 
alliaceous  smell.  It  boils  at  370°.  Boiling  water  decomposes  it  into  acid  sul- 
phate and  hydrate  of  oxide  of  methyle.  "When  heated  with  chlorides,  cyanides, 
&c.,  it  yields  the  compound  of  methyle  with  chlorine,  cyanogen,  &c. ;  with  a 
salt  of  benzoic,  succinic,  or  other  organic  acid,  it  yields  benzoate,  &c.  of  oxide 
of  methyle.     Ammonia  converts  it  into  sulphamethylane. 

TABLE  OF  SALTS  OF  OXIDE  OF  METHYLE. 
Bisulphate  of  Oxide  of  Metbyle      ....        MtO,HO,2S03 

Nitrate MtOjNOg 

Oxalate MtO,C203 

Benzoate MtO,BzO 

Acetate   .        , MtO,Ac03 

2.  Bisulphate  of  Oxide  of  Methyle.  Syn.  Sulphomethylic  Acid.  HO,MtO, 
2SO3,  is  perfectly  analogous  to  sulphovinic  acid^,  and  forms  doubFe  salts,  such  as 
that  of  potassa,  KO,MtO,2SO  ,  which  are  often  called  sulphomethylates,  and 
correspond  exactly  to  the  sulphovinates.    The  acid  sulphate  itself  may  be  ob- 

43 


642  OXIDATION  OF  OXIDE  OF  METHYLE.  • 

tained  in  crystals,  which  are  very  soluble  and  very  acid.  It  is  best  obtained  by 
the  action  of  hot  water  on  the  neutral  sulphates.  The  double  salts,  or  sulpho- 
metbylates,  are  of  no  particular  importance.     They  crystallize  readily. 

3.  Nitrate  of  Oxide  of  Methi/le,  MtO,NO  ,  is  obtained  when  pyroxilic  spirit  is 
distilled  with  nitrate  of  potassa  and  sulphuric  acid.  It  is  an  oily  liquid,  the 
vapour  of  which,  if  heated  beyond  248°,  explodes  violently. 

The  neutral  carbonate  of  methyle  is  not  known ;  but  double  carbonates,  analo- 
gous to  those  of  ethyle  with  alkalies,  may  be  prepared  in  the  same  way  as  those 
compounds. 

4.  Oxalate  of  Oxide  of  Methyle^  MtO,C20^  =  C^H^O^,  is  obtained  in  a  manner 
analogous  to  that  in  which  oxalic  ether  is  prepared.  It  forms  a  crystalline  solid, 
soluble  in  alcohol  and  pyroxilic  spirit,  which  deposit  it  in  large  cry^stals.  By 
the  action  of  dry  ammonia,  it  is  converted  into  oxameihylane  (analogous  to  oxa- 
methane),  which  is  the  oxaniate  of  oxide  of  methyle.^  ^e^^s^^e  "^  ^2^?'^  "'"  ^4 
H^NO  .  Liquid  ammonia  converts  it  into  oxamide,  as  is  the  case  with  oxalic 
ether,  only  here  pyroxilic  spirit  and  not  alcohol  is  formed  at  the  same  time. 
C  H  0,C  O,  +  NH,  =  C  H  0,H0  +  C  0„,NH  .    This  is  perhaps  the  easiest 

232      o  323  222  tx 

way  of  obtaining  oxamide  in  large  quantity. 

Bisulphuret  of  carbon  and  hydrated  cyanic  acid  act  on  pyroxilic  spirit  exactly 
as  on  alcohol,  producing  analogous  compounds. 

5.  Benzoate  cf  Oxide  of  Methyle^  MtO,BzO,  is  best  obtained  by  distilling  dry 
benzoate  of  lime  or  soda  with  neutral  sulphate  of  methyle.  It  is  an  oily  liquid,. 
of  a  balsamic  odour,  analogous  in  other  respects  to  benzoic  ether. 

6.  Acetate  of  Oxide  of  Methyle,  MtO,AcO^,  is  obtained  in  the  same  way  as 
acetic  ether,  which  it  resembles.  It  occurs  in  considerable  quantity  in  raw 
pyroxilic  spirit,  and  even  in  that  which  has  only  been  purified  by  rectification. 
"When  quicklime  is  used  in  the  rectification,  it  is  destroyed,  yielding  an  addi- 
tional quantity  of  the  pure  hydrate  of  oxide  of  methyle.  It  is  very  volatile  and 
inflammable,  and  for  most  purposes  its  presence  in  the  wood  spirit  is  not  at  all 
injurious.     It  is  isomeric  with  formiate  of  oxide  of  ethyle :  for  C  H  O  -f-  C  H 

0,  =  CHOt  CHO,. 

3         4    J      '      2       3 

The  mucate  of  oxide  of  methyle  is  a  crystalline  solid,  analogous  in  its  prepa- 
ration and  properties  to  the  corresponding  salt  of  ethyle. 

The  action  of  chlorocarbonic  acid  on  pyroxilic  spirit  is  exactly  analogous  to 

its  action  on  alcohol,  producing  an  oily  liquid,  C^H^CLO^  =  C^  j  p?  +  C^  H^ 

O.  By  the  action  of  ammonia  this  liquid  produces  a  compound,  urethyJnne^ 
(corresponding  to  urethane)  C^H^NO^  or  C^Hj^N^Og  =  C^H^N^O^  f  2{C^p, 
CO^);  that  is,  a  compound,  possibly,  of  1  eq.  urea,  with  2  eq.  neutral  carbonate 
of  methyle. 

When  a  current  of  ammonia  is  made  to  act  on  the  neutral  sulphate  of  methyle, 
there  is  produced  a  crystalline  compound,  C  H  NS  0^,  whicH  has  been  called 
su/phamethylane,  and  may  be  viewed  as  oxamethylane,  in  which  sulphamide, 
SOjiNH^,  has  been  substituted  for  oxamide,  CjO^,NH2;  or  SO^  for  C^O^.  It 
may  also  be  considered,  if  oxamethylane  be  the  oxamate  of  oxide  of  methyle, 
C  H  0  -f-  C^H^NO^,  as  composed  of  oxide  of  methyle  and  a  peculiar  acid, 
formed  of  hyp6sulphuric  acid  and  amide  ;  C^H^O  -\-  (^2^s^^^2^' 

When  hydrated  oxide  of  methyle  is  oxidized  by  means  of  plantinum  powder, 
it  is  finally  converted  into  pure  formic  acid.     There  is  evidently,  therefore,  the 


FORMYLE.  643 

same  relation  between  methyle  and  formic  acid,  as  between  ethyle  and  acetic 
acid  ;  and  on  comparing  the  formulae  of  pyroxilic  spirit  and  of  formic  acid,  C 
H^OjHO  and  0^110^,110,  we  perceive  that  the  former,  to  be  converted  into  the 
latter,  must  have  lost  2  eq.  of  hydrogen,  and  taken  up  2  eq.  of  oxygen.  This  is 
exactly  what  takes  place  with  alcohol,  and  there  can  be  no  doubt,  that  the  pyrox- 
ilic spirit  yields  an  intermediate  compound,  exactly  analogous  to  aldehyde, 
although  this  has  not  yet  been  isolated.  Such  a  compound  would  be  the 
hydrated  protoxide  of  a  derived  radical, /ormy/e,  analogous  to  acetyle,  of  which 
formic  acid  is  the  hydrated  peroxide;  and  its  formula  would  be  (C  H)0  -|-  HO. 
We  shall,  therefore,  assume  the  existence  of  this  radical,  and  proceed  to  describe 
its  compounds,  which  are  quite  analogous  to  those  of  acetyle. 

7.  Salicylate  of  Oxide  of  Methyle,  MtO,SaO  =  C^gHgOg,  is  found,  nearly  pure, 
in  the  oil  obtained  by  distilling  with  water  the  flowers  of  Gaultheria  procumbens, 
a  plant  found  abundantly  in  New  Jersey.  This  oil  is  most  remarkable  as  con- 
taining two  compounds,  salicylic  acid  and  oxide  of  methyle,  neither  of  which 
was  previously  known  except  as  a  product  of  decomposition  of  organic  sub- 
stances by  artificial  means. 

The  oil  is  very  fragrant.  When  acted  on  by  nitric  acid,  the  salicylic  acid  is 
first  converted  into  nitrosalicylic  or  anilic  (indigotic)  acid,  and  the  anilate  of 
oxide  of  methyle  is  obtained  in  crystals.  The  further  action  of  nitric  acid  pro- 
duces nitropicric  acid. 

When  the  oil  of  gaultheria  is  added  to  an  excess  of  solution  of  potassa,  scaly 
crystals  are  formed,  w^hich  are  a  compound  of  the  oil  with  potassa,  and  from 
which  acids  separate  the  oil  unchanged.  But  if  heated  with  the  potassa,  hydrated 
oxide  of  methyle  is  given  off,  and  salicylate  of  potassa  is  left,  from  which  acids 
separate  pure  salicylic  acid. 

Salicylamide.  When  the  oil  is  left  for  a  few  days  in  contact  with  six  times 
its  bulk  of  strong  aqua  ammoniae,  it  is  entirely,  although  slowly,  dissolved,  and 
the  solution  leaves,  on  evaporation,  a  mass  of  brown  crystals  of  a  peculiar  aro- 
matic odour.  By  distillation,  this  mass  yields  colourless  prismatic  crystals  of  a 
new  compound,  which  is  found  to  be  salicylamide  (Cj^H^O^,NH  )  —  HO  =  C^^ 
H  NO  .  This  compound  is  isomeric  (or  polymeric)  with  protonitrobenzoene, 
and  with  anthranilic  acid;  but  when  distilled  with  lime  or  baryta,  it  does  not 
yield  aniline,  as  both  these  compounds  do,  but  is  resolved  into  carbolic  acid, 
ammonia,  and  a  carbo-hydrogen. 

When  the  oil  of  gaultheria  is  made  to  drop  on  red-hot  baryta,  it  is  resolved 
into  carbonic  acid  and  anisole,  C,  H  O^  +  2BaO  =  2(BaO,COJ  -}-  C,  H  O  .  It 
would  appear  that  the  formula  of  anisole,  (which  see  farther  on,)  contains  1 
eq.  of  hydrogen  too  little,  and  that  the  formula  now  given,  namely,  C  H^O  , 
is  the  correct  one,  according  to  the  most  recent  experiments. 

XX.   FORMYLE.      C2H=Fo. 

This  radical  is  unknown  in  a  separate  form,  as  are  its  protoxide  and  deutox- 
ide,  corresponding  to  aldehyde  and  aldehydic  acid.  But  when  hydrated  oxide 
of  methyle  is  distilled  with  sulphuric  acid,  water,  and  peroxide  of  manganese,  a 
volatile  liquid  is  obtained,  which  is  a  mixture  of  formiate  of  oxide  of  methyle 
and  another  liquid  called  methylal.  When  purified,  this  letter  has  the  formula 
CgHgO^,  which  indicates  that  it  is  composed  of  C^HOjHO,  or  hydrated  oxide  of 
formyle,  and  2  eq.  of  oxide  of  raeihyle,  'ii{C^jd),    This  compound,  briefly, 


644  FORMIC  ACID. 

FoO,HO  4- 2MtO,  corresponds  to  aceial  in  the  series  of  ethyle;  acetal  being 
AcO,HO-hAeO. 

TABLE  OF  COMPOUNDS. 

Formic  acid  (anhydrous)         .....  FoO- 


Formic  acid  (hydrated) 


Fo03,2HO 


Chlorides  of  Formyle  .....  Fo-[-(Cl,Cl2,  CI3) 

Perbromide        **......  FoBrj 

Periodide  *«......  F0I3 

Formic  Acid.     C2H03,HOs=Fo03,HO. 

This  remarkable  acid  occurs  in  the  red  znt,  formica  rufa,  and  may  be  obtained, 
in  a  diluted  and  impure  state,  by  infusing:  these  insects  in  water.  Its  production 
from  pyroxylic  spirit  has  been  described  above.  It  may  also  be  prepared  by  dis- 
tilling a  mixture  of  starch  or  sugar  with  peroxide  of  manganese,  water,  and  sul- 
phuric acid  :  and  it  is  formed  under  a  great  variety  of  circumstances  from  many 
organic  compounds. 

To  prepare  the  hydrated  acid  pure  and  concentrated,  the  dry  formiate  of  lead, 
PbO,FoO^,  is  decomposed  by  sulphuretted  hydrogen  gas,  and  the  vapour  of  the 
formic  acid  condensed  in  a  well  cooled  receiver.  It  is  boiled  for  a  few  moments 
to  expel  any  sulphuretted  hydrogen.  It  is  a  clear  liquid  of  sp.  gr.  1*235,  fuming 
slightly,  and  has  a  very  pungent  acid  smell.  Below  32°  it  crystallizes  in  bril- 
liant scales.  It  boils  at  2l6°,  and  its  vapour  is  inflammable,  burning  with  a  blue 
flame.  This  is  probably  owing  to  the  formation  of  carbonic  oxide,  for  the  acid 
C  HO^,HO,  contains  the  elements  of  2  eq.  carbonic  oxide,  C  O  ,  and  2  eq.  water, 

With  1  eq.  of  water  it  forms  the  second  hydrate  FoO^-fSHO,  which  much  re- 
sembles the  first  in  properties.   Its  boiling  point  is  221°, and  its  sp.  gr.  is  I'llO. 

Both  these  hydrates  are  highly  corrosive;  a  drop  of  either  on  any  delicate 
portion  of  the  skin  causes  a  severe  burn,  which  blisters,  suppurates  and  is  very 
painful  and  difficult  to  heal.  In  this  respect,  the  formic  acid  can  only  be  com- 
pared to  hydrofluoric  and  hydrated  cyanic  acids. 

A  weaker  acid  is  obtained  by  distilling  formiate  of  soda,  lime,  or  lead,  with 
sulphuric  acid,  previously  diluted  with  half  its  weight  of  water.  Ten  parts  of 
formiate  of  lime,  8  of  oil  of  vitriol,  and  4  of  water,  yield  9  of  formic  acid,  of  sp. 
gr.  1-075. 

The  salts  of  the  acid  are  best  prepared  from  the  weak  and  impure  acid  obtained 
by  distilling  a  mixture  of  10  parts  of  starch,  37  of  peroxide  of  manganese,  30  of 
oil  of  vitriol  and  30  of  water.  These  materials  yield  3'35  parts  of  formic  acid, 
such  that  100  parts  neutralize  15  of  dry  carbonate  of  soda.  From  this  acid,  the 
formiate  of  lead  may  be  easily  prepared  and  purified ;  and  from  it,  by  the  addi- 
tion of  carbonate  of  soda,  formiate  of  soda  may  be  obtained. 

Formic  acid  is  easily  recognized  by  the  action  of  sulphuric  acid,  which  de- 
composes, without  blackening,  both  it  and  its  salts,  causing  the  disengagement 
of  pure  carbonic  oxide.  It  also  reduces  the  oxides  of  all  the  noble  metals,  and 
is  itself  oxidized  into  carbonic  acid.  Formic  acid  not  only  reduces  the  oxides, 
but  also,  in  most  cases,  the  soluble  salts,  of  the  noble  metals.  1  eq.  formic  acid 
can  reduce  2  eq.  of  «  protoxide,  such  as  that  of  silver,  2AgO+C  HO  =Ag  -f- 
H04-2C02;  or  1  eq.  of  a  deutoxide,  such  as  that  of  mercury  ;  HgO^H-C^HO^ 
«Hg+H0  +  2C0^. 


COMPOUNDS  OF  FORMYLE  WITH  CHLORINE.  645 

Formic  acid  is  a  very  powerful  acid,  and  forms  salts  with  bases,  all  of  which 
are  soluble.  They  are  generally  similar  to  the  acetates;  but  yet  quite  distinct. 
Many  metallic  formiates,  when  heated  in  close  vessels,  give  off  carbonic  acid 
and  carbonic  oxide,  leaving  the  metal  reduced  :  others  give  off  carbonic  oxide, 
leaving  the  oxide. 

Formiate  of  ammonia,  NH^OjC^HO^,  contains  the  elements  of  hydrocyanic 
acid  and  water,  C  NH+4H0 ;  and  is  converted  into  these  compounds  when  its 
vapour  is  passed  through  a  red-hot  tube.  Formiate  of  oxide  of  eihyle,  prepared 
like  the  acetate,  is  a  volatile  ethereal  liquid,  with  a  peculiar  aromatic  smell.  The 
corresponding  salt  of  oxide  of  methyle  is  quite  analogous.  Formiate  of  potassa 
is  very  deliquescent.  Formiate  of  soda  is  also  very  soluble,  but  may  be  obtained 
in  crystals.  It  is  a  very  powerful  reducing  agent,  both  in  the  moist  and  dry  way. 
In  the  former,  it  reduces  the  noble  metals,  in  the  latter,  at  a  red  heat,  by  virtue 
of  the  carbonic  oxide  it  gives  off,  it  reduces  most  of  the  reducible  metals,  such 
as  lead,  copper,  antimony,  arsenic,  cobalt,  nickel,  &c.  Formiate  of  lead  is  spar- 
ingly soluble  in  cold  water,  and  is  therefore  easily  purified,  and  serves  to  prepare 
formic  acid  and  formiate  of  soda.  Formiate  of  deutoxide  of  mercury  and  formiate 
of  protoxide  of  mercury  both  exist.  When  red  oxide  of  mercury  is  dissolved  in 
cold  formic  acid,  the  former  salt  is  produced :  but  the  slightest  heat  causes  an 
effervescence,  while  formiate  of  the  protoxide  is  deposited  in  silvery  scales  like 
the  acetate.  These,  when  warmed,  are  decomposed  with  effervescence  and  de- 
position of  metallic  mercury.  Formiate  of  silver  resembles  the  acetate ;  but  is 
very  easily  decomposed  by  heat,  the  metal  being  reduced. 

COMPOUNDS  OF  FORMYLE  WITH  CHLORINE,  ETC. 

When  chlorine  or  hypochlorites  act  on  oxide  of  methyle,  hydrated  oxide  of 
methyle,  and  chloride  of  ethyle,  a  great  variety  of  new  compounds  are  produced, 
corresponding  in  most  cases  to  the  compounds  obtained  by  the  action  of  chlorine, 
&c.,  on  alcohol,  ether,  and  chloride  of  ethyle.  Our  space  forbids  us  to  give  the  de- 
tails of  these  decompositions;  but  we  may  mention  that  two  of  the  compounds 
formed  by  the  action  of  chlorine  on  the  compounds  of  ethyle  and  acetyle,  may  be 
viewed  as  protochloride  and  bichloride  offormyle.  These  are  C^H2Cl2=2(C2H,Cl) ; 
and  C^H2Cl^=3(C2H,Cl2).  The  perchloride  offormyle,  FoCl3=C^H,Cl3,  is  also 
produced  from  a  compound  of  the  ethyle  series,  namely  from  chloral,  by  the  ac- 
tion of  alkalies.  It  is  an  oily  liquid  of  a  sweet  taste  and  ethereal  smell.  When 
acted  on  by  alkalies,  it  yields  chlorides  and  formiates ;  thus,  with  potassa, 
C2HCl3t4KO=3KCl+KO,C3H03. 

When  acted  on  by  chlorine,  perchloride  of  formyle  yields  perchloride  of  car- 
bon C2Cl^=C2Cl,Cl3,  just  as  perchloride  of  acetyle,  C^H3,Cl3  yields  sesquichlo- 
ride  of  carbon  C  CI  =C  C!  .CI  . 

4        0  4        3  3  , 

Perbromide  offormyle  is  obtained  from  b»omal.  Period ide  of  formyle,  obtained 
by  the  action  of  alcohol  on  iodine  and  potassa,  is  a  yellow  crystalline,  volatile, 
solid,  having  an  odour  analogous  to  that  of  saffron. 

When  chlorine  acts  on  an  oxide  of  methyle,  C^H^O,  it  produces,  by  substitu- 

tion  of  chlorine  for  hydrogen,  the  compounds  C^  <  q?  O;  C^  ^  p,  O;  and  finally, 

C  CL,0.     The  second  may  be  considered  as  formic  acid,  C  HO,,  in  which  two- 

CO 
thirds  of  the  oxygen  are  replaced  by  chlorine,  C^H  j  p,  •     It  will  then   be  an 

^         2 

oxychl^'^^^®  of  formyle,  analogous  to  oxychloride  of  acetyle. 


646  CETYLE.    AMYLE. 

When  chlorine  acts  on  chloride  of  methyle,  C^^H^Cl,  three  compounds  are 
formed  by  substitution.    These  are,  1st,  (^^^^C\=C^  $  ^2,  Cl ;  2d,perchloride 

of  formyle,  0^11013=  C^  ]  C]  '^^'  ^^^  ^^'  ^®  ^^^^^^  explained,  perchloride  of 
carbon,  C2Cl^=rC2Cl3,Cl. 
V   The  action  of  chlorine  on  sulphuret  of  methyle,  C2H2,S,  appears  to  yield,  C^ 

The  action  of  chlorine  on  oxalate,  benzoate,  and  acetate  of  oxide  of  methyle 
is  quite  analogous  to  its  action  on  the  corresponding  compounds  of  ethyle,  pro- 
ducing- the  oxalate,  benzoate,  and  acetate  of  oxychloride  of  formyle,  C^O^-j-C^H 

5  Cl    »     ^14^.03'  +  ^fl   5  Cl    '     ^"^   ^4^3^3  +  ^3^   5  Cl         ^^^^^  '^""''"'  '^" 

suits,  like  those  which  precede  them,  are  here  merely  indicated,  as  we  have  ex- 
plained the  principle  of  their  formation  under  the  heads  of  ethyle  and  acetyle. 

In  some  specimens  of  raw  pyroxilic  spirit  there  occurs  a  large  proportion  of  a 
peculiar  volatile  liquid,  which  has  been  called  lignone  or  xylite.  As  its  consti- 
tution is  quite  uncertain,  although  it  is  believed  to  contain  some  compound  of 
oxide  of  methyle,  we  shall  state  what  is  known  of  it  when  treating  of  the  pro- 
ducts of  the  dry  distillation  of  wood. 

XXI.  Cetyle.    C32H33=Ct. 

This  is  the  hypothetical  radical  of  a  series  of  compounds,  derived  from  sperma- 
ceti. The  principal  one  is  ethal^  the  hydrated  oxide  of  cetyle,  analogous  to  alcohol. 

Hydrated  Oxide  of  Cetyle.    C32H3^0,HO=CtO,HO. 

Syn.  Ethal.  This  compound  exists  in  spermaceti,  in  combination  with  mar- 
garic  and  oleic  acids.  When  spermaceti  is  digested  with  strong  caustic  potassa, 
a  soap  is  produced  ;  and  this  being  decomposed  by  sulphuric  acid,  yields  a  fatty 
mixture,  composed  of  margaric  and  oleic  acids  and  ethal.  The  whole  is  acted  on 
by  baryta,  with  which  the  acids  unite;  and  the  ethal  is  dissolved  from  the  mix- 
ture by  cold  alcohol.     It  is  afterwards  purified  by  means  of  ether. 

Ethal  forms  a  white  crystalline  solid,  like  wax,  fusible  about  118°,  volatile  at 
a  higher  temperature,  soluble  in  alcohol.  As  above  mentioned,  it  is  analogoxis 
to  alcohol ;  and  although  the  oxide  of  cetyle  has  not  yet  been  obtained  in  a  sepa- 
rate form,  yet  there  have  been  formed  the  chloride  of  ctiyle,  and  the  double  sul- 
phate of  oxide  of  cetyle  and  potassa,  analogous  to  the  corresponding  compounds  of 
ethyle. 

When  ethal  is  repeatedly  distilled  with  anhydrous  phosphoric  acid,  it  loses 
the  elements  of  2  eq.  of  water,  yielding  a  new  compound,  cetene=C^2W33»  analo- 
gous to  olefiant  gas  or  etherine.     It  is  an  oily  inflammable  liquid. 

XXII.  Amyle.    C,oH„:fi=Ayl. 

This  is  the  hypothetical  radical  of  a  sejies  of  compounds,  derived  from  oil 
of  potato  spirit,  which  is  itself,  when  pure,  the  hydrated  oxide  of  amyle,  analo-- 
gous  to  alcohol.     Both  the  radical  and  its  anhydrous  oxide  are  unknown  in  the 
separate  state  :  bnt  a  sufficient  number  of  compounds  has  been  obtained  to  render 
its  existence  highly  probable. 


OXIDE  OF  AMYLE.    ••  647 

*»"       Hydrated  Oxide  of  Amyle.     C,oHnO,HO=Ay]0,HO. 

TABLE  OF  COMPOUNDS. 

Hydrated  Oxide  of  Amyle        ....  AylO,HO. 

Chloride  of  Amyle  .....  AylCl? 

Bromide        do.  .....  AylBr. 

Iodide  do.     ......  Ayll. 

Sulphamylic  Acid  .....  AylO,HO,2S03. 

Acetate  of  Oxide  of  Amyle  ....  AylO,Ac03. 

Hydrosulphuret  of  Sulphuret  of  Amyle  .  .  AylSjHS. 

Valerianic  Acid     ......  CjoHgOgjHO. 

Amilene  .  .  .  .  .  .  CiqHjq. 

Syn.  Oil  of  potato  spirit  i  in  German,  i^M3c/oe/.  This  compound  distils  over 
towards  the  end  of  the  first  distillation  of  spirits  made  from  potatoes,  rendering 
these  last  portions  of  the  spirit  milky  and  very  offensive.  It  separates  on  stand- 
ing as  an  oily  liquid,  w^hich  is  M^ashed  with  water  to  remove  alcohol,  dried  by 
chloride  of  calcium,  and  rectified  till  its  boiling  point  becomes  steady  at  269°  or 
270°.     It  is  then  pure. 

It  is  a  colourless  oily  liquid,  very  mobile,  of  a  strong  and  nauseous  odour, 
which  produces  stupefying  effects.  Its  vapour,  when  inhaled,  causes  cough  and 
spasmodic  dyspnoea,  resembling  asthma,  often  followed  by  vomiting.  Its  taste 
is  vciy  acrid  and  nauseous.  Its  sp.  gr.  is  0*812.  At  — 4°  it  crystallizes  in 
shining  scales.  When  heated  with  dry  hydrate  of  potassa  it  is  oxidized,  hydro- 
gen being  given  off,  and  the  potassa  is  found  combined  with  valerianic  acid, 
C^^Fi^Og.  When  distilled  with  anhydrous  phosphoric  acid,  it  yields  a  new  car- 
bohydrogen,  amilene,  =  C   H   . 

The  chloride  of  amyle  has  not  yet  been  obtained  ;  but  the  ftrowttZe  and  iodide  ^re 
formed  when  the  hydrated  oxide  is  distilled  along  with  phosphorus  and  bromine 
or  iodine.  They  are  both  heavy  oily  liquids,  and  their  formulae  are  AylBr.  and 
Ayll. 

The  hisulphate  of  oxide  of  amyle  or  sulphamilic  acid,  AylO,HO,2SOg,  is  analo- 
gous to  sulphovinic  acid.  With  bases,  it  forms  double  salts,  the  formula  of 
which  is  MO,AylO,2S02,  which  are  soluble  in  water  and  crystallizable.  The 
solutions,  when  boiled,  yield  hydrated  oxide  of  amyle,  free  sulphuric  acid,  anda 
neutral  sulphate. 

The  acetate  of  oxide  of  amyle  is  an  ethereal  liquid,  analogous  to  acetic  ether. 
Its  formula  is  (^,,^,fi^-=^G,o^,fl,CJ^P,==^y^OMO,- 

The  hydrosulphuret  of  sulphuret  of  amyle,  AylS,HS,  is  prepared  in  the  same 
way  as  mercaptan,  to  which  it  is  quite  analogous.  It  is  an  oily  liquid,  boiling 
at  243°,  of  sp.  gr.  0*835.  It  has,  like  the  corresponding  compounds  of  ethyle 
and  methyle,  a  most  penetrating  odour  of  onions ;  and  like  them,  it  acts  on  red 
oxide  of  mercury,  forming  a  white  crystalline  compound  AylS,HgS. 

The  sulphocarboiiate  of  oxide  of  amyle,  very  analogous  to  the  bisulphocarbonate 
of  oxide  of  ethyle,  is  formed  when  bisulphuret  of  carbon  acts  on  a  solution  of  po- 
tassa in  oil  of  potato  spirit. 

OXIDATION  OF  HYDRATED  OXIDE  OF  AMYLE. 

Valerianic  Acid.    CjoHgOgjHO. 

It  has  already  been  mentioned,  that  when  oil  of  potato  spirit  is  heated  with  dry 
hydrate  of  potassa,  hydrogen  is  given  off,  and  valerianate  of  potassa  is  formed. 


648  ^      ORGANIC  ACIDS. 

Here  the  oil,  C^^HjjO,HO,  loses  2  eq.  hydrogen,  and  gains  2  eq.  ox}'gen ;  so 
that  valerianic  acid  stands  to  amyle  in  the  same  relation  as  acetic  acid  to  ethyle, 
and  formic  acid  to  methyle.  The  acid  is  easily  separated  by  distilling  the  salt 
of  potassa  with  diluted  sulphuric  acid.  In  composition  and  in  all  its  properties, 
it  agrees  with  the  native  valerianic  acid,  obtained  by  distilling  the  root  of  Valeri- 
ana officinalis  with  water. 

Valerianic  acid  is  a  limpid,  oily  fluid,  of  a  disagreeable  and  peculiar  smell. 
Its  sp.  gr.  is  0-944,  and  it  boils  at  270°.  With  bases  it  forms  soluble  salts, 
which  have  a  sweet  taste. 

The  action  of  chlorine  on  hydrated  oxide  of  amyle  gives  rise  to  the  formation 
of  a  compound,  chloramilal.,  supposed  to  be  analogous  to  chloral,  but  the  compo- 
sition and  nature  of  which  are  not  fully  known. 

Amilene^  the  carbo-hydrogen  obtained  by  distilling  hydrated  oxide  of  amyle 
with  dry  phosphoric  acid,  has  the  formula  C^^H  ,  and  is,  like  cetene,  isomeric 
with  defiant  gas. 

XXIII.    Glvceryle.    C6H7=GI. 

This  is  the  hypothetical  radical  of  glycerine,  a  basic  compound  which  exists 
in  all  neutral  fat  oils  combined  with  oily  acids. 

Hydrated  Oxide  of  Glyceryle.    C6H706-|-H0=GlO6HO. 

'  Syn.  Glycerine.  To  obtain  it,  olive  oil  is  converted  into  plaster  by  long  boil- 
ing with  litharge  and  water.  When  the  plaster  is  completely  formed,  the  gly- 
cerine is  found  dissolved  in  the  water.  It  is  purified  from  lead  by  sulphuretted 
hydrogen,  and  is  then  concentrated  in  the  vapour  bath  and  finally  in  vacuo. 
When  pure,  it  forms  a  viscid  syrup,  colourless  or  slightly  yellow.  It  has  a  de- 
cided sweet  taste,  and  its  sp.  gr.  is  1-252.  By  the  action  of  heat  it  is  decom- 
posed, yielding  a  peculiar  volatile  compound,  acroleine,  which  attacks  the  eyes 
most  powerfully.  This  substance  has  lately  been  studied  by  Redtenbacher :  we 
shall  give  his  results  when  treating  of  the  action  of  heat  on  fat  oils. 

With  sulphuric  acid,  glycerine  forms  an  acid  sulphate,  C  H  O  ,H0,2S0  ; 
which  forms  double  salts,  analogous  to  the  sulphovinates,  the  formula  of  which 
is,  MO,GlO^,2S03. 

Having  now  briefly  described  the  known  or  admitted  organic  radicals  and  their 
derivatives,  we  proceed  to  consider  the  organic  acids  whose  composition  is 
known,  although  we  cannot  speak  with  certainty  of  their  constitution,  their  radi- 
cals being  yet  unknown. 

ORGANIC  ACIDS. 
1.  Citric  Acid.    C,2H50n,3HO=:"ci,3HO. 

This  acid  is  found  in  many  vegetable  juices,  especially  those  of  sour  fruits,  as 
the  lemon,  lime,  orange,  red  currant,  &c.  It  is  extracted  by  adding  chalk  to  the 
acid  juice,  by  which  means  an  insoluble  citrate  of  lime  is  formed.  This  is  de- 
composed by  diluted  sulphuric  acid  with  the  aid  of  heat,  and  the  solution,  filtered 
from  the  sulphate  of  lime,  gives  on  evaporation  and  cooling  crystals  of  citric 
acid,  consisting  of  clj  2H0-|-aq,  A  slight  excess  of  sulphuric  acid  promotes 
the  crystallization. 

It  forms  large  transparent  crystals,  very  soluble  in  water,  of  a  very  strong  and 


SALTS  OF  CITRIC  ACID.  649 

agpreeable  acid  taste.  A  diluted  solution  is  soon  decomposed,  becoming  mouldy. 
By  spontaneous  evaporation  of  a  saturated  solution,  crystals  may  be  obtained, 
which  are  Ci,3HO-|-2  aq.  At  212°,  these  lose  the  2  eq.  of  water  of  crystalliza- 
tion. The  other  crystals,  above  mentioned,  do  not  lose  water  at  212°,  but  melt 
at  256° ;  and  when  heated  beyond  300°,  both  kinds  are  decomposed.  Heated 
with  oil  of  vitriol  in  excess,  citric  acid  is  decomposed,  yielding 

•  From  1  eq.  citric  acid  .  ,  .        Cj2HgOj4 


2  eq.  carbonic  acid            .            .  ,  Cj      0^ 

2  eq.  carbonic  oxide                .  .          Cj      Oj 

2  eq.  acetic  acid    ...  Cg  HgOg 

2  eq.  water                   .            .  •              HjOg 


ClnHaO, 


In  like  manner,  when  fused  with  caustic  potassa,  citric  acid  is  resolved  into 
2  eq.  of  acetic  acid,  2  eq.  oxalic  acid,  and  2  eq.  water. 

When  citric  acid  is  added  to  lime  water,  the  liquid  remains  clear,  but  when 
heated  becomes  turbid,  and  deposits  citrate  of  lime.  This  character  serves  to 
distinguish  citric  acid  from  most  other  vegetable  acids. 

SALTS  OF  CITRIC  ACID. 

Oitrio  aciJ.  lo  tribaoio,  an<3  forms  three  scrics  of  neutral  salts,  that  is,  of  salts 
with  3  eq.  of  base,  whether  fixed  base  or  basic  water.  It  also  forms  basic  salts, 
of  the  formula  Ci,3M0+M0  or  ci,3M0  -|-  MO-}-aq.  These  basic  salts  corre- 
spond in  constitution  to  the  two  forms  of  crystallized  acid. 

When  a  drj'^  citrate,  with  3  eq.  of  fixed  base,  is  decomposed  by  an  alcoholic 
solution  of  hydrochloric  acid,  so  that  no  more  water  is  presented  to  the  citric 
acid  than  the  3  eq.  of  basic  water  derived  from  the  hydrogen  of  the  hydrochloric 
acid  and  the  oxygen  of  the  base,  there  are  formed,  from  3  eq.  dry  citric  acid,  2 
eq.  of  the  acid  with  2  eq.  of  water  of  crystallization,  and  3  eq.  of  the  hydrated 
aconiticacid.  3(^C^^Up^^,3HO)f:^2{C^liP^^,3KO-\-?iq.)-\-3{C^liO^,liO).  This 
is  the  same  change  which  takes  place  in  citric  acid  when  heated  to  a  certain 
point,  water  being  given  off. 

Citrate  of  Oxide  of  Ethyk,  c'i,3AeO,  is  an  oily  liquid  of  sp.  gr.  M42.  By  al- 
kalies it  is  converted  into  citrates  and  alcohol. 

Citrate  cf  Potassa  occurs  in  three  forms.     cljSKO  ;  Cl»  \    „„andcl  s    nxir\ 

All  are  very  soluble  and  crystallize  with  difficulty. 

0?7ra/e  of  A^of/a  also  forms  three  salts.  1.  ci,3NaO-|-ll  aq.  This  salt  forms 
large  regular  crystals.  2.  Ci,2NaO,HO  ;  formed  by  adding  to  a  solution  of  the 
preceding  salt  half  as  much  citric  as  it  already  contains.  It  forms,  by  evapora- 
tion, needles  of  a  very  pleasant  subacid  taste.  3.  Ci,NaO,2HO.  Formed  by 
adding  to  a  solution  of  No.  I,  as  much  citric  acid  as  it  already  contains.  This 
salt  does  not  crystallize  in  water,  but  forms  a  gummy  mass.  A  saturated  alco- 
holic solution,  however,  deposits  crystalline  grains.  Citrate  of  baryta  forms  two 
varieties.     1.  CiiSBaO-f?  aq.  which  falls  when  citrate  of  soda  is  added  to  chlo- 

ride  of  barium.     2.  2Ci  j    ^^^  +7  aq.==Ci  J    j^j^ -f  Ci,3BaO+7  aq.     This  ia 

deposited  on  cooling,  when  a  boiling  solution  of  citrate  of  soda  is  added  to  a 


650  ACONITIC  ACID. 

"boiling  solution  of  chloride  of  barium  and  free  citric  acid.  Citrate  of  lime  also 
yields  two  salts.  1,  neutral,  Ci,3CaO+4  aq.  formed  by  mixing  chloride  of  cal- 
cium and  citrate  of  soda.  It  is  insoluble.  2,  basic  :  ci,3CaO  -|-  CaO  -|-aq.  formed 
when  citric  acid  is  heated  with  excess  of  lime  water.  The  citrate  of  lime  formed 
from  lemon,  or  currant  juice,  by  chalk,  is  an  impure  mixture  of  the  basic  and 
neutral  s^ts.  Citrates  of  lead,  1,  Ci,3PbO+aq.  2,  Ci,2PbO,H04-2  aq.:  3, 
basic:  Ci,3PbO+3PbO :  4,  also  basic.  CiiSPbOfPbO+aq.  These  are  all 
sparingly  soluble  or  insoluble,  aild  are  decomposed  by  washing.  Citrate  of  cop- 
per is  basic,  Ci,3CuOf  CuO.  Citrate  rf  silver  is  a  brilliant  white,  insoluble 
powder.  Ci,3 AgO-haq.  It-  loses  its  water  under  80°.  Citrate  of  antimony  and 
potassa  is  a  double  salt,  CijSb^O^f  Oi,3KO+5  aq.  It  forms  hard,  brilliant,  while 
prisms,  which  lose  their  water  at  212°. 

ACTION  OF  HEAT  ON  CITRIC  ACID. 

The  first  effect  of  heal  on  crystallized  citric  acid  is  to  melt  it,  and  the  next,  to 
expel  the  water  of  crystallization.  The  acid,  if  now  dissolved,  crystallizes  un- 
changed. But  if  the  heat  be  continued,  there  is  given  off  gas  and  inflammable 
vapours,  and  the  residue  is  no  longer  citric  acid  but  hydrated  aconitic  acid. 

1  eq.  crystallized  citric  acid  CjgHg  -\-  0,,3H0  -}-  2aq. 


ields,  first, — 5  eq.  of  water 

then —         1  eq.  aconitJo  acid  (liydraied] 

C4  H2U4 

4  eq.  carbonic  oxide      . 

C4      0, 

1  eq.  acetone         . 

.        C3H3O 

1  eq.  carbonic  acid 

C        O2 

3H0  +  2  aq. 


C^HgOn  -f-  3H0  -f-  2  aq. 


When  the  heat  is  increased,  other  products  appear,  particularly  two  new  acids  : 
but  these  are  derived  from  aconitic  acid.     They  are  itaconic  and  citraconic  acids, 

Aconitic  Acid.    C^HOgjHO  =  Xt 

Syn.  Equisetic  Acid. — This  acid  occurs  native  in  aeoniiuvi  napellus  and  in 
equisetum  Jluviatile,  It  is  formed  by  the  action  of  heal  on  citric  acid,  as  above. 
To  obtain  it,  citric  acid  is  heated  till  it  ceases  to  give  off  inflammable  vapours, 
and  the  residue,  dissolved  in  alcohol,  islreated  with  hydrochloric  acid  gas,  which 
causes  the  formation  of  aconitic  ether.  The  addition  of  water  causes  this  to 
separate,  and  by  caustic  potassa  it  is  converted  into  aconitate  of  potassa.  From 
this  aconitate  of  lead  is  prepared,  and  this  salt,  decomposed  by  sulphuretted 
hydrogen,  yields  the  acid. 

It  forms  indistinct  crystals  ;  and  although  the  acid  thus  prepared  has  the  same 
composition  as  that  from  aconite,  and  that  from  equisetum,  yet  each  of  the  three 
varieties  has  some  peculiarities.  They  may  not,  therefore,  be  identical,  especi- 
ally as  two  acids  derived  from  malic  acid,  the  maleic  and  paramaleic,  o^fumaric 
acids,  have  the  same  composition.  The  aconitic  acid  from  citric  acid,  when 
heated,  yields  itaconic  and  citraconic  acids:  it  is  doubtful,  at  present,  whether 
the  other  two  varieties  do  so. 

Aconitic  acid,  according  to  the  present  state  of  our  knowledge,  is  monobasic, 
and  the  general  formula  of  its  salts  is  AtjMO.     The  aconitates  are  not  important. 


TARTARIC  ACID.  651 

When  aconitic  acid  (from  citric  acid)  is  heated  to  from  356'^  to  392°,  it  boils 
and  yields  a  mixture  of  two  acids;  itaconic  acid,  which  condenses  in  crystals, 
and  citraconic  acid,  which  appears  as  an  oily  liquid.  When  the  distillation  is 
very  rapid,  itaconic  acid  predominates;  when  it  is  slow,  there  is  more  citraconic 
acid.     These  two  acids  have  both  the  formula  C^Hp^.HO. 

Itaconic  acid  is  readily  purified  by  solution  in  hot  water,  as  it  crystallizes  with 
great  facility.  It  is  soluble  in  water,  alcohol,  and  ether.  When  heated  it  is 
resolved  into  water  and  anhydrous  citraconic  acid.  It  is  a  monobasic  acid,  and 
its  formula  is  Cflfi^,llO  =  It;HO.  The  formula  of  its  salts  is  it,  MO.  It  also 
forms  acid  salts,  the  formula  of  which  is  2  ItjMO,HO.  The  itaconates  are  not 
of  special  interest. 

Citraconic  acid  is  formed  when  the  preceding  acid  is  distilled,  and  then 
appears,  in  the  anhydrous  state,  as  a  limpid  oily  liquid.  It  distils  unaltered  at 
410°,  and  volatilizes  slowly  at  much  lower  temperatures.  It  attracts  moisture 
from  the  air,  forming  a  crystalline  hydrate,  which,  when  heated,  is  again  resolved 
into  water  and  anhydrous  acid.  The  formula  of  the  anhydrous  acid  is  C^H^Og 
=  C7;  that  of  the  hydrate  cr,HO.  It  forms,  like  the  preceding,  both  neutral 
and  acid  salts;  and  produces,  with  oxide  of  silver,  a  neutral  salt  with  water  of 
crj-stallization;  an  apparently  anomalous  case.  The  formation  of  these  two 
acids  takes  place  as  follows- — 3  eq.  of  aconitic  acid,  3  (C^H^OJ  yield  2  eq. 
itaconic  acid,  2  {Q^Hfi^.YiO),  and  2  eq.  carbonic  acid,  2CO2.  The  itaconic 
acid,  when  formed,  is  partially  resolved  into  water  and  anhydrous  citraconic  acid. 

The  three  acids  just  described,  aconitic,  itaconic,  and  citraconic  acids,  require 
further  investigation.  It  is  probable  that  it  will  be  found  that  they  are  not  all 
monobasic.  The  existence  of  water  of  crystallization  in  the  neutral  citraconate 
of  silver  is  a  most  unusual  circumstance,  and  would  seem  to  indicate  that  we  do 
not  yet  know  the  constitution  of  the  acid  in  that  salt. 


2.  Tartaric  Acid.    C8H40io,2HO  =  T,2H0. 

This  acid  occurs  in  the  juice  of  the  grape  as  acid  tartrate  of  potassa ;  also  in 
many  other  plants.  It  is  prepared  from  tartrate  of  lime,  exactly  as  citric  acid  is 
from  citrate  of  lime.  Tartrate  of  lime  is  obtained  by  the  action  of  chalk  on  acid 
tartrate  of  potash,  or  cream  of  tartar. 

Tartaric  acid  crystallizes  in  large  rhombic  prisms,  transparent  and  colourless. 
They  are  very  soluble  in  water,  and  have  a  pleasant  acid  taste.  When  boiled 
with  alcohol,  tartaric  acid  forms  acid  tartrate  of  oxide  of  ethyle.  A  high  tem- 
perature decomposes  tartaric  acid,  giving  rise  to  several  new  products. 

An  excess  of  potassa  aided  by  heat,  transforms  it  into  acetate  and  oxalate  of 
potassa.  CgH^0j^,2H0  =  C^H303,HO  +  2  (C203,HO).  By  peroxide  of  man- 
ganese and  sulphuric  acid  it  is  converted  into  formic  acid,  carbonic  acid,  and 
other  products.  There  is  some  relation  between  tartaric  and  formic  acids :  for 
if  formic  acid  be  FoO^  (Fo  =  C^H),  tartaric  acid  is  2  (Fo^O^). 

Tartaric  acid  precipitates  lime-water  white,  but  an  excess  dissolves  the  pre- 
cipitate. In  solution  of  potassa,  if  the  acid  be  added  in  excess,  it  causes  a  crys- 
talline deposit  of  cream  of  tartar,  which,  where  the  potassa  is  in  very  minute 
proportion,  is  rendered  more  visible  by  the  addition  of  alcohol. 

It  is  a  bihasic  acid,  and  forms  two  series  of  salts:  1.  Neutral  T\2M0 ;  2. 
acid,  T  MO,HO.     It  forms  also  two  kinds  of  double  salts:  in  one  the  2  eq.  of 


652  TARTRATE  OF  POTASSA  AND  ANTIMONY. 

fixed  base  are  different  protoxides,  T^j     n  *  ^°  ^^®  other,   one   of  the  equiva- 

C  MO 

lents  of  fixed  base  is  replaced  by  1  eq.  of  a  sesquioxide  ;  T,  ^  -^  .  This  lat- 
ter kind  may  be  considered  basic,  since  the  sesquioxide,  012^31  usually  neutra- 
lizes as  much  acid  as  3  eq.  of  protoxide.  Tartaric  acid  is  remarkable  for  its 
tendency  to  form  double  salts. 

Among  the  neutral  tartrates  are,  tartrate  of  ammonia  Tr,2NH  O  -f-  2  aq.  ;  tar- 
trate of  potassa,  or  soluble  tartar,  t'jSKO  ;  tartrate  of  aoda^  T,2NaO  -|-  4  aq. ; 
tartrate  of  lime,  T,2CaO  -f  8  aq.,  &c.  &c. 

Among  the  acid  salts  are,  acid  tartrate  of  ethyle,  or  tartrovinic  acid  T,AeO,HO — 
a  crystallizable  compound  :  acid  tartrate  of  potassa,  or  tartar,  I^KO,HO.  This 
is  the  principal  compound  of  tartaric  acid.  It  exists  in  the  juice  of  the  grape, 
dissolved  by  the  acid  of  the  sugar  present,  and  when  that  sugar  is  converted  into 
alcohol,  in  which  the  tartar  is  insoluble,  it  is  deposited  on  the  sides  of  the  fer- 
menting casks.  When  purified  it  is  quite  white,  and  is  called  cream  of  tartar. 
It  is  much  used  in  medicine  as  a  safe  and  mild  laxative.  When  calcined  in  a 
covered  crucible  it  leaves  a  mixture  of  carbonate  of  potassa  and  charcoal,  called 
black  flux.  Hence  carbonate  of  potassa  is  called  salt  of  tartar.  Like  all  the 
tartrates,  cream  of  tartar,  when  heated,  gives  oflf  a  very  peculiar  smell  of  burnt 
vegetable  matter,  peculiar  to  tartaric  and  racemic  acids  and  their  salts. 

Among  the  very  numerous  double  tartrates  may  be  mentioned  the  tartrate  of 
potassa  and  ammonia^  T,KO,NH^O  :  the  tartrate  of  potassa  and  oxide  of  ethyle^  T, 
AeO,KO;  tartrate  of  potassa  and  boracic  acid,  T,KO,BO^;  this  is  the  soluble 
cream  of  tartar  used  as  a  laxative  on  the  continent : — tartrate  of  potassa  and  soda, 
T,KO,NaO  -j-  10  aq.  This  is  the  salt  of  Seignette  or  Rochelle  salt.  It  crys- 
tallizes in  very  large  transparent  prisms,  and  is  used  as  a  mild  laxative : — tav 
irate  of  potassa  and  peroxide  of  iron;  TJKO,Fe  O  ;  this  is  the  tartarized  iron  of 
the  pharmacopoeias : — tartrate  of  potassa  and  antimony,  l\KO,Sb  O  .  This  is 
tartar  emetic,  one  of  the  most  valuable  remedies.  It  must  be  considered  as  a 
basic  salt;  for  Sb  O  ,  here  substituted  for  HO  or  KO,  in  short  for  a  protoxide, 
requires  for  its  neutralization  an  additional  equivalent  of  tartaric  acid.     It  then 

_        C  KO 

yields  the  compound  2  T  +  J  ol  ri    which  is  neutral,  since  the  bases  contain 

4  eq.  of  oxygen  for  2  eq.  of  acid. 

Tartar  emetic  is  formed  when  3  parts  of  oxide  of  antimony  and  4  of  cream  of 
tartar  are  ground  together,  and  made  into  a  thin  cream  with  water,  which  is 
heated  to  158°,  till  a  portion,  tried  separately,  dissolves  in  15  parts  of  cold  water. 
When  this  is  the  case,  6  or  8  parts  of  water  are  added,  and  the  whole  boiled  for 
half  an  hour.  The  liquid,  filtered  while  hot,  deposits,  on  cooling,  crystals  of 
tartar  emetic.  It  forms  white  brilliant  crystals  which  soon  become  opaque.  It 
is  soluble  in  14  or  15  parts  of  cold  water,  and  2  parts  of  boiling  water.  The  crys- 
tals are  T,  KO,  Sb203,-|-2  aq. 

When  heated,  the  crystals  first  lose  the  2  eq.  of  water  of  crystallization  ;  and 
when  the  heat  rises  to  390°,  2  or  more  eq.  df  water  are  given  off,  without  the 

C  HO 

acid  being  destroyed.     The  salt  is  then  CgH^Oj^j-f  <  g,  ^.       That  is  to  say,  2 

eq.  of  oxygen,  from  the  oxide  of  antimony,  have  been  expelled  along  with  2  of 
hydrogen  from  the  acid.    It  has  been  already  shown  that  tartar  emetic  O^Ufi^^ 


TARTRALIC  ACID.      •  653 

C  TCO 

"^    /  Sh  O   ^^"^^''"^  ^  ^^'  °^  oxygen  in  the  bases,  more  than  is  required  for  a 

^         2     3 

neutral  salt,  and  it  is  apparently  these  2  eq.  of  oxygen  which  are  thus  expelled 
as  w'ater.  If  we  bear  in  mind  that  Sb^O^  is  the  equivalent  of  3K0  ;  or  in  other 
Words,  that  Sb|  is  equivalent  to  K  or  to  H,  we  can  then  see  that  tartar  emetic 
heated  to  390°  is  analogous  in  composition  to  neutral  tartrate  of  potash. 

Tartrate  of  potassa  is  .         .         .        .        Cg     H^  0^  +  Kj 

Tartar  emetic,  heated  to  390"  is,        .        .        Cg  S  ?i?40,2  +  K  ^ 

V       3  3 

In  this  point  of  view  the  2Sb  are  divided,  |Sb  replacing  hydrogen  in  the  radi- 
cal, and  |Sb  replacing  potassium  in  the  base. 

—    C  KO 

The  neutral  tartrate  of  potassa  and  antimony,  2T,  <   ou  n    +  7  aq.  is  always 

V.  2     3 

formed  in  the  mother  liquors  of  tartar  emetic.  It  is  also  formed  when  tartar 
emetic  is  dissolved  in  tartaric  acid. 

Tartar  emetic  forms  a  double  salt  with  cream  of  tartar,  T,K0,Sb20^  -f-  3(T, 
KO,HO).     It  crystallizes  in  scales. 

ACTION  OF  HEAT  ON  TARTARIC  ACID. 

When  crystallized  tartaric  acid  is  heated  it  melts,  then  loses  \  of  its  water, 
leaving  a  new  acid,  tartralic  acid  ;  next  it  loses  ^  its  water,  and  is  converted  into 
tartrelic  acid  ;  and  finally  it  loses  all  its  water  and  is  converted  into  anhydrous 
tartaric  acid.  We  may  represent  these  changes  as  follows,  doubling  the  formula 
of  tartaric  acid. 

CieHgO20-J-4HO  =  crystallized  tartaric  acid. 
^leHgOao  +  3H0  =  tartralic  acid. 
CigHgOgo  -f-  2H0  =  tartrelic  acid. 
CigHgOjQ  =  anhydrous  tartaric  acid. 

In  tartralic  and  tartrelic  acids,  the  neutralizing  power  is  diminished,  in  so  far 
that  tartralic  acid  neutralizes  |th  less  base,  and  tartrelic  acid  |  less  base  than 
tartaric  acid.  Both  of  these  acids,  as  well  as  the  anhydrous  acid,  are,  by  long 
boiling  with  water,  reconverted  into  tartaric  acid.  It  would  appear  as  if  in  the 
tartralic  and  tartrelic  acids,  an  additional  quantity  of  anhydrous  acid  has  been 
added  to  the  radical  without  affecting  the  neutralizing  power,  just  as  in  phos- 
phoric, pyrophosphoric,  and  iMlaphosphoric  acids.  If  we  represent  the  anhy- 
drous acid  by  C^H^O^,  then  we  have 

2(C4H205)  -f-  2H0  =  crystallized  acid. 
SCCjHjOs)  4-  2H0  =  tartralic  acid. 
4(C4H205)  +  2H0  =  tartrelic  acid. 

When  tartaric  acid,  or  rather  anhydrous  tartaric  acid,  is  more  strongly  heated, 
it  yields  two  pyrogenous  acids,  one  liquid,  the  other  crystallized.  The  former, 
CgH^O^,HO,  the  latter,  CjH^O^,HO.  In  fact,  2  eq.  of  anhydrous  tartaric  acid 
contain  the  elements  of  1  eq.  of  each  of  these  new  acids,  5  eq.  of  carbonic  acid, 
and  2  eq.  of  water.  The  liquid  acid  is  called  pyroracemic  acid,  being  obtained 
also  from  racemic  acid :  the  solid  acid  may  be  called  pyrotartaric  acid. 

Tartralic  acid,  C^^HgO^,2HO,  is  obtained  by  cautiously  heating  tartaric  acid, 


654  •       RACEMIC  ACID. 

taking  care  not  to  cause  it  to  become  brown.  It  is  combined  with  baryta,  and 
the  baryta  separated  from  the  soluble  tartralate  by  dilated  sulphuric  acid.  Tar- 
tralic  acid  forms  a  transparent  mass,  not  crystalline,  deliquescent  and  soluble  in 
alcohol.  It  is  converted  into  tartaric  acid,  slowly  by  cold  water,  rapidly  by  hot 
water.  It  appears  to  be  bibasic,  and  most  of  its  salts  are  soluble.  By  long 
contact  with  water,  they  are  converted  into  tartrates  and  free  tartaric  acid. 

Tarirelic  acid,  C^^HgO  ,2H0,  is  obtained  by  keeping'  the  preceding  acid  long 
melted  without  raising  the  temperature.  It  is  coloured  brown,  is  deliquescent, 
and  dissolves  both  in  water  and  alcohol.  Water  rapidly  changes  it  into  tartralic 
and  tartaric  acids.  Its  salts  are  soluble,  and  undergo  the  same  change  as  those 
of  tartralic  acid. 

Anhydrous  tartaric  acid,  ^4^2^^'  ^^  pT^pared  by  rapidly  heating  ^  oz.  of  tar- 
taric acid  in  a  porcelain  capsule.  It  swells  up  very  much,  gives  off  water,  and 
is  at  last  converted  into  a  porous  white  mass.  This  is  now  heated  for  some  time, 
in  an  oil-bath,  to  a  temperature  of  302°,  then  powdered  and  well-washed  with 
cold  water,  and  dried.  It  forms  a  white  powder  insoluble  in  water,  alcohol,  and 
ether.  By  the  action  of  water  and  bases  it  is  converted  successively  into  tar- 
trelic  and  tartaric  acids. — Pyroracemic  acid;  or  liquid pyrotariaric  acid,  C  H  O  , 
HO  =  pR,HO,  is  one  of  the  products  of  the  distillation  of  tartaric  and  racemic 
acids.  It  is  separated  from  the  crystals  which  accompany  it,  combined  with 
oxide  of  lead,  and  the  well-washed  pyrotartrate  of  lead  decomposed  by  sulphur- 
etted hydrogen.  It  is  concentrated  in  vacuo,  and  forms  a  thick  syrup  nearly 
colourless,  which  cannot  be  distilled  without  partial  decomposition.  Its  salts  are 
not  easily  obtained  in  crystals,  and  when  their  solutions  are  heated,  they  lose  the 
power  of  crystallizing.  The  general  formula  of  the  pyroracemates  is  C  H  O  , 
MO.  They  are  coloured  dark-red  by  salts  of  protoxide  of  iron,  and  a  crystal  of 
sulphate  of  copper  introduced  into  the  solution  of  a  pyroracemate  causes  a  white 
precipitate.  Pyroracemate  of  oxide  of  ethyle  is  a  colourless  liquid,  of  an  aro- 
matic smell,  resembling  that  of  acorus. 

Pyrotartaric  acid,  C^H^O  ,H0  =  pT,HO,  is  formed  along  with  the  preceding 
acid  in  small  quantity  by  the  distillation  of  tartaric  acid ;  it  is  obtained  far  more 
abundantly  by  the  distillation  of  cream  of  tartar.  The  product  of  the  distilla- 
tion, which  is  liquid,  is  evaporated  till  it  crystallizes,  and  the  mother  liquid, 
acted  on  by  nitric  acid  to  destroy  the  oily  impurities,  and  again  evaporated,  yields 
an  additional  quantity.  The  crystals  melt  at  230°  and  volatilizes  at  from  284° 
to  300°.  The  salts  of  this  acid  are  soluble,  that  of  lead  appears  to  be  rather 
sparingly  so.  But  the  results  of  different  experimenters  on  this  subject  are  so 
discordant  that  we  must  wait  for  further  researci^*3. 

3.    Racemic  Acid.    C^HjOgjHO  =  rjHO. 

Stn.  Paraiariaric  acid. — This  remarkable  acid,  which  has  the  same  composi- 
tion in  100  parts  as  tartaric  acid,  and  very  similar  properties,  is  found  along 
with  tartaric  acid  in  the  grapes  of  certain  districts.  When  both  acids  are  pre- 
sent, the  liquid  obtained  by  boiling  the  tartrate  and  raceraate  of  lime  with  diluted 
sulphuric  acid  deposits,  on  evaporation,  racemic  acid  in  hard  crystalline  crusts, 
before  tartaric  acid,  which  is  more  soluble,  begins  to  crystallize.  It  may  be 
distinguished  from  tartaric  acid  by  not  forming  a  double  salt  of  potassa  and  soda. 

The  crystals  of  the  racemic  acid  have  a  very  sour  taste,  and  are  composed  of 
R,HO  -|-  aq.     At  212°  they  lose  the  I  eq.  of  water  of  crystallization,  and  when 


MALIC  ACID.  655 

more  strong-ly  heated,  yield  the  same  products  as  tartaric  acid.  The  solution  of 
racemic  acid  forms  a  precipitate  of  racemate  of  lime  when  mixed  with  chloride 
of  calcium,  which  serves  to  distinguish  it  from  tartaric  acid ;  but  like  tartaric 
acid,  it  causes  a  crystalline  precipitate  in  the  salts  of  potassa. 

Racemic  acid  is  monobasic,  and  for  this  reason  does  not,  like  tartaric  acid, 
form  double  salts  with  two  strong  bases.  It  forms  neutral  salts,  R,MO,  and  acid 
salts,  R,MO  -f-  R,HO.  Thus  the  neutral  racemate  of  potassa  is  R,KO  -j-  2  aq., 
and  the  acid  racemate  of  potassa,  analogous  to  cream  of  tartar,  is  R,KO  -\-  R, 
HO.  These  two  salts,  therefore,  have  precisely  the  same  composition  as  the 
corresponding  tartrates.  The  acid  racemate  of  potassa,  with  oxide  of  antimony, 
yields  a  double  salt  analogous  to  tartar  emetic,  but  of  a  different  crystalline  form. 
The  relations  of  racemic  acid  to  the  oxides  of  ethyle  and  methyle  are  similar  to 
those  of  tartaric  acid.  On  the  whole,  racemic  acid  is  interesting,  from  its  pre- 
senting one  of  the  best  marked  cases  of  isomerism,  namely,  with  tartaric  acid. 
In  this  case,  not  only  is  the  composition  the  same,  but  the  general  properties, 
and  most  of  the  special  ones,  are  identical.  In  fact,  were  it  not  that  we  must 
admit  tartaric  acid  to  be  bibasic,  we  should  find  it  difficult  to  account  for  the 
differences  which  exist  between  the  two  a«ids.  We  have  here  a  very  near 
approach  to  the  occurrence  of  different  properties  with  the  same  composition, 
and  even  the  same  arrangement.     The  two  acid  salts  of  potassa,  for  example, 

C  KO 

are   C  H  O,^    >  ^^  for  the  bitartrate :  and  C  H  O  .KO  f  C  H  O  .HO  for  the 

o      4      Xxj       J   1^  yj  4      2      3  4      2      d 

bicarcemate.     If  we  represent  the  latter  as  follows : 

C  H  O,  C  KO  ^  ,      ,.,      , 

p  rr  r\   j  tt/-)^  ^6  scc  how  vcTy  nearly  alike  they 

4      2     5   ' 

are,  even  on  the  view  we  have  adopted  of  the  one  acid  being  bibasic,  and  the 
other  monobasic  ;  and  we  must  bear  in  mind  that  these  two  salts  are  strikingly 
similar  in  properties.  The  same  remarks  apply  to  the  crystallized  acids  and  to 
the  double  salts  with  antimony,  although  in  the  case  of  the  two  acids,  we  havo 
evidence  of  one  point  of  difference  in  the  arrangement.  Tartaric  acid  is  O^H^ 
Oj^,2HO,  while  racemic  acid  is  C^H20^,HO  H-aq.,  and  loses  the  water  of  crys- 
tallization at  212°. 

r'  4.    Malic  Acid.    C8H408,2HO  =  m,2H0. 

This  acid  is  of  very  frequent  occurrence  in  acid  fruits,  as  in  the  apple,  and 
especially  in  the  unripe  berries  of  Sorbus  aucuparia,  or  mountain  ash.  The  best 
method  of  extracting  it  is  to  express  the  berries  when  they  begin  to  turn  red,  and 
to  add  to  the  strained  liquid  a  thin  milk  of  lime  so  as  not  entirely  to  neutralize 
the  acid.  On  heating,  neutral  malate  of  lime  is  deposited  and  removed  by  a 
skimmer.  To  the  mother  liquid  more  milk  of  lime  is  added  cautiously,  so  as  to 
produce  an  additional  quantity  of  salt.  The  malate  of  lime  is  washed  with  cold 
water,  and  dissolved  with  the  aid  of  heat  in  a  mixture  of  1  part  nitric  acid,  and 
10  of  water.  On  cooling,  acid  malate  of  lime  is  deposited  in  regular  crystals, 
which  are  almost  always  colourless.  They  are  rendered  quite  pure  by  a  solution 
in  hot  water  and  crystallization.  From  this  salt,  by  the  addition  of  acetate  of 
lead,  malate  of  lead  is  precipitated  as  a  curdy  white  solid,  which,  if  left  in  the 
liquid,  changes  into  shining  silky  crystals.  These,  which  are  pure  malate  of 
lead,  being  decomposed  by  sulphuretted  hydrogen,  yield  the  acid,  which  when 
evaporated  to  a  syrup  forms  a  granular  crystalline  mass,  deliquescent  in  the  air, 
of  a  strong  but  agreeable  acid  taste.     When  the  crystallized  acid  is  kept  for 


I 


656  FUMARIC  ACID. 

some  time  at  a  heat  of  280°  it  melts,  and  the  melted  acid  is  ^dually  filled  with 
crystals.  Cold  water  removes  the  unchanged  malic  acid,  which  if  again  heated 
undergoes  the  same  change,  till  at  length  gill  the  malic  acid  is  converted  into 
these  crystals,  which  are  paramaleic  or  fumaric  acid. 

If  malic  acid  be  distilled  by  a  sharp  heat,  a  great  part  passes  over  in  the  form 
of  a  volatile  crystallizable  acid,  the  maleic  acid.  At  a  certain  period  of  the  dis- 
tillation, if  the  retort  be  removed  from  the  fire,  the  boiling  residue  having  become 
turbid  and  thick,  it  suddenly  becomes  quite  solid,  and  is  found  to  consist  of 
fumaric  acid. 

Malic  acid  is  bibasic ;  in  proof  of  which,  it  forms  acid  salts  with  lime,  mag- 
nesia, and  oxide  of  zinc,  which  monobasic  acids  never  do.  There  are  two  series 
ofmalates:  1.  neutral,  M,2M0  ;  2.  acid  M,MO,HO.  Most  of  the  malates  are 
soluble  in  water,  but  not  in  alcohol.  Lime  water  neutralized  by  malic  acid, 
continues  clear  whether  cold  or  hot,  which  serves  to  distinguish  it  from  tartaric, 
citric,  racemic  and  oxalic  acids. 

Acid  malatt  of  ammonia,  M,NHJiO,  is  best  formed  by  neutralizing  with  am- 
monia one  of  two  equal  portions  of  malic  acid  (as  prepared  from  the  crude  malate 
of  lead  by  diluted  sulphuric  acid),  and  then  adding  the  other  portion  and  evapo- 
rating to  a  syrup.  On  cooling,  large  and  very  regular  crystals  of  the  acid  salt 
are  deposited,  which  are  easily  decolorized  by  animal  charcoal.  This  is  an 
excellent  method  of  purifying  malic  acid,  when  it  is  much  contaminated  with 
other  substances.  Acid  malate  of  /meM,CaO,HO  -f  6  aq.,  is  prepared  as  above 
described.  It  forms  very  regular  and  pure  crystals,  soluble  in  their  own  weight 
of  boiling  water,  but  requiring  20  parts  of  cold  water.  When  malic  acid  is 
saturated  with  chalk,  an  acid  liquid  is  obtained,  which,  when  boiled,  deposits 
the  neutral  malate  of  lime,  M,2CaO.  The  malate  of  lead  M,2PbO  -|-  6  aq.  is 
remarkable  for  changing  when  left  in  the  liquid  in  which  it  has  been  formed, 
from  a  curdy  white  precipitate  to  a  mass  of  fine  silky  needles.  In  hot  water 
this  salt  melts  into  a  mass  like  pitch  in  consistence.  Acid  malate  of  copper,  M, 
CuO,HO  -\-  2  aq.  forms  splendid  large  crystals  of  a  fine  cobalt  blue  colour. 
There  appears  to  be  a  basic  malate  of  copper,  M,2CuO  -}-  CuO  -f-  6  aq.,  which 
forms  green  crystals,  Malate  of  silver,  M,2AgO  is  a  while  powder,  soluble  in 
boiling  water.  The  other  malates  are  analogous  to  these,  and  possess  little 
interest. 

Maleic  Acid,  C^jd^,'iViO  =  Ma,2H0,  is  prepared  as  above  mentioned,  by 
distilling  malic  acid.  This  acid  is  bibasic,  but  has  the  same  composition,  in  100 
pans,  as  aconitic,  or  equisetic  acid.  It  forms  crystals,  which  are  very  soluble  in 
water,  alcohol,  and  ether.  When  heated  sharply,  it  yields  water,  and  a  white 
volatile  solid,  melting  at  134°,  and  boiling  at  350°,  which  appears  to  be  anhy- 
drous maleic  acid.  When  the  hydrated  acid  is  kept  melted  for  some  time,  it  is 
changed,  exactly  as  malic  acid  is,  into  furAaric  acid.  Hydrated  maleic  acid  has 
precisely  the  same  composition  as  anhydrous  malic  acid,  which  at  once  explains 
its  formation. 

The  general  formula  of  its  salts  is  Ma,2M0  for  the  neutral,  and  Ma,MO,HO 
for  the  acid  maleales.     It  forms  an  acid  maleate  of  silver,  Ma,4gO,HO. 

Fumaric  or  Paramaleic  Acid,  C^HO^,HO  =  Fu.HO,  is  formed  as  above 
stated,  by  heating  either  malic  or  maleic  acids  to  their  melting-point,  and  keep- 
ing them  melted  for  along  time.  It  occurs  in  fuTnaria officinalis,  and  in  Iceland 
moss.  It  forms  micaceous  scales  requiring  200  parts  of  cold  water  for  solution. 
It  is  soluble  in  alcohol. 


TANNIC  ACID.  657 

It  is  a  monobasic  acid,  but  has  the  same  composition  in  100  parts  as  maleic 
acid,  which  at  once  explains  its  formation  from  malic,  or  from  maleic  acid.  Its 
salts  are  sparinorly  soluble.  The  fumarate  of  oxide  of  elhyle  is  a  heavy  oily 
liquid  of  an  aromatic  smell  of  fruits.  When  this  ether,  Fu,AeO,  is  acted  on  by 
aqua  ammoniae,  it  forms  a  white  insoluble  powder,  which  is  funiar amide  C^HO^ 
-f-  NH  .     This  body  has  all  the  characters  of  a  compound  amide. 

5.  Tannic  Acid.     CigHjOgjSHO  =  Qr,3H0. 

Syn,   Quercifannic  Acid.     Tannine.     This  acid  occurs  chiefly  in  oak-bark  and 
in  nut-galls,  an  excrescence  on  oak-leaves   caused  by  the 
attacks   of  an  insect  which  apparently  pierces  the  leaf  in 
order  to  deposit  its  egs^s, 

To  obtain  it,  coarsely-powdered  nut-galls  are  acted  on, 
in  an  apparatus  of  displacement  by  ether,  free  from  alcohol, 
but  saturated  with  water.  When  the  ether,  after  being  left 
some  time  in  contact  with  the  powder,  is  allowed  to  drop 
into  the  lower  vessel,  it  separates  into  two  strata  of  liquid, 
the  lower  of  which  is  a  pure  solution  of  tannic  acid  in 
water,  which  is  drawn  off  and  dried  up  after  being  washed 
with  ether.  The  dry  mass  is  redissolved  in  water,  and 
again  dried  up  in  vacuo. 

Tannic  acid  thus  obtained  is  nearly  white,  and  not 
at  all  crystalline.  It  is  very  soluble  in  water,  and  has  a 
most  astringent  taste  without  bitterness.  It  is  soluble  in  weak  alcohol,  but 
hardly  soluble  in  ether.  The  aqueous  solution,  if  exposed  to  the  air,  absorbs 
oxygen,  produces  an  equal  volume  of  carbonic  acid,  and  is  converted  into  gallic 
and  ellagic  acids.  The  addition  of  the  mineral  acids  to  a  solution  of  tannic 
acid,  causes  a  precipitate,  which  is  composed  of  tannic  acid  and  >the  acid  em- 
ployed (sulphuric,  &c.),  and  which  is  very  soluble  in  pure  water.  The  precipi- 
tate formed  by  sulphuric  acid,  in  a  hot  solution,  dissolves  in  hot  diluted  sul- 
phuric acid,  and  when  this  solution  has  been  boiled  a  short  time,  it  containsjio 
tannic  acid,  the  whole  being  converted  into  gallic  acid. 

Tannic  acid  combines  with  animal  gelatine,  forming  an  insoluble  curdy  pre- 
cipitate. A  piece  of  prepared  skin,  introduced  into  a  solution  of  tannic  acid, 
absorbs  the  acid,  and  is  converted  into  leather.  When  heated,  tannic  acid  is 
converted  into  metagallic  and  pyrogallic  acids. 

Tannic  acid  and  its  salts  strike  a  deep  blue,  nearly  black  colour  with  persalts 
of  iron;  and  it  likewise  causes  a  precipitate  in  the  solutions  of  most  of  the  vege- 
table bases. 

It  is  a  tribasic  acid,  and  the  general  formula  for  the  neutral  tannates  is  Qt, 
3M0  in  the  case  of  protoxides,  and  3  Qi,  M^O  ,  in  the  case  of  sesquioxides. 
These  salts,  however,  have  been  but  little  studied. 

The  conversion  of  tannic  acid  into  gallic  acid  is  not  fully  understood.  In 
some  circumstances,  it  appears  to  depend  on  the  absorption  of  oxygen ;  and  in 
fact,  1  eq.  tannic  acid,  plus  8  eq.  oxygen,  contains  the  elements  of  2  eq.  gallic 
acid,  4  eq.  carbonic  acid,  and  2  eq.  water.  But  when  the  conversion  is  pro- 
duced by  sulphuric  acid,  no  other  substance  is  formed  with  the  gallic  acid,  ex- 
cept a  colouring  matter,  which  appears  not  to  be  essential.  There  is  some 
probability  that  gallic  acid  exists  ready  formed  in  tannic  acid,  and  if  we  subtract 

44 


658  GALLIC  ACID, 

2  eq.  anhydrous  gallic  acid,  2(C^HgO^)  from  1  eq.  of  hydrated  tannic  acid,  C^^ 
HgOjj,  there  is  left  C^H^O^,  which  is  the  composition  of  hydrated  acetic  acid  ; 
or,  tripled,  that  of  dry  grape  sugar.  As  tannic  acid,  or  at  least  the  powder  of 
nut-galls,  if  moistened,  is  said  to  be  susceptible  of  the  vinous  fermentation,  it  is 
not  impossible  that  tannic  acid  may  contain  gallic  acid,  plus  sugar,  if  not  gallic 
acid,  j9/t^s  acetic  acid.  Tannic  acid  is  converted  into  gallic  acid  as  rapidly  by  the 
action  of  an  excess  of  alkali  as  by  that  of  acid ;  but  the  whole  subject  requires 
investigation. 

6.  Gallic  Acid.    C7H03,2HO=G,2HO. 

This  acid  exists  in  the  seeds  of  mango,  and  is  formed  as  above  described  by  the 
decomposition  of  tannic  acid.  It  is  puriiied  from  colouring  matter  by  combining 
it  with  oxide  of  lead,  and  decomposing  the  gallate  of  lead,  suspended  in  water, 
by  sulphuretted  hydrogen;  the  eulphuret  of  lead  acts  as  a  decolorizing  agent. 

Pure  gallic  acid  forms  beautiful  prisms  of  a  silky  lustre,  and  a  slight  yellow- 
i'jh  colour,  of  the  formula  C^H0^,2H0-f-aq.  It  is  sparingly  soluble  in  cold 
water,  requiring  100  parts,  but  dissolves  in  3  parts  of  boiling  water.  Solutions 
of  the  acid  and  its  salts,  strike  a  black  colour  with  persalts  and  proto-persalts  of 
iron.  When  exposed  to  the  air,  the  solution  of  gallic  acid  absorbs  oxygen,  and 
becomes  dark-coloured;  this  change  is  very  rapid  in  the  presence  of  alkalies,  so 
that  the  alkaline  gallales,  especially  if  the  alkali  be  in  excess,  are  rapidly  decora- 
posed,  and  become  nearly  black. 

When  dissolved  in  hot  oil  of  vitriol,  and  precipitated  from  the  cold  solution 
by  water,  gallic  acid  is  obtained  in  a  peculiar  form,  as  C  H  0  ,  perhaps  C  HO^ 
-f-HO,  in  which  the  crystals  have  lost  2  eq.  of  water,  1  basic  or  hydratic,  the 
other,  water  of  crystallization.  This  peculiar  gallic  acid  is  a  reddish-brown  crys- 
talline powder,  which  might  be  used  in  dyeing,  as  it  yields  colours  on  cloth  like 
those  from  madder.  When  heated  it  forms  fine  red  prisms,  which  call  to  mind 
alizaripe,  the  crystalline  matter  found  in  madder. 

By  the  action  of  heat,  crystallized  gallic  acid  yields,  like  tannic  acid,  pyro- 
gallic  and  metagallic  acids. 

The  gallates  are  little  known.  They  are  very  easily  decomposed  by  the  ac- 
tion of  the  air.  The  acid  gallate  of  ammonia  is  G,NH  0-i-G,2H0.  Acid  gallate 
of  lead  has  a  similar  composition.     There  is  a  bibasic  gallate  of  lead,  G,2PbO. 

When  tannic,  or  gallic  acid,  is  heated  by  a  sharp  fire,  carbonic  acid,  water, 
And  pyrogalltc  acid  distil  over,  while  a  dark  solid  remains  in  the  retort,  which  is 
metagallic  acid. 

Pyrugallic  Acid,  C^FI0 1  CgH^O^  1  or  C^H^O^I  forms  shining  scales  of  a  bitter 
and  astringent  taste;  fusible  at  240°,  volatile  at  410°.  It  is  converted  by  a 
stronger  heat  into  metagallic  acid.  It  is  formed  from  gallic  acid,  C  H^O^,  by 
the  loss  of  1  eq.  carbonic  acid.  If  acid  at  all,  it  is  a  very  feeble  acid,  and  nothing 
is  known  of  its  salts. 

Metagallic  Acid,  ^12^3^3^  ^e^a^a^  '®  produced  as  above  mentioned  from 
tannic,  gallic,  and  pyrogallic  acids.  It  is  a  black  powder,  insoluble  in  water, 
soluble  in  alkalies.  Of  its  salts  little  is  known.  It  differs  from  gallic  acid  only 
by  the  elements  of  carbonic  acid;  ^{^.j^fi^=''^GO^-\-C^f\0^.  From  pyro- 
gallic acid  it  only  differs  by  the  elements  of  water. 

Tannic  acid  contains  the  elements  of  gallic  and  pyrogallic  acids.  ^(CjgHg 
Oj2)=6(C^H^O^)-|-2(CgH202) ;  and  since  either  gallic  or  pyrogallic  acid  may 


I 


I 


I 


CATECHU.  iH 

produce  metagallic  acid,  it  is  obvious  that  there  is  a  close  connection  among 
these  four  compounds.  The  precise  nature  of  this  connection  future  experiments 
must  ascertain. 

When  an  infusion  of  nut-galls  has  been  so  long  exposed  to  the  air,  that  all  the  tan- 
nic acid  has  disappeared,  the  gallic  acid  is  found  mixed  with  an  insoluble,  or  spar- 
ingly soluble  powder,  which  is  a  new  acid,  ellagic  acid.  Its  composition  is  C 
H^O^,  and  when  dried  at  240°  C^H^O^ ;  so  that  it  is  isomeric  with  gallic  acid, 
and  with  the  modified  acid  produced  by  the  action  of  oil  of  vitriol.  It  has  not 
been  much  studied,  and  we  do  not  know  its  actual  atomic  weight.  When 
heated,  it  yields  greenish-yellow  vapours,  which  condense  into  crystals  of  the 
same  colour,  insoluble  in  water,  alcohol,  or  ether;  soluble  in  sulphuric  acid  and 
in  alkalies. 

This  acid  is  said  to  occur  in  the  root  of  Tormentilla  vulgaris. 

Tannic  acid,  and  the  substances  derived  from  it,  occur  in  a  good  many  plants, 
besides  those  of  the  genus  (juercus ;  the  infusions  of  all  of  which  are  recognized 
by  their  striking  a  bluish-black  with  persalts  of  iron.  But  the  astringent  taste, 
and  the  property  of  tanning,  or  combining  with  animal  gelatine,  are  found  in 
many  plants,  such  as  cinchona,  kino,  catechu,  pinus,  &c.  These  are  distin- 
guished by  giving,  with  persalts  of  iron,  either  a  dark  green  or  a  gray  colour.  It 
has  not  been  proved  that  they  contain  tannic  acid,  but  Geiger  has  shown  that 
these  different  colours  may  occur  even  when  the  same  tanning  principle  is  pre- 
sent, and  that  the  green  is  owing,  at  all  events  frequently,  to  the  presence  of  free 
acid,  while  the  addition  of  chalk,  in  some  cases,  changes  the  green  to  the  cha- 
racteristic bluish-black  due  to  tannic  acid.  There  are,  however,  some  reasons 
for  admitting  more  than  one  tanning  or  astringent  principle.  The  whole  subject 
requires  investigation. 

Catechu.    Mimotannic  A.cid. 

When  catechu,  the  dried  extract  of  mimosa  catechu^  is  acted  on  by  cold  water, 
it  yields  a  soluble  matter  very  similar  to  tannic  acid,  if  not  identical  with  it  when 
pure.  It  is,  however,  contaminated  by  some  compound  which  causes  it  to  redden 
when  exposed  to  air.  It  does  not  appear  to  yield  the  same  products  when  heated, 
as  tannic  acid  does;  but  this  is  uncertain,  and  may  be  caused  by  the  presence  of 
impurities.  Berzelius  proposes  to  call  this  tannic  acid  mimotannic  acid^  from 
mimosa,  to  distinguish  it  from  the  tannic  acid  of  galls,  which  he  calls  querciian- 
flic  acid  from  quercus. 

The  portion  of  catechu  insoluble  in  cold  water  contains  a  peculiar  compound, 
called  catechine  or  tannigenic  acid.  It  is  soluble  in  hot  water,  and  when  pure 
forms  a  white  silky  crystalline  powder,  which  is  said  to  be  composed  of  C^^Hg 
Og.  When  heated  it  is  said  to  be  transformed  into  (mimo?)  tannic  acid.  By 
the  action  of  caustic  potassa  it  yields  a  black  acid,  japonic  acid,  ^^^^fi^^^O  1 
Carbonate  of  potassa  converts  it  into  a  red  acid,  rubinic  acid,  ^^^^figO)  in  the 
anhydrous  state.  The  hyd rated  acid  is  said  to  have  the  same  composition  as 
japonic  acid,  possibly  therefore  C^gH^Og?  But  as  the  japonic  acid,  on  the  same 
authority,  Svanberg,  in  combining  with  silver  forms  a  salt  C2^HgOg,AgO,  in 
which  2  eq.  of  the  acid  have  lost  2  eq.  of  water  and  gained  only  1  eq.  oxide  of 
silver,  it  is  evident  that  our  knowledge  of  these  compounds  is  very  imperfect. 


MECONIC  ACID. 


7.  Meconic  Acid.    Cj4HOip3HO=Me,3HO. 


A  Iribasic  acid,  found  only  in  opium,  the  drie^  juice  of  papaver  somniferum. 
To  prepare  it,  the  crude  meconate  oflirae,  obtained  in  the  manufacture  of  muriate 
of  morphia  is  mixed  with  30  parts  of  boiling  water,  and  3  parts  of  strong  hydro- 
chloric acid  added  to  the  mixture,  which  must  be  removed  from  the  fire,  and  not 
boiled  after  the  acid  has  been  added.  On  cooling,  acid  meconate  of  lime  is  de- 
posited in  shining  crystals,  which  are  collected  on  a  cloth  filter,  squeezed,  and 
treated  a  second  time  with  the  same  quantities  of  acid  and  hot  water.  The 
strained  acid  liquid  contains  a  large  but  variable  proportion  of  sulphate  of  lime, 
always  present,  sometimes  even  to  the  extent  of  ^  or  |  in  the  crude  meconate  of 
]ime.  Hence  the  advantage  of  using  so  much  hydrochloric  acid,  which  also  ren- 
ders the  meconic  acid  less  soluble.  This  time  the  crystals  are  meconic  acid,  still 
much  coloured.  They  are  collected  and  squeezed  as  before,  and  to  make  sure 
that  all  lime  is  removed,  a  third  time  dissolved  in  20  parts  of  hot  water  and  2  of 
hydrochloric  acid.  The  addition  of  the  acid  not  only  removes  the  last  traces  of 
lime,  but  causes  the  meconic  acid  to  crystallize  almost  entirely  out  of  the  liquid, 
it  being  nearly  insoluble  in  diluted  acid.  The  crystals,  washed  with  a  little  cold 
water,  and  dried  at  the  ordinary  temperature,  are  now  pure  from  everything  but 
colouring  matter,  and  when  heated  to  redness  leave  no  residue. 

To  get  rid  of  the  colour,  the  crystals  are  now  mixed  with  w^arm  water,  and 
caustic  potassa  gradually  added,  so  as  nearly  but  not  quite  to  neutralize  the  acid. 
As  soon  as  the  point  of  neutralization  is  reached,  the  reddish  colour  changes  to 
green,  and  so  much  potassa  must  be  added  that  any  further  quantity  would  pro- 
duce the  green  colour.  The  whole  is  then  heated  in  the  water  bath,  till  all  is 
dissolved,  hot  water  being  added,  if  necessary.  (Were  the  potassa  now  in  ex- 
cess, the  whole  acid  would  be  decomposed  into  oxalic  and  carbonic  acids.)     On 

cooling,  the  meconate  of  pQtassa,Me  ^    „q  crystallizes,  forming  a  semisolid 

mass,  which  is  to  be  squeezed  out.  The  colour  is  carried  off  for  the  most  part 
in  the  mother  liquor,  which  is  very  dark,  and  the  squeezed  salt,  after  a  second, 
or  if  necessary  a  third,  solution  in  hot  water,  crystallization,  and  squeezing,  is 
snow  white.  This  purified  meconate  of  potassa  is  then  acted  on  by  pure  hydro- 
chloric acid,  exactly  as  recommended  for  the  meconate  of  lime,  and  after  the 
third  operation  yields  perfectly  pure  and  white  meconic  acid  in  beautiful  silvery 
scales,  which,  to  remove  any  traces  of  the  acid  mother  liquid  adhering  to  them, 
may  be  once  more  dissolved  in  the  smallest  possible  quantity  of  hot  water,  avoid- 
ing a  heat  of  212°,  which  decomposes  the  acid  ;  the  pure  acid  is  deposited  on 
cooling,  as  Me,3HO-}-6aq. 

Meconic  acid,  when  gently  heated,  loses  6  eq.  of  water  of  crystallization..  It 
is  soluble  in  water  and  in  alcohol.  When  boiled,  its  solution  becomes  coloured, 
producing  comenic  acid,  carbonic  acid,  and  a  dark  brown  colouring  matter.  If 
boiled  with  hydrochloric  acid,  it  is  resolved  into  comenic  acid  and  carbonic  acid, 
without  the  production  of  colouring  matter.  When  the  dry  acid  is  heated  to 
250°,  the  same  change  takes  place.  When  heated  with  excess  of  aqua  potasssc:, 
meconic  acid  is  entirely  decomposed  into  oxalic  acid,  #arbonic  acid,  and  a  dark 
colouring  matter.  Its  distinguishing  character  is  that  of  causiug,  in  persalts  of 
iron,  a  deep  blood-red  colour,  but  no  precipitate. 

It  forms  three  series  of  salts,  like  other  tribasic  acids.  Thus  there  are  three  meco- 


I 


KINIC  ACID.  gm 

nates  of  potassa:  1,  acid,  Me,    <  oirr)  »  2*  neutral,  above  mentioned,  Me    ^  Tjp. 

aq.  Both  of  these  crystallize.  3.  tribasic,  MeSKO.  This  is  yellow,  and  does 
not  crystallize.  There  are  also  three  meconates  of  soda;  two  of  lime,  acid  and 
neutral  or  bibasic,  and  two  of  silver,  bibasic  Mp,,2AgO,HO,  and  tribasic  Me  3 
AgO.  The  meconate  of  peroxide  of  iron  is  very  soluble,  of  an  intense  blood- 
red  colour,  but  as  it  cannot  be  obtained  pure  or  crystallized,  its  composition  is 
still  unknown. 

8.  Comenic  Acid.     CuH209,2HO=Co2HO.  j^^ 

This  acid  is  formed  as  above  described,  from  meconic  acid  by  the  action  of 
heat,  orof  heatand  an  acid  combined.  1  eq.  dried  meconic  acid,  Kj^H0jj-f-3H0 
=  C  H^O  ,  yields  1  eq.  comenic  acid,  C^^H  Og,2HO,  and  2  eq.  carbonic  acid, 
200^.  The  acid  is  readily  obtained  by  boiling  meconate  of  lime  with  an  excess 
of  diluted  hydrochloric  acid.  It  is  deposited  on  cooling  in  coloured  crystals, 
which  may  be  decolorized  by  recrystallization  with  the  aid  of  animal  charcoal. 
The  pure  acid  has  a  slight  yellow  tinge,  and  is  very  sparingly  soluble  in  cold 
water.  When  heated,  it  is  resolved  into  carbonic  acid,  pyromeconic  acid^  and  a 
small  quantity  of  a  third  substance,  paramcomenic  acid^  which,  in  some  few  points, 
differs  from  comenic  acid,  but  has  the  same  composition,  and  in  many  points  is 
so  similar  that  it  may  possibly  turn  out  to  be  essentially  the  same. 

Comenic  acid  forms  two  series  of  salts,  with  1  and  2  eq.  of  fixed  base  respect- 
ively. With  persalts  of  iron  it  forms  a  deep  red  solution  which  deposits  black 
crystals,  of  unknown  composition. 

Pyromeconic  acid,  C  H  0  ,H0,  is  obtained  as  a  crystalline  sublimate  by  heat- 
ing meconic  or  comenic  acids.  In  fact  1  eq.  comenic  acid,  C^^^^^io'  ^^^^ains 
the  elements  of  1  eq.  pyromeconic  acid,  C  H  O^,  and  2  eq.  carbonic  acid,2C02. 
It  forms  very  soluble  four-sided  prisms,  rather  styptic  to  the  taste;  the  solution 
of  which  forms  with  persalts  of  iron  a  crystalline  salt  of  a  fine  red  colour,  the 
powder  of  which  is  like  vermilion.  This  salt  is  Fe^Og-f-SCj^H^O^.  Pyrome- 
conic acid  is  so  feeble  an  acid,  that  we  can  hardly  class  it  with  acids.  It  has 
more  analogy  with  such  bodies  as  acetone,  derived  from  acetic  acid,  as  pyrome- 
conic acid  is  from  meconic  or  comenic  acid.  It  has  the  same  composition  as 
pyromucic  acid. 

9.  Kinic  Acid.     C7H464,2HO  ?  or  Cj^HipOjijHO  1 

This  very  remarkable  acid  occurs  in  cinchona  bark.  It  is  obtained  in  the 
manufacture  of  sulphate  of  quinine,  in  the  form  of  kinate  of  lime,  from  which  the 
lime  is  easily  separated  by  means  of  oxalic  acid.  The  liquid  filtered  from  the 
oxalate  of  lime  yields,  on  evaporation,  the  kinic  acid  in  crystals.  The  lime  may 
also  be  removed  by  sulphuric  acid,  and  any  adhering  sulphate  of  lime  separated 
by  alcohol. 

The  salts  of  kinic  acid  are  somewhat  anomalous.  Thus  there  is  a  salt  of  lead, 
C^H^0^2PbO,  and  a  salt  of  copper,  C^H^O^,CuO,HO,  while  the  crystals  of  kinic 
acid  are  C  H  O  .     All  this  would  lead  to  the  conclusion  that  the  acid  was  a  bi- 

7      6     6 

basic  one,  C^H^0^,2H0.  But  the  kinate  of  lime,  and  the  kinate  of  silver,  both 
quite  neutral  salts,  are  C^^H^jO^j.CaO,  and  ^14^11^11'-^^^'  ^^  ^^  ^^^  ^^^^  ^^^® 
monobasic,  ^i4H  O  ,H0  =  ^14^^20  .  If  we  assume  the  acid  to  be  quadriba- 
sic,  we  can  then  bring  all  the  above  salts  into  one  series. 


DECOMPOSITION  OF  KINIC  ACID. 

Thu8,=Kinic  acid  would  be  .  .  Ci4Hg08,4HO  • 

Kinate  of  lead  .  .  .        Ci4H808,4PbO 

Kinate  of  copper  .  .  Cj.HgOg,    ^^^ 

Kinate  of  lime  .  .  .         C^HgOg,    {3^0^  t  10  aq. 

Kinate  of  silver     .,         .  .  C^HsOg,    ^^^ 

But  the  objection  to  this  view  is  that,  if  this  be  the  true  constitution  of  the 
acid,  the  salts  of  lime  and  silver  ought  to  be  very  acid  instead  of  being  quite 
neutral. 

PRODUCTS  OF  THE  DECOMPOSITION  OF  KINIC  ACID. 

When  kinic  acid  or  kinate  of  lime  is  distilled  with  diluted  sulphuric  acid  and 
peroxide  of  manganese,  there  is  obtained  a  new  compound  called  kinont^  as  a 
sublimate  of  fine  golden  yellow  crystals,  soluble  in  water,  and  very  volatile, 
having  a  pungent  smell  in  the  state  of  vapour.  Their  composition  is  C  HO. 
When  acted  on  by  reducing  agents,  it  takes  up  2  and  4  eq.  of  hydrogen,  forming 
two  new  compounds,  green  and  white  hydrokinone.  The  green  hydrokinone, 
C^Hj^Og,  is  one  of  the  most  beautiful  compounds  known  to  chemists,  forming 
long  prisms  of  the  most  brilliant  gold-green  metallic  lustre,  surpassing  those  of 
murexide  in  beauty.  It  is  best  formed  by  adding  a  few  drops  of  sulphurous 
acid  to  a  solution  of  kinone.  When  an  excess  of  sulphurous  acid  is  used,  the 
white  hydrokinone^  ^35^12^8'  ^'^  formed,  which  crystallizes  in  six-sided  prisms. 
When  acted  on  by  oxidizing  agents,  the  solution  of  white  hydrokinone  becomes 
dark-red,  nearly  black,  and  almost  immediately  deposits  the  splendid  crystals  of 
the  green  compound.  The  latter  is  also  formed  by  simply  mixing  solutions  of 
kinone  and  white  hydrokinone,  being  intermediate  in  composition  between  those 
bodies.  Wohler,  to  whom  we  are  indebted  for  most  of  our  knowledge  in  regard 
to  these  very  curious  compounds,  has  described  a  series  of  bodies  obtained  from 
the  above  by  the  action  of  hydrochloric  acid,  chlorine,  and  sulphy retted  hydro- 
gy.  The  following  tabular  view  contains  the  names  and  composition  of  these 
substances,  as  far  as  we  yet  know  them. 

Kinone  .  .  . 

Green  hydrokinone 

White  hydrokinone  , 

fblorobydrokinone 

Chlorokinone 

I  Brown  sulphohydrokinone  . 

Yellow        ditto 
Brown  chlorosulphokinone 
Orange        ditto 

It  will  be  observed,  that  in  all  these  formulae  the  carbon  remains  unaltered, 
and  that  several  are  instances  of  pure  substitution,  as  C    H  O   compared  with 

(  H  C  H 

^a«  /  cf  ^8  ^"^  ^23^12^8'  compared  with  C^    j     w  0,^.     We  can  also  see  the 


CZ6 

H8 

Os 

C25 

H.0 

Og 

C25 

H,, 

Os 

C25 

Os 

Cos 

(CI2 

% 

c« 

H„ 

0,S, 

C,5 

Hu 

O7S, 

C2S 

He 

ClOgS^T 

C25 

H. 

CiOgS^T 

BUTYRIC  ACID.  663 

relation  of  the  sulphohydrokinones  to  kinone  if  we  express  them  as  follows  — 

We  now  come  to  a  class  of  acids  of  very  distinct  and  peculiar  characters ; 
those,  namely,  which  occur  as  the  chief  constituents  of  fat  oils  and  fats,  vegeta- 
ble or  animal.  Of  these  oily  acids  there  are  two  kinds:  1.  those  which  are 
volatile,  and  usually  somewhat  soluble  in  water;  2.  those  which  have  more 
the  character  of  the  oils  and  fats  from  which  they  are  derived,  and  can  seldom  be 
distilled  without  decomposition.     We  shall  begin  with  the  volatile  oily  acids. 

10.  Butyric  Acid.     CgH^OjjHO. 

This  acid  exists  in  small  proportion  in  butter,  in  the  form  of  a  neutral  butyrate 
of  glycerine  or  butyrine,  to  which  the  butter  owes  its  peculiar  and  agreeable  fla- 
vour. When  butter  is  saponified  by  potassa,  and  the  solution  of  the  soap  is  de- 
composed by  tartaric  acid,  the  oleic  and  margaric  acids  are  separated  as  an  oily 
stratum,  while  three  or  four  volatile  acids  are  dissolved  in  the  water.  These  are 
butyric,  caproic,  capric  and  caprylic  acids.  The  butyric  acid  may  be  extracted 
from  the  mixture;  but  it  is  far  better  obtained  by  the  fermentation  of  sugar. 
When  sugar,  either  cane,  grape  or  milk  sugar,  is  mixed  with  cheese,  water,  and 
chalk,  and  kept  in  a  warm  place,  lactic  acid  is  at  first  formed,  which  combines 
with  the  lime.  But  if  the  fermentation  be  continued  at  a  pretty  high  tempera- 
ture, 90°  to  100°  for  example,  the  lactate  of  lime  disappears,  and  is  at  last  re- 
placed by  butyrate  of  lime.  This  salt  is  now  distilled  with  diluted  hydrochloric 
acid,  and  the  distilled  liquid  treated  with  chloride  of  calcium,  when  it  divides 
into  two  strata.  The  lighter  is  butyric  acid,  still  containing  water.  It  is  recti- 
fied until  the  boiling  point  rises  to  318°.  The  previous  portions- contain  water  ; 
what  now  passes  is  pure. 

It  is  a  clear,  colourless,  mobile  liquid,  of  an  odour  resembling  that  of  acetic 
acid  and  that  of  butter.  An  intense  cold  solidifies  it.  It  is  very  acid  and  cor- 
rosive.    Its  sp.  gr.  is  0*963.     It  dissolves  fats  and  fat  oils. 

Chlorine  decomposes  butyric  acid,  producing  by  substitution  two  acids,  C^ 

C  H  C  H 

i  .^5  0,,H0;  and  C„  >  ^3  o,,HO.     The  latter  crystallizes;    and  both  form 

volatile  fragrant  compounds  with  oxide  of  ethyle. 

Butyrate  of  lime  is  remarkable  as  being  very  soluble  in  cold  water,  but  sepa- 
rating from  tiie  liquid  in  transparent  prisms  when  it  is  boiled.  Butyrate  nf 
baryta,  when  placed  on  the  surface  of  water,  exhibits  the  same  motions  as  cam- 
phor. Butyrate  of  oxide  of  ethyle  or  butyric  ether,  AeO,C  H  0^,  is  formed  with 
singular  facility  if  a  mixture  of  alcohol  and  butyric  acid  is  distilled  with  the 
addition  of  a  little  sulphuric  acid.  It  is  a  very  mobile  liquid  of  an  odour  some- 
what similar  to  that  of  pineapples.  It  is  very  soluble  in  alcohol.  This  ether  is 
euiployed  to  flavour  spirits  :  and  there  is  reason  to  believe  that  the  peculiar 
flavour  of  rum  depends  on  the  presence  of  a  little  butyric  ether,  Butyrate  of 
oxide  of  methyle  is  quite  analogous.  Butyrate  of  oxide  of  glyceryle  or  Butyrine 
exists  in  butter,  and  is  supposed  to  be  capable  of  being  formed  artificially,  by 
warming  a  mixture  of  butyric  acid,  glycerine  and  sulphuric  acid.  If  the  oil  thus 
formed  is  really  butyrine,  it  will  be  the  first  example  of  a  compound  of  glycerine 
formed  or  reproduced  artificially. 

Butyramide,  CgH  0^+  NH^  is  formed  when  liquid  ammonia  acts  on  butyric 


0g4  CAMPHORIC  ACID. 

ether.     AeO,CgH^03  +  NH3  =  AeO,HO  f  CgH^0^,NH2.     ^^  crystallizes  in 
pearly  scales. 

Butyrone,  C^H^O,  analogous  to  acetone,  is  formed  along-  with  carbonate  of 
lime,  when  butyrate  of  lime  is  distilled.  CgH^03,CaO  =  C^H^O  -j-  CaO,CO  . 
By  the  action  of  nitric  acid,  butyrone  is  converted  into  two  new  compounds ; 
one,  an  ethereal  fragrant  liquid,  lighter  than  water,  the  composition  of  which  is 
not  yet  known :  the  other,  an  oily  liquid,  heavier  than  water,  of  an  aromatic 
smell  and  a  sweet  taste,  which  is  an  acid,  niirobufi/rtc  or  hutyronitric  acid.     It 

C  H 

is  formed  by  substitution  of  NO^  for  H ;  C^  j   j^«     0,2H0    from    C^H^O.      It 

^         4 
forms  crystallizable  salts,  and  is  bibasic,  yielding  two  salts  with  oxide  of  silver, 

with  1  and  2  eq.  of  that  oxide  respectively. 

By  distillation  with  perchloride  of  phosphorus,  butyrone  is  converted  into  an 
ethereal  liquid,  chlorobutyrene,  the  composition  of  which  is  C    H    CI. 

The  caproic,  capric  and  caprylic  acids  found  in  butter,  are  very  analogous  to 
butyric  acid,  but  are  not  yet  so  well  known.  Caproic  acid  is  C  H  O  ,H0.  Its 
odour  is  like  that  of  sweat.  Caproate  of  oxide  of  ethyle  has  an  odour  somewhat 
analogous  to  that  of  butter.  Capric  acid  is  C  H  O  ,H0.  It  is  very  analogous 
to  the  preceding,  but  its  odour  is  more  like  that  of  the  goat.  Caprylic  acid  is 
Cj^Hj^O  ,H0,  and  it  is  very  analogous  to  the  others. 

It  occasionally  happens  that  butter,  instead  of  yielding  a  mixture  of  volatile 
oily  acids,  of  which  butyric  and  caproic  acid  constitute  the  principal  part,  gives 
a  mixture  devoid  of  these  acids,  but  containing  in  their  place  another  acid,  vac- 
cinic  acid,  which  is  easily  transformed  into  the  other  two.  There  can  be  no 
doubt  that  it  contains  the  elements  of  butyric  and  caproic  acids,  C^H  O  ,H0  -f- 
C„H„03,H0  =.  C^H^O,  or  possibly  C^H,,0,  =  C^H„0^,HO.  In  the  latter 
case,  it  would  require  1  eq.  of  water  to  yield  the  other  acids.  As,  however,  the 
solution  remains  neutral  when  vaccinic  acid  passes  into  caproic  and  butyric  acids, 
it  is  most  probably  bibasic,  02^11^^0^,2110,  and  is,  in  fact,  the  sum  of  the  other 
two.     The  cause  of  its  occurrence  is  unknown. 

Hircic  Acid^  the  composition  of  which  is  unknown,  is  obtained  from  the  fat  of 
the  goat,  just  as  the  preceding  acids  are  from  butter.  It  has  an  acid  smell  of 
goats,  but  is  otherwise  little  known. 

Phocenic  Acid^  C^^H^O^,!!©,  is  a  volatile  acid  occurring  in  the  blubber  of  the 
dolphin,  and  in  the  berries  of  viburnum  opulus.  It  is  extracted  like  the  acids  of 
butter,  and  is  a  liquid  of  a  strong  smell  like  that  of  rancid  butter.  It  forms 
crystallizable  salts  with  bases.     It  may  possibly  be  the  same  as  valerianic  acid, 

Cevadic  Mid  is  a  crystalline  volatile  acid,  obtained  from  the  seeds  of  t'era/ru/?» 
Babndilla:  composition  unknown.  ^ 

Veratric  Acid  is  contained  in  the  same  seeds.  It  is  solid,  crystallizable,  and 
volatile.  Its  formula  is  C  H  O  ,H0.  It  forms  a  crystalline  ether  with  oxide 
of  ethyle;  AeO,CjgHgO^. 

Crolonic  Acid  is  another  solid  volatile  acid,  found  in  the  seeds  o( croton  ti^lium. 
It  has  a  pungent,  acrid  taste,  and  a  nauseous  smell.  It  forms  crystallizable 
pits. 

11.  Camphoric  Acid.    CioH^Og.HOsrs  Caijio. 

This  acid  is  formed  by  the  action  of  nitric  acid  on  camphor.  It  forms  crys- 
talline scales,  sparingly  soluble  in  cold  water,  very  soluble  in  alcohol  and  ether, 
fusible  at  158°.     These  are  the  hydrated  acid,  which,  if  distilled,  is  resolved 


I 


1 


CAMPHOR.  (Jg5 

into  water  and  anhydrous  camphoric  acid.  The  camphorates  are  not  peculiarly- 
interesting.  With  oxide  of  ethyle,  camphoric  acid  forms  two  compounds: — 
1.  neutral,  or  camphoric  ether^  Ca,AeO,  an  oily  liquid,  of  a  bitter  taste  and  nau- 
seous smell.  2.  acid,  2Ca,AeO,Ho,  also  called  camphovinic  acid,  as  it  forms 
double  salts,  2  Ca,AeO,MO.      When  chlorine  acts  on  camphoric  ether,  CajC 

HO,  it  gives  rise  to  the  compound  Ca,C .  \  _,3  O. 

Anhydrous  Camphoric  Acid^  ^10^7^3'  for™s,  with  bases,  salts  different  from 
those  formed  by  the  hydrated  acid.  It  is  probable  that  it  still  retains  some 
water  replaceable  by  bases,  being  perhaps  C  H  0  ,H0 ;  or  it  may  differ  from 
ordinary  camphoric  acid  as  metaphosphoric  acid  does  from  common  phosphoric 
acid.  It  is  solid,  crystalline,  and  volatile,  and  with  dry  ammonia  forms  a  com- 
pound from  which  potassa  disengages  no  ammonia  :  with  liquid  ammonia  it 
yields  a  salt  different  from  camphorate  of  ammonia.  Its  action  on  oxide  of 
ethyle  has  not  been  studied  ;  but  the  subject  deserves  investigation. 

It  is  worthy  of  notice  that  camphoric  acid  is  isomeric  with  phocenic  acid,  and 
has  apparently  the  same  atomic  weight.     Qu.  !  Is  one  or  the  other  bibasic  ? 

By  the  action  of  sulphuric  acid  on  anhydrous  camphoric  acid,  there  is  formed, 
with  disengagement  of  carbonic  oxide,  a  new  acid,  sulphocamphoric  acid,  (C  H 
0^,80^)  HO  -j-  2  aq.  This  acid  is  crystalHzable,  and  forms  crystallizable  salts 
of  the  formula  (C^Ufi^^SO^)  MO  =  CgH^SO^,MO. 

CAMPHOR. 

There  are  two  kinds  of  camphor ;  that  of  Japan,  or  common  camphor,  C  H 
0  ;  and  that  of  Borneo,  C  H  0,  or  C  H  0  .  The  properties  of  common  cam- 
phor, and  its  peculiar  smell,  are  well  known.  Its  sp.  gr.  is  0985  to  0-996  ;  it 
is  very  volatile,  evaporating  at  ordinary  temperatures.  Small  fragments  of  cam- 
phor, on  the  surface  of  water,  evaporate  more  rapidly,  with  rotatory  movements. 
It  dissolves  in  alcohol,  and  is  precipitated  by  water.  When  distilled  with  an- 
hydrous phosphoric  acid,  it  yields  a  carbo-hydrogen,  called  camphogen  C^^H   , 

When  camphor  is  passed  in  vapour  over  a  heated  mixture  of  hydrates  of  potassa 
and  lime,  it  yields  a  new  acid,  campholic  acid,  C  H  0^,H0.  Nitric  acid,  with 
the  aid  of  heat,  converts  camphor  into  camphoric  acid.  The  essence  or  oil  of  cam- 
phor of  commerce  is  C    H   0  =  2  eq.  camphor  minus  I  eq.  oxygen. 

Borneo  camphor  occurs  in  small  crystalline  fragments.  Its  odour  is  different 
from  that  of  common  camphor.  I  find  that,  if  wrapped  in  paper,  a  distinctly 
alliaceous  odour  traverses  the  paper,  and  may  thus  be  detected.  Heated  with 
phosphoric  acid,  it  yields  a  carbo-hydrogen,  C  H  ;  and  this  is  also  the  compo- 
sition of  the  essence  which  accompanies  Borneo  camphor.  This  essence  is, 
therefore,  Borneo  camphor,  C    H   O  ,  minus  2  eq.  water. 

Common  camphor  is  produced  by  the  Lauriis  camphor  a ;  Borneo  camphor  is 
the  produce  of  Dryolalanops  camphora,  and  is,  for  some  unknown  reason,  so 
highly  prized  by  the  Japanese,  that  it  is  not  found  in  the  markets  of  Europe. 

Camphogen,  C  H  ,  is  the  name  given  to  the  carbo-hydrogen  obtained  when 
common  camphor  is  distilled  with  dry  phosphoric  acid.  It  occurs  naturally  in 
the  oil  of  cumin.  When  acted  on  by  sulphuric  acid,  it  forms  a  new  acid,  su/- 
phocamphic  or  hyposulphocamphic  acid,  C^^H    S^O^,HO. 

When  camphor  is  passed  over  red-hot  lime,  another  new  compound  is  formed, 
namely,  camphrone,  C^^H^^O  =  3  (Cj^H^O)  — H^-t-  0^.    At  a  white  heat,  cam- 


VALERIANIC  ACID. 

phor  yields  naphthaline,  carburetted  hydrogen,  and  carbonic  oxide.  4  eq.  cam- 
phor contain  the  elements  (G^^U^p^)  of  1  eq.  naphthaline,  C^H^;  olefiant  gas, 
2C^H^;  marsh  gas,  SCH^;  and  carbonic  oxide,  4C0. 

12.  Valerianic  Acid.    C,oH903,HO  =  Va,HO. 

This  acid  has  already  been  mentioned  as  produced  from  hydrated  oxide  of 
amyle.  It  also  occurs  in  the  root  of  Valerian.  It  forms  two  hydrates,  Va,HO, 
and  vi,HO  +  2  aq. 

__The  general  formula  of  the  valerates  is  Va,MO.  Valerate  of  oxide  of  ethyle, 
Va»AeO,  is  an  oily  liquid,  of  a  smell  like  that  of  fruits  and  that  of  valerian  at 
the  same  time. 

By  the  action  of  chlorine,  valerianic  acid  yields  two  new  acids  :  1.  Chlorova- 

krisicacid^C^^  5^6  03,H0.     2.  aiorovalerosic  acid,  C^^  S^s  Q^.UO.      Both 

these  compounds  are  formed  by  substitution  without  change  of  type. 

When  valerate  of  lime  is  distilled,  it  is  said  by  Lowig  to  yield  a  volatile  oily 
compound,  valerone,  C^UJO  =  Cj^Hg03  —  CO^. 

13.  Anisic  Acid.    CjgHeOg.HO. 

This  acid  is  obtained  when  the  concrete  essence  of  anise-seed  is  acted  on  by 
nitric  acid.  It  is  crystallizable  and  volatile,  and  forms  salts  which  crystallize 
readily.  When  heated  with  an  excess  of  baryta,  it  yields  an  oily  liquid,  called 
antsole. 

The  prolonged  action  of  nitric  acid  on  the  concrete  essence  of  anise  produces 
another  acid,  mtro-anisic  acid,  in  small  yellow  crystals.     Its  formula  is  C^gH 

NOg,HO  s=  Cjg   j     s    0^,H0.     It  is  now  found   to  be  identical  with  nitro- 

dracinic  acid. 

AnisoUy  the  product  formed  when  anisic  acid  is  heated  with  baryta,  is  com- 
posed of  C,  H  O^  =  C,  H  O  .HO  —  2C0  .  It  is  formed,  also,  when  the 
salicylate  of  oxide  of  methyle  is  heated  with  baryta.  By  the  action  of  bromine, 
anisole  gives  rise  to  two  new  products,  in  which  1  and  2  eq.  of  hydrogen  are 

respectively  replaced  by  bromine;  C,    S„7  O  and  C,,  ^„6    0,.      The  lat- 

•  ^  ^      2 

ter  is  crystalline.     Nitric  acid  acts  violently  on  anisole,  forming  a  crystalline 

mass,  which  dissolves  in  alcohol,  with  a  rich  green  colour,  but  is  deposited  in 

colourless  needles,  corresponding  to  one  of  the  bromine  compounds.     Fuming 

sulphuric  acid  dissolves  anisole,  producing  two  compounds;  one,  insoluble  in 

water,  analogous  to  sulphobenzine :  the  other,  soluble,  an  acid  analogous  to  sul- 

phovinic  acid.     SSO^  -+-  Cj^H^02,H0. 

Anisole,  C   H  0  ,  contains  2  eq.  of  hydrogen  more  than  hyduret  of  benzoyle, 

14.  (Enanthic  Acid.    C^HjaO^jHO. 

This  acid,  in  combination  with  oxide  of  ethyle,  forming  oenanthic  ether,  is 
found  in  wine,  in  the  oil  of  grain  spirit,  and  in  some  other  fermented  liquors.  It 
is,  as  oenanthic  ether,  the  cause  of  that  peculiar  odour  of  wine  which  adheres  so 
remarkably  to  vessels  in  which  wine  has  been  kept,  and  enables  us  at  once  to 


CUMINIC  ACID.  667 

say  that  an  empty  bottle  or  cask  has  contained  wine.  To  obtain  the  acid, the 
ether  is  decomposed  by  caustic  potash,  and  the  oenanlhate  of  potash  distilled 
with  dilute  sulphuric  acid.  The  hydrated  acid  is  semisolid  like  butter,  and  is, 
in  fact,  a  fat  oil,  insoluble  in  water,  soluble  in  alcohol  and  ether. 

Of  its  salts,  the  cenanikate  of  oxide  of  ethi/ky  cenanthic  ether,  is  best  known. 
It  is  a  colourless  liquid,  of  a  peculiar  vinous  smell,  which,  when  strong,  has  a 
stupefying  effect.  When  hydrated  cenanihic  acid  is  distilled,  it  yields  water, 
and  anhydrous  acid,  more  solid  than  the  hydrate. 

15.  Roccellic  Acid.    C^^U^fi^yB0 1 

This  acid  occurs  in  Bocella  tindoria.  It  is  crystallizable,  insoluble  in  water, 
soluble  in  alcohol  and  ether.  It  has  most  of  the  properties  of  a  fat  acid,  and  its 
salts  with  the  alkalies  resemble  soaps. 


This  acid  is  formed  from  the  essential  oil  of  cumin  by  oxidation  with  hydrated 
alkalies.  It  forms  tabular  crystals  of  singular  beauty.  It  is  fusible  and  volatile, 
insoluble  in  cold  water,  soluble  in  alcohol  and  ether.  When  heated  with  caustic 
baryta,  it  yields  a  carbo-hydrogen,  analogous  to  benzole,  which  is  called  cumene. 

It  forms  well-defined  salts  with  bases.  Cuminate  of  oxide  of  ethyle,  formed 
by  passing  hydrochloric  acid  gas  through  a  solution  of  cuminic  acid  in  alcohol, 
is  an  ethereal  liquid,  of  a  fragrant  smell  like  that  of  apples. 

Cumene,  obtained  by  heating  cuminic  acid  with  baryta,  is  a  colourless  liquid 
of  a  sweet  smell.  It  is  formed  from  cuminic  acid,  C^^jH^^O  ,  by  the  loss  of  2 
eq.  carbonic  acid,  exactly  as  benzole  is  formed  from  benzoic  acid  ;  and  its  for- 
mula is  consequently  C^gH^^*  ^oih  nitric  and  sulphuric  acid  act  on  it  and  form 
new  compounds,  not  yet  fully  examined.  That  formed  by  sulphuric  acid  is  an 
acid,  sulphocuminic  acid,  ^ig^iiiS^O^  ^  HO. 

Essence  of  cumin  {cuminum  cyminum)  contains  two  oils:  1.  Cuminole,  C^ 
HO,  which  is  the  true  oil  of  cumin,  analogous  to  hyduret  of  benzoyle;  2. 
Cymene,  C  H  ,  isomeric  with  camphogen.  It  is  an  oil  of  an  agreeable  odour 
of  lemons.  The  oil  is  acted  on  by  nitric  and  sulphuric  acids,  which  produce  two 
new  acids.     That  formed  with  sulphuric  acid  is  C^^H^, 8^0^30. 

The  cuminole,  ^^ifi^->  ^^J  be  viewed  as  analogous  to  hyduret  of  benzoyle, 
in  which  case  it  becomes  C  HO  -|-  H,  the  hyduret  of  a  new  radical,  cumyle, 
Cuminic  acid  then  becomes  ^^^fi^'^  "^  ^^'  ^^^^o^^us  to  benzoic  acid. 
Chlorine  acts  on  hyduret  of  cumyle,  producing  a  compound,  C2qH^^02,C1,  which 
is  chloride  of  cumyle.  Adopting  the  symbol  Cm  =  C^^H^^O^,  we  have  CmH, 
CmO  t  HO,  and  CmCl,  analogous  to  BzH,BzO  +  HO,  and  BzCl. 

17.  Eugenic  Acid.     C20H12O4?  or  CjoHjgOg? 

This  acid  is  found  in  cloves,  along  with  a  neutral  oil,  C^^Hg,  or  C^H^^.  The 
latter  is  separated  by  potassa,  and  the  eugenic  acid  obtained  by  distilling  the  salt 
of  potassa  with  dilute  sulphuric  acid.  It  is  an  oily  liquid,  of  sp.  gr.  1*079,  hav- 
ing the  strongest  odour  of  cloves.  It  forms  crystallizable  salts  with  bases,  and 
among  them  an  acid  salt  of  potassa,  SC^^Hj^O^-i-KOH-HO'? 

Cloves,  likewise,  contain  two  crystallizable  compounds:  1.  Caryophylline, 
which  forms  yellow  prisms ;  of  the  formula  C   H   0  ,  an  oxide,  therefore,  of  the 


66S  PALMITIC  ACID. 

neutral  oil  of  cloves,     2.  Eugenine,  which  forms  yellow  pearly  scales,  the  com* 
position  of  which  is  the  same  as  that  of  eugenic  acid. 

18.  Cocinic  Acid.     Cj^HggOg.HO. 

This  acid,  the  first  of  the  proper  fat  acids  which  we  have  come  to,  is  found  in 
the  butter  of  the  cocoa-nut  combined  with  glycerine.  The  butter  is  saponified 
by  potassa,  and  the  soap  produced  is  decomposed  by  a  mineral  acid,  when  the 
fatty  acid  rises  to  the  surface.  It  is  purified  by,  being  again  saponified,  and 
finally  by  crystallization  in  alcohol.  It  forms  snow-white  crystalline  scales,  fu- 
sible at  95°,  and  volatile.  The  salts  of  this  acid  with  the  alkalies  are  soaps  like 
those  of  all  fatty  acids.  Cocinate  of  oxide  of  ethyle  is  a  colourless  ether,  with  a 
very  fragrant  smell  of  apples. 

19.  Myristic  Acid.    CggHg^OgjHO. 

This  acid  is  found  combined  with  glycerine,  as  a  fat  or  butter  in  the  berries  of 
myristica  moschata  or  nutmeg.  There  are  two  fats  in  the  seeds,  one  red  and 
unctuous,  the  other,  myristine,  white,  and  crystalline.  It  is  easily  purified  by 
dissolving  it  in  hot  alcohol,  in  which  it  is,  like  the  cocinate  of  glycerine,  very 
soluble.  On  cooling,  the  pure  myristine  or  myristate  of  glycerine  is  deposited 
as  silky  needles,  which  being  saponified  by  potassa,  and  the  soap  decomposed 
by  an  acid,  yield  myristic  acid.  The  acid  is  purified  by  means  of  alcohol.  It 
melts  at  118°,  and  is  decomposed  by  distillation. 

The  salts  of  this  acid  with  the  alkalies  are  soaps  :  very  soluble  in  alcohol ;  and 
their  aqueous  solutions  do  not  become  viscid  or  ropy  when  concentrated.  My- 
ristate of  oxide  of  ethyle  is  a  colourless  oil.  Myristate  of  oxide  of  glycerine  or 
myristine  is  purified  as  above  described.  It  is  a  beautifully  crystalline  fat,  melt- 
ing at  88°.  It  is  saponified  with  difficulty,  and  only  by  fusion  with  solid  po- 
tassa. It  does  not  appear  to  contain  ordinary  glycerine :  at  least  its  formula 
would  indicate  a  glycerine  composed  of  ^  H  O.  This  point  is  at  present  very 
obscure. 

The  formula  of  hydrated  cenanthic  acid,  doubled,  or  C^^H^^Og,  contains  2  eq. 
of  oxygen  more  than  1  eq.  of  hydrated  myristic  acid,  ^c^^^fi^  \  or  the  formula 
of  dry  cenanthic  acid  doubled,  C^j^H^^O^,  contains  1  eq.  of  hydrogen  less  and  1 
eq.  of  oxygen  more  than  dry  myristic  acid.  CJ^gH^O^. 

20.  Palmitic  Acid.    CajHaiO^jHO. 

This  is  the  principal  fat  acid  of  palm  oil.  It  is  extracted  by  the  usual  process 
for  fatty  acids,  and  purified  from  oleic  acid  by  crystallization  in  alcohol.  It 
forms  brilliant  scales,  similar  to  margaric  acid,  and  melting  at  the  same  point, 
140°,  as  that  acid.  It  may  be  distilled  in  great  part  unchanged.  Chlorine  de- 
composes it,  giving  rise  to  new  compounds. 

The  salts  of  this  acid  with  the  alkalies  are  soaps,  and  palm  oil  is  much  used 
in  soap-making.  Palmitate  of  glycerine,  or  palmitine,  is  the  fat  or  butter  of  the 
palm  oil,  purified  from  the  oleine  or  liquid  part,  by  pressure,  and  then  by  crys- 
tallization in  ether.  It  melts  at  118°,  and  on  cooling  assumes  the  aspect  of 
wax.  Like  myristine,  it  appears  to  contain  the  modified  glycerine  C^H^O, 
which  is  CgH^O^ — 3H0 ;  that  is,  glycerine,  minus  3  eq.  of  water,  and  divided 

2 

by  2.     Pure  palmitine  (as  also  pure  myristine),  when  distilled,  yields  acroleine. 


STEARIC  ACID.  669 

derived  from  the  glycerine ;  but  no  sebacic  acid.  The  crude  palm  oil,  or  impure 
palmitine,  however,  yields  abundance  of  sebacic  acid,  a  compound  derived  from 
oleic  acid,  and  proving,  therefore,  the  presence  of  oleic  acid  or  rather  oleine. 

21.  Cetylic  Acid.     CgaHsiOgjHO. 

Syn.  Ethalic  Add.  This  acid,  which  is  isomeric  with  the  preceding,  is  formed 
when  ethal  (hydrated  oxide  of  cetyle)  is  heated  with  hydrates  of  lime  and  po- 
tassa.  It  is  separated  as  usual  in  the  case  of  fatty  acids.  It  is  a  solid,  fusible 
between  130°  and  140°,  and  at  131°,  solidifying  in  radiated  groups  of  needles. 
It  may  be  distilled  unaltered.     Its  salts  are  like  those  of  the  preceding  acids. 

22,  Margaric  Acid.     C34H3303,HO  ;  or,  C68H660g,2HO. 

This  is  one  of  the  most  abundant  and  important  of  the  fatty  acids.  Combined 
with  glycerine,  as  margarine,  it  occurs  in  human  fat  and  some  other  animal  fats, 
and  in  many  vegetable  fats,  such  as  olive  oil.  The  acid  may  be  extracted  from 
soap  made  of  these  fats,  but  as  it  is  mixed  with  much  oleic  acid,  it  is  better  to  pre- 
pare it  by  oxidizing  stearic  acid  (see  below)  by  nitric  acid,  or  by  distilling  either 
tallow  or  crude  stearic  acid.  In  the  latter  case,  the  product  is  well  squeezed  and 
purified  by  solution  in  alcohol,  and  crystallization.  If  prepared  from  pure  stearic 
acid  by  nitric  acid,  it  is  pure  from  the  first. 

Margaric  acid  is  a  white  solid  fat,  of  distinct  acid  properties,  fusible  at  140°, 
very  soluble  in  hot  alcohol  and  in  ether.  It  instantly  combines  with  bases, 
decomposing  the  carbonates  and  forming  perfect  soaps  with  potassa  and  soda 
The  neutral  margarates  of  potassa  and  soda  are  decomposed  by  the  addition  of 
much  water,  depositing  the  acid  margarateg  in  pearly  scales.  Margaraie  of  gly- 
cerine^ or  margarine,  is  found  pure  in  the  solid  part  of  human  fat  or  of  olive  oil. 
It  dissolves  in  hot  alcohol,  and  crystallizes  on  cooling.  Margaraie  of  oxide  of 
ethyle  is  a  white  fusible  solid. 

The  general  formula  of  the  neutral  margarates  is  C  H  02,M0,  or  C  Hg^O  , 
2M0.  We  cannot  say  with  certainty  whether  margaric  acid  is  unibasic,  as  the 
first  of  these  formulae  would  indicate,  or  bibasic,  according  t©  the  second.  We 
shall  return  to  this  point  after  describing  stearic  acid,  and  we  shall  also  then 
describe  the  action  of  heat  on  both  acids. 

23.    Stearic  Acid.    C68H6605,2HO  =  5^2HO. 

This  is,  perhaps,  j:he  most  important  and  most  abundant  of  the  fatty  acids.  It 
exists,  in  combination  with  glycerine,  as  stearine,  in  beef  and  mutton  fat,  and  in 
several  vegetable  fats,  such  as  the  butter  of  cacao.  To  obtain  it,  mutton  suet  is 
saponified  by  boiling  with  potassa,  and  the  purified  soap  decomposed  by  an  acid, 
when  a  mixture  of  stearic  and  oleic  acids,  the  latter  in  small  proportion,  rises  to 
the  surface.  It  is  strongly  pressed  between  warm  plates,  so  as  to  get  rid  of  the 
oleic  acid  in  great  part,  and  it  is  finally  purified  by  solution  in  hot  alcohol,  and 
crystallization,  repeated  till  its  melting  point  is  constant  at  167°.  Or  the  stearic 
acid  of  commerce,  which  is  nearly  pure,  may  be  purified  by  means  of  alcohol. 
Or  again,  tallow  may  be  mixed  with  half  its  weight  of  oil  of  vitriol,  and  the 
m^ss  melted  in  hot  water,  which  removes  a  compound  of  sulphuric  acid  with 
glycerine,  while  the  stearic  acid  rises  to  the  surface  and  is  to  be  purified  as 
above.  Finally,  pure  stearine,  if  saponified,  and  the  soap  acted  on  by  an  acid, 
yields  at  once  pure  stearic  acid. 


670  STEARINE. 

Stearic  acid  is  a  white  solid,  fusible  at  167°,  and  on  cooling  forming  brilliant 
white  needles.  It  may  be  reduced  to  powder,  and  is,  like  all  fat  acids,  insoluble 
in  water,  soluble  in  alcohol  and  ether.  It  burns  like  wax,  and  is-  used  in  the 
formation  of  improved  candles. 

B)'  the  action  of  nitric  acid  and  other  oxidizing-  agents,  stearic  acid  is  at  once 
converted  into  margaric  acid,  and  it  will  be  seen  that  the  addition  of  1  eq.  oxy- 
gen is  sufficient  to  effect  this  change.     C^U^0^,'2U0  4-  O  =  C    H   O  ,2H0. 

Stearic  acid  is  bibasic,  and  forms  two  series  of  salts;  sI,2M0,  and  gt,MO, 
HO.  The  neutral  stearates  of  the  alkalies  are  perfect  soaps.  They  dissolve  in 
from  10  to  20  parts  of  hot  water,  and  the  addition  of  a  large  quantity  of  water 
decomposes  them  into  acid  stearates  which  are  deposited,  and  basic  stearates 
which  remain  dissolved.  For  the  same  reason  a  hot  solution  of  a  neutral  stea- 
rate  becomes  gelatinous  on  cooling,  from  the  separation  of  the  acid  salt.  Jcid 
siearate  of  oxide  of  ethyle,  St,AeOHO,  and  neutral  stear ate  of  the  same  base,  St, 
2AeO,  are  both  white  crystalline  fusible  solids ;  as  is  likewise  the  siearate  of 
oxide  of  meihyle^  St,2MtO. 

Siearine,  the  chief  ingredient  of  suet  and  tallow,  appears  to  be  the  acid  siea- 
rate of  oxide  of  glyceryle^  but  its  precise  formula  cannot  be  determined  as  long 
as  we  are  doubtful  about  that  of  glycerine.  If  glycerine  be  C^H^O,  then  stea- 
rine  will  be  CggHg^O^  f  C^H30  +  2HO  =  St,GlyO,2HO  ;  but  if  stearine  be  C^H^ 
O^,  the  formula  will  be  2C'C^^Hg^0^)  +  GlyO  -f  2H0  ;  (using  the  older  formula 
for  stearic  acid).  Neither  of  these  formulae  is  satisfactory,  as  both  exhibit  3  eq. 
of  base  and  basic  water,  instead  of  two  or  four.  When  boiled  with  alkalies, 
stearine,  like  all  other  fats,  is  saponified  :  that  is,  the  stearic  acid  combines  with 
the  alkali,  forming  soap,  and  glycerine  is  separated.  Pure  stearine  is  obtained 
by  pressing  tallow  between  hot  plates,  and  afterwards  dissolving  in  hot  ether, 
which  on  cooling  deposits  the  stearine.  It  is  like  wax  in  appearance  when  it 
has  been  melted,  and  it  may  be  powdered. 

Stearate  of  lead  is  an  insoluble  fusible  soap,  or,  as  it  is  called,  a  plaster.  The 
same  is  true  of  margarate  of  lead,  and  in  general  of  the  compounds  of  lead  with 
fat  acids-  v 

The  composition  of  stearic  acid  stands  in  a  very  simple  relation  to  that  of  mar- 
garic acid.  If  we  call  the  compound  C^^H^,  margaryle,  and  view  it  as  a  com- 
pound radical,  representing  it  by  the  symbol  Ml,  then  Ml^O^  =  stearic  acid  and 
M1^0g  =  2M10^  =  margaric  acid.  These  acids,  therefore,  bear  to  each  other  the 
same  relation  as  that  which  subsists  between  sulphuric  and  hyposulphuric  acids, 
SO  and  S^O  .  The  only  difference  is  that,  while  SO  neutralizes  as  much  base 
as  S^0^,M10^  only  neutralizes  half  the  quantity  of  base  neutralized  by  Ml^O^, 
or  in  other  words  Ml  O   neutralizes  as  much  base  as  Ml  O  . 

When  stearic  acid  is  distilled  alone,  or  with  lime,  it  yields  much  margaric 
acid,  and  a  neutral  fusible  crystalline  fat,  margarone,  besides  a  solid  carbohy- 
drogen  C^^H^,  carbonic  acid,  and  water.  Margarone  is  either  O^^H  O,  or  C^ 
HO.  In  the  former  case  it  is  formed  from  margaric  acid  by  the  loss  of  1  eq. 
carbonic  acid  ;  in  the  latter,  it^  is  the  oxide  of  the  supposed  radical  magaryle, 
MIO.  The  production  of  these  compounds  is  easily  understood,  for  2  eq.  stearic 
acid  are  equal  to  3  eq.  margaric  acid  and  1  eq.  oxide  of  margaryle;  2M1  O^  =« 
SMlOg  =  MIO.  Again,  4  eq.  of  hydrated  stearic  acid  contains  the  elements  of 
6  eq.  hydrated  margaric  acid,  1  eq.  margarone,  (C^^H^O),  1  eq.  water,  1  eq. 
carbonic  acid,  and  1  eq.  of  the  carbo-hydrogen  C  H  .  It  would  appear  that 
according  to  circumstances  the  margarone  has  a  different  composition,  its  pro- 


SUCCINIC  ACID.  671 

perties  varying  little,  so  that  different  chemists  have  obtained  different  marga- 
rones:  namely  ^33H330  ;  C^^H^O ;  and  even  CggHg^O  =  Ml^O.  When  mar- 
garic  acid  is  heated,  part  distils  unchanged,  and  part  is  converted  into  the  above 
products. 

When  margarine  or  stearine  are  distilled,  they  yield  the  very  acrid  vapours  of 
acroleine,  a  product  derived  from  the  glycerine  contained  in  these  fats;  but  pure 
stearic  and  margaric  acids  yield  not  a  trace  of  acroleine.  Neither  do  they  yield 
any  sebacic  acid  among  the  products  of  their  distillation,  this  acid  being  derived, 
exclusively  from  oleic  acid. 

ACTION  OF  NITRIC  ACID  ON  MARGARIC  ACID. 

By  the  action  of  nitric  acid  stearic  acid  is  converted  into  margaric  acid,  with 
disengagement  of  nitrous  acid  vapours.  But  if  the  action  of  the  nitric  acid  be 
prolonged,  the  margaric  acid  is  gradually  oxidized  and  dissolved,  being  eon- 
verted  into  suberic  acid,  succinic  acid,  and  an  oil  soluble  in  nitric  acid,  - 

24.  Suberic  Acid.    CgHgOajHO  =  Su^HO. 

This  acid  is  formed  when  cork  is  oxidized  by  nitric  acid,  but  especially  when 
nitric  acid  acts  on  stearic  acid,  margaric  acid,  oleic  acid,  and  other  fatty  bodies. 
The  acid  solution,  obtained  by  boiling  stearic  or  margaric  acid  with  nitric  acid 
till  it  is  entirely  dissolved,  is  evaporated  to  one  half,  and  on  cooling  deposits  a 
large  quantity  of  suberic  acid,  which  is  easily  purified  by  crystallization. 

It  forms  small  granular  crystals,  fusible,  when  moist,  at  130°,  when  dried,  at 
248°,  volatile  at  a  higher  temperature,  and  subliming  in  the  form  of  long 
needles.  It  is  sparingly  soluble  in  cold  water,  very  soluble  in  hot  water,  in  alco- 
hol, and  in  ether. 

The  general  formula  of  the  suberates  is  SuiMO,  The  suberate  of  oxide  of 
ethyle  is  prepared  like  the  ethers  of  all  the  fatty  acids,  by  passing  hydrochloric 
acid  gas  through  the  alcoholic  solution  of  the  acid.  When  suberate  of  lime  is 
distilled,  it  yields,  among  other  oily  products,  a  liquid  boiling  at  366°,  the  for- 
mula of  which  is  0^11^0.  It  may  be  either  the  oxide  of  C^H^,  or  the  hyduret  of 
CgHgO.  It  is  converted  into  suberic  acid  by  the  action  of  the  air  and  of  nitric 
acid.  In  fact,  the  addition  of  3  eq.  of  oxygen  gives  the  composition  of  hydrated 
suberic  acid,  C  H  O  .  It  is  probable  that  there  exists  a  radical  suberyle  =  C 
HgO  =  Su;  and  that  we  have  SuH,  and  SuO  ,H0  for  the  oil  and  suberic  acid, 
analogous  to  the  hyduret  of  benzoyle  and  benzoic  acid. 

25.  Succinic  Acid.    C4H304,HO  =  S^HO. 

This  acid  exists  ready  formed  in  amber,  and  may  be  obtained  by  distilling, 
that  body.  But  the  mother  liquor  of  the  suberic  acid,  formed  from  margaric 
acid,  &c.,  by  nitric  acid,  contains  a  large  quantity  of  succinic  acid,  along  with  a 
little  suberic  acid.  The  mixture,  being  dried  up,  is  acted  on  by  ether,  which 
dissolves  the  suberic  acid,  leaving  the  succinic  acid;  it  is  finally  purified  by 
sublimation. 

It  forms  regular  crystals,  which  maybe  easily  sublimed.  The  formula  of  the 
sublimed  crystals  is  2  (C^H^O^)  +  HO  ;  but  by  repeated  sublimation  it  may  be 
obtained  anhydrous.     The  first  hydrate  sj'HO,  melts  at  356°,  and  boils  at  455°, 


672  lOLEIC  ACID. 

6ubliming,  however,  slowly  at  284°.  The  sublimed  hydrate,  2  Su  + HO,  melts 
at  320°,  and  boils  at  468°  ;  and  the  anhydrous  acid  melts  at  257°,  and  boils 
at  482°. 

By  the  action  of  anhydrous  sulphuric  acid,  it  yields  a  new  acid,  apparently 
C  H  S,0   ,4H0,  hyposulphosuccinic  acid. 

The  constitution  of  the  succinates  is  still  doubtful ;  but  the  most  recent  re- 
searches of  Fehling,  who  has  twice  examined  these  salts  with  care,  lead  to  the 
general  formulae  o(C^Hfi^MO  for  the  neutral,  and  2  (C^H^O^)  -\-  MO,HO,  for 
the  acid  salts.  The  succinates  of  lead  present  some  anomalies.  By  the  action  of 
ammonia,  NH^,  on  succinic  ether,  C^H202,C^H^O,  there  is  formed  succinamide, 
C^H202,NH2,  while  alcohol,  C^H^O,HO  is  given  off.  When  acid  succinate  of 
ammonia  is  heated  there  is  sublimed  a  new  body,  bisuccinamide,  CgH^O^,^!^^. 
It  is  formed  from  2  eq.  succinic  acid  and  1  eq.  ammonia,  by  the  separation  of  2 
eq.  water.  In  their  mode  of  formation  these  two  bodies  resemble  oxamide  and 
oxamic  acid,  only  bisuccinamide  has  no  acid  properties. 

The  origin  of  amber  is  very  uncertain :  but  it  is  most  probably  derived  from 
some  resin,  formerly  liquid  or  soft.  It  may  possibly  have  arisen  from  the  slow 
oxidation  of  a  fatty  matter,  as  we  see  succinic  acid  formed  from  fdts  by  oxidation. 
Amber  is  a  clear  brittle  yellow  solid,  becoming  electric  by  friction.  It  is  for 
the  most  part  insoluble  in  all  menstrua.  "When  heated  it  yields  succinic  acid 
and  a  volatile  oil,  and  there  is  left  a  large  proportion  of  a  matter  which  may  be 
called  bituminous,  and  forms  the  principal  part  of  the  amber. 

26.    Oleic  Acid.     C44H39O4,  HOt  =  OT,  HO. 

This  acid,  in  combination  with  glycerine,  constitutes,  as  oleine,  the  liquid  or 
most  fusible  portion  of  fats  and  fat  oils.  It  exists  in  small  proportion  in  tallow 
or  suet;  more  abundantly  in  human  fat  and  hog's  lard  ;  and  it  predominates  in 
olive  oil  and  especially  in  almond  oil.  To  obtain  it,  almond  oil  is  saponified, 
and  the  mixed  fat  acid  obtained  from  the  soap  is  digested  with  half  its  weight  of 
oxide  of  lead,  by  which  means  margarate  and  acid  oleate  of  lead  are  formed. 
Ether  dissolves  the  latter  only,  and  the  ethereal  solution  of  oleate  of  lead  is  acted 
on  by  hydrochloric  acid,  when  the  ether  rises  to  the  surface,  holding  the  oleic 
acid  in  solution.  The  ether  being  distilled  off,  the  oleic  acid  is  left  somewhat 
coloured.     When  pure  it  is  a  nearly  colourless  oily  fluid,  freezing  in  cold  weather. 

It  forms  salts  with  bases,  and  the  oleates  of  the  alkalies  are  soaps.  Naples 
soap  is  chiefly  oleate  of  potash :  oleate  of  soda  is  harder. 

Nitric  acid  converts  oleic  acid  into  suberic  acid  and  other  products.  By  hypo- 
nitric  (nitrous)  acid  or  nitrate  of  mercury  it  is  converted  into  elaidic  acid. 

When  distilled,  oleic  acid  gives  rise  to  sebacic  acid,  and  this  is  an  infallible 
test  of  the  presence  of  oleic  acid  or  oleine  in  any  fat.  This  character  applies  to 
^11  the  varieties  of  oleic  acid,  although  we  have  reason  to  think  that  the  oleic 
acids  of  fat  oils  and  of  drying  oils  are  very  diflferent.  Indeed,  according  to  recent 
researches,  the  oleic  acid  of  linseed  oil  is  C^gH2gO^,HO. 

Of  the  oleates,  the  most  important  are  those  of  potash  and  soda,  which  exist 
in  most  soaps,  and  constitute  the  chief  part  of  those  made  with  olive  or  almond 
oil,  or  whale  oil,  and  that  of  lead,  which  is  a  valuable  ingredient  of  most  plasters. 
Oleate  of  oxide  (f  glycerile^as  already  mentioned,  is  oleine,  the  liquid  part  of  fats 
and  fat  oils,  which  is  hardly  known  in  a  perfectly  pure  state.  Oleate  of  oxide 
of  ethyle  is  an  oily  liquid. 


ACTION  ON  NITRIC  ACID  ON  OLEIC  ACID.  673 

27.    SebaicAcid.    C,oH803,HO  =  si,HO. 

When  any  oil  or  fat,  containing'  oleine  or  oleic  acid,  is  distilled,  and  the  pro- 
duct boiled  with  water,  the  hot  filtered  liquid  deposits,  on  cooling,  sebacic  acid 
in  small  crystals  resembling  benzoic  acid.  It  is  soluble  in  alcohol  and  ether, 
and  sublimes  without  alteration.  The  salts  of  sebacic  acid  are  not  remarkable, 
with  the  exception  of  the  sebate  of  oxide  of  ethyle,  which  has  a  fragrant  smell  of 
melons.  When  we  wish  to  ascertain  the  presence  of  oleine  in  a  fat,  a  portion  is 
distilled,  the  product  is  boiled  with  water,  and  the  liquid,  even  if  it  deposit 
nothing,  is  tried  by  acetate  of  lead,  with  which  it  forms  a  white  precipitate  if 
sebacic  acid  be  present. 

28.    Elaidic  Acid.    C72H66O5. 

This  acid  is  formed  by  the  action  of  nitrous  acid  on  oleic  acid.  If  a  current 
of  nitrous  acid  be  passed  through  well-cooled  oleic  acid,  the  latter  soon  solidi- 
fies in  large  scales,  which  are  elaidic  acid.  It  is  purified  by  solution  in  alcohol. 
It  forms  silvery  scales,  melting  at  112°,  very  soluble  in  alcohol,  and  volatile 
without  decomposition,  except  to  a  very  small  extent.  The  salts  of  this  acid 
are  soaps,  and  resemble  those  of  the  other  fat  acids. 

Oleine  is  converted  into  elaidine  (elaidate  of  glycerine),  and  oleic  ether  into 
elaidic  ether,  by  the  action  of  nitrous  acid;  but  we  cannot  yet  account  for  the 
production  of  elaidic  acid  in  these  cases  or  in  that  of  its  fermentation  from  oleic 
acid ;  since  the  reaction  is  accompanied  by  the  production  of  other  substances, 
not  yet  examined. 

ACTION  OF  NITRIC  ACID  ON  OLEIC  ACID. 

When  oleic  acid  is  acted  on  by  nitric  acid,  it  yields  several  acids,  only  one  of 
which,  suberic  acid,  occurs  in  the  action  of  nitric  acid  on  other  fat  acids.  The 
remaining  acids  are,  azelaic  acid?  pimelic  acid,  adipic  acid,  lipic  acid,  and  azoelic 
acid. 

The  action  of  nitric  acid  on  oleic  acid  is  violent.  When  completed,  the  liquid 
is  evaporated  to  one-half,  and  on  cooling  deposits  suberic  acid,  which  according 
to  Laurent,  is  accompanied  by  azelaic  acid,  very  similar  to  it,  the  composition 
of  which  he  describes  as  the  same  as  that  of  suberic  acid,  or  only  differing  by  1 
eq.  of  water,  while  he  gives  the  formula  C^^HgO^,HO,  that  of  suberic  acid  being 
CgHg02,H0.  There  is  probably  here  an  error  of  the  press.  But  the  existence 
of  azelaic  acid  is  very  doubtful. 

Pimelic  acid  crystallizes  on  evaporation  after  the  suberic  acid  has  been 
removed,  in  hard  granular  crystals,  fusible  and  volatile.  Its  formula  is  C^H^ 
0^,H0.  In  the  mother  liquid  are  found  : — Mipic  acid  in  round  radiated  masses, 
fusible  and  volatile.  Formula  CgH^03,H0  (Laurent),  Cj^H^-0^,2H0  (Bromeis), 
probably  different  acids.  The  Lipic  acid  forms  long  tables,  very  fine  when 
formed  in  alcohol.  Formula  C^^^.llO.  Azoleic  acid,  according  to  Laurent, 
occurs  in  the  form  of  an  oily  liquid,  and  cenanthic  acid  is  also  found.  According 
to  Bromeis,  azoleic  acid  is  doubtful,  and  the  acid  taken  for  it  and  for  cenanthic 
acid  is  impure  butyric  acid,  the  formation  of  which  is  not  improbable,  since 
butyric  acid  contains  exactly  1  eq.  hydrogen  more  than  suberic  acid. 

When  oleic  acid  and  elaidic  acids  are  heated  with  potassa  there  are  produced 
acetic  acid  and  a  new  fatty  acid,  C22H^pOg,HO.    The  difference  between  the 

45 


g74  ACTION  OF  HEAT  ON  OILS  AND  FATS. 

formula  of  this  acid  and  that  of  oleic  acid  is  equal  to  3  eq.  acetic  acid,  which 
accounts  for  its  production.  Again,  elaidic  acid,  C^^H^gO^,  ja/us  7  eq.  oxygen, 
yields  2  eq.  of  the  new  acid,  and  2  eq.  acetic  acid.  This  acid  only  differs  from 
palmitic  (ethalic)  acid  by  1  eq,  hydrogen. 

ACIDS  OF  CASTOR  OIL. 

Castor  oil  is  a  very  peculiar  oil.  When  saponified,  it  yields  two  fat  acids,  one 
crystallizable,  margariiic  acid  ,•  the  other  liquid,  ricinic  acid.  The  latter  is  little 
known.  The  former  is  said  to  be  ^^^11^^,0^.  Castor  oil  is  a  mixture  of  the 
compounds  of  glycerine  with  these  two  acids.  It  is  soluble,  when  pure,  in  its 
own  bulk  of  alcohol.  Nitrous  acid  converts  it  into  a  solid  crystallizable  fat, 
palmine,  analogous  to  elaidine,  but  differing  from  it. 

When  castor  oil  is  acted  on  by  nitric  acid,  it  yields  a  new  volatile  oily  acid, 
of  an  agreeable  aromatic  odour,  which  is  called  (tnanthilic  acid,  as  its  formula  is 
that  of  cenanthic  acid,  plus  1  eq.  oxygen ;  Cj^Hj^Og,HO.  It  forms  an  ether  of  a 
very  agreeable  aromatic  smell.     In  the  residue  is  found  suberic  acid. 

Palmine,  the  fat  formed  by  the  action  of  nitrous  acid  on  castor  oil,  is  a  white 
crystalline  fat,  which  when  saponified,  yields  glycerine  and  a  fatty  acid,  palmic 
ticid,  not  yet  fully  investigated.  A  current  of  sulphurous  acid  passed  through 
castor  oil  is  said  to  produce  palmine,  or  at  all  events  a  fat  which  yields  palmic 
acid.  This,  if  true,  is  a  very  singular  fact,  since  nitrous  acid,  an  oxidizing 
agent,  and  sulphurous  acid,  a  deoxidizing  one,  would  thus  produce  the  same 
result. 

NATURAL  FATS  AND  FIXED  OILS. 

These  are  all  compounds  of  glycerine  with  fatty  acids.  When  heated  with 
alkalies  they  yield  soaps  ;  with  oxide  of  lead,  plasters  ;  while  in  both  cases  gly- 
cerine is  set  free.  The  most  common  of  all  these  compounds  are  stearine,  mar' 
garine,  and  oleine,  of  which  always  too,  and  often  all  ^three,  are  present,  stearine 
predominating  in  the  hard,  margarine  in  the  soft,  and  oleine  in  the  liquid  fats.  It 
is  only  the  compounds  of  glycerine  with  volatile  acids,  such  as  butyric  acid,  that 
have  a  strong  smell. 

There  are  two  kinds  of  fat  oils :  the  fat  oils  proper,  and  the  drying  oils-  The 
latter  contain  much  oleine,  the  oleic  acid  of  which  is  different  from  the  usual 
oleic  acid,  and  ihey  absorb  oxygen  from  the  air,  drying  into  a  kind  of  varnish. 
When  oils  become  rancid,  they  are  partly  decomposed  :  and,  generally,  some  of 
the  acid,  as  well  as  of  the  glycerine,  is  set  free,  while  oxygen  is  absorbed.  Pure 
stearine,  margarine,  and  oleine  do  not  become  rancid,  and  that  change  depends  on 
a  process  of  decay  or  slow  oxidation  going  on  in  the  impurities  of  the  oil,  and 
from  them  passing  to  the  oil  itself. 

ACTION  OF  HEAT  ON  OILS  AND  FATS.    ACROLEINE. 

When  oils  are  distilled  they  produce  a  variety  of  compounds,  such  as  mar- 
garic  acid,  sebacic  acid,  margarone,  carbohydrogens,  &c.  &c.,  and  one  most 
remarkable  compound,  acroleine,  derived  from  glycerine. 

^croUine,  C^H^O^,  is  best  obtained  by  distilling  glycerine  with  phosphoric 
acid.    The  whole  operations  must  be  carried  on  in  vessels  full  of  carbonic  acid 


ACTIQN  OF  SULPHURIC  ACID  ON  FAT  OILS.  ^^^ 

gas,  as  the  acroleine  is  very  rapidly  oxidized  by  the  air.  Its  vapour  attacks  the 
eyes  and  nose  in  a  most  painful,  indeed  intolerable,  degree.  It  may  be  considered 
as  the  hydrated  oxide  of  a  radical  CgH^,  {acryle^  analogous  to  acetyle)  C  H  ,0 
+  HO,  analogous  to  aldehyde.  It  rapidly  absorbs  oxygen  and  forms  acrylic  acid, 
CgH  O  fHO,  analogous  to  acetic  acid.  In  certain  circumstances,  the  solution  of 
acroleine  exposed  to  the  air,  deposits  a  white  solid,  C   H  O  . 

The  presence  of  acroleine  among  the  products  of  the  distillation  of  an  oil  or 
fat  is  a  convincing  proof  of  the  presence  of  glycerine  in  that  oil.  It  is  worthy 
of  remark  that  glycerine,  C^H^O^,  is  hydrated  oxide  of  acryle,  plus  3  eq.  water, 
so  that  oils  and  fats  may  be  called  compounds  of  acroleine  as  well  as  of  glyce- 
rine. It  is  even  conceivable  that  acroleine  may  be  C  H  0,  which  we  have  seen 
to  be  a  probable  form  of  glycerine  in  some  fats ;  or  that  the  glycerine  in  these 
fats  may  be  acroleine,  as  above  given,  CgH^O^,  and  that  when  this  glycerine  is 
separated  by  an  alkali,  it  takes  up  3  eq.  of  water. 

Castor  oil,  so  peculiar  in  other  respects,  exhibits  a  peculiar  decomposition  by 
heat.  It  yields  acroleine,  and  a  volatile  oil,  composed  of  two  oils  insoluble  in 
alkalies  ;  besides  some  saponifiable  acids.  When  about  one-fifth  has  been  dis- 
tilled, the  residue  suddenly  consolidates  into  a  spongy,  yellow,  elastic  mass, 
insoluble  in  all  menstrua,  except  caustic  alkalies,  with  which  it  forms  peculiar 
soaps.  These,  when  decomposed  by  an  acid,  yield  a  tough  viscid  substance 
having  the  characters  of  an  acid.  The  product  of  the  distillation  again  distilled 
with  water,  yields  several  oily  compounds,  one  of  which  is  crystalline,  and  not 
yet  fully  studied.  The  less  volatile  residue  being  again  distilled  yields  a  pecu- 
liar crystalline  fatty  acid,  and  another  oily  acid.  Neither  of  these  has  been  pro- 
perly investigated. 

When  oils  or  fats  are  decomposed  at  a  red  heat,  they  yield  much  combustible 
gas  (oil  gas),  formed  of  olefiant  gas  and  marsh  gas,  and  several  liquid  carbohy- 
drogens:  in  particular  benzole,  C^^Hg,  Faraday's  quadricarburetted  hydrogen, 
C^H^,  or  C^H^,  and  another  isomeric  compound,  which  is  only  liquid  at  very 
low  temperatures. 

ACTION  OF  SULPHURIC  ACID  ON  FAT  OILS.  * 

Sulphuric  acid,  if  added  in  small  quantity  to  oils,  combines  with  their  glyce- 
rine ;  but  if  used  in  excess  gives  rise  to  a  number  of  new  products.  In  the  first 
instance  they  are  formed,  when  a  mixture  of  oleine  and  margarine  is  acted  on, 
two  new  acids  sulphokic  acid  and  sulphomargaric  acid.  These  acids  have  not 
been  isolated,  but  when  their  solution  in  water  is  heated,  the  sulphuric  acid 
separates,  and  the  oleic  and  margaric  acids  are  transformed  into  four  new  acids, 
metamargaric  and  hydromargaritic  acids,  and  metokic  and  hydr oleic  acids.  The 
two  former  are  solid,  crystallizable,  and  partly  volatile.  A  compound  of  the  two 
exists,  which  acts  like  a  single  acid  and  has  been  called  hydromargaric  acid;  it 
is  also  a  fusible  solid.  The  two  latter  are  oily,  and  all  five  appear  to  be  biba- 
sic.  Their  composition  cannot  be  considered  as  ascertained,  but  the  three  first 
are  nearly  allied  to  margaric  acid.  It  would  lead  to  confusion  here  to  mention 
the  different  formulae  proposed  by  Fremy,  Berzelius,  and  Liebig,  for  these  acids, 
more  especially  when  it  is  considered  that  we  have  no  sufficient  evidence  of  the 
perfect  freedom  from  foreign  admixture  of  the  acids  analyzed,  and  that  the  recent 
observations  of  Miller  show  an  amount  of  variation  in  the  melting  points  which 
leads  to  the  suspicion  of  impurity.  The  subject  is  interesting,  but  difficult,  and 
requires  a  very  minute  investigation. 


676  ACTION  OF  BASES  ON  FAT  OILS. 

Metoleic  and  hydroleic  acids,  when  distilled,  yield  water,  carbonic  acid,  and 
two  carbo-hydrogens,  oleene  and  elaene,  both  of  which  contain  carbon  and  hydro- 
gen in  an  equal  number  of  equivalents  ;  oleene  is  supposed  to  be  C  H  ,  and 
elaene,  O^  H^  :  but  this  is  not  established. 

ACTION  OF  NITROUS  ACID  ON  FAT  OILS. 

Nitrous  acid,  or  solution  of  nitrate  of  mercury,  as  already  mentioned,  causes 
fat  oils  to  become  solid,  converting  oleine  into  elaidine.  This  curious  change 
takes  place  in  olive  oil,  almond  oil,  rape-seed  oil,  hazel-nut  oil,  castor  oil  and 
others  :  but  the  drying  oils,  such  as  oils  of  linseed,  hemp-seed,  walnut,  poppy- 
seed,  &c.,  are  not  at  all  affected  by  nitrous  acid.  In  all  the  oils  which  are 
changed  into  elaidine,  except  in  castor  oil,  the  product  is  the  same.  It  is  the 
formation  of  this  solid  fat  which  causes  the  mercurial  ointments,  made  with  ni- 
trate, to  become  hard  when  kept.  The  elaidine,  when  purified  by  pressure  and 
crystallization  in  alcohol  and  ether,  yields  neither  margaric  nor  oleic  acid  when 
saponified,  but  only  elaidic  acid.  Hence,  the  elements  of  both  the  original  acids 
have  taken  a  share  in  the  transformation.  The  conversion  of  oleic  acid  into 
elaidic  acid  by  means  of  nitrous  acid  is  accompanied  by  the  formation  of  a  red 
substance.  The  probable  formula  of  elaidic  acid  is  C^^,HggOg.  As  elaidine  con- 
tains 2  per  cent,  more  carbon  than  elaidic  acid,  it  is  plain  that  elaidine  cannot 
be  a  compound  of  elaidic  acid  with  a  glycerine  containing  5  eq.  of  oxygen  to  6 
eq.  carbon.  (CgH^O^).  It  is  therefore  probable  that  elaidine  is  one  of  those 
fats  in  which  the  base  is  not  ordinary  glycerine  but  acroleine  C^H^Og,  or  C^H^O. 

Castor  oil,  as  has  been  already  mentioned,  yields,  with  nitrous  acid,  a  new  fat 
palmine,  which  contains  a  new  acid,  palmic  acid.  These  resemble  elaidine  and 
elaidic  acid,  but  are  quite  distinct. 

ACTION  OF  BASES  ON  FAT  OILS.     SOAPS  AND  PLASTERS. 

When  fat  oils  are  boiled  with  solution  of  caustic  alkalies,  they  are  gradually 
dissolved  in  the  water,  if  there  be  not  too  great  an  excess  of  alkali  present,  form- 
ing ropy  or  gelatinous  solutions,  which  gelatinize  on  cooling.  These  are  solu- 
tions of  soaps,  that  is,  potassa  and  soda  salts  of  the  fatty  acids,  along  with  the 
glycerine  set  free.  In  order  to  have  the  soaps  in  a  solid  form,  the  solutions  are 
boiled  down,  and  when  the  alkali  reaches  a  certain  concentration,  the  soap  be- 
comes insoluble,  and  rises  to  the  surface  in  a  soft,  half  melted  state.  This  is 
drawn  off  into  moulds,  and  the  mass  formed  on  cooling  is  soap.  Another  method 
of  causing  the  soap  to  separate  from  the  water  in  which  it  is  dissolved,  consists 
in  adding  sea-salt,  which  at  once  coagulates  the  soap,  converting  it  into  a  soap 
of  soda,  if  it  is  a  soap  of  potassa.  Of  course,  the  glycerine,  in  both  cases  is 
carried  off  in  the  mother  liquor.  Such  is  the  theory  of  soap-making,  which  is 
very  simple,  depending  on  the  affinity  between  the  alkalies  and  the  fat  acids  ;  on 
the  solubility  in  water  of  the  alkaline  stearates,  margarates,  oleates,  palmitates, 
&c.;  and  finally  on  the  power  of  a  certain  amount  of  free  alkali  or  of  sea-salt  to 
coagulate  the  soap  and  render  it  insoluble  in  the  liquid  in  which  it  swims,  and 
which  in  fact,  runs  off  its  surface  as  water  does  off  the  surface  of  fat,  while  yet 
the  soap  retains  perfectly  its  solubility  in  pure  water. 

The  soaps  of  lime,  baryta,  &c.,  are  insoluble  in  water,  and  have  no  detergent 
power :  hence  the  waste  occasioned  by  using  hard,  that  is,  calcareous,  water  for 
washing.    All  the  salts  of  lime  in  such  water  must  first  be  entirely  precipitated 


ACTION  OP  BASES  ON  FAT  OILS.  57| 

in  the  form  of  curdy  flocculi  before  any  soap  can  be  dissolved  so  as  to  act  as  a 
detergent. 

The  soaps  of  potassa  are  soft,  compared  with  those  of  soda,  which  are  called 
hard  soaps.  White  soap  is  stearate  with  some  oleate,  of  soda.  Naples  soap  is 
oleate  and  raargarate  of  potassa.  Common  soft  soap  is  chiefly  oleate  of  potassa, 
but  as  it  is  made  from  whale  oil  or  seal  oil,  it  contains  also  phocenate  of  potassa, 
which  gives  it  a  disagreeable  smell. 

Castile  soap  is  oleate  and  margarate  of  soda,  coloured  by  metallic  oxides, 
chiefly  oxides  of  iron,  in  such  a  way  as  to  give  the  desired  mottled  appearance. 
Much  and  excellent  soap  is  now  made  of  palm  oil,  and  is,  therefore,  palmitate 
of  soda. 

Soaps  are  soluble  in  alcohol,  forming  tincture  of  soap,  which  is  an  admirable 
liniment  for  bruises,  and  is  much  used  along  with  laudanum,  as  tincture  of  soap 
and  opium ;  also  with  camphorated  spirit,  forming  opodeldoc. 

Plasters  are  soaps  of  certain  metallic  oxides,  chiefly  oxide  of  lead,  which  are 
insoluble  in  water,  but  fusible,  and  possess  useful  properties.  Litharge  plaster 
is  made  by  boiling  finely  5  parts  of  powdered  oxide  of  lead  with  9  parts  of  olive 
oil  and  some  water,  till  the  combination  is  complete.  It  is  plastic  at  ordinary 
temperatures,  and  melts  when  heated.  When  solution  of  acetate  of  lead  is  added 
to  solution  of  soap,  plaster,  that  is  oleate  and  margarate  of  lead,  is  precipitated. 
When  prepared  in  tliis  way  it  becomes  hard.  White  lead  plaster,  made  with 
carbonate  of  lead,  is  very  plastic  and  fusible,  and  is  much  used.  Iron  plaster 
and  mercurial  plaster  are  of  small  importance. 

The  chief  liquid  fat  oils  and  drying  oils  of  the  vegetable  kingdom  have  already 
been  mentioned.  In  the  animal  kingdom,  there  are  fish  oils,  characterized  by 
containing  phocenine  ;  also  cod  liver  oil,  &c.  &c. 

The  solid  oils  or  fats  of  the  vegetable  kingdom,  are  butter  of  cacao  {theobroma 
cacao)  ;  of  nutmeg  {rnyristica  moschata)  ;  of  cocoa-nut  {cocos  nucifera) ;  of  laurel 
(laurus  nobilis)  ;  palm-oil  (Avotra  elais:  elais  Guianensis);  galam  butter  (Bassia 
hutyracea)  ;  and  some  others.  Those  of  the  animal  kingdom  are  tallow,  or  suet, 
butter,  hog's  lard,  human  fat,  &c. 

Spermaceti  is  a  peculiar  fat  found  in  the  head  oi  physeier  macrocephalus.  When 
purified  from  a  small  quantity  of  a  liquid  oil,  it  constitutes  ceiine,  which  is  a 
compound  of  ethal  (hydrated  oxide  of  cetyle)  with  oleic  and  margaric  acids. 
Cetine  crystallizes  beautifully  when  melted  or  when  dissolved  in  hot  alcohol. 

Cholesterine  is  a  fat  found  in  bile,  and  also,  in  small  proportion,  in  the  blood, 
and  in  much  larger  quantity  as  an  ingredient  of  cerebral  matter.  It  forms  the 
chief  ingredient  of  biliary  calculi.  It  dissolves  in  hot  alcohol,  crystallizes  on 
cooling,  in  silvery  scales,  but  cannot  be  saponified  by  boiling  with  potassa.  Its 
formula  is  either  C^gH^O,  or  ^36^320.  When  acted  on  by  nitric  acid,  it  yields 
a  new  acid,  cholesieric  acid,  which  contains  nitrogen,  probably  as  nitrous  acid. 

Ambreine,  a  fat  analogous  to  cholesterine,  is  found  in  ambergris.  It  yields, 
with  nitric  acid,  ambreic  acid.     Castorine  is  a  similar  fat  found  in  castoreum. 

Wax  is  another  peculiar  fatty  body,  the  origin  of  which  is  derived  from 
flowers,  whence  it  is  collected  by  the  bee.  It  melts  at  about  150°.  It  is  a  mix- 
ture of  two  fats,  ctrine  and  myricine,  the  former  soluble,  the  latter  insoluble,  in 
hot  alcohol.  Cerine  is  partly  saponified,  by  boiling  with  potassa,  yielding  appa- 
rently magaric  and  oleic  acids  (1)  along  with  a  neutral  fat,  ceraine  having  the 
same  composition  as  myricine.  There  are  several  kinds  of  vegetable  wax,  but 
they  are  all  much  more  easily  saponified  than  bees'  wax.      W^hen  bees'  wax  is 


678  VOLATILE  OR  ESSENTIAL  OILS. 

distilled,  it  yields  neither  acroleine  nor  sebacic  acid,  and  would  therefore  appear 
to  contain  neither  oleic  acid  nor  glycerine. 

Cerosine  is  the  name  given  to  a  waxy  substance  occasionally  found  on  the  sur- 
face of  the  sugar-cane.     It  is  not  saponifiable,  and  appears  to  contain  C    H   0  . 

Athamantine^  from  the  root  of  athamanta  creoselinum^  is  a  crystalline  fat-like 
body,  containing  valerianic  acid,  united  to  a  body,  oreoselone,  which  supplies  the 
place  of  glycerine  in  the  neutral  alhamantine.  Oreoselone  is  C  H  O  ,  that  is, 
isomeric  with  dry  benzoic  acid.  Athamantine  is  ^ 24^^ is^ 7 ^^u^s^ 3  (^  ^^* 
oreoselone)  -|-  C^^H'^^O^  (2  eq.  valerianic  acid).  Athamantine  combines  with 
hydrochloric  acid,  and  the  compound,  when  boiled  with  water,  deposits  crystals, 
which  are  ereoselone  plus  water  =  Cj^HgO^,  and  isomeric  with  crystallized  ben- 
zoic acid. 

Having  now  briefly  described  the  best  known  organic  acids,  it  is  necessary  to 
mention  a  number  of  acids,  found  in  the  analyses  of  different  vegetables,  but  not 
yet  sufficiently  studied  to  decide  whether  they  exist  independently  or  may  not 
rather  be,  in  many  cases,  identical  with  some  of  the  acids  above  described. 
Such  are  chelidonic  acid,  caincic,  crameric,  cajQTeic,  boletic,  fungic,  tanacetic, 
lactucic,  atropic,  cocognidic,  solanic,  coneic,  aceric,  moroxylic,  kinovic,  and 
menispermic  acids,  besides  others. 

VOLATILE  OR  ESSENTIAL  OILS. 

These  oils  are  so  called  because  they  are  obtained  by  distillation  of  vegetables, 
generally  along  with  water,  and  because,  having,  in  most  cases,  the  concentrated 
odour  of  the  plant,  they  are  usually  called  essences.  Most  of  them  exist  ready- 
formed  in  the  plant,  which  owes  its  smell  to  them :  but  some,  as  oil  of  bitter 
almonds  and  oil  of  spiraja,  are  formed  by  a  kind  of  fermentation,  excited  in  the 
case  of  the  former,  as  already  stated,  by  the  contact  of  amygdaline,  emulsine 
and  water. 

Many  plants,  when  cut,  yield  balsams,  which  are  mixtures  of  essential  oils 
and  resins.  In  many  essential  oils  a  crystalline  matter  is  deposited,  called  a 
camphor  or  stearoptene.  They  are  all  soluble  in  alcohol.  Many  absorb  oxygen 
from  the  air  and  become  acid,  as  oil  of  cinnamon.  They  are  violently  acted  on 
by  nitric  acid  and  iodine,  chlorine,  bromine,  &c. 

They  may  be  divided  into  three  kinds:  1st,  those  containing  only  carbon  and 
hydrogen,  as  oil  of  turpentine.  2nd,  those  containing  also  oxygen,  as  oil  of 
cloves.  3rd,  those  containing  sulphur,  as  oil  of  garlic. 

1.  Non-Oxygenated  Essential  Oils. 

Almost  every  one  of  these  (which  constitute  a  very  numerous  class  of  oils), 
as  yet  accurately  analyzed,  has  been  found  to  contain  carbon  and  hydrogen  in 
the  proportion  C^^Hg,  or  what  is  the  same  thing,  C^H^,  or  C^qH^q.  The  fol- 
lowing are  the  most  important. 

Oil  of  turpentine,  C^^Hg,  or  C^^Hjg,  is  obtained  by  distilling,  with  water,  tur- 
pentine, the  juice  exuding  from  many  species  of  pinus.  Rosin,  resin,  or  colo- 
phonium,  remains  in  the  retort.  The  oil  has  a  peculiar  smell,  and  burns  with  8 
smoky  flame.  Its  sp.  gr.  is  0*86.  It  boils  at  312°.  Strong  nitric  acid  sets  fire 
to  it,  and  it  is  also  decomposed  with  flame  by  chlorine.     It  dissolves  sulphur, 


OXYGENATED  ESSENTIAL  OILS.  679 

phosphorus,  and  fat  oils.  When  exposed  to  hydrochloric  acid  gas,  it  combines 
with  it,  forming  a  white  crystalline  solid  like  camphor,  and  a  liquid  compound. 
The  solid  is  G^^U^^C\=C^^U^^,I{C\.  When  heated  with  lime,  it  yields  a  pure 
oil,  dadyle  C^^H^g.  The  liquid  hydrochlorate,  heated  with  lime,  yields  another 
pure  oil,  peucyle,  rather  more  volatile  than  dadyle,  but  having  the  same  compo- 
sition. Oil  of  turpentine  would  seem  to  be  composed  of  peucyle  and  dadyle, 
both  C  H  ;  the  former  giving  a  liquid,  the  latter  a  solid  compound,  with 
hydrochloric  acid. 

Nitric  acid,  by  long  boiling,  converts  oil  of  turpentine  into  an  acid,  turpentinic 

acid.   C,  HO, HOI 

14     y    7 

Oil  of  turpentine  is  used  in  medicine,  internally,  as  a  vermifuge,  especially  in 
cases  of  the  larger  worms,  such  as  taenia  ,•  externally,  as  an  excellent  rubefacient 
and  counter-irritant.  In  the  arts  it  is  much  prized  as  a  solvent  for  resins  in 
making  varnishes. 

Oil  ff  juniper  has  the  same  composition  as  oil  of  turpentine,  but  possesses  its 
own  peculiar  odour,  which  it  communicates  to  alcohol  in  gin.  This  oil  is 
diuretic. 

Oil  of  saving  has  the  same  composition.  It  is  also  diuretic.  Oil  of  elemi  has 
the  same  composition,  and  a  pleasant  odour.  Oil  of  siorax,  or  sii/role,  appears  to 
have  the  composition  of  C^H,  or  some  multiple  of  it.  Nitric  acid  acts  on  it,  pro- 
ducing hydrocyanic  acid,  benzoic  acid,  and  a  fragrant  crystalline  body,  nitrosty- 
role.  Styrole  itself  is  a  very  remarkable  substance,  differing  as  it  does  from  all 
the  other  non-oxygenated  oils.  Dr.  Blyth  has  been  for  some  time  engaged  in  its 
investigation,  and  has  obtained  very  interesting  results,  not  yet  ready  for  publi- 
cation. 

[The  formula  recently  assigned  to  styrol  by  Drs.  Blyth  and  Hoffman  is  C^^ 
Hg.  When  heated  in  a  closed  tube  to  the  temperature  of  about  425°,  it  curiously 
changes  from  a  limpid  fluid  to  that  of  a  vitreous  solid,  having  precisely  the  same 
composition,  as  the  fluid  styrol,  to  which  they  gave  the  name  of  metasiyrol,'] 

Oil  of  lemons  has  the  probable  composition,  C  H  .  Like  oil  of  turpentine  it  is 
composed  of  two  isomeric  oils,  citrene  and  citrylene^  which  combine  with  hydro- 
chloric acid,  forming  a  liquid  and  a  solid  compound,  decomposed  by  heating 
with  lime.  The  solid  camphor  seems  to  be,  Cj^HgCl=Cj^Hg,HCl.  The  oils 
of  cedro^  cedrat,  oranges,  and  limes,  are  all  essentially  identical  with  oil  of  lemons. 
Oil  of  neroli,  or  of  orange-Jlower,  is  quite  distinct,  having  the  odour  of  the  flower, 
while  the  others  have  that  of  the  rind  of  the  fruit.  Its  composition  is  not  accu- 
rately known. 

Oil  of  copaiva  is  another  isomeric  form  of  oil  of  turpentine,  which  it  very 
much  resembles,  forming  a  camphor  with  hydrochloric  acid.  It  is  diuretic,  and 
much  used  in  affections  of  the  bladder  and  urethra.  Oils  of  pepper  and  of  cubebs 
are  still  of  the  same  composition  in  100  parts,  although  the  latter  is  supposed  to 
be  C„H,. 

2.  Oxygenated  Essential  Oils. 

The  principal  oils  of  this  class  have  been  already  considered,  their  radicals 
being  known.  These  are  oil  of  bitter  almonds,  or  hyduret  of  benzoyle;  oil  of 
spirsea,  or  hyduret  of  salicyle;  oil  of  cinnamon,  or  hyduret  of  cinnamyle;  oil  of 
cloves  (eugenic  acid)  oil  of  cumine,  or  hyduret  of  cumyle ;  oil  of  aniseed,  the 
solid  part  of  which  is  C^^H^O^,  and  with  nitric  acid  yields  anisic  acid,  and  other 


^gO  ESSENCES  OF  CINNAMON  AND  ANISE. 

compounds  already  described  at  p.  666;  oil  of  valerian,  chiefly  valerianic  acid, 
&c.  The  essence  of  valerian,  according  to  Gerhardt,  generally  contains  several 
compounds,  especially  if  old.  When  fresh,  it  contains  no  valerianic  acid,  but 
an  oil,  valerok,  which  is  crystallizable,  and  soon  passes  into  valerianic  acid  in 
the  air.  This  oil  is  C^H^^Og,  and  is  isomeric  with  raetacetone,  also  with  Kane's 
oxide  of  mesityle,  and  with  oxide  of  allyle  (see  oil  of  garlic,  p.  683).  Besides 
valerole,  the  essence  contains  a  carbo-hydrogen,  borneene,  0  H  ,  identical  with 
the  oil  obtained  from  borneo  camphor;  and  finally,  a  camphor,  which  is  identical 
with  borneo  camphor. 

Oil  of  cinnamon^  according  to  Mulder,  is,  when  quite  fresh,  C  H  0  .  It 
rapidly  attracts  oxygen,  and  3(0^^11  ^j02)H-0g=l  eq.  cinnamic  acid,  1  eq.  resin 
alpha,  CjgH^O,  1  eq.  resin  beta,  C^Hj^O^,  and  6  eq.  water  HgO^.  With  hydro- 
chloric acid  it  yields  two  different  resins,  C^^HgO,  and  C^^H^O,  besides  other 
products.  With  oil  of  vitriol  it  yieldsHwo  more  resins,  ^goH^^O^,  and  C^H^^O, 
"which  together  are  equal  to  3  eq.  of  the  oil  minus  3  eq.  water.  With  nitric  acid 
the  fresh  oil  forms  a  crystalline  compound,  C,  H  NO,=C,  H  0,H-NO,H-HO. 

*■  18       y  7  To       8      3  o 

With  water  this  body  yields  hyduret  of  cinnamile,  C  gH^^O^.  If  dissolved  in 
sulphuric  acid  and  mixed  with  water  it  gives  cinnamic  acid,  C^j^H^O^.  Along 
with  the  crystals,  nitric  acid  yields  a  red  oil,  which,  with  water,  gives  another 
oil,  C,,H,0,. 

Oil  of  anise^  ^20^12^2'  7^®^^^  ^^^^  bromine  a  compound  in  fine  crystals,  C^ 
<  pf  ^2*  ^^6n  acted  on  by  strong  acids,  or  by  the  chlorides  of  tin  or  anti- 
mony, oil  of  anise  is  converted  into  an  isomeric  body,  anisoine,  analogous  to 
benzoine. 

Of  the  remaining  oils  of  this  class  may  be  mentioned  the  oils  of  dill,  of  fen- 
nelf  of  parsley,  of  carraway,  of  coriander^  of  pimpernel,  of  peppermint  (Cj^H^^O, 
or  C^qH^jjO^;  this  oil  yields  several  new  compounds  with  chlorine),  of  marjo^ 
ram,  of  lavender,  rosemary,  basil,  thyme,  fue  (C„H  O  ),  cascarilla,  chamomile, 
wormwood,  tea,  cardamom,  nutmeg,  cajeput,  rhodium,  rose  (otto  or  attar  of  roses), 
bergamot,  saffron,  sassafras,  znd  sweet  iay  (C  H^^O).  Of  these,  little  certain  is 
known,  and  almost  all  require  a  careful  study.  The  oil  of  sassafras,  C^^H^O^, 
when  cooled,  deposits  very  large  and  beautiful  crystals,  measuring  1^  inch  on 
the  side.     With  bromine,  the  solid  essence  yields  crystals,  composed  of  C^^H 

The  oil  or  essence  of  semen  contra  is  said  to  be  C^gH^^O^.  That  of  artemisia 
dracunculus,  or  essence  of  estragon,  yields,  when  treated  with  sulphuric  acid, 
anisoine,  identical  with  that  of  oil  of  anise,  and  in  fact  contains  the  same  oxy- 
genated oil  (stearoptene  of  anise),  along  with  a  different  carbo-iiydrogen.  Lau- 
rent has  obtained  from  essence  of  estragon  a  series  of  new  compounds.  He 
represents  the  essence  by  Cg^H^^O^.  With  nitric  acid  it  yields  draconic  acid, 
C  H  0  ,2H0 ;  this,  with  chlorine  and  bromine,  gives  chlorodraconesic  and 
bromodraconesic  acids,  C   H,  CI  0,o,2HO,  and  C   H„Br  0,o,2HO.     Nitric  acid 

.1        3  32       xl        2 


yields  further;   C^^  ]  ^^12    Oio,2HO,  which  is  called  nitrodraconasic acid:  and 

C^  j      "     0jQ,2H0,  which  is  nitrodraconesic  acid.    The  former  of  these  two 
^  4 

acids,  with  chlorine  and  bromine,  yields  nitrochlorodraconesic  acid. 


(NO, 


SULPHURETTED  ESSENTIAL  OILS.  ^} 


2H0  ;  and  nitrobromodraconesic  acid,  C^^  j  Br     ^lo'^^^*     With  chlorine,  the 

essence,  C^^H^qO^,  gives  chloride  of  draconyle,  CHj^Cl^OgC?),  which,  when 
acted  on  by  potassa,  yields  chloride  of  potassium  and  chlorodraconyle,  C^^Hj^ 
ClgO^.     If  formed    by  direct  substitution,  like  the  preceding  compounds,  the 

C  H 

chloride  of  draconyle  ought  to  be  C^^  j  pi'^^3'  *^^  ^^^  °^  *^^  chlorine  and  hy- 
drogen being  20  eq.  as  in  the  chlorodraconyle,  in  which,  however,  Laurent  admits 
^  eq.  of  hydrogen  more.  These  researches  of  Laurent  are  very  interesting ; 
and  it  has  very  recently  been  established  by  Gerhardt  and  Laurent  that  draconic 
acid  is  identical  with  anisic  acid,  and  that  dracole,  an  oil  obtained  b)'-  heating 
draconic  acid  with  baryta,  is  identical  with  anisole.  I  presume  that  the  true 
formulae  are  those  of  draconic  acid  and  its  derivatives,  so  that  the  formula  of 
anisic  acid  will  have  to  be  doubled. 

The  concrete  essence  of  the  tonka  bean  is  called  coumarine.  It  is  very  fra- 
grant, and  its  formula  is  said  to  be  C  H  O  .  Potassa  changes  it  into  salicylic 
acid,  and  hot  nitric  acid  converts  into  nitropicric  acid.   Cold  nitric  acid  produces 

a  white  volatile  crystalline  solid,  C  „   ^   _  ^     q.  Coumarine  also  combines  with 

^^    (J;  NO      4 

chloride  of  antimony,  forming  yellow  crystals. 

3.    Sulphuretted  Essential  Oils.  • 

This  class  of  oils  is  distinguished  by  a  pungent  poculiar  smell,  and  acrid 
burning  taste,  as  in  oil  of  mustard,  or  an  intense  alliaceous  odour,  as  in  oil  of 
garlic  or  of  onio/is.  The  more  important  of  them  have  been  lately  investigated, 
and  have  yielded  very  striking  results.  ^    * 

Essence  of  mustard  is  prepared  from  mustard-seed  in  the  same  way  as  oil  of 
bitter  almonds  from  that  seed.  The  seed  is  macerated  with  water  and  after- 
wards distilled,  when  it  yields  an  oil  of  a  most  remarkable  nature,  containing 
not  only  sulphur,  but  also  nitrogen.  The  pure  oil  is  colourless,  of  sp.  gr.  1*010, 
and  boils  at  298°  or  300°.  Its  formula  is  C^H^NS^,  so  that  it  contains  no  oxy- 
gen. With  ammonia  it  forms  a  crystalline  compound,  which  is,  in  fact,  an 
organic  base  or  alkali,  Thiosinnamine  =  C  H  N  S  .  This  is  a  bitter  compound, 
which  forms,  like  nearly  all  organic  bases,  crystalline  compounds  with  chloride 
of  platinum  and  chloride  of  mercury. 

Thiosinnamine,  acted  on  by  dry  oxide  of  lead  or  of  mercury,  loses  all  its  sul- 
phur, forming  a  new  base,  sinnamine  =  C  H  N„=C„H„N  S^--2HS.  It  is, 
therefore,  Thiosinnamine,  minus  2  eq.  sulphuretted  hydrogen,  which  have  acted 
on  the  oxide  of  lead,  forming  water  and  sulphuret  of  lead.  Sinnamine  forms 
definite  compounds  with  chlorides  of  mercury  and  platinum.  It  is  a  powerful 
base,  and  very  bitter  to  the  taste. 

When  oil  of  mustard  is  acted  on  by  moist  hydrated  oxide  of  lead,  it  loses  both 
sulphur  and  carbon,  in  the  proportion  CS  ,  forming  sulphuret  of  lead  and  carbo- 
nate of  lead,  along  with  a  new  base,  sinapoline^  which  dissolves  in  hot  water, 
in  alcohol  and  in  ether.  lis  formula  is  C^  ^12^9^2'  ^""^  ^^  ^®  formed  from  2  eq. 
oil  of  mustard,  with  6  eq.  oxide  of  lead  and  2  eq.  water,  as  follows:  2  (CgH^ 
NS^)  1 6PbO  1 2H0=C^^H^^N  O^t 4PbS+2(PbO,CO^). 

When  oil  of  mustard  is  acted  on  by  an  alcoholic  solution  of  potash,  there  is 
separated  neutral  carbonate  of  potassa,  and  the  addition  of  water  causes  the  sepa- 
ration of  an  oily  liquid,  which  is  in  its  relations  analogous  to  oil  of  mustard.    Ik 


682  OIL  OF  MUSTARD. 

appears  to  be  ^<is^25^3^fi4'  ^^  ^^®  action  of  baryta  upon  it,  sulpburet  'of 
barium  is  formed,  and  a  basic  compound  not  further  examined.  Tlie  liquid  from 
which  this  oil  has  separated  contains  the  potassium  salt  of  a  very  remarkable 
acid,  which  forms  with  a  salt  of  lead  the  compound  CgNHgS^,Pb,=CgH^NS2, 
HS-|-PbS.  These  compounds  are  produced  as  follows  :  6  eq.  oil  of  mustard,  10 
of  water,  and  2  eq.  of  potassa,  6(C^H^NSJ  +  10HO-t2KO,  yield  1  eq.  of  the 
new  oil  C^gH^^N^S^O^,  1  eq.  ammonia  NH^,  4  eq.  carbonic  acid,  C^O^,  and  2  of 
the  new  salt  of  potassium  ^(Cj^HgNS  ,K).  It  is  probable,  however,  that  the 
first  change  is  more  simple,  and  that  3  eq.  oil  of  mustard,  5  of  water  and  1  of 
potassa,  yield  1  eq.  of  an  oil  C  H  ^N^S^O^,  2  eq.  carbonic  acid,  C^O^,  and  1  of 
the  potassium  salt  Cj,HgNS^,K.  Two  eq.  of  the  oil  C^^H^^N^S^O^  lose  1  eq. 
ammonia,  and  give  rise  to  the  oil  C   H   N  S  O  . 

'  ^  28      25      3    4     4 

These  very  interesting  facts,  important  in  a  high  degree  from  their  bearing  on 
the  theory  of  organic  bases,  are  taken  from  a  paper  by  Dr.  Will  lately  published, 
to  which  I  refer  the  reader.  Dr.  Will  points  out  some  curious  relations.  Thus 
sinapoline,  Cj^H^^N^O  ,  may  be  derived  from  2  eq.  oil  of  mustard  and  6  eq. 
water,  which  yield  1  eq.  sinapoline,  2  eq.  carbonic  acid,  and  4  eq.  sulphuretted 
hydrogen.  If  we  now  suppose  2  of  the  4  eq.  of  HS  to  combine  with  1  eq.  sina- 
poline, they  will  produce  the  oil,  C  H^^N^O^S^,  which  is  supposed  to  be  first 
formed  and  afterwards  to  lose  ammonia :  while,  if  the  2  other  eqs.  of  HS  combine 
with  1  eq.  of  unchanged  oil  of  mustard  they  will  form  the  acid  of  the  new 
potassiuni  salt:  C  H  NS  +2HS=C  H  NS  . 

•  8      5  2  8/4 

Again,  sinapoline  may  be  viewed  as  hyduret  of  benzoyle,  jo/ws  2  eq.  ammonia, 
Cj^Hg02,3Nil^;  and  the  hypothetical  oil  is  then  Cj4Hg02,N2HgS2,  or  hyduret 
of  benzoyl e,  j9/m5  2  eq.  sulpburet  of  ammonium. 

The  separation  of  the  elements  of  bisulphuret  of  carbon  from  oil  of  mustard, 
and  the  simultaneous  formation  of  a  series  of  basic  compounds,  would  indicate 
that  oil  of  mustard  might  be  a  compound  of  sulphocyanogen;  since  sulphocya- 
nide  of  ammonium  (see  p.  576),  when  heated,  gives  off  bisulphuret  of  carbon, 
and  gives  rise  to  a  series  of  basic  compounds,  melamine,  ammeline,  &c.  Now 
it  is  very  remarkable  that  oil  of  mustard  admits  of  being  considered  as  CgH^-f- 
C^NS^,  that  is,  the  sulphocyanide  of  a  new  radical  allyle,  CJgH^;  of  which,  as 
we  shall  presently  see,  oil  of  garlic  is  the  sulpburet.  Finally,  oil  of  mustard 
may  be  a  compound  of  hydrocyanic  acid  with  the  hydrosulphuret  of  sulpburet 
of  acryle:  CgH  S,HS-f-C  NH.  Its  very  pungent  smell  and  powerful  action  on 
the  eyes  certainly  rank  it  beside  acroleine,  CgH^O,HO.  But  all  these  views  and 
relations  are  mentioned  here  as  an  example  of  the  way  in  which  such  relations 
raay  be  discovered,  rather  than  as  being  in  any  way  demonstrated. 

Oil  of  mustard  contains  an  indifferent  nitrogenized  body,  myrosine^  which, 
analogous  to  emulsine,  yields  the'  essential  oil  after  maceration  of  the  seed  with 
water,  and  fermentation.  The  fermentation  of  myrosine  is  prevented  in  the 
same  way  as  that  of  emulsine,  namely,  by  coagulation.  The  seeds  also  contain 
a  crystalline  body,  sinapisine^  resembling  a  fat.  The  substance,  which,  along 
with  myrosine,  yields  the  oil,  appears  to  be  myronic  acid^  or  rather  myronate  of 
potash^  a  body  not  yet  fully  studied.  The  seeds  of  sinapis  alba  contain  the 
myrosine,  as  sweet  almonds  contain  emulsine;  but,  being  destitute  of  myronic 
acid  or  myronate  of  potassa,  as  sweet  almonds  are  of  amygdaline,  they  yield 
none  of  the  oil. 

It  has  very  recently  been  shown,  by  Hnbatka  and  Wertheim,  that  the  essen- 
tial oils  of  cochlearia  armoracia  (horse-radish),  cochlearia  officinalis,  and  alliaria 
officinalis,  consist  almost  entirely  of  oil  of  mustard,  although  the  latter  oil  has 


OIL  OF  GARLIC.    ASARONE.  683 

also  a  very  strong  smell  of  oil  of  garlic,  an  oil  which  has  not  been  discovered 
in  it. 

The  essential  oil  of  garlic,  from  the  bulbs  of  allium  sativum,  is  a  peculiar  sul- 
phurized compound.  Wertheim  has  lately  studied  it,  and  shown  that  it  is  the 
sulphuret  of  a  new  radical  Allyle=C  H  =A11,  and  its  formula  is  C  H  ,S=A11S. 
The  crude  oil  contains  a  little  of  a  higher  sulphuret,  possibly  AllS  ,  and  also 
some  of  the  oxide  of  allele,  CgH^0=A110,  which  is  an  oily  liquid  of  an  offen- 
sive smell.  The  radical  allyle  appears  to  enter  into  numerous  combinations,  and, 
among  others,  Wertheim  analyzed  the  following:  the  sulphuret,  or  pure  oil  of 
garlic,  AllS;  the  compounds  of  that  sulphuret  with  the  sulphurets  of  platinum, 
palladium  and  silver,  SAlls+GPtS^;  SAllS+SPtS^;  2AllS+3PdS  ;  and  xAllSf 
AgS? ;  double  compounds  with  the  sulphurets  and  chlorides  of  mercury  and  pla- 
tinum; 3(AllStPtS2)-l-(AllCltPtCy;  and  (AllS+2HgS)+(AllCl  +  2HgCl); 
and  lastly  nitrate  of  the  oxides  of  silver  and  allyle,  (AllOH-AgO)-j-NO^.  Our 
space  does  not  permit  us  to  do  more  than  point  out  the  existence  of  these  curious 
compounds. 

The  essential  oil  of  assafeiida  appears  to  consist  of  at  least  two  oils,  one  of 
which,  if  not  both,  contains  sulphur.  It  has  a  very  offensive  odour.  It  does 
not  combine  with  ammonia  like  the  oil  of  mustard.  Dr.  Douglas  Maclagan  finds, 
as  might  be  expected  from  the  odour,  that  one  of  the  oils  it  contains  is  sulphuret 
of  allyle. 

The  essential  oils  of  hops,  of  water  pepper,  and  of  arum  maculatum,  are  be-, 
lieved  to  contain  sulphur. 

CONCRETE  VOLATILE  PRINCIPLES,  ALLIED  TO  THE  ESSENTIAL  OILS. 

There  are  several  substances  which  may  be  classed  under  this  head ;  such  as 
Hellenine  from  inula  helenium,  which  is  a  volatile  crystalline  solid,  C    H    O  . 

C  H 

With  nitric  acid  it  yields  nitrohellenine  C^^  ^   ^     O  .  When  distilled  with  an- 

'^  4 

hydrous  phosphoric   acid,   hellenine  loses  2  eq.    water,   yielding  hellenine,   a 

C  TT 

carbo-hydrogen,  C^^Hg.     With  chlorine  it  yields  the  compound  C^^  j   p?^2  "f" 

HCl. 

Asarone  from  asarum  europseum  is  a  volatile  solid,  having  a  remarkable  ten- 
dency to  crystallize  in  beautifully  defined  forms,  and  also  to  pass  into  the  amor- 
phous condition,  from  which  it  may  be  again  brought  into  the  crystalline  state. 
Schmidt  has  very  recently  studied  its  crystallization,  under  the  microscope,  and 
has  obtained  results  which  are  most  interesting  in  reference  to  the  formation  of 
crystals  in  general.  I  must  refer  to  his  elaborate  paper  in  the  "  Annalen  der 
Chemie  and  Pharmacie,"  for  February,  1845.     Its  composition  is,  C^H^^O^. 

Anemonine,  from  various  species  of  anemone,  is  a  volatile,  crystallizable  solid, 
the  formula  of  which  is  C^H^O^.  It  forms  with  oxide  of  lead  a  compound,  3 
(C^H^O^)  -f-PbO.  With  bases  it  yields  anemonic  acid,  the  composition  of  which 
is  unknown. 

Cantharidine,  the  active  principle  of  Spanish  flies,  is  a  volatile  acrid  solid,  the 
composition  of  which  is  C^^Ufi^. 

The  following  plants,  epidendron  vanilla,  quassia  amara,  tanghinia  madagasca- 
riensis,  primula  auricula,  and  primula  veris,  contain  concrete  volatile  essences, 
not  yet  analyzed. 


684  RESINS. 


CAOUTCHOUC,  OR  GUM  ELASTIC. 

Caoutchouc  is  a  substance  sui  generis,  which  in  composition  approaches  more 
nearly  to  the  essential  oils  than  to  any  other  class  of  compounds.  It  is  the  co- 
agulated or  inspissated  juice  of  many  tropical  trees,  the  chief  of  which  is  siphonia 
tlastica  {iatropha  elastica,  hevea  guianensis).  The  juice,  as  it  flows  from  the  tree 
is  made  to  dry  on  moulds  of  clay,  which  are  afterwards  broken  out,  leaving  a 
bottle  of  caoutchouc.  It  is  generally  blackened  by  smoke,  but  when  pure  it  is 
white  and  transparent,  it  is  highly  elastic,  and  the  freshly  cut  surfaces  adhere 
strongly  if  pressed  together.  It  is  insoluble  in  water,  alcohol,  and  acids  ;  but  it 
dissolves  in  ether,  naphtha,  coal-tar  naphtha,  bisulphuret  of  carbon  and  essential 
oils.  Its  solutions  in  ether  and  coal-tar  naphtha,  when  dried  up,  leave  the  caout- 
chouc in  an  elastic  state.  On  this  principle  waterproof  cloth  is  made.  Caout- 
chouc is  much  used  in  chemical  operations  to  form  flexible  connecting  tubes. 

"When  exposed  to  heat,  caoutchouc  first  melts,  and  then  distils,  yielding  a  mix- 
ture of  several  oily  liquids,  all  of  which,  as  well  as  pure  caoutchouc  itself,  are 
carbo-hydrogens.  Some  of  these  oils  boil  at  90°,  others  at  680°,  and  at  inter- 
mediate points.  I  found  that  one  highly  rectified  oil  which  boiled  at  96°,  and 
had  the  composition  of  olefiant  gas,  when  acted  on  by  sulphuric  acid,  yielded  an 
oil  which  boiled  at  428°,  and  had  the  same  composition.  But  most  of  these 
oils  have  the  composition  of  oil  of  turpentine,  C^H^  or  C^^H^.  One  of  these, 
called  caoutchine^  gives  with  chlorine  an  oil,  C   Hg-f-HCl. 

RESINS. 

Resins  are  generally  found  along  with  essential  oils,  and  many  of  these  oils, 
by  the  action  of  the  air,  are  converted  into  resins.  In  this  change,  the  essential 
oils  lose  a  part  of  their  hydrogen,  which  is  converted  into  water,  and  take  up 
some  oxygen  besides.  In  fact,  the  resins,  as  a  class,  are  acid  bodies,  they  are 
insoluble  in  water,  but  become  soft  in  boiling  water.  They  dissolve  in  alcohol, 
and  often  crystallize  from  that  solvent. 

The  acid  resins  combine  with  bases ;  their  salts  with  the  alkalies  are  called 
resinous  soaps.  The  resins  are  not  volatile,  although  very  inflammable.  They 
are  purified  from  essential  oils  by  distilling  off  the  latter  along  with  water ;  but, 
as  thus  obtained,  they  are  generally  mixtures  of  several  resins. 

Turpentine  and  Colophony,  or  Common  Resin.  Turpentine  is  the  semifluid 
juice  which  exudes  from  many  species  of  pnus.  When  distilled  with  water,  it 
yields  oil  of  turpentine,  C^^Hg  or  C^^H^^'  while  colophony  or  resin  remains  be- 
hind, which  is  C^pH^O  or  C^^H^jjO^,  or,  more  accurately,  C^^H^^O^.  Here  the 
oil,  C^H^,  has  lost  2  eq.  hydrogen,  replaced  by  2  eq.  oxygen,  C^^H^^O^,  and 
this  compound,  like  aldehyde,  has  taken  up  2  eq.  of  oxygen  to  form  the  acid 
resin,  C^^H3^0^. 

Colophony  contains  two  different  resins :  resin  alpha,  or  pinic  acid,  and  resin 
beta,  or  st/lvic  acid.  The  latter  is  said  to  be  C^^Hj^O^,  the  former  C^^^H^O^;  and 
their  properties  are  isomeric  with  it,  very  similar,  being  those  of  colophony  which 
is  formed  of  them.     The  sylvic  acid  is  crystallizable. 

When  distilled  with  lime,  colophony  yields  two  oily  liquids,  resineone,  G^H^ 
O,  and  retinone,  C    H  O. 

The  resin  of  copaiva  is  ^^^H^O^,  according  to  Rose  ;  but  there  is  some  rea- 
son to  believe  that  it  is  isomeric  with  the  preceding.    A  variety  of  it  has  occurred, 


RESINS.  685 

containing  C^^H^^Og,  and  when  combined  with  oxide  of  lead,  C^oH^gOg.  This 
resin  crystallizes. 

The  resin  of  elemi  contains  two  resins,  one  crystallizable.  Both  are  said  to 
be  C  HO  .  Anime  also  contains  two  resins.  Euphorhium  yields  a  resin 
having  the  same  composition  as  elemi.  Benzoin  contains,  besides  benzoic  acid 
and  a  volatile  oil,  three  resins,  alpha,  ^70^42^14'  *^^^'  ^40^22^9'  ^"^  gamma, 
^.TO^2  ^  •  '^^^'  resm  alpha  contains  the  sum  of  the  other  two,  and  by  long  boil- 
ing with  carbonate  of  soda,  which  dissolves  the  resin  gamma  alone,  is  resolved 
into  them. 

Balsam  of  Tolu  contains,  besides  essential  oil,  benzoic  and  cinnamic  acids, 
and  a  carbo-hydrogen,  C^  H^  .  a  resin,  C,  H,  O  .  It  contains  the  elements  of 
benzoic  ether,  plus  1  eq.  oxygen.  When  the  balsam  is  distilled,  jser  se,  it  ac- 
tually yields  benzoic  ether,  along  with  a  new  carbo-hydrogen,  called  benzoene, 
Cj^Hg.     This  last  compound  yields  with  sulphuric  acid  a  new  acid,  C    H  SO 

-j-  3H0 ;  and,  with  nitric  acid,  two  new  nitrogenized  compound,  C      ^      7 

called  profonitrobenzoene,  and  another,  binitrobenzoene.  The  former  is  isomeric 
salicylamide.     With  chlorine,  benzoene  also  yields  several  new  products. 

Sti/racine,  the  resin  of  styrax,  is  C^^H^^O^.  When  acted  on  by  nitric  acid,  it 
yields  the  products  of  decomposition  of  cinnamic  acid. 

The  resin  of  guaiacum  is  remarkable  to  its  tendency  to  become  blue  by  the 
contact  of  may  different  substances.  It  contains  two  resins,  but  their  composi- 
tion is  not  ascertained.  Lac  contains  four  resins,  besides  colouring  matter. 
Dammara,  mastic^  dragon's  blood,  and  sandarachy  are  resins  much  used  in  making 
varnishes. 

Jalap  contains  two  resins;  one,  a  soft  resin,  soluble  in  ether,  ^^:^^^^^^  and 
an  acid  resin  insoluble  in  ether,  which,  from  striking  a  fine  red  colour  with  sul- 
phuric acid,  is  called  rhodeoretine,  C^^^g^^^o*  When  combined  with  bases,  it 
takes  up  I  eq.  water,  forming  hydrorhodioretine,  very  similar  to  rhodeoretine, 
but  soluble  in  water,  C^^H^^O^^.  When  rhodeoretine  is  acted  on  by  hydro- 
chloric acid,  it  is  resolved  into  grape  sugar,  C^^Hj^Oj^iand  an  oily  liquid  rhodeo- 
retinole,  C  H  O  .  This  reaction  places  rhodeoretine  near  to  salicine  and 
phloridzine.  On  the  other  hand,  if  we  compare  7  eq.  of  starch,  7  (^j,^  10^10)^^ 
^84^70^70  ^^^^  2  ^q-  rhodeoretine,  2  (^ ,fi,P^,)=<^,,^,P,,^  we  can  s°ee  how 
this  resin  may  be  formed  from  starch,  &c.  by  deoxidation.  It  is  also  worthy  of 
notice  that  rhodeoretine  agrees  with  salicine  and  phloridzine  in  the  number  of 
eqs.  of  carbon.  Salicine  is  0^^^29022^"^  phloridzine  C^^H^gO^^.  Rhubarb  con- 
tains 3  resins,  aporetine,  phscoretine,  and  erythroretine.  The  two  first  are  both 
C^gHgO^;  the  third  is  C^^HgO^.  They  are  accompanied  by  an  intensely  yellow 
crystallizable  acid,  chrysophanic  acid  C^^H^O^  or  C^^H^gO^^.  This  latter  sub- 
stance is  also  found  in  lichens,  such  as  parmelia  parietina,  squamaria  elegans,  &c. 
Copal,  which  of  all  the  resins  is  the  most  insoluble,  is  said  to  contain  five. 
Copal  varnish  is  made  by  adding  hot  oil  of  turpentine  to  copal  fused  at  a  gentle 
heat. 

Turf  or  peat  contains  several  resinous  bodies,  examined  by  Mulder.  In  the 
turf  of  Friesland  he  found  four  resins:  alpha,  ^SQ^^^g'^  ^^ia,  C^^H^^O^;  gamma, 
^io4^Q4^9'  ^^^  delta,  Cj^jHj2i^9*  -^  lighter  kind  of  turf  from  another  locality 
yielded  two  resins :  alpha,  C^^H^gO^ ;  and  gamma,  C^^Hg^O^. 

Resinous  varnishes  are  made  by  dissolving  resins  in  oil  of  turpentine  and 
Other  essential  oils;  or  in  drying  oils.  Spirit  varnishes  are  made  by  dissolving 
lesins  in  very  strong  alcohol. 


686  YELLOW  AND  RED  COLOURING  MATTERS. 

ACTION  OF  HEAT  ON  RESINS. 

When  resins  are  distilled  in  close  vessels,  they  yield  a  great  deal  of  gas  of  a 
high  illuminating  power,  and  many  volatile  liquid  compounds  of  carbon  and 
hydrogen. 

Pinic  acid  yields,  when  heated,  colophoUc  acid.  Colophony  yields  resineine, 
an  oil,  ^'20^15^'  ^^^°  retinaphtha^  ^14^8'  ^^^^^  ^'\\h  chlorine  forms  a  compound 
Cj^HgCl^;  retinylene,  ^is^ia'  ^'^^^^^  ^^^^'^  sulphuric  acid  yields  an  acid,  isomeric 
with  sulphocumenic  acid,  C^gHj^S^O^jHO ;  7'dinole,  Cg^H^^;  and  finally  a  solid 
product,  retister^ne,  fusible  at  152°,  having  the  same  composition  as  naphthaline, 

COLOURING  MATTERS  CONTAINING  NO  NITROGEN, 
1.  Yellow  colouring  matters. 

The  following  are  the  most  important  of  the  yellow  vegetable  colouring 
matters,  many  of  which  are  used  in  dyeing. 

Ourcumine,  from  the  root  of  curcuma  longa^  is  resinous,  and  is  dissolved  by 
alkalies,  which  change  it  to  brown.  Hence  it  is  used  as  a  test  for  alkalies, 
under  the  name  of  turmeric.  Gamboge  yellow  is  extracted  from  gamboge,  the 
dried  juice  of  Garcinia  gambogia.  It  is  resinous  and  powerfully  purgative, 
Annotto  or  Anatto  is  obtained  from  the  seeds  of  Bixa  orellana  and  Metella  tinctoria, 
Caroline  is  the  colouring  matter  of  the  carrot,  Daucus  carota.  Rhabarberine  is  a 
name  formerly  given  to  the  yellow  acid  of  rhubarb,  now  called  chrysophanic  acid, 
which  is  found  also  in  lichens  as  above  stated.  It  has  great  colouring  power, 
and  yields  a  fine  violet  with  alkalies.  It  is  fusible  and  volatile.  Formula,  C 
H  O  .  From  occurring  in  parmelia  parietina,  it  has  been  called  parietine  and 
parietinic  add.  Luteoline,  the  colouring  principle  of  Reseda  luteola  or  Woad,  is 
volatile  and  crystallizable.  Quercitrine,  from  the  bark  of  quercus  tincioria,  is 
crystalline,  and  its  composition  is  CjgHgOp,HO.  Other  yellow  colouring  matters 
are  Morine,  from  Morus  tincioria;  Saffiower  yellow,  from  Carthamus  tinctoriusi 
Polychroite  from  Saffron,  and  others  of  less  interest. 

I  2,  Red  colouring  matters. 

Draconint,  or  Dragon's  blood,  is  a  red  gum  resin,  from  Dracaena  draco.  It  is 
much  used  to  colour  varnishes.  Santaline^  the  colouring  matter  of  pterocarpus 
ianlalinus,  is  also  resinous,  and  has  an  intense  red  colour.  Anckusine,  from 
Anchusa  tincioria^  is  the  source  of  the  colour  of  alkanet;  it  is  resinous  and  yields 
violet  vapours  when  heated.  Carthamine  is  the  red  colouring  matter  of  saffiower, 
carthamus  tinctorius.  It  is  a  very  fine  and  intense  red,  much  used  for  dyeing 
rose  colour,  for  pink  saucers  and  for  rouge,  at  least  the  rouge  vSg^tale. 

Madder,  the  root  of  rubia  tinctorum,  contains  three  different  red  colouring  mat- 
ters, madder  purple,  red,  and  orange.  All  three  are  volatile,  and  the  sublimed 
crystals  of  madder  red,  which  are  of  a  fine  orange  red  colour,  are  called  alizarine. 
This  is  the  substance  which  yields  the  turkey  red  dye.  With  alkalies  it  yields 
purple  or  violet  colour,  with  acids  yellow.  When  dissolved  in  hot  water  or 
alcohol,  alizarine  yields  rose-coloured  solutions.  The  composition  of  pure 
madder  red  is  unknown. 

JJscmatoxy line  is  the  red  of  logwood,  hamaioxylum  campechianum.  It  is  soluble 
in  water  and  alcohol,  and  yields  orange  crystals,  which  give  to  water  a  red 
colour,  brightened  by  acids  and  turned  to  a  violet  or  blue  by  alkalies.     With 


I 


NON-AZOTIZED  VEGETABLE  COMPOUNDS.  (387 

alum,  logwood  yields  various  shades  of  violet;  with  an  iron  mordant,  grey  and 
black.  Black  cloth  and  hats  are  dyed  with  it,  which  is  the  reason  they  are 
reddened  by  acids.  According  to  Erdmann,  pure  haematoxyline  is  pale  yellow, 
and  is  coloured  red  by  the  atmosphere.  Its  formula  he  found  to  be  C  H  0  . 
When  acted  on  by  ammonia  it  yields  hemateine,  which  is  dark  red,  and  forms 
with  excess  of  ammonia  a  splendid  purple  matter.  Hsemateine  is  C  H  .0  ; 
and  the  purple  compound  with  ammonia  is  C^^Hj^O^g-j- 2NHg4-aq.  Brazil- 
wood and  Camwood  yield  colouring  matters  very  similar  to  haematoxyline,  if  not 
identical  with  it. 

Many  flowers  contain  a  red  colouring  matter,  which  is  turned  green  by  alka- 
lies, and  is  very  fugitive.     It  is  soluble  in  water  and  alcohol. 

3.  Blue  colouring  matters. 

These  are  chiefly  found  in  flowers  and  fruits.  They  are  very  closely  allied  to 
the  red  of  flowers  and  fruits,  which  are  no  doubt  often  derived  from  them  by  the 
action  of  acids.  They  are  all  turned  green  by  alkalies  and  red  by  acids.  Such 
blue  colouring  matters  as  are  more  permanent  contain  nitrogen,  and  will  be 
considered  hereafter. 

4.  Green  colouring  matter.    Chlorophylle. 

This  is  the  green  of  leaves.  It  is  of  a  nature  allied  to  that  of  wax,  soluble 
in  ether  and  alcohol,  insoluble  in  water.  It  is  very  neutral  or  indifferent  in  its 
relations  to  other  substances. 

Polychrome  is  the  name  given  to  a  peculiar  crystalline  principle  found  in  some 
vegetables,  such  as  quassia.  It  gives  to  water  the  quality  of  exhibiting  a  curi- 
ous play  of  colours,  among  which  blue  predominates,  like  that  of  the  opal, 
when  the  solution  is  viewed  by  reflected  light,  1  part  will  give  this  property  to 
1,500,000  of  water.  Its  formula  is  said  to  be  CjgHgOg,HO,  which  is  the  same 
as  that  of  quercitrzne,  and  contains  2  eq.  of  oxygen  more  than  Uie  aporetine  of 
rhubarb. 

NON-AZOTIZED  VEGETABLE  COMPOUNDS,  THE  NATURE  OF  V^HICH  IS  NOT 
YET  ASCERTAINED. 

In  this  subdivision  may  be  included  a  number  of  compounds,  most  of  which, 
crystallize  and  have  a  bitter  taste,  but  are  neutral  and  cannot  yet  be  referred  to 
any  particular  series  of  compounds.  Salicine,  phloridzine,  and  rhodeoretine, 
which  would  formerly  have  been  here  described,  are  now  treated  of  along  with 
substances  allied  to  them.  The  substances  now  to  be  briefly  mentioned  have 
usually  been  termed  the  bitter  and  extractive  principles  of  plants. 

Gentianine^  from  Gentiana  lutea,  forms  yellow  needles,  very  bitter.  Menyan- 
thine,  from  Menyanthes  trifoliata,  is  bitter,  but  does  not  crystallize.  Msinthine, 
from  Artemisia  absintheum  or  wormwood,  is  a  semi-crystalline  mass,  very  bitter, 
soluble  in  alcohol.  Tanacetine,  from  tanacetum  vulgare,  is  very  similar  to  it. 
Santonine  is  a  beautifully  crystallizable  compound,  obtained  from  Artemisia  con- 
tra. It  is  soluble  in  alcohol,  bitter  to  the  taste,  volatile,  and  coloured  yellow  by 
the  action  of  light.  Populine,  from  the  bark  and  leaves  of  populus  tremula,  forms 
white  crystals,  of  a  sweetish  and  acrid  taste,  coloured  red  by  sulphuric  acid.  It 
may  possibly  be  connected  with  salicine.  Liriodendrine  is  a  crystalline  bitter 
substance,  from  the  bark  of  liriodendron  tulipifera.  Picrolichenine  is  an  intensely 
bitter  crystalline  compound,  found  in  the  lichen  variolara  ajnara.     It  is  princi- 


6S8  NON-AZOTIZED,  NEUTRAL,  BITTER, 

pally  febrifuge.  In  contact  with  ammonia  and  without  the  excess  of  air,  it  is 
changed  into  a  reddish  yellow-matter,  which  finally  deposits  yellow  crystals,  not 
bitter.  With  access  of  air,  it  yields  with  ammonia  a  deep-red  very  soluble  mat- 
ter. Cetrarine  is  another  bitter  principle,  from  the  lichen,  cetraria  islandica,  or 
Iceland  moss.  It  is  coloured  deep  blue  by  hydrochloric  acid.  It  is  said  also  to 
be  febrifuge.  Ilicine,  from  ilex  aquifolium,  forms  brownish-yellow  crystals  very 
bitter  and  febrifuge.  Syringine  is  the  bitter  principle  of  the  lilac,  syringa  vul- 
garis. It  is  crystalline  and  soluble  in  alcohol.  Daphnine  is  a  bitter  crystalline 
substance,  obtained  from  Daphne  Mezereon.  Hesperidine  is  a  crystalline  body 
found  in  the  spongy  envelope  of  oranges  and  lemons.  Elaterine  is  the  active 
principle  of  Momordica  Elaterium,  is  crystalline,  bitter,  and  very  purgative.  Its 
formula  is  C^qH^^O^.  Colocynthine,  the  active  principle  of  colocynth,  is  amor- 
phous, intensely  bitter  and  purgative.  Bryunine^  from  Bryonia  alba  and  dioica, 
is  similar  in  its  properties.  Mudarine  is  the  emetic  principle  of  caloirnjns  mu- 
darii.  It  is  a  brown  amorphous  matter,  the  solution  of  which  in  water  gelati- 
nizes at  95°  and  becomes  again  liquid  on  cooling.  Scillitine  is  the  bitter  of  scilla 
maritima.  It  is  amorphous,  bitter,  purgative  and  emetic.  Cathartine  is  the  bit- 
ter purgative  principle  of  senna.  Antiarine,  CJ^^H^^O^,  is  the  active  principle  of 
the  poison  called  upas  aniiar.  It  is,  when  introduced  into  a  wound,  especially 
along  with  soluble  matters  such  as  sugar,  a  most  powerful  poison,  and  hitherto 
no  means  are  known  by  which  its  fatal  action  can  be  arrested. 

Zanthopicrine  is  a  bitter  crystalline  substance  from  the  bark  of  Zanthoxylum 
Clava  Herculis.     It  has  been  little  studied.     Picrotoxine^  the  bitter  principle  of 
menispermum  cocculus  (cocculus  indicus),  forms  white  prisms.    The  composition 
of  these  is  not  certain,  and  recent  researches  seem  to  show  that  picrotoxine  is  a 
vegetable  base,  and  contains  nitrogen,  like  all  that  class  of  compounds.     Colum- 
bine is  a  crystalline  bitter  substance,  obtained  from  columbo,  the  root  of  menis- 
permum palmatum,  and  somewhat  analogous  to  picrotoxine.  Quassine  is  a  yellow, 
Crystalline,  and  very  bitter  substance  from  the  wood  of  quassia  amara.     Its  for- 
mula is  said  to  be  C^H^O^.     Lupuline,  the  bitter  principle  of  hops,  is  not 
crystallizable.     Lactucine  is  a  crystalline  resinoid   bitter  substance,  from  the 
juice  of  laciuca  virosa  (lactucarium).     It  has  anodyne  properties.    ErgoUne  is  an 
uncrystallized  brown  powder,  extracted  fi;om  ergot  of  rye  by  hot  alcohol,  after 
the  fatty  matters  have  been  removed  by  ether.     It  appears  to  be  poisonous,  and 
is  probably  the  active  matter  of  the  ergot.     Porphyroxine  is  a  crystallizable  sub- 
stance found  in  Bengal  opium.     Its  solution  in  diluted  acids  becomes  red  when 
boiled.    It  requires  further  investigation.    Saponine  is  a  peculiar  principle,  found 
in  the  root  of  saponaria  officinalis.     It  is  white,  amorphous,  and  has  a  taste  first 
sweet,  then  styptic,  and  finally  acrid.     It  is  a  powerful  sternutatory.     It  is  solu- 
ble in  water,  and  its  solution,  even  when  much  diluted,  froths  when  agitated, 
like  a  solution  of  soap.     The  root  is  used  as  a  tetergent.     When  acted  on  by 
alkalies,  it  is  converted  into  an  acid,  saponic  acid,  ^^^-P^'   ^sparagine,  C^H 
N20g,2HO,  is  a  crystallizable  substance  found  in  asparagus,  inalthaa  ofiicinalis, 
and  in  other  plants,  especially  those  grown  in  the  dark.     When  boiled  with 
alkalies  it  loses  ammonia,  NH^,  and  forms  aspartic  acid  Cj^H^N0g,2H0,  which 
is  a  bibasic  acid.    The  crystals  of  asparagine  are  very  large,  colourless,  and 
transparent,  also  hard  and  brittle.     Not  only  alkalies,  but  acids,  and  ferments 
transform  it  into  aspartic  acid  and  ammonia.     Smilacine  is  a  crystalline  sub- 
stance, found  in  smilax  sarsaparilla.  Its  composition  is  Cj^Hj^O^.  In  China  nova 
there  is  found  a  substance  rery  analogous  to  smilacine,  the  composition  of  which 


NITROGENIZED  COLOURING  MATTERS.  689 

is  C^.Hj^O^:  that  is,  smilacine,  minus  1  eq.  water.  Senegmne  is  an  acrid  and 
astringent  substance  found  in  Polygala  senega.  It  excites  sneezing  powerfully. 
Formula,  ^2^^iS^n'  ^^^^^^^^  appears  to  be  the  active  principle  of  guaiacum. 
It  is  acrid  and  bitter.  Plumhagine,  extracted  from  the  root  of  plumbago  europxa, 
forms  yellow  prisms,  the  taste  of  which  is  first  sweet  and  styptic,  then  acrid 
and  hot.  The  yellow  colour  of  its  aqueous  solution  is  turned  cherry-red  by 
alkalies.  Cydandnt  is  a  crystalline  matter  from  the  root  of  cylamen  europseum. 
It  is  very  acrid,  purgative,  and  emetic.  Feucedanine  is  a  very  acrid  crystalline 
principle  derived  from  the  root  of  peucedanum  officinale.  Formula,  C  H  O. 
Imperaiorine^  ^24^12^5'  ^^  ^  crystallizable  compound,  obtained  from  the  root  of 
imperatoria  ostruthium.  It  is  very  acrid  and  styptic.  Phillyrine.,  from  the  bark 
of  various  species  of  phillyrea^  crystallizes  in  silvery  scales,  which  are  bitter. 
Fraxtnine,  from  the  bark  of  fraxinus  excelsior^  is  a  crystallizable  bitter  principle. 
Tanguine  is  a  similar  substance  from  tanghinia  madagascariensis.  It  is  poison- 
ous. Melampyrine  is  a  taste^ss,  neutral,  crystalline  substance,  from  melampyrum 
nemorusum.  Meconine  is  a  neutral,  crystalline  compound  contained  in  opium.  It 
is  soluble  in  water,  alcohol,  and  ether.  It  is  acrid  to  the  taste,  fusible,  and  vola- 
tile. Formula  C,^H,0  .  With  nitric  acid  it  yields  nitromeconine  or  nitromeconic 
10    5    4  ■' 

C  H 

acid,  C^^HgNOj^*     ^^  meconine  may  be  C^^Hj^Og,  nitromeconine  is  C^^  <  ^^ 

O^;  in  which  1  eq.  hydrogen  is  replaced  by  1  eq.  nitrous  acid.  Chlorine  trans- 
forms meconine  into  crystals,  containing  chlorine,  which,  however,  by  the  action 
of  alkalies,  yield  an  acid  free  from  chlorine,  mechloic  acid,  C    H  O    ? 

Cubebine,  C  HO,  is  a  crystalline  compound  contained  in  cubebs.  Olivile^ 
C^^H  H^,  is  a  crystallizable  acrid  substance,  found  in  the  gum  of  the  olive-tree.' 
Olivine  is  another  crystalline  matter  found  on  the  leaves  of  the  same  plant.  It 
is  bitter.  Cnidne  is  a  crystalline  matter,  found  in  centaurea  benedida,  and  in  the 
numerous  family  of  the  cynarocephakse.  It  is  neutral  and  bitter,  and  very  similar 
to  columbine.     Its  formula  is  C„„H,„0,  -  or  C^  H   O,  .  and  in  some  respects  it 

2n       lo      10  42      27      15  * 

approaches  to  salicine  and  phloridzine,  which  may  render  the  second  formula 
more  probable,  as  these  bodies  contain  42  eq.  carbon.  Limonine^  or  Limonef  a 
bitter  crystalline  matter  found  in  the  seeds  of  oranges,  lemons,  &c.,  is  C  H  O  , 
when  reduced  to  42  eq.  carbon.  This  would  be  Cnicine,  minus  3  eq.  water. 
Angelicine  is  a  crystallized  compound  found  in  angelica  root. 

Besides  the  above,  which  have  merely  been  briefly  catalogued  for  want  of 
space,  at  least  an  equal  number  of  substances,  chiefly  crystallizable,  and  either 
bitter,  acrid,  or  in  a  few  cases  tasteless,  have  been  extracted  by  various  chemists, 
from  many  diflferent  genera  and  species  of  plants,  but  have  been  so  little  examined 
hitherto  that  we  cannot  safely  describe  them  as  distinct  and  peculiar. 

NITROGENIZED  COLOURING  MATTERS,  AND  ALLIED  SUBSTANCES. 

There  are  several  fine  and  valuable  colours,  which  contain  nitrogen  as  an  es- 
sential element,  and  probably  A  the  form  of  ammonia  or  amide.  Such  colours 
are  archil,  litmus,  cudbear,  derived  from  certain  species  of  lichens ;  and  indigo, 
derived  from  the  juice  of  various  plants,  especially  different  species  of  indigofera. 
All  these  colours  are  derived  from  colourless  compounds,  by  the  combined  action 
of  air  and  ammonia.  Of  these  colourless  substances,  the  most  important  are, 
Lecanorine,  Orcine  and  Erythrine, 

1.  Lecanorine  occurs  in  lecanora  tartarea,  variolaria  lactea,  and  other  lichens. 

46 


690  ORCINE.—ERYTHRINE. 

It  is  extracted  by  ether,  and  forms  minute  white  crystals,  insoluble  in  water, 
soluble  in  alcohol  and  ether.  Its  formula  is  C  H  0  .  "When  heated  with  alka- 
lies, such  as  baryta,  a  carbonate  is  deposited,  and  a  sweet  substance  remains 
dissolved,  which  crystallizes  on  evaporation.  This  is  orcine,  C^^HgO^,  that  is, 
lecanorine,  minus  2  eq.  carbonic  acid,  C  O^.  The  same  change  takes  place  when 
lecanorine  is  boiled  with  water,  or  even  with  ordinary  alcohol,  and  for  this  rea- 
son orcine  alone  is  obtained  when  the  lichens  are  extracted  by  these  solvents. 

2.  Orcine  forms  large  transparent  crystals,  is  very  soluble  in  water,  and  has  a 
sweet  taste.  When  anhydrous,  it  may  be  distilled  unchanged.  When  mixed 
with  ammonia,  and  exposed  to  the  air,  it  gradually  acquires  a  deep  blood-red 
colour,  forming  a  nitrogenized  colouring  matter,  orceine,  soluble  in  ammonia  with 
a  deep  red,  in  fixed  alkalies  with  a  rich  violet  colour.  Crystallized  orcine,  C^^ 
HjjO^  (CjgHgO^-|-3HO)  with  the  addition  of  5  eq.  of  oxygen  and  1  eq.  of  am- 
monia, NHg,  yields  1  eq.  orceine=Cj^HgNO^,  and  5  eq.  water,  H^O^. 

3.  Erythrine  is  another  colourless  substance,  found  in  Parmelia  rocella^  when 
that  lichen  has  been  boiled  with  alcohol.  It  is  probably  a  product  of  decompo- 
sition (just  as  orcine  is)  of  some  substance  analogous  to  lecanorine.  W'hen  ex- 
posed to  the  air  along  with  ammonia,  it  slowly  becomes  red,  and  finally  yields  a 
brown  bitter  compound,  which  dissolves  in  fixed  alkalies  with  a  purple  colour. 

4.  Pseudo-erythrine  is  a  similar  substance,  occasionally  obtained,  and  occa- 
sionally altogether  wanting,  in  the  alcoholic  solutions  of  the  lichens.  It  is  evi- 
dently subject  to  decomposition,  when  its  solutions  are  boiled.  Schunck  has 
rendered  it  highly  probable  that  it  is  a  compound  of  lecanorine  with  oxide  of 

I  ethyle. 

5.  Variolarine  is  a  substance  quite  analogous  to  the  above-mentioned,  and 
found  in  variolaria  dealbaia.  The  whole  subject  of  the  substances  actually  ex- 
isting in  these  lichens  is  still  very  obscure.  With  the  exception,  perhaps,  of 
lecanorine,  all  the  above  substances  are  products  of  decomposition.  Even  leca- 
norine may  be  a  product  of  the  decomposition  of  another  substance,  not  yet  iso- 
lated. 

'    Jlccording  to  Kane,  the  following  is  the  composition  of 


Erythrine  (Erythriline,  Kane)            ....  ^22^1503 

Pseudo-erythrine  (Erythrine,  Kane)                    .        •    .  .      CjjHjgOg 

Amarythrine  (the  bitter  product)        ....  CjjHijO,^ 

Telerythrine  (a  further  product  of  oxidation)     .            .  .        ^s^  10^^19 


6.  Archil  contains,  according  to  the  same  chemist,  two  blue  compounds,  which 
he  calls  alpha-orceine  and  beta-orceine^  C,  II    NO  .  and  C,H,NO„;  besides  a 

-^  18       10  5  13       10  o 

third  of  an  acid  nature,  erythroleic  acid^  ^96^22^8* 

7.  Litmus  contains  (according  to  Kane)  a  red  fluid,  cry/Aro/etne,  C  H  O^;  and 
three  solids,  of  a  purple  colour,  erythrolitmine,  C^H^^O^j^;  azolitmine.,  which 
contains  nitrogen,  and  is  the  principal  constituent  of  litmus ;  and  spaniolitminey 
C  H  O  .  According  to  Gelis,  litmus  contains  three  colouring  matters,  one  so- 
luble in  ether,  which  is  orange  red;  one  soluble  in  alcohol,  blood-red,  and  one 
soluble  in  water.  The  second  is  the  chief  ingredient  of  the  dye.  All  give  blue 
compounds  with  alkalies. 

8.  Phloridzeine  is  the  deep  blue  compound  formed  from  phloridzine  by  the 
action  of  air  and  ammonia.     Its  formula  is  CJ^gH^Nj^O^. 


INDIGO.  691 

9.  Indigo. 

This  valuable  dye  has  been  long  known;  but  it  is  only  since  1827  that  its 
chemical  relations  have  been  accurately  studied.  No  substance,  in  the  whole 
range  of  chemistry,  has  yielded  a  greater  variety  of  most  interesting  products; 
and  the  study  of  the  metomorphoses  of  indigo  has  already  thrown  much  light  on 
the  laws  of  the  decomposition  of  organic  substances.  For  what  is  known  on 
this  subject,  we  are  indebted,  first,  in  point  of  time,  to  Chevreuil,  Runge,  Wal- 
ter, Crum,  Liebig,  Berzelius,  and  Dumas  ;  more  lately,  and  in  an  especial  man- 
ner, to  the  comprehensive  researches  of  Erdmann,  Fiitzche,  and  Laurent;  the 
last  of  whom  h^  made  known  several  interesting  series  of  new  compounds  de- 
rived from  indigo,  and  has  both  confirmed  and  extended,  as  well  as  corrected,  in 
some  cases,  the  previous  results  obtained  by  Erdmann. 

Indigo  is  obtained  from  various  plants,  chiefly  of  the  genus  indigo/era,  as  /. 
iincturia,  anil,  argentea,  &c.,  but  also  of  other  genera,  as  Nerium,  Isatis,  Pergu- 
laria,  Gymnema,  Polygonum,  Terphrosia,  Jmorpha,  and  others.  In  the  juice  of 
these  plants,  it  exists  in  the  form  of  a  colourless  soluble  compound,  probably  a 
compound  of  white  indigo  with  an  alkali.  When  exposed  to  the  air,  it  is  con- 
verted into  the  blue  compound,  and  becomes  at  the  same  time  insoluble,  just  as 
in  an  artificial  solution  of  white  or  reduced  indigo  in  an  alkali.  The  manufac- 
ture of  indigo  is  not  thoroughly  understood,  but  it  would  appear  that  ammonia, 
as  well  as  air  contributes  to  the  formation  of  the  colour,  probably  by  converting 
into  white  indigo  some  compound  present  in  the  fresh  juice,  the  nature  of  which, 
however  is  still  uncertain.  In  the  Antilles  and  in  the  East  Indies,  the  leaves 
are  made  to  ferment  in  water,  during  which  much  ammonia  is  formed,  and  the 
indigo  is  found  in  the  soluble  state,  ready  to  become  blue  and  insoluble  by  ab- 
sorbing oxygen.  But  in  North  America,  the  dried  leaves  are  infused  in  warm 
water,  or  boiled  with  water,  till  the  liquid  becomes  green,  when,  on  exposure  to 
the  air,  it  deposits  blue  insoluble  indigo.  Here  the  same  change  must,  in  great 
part  at  least,  have  taken  place  during  the  drying,  as  during  the  fermentation  of 
the  other  process. 

The  indigo  of  commerce  is  a  deep  blue  powder,  often  cohering  in  cakes,  and 
exhibiting,  when  polished  by  rubbing  with  the  nail  or  any  hard  substance,  a  cop- 
pery colour  and  lustre.  It  is  tasteless  and  inodorous,  insoluble  in  water,  and 
nearly  so  in  alcohol  and  ether.  It  may  be  purified  by  treating  it  successively 
with  boiling  diluted  sulphuric  acid  and  with  water,  which  remove  a  glutinous 
matter  ;  with  aqua  potassa,  at  a  gentle  heat,  which  dissolves  a  brown  colouring 
matter;  and  with  boiling  alcohol,  which  takes  up  a  red  colouring  matter.  When 
fresh  alcohol  becomes  no  longer  red,  but  blue,  the  indigo  is  as  pure  as  it  can  be 
made  by  such  means. 

To  purify  it  still  further,  it  is  digested  with  water,  lime,  and  grape  or  starch 
sugar,  which  deoxidizes  or  reduces  the  indigo,  while  the  lime  combines  with 
the  reduced  indigo,  forming  a  soluble  compound,  of  a  wine  yellow  tint.  This 
being  filtered  into  dilute  hydrochloric  acid,  which  removes  the  lime,  deposits 
pure  indigo  as  a  blue  powder.  Cloth  steeped  in  the  above  solution  of  indigo, 
and  exposed  to  the  air,  is  quickly  dyed  blue,  as  the  indigo,  at  the  moment  of 
being  rendered  insoluble,  combines  with  the  fibre  of  the  cloth,  to  which  it  ad- 
heres very  firmly,  so  that  it  cannot  be  washed  away.  If  indigo,  grape  sugar, 
soda,  and  alcohol,  be  digested  together  in  proper  proportions,  a  yellow  solution 
is  obtained,  which,  when  exposed  to  air,  deposits  pure  indigo  in  crystals. 
(Fritzche.) 


WHITE,  OR  REDUCED  INDIGO. 

Pure  indigo,  whenjapidly  heated  on  a  slip  of  platinum,  volatilizes,  yielding 
purple  vapours,  which  condense  in  purple  crystals  on  a  cold  surface.  These 
crystals  are  called  Indigotine:  but  they  are  nothing  else  than  sublimed  indigo, 
and  have  all  the  chemical  characters  of  pure  indigo.  When  distilled,  indigo 
yields,  among  other  products  common  to  all  nitrogenized  organic  matters,  a  very 
curious  oily  liquid,  of  powerfully  basic  properties,  and  forming  salts  with  acids 
which  crystallize  with  singular  facility.  This  base  is  aniline  [crystalline^  ky- 
(inol),  and  is  found  in  the  oil  of  coal  tar,  as  well  as  in  the  products  of  distilla- 
tion of  many  nitrogenized  bodies. 

Oil  of  vitriol  dissolves  indigo  with  a  deep  blue  colour,  forming  two  blue  acids. 
This  solution  is  much  used  in  dyeing.  Nitric  acid,  chloric  acid,  chromic  acid, 
chlorine  and  bromine,  all  dissolve  indigo,  giving  rise  to  oxygenized  and  chlorin- 
ized  or  brominized  products,  all  of  which  are  yellow  and  orange-coloured.  When 
boiled  with  strong  aqua  potassa,  indigo  is  also  oxidized  and  dissolved  in  the  form 
of  new  acids. 

When  placed  in  contact  with  deoxidizing  or  reducing  agents,  such  as  proto- 
salts  of  iron,  tin,  and  manganese,  or  honey  and  grape  sugar,  along  with  an  alkali 
such  as  soda  or  lime,  indigo  is  decolorized  and  dissolved  in  combination  with 
the  alkali.  The  addition  of  diluted  hydrochloric  acid,  air  being  carefully  ex- 
cluded, precipitates  reduced  or  white  indigo. 

White  or  reduced  indigo^  C  H^NO  ,  obtained  as  above  described,  is  a  crys- 
talline powder  of  a  dirty  white,  which,  if  washed  with  water  previously  boiled 
to  expel  air,  and  cooled  in  closed  vessels,  and  dried  in  vacuo,  is  bluish  exter- 
nally, but  grey  within.  The  blue  parts  being  removed,  the  remainder  is  reduced 
indigo.  When  moist,  it  very  rapidly  passes  into  blue  indigo,  oxygen  being 
absorbed:  when  dry,  the  change  is  more  slowly  effected.  It  is  insoluble  in 
water  and  acids,  very  sojuble  in  alkaline  solutions ;  its  solutions,  if  exposed  to 
the  air,  deposit  pure  indigo  blue  as  a  powder. 

The  first  accurate  analysis  of  indigo  blue  was  made  by  Walter  Crum;  and 
his  results  have  been  confirmed  by  all  succeeding  experimenters.  The  formula 
liow  adopted  for  indigo,  as  agreeing  best  with  its  numerous  metamorphoses,  is 
one  first  proposed  by  Dumas;  namely,  ^  H  NO  .  This  formula  is  the  same 
with  that  of  cyanide  of  benzoyle,  or  of  benzile,  C^^H^O^  -|-  C2N:=Cj^H^N02. 

The  relation  of  white  indigo  to  blue  indigo  is,  according  to  one  view,  the  same 
as  that  of  hyduret  of  benzoyle  to  benzoyle,  or  of  alloxantine  to  alloxan.  Thus 
we  have 

Benzoyle  CjjII^     Oj  Hyduret  of  Benzoyle  C,4H5     Oj  -f  H 

Alloxan  Cg  H^NgOio  Alloxantine  CgH^NjOiQ-fH 

Indigo  blue        CigHjN  Oj  Indigo  white  ^16^5  NOj   -f  H 

According  to  another  hypothesis,  white  indigo  is  the  hydrate  of  an  inferior 
degree  of  oxidation  of  the  same  radical  of  which  blue  indigo  is  the  higlif  r  oxide. 
Blue  indigo,  on  tliis  view,  is  Cj^H^N  +  O^,  and  white  indigo  is  a  hydrate  C^^Hj 
N+O-j-HO.  This  latter  view  is  the  more  probable,  not  only  in  regard  to  indigo, 
but  also  in  regard  to  alloxan,  for,  assuming  uryle  to  be  CgNg0^a=Ul,  alloxan  will 
be  Ulf  03t4HO,  and  alloxantine  will  be  UlfOf^HO. 

The  action  of  grape  sugar,  in  reducing  indigo,  tells  in  favour  of  the  latter  hy- 
pothesis. For  if  white  indigo  is  blue  indigo  pliu  hydrogen,  this  hydrogen  is 
derived  from  water,  the  oxygen  of  which  must  have  combined  with  the  hydro- 
gen of  the  sugar  (to  convert  the  sugar  into  formic  acid,  which  is  produced  in 


ACTION  OF  SULPHURIC  ACID  ON  INDIGO.  693 

this  operation).  Here,  then,  we  should  have  oxygen  leaving  hydrogen  to  com- 
bine with  hydrogen,  or,  in  other  words,  water  produced  and  decomposed  at  the 
same  time,  which  is  in  the  highest  degree  improbable.  To  demonstrate  this,  let 
the  radical  of  indigo  be  assumed  to  be  Anyle=  C^^H^N  =  An:  let  blue  indigo 
be  An  O^,  and  white  indigo  An  O^,  H  or  An  O,  HO.  Then  12  eq.  of  blue  in- 
digo, 12  of  water,  and  1  of  grape  sugar  act  on  each  other,  and,  according  to  the 
view  which  makes  white  indigo  the  hyduret  of  blue  indigo,  the  reaction  is  as 
follows:  12  An  0^-\-12U0-YC^^U^p^^:=n  (An  02,H)t6  (C2H03)t6HO. 
In  tills  explanation  it  is  evident  that  G  eq.  of  oxygen  have  quitted  hydrogen  to 
combine  with  hydrogen.  On  the  other  view,  the  reaction  is  as  follows,  free  from 
any  such  absurdity:  12An02+12H04-C^2Hj20j2=  12AnO,HO  +  6(C2H03)  + 
6H0.  Here  the  12  eq.  of  deutoxide  of  anyle  (blue  indigo)  lose  12  eq.  oxygen, 
which  are  replaced  by  12  eq.  water;  and  the  12  eq.  oxygen  acting  on  the  sugar,' 
6  eq.  take  6  eq.  hydrogen,  forming  water,  and  6  eq.  convert  the  residue  into  for- 
mic acid.  The  student  will  bear  in  mind  that  C^HO^  is  the  formula  of  formic 
acid,  and  C   H   0     that  of  dry  grape  sugar. 

We  shall  therefore  consider  white  indigo  as  the  hydrated  protoxide  of  anyle 
(CjgH^N,0-|-HO),  and  blue  indigo  as  the  anhydrous  deutoxide  (CjgH^N,02). 
White  indigo  forms  compounds  with  bases,  in  which,  no  doubt,  its  hydratic 
water  is  replaced  by  an  equivalent  of  metallic  oxide,  as  in  the  general  formula, 
C^,H^N,OtMO. 

ACTION  OF  SULPHURIC  ACID  ON  INDIGO. 

When  powdered  pure  indigo  is  added  to  15  parts  of  oil  of  vitriol,  and  gently 
warmed,  a  deep  blue  solution  is  formed,  which  mixes  perfectly  with  water.  But 
if  only  8  or  10  parts  of  acid  are  used,  the  addition  of  water  causes  the  deposition 
of  a  purple  powder,  while  a  blue  solution  is  obtained.  The  purple  powder, 
which,  although  insoluble  in  dilute  acid  is  soluble  in  pure  water,  is  sulphopur- 
puric  acid  ;  the  blue  solution  contains  two  acids,  sulphoindigotic  and  hyposul- 
phoindigotic  acids.  When  neutralized  with  potassa,  these  acids  form  salts, 
which  separate  from  the  liquid  when  it  is  saturated  with  any  alkaline  salt,  such 
as  acetate  or  carbonate  or  potassa.  The  two  blue  salts  may  be  separated  from 
each  other  by  alcohol,  but  the  composition  of  the  hyposulphoindigotate  of  po- 
tassa is  not  known.  The  sulphoindigotate  appears  to  be  strictly  a  hyposulpho- 
indigotate, and  its  formula  is  in  all  probability  C ^^H^N 02,820^-}- KO.  Here  the 
indigo  has  lost  1  eq.  of  hydrogen,  and  the  2  eq.  sulphuric  acid  1  eq.  oxygen. 
Dumas's  view,  according  to  which  the  salt  is  a  double  sulphate,  analogous  to 
sulphovinate  of  potassa,  C^gH^NO,S03-f-KO,S03,  is  not  supported  by  the  che- 
mical relations  of  these  substances.  Dumas  conjectured  that  indigo  blue  was 
analogous  to  alcohol,  and  that  its  formula  was  CjgH^N,0-|-HO,  the  body  C^^H^ 
N,0  being  analogous  to  oxide  of  ethyle.  But,  as  already  stated,  this  view  is 
far-fetched,  and  does  not  agree  with  the  chemical  relations  of  indigo.  It  would 
make,  for  example,  white  indigo  CjgH^N,0-|-H+HO  or  C^gNH^+2H0,  both 
most  improbable  formulae. 

The  blue  solution  of  indigo  in  oil  of  vitriol,  if  diluted  and  digested  with  flannel 
or  woollen  cloth,  is  entirely  deprived  of  blue  colour,  while  the  cloth  is  so  effec- 
tually dyed  that  the  colour  cannot  be  washed  out.  It  can,  however,  be  dis- 
solved from  the  cloth  by  carbonate  of  ammonia,  and  by  this  means  the  ^ulphoin- 


.09^  OXIDATION  OF  INDIGO. 

digotates  of  ammonia,  and  from  these,  the  other  salts  of  the  blue  acids,  are 
prepared. 

The  sulphopurpuric  acid,  according  to  Dumas,  contains  the  elements  of  2  eq. 
sulphuric  acid  and  2  eq.  indigo,  and  neutralizes  only  I  eq.  of  base.  But  the 
indigo  in  it  has  probably  lost  hydrogen  (while  the  acid  has  lost  oxygen),  or 
hydrogen  and  oxygen. 

PRODUCTS  OF  THE  OXIDATION  OF  INDIGO. 

Isatine^  C^gH^NO^.  This  interesting  compound,  which  is  blue  indigo,  plus  2 
eq.  oxygen,  is  formed  by  digesting  indigo  along  with  water,  sulphuric  acid,  and 
bichromate  of  potassa,  or  by  heating  indigo  with  weak  nitric  acid.  It  dissolves, 
and  the  solution  on  evaporation  deposits  aurora  red  crystals  of  isatine,  sparingly 
soluble  in  cold  water,  more  soluble  in  hot  water  and  in  alcohol.  By  the  action 
of  chlorine,  it  yields  two  compounds  in  which  hydrogen  is  partially  replaced  by 
chlorine.  It  may  be  volatilized  if  heated  on  a  plate  of  metal.  When  acted  on 
by  a  strong  solution  of  potassa,  isatine  is  dissolved  with  an  intense  violet  colour, 
which  an  addition  of  water  and  evaporation  changes  to  yellow,  and  the  liquid 
deposits  pale  yellow  crystals,  which  contain  potassa,  united  to  a  new  acid,  isa- 
tinic  acid,  formed  from  isatine  by  the  addition  of  1  eq.  water.  When  separated 
from  its  salts  by  stronger  acids,  isatinic  acid  is  at  once  resolved  into  isatine  and 
water;  but  if  isatinate  of  lead  be  decomposed  by  sulphuretted  hydrogen,  and  the 
filtered  solution  evaporated  spontaneously  in  vacuo,  the  acid  is  obtained  as  a 
white  tlocculent  powder,  which  when  dissolved  in  boiling  water,  instantly  be- 
comes red,  and  the  solution  on  cooling  deposits  crystals  of  isatine.  Isatinic  acid 
is   C   H,NO  HO.     Its   salts   have   the  formula  C    H  NO.,MO.    The  violet- 

16      6  5  16      0  a'    ^ 

coloured  compound  first  formed  when  isatine  acts  on  potassa  is  a  compound  oi 
isatine  and  potassa,  which,  when  heated  with  water,  soon  passes  into  isatinate 
of  potassa. 

With  sulphurous  acid,  or  rather  sulphites,  isatine  forms  salts  of  the  formula 
CjgH^NO^,2S02-f-MO ;  which  may  be  formed  also  by  the  action  of  sulphurous 
acid  on  isatinates. 

By  the  action  of  chlorine,  isatine  is  converted  into  two  compounds,  chlorisa- 
tine  and  bichlorisatine.  When  chlorine  is  passed  through  isatine  or  indigo  sus- 
pended in  water,  both  these  compounds  are  formed,  and  they  are  separated  by 
crystallization,  chlorisatine  being  the  least  soluble  of  the  two, 

H"  C  H        ' 

'  Chloriaatine^  C       <  ^f  NO  ,  forms  transparent  orange  yellow  4-sided  prisms, 

isomorphous  with  isatine,  and  very  analogous  to  it  in  all  respects.  When  acted 
on  by  potassa,  there  is  first  formed  a  deep  red  solution,  which  when  heated  soon 
becomes  yellow,  and  on  cooling  deposits  brilliant  pale  yellow  crystals  of  chlori- 

C  H 

satinate  qf  potassa,  ^^^j  pf  NO^,KO,  a  salt  perfectly  analogous  to  isatinate  of 

potassa,  and  containing  an  acid,  chlorisatinic  acid,  which  is  chlorisatine,  plus  1 
eq.  water,  C,^H  CINO  .     Like  isatinic  acid,  when  separated  from  its  salts  it  is 

CH 

speedily  resolved  into  chlorisatine  and  water,     Chlurisatinale  of  silver,  C^^    <  ^| 

NO  ,AgO  forms  yellow  crystals,  soluble  in  hot  water.     Chlorisatinate  of  baryta, 

C  H 

^w  ;  pf  ^^5'^^^'  +  ^  ^^'  forms  golden  yellow  tables.     Chlorisatinate  of  lead. 


BICHLORISATINE. 


md 


C  H 
^16  J  rf  N^i'P^^'  when  first  precipitated  from  the  salt  of  potassa  by  nitrate  of 

lead,  forms  a  gelatinous  yellow  precipitate,  which  soon  becomes  flocAilent, 
acquiring  a  splendid  scarlet  colour.  The  red  salt  is  crystalline,  the  yellow  amor- 
phous. Chlorisatinate  of  copper  forms  at  first  a  brownish  yellow  bulky  preci- 
pitate, which  soon  changes  to  a  heavy  granular  blood-red  powder. 

Like  the  isatinates,  the  chlorisatinates  combine  with  the  sulphurous  acid, 

C  H 

forming  salts  of  the  formula  C^^  j  ^4  NO^,2S02-[-  MO.     In  short,  the  analogy 

between  isatine  and  chlorisatine,  insatinates  and  chlorisatinates,  &c.,  is  such  as 
to  furnish  a  very  beautiful  example  of  the  substitution  of  chlorine  for  hydrogen, 
while  the  type  or  chemical  character  of  the  compound  is  unaffected.  In  bichlo- 
risatine,  we  shall  see  an  aditional  example  of  the  same  truth. 

Bichlortsatine,  C     ^  ^3  NO  ,  is  formed  along  with  the  preceding  compound. 
'    '  2  ^ 

It  is  more  soluble  than  chlorisatine,  but  is  otherwise  remarkably  similar  to  it. 

With  aqua  potassae  it  first  forms  a  deep  red  solution  (here  as  in  the  case  of  isa- 
tine and  chlorisatine  a  compound  of  it  with  potassa),  which  when  heated  changes 
to  yellow,  and  on  evaporation  yields  yellow  scales  of  a  salt  compound  of  potassa 
and  hichlorisatinic  acid.  The  acid  may  be  separated  by  stronger  acids  as  a  yellow 
powder,  which  when  dissolved  and  warmed  is  resolved  into  bichlorisatine  and 

water.    Its  formula  is  C^    5     4    NO^.HO.    The  salt  of  5ary /a,  C^    5      *  NO^, 

BaO,  forms  golden  yellow  needles.  The  salt  of  copper  is  at  first  bulky  and 
brown,  but  soon  becomes  greenish  yellow  and  crystalline,  and  finally,  a  heavy 
granular  powder  of  a  fine  carmine  red  colour. 

Bichlorisatine  with  sulphites  forms  compounds  analogous  to  those  above  men- 
tioned of  isatine  and  chlorisatine.  In  this  case  also,  therefore,  the  type  is  per- 
fectly retained,  although  2  eq.  of  the  hydrogen  of  isatine  have  been  replaced  by 
chlorine. 

Bromine  acts  on  isatine,  and  forms  two  compounds,  hromisatine  and  hihromisa- 


tine,  entirely  analogous  to  chlorisat 


and  hihromisatinic  acids,  and  also  compounds  with  sulphites  analogous  to  these 


just  mentioned.      We  have,  therefo 
tution,  the  following  compounds  : — 


Isatine 
isatinic  Acid 

Chlorisatine  . 

Chlorisatinic  Acid 

Bichlorisatine 

Bichlorisatinic  Acid 

Bromisatine 

Bromisatinic  Acid 

Bibromisatine 

Bibrornisatinic  Acid 

Isatinosulphites    . 


ne  and  bichlorisatine,  forming  bromisaiime 


e,  from  isatine,  and  isatinic  acid,  by  substi- 


H5NO4 
H«  N0« 


HO 


c« 

ct  NO4 

:?i;no,+ho 

Br'  ™. 

c,J 

B?NO,tHO 

c.. 

k-0. 

c,. 

"?NO,  +  HO 

C16    H5  N04,2S02  +  MO 


696  PRODUCTS  DERIVED  FROM  INDIGO. 

Chlorisatinosulphites  .  .  C,g  J^^^  n04,2S0.2  +  MO    ; 

Bichlorisatinosulphites  .  .  C,6  <  Jj^  N04,2S02  4-M0 

Bromisatinosulphites  .  .  Cje  j^^  n04,2S02 -f- MO 

Bibromisatinosulpbites  .  .  Cjg  <g|?  N04,2S02 -f  MO 

Isatyde,  CjgHgNO^=  C^^H^NOj,!!,  is  formed  when  an  alcoholic  solution  of 
isatine  is  acted  on  by  sulphuret  of  ammonium.  It  is  a  grey  crystalline  powder, 
and  may  be  considered  to  represent  isatine  plus  I  eq.  hydrogen. 

Sulphesafyde,   C^^HgN  ^  ^.^  is  isatyde,  in  which  2  eq.  oxygen  are  replaced 

2 

by  sulphur.  It  is  formed  by  the  action  of  sulphuretted  hydrogen  on  isatine  dis- 
solved in  alcohol,  and  is  a  greyish  yellow  amorphous  powder.  Sulphisatine  is 
the  name  of  a  compound  obtained  in  the  same  way  by  Erdmann,  which  he  con- 
siders to  be  different  from  sulphesatyde. 

C  H 

Chlorisaiydey  C^^  j  ^^  NO^,  is  a  white  powder  somewhat  crystalline,  ob- 
tained by  the  action  of  sulphuret  of  ammonium  on  chlorisatine.  It  is  perfectly 
analogous  to  isatyde.     By  the  action  of  sulphuretted  hydrogen  on  chlorisatine,  a 

C  H 

compound  is  formed  which  is  C^^  j     «  NS^ :  that  is  chlorisatyde,  in  which  all 

the  oxygen  is  replaced  by  the  sulphur. 

Bichlorisatyde,  C^^  <  ^^ 'NO^^xx^  hihromisatyde,  C^^  ^4  NO^,  are  per- 
fectly  analogous,  in  formation  and  properties,  to  chlorisatyde. 

Sulphasatyde,  C^gHgN  j  ^^  3  is  formed  by  the  action  of  potash  on  sulphesatyde, 

from  which  it  differs  in  having  only  1  eq.  oxygen  replaced  by  sulphur.  It  is  a 
white  crystalline  powder. 

Indine,  C^^H^NO^  is  a  crystallized  substance,  of  a  beautiful  rose  colour, 
formed  by  the  action  of  potash  on  sulphesatyde,  along  with  the  preceding;  or 
by  the  action  of  potash  on  sulphasatyde  or  isatyde.  In  the  last  case,  isatinate 
of  potash  is  also  formed,  thus,  3  (C^gHgNOJ -+-2K0  =  2  (KO,Cj^HgNO^)  + 
Cj^HgNO^.  It  is  sulphesatyde,  minus  2  eq.  sulphur,  and  is  also  isomeric  with 
white  indigo.  It  is  decomposed  by  nitric  acid,  and  by  bromine,  which  give  rise 
to  new  products. 

When  indine,  moistened  with  alcohol,  is  covered  with  a  lukewarm  solution 
of  potash,  it  forms  a  black  solution  which  in  a  few  moments  becomes  a  semi- 
solid mass  of  black  needles,  which  are  a  compound  of  potash  with  indine  or 
rather  with  indinic  acid,  an  acid  formed  from  indine,  like  isatinic  acid  from 
isatine,  by  the  assimilation  of  1  eq.  water,  and  which  is  very  easily  again 
resolved  into  indine  and  water. 

Hydrindine  is  a  yellow  crystalline  compound  formed  by  healing  indine,  sul- 
phasatyde, or  isatyde  with  potash.  Its  composition  is  C  H  N  O  ,  that  is  2  eq. 
indine  plus  1  eq.  water;  and  when  strongly  heated,  it  is  resolved  into  indine  and 
water.  It  is  not  composed  of  these  substances,  however,  for  it  forms  with  pot- 
ash white  salt,  hydrindinate  of  potash.  The  acid  in  this  salt  appears  to  be 
formed,  like  some  of  those  already  described,  by  the  addition  of  water  to  hydrin- 
dine i  its  formula  is  probably  C^gH^^N  O  ,2H0- 


PRODUCTS  DERIVED  FROM  INDIGO. 

Nitrindine,  C?  ^H  N^O  ,  is  a  beautiful  violet-coloured  powder  formed  by  the 
action  of  nitric  acid  on  indine  and   hydrindine.     It  is  indine,  in  which  2  eq. 

hydrogen  are  replaced,  one  by  oxyg-en,  the  other  by  nitrous  acid  ;  C^^  <  NO^  > 

(    O    ) 

C  H 

Chlorindine  C^^  j  r{^^2'^  2H0,  is  a  powder  of  a  dirty  violet  colour,  formed 

by  the  action  of  heat  on  chlorisatyde.  Analogous  compounds  are  obtained  from 
hichlorisatyde  and  hihromisatyde.  Bichlorindine  is  like  chlorindine.  Bibromin- 
dine  is  very  dark  red,  and  dissolves  in  alcohol  with  a  fine  purple  colour. 

The  action  of  potash  on  isatyde  appears  to  be  the  type  of  its  action  on  chlorisa- 
tyde, bromisatyde,  hichlorisatyde,  and  bibromisatyde.  When  isatyde  is  acted 
on  by  potash,  it  yields  isatine  (or  isatinate  of  potash);  indine  (or  indinate  of 
potash);  and  hydrindine  (or  hydrindinate  of  potash).  6  eq.  isatyde,  (GC^gHg 
NOJ  are  equal  to  4  eq.  isatine  (4CjgH^N0J  f  2  eq.  indine  (SC^gHgNO^)  t 
4  eq.  water:  or  they  are  equal  to  4  eq.  isatine  (46^^11  NO^)  -f-  1  eq.  hydrindine 
(C^^H^^N^O.)  -\-  3  eq.  water.  Both  changes  probably  occur,  and  the  three  com- 
pounds, isatine,  indine,  and  hydrindine,  alike  take  up  the  elements  of  water  to 
form  the  acids,  which,  to  avoid  confusion,  are  not  here  expressed.  Now  there 
is  good  reason  to  believe  that  precisely  analogous  changes  occur  when  potash 
acts  on  hichlorisatyde  and  on  bibromisatyde,  each  yielding  three  corresponding 
compounds  and  the  three  acids  derived  from  these.  The  reader,  by  strictly  fol- 
lowing the  analogy  of  the  formulae  given  above  for  the  action  of  potash  on 
isatyde,  will  easily  be  able  to  construct  the  equations  for  the  other  analogous 
cases. 

When  sulphesatyde  is  acted  on  by  bisulphite  of, ammonia,  there  is  formed 
among  other  products  not  fully  investigated,  a  salt  formed  of  ammonia  united  to 
a  new  acid,  sulphisalanous  acid^  quite  different  from  the  acid  in  the  salts  formed 
when  isatine  is  acted  on  by  sulphites.     This  new  acid  is  CjgH^N02,2S02-j- 

HO,  or  perhaps  rather  C^gHgN    \  ^^r^  f    +  HO ;    that   is    sulphesatyde,    in 

which  the  2  eq.  of  sulphur  have  been  replaced  by  2  eq.  sulphurous  acid. 

The  action  of  bisulphate  of  ammonia  on  sulphesatide  sometimes  gives  rise  to 
the  formation  of  different  products  ;  among  others,  to  an  insoluble  white  powder, 
isatan^  C^gHgNO^,  which  when  heated  yields  isatine  an^  indine;  3(C^gHgN0g) 
=CjgH^NO^-f-2(Cj^HgN02)-t-HO.  Both  indine  and  nitrindine,  when  acted  on 
by  bisulphite  of  ammonia,  appear  to  produce  compounds  analogous  to  those 
derived  from  sulphesatyde. 

Chlorindnpten  is  the  name  given  by  Erdmann  to  a  volatile  crystalline  sub- 
stance, formed  along  with  chlorisatine  and  bichlorisatine,  when  chlorine  acts  on 
indigo.  When  the  chlorinised  mass  is  distille^  with  water,  this  substance 
passes  over  in  white  crystals,  which  are  acid,  and  evidently  a  mixture  of  two 
substances.  When  this  chlorindopten  is  heated  with  potassa,  a  neutral  sub- 
stance passes  over,  in  white  crystals  similar  to  the  original  ones  ;  this  is 
chlorindatmit ;  while  the  potassa  retains  an  acid  of  a  disagreeable  odour,  chlorin- 
dopi»nic  acid, 

.  Chlorindoptenic  acid,  C  H^C1^0,H0,  is  separated  from  its  potash  salt  by 
acids,  as  a  white  flocculent  matter  of  a  very  disagreeable  odour.  Laurent  has 
identified  it  with  his  chlorophenisic  acid,  an  acid  derived  from  coal  tar  by  the 


PRODUCTS  DERIVED  FROM  INDIGO. 

C  FT     ') 

action  of  chlorine,  and  makes  its  formula  C^^  j  ^2    C    0,  HO.      Chlorindatmit 

appears  to  be  C^^  ^  qj*  ^  N  (Hoffmann). 

By  the  further  action  of  chlorine  on  chlorisatine  or  bichlorisatine,  dissolved  in 
alcohol,  new  compounds  are  formed,  among  which  are,  chlorinized  chlorindopien^ 
which,  like  chlorindopten,  is  a  mixture  apparently  of  chlorindatmit,  with  an 
acid,  chlorinized  chlorindoptenic  acid,  C  CI  0,H0  ;  which  is  the  chlorophenusie 
acid  of  Laurent.  This  acid  is  accompanied  by  chloranile^  ^i2^^4^4'  ^  "^"^i^l 
body  in  volatile  golden  yellow  scales,  soluble  in  hot  alcohol,  which  is  also  derived 
from  the  oil  of  coal  tar,  or  rather  from  the  hydrate  of  phenyle  or  carbolic  acid  of 
that  oil,  from  which  chlorophenisic  and  chlorophenusie  acids  are  obtained. 

Chloranile  dissolves  in  weak  potassa  with  a  deep  purple  colour,  and  the  solu- 
tion deposits  dark,  purplish-red  crystals,  composed  of  potassa  and  a  new  acid, 
chloranilic  acid.  This  acid  forms  scarlet  or  yellow  crystals,  according  as  it  con- 
tains water  of  crystallization  or  not.  Its  formula  is  C  CI  0  ,2H0,  or  C  CI 
03,H0. 

When  chloranile  is  acted  on  by  aqua  ammoniae,  it  is  dissolved,  forming  a 
blood-red  solution,  which  deposits  chesnut-brown  crystals  of  chloranilammon  C^ 
H3NCIO2-I-4  aq.ssCpClO^fNH^-}-  4  aq.  It  dissolves  in  water  with  a  purple 
colour,  and  when  a  saturated  solution  is  mixed  with  hydrochloric  acid,  it  deposits 
very  brilliant  black  needles  of  great  length.  These  are  a  new  compound,  chlo' 
ranilam,  C^^C\fl^l^O=C^^C\fi^'^Nl{^{  that  is  2  eq.  of  chloranilammon,  2(Cq 
C10,,NH,)=C,  CI  0^,N  H^;    minus  1  eq.  ammonia  NH,.     Both  these  com- 

o  3 '  12        2      0         2       0  *■  3 

pounds  give  precipitates  with  metallic  solutions,  which  are  the  same  from  both, 
but  distinct  from  those  formed  by  chloranilic  acid  or  its  salts.  Chloranilammon, 
according  to  Laurent,  is  the  ammonia  salt  of  an  acid  containing  amide  as  an 
ingredient.     Chloranilam  is  the  acid  itself. 

By  the  action  of  ammonia  on  isatine  there  are  produced  several  new  compounds, 
varying  with  the  strength  of  the  ammonia,  and  the  menstruum  employed.  In 
these  compounds,  oxygen  is  replaced  by  amide,  NH  ,  or  imide,  |  NH=Im. 

Imasatine  is  formed  when  dry  ammonia  is  passed  through  an  alcoholic  solution 
of  isatine.    It  forms  fine  deep  yellow  crystals,  the  formula  of  which  is  C^^Hg 

Imasatine  is  formed  when  aqua  ammonise  acts  on  a  solution  of  isatine  in  alco- 
hol.    It  is  a  greyish  yellow  crystalline  substance,  the  formula  of  which  is  C^g 

H,N  JJ^M 

*       ^Im 

Imasatinic  acid  is  formed  along  with  the  preceding,  and  is  dissolved  along 
with  ammonia.  By  the  addition  of  an  acid  it  is  precipitated  as  a  beautiful  scar- 
let crystalline  powder,  soluble  in  hot  alcohol,  which  deposits  it  in  splendid  tabu- 
lar crystals  similar  to  the  sublimed  periodide  of  mercury.  It  dissolves  sparingly 
in  acids  with  a  violet  colour,  and  these  solutions  deposit  violet  crystals.     Its 

formula  is  C,^  H  N  S  ^3  ?  f  HO. 

Amamfine  is  formed  along  "s^ith  the  two  preceding  bodies.  It  has  a  fine  yellow 
colour,  and  dissolves  in  acids  with  a  violet  colour,  apparently  passing  into  ima- 
satinic acid.    Its  formula  is  C^^H^N  ^  .^?  +H0.  (Ad=NH^=amide.) 


ANILIC  ACID.— PICRIC  ACID.  699 

The  analogy  between  chlorisatine,  &c.  and  isatine,  holds  in  regard  to  the 
action  of  ammonia  on  them.  By  the  action  of  dry  ammonia  on  an  alcoholic 
solution  of  chlorisatine  there  is  formed  a  yellow  crystalline  compound,  analo- 

C  H    ^ 

gous  to  imesatine.     It  is  called  Imachlorisattnase,  and  its  formula  is  C  ^  pi*  c 

N  r^ 

Imachlorisalinase  is  analogous  to  imasatine.     Its  formula  is  C     ^  pi'*  r    N 

^     3        It  forms  brownish  yellow  crystals. 

Imabramtsatinase,  formed  by  the  action  of  dry  ammonia  on  bibronlisatine  in 
alcohol,  is  C^^  ^  p^  r    N  j     ^        it  is  a  deep  orange  crystalline  powder. 

We  have  now  briefly  run  over  the  catalogue  of  the  very  remarkable  com- 
pounds derived  from  indigo  by  the  action  of  sulphuric  acid  and  bichromate  of 
potassa,  which  produces  isatine,*  and  by  the  action  of  chlorine  either  on  indigo 
or  on  isatine,  of  bromine  on  the  same,  and  of  potassa,  ammonia,  sulphuretted 
hydrogen  and  sulphuret  of  ammonium  on  the  products  of  these  actions.  The 
nomenclature  of  these  compounds  is  in  a  very  imperfect  state,  and  requires 
reformation,  but  this  cannot  be  effected  until  the  substances  themselves  have 
been  more  thoroughly  studied.  It  is  most  important  to  observe,  that  by  or 
through  chloranile  and  the  chlorindoptenic  acids,  the  series  to  which  indigo 
belongs  connects  itself  with  that  of  carbolic  acid  or  hydrate  of  phenyle  (to  be 
afterwards  described),  and  these  again  with  the  series  of  salicyle.  "We  have' 
now  to  mention  one  or  two  products  of  the  action  of  nitric  acid  on  indigo  which 
are  common  to  all  these  series,  and  like  chloranile,  seem  likely  to  be  very  fre- 
quently met  with  as  products  of  the  decomposition  of  organic  compounds. 

Anilic  acid,  Syn.  Indigotic  acid,  Nitrosalicylic  acid,  C  H  NOg.HO.  This  acid 
is  formed  by  the  long-continued  action  of  weak  nitric  acid  on  indigo.  It  is  also 
formed  in  the  preparation  of  isatine,  if  the  action  be  pushed  too  far.  It  is  iden- 
tical with  nitrosalicylic  acid,  obtained  by  the  action  of  nitric  acid  on  salicylic 
acid  or  on  salicine.  It  forms  fine  yellowish-white  prisms,  which  are  light  and 
bulky,  and  shrink  much  in  drying.  It  is  fusible  and  volatile.  By  the  action  of 
strong  nitric  acid  it  is  converted  into  oxalic  and  picric  acids.  It  requires  1000 
parts  of  cold  water  for  solution.  Its  salts  crystallize  well,  and  their  general  for- 
mula is  C  H  NO  ,M0.  The  anilate  of  oxide  of  methyle  is  obtained  as  a  crys- 
talline compound  By  the  moderated  action  of  nitric  acid  on  the  salicylate  of  oxide 
of  methyle  (oil  of  gaultheria).  The  anilate  of  oxide  of  ethyle  is  exactly  sim- 
ilar. 

Picric  acid,  Syn.  Carbazotic  acid,  Nitropicric  acid,  Nitrophenisic  acid,  C 

C  FT        ^ 

J  qivn   Q  0)110.     This  acid  is  formed  by  the  action  of  nitric  acid  on  anilic 

acid,  indigo,  salicine,  salicylic  acid,  hydrate  of  phenyle  or  carbolic  acid,  couma- 
rine,  silk,  aloes  (?)  and  other  substances.  It  is  most  easily  formed  from  carbo- 
lic acid,  salicine  or  oil  of  gaultheria,  by  the  action  of  an  excess  of  fuming  nitric 
acid  assisted  by  heat.  It  is  purified  by  solution  in  hot  water  and  recry stall iza- 
tion.  It  forms  pale  yellow  or  even  white  scales  of  a  silvery  lustre.  They  dis- 
solve in  hot  water  with  a  strong  yellow  colour,  and  a  very  bitter  taste.  The  acid 
is  fusible  and  volatile.     Its  salts  crystallize  most  readily,  and  all  explode  when 


70a  ANTHRANILIC  ACID.— ANILINE. 

heated.  When  these  salts  are  put  in  contact  with  lime  and  green  vitriol,  blood- 
red  solutions  are  formed,  containing  the  lime  salt  of  a  new  acid.  The  picrate 
of  potassa  is  so  sparingly  soluble,  especially  in  alcohol,  that  an  alcoholic  solu- 
tion of  picric  acid  may  be  used  as  a  test  for  potassa. 

;Picric  acid  is  interesting  as  occurring  among  the  products  of  the  decomposi- 
tion by  nitric  acid  of  so  many  different  substances.  It  is  easily  derived  from 
the  series  of  phenyle,  that  is,  from  carbolic  acid,  C^^H^O,  HO.     Derived  frodi 

r  TT     -^ 

this,  we  have  Chlorophenesic  acid,  C^^  <  p?  ^  0,  HO,    Chlorophenusic   acid, 

C2C1^0,H0,  and  Picric  acid,  C^^  5  ^^  I  0,H0.     It  is,  therefore,    carbolic  - 

acid  in  wUich  3  eq.  of  hydrogen  are  replaced  by  3  eq.  of  nitrous  acid. 

When  indigo  is  heated  with  concentrated  potassa,  there  are  formed  two  new 
acids :  chrysanilic  acid,  the  composition  of  which  is  uncertain,  and  anihranilic 
acid,  C,  H  NO,  =  C,  H^N0,,H0.  The  latter  is  purified  in  the  form  of  anthra- 
Dilate  of  potassa,  a«d  the  acid  separated  by  an  excess  of  acetic  acid.  It  forms 
transparent  yellow  scales,  which,  however,  wheji  quite  pure,  are  colourless.  It 
is  derived  from  blue  indigo,  Cj^H^NO^,  by  the  loss  of  2  eq.  carbon  and  the  ad- 
dition of  2  eq.  water. 

When  anthranilic  acid  is  mixed  with  powdered  glass,  and  rapidly  heated,  it 
is  resolved  into  carbonic  acid  and  an  oily  liquid,  which  is  aniline^  a  very  power- 
ful base,  devoid  of  oxygen,  identical  with  the  crystalline  of  Unverdorben,  and 
the  kyanol  of  Runge,  C  H^N.  This  metamorphosis  is  very  simple:  C  H 
NO  =0  0  4-0  HN.  Since  aniline  is  obtained  in  many  other  cases  of  de- 
composition of  organic  matters  by  heat,  it  becomes  a  substance  of  great  interest. 
,  Aniline  is  recognized  by  its  property  of  striking  a  deep  violet  blue  colour  with 
chloride  of  lime.  It  obtained  the  name  kyanol  from  this  property.  Its  other 
name,  crystalline,  indicates  its  great  tendency  to  form  crystallizahle  salts  with, 
acids. 

,  The  recent  researches  of  A.  W.  Hofmann  have  greatly  extended  our  know- 
ledge of  this  remarkable  compound.  He  has  shown  that  it  is  not  confined  to 
the  products  of  the  decomposition  of  indigo,  but  that  it  is  formed  when  other 
substances,  isomeric  with  anthranilic  acid,  are  exposed  to  heat  along  with  bases, 
such  as  lime  or  baryta.  Such  substances  are  salicylamide  and  protonitroben- 
zoene,  both  of  which  have  the  empirical  formula  C  H  NO  .  The  former  yields 
little,  but  the  latter  is  entirely  resolved  into  aniline  and  carbonic  acid.  He  has 
also  fully  identified  aniline  with  the  crystalline  of  Unverdorben,  a  base  occurring 
with  others  among  the  products  of  distillation  of  animal  matter,  and  in  coal  tar. 
It  is  worthy  of  remark  that  a  close  connection  may  be  traced  between  aniline 
and  carbolic  acid  (hydrate  of  phenyle).  The  latter  is  Cj^H^O,HO.  The  car- 
bolate  of  ammonia,  Cj^H^Oj.NH^O,  minus  2  eq.  water  would  yield  an  amide, 
phenylamide,  which  would  be  ^ja^^i'^ ^2  ^^  ^12^7^  ♦  ^"^  ^^^®  '^  aniline.  Now 
in  Hofmann's  experiment  above  mentioned,  in  which  salicylamide  was  heated 
■with  lime,  it  did  not  yield  much  aniline,  but,  on  the  other  hand,  it  furnished  a 
Jarge  quantity  of  carbolic  acid. 

It  is  further  to  be  noticed  that  carbolic  acid  (hydrate  of  phenyle)  and  aniline 
(phenylamide)  occur  together  in  coal  tar;  and  that  all  the  substances  which 
yield  either  one  or    other    of  these   are  also  converted  into  picric    acid,   Cj^ 

5     2      C  0,H0,  by  the  action  of  nitric  acid.     Thus  carbolic  acid,  indigo,  sa- 


ANILINE.— CHLORANILE.  701 

licine,  and  salicylic  acid,  aro  all  transformed  into  pricric  acid  by  excess  of  nitric 
acid. 

Another  point  in  which  all  these  substances  agree  is  this,  that  when  acted  on 
by  a  mixture  of  hydrochloric  acid  and  chlorate  of  potassa,  they  are  all  converted 
into  chloranile,  C^^Cl^O^.  It  is  more  than  probable  that  all  those  bodies,  such 
as  indigo,  salicine,  carbolic  acid,  &c.  which  in  this  way  yield  chloranile,  either 
belong  to  the  series  of  phenyle  or  are  nearly  allied  to  that  series,  and  readily  pasg 
itito  it.  The  fundamental  or  primitive  compound  of  that  series  appears  to  be 
some  compound  of  the  formula  C^^Agi  yvheve  A  stands  for  hydrogen,  chlorine, 
bromine,  iodine,  oxygen,  nitrous  acid,  &c.,  &c.  Assuming  this,  and  supposing 
A  to  be  represented  by  H,  then  we  have  the  following  series,  which  will  exhibit 
in  a  practical  form  the  doctrine  of  substitutions. 

C,2    Hg        =  Supposed  origin  or  nucleus  of  the  series. 
0,2^^6 1      _c^2     Hg     0,HO=hydrate  of  phenyle. 


0,2^  CO  =C,2  1^3^  0,HO=chlorophenesic  acid 
C,2  )  Og  i  ==Ci2  \q^  I  0,HO=chlorophenisic  acid. 
^12  \  ^'5  (      =Cj2Cl5,0,HO=chlorophenu6ic  acid. 


9  A 


jhloranile 


Ci2)isj''J      =aniline. 
C 


12<2N04>  =C,2    <2]^o  (  ^'^^"^"^^'^P^^"'^^'^  ^^^*^* 

(^3      )  C  H     > 

12<3N0^V  =Cj2    {3^5  (    0,H0=mtropheni8ic  (picric)  acid 
' '-'2      / 

12  s  fi^g    >  =Ci2    \^j      >    0,HO=bromophfenisic  acid. 
(O2      )  C     3     )  ' 


Hofmann  has  shown  that  isatine,  when  distilled  with  potassa,  yields  aniline ; 
and  that  chlorisatine,  so  analogous  in  all  respects  to  isatine,  undergoes  a  similar 
decomposition,  yielding  a  new  base  chloraniline ;  also  that  other  compounds  may 
be  formed  containing  more  chlorine,  but  still  belong  to  the  same  series;  finally, 
that  bromisatine  also  yields  a  base,  bromaniline.  The  following  are  the  formulae 
of  these  new  compounds,  which,  it  will  be  observed,  are  still  referable  to  thd 
original  formula,  C^^^  or  C^^Hg.  '"^ 

(He  ) 
^12  "x^^    C      =chloraniline,  a  powerful  base. 

(N    ) 

(H5  ) 
C12  i  CJg  >     =dichloraniline,  a  weak  base. 

(N    ) 

^^4    )  , 

^iz^^'sr      =trichloraniline=chlorindatmit  of  Erdmann,  a  neutral  body. 


^12  ■\^''   (     =bromaniline,  a  base. 

Cja  <  Br2  >      =dibromaniline,  a  weak  base. 


702  CHRYSAMMICjACID. 

:tribromaniIine=broinaniIoid  of  Fritzsche,  a  neutral  compound. 


'l2<A?      =^11 


It  may  here  be  mentioned,  that  although,  in  order  to  include  the  water  of  the 

hydrated  acids,  I  have  adopted  C    H   as  the  nucleus  of  these  compounds,  we 

may  also  refer  them  to  C^Hg=phene  or  benzine.     The  oxide  of  phenyle  and  the 

C  TT 
different  acids  will  then  be  represented  as  anhydrous,  thus,  C^^  j  ^^  oxide  of 

C  H  C  H 

phenyle,  &c.    Aniline  will  be  C^^  <  ^U  ^=^^  j  A    =pbenylamide:  and  chlo- 

raniline  will  be  C^^  <  CI ;  and  so  on.     The  only  compound  which  does  not  adapt 

(Ad 
itself  to  this  formula  is  chloranile,  C^^^l^O^;  which  might,  however,  be  C^ 


) 


cio^  hc\o 


Our  space  will  not  permit  us  to  enter  into  any  details  concerning  the  prepara- 
tion and  properties  of  these  interesting  compounds;  but  it  may  be  remarked  that 
chloraniline  by  the  action  of  hydrochloric  acid  and  chlorate  of  potassa,  yields 
chloranile;  and  that  the  same  substance,  when  passed  over  lime  (hydratedl)  at  a 
low  red  heat,  yields  aniline,  thus  affording  additional  proof  that  all  these  com- 
pounds belong  to  one  series,  and  are  different  subtypes  of  one  general  type.  Nor 
must  it  be  forgotten,  that  in  the  case  of  aniline,  chloraniline,  and  bromaniline, 
we  have  chlorine  and  bromine  substituted  for  hydrogen  in  a  basic  compound, 
without  affecting  its  basic  characters.  This  is  the  first  known  example  of  a  base 
formed  by  substitution  from  another  base,  although  similar  facts,  in  regard  to 
acids  and  neutral  bodies  had  long  been  known. 

10.  Carmine. 

This  name  has  been  given  to  the  colouring  matter  of  cochineal  which  is  nitro- 
genized,  and  may  be  obtained  in  dark  red  crystalline  grains,  very  soluble  in  water 
and  alcohol.  It  forms  with  alumina  a  beautiful  red  lake,  well  known  as  carmine. 
Its  precise  formula  is  not  determined,  but  it  approaches  to  ^^3  H    NO   . 

ACTION  OF  NITRIC  ACID  ON  ALOES. 

This  action  so  much  resembles,  in  some  points,  the  action  of  nitric  acid  on 
indigo,  that  it  may  be  properly  mentioned  here.  Aloes  is  the  well-known  in- 
spissated juice  of  certain  species  of  aloe,  and  is  very  bitter  and  purgative.  The 
nature  of  its  active  principle  is  still  unknown :  but  when  heated  with  nitric  acid 
it  yields  a  yellow  bitter  substance,  which  is  converted,  by  the  further  action  of 
the  acid,  into  two  crystallizable  acids,  chrysammic  and  chrysolepic  acid.  The 
artificial  bitter  of  aloes  appears  to  be  formed  of  two  acids,  aloetic  and  aloeretinic 
acids,  which  form  red  salts,  but  the  composition  of  which  is  not  exactly  ascer- 
tained. 

Chrysammic  acid,  Cj^HN^Oj^^,!!©,  is  obtained  as  a  yellow  precipitate,  when 
water  is  added  to  the  solution  obtained  by  heating  aloes  with  excess  of  nitric 
acid.  It  is  purified  by  being  combined  with  potassa,  and  this  salt,  after  recrys- 
tallization,  is  dissolved  in  hot  water  and  decomposed  by  diluted  nitric  acid.     The 


ALKALOIDS  OR  ORGANIC  BASES.  703 

chrysammic  acid  is  deposited  as  a  powder  formed  of  golden  yellow  shining 
scales.  Its  solution  is  of  a  fine  purple.  All  its  salts  are  crystallizable  and  of  a 
deep  red  colour,  frequently  with  green  reflection,  like  muroxide.  The  chrysam- 
mate  of  ammonia  forms  dark  green  crystals,  which,  when  dissolved  and  acted  on 
by  nitric  acid,  deposit  brilliant  black  scales,  which  are  not  chrysammic  acid,  but 
are  transformed  into  it  when  boiled  with  acids  or  bases.  The  solution  of  chry- 
sammat3  of  ammonia  gives  with  metallic  salts  peculiar  precipitates  distinct  from 
those  formed  with  the  same  salts  by  chrysammate  of  potassa. 

Chrysokpic  acid,  ^12^2^3^13'^^'  ^^^  *^^  formula  and  many  of  the  properties 
of  picric  acid ;  but  it  is  said  by  Schunck,  who  discovered  it,  to  be  different.  It 
is  darker  in  colour,  and  its  salts  with  potassa,  is  much  more  soluble  than  picrate 
of  potassa.  It  would,  however,  appear  that  the  two  acids  are  essentially  the 
same ;  for  their  salts  are  in  general  very  similar,  and  all  explode  when  heated. 
Now  that  picric  acid  is  recognized  as  so  frequent  a  product  of  the  action  of  nitric 
acid,  we  have  no  difficulty  in  understanding  its  occurrence  here. 

ALKALOIDS  OR  ORGANIC  BASES. 

These  names  are  given  to  a  class  of  nitrogenized  organic  compounds  which, 
in  their  relations,  are  quite  analogous  to  ammonia,  or  rather  to  oxide  of  ammo- 
nium. They  are  to  be  distinguished  from  such  basic  oxides  as  oxide  of  ethyle, 
oxide  of  methyle,  &c.,  which  contain  no  nitrogen,  and,  although  they  form  neu- 
tral compounds  with  acids,  yet  exist  in  a  peculiar  state  .in  these  compounds, 
which  cannot  be  decomposed,  like  ordinary  salts,  by  double  decomposition. 
Thus  oxalate  of  oxide  of  ethyle,  does  not  precipitate  with  nitrate  of  lime,  and 
chloride  of  ethyle  does  not  decompose  nitrate  of  silver.  But  the  case  is  quite 
different  with  the  alkaloids ;  for  their  salts  undergo  the  same  decompositions  as 
those  of  ammonia. 

Most  of  the  alkaloids  are  found  in  vegetable  juices,  seeds,  or  roots;  these  are 
called  vegetable  alkalies,  and  they  are  generally  the  active  principles  of  the 
plants,  for  the  most  part  poisonous,  in  which  they  are  found.  But  of  late  organic 
bases  quite  analogous  to  those  produced  by  nature,*have  been  formed  in  a  variety 
of  processes  ;  as,  for  example,  the  singular  bases  containing  platinum,  described 
at  pp.  2B9-271 ;  the  bases  containing  arsenic,  or  arsenic  and  platinum,  mentioned 
at  pp.  382-384  ;  the  bases  of  coal-tar,  of  which  aniline,  formed  in  several  differ- 
ent processes,  is  one ;  the  bases,  chloraniline,  &c.,  derived  from  aniline ;  the 
bases  derived  from  oil  of  mustard,  (see  p.  349) ;  those  derived  from  the  decom- 
position of  natural  alkaloids,  as  quinoleine  and  cotarnine ;  and,  finally,  those 
formed  by  the  action  of  sulphuret  of  ammonium  on  certain  nitrogenized  bodies, 
as  aniline  from  nitrobenzide,  naphthalidine  from  nitronaphthalese,  &c.  Most 
of  these  artificially  formed  bases  are  of  very  recent  discovery,  and  it  is  evident 
that  they  must  throw  much  light  on  the  theory  of  the  production  of  the  natural 
alkaloids,  and  that  the  careful  study  of  this  part  of  the  subject  will,  in  all  pro- 
bability, eventually  lead  to  the  artificial  formation  of  the  natural  organic  bases. 

The  alkaloids  possess,  for  the  most  part,  very  decided  basic  properties  ;  when 
dissolved  they  act  on  vegetable  colours  like  the  inorganic  alkalies  ;  and  they 
neutralize  the  strongest  acids  completely,  generally  forming  crystallizable  salts. 
Most  of  them,  at  the  ordinary  temperature,  are  expelled  from  their  salts  by  am- 
monia, but  many  of  them  at  the  heat  of  boiling  water  expel  ammonia  from  its 
salts,  owing  to  the  volatility  of  the  latter  alkali. 


704  LIQUID  VOLATILE  BASES.  * 

Their  basic  properties  are  not  derived  from  the  oxygen  they  contain,  for  no 
variation  in  the  amount  of  that  element  affects  their  neutralizing  power.  On  the 
other  hand,  there  is  every  reason  to  believe  that  their  basic  character  depends  on 
the  nitrogen  they  contain ;  for  they  all,  without  exception,  contain  nitrogen, 
although  several  are  devoid  of  oxygen.  Moreover,  most,  if  not  all  of  those  which 
have  been  formed  artificially,  are  prepared  with  the  aid  of  ammonia,  or  some 
compound  of  ammonia,  or  amidogen.  It  is  quite  conceivable  that  they  may  be 
composed  of  ammonia  or  amidogen, //us  some  compound  of  carbon  and  hydrogen, 
or  of  carbon,  hydrogen,  and  oxygen,  the  addition  of  which  does  not  diminish  the 
basic  energy  of  the  ammonia,  or  amidogen.  Thus,  the  three  bases  containing 
platinum,  formerly  described,  may  be  represented  as  PtO,NH^,PtO,2NH  ,  and 
PtC10,2NH  ;  and  these  formulae  will  at  all  events  show  their  relation  to  am- 
monia. 

The  alkaloids  occur  in  combination,  generally  with  vegetable  acids ;  and  they 
are  separated  from  these  combinations  by  the  same  means  which  are  employed  in 
the  case  of  inorganic  bases,  modified  in  each  case,  according  as  the  alkaloid  is 
soluble  or  insoluble  in  water  and  other  solvents,  fixed  or  volatile  when  heated. 
Thus  quinine,  morphia,  and  strychnia,  are  separated  by  adding  to  their  soluble 
salts,  lime,  ammonia,  or  magnesia,  which  form  soluble  salts  with  the  acids 
which. are  present,  while  the  alkaloids,  being  insoluble,  are  precipitated;  codeine, 
being  soluble  in  ether  as  well  as  water,  is  first  set  free  by  potassa,  and  ether 
being  added  to  the  aqueous  liquid,  is  agitated  with  it,  and  rises  to  the  surface, 
carrying  the  codeine  along  with  it,  and  the  same  process  applies  to  other  alka- 
loids. Lastly,  conia,  nicotine,  and  other  volatile  alkaloids,  are  obtained  by  dis- 
tilling their  salts  with  an  excess  of  liquor  potassae. 

The  alkaloids,  like  ammonia,  combine  with  hydrogen  acids  forming  salts, 
without  the  addition  of  water  or  its  elements  being  necessary ;  they  also,  like 
ammonia,  refuse  to  combine  with  anhydrous  oxygen  acids,  requiring  1  eq.  of  water 
to  form  dry  salts.  Their  hydroch  I  orates,  like  sal  ammoniac,  form  double  salts 
with  the  bichlorides  of  platinum  and  of  mercury. 

The  salts  of  mosti^f  the  alkaloids  are  precipitated  as  tannates  by  infusion  of 
galls. 

The  alkaloids  are  generally  decomposed  by  chlorine,  bromine,  and  iodine, 
forming  coloured  compounds  not  yet  fully  investigated.  They  are  also  decom- 
posed by  nitric  acid,  some  of  them  with  a  deep  red  colour. 

Some  of  them,  such  as  quinine,  strychnia,  &c.  when  heated  with  strong  caus- 
tic potassa,  yield  an  oily  compound,  which  is  also  a  base,  and  is  called  quino- 
leine. 

We  shall  now  briefly  describe  the  individual  alkaloids,  dividing  them  into 
groups,  according  to  their  characters. 

1.    Liquid  Volatile  Bases. 

a,  Aniline,  C^^H^N,  has  been  already  mentioned  as  formed  by  the  action  of 
potassa  on  isatine,  and  by  the  action  of  heat  and  bases  on  anthranilic  acid  and 
protonitrobcnzoene,  and  on  salicylamide,  although  the  latter  only  yields  a  very 
small  proportion.  It  also  occurs  as  one  of  the  most  remarkable  ingredients  in 
the  oil  of  coal-tar,  where  it  is  associat,ed  with  two  other  bases,  leukol  and  pyr- 
rol ;  also  in  the  oil  obtained  by  distilling  indigo,  or  animal  matter.  In  coal-tar 
it  is  associated  or  combined  with  carbolic  acid,  arid  the  relation  between  aniline 


LEUKOL.    NICOTINE.    CONINE.    QUINOLINE.  W$^ 

(phenylamide)  and  carbolic  acid  (hydrate  of  phenyls)  has  already  been  ex- 
plained.    It  is  obtained  pure  by  rather  a  tedious  process. 

Aniline  is  an  oily  liquid,  boiling  at  358°,  rather  heavier  than  water  (sp.  gr. 
1*028),  of  a  very  high  dispersive  and  refractive  power.  It  has  a  hot  pungent 
taste,  and  an  agreeable  vinous  odour.  It  forms  crystalline  salts  with  most  acids, 
and  strikes  a  deep  violet-blue  colour  with  solution  of  bleaching-powder.  By  the 
action  of  nitric  acid  it  is  converted  into  picric  acid,  and  by  that  of  a  mixture  of 
hydrochloric  acid,  and  chlorate  of  potash,  it  is  converted  into  chloranile.  Chromic 
acid  causes  a  deep  bluish-black  colour.  With  chlorine  it  yields  chlorinized  com- 
pounds, especially  chlorophenisic  (chlorindoptenic)  acid,  and  tricloraniline  (chlo- 
rindatmit).  Bromine  converts  it  into  tribromaniline  (bromaniloide).  Aniline  is 
very  acrid  and  poisonous.  The  two  bases,  chloraniline,  C^HgClN,  and  bromani- 
line,  C^HgB^N,  derived  from  aniline  by  substitution,  have  been  already  men- 
tioned.    They  are  very  analogous  to  aniline. 

b.  Leukol,  C^gHgN.  This  base  is  found  in  the  oil  of  coal-tar,  along  with  ani- 
line, from  which  it  is  separated  by  distillation,  aniline  being  the  more  volatile  of 
the  two.  Leukol  is  an  oily  liquid,  of  a  still  higher  refractive  and  dispersive 
power  than  aniline ;  it  has  an  unpleasant  smell,  and  a  burning  taste.  It  boils  at 
463°.  Its  sp.  gr.  is  1*081.  Neither  bleaching-liquor  nor  chromic  acid  produce, 
with  leukol,  the  blue  colour  which  they  give  rise  to  with  aniline.  It  combines 
with  acids,  but  its  salts  do  not  crystallize  so  readily  as  those  of  aniline. 

c.  Nicotine^  Cj^HgN.  This  base  is  found  in  tobacco,  and  is  obtained  by  dis- 
tilling the  concentrated  infusion  of  the  leaves  along  with  potassa.  The  distilled 
liquid,  which  contains  nicotine,  water,  and  ammonia,  is  neutralized  by  sulphuric 
acid  and  the  neutral  solution  dried  up.  Alcohol  then  dissolves  the  sulphate  of 
nicotine,  leaving  undissolved  the  sulphate  of  ammonia.  The  pure  sulphate,  dis- 
tilled with  potassa,  yields  pure  nicotine,  which  appears  as  an  oily,  limpid,  colour- 
less liquid,  having  a  weak  smell  of  tobacco.  Its  sp.  gr.  is  1'048.  It  is  decidedly 
alkaline,  and  mixes  with  water,  alcohol,  and  ether.  It  is  highly  poisonous.  With 
acids  it  forms  salts  which  crystallize  with  difficulty.  The  hydrochlorate  of  nico- 
tine combines  with  bichloride  of  platinum,  formings  double  salt,  which  yields 
large  regular  orange-red  crystals,  of  the  formula  Oj^HgNjHCl  -f-  PtCl^.  It  is 
probable  that  nicotine,  besides  being  found  in  the  fresh  leaves  of  tobacco,  is  pro- 
duced in  larger  quantity  during  the  fermentation  to  which  the  leaves  are  subjected 
in  the  manufacture  of  tobacco  ;  and  there  is  also  reason  to  believe  that  it  is  pro- 
duced by  the  action  of  heat  on  tobacco,  as  in  smoking,  and  that,  from  the  com- 
parative simplicity  of  its  formula,  it  will  be  found  among  the  products  of  the 
distillation  of  organic  compounds,  containing  nitrogen.  Its  analogy,  in  compo- 
sition and  properties,  to  the  two  preceding  bases,  is  very  obvious. 

d.  Conine.     Syn.      Coma.      C,^H,^N  ?     This  base  occurs  in  the  hemlock, 

16      16 

coinum  maculatum,  and  is  extracted  by  a  process  quite  analogous  to  that  above 
described  for  nicotine.  It  is  also  an  oily  liquid,  boiling  at  338°,  highly  poison- 
ous, and  easily  decomposed.  Its  taste  and  smell  are  both  very  acrid  and  dis- 
agreeable, and  somewhat  analogous  to  those  of  nicotine.  Its  salts  are  acrid  and 
poisonous,  crystallizing  with  difficulty.  As  it  is  the  active  principle  of  the 
coniiim,  conine,  either  pure  or  as  a  salt,  ought  to  be  used  instead  of  the  extract 
or  tincture,  which  are  very  variable. 

e.  Quinoline,  C  H  N.  This  base  is  formed  artificially,  by  distilling  quinine, 
cinchonine,  or  strychnine,  along  with  caustic  potassa.  It  is  an  oily  liquid,  of 
sp.  gr.  1*084,  which  is  volatile  at  a  high  t«mperature.    It  forms  two  hydrates, 

47 


706  BASES  OF  CINCHONA  BARK. 

with  1  and  3  eq.  of  water  respectively.  It  is  very  bitter,  and  strongly  alkaline, 
and  forms  crystalHzable  salts  with  acids.  Its  production  from  quinine  and  cin- 
chonine  will  be  explained  under  these  bases.  Quinoleine  is  now  believed  to  be 
identical  with  leukol. 

2.  Bates  derived  from  Oil  of  Mustard. 

Under  the  head  of  Oil  of  Mustard,  these  bases  have  been  already  described. 
They  are  Thiosinnamtne,  C  H  NS  ;    Sinnamine,  C  HJ^;   and  SinapolinCj  C 
H,NO,. 

3.  Bases  of  Cinchona  Bark. 

a.  Quinine^  ^ao^ia^^a*  '^^^  important  alkaloid  is  found  along  with  cincho- 
nine,  in  most  species  of  cinchona  bark.  It  predominates  in  yellow  bark,  Cin- 
chona  Jlava,  China  regiut  or  C.  calisaya ,-  and  is  obtained  by  boiling  with  an  excess 
of  milk  of  lime  the  decoction  in  diluted  hydrochloric  acid  of  the  bark,  and  treat- 
ing the  precipitate  with  hot  alcohol,  which  dissolves  cinchoninc  and  quinine. 
On  evaporation,  the  cinchonine  is  deposited  in  crystals,  and  the  quinine  remains 
diMolved.  Water  is  added,  which  causes  the  quinine  to  separate  as  a  resinous 
maM.  It  may  be  obtained  in  crystals  by  the  spontaneous  evaporation  of  its 
solution  in  absolute  alcohol.  It  is  very  sparingly  soluble  in  watfir,  but  very 
soluble  in  alcohol  and  in  acids.  Its  solutions  are  very  bitter.  When  heated 
with  hydrate  of  potassa,  it  yields  carbonate  of  potassa,  hydrogen  gas,  and  quino- 
line.     C^H^NO,+KO  +  K0,C02+  C^^H^N-f  H^. 

Quinine  is  decidedly  alkaline,  and  neutralizes  the  acids.  Its  salts,  especially 
the  sulphate,  are  very  much  used  in  medicine,  especially  as  febrifuge  and  tonic 
remedies,  in  most  cases  very  superior  to  the  bark  in  substance.  The  sulphate 
of  quinine  used  in  medicine  is  a  basic  salt,  2(C^H^N02)-f-S02-|-8HO.  The 
neutral  sulphate  is  much  more  soluble  in  water;  hence,  in  draughts,  sulphate  of 
quinine  is  generally  dissolved  in  diluted  sulphuric  acid.  The  hydrochlorate, 
phosphate,  citrate,  and  ferrocyanate  of  quinine  have  also  been  employed  in 
medicine. 

b.  Cinchonine f  C^qH^^NO.  This  base  predominates  in  the  grey  bark,  (Jin- 
chona  condaminea^  or  C.  ruhiginom^  and  is  also  found  in  large  quantity,  as  well 
as  quinine  in  red  bark,  C.  oblongifolia.  Its  preparation  has  been  above  described. 
It  crystallizes  very  readily,  and  is  not  so  bitter  as  quinine,  although  highly 
febrifuge.  When  heated,  a  considerable  part  is  sublimed.  When  distilled  with 
potassa,  it  yields  quinoline.  C^^^O-\-}\0,KO^KO,CO^-^Q^^^^-\^^^. 
It  neutralizes  the  acids,  forming  crystalHzable  salts,  which  may  be  substituted 
for  those  of  quinine. 

It  is  very  important  to  observe  that  cinchonine  only  differs  from  quinine  by  1 
eq.  oxygen  ;  and  although  hitherto  no  one  has  succeeded  in  converting  one  into 
the  other,  little  doubt  can  be  entertained  that  this  will  be  accomplished  in  pro- 
cess of  time.    The  fact  that  both  yield  quinoline  is  very  interesting. 

c.  Quinoidine,  This  name  has  been  given  by  Sertuemer  to  a  third  alkaloid, 
which  he  has  found  in  the  mother  liquors  of  the  preceding.  It  would  appear  to 
possess  a  very  great  neutralizing  power,  but  it  is  not  yet  known  in  a  state  of 
purity.    The  subject  requires  investigation. 

d.  Jlricine^C^\J^O^.  Tliis  base  was  found,  in  1828,  in  a  cinchona  bark 
from  Arica,  in  Peru,  and  has  not  since  occurred.    It  is  very  similar  to  cincho- 


I 


BASES  OF  THE  PAPAVERACEJE. 

nine,  from  which  it  differs  in  being  solable  in  ether.  According  to  the  analjms 
of  Peiletier,  it  eontaios  1  eq.  oxjgen  more  than  qainine,  and  2  eq.  more  Uian 
cinchonine,  so  the  three  bases  may  be  riewed  as  oxides  of  die  same  radical. 
-Aricinc  forms  salts  which  arc  crystal! izable,  bitter  and  febrifage. 

Besides  the  abore  four,  other  alkaloids  are  said  to  hare  been  fonnd  in  different 
species  of  cmchona ;  as  pitoyine,  in  the  China  pit/nfa,  eMiwvine  in  the  Otina  nova^ 
another  alkaloid  in  the  f^na  rf  Carthagena,  hlaiujuitdne  in  the  the  China  blanea, 
which  is  the  bark  of  einchma  otifolia  and  C  matrocarpa;  and  dnehovatine  in 
Cinchona  ovata.  This  last  crntzWne*  well,  and  forms  crystalltzable  salts.  It 
has  been  analyzed,  and  tbeiesalts  lead  to  the  formnla  ^^^j^i' 

4.  i^ses  of  the  Papavenceae. 

a.  Morphint,  C^^NO^  fhis  alkaloid  oocorsin  opimiiy  whieh  is  the  inspis- 
sated jaice  of  papaver  $omn^erum.  Perhaps  the  earnest  method  of  extracting  it 
is  the  following.  The  soluble  part  of  opium  is  extraeled  by  water,  and  the 
concentrated  infusion  is  mixed  with  solotioD  of  ehlofide  of  ealeiom,  this  salt 
being  added  in  slight  excess.  On  standing,  espedally  if  warmed,  the  mixture 
deposits  a  eopioos  browmsh  grey  pieeipitate  of  mixed  meconaie  and  salphate  of 
iime  (the  morphia  being  in  the  opiam  partly  as  meeooate,  partly  as  snlphate), 
while  hydrochlorate  of  morphia  remains  in  s<dation  with  a  rery  large  proportion 
of  dark  brown  colouring  matter.  The  brown  solation  is  evaporated  till,  on  cool- 
ing, the  hydrochlorate  crystallizes,  forming  a  nearly  solid  mass^  which  is  snb- 
jected  to  very  strong  piessnns  in  ihnnel.  A  tliidic  Tiseid,  nearly  black  mother 
liquor  is  thos  expressed,  which  contains  all  the  naioottne  and  colouring  matter. 
The  squeezed  mass  or  cake  of  hydrochlorate  of  morphia  is  of  a  &wn  colour.  It 
viissolred  in  hot  water,  filtered  if  necessary,  and  recrystallized,  so  much 
.g  used,  that  on  cooling  a  semisolid  mass  is  obtained.  This  is  again 
/.Tu  out,  and  if  the  sqoeexed  cake  is  not  quite  white,  it  is  only  necessary 
t:  repeat  the  operation.  A  little  animal  charcoal,  in  the  second,  or  better  still 
in  the  third,  crystallisation,  assists  in  remoring  the  last  traces  oT colour.  The 
second  and  third  mother  liquds,  althoogfa  coloered,  are  not  to  be  thrown  away, 
r; ::  should  be  added  to  the  solution  of  a  fresh  portion  of  opium,  so  that  the 
soaall  quantity  of  hy^sseUoibte  which  is  lelained  in  solution  shall  not  be  lost. 
In  crystallizing  hydrochlorate  of  morphine,  the  liquid  should  always  beacido- 
lated  with  hydrochloric  acid  (after  the  animal  charcoal  is  separated),  because  in 
i:  is  way  rery  little  indeed  is  retained  in  s<rfotion. 

ified  hydrochlorate,  whicfa  still  contains  about  ^  of  codeine,  is  how 

in  hot  water, and  sapefsatarated  with  ammonia;  on  cooling,  the  mor- 

.«d  as  a  snow-while  ciystalKne  powder,  which  may  be  crystalltzed 

ot  alcohoL    The  codeine  remains  in  the  mother  liquor. 

Morphine  fivms  hard  transparent  brilliant  crystals,  almost  insoluble  in  water, 

solable  in  hot  alcohol,  insoluble  in  ether.    It  is  decidedly  alkaline,  neutralizing 

and  forming  crystal lizable  salts.    All  its  solutions  are  bitter,  and  act  as 

poisons.    It  is  coloured  red  by  nitric  acid,  and  brownish-red  by  iodic 

add ;  it  also  strikes  a  deep  blue  with  perch  loride  of  iron. 

The  salts  of  morphine  are  nneii  need  in  medicine,  especbUy  Uie  hydrochlo- 
rate, the  acetate,  and  the  sulphate.  A  solution  of  any  of  these  salts,  of  fire 
grains  to  the  oonee,  may  be  admimsteied  in  the  same  dose  as  tincture  of  opium 
(iaodanom).  The  hydrochlorate  or  mnriate  js  prepared  as-aiN»ve-4ksa9>ed,  and 
is  osed  in  the  state  in  which  it  is  obtained  by  repealed  cM|litoMiMl^  contain- 


708  NARCOTINE. 

ing  y*5  of  its  weight "of  a  double  hydrochlorate  of  morphia  and  codeine,  which 
has  much  the  same  action.  The  acetate  and  sulphate  are  best  made  directly  by 
dissolving  in  acetic  and  sulphuric  acids  the  precipitated  morphine  till  they  are 
neutralized,  and  then  evaporating.  1  lb.  of  good  opium  yields  1|  oz.  of  hydro- 
chlorate  of  morphine.  These  salts  are  most  valuable  anodynes,  and  do  not  de- 
range the  stomach  nearly  so  much  as  an  equivalent  dose  of  laudanum;  but  they 
do  not  act  so  decidedly  in  producing  sleep  as  in  allaying  pain  and  irritation ;  at 
least  the  sleep  they  induce  does  not  come  on  so  soon  as  in  the  case  of  laudanum. 
The  patient,  however,  even  when  he  does  not  sleep,  feels  refreshed,  almost  as  if 
he  had  slept,  and  on  the  whole  the  preparations  of  morphine  are  preferred  by  the 
physician,  and  have,  in  this  country  at  least,  nearly  banished  the  use  of  lauda- 
num.   The  black  drop  contains  impure  citrate  of  morphine. 

b.  Codeine,  C  H  NO^.  This  alkaloid  is  obtained  as  above  described  from  the 
mother  liquor  of  the  precipitated  morphine,  which,  being  evaporated,  deposits 
the  double  hydrochlorate  of  morphine  and  codeine.  This  salt  being  purified,  is 
acted  on  by  potassa,  which  dissolves  the  morphine,  while  the  codeine  is  left  as 
a  viscid  mass,  which  soon  becomes  hard  and  crystalline.  It  is  purified  by  solu- 
tion in  ether  or  in  water,  both  of  which  solvents  leave  the  morphine,  which 
may  be  mixed  with  it,  undissolved.  The  ethereal  solution,  by  spontaneous  evapo- 
ration, deposits  it,  especially  if  a  little  water  be  added,  in  fine  anhydrous  prisms  ; 
the  aqueous  solution  gives  large  octahedral  crystals,  which  are  a  hydrate,  with 
2  eq.  of  water. 

Codeine  is  a  powerful  base,  forming  neutral  salts  with  acids.  Its  solutions 
are  bitter,  and  would  seem  to  have  an  anodyne  action  on  the  system.  But  in 
certain  circumstances  they  appear  to  excite  intolerable  itching  of  the  whole  skin. 
It  is  therefore  possible,  that  the  itching  caused  in  some  persons  by  opium,  and 
by  the  commercial  muriate  of  morphine,  proceeds  from  codeine. 

It  is  important  to  observe  that,  as  cinchona  bark  contains  three  alkaloids  dif- 
fering only  in  the  proportion  of  oxygen  they  contain,  so  the  two  principal  bases 
of  opium  diflfer  only  by  1  eq.  oxygen.  Hitherto,  however,  it  has  been  found 
impossible  to  convert  codeine  into  morphine  by  oxidation,  or  morphine  into  co- 
deine by  deoxidation. 

c.  Thehaine.  This  base  also  occurs  in  opium.  It  is  nearly  insoluble  in  water, 
soluble  in  alcohol  and  ether.  Its  solutions  are  alkaline,  and  have  an  acrid  me- 
tallic taste.  It  forms  crystallizable  salts  with  acids.  According  to  Kane,  its 
formula  is  C„  H,  NO,. 

25      14  3 

d.  Pseudamorphine,  ^27^13^^14^  1'his  base  is  occasionally  found  in  opium. 
It  forms  shining  scales.  It  is  sparingly  soluble  in  water  and  weak  alcohol,  in- 
soluble in  absolute  alcohol  and  in  ether.  It  is  readily  dissolved  by  caustic  po- 
tassa or  soda.  It  is  coloured  blue  by  perchloride  of  iron.  It  forms  salts  with 
acids,  which  are  as  yet  little  known. 

e.  JVarceine,  C^gH^^NOj^?  This,  which  is  a  feeble  base,  also  occurs  in  opium. 
It  is  sparingly  soluble  in  water,  soluble  in  alcohol,  insoluble  in  ether.  It  melts 
at  197°.  It  is  coloured  blue  by  hydrochloric  acid,  but  not  by  perchloride  of  iron. 
Acids  dissolve  it,  but  hardly  form  definite  salts  with  it.  In  short,  it  ought  rather 
to  be  described  as  an  indifferent  substance,  were  it  not  that  its  composition  so 
much  resembles  that  of  the  alkaloids. 

/.  Narcoiine,  ^46^23^^14*  ^^^^®  ^®  another  weak  base,  found  ia  opium  in 
larger  proportion  than  any  other,  except  morphine.  It  may  be  obtained,  either 
from  the  mother  liquor  of  muriate  of  morphia  by  adding  ammonia,  or  by  digesting 


PRODUCTS  DERIVED  FROM  NARCOTINE.  709 

the  insoluble  part  of  opium  in  diluted  acetic  acid,  and  precipitating"  by  ammonia. 
The  impure  narcotine  is  purified  by  solution  in  hot  alcohol,  with  the  aid  of  ani- 
mal charcoal.  On  cooling,  narcotine  is  deposited  in  crystals,  which  are  insolu- 
ble in  water  and  alkalies,  soluble  in  alcohol,  ether,  and  acids.  Its  salts  are  bit- 
ter, and  crystallize  with  great  difficulty. 

The  very  recent  researches  of  Liebig,  Wohler,  and  Blyth,  have  made  known 
a  series  of  products  of  decomposition  derived  from  narcotine,  when  acted  on  by 
peroxide  of  manganese  and  sulphuric  acid,  and  also  by  bichloride  of  platinum. 
These  our  space  will  only  permit  us  briefly  to  mention. 

1.  Opianic  acid,  ^^g^^Q='^2^fi<i^^^'  '^^^^  ^^^^  crystallizes  in  slender 
prisms,  and  forms  soluble  and  crystallizable  salts  with  baryta  and  the  oxides  of 
lead  and  silver,  and  with  oxide  of  ethyle.  When  melted,  opianic  acid  passes 
into  an  insoluble  state,  its  composition  remaining  the  same. 

2.  Opiammon^  C^^Hj^NOjg.  This  compound  is  derived  from  2  eq.  opianate  of 
ammonia  by  the  loss  of  1  eq.  ammonia  and  4  eq.  water.  It  is  a  pale  yellow  pow- 
der, which,  by  boiling  with  water,  is  converted  into  opianic  acid  and  opianate  of 
ammonia. 

3.  Xanthopenic  acid.  When  opiammon  is  acted  on  by  alkalies,  it  gives  off 
ammonia  and  yields  opianate  and  xanthopenate  of  potassa.  An  acid  separates 
the  xanthopenic  acid  as  a  yellow  flocculent  precipitate.  It  forms  salts  of  a  fine 
yellow  colour,  but  has  not  been  fully  examined.     It  contains  nitrogen. 

4.  OpianO'Sulphurous  acid,  0^^11^0^^82,110,  is  formed  by  the  action  of  sulphu- 
rous acid  and  opianic  acid,  and  is  produced  by  the  substitution  of  2  eq.  sulphu- 
rous acid  for  2  eq.  water.     It  has  a  bitter  taste,  and  forms  crystallizable  salts. 

5.  Sulphopianic  acid.     C^Hg  ^  v^^  r  5HO.   This  acid  is  formed  by  the  action 

of  sulphuretted  hydrogen  on  opianic  acid,  and  is,  in  fact,  opianic  acid,  in  which 
2  eq.  oxygen  are  replaced  by  2  eq.  sulphur.  It  is  an  amorphous  yellow  powder, 
which  crystallizes  from  alcohol.  Its  salts  are  soon  decomposed,  yielding  sul- 
phurets  of  the  metals. 

According  to  Wohler,  opianic  acid  is  (C2^HgO^,2HO)-j-HO ;  and  in  the  two 
preceding  acids  the  2  eq.  of  water  represented  within  the  brackets  are  replaced 
by  2  eq.  sulphurous  acid  and  2  eq.  sulphuretted  hydrogen.  Opiammon,  on  this 
view,  is  (C2QHgO^,2HO)f  (C2QHgO^,NH3).  He  considers  it  probable  that  nar- 
cotine is  a  compound  analogous  to  opiammon,  and  containing  opianic  acid. 

6.  Himipinic  acid.  C^^H^O^,HO.  This  is  a  product  of  oxidation  of  opianic 
acid.  1  eq.  anhydrous  opianic  acid,  C^^HgOg,  jo/ws  1  eq.  oxygen,  is  Cg^HgO^^ss 
2(C  H  O  ).  The  hemipinic  acid  crystallizes  in  regular  four-sided  prisms.  It 
forms  insoluble  salts  with  the  oxides  of  lead  and  silver. 

7.  Coiarnine.  O^^H^^NOg.  This  is  a  base  formed  along  with  opianic  acid. 
1  eq.  narcotine,  C^gH^^NO^^,  and*  7  eq.  oxygen  yield  1  eq.  cotarnine,  C^^H^^ 
N0g-|-1  eq.  opianic  acid  O^^HgO^^-f-  1  eq.  carbonic  acid  00^+3  eq.  water, 
3H0. 

Cotarnine  forms  a  deep  yellow  radiated  mass,  soluble  in  alcohol  and  in 
water.  It  is  bitter  and  alkaline,  and  forms-  crystallizable  double  salts  with  the 
bichlorides  of  mercury  and  platinum. 

8.  Humopinic  acid  is  a  dark  brown  humus-like  acid  formed  by  the  action  of 
heat  on  narcotine.  Its  composition  is  not  established  with  certainty,  but 
resembles  that  of  other  similar  bodies.     It  contains  no  nitrogen. 

9.  Jpopkyllic  acid.    This  seems  to  be  a  product  of  decomposition  of  cotarnine. 


710  HYOSCYAMINE.    DATURINE. 

It  forms  crystals  very  like  those  of  apophyllitg  and  equally  cleavable.  When 
heated  it  yields  an  oily  liquid,  evidently  quinoline.  Its  composition  is  not  yet 
knovj^n,  but  it  contains  nitrogen. 

10.  Narcogenine,  CggH^gNO^^,  is  formed,  along  with  opianic  acid,  when  nar- 
cotine  is  not  so  far  oxidized  as  to  yield  cotarnine.  2  eq.  narcotine  with  5  eq. 
oxygen  yield  2  eq.  narcogenine,  1  eq.  opianic  acid,  and  3  eq.  water.  It  forms  a 
crystallizable  double  salt  with  bichloride  of  platinum,  but  when  separated,  it  is 
resolved  into  narcotine  and  cotarnine.  2  eq.  narcogenine,  with  2  eq.  oxygen, 
contain  the  elements  of  1  eq.  narcotine,  1  eq.  cotarnine,  and  1  eq.  carbonic  acid. 

11.  Narcotinic  acid  When  narcotine  is  heated  with  potassa  it  forms  a  soluble 
compound  which  contains  an  acid,  apparently  isomeric  with  narcotine,  or  differ- 
ing from  it  only  by  1  or  2  eq.  water.  When  this  acid,  which  is  called  narcotinic 
acid,  is  separated  from  its  salts,  it  rapidly  passes  into  narcotine,  so  that  it  is 
unknown  in  a  separate  form.  Its  atomic  weight  seems  to  be  half  that  of  narco- 
tine, so  that  1  eq.  narcotine  probably  forms  2  eq.  of  the  acid. 

Such  is  a  very  brief  and  imperfect  account  of  the  results  of  the  recent 
researches  of  Wohler  and  of  Bly  th  on  narcotine.  They  are  of  very  great  import- 
ance as  indicating  a  method  which  may  lead  to  the  discovery  of  the  true  consti- 
tution of  the  alkaloids. 

g,  Chelidonine  C^H^QN^Og.  This  al keloid  occurs  in  ehelidonium  majus,  along 
with  cheleryihrine.  It  is  bitter,  insoluble  in  water,  and  alkaline,  forming  crys- 
tallizable salts. 

h.  Chelerythrine  is  found  in  the  same  plant,  forms  a  grey  powder  which  excites 
violent  sneezing.  With  acids  it  forms  red  salts,  which  are  narcotic  and 
poisonous. 

i.  Glaucine.  This  alkaloid  occurs  in  the  leaves  and  stem  of  Glaucium  luteum. 
It  may  be  obtained  in  pearly  scales;  its  taste  is  bitter  and  acrid,  and  it  forms 
salts  with  acids.     Its  composition  is  not  yet  ascertained. 

k.  Glaucopicrine  is  found  in  the  root  of  the  same  plant.  It  is  bitter  and  forms 
salts  of  a  bitter  and  nauseous  taste.    Its  composition  is  unknown. 

5.  Alkaloids  of  the  Solanaceae,  the  Strychneae,  and  other  Vegetable  Families. 

a.  Hyoscyamine,  This  base  is  found  in  Hyoscyamm  niger  and  other  species 
of  hyoscyamus.  Its  composition  is  not  yet  known.  It  is  extracted  from  the 
seeds  by  a  difficult  and  tedious  process,  and  may  also  be  obtained,  although  with 
much  loss,  by  distillation  with  potassa,  like  conine.  It  is  very  prone  to  decom- 
position when  in  contact  with  mineral  alkalies.  It  crystallizes,  when  pure,  in 
radiated  groups  of  needles,  but  sometimes  forms  a  viscid  amorphous  mass. 
When  moist  it  has  a  stupefying  smell  like  that  of  tobacco.  It  is  very  poisonous, 
causing,  like  conine,  tetanic  spasms.  It  dilaies  the  pupil  powerfully.  It  is 
fusible  and  volatile,  but  is  partly  decomposed  when  distilled.  It  dissolves  in 
water,  alcohol,  and  ether.  It  neutralizes  the  acids,  forming  crystallizable  salts 
which  are  very  poisonous. 

b.  Daturine.  This  base  is  obtained  from  the  seeds  o^  Datura  stramonium.  It 
is,  in  preparation  and  properties,  very  analogous  to  hyoscyamine.  It  is,  how- 
ever, less  soluble  in  water,  and  crystallizes  in  fine  brilliant  prisms,  from  its  alco- 
holic solution.  It  is  fusible,  volatile,  and  very  poisonous,  dilating  the  pupil. 
Its  salts  are  crystallizable  and  very  poisonous.  Its  precise  composition  is 
unknown. 


COLCHICINE.  711 

c.  Stramontne.  This  is  another  crystalline  compound  found  in  stramonium. 
It  is  crystallizable,  volatile,  soluble  in  alcohol  and  ether,  insoluble  in  water. 
Its  nature  is  uncertain  and  its  composition  unknown. 

d.  Mropine,  ^^fi^^^'^  This  alkaloid  is  the  active  principle  of  Atropa 
belladonna.  It  is  obtained  like  daturine,  and  being  equally  prone  to  decomposi- 
tion, much  is  always  lost.  It  is  sparingly  soluble  in  water  and  ether,  more 
soluble  in  alcohol.  It  crystallizes  in  white  silky  prisms,  and  sometimes  forms 
an  amorphous  mass  like  glass.  It  is  very  bitter,  acrid,  and  poisonous,  dilating 
the  pupil  like  hyoscyamine  and  daturine.  It  is  fusible  and  volatile,  and  neutra- 
lizes acids,  forming  salts  which  are  bitter,  acrid  and  poisonous,  and  which  crys- 
tallize. These  salts,  from  their  very  powerful  action  in  permanently  dilating 
the  pupil,  are  very  well  adapted  for  medical  use,  being  much  more  uniform  than 
the  extract. 

e.  Solaninet  ^^^■rfi^^2s^  This  alkaloid  occurs  in  many  species  o{  Solanum, 
as  in  S.  nigrum,  S.  dulcamara,  and  in  the  potato,  S.  tuberosum.  In  the  latter  it 
is  found  especially  in  large  quantity  in  the  shoots,  when  the  tubers  have  germi- 
nated in  dark  cellars.  The  shoots  are  extracted  with  dilute  sulphuric  acid,  and 
the  solutioii  precipitated  while  hot  by  ammonia.  The  precipitate  is  purified  by 
solution  in  alcohol.  It  forms  a  crystalline  powder,  very  bitter  and  acrid,  and 
highly  poisonous,  but  not  dilating  the  pupil.  Its  salts  do  not  crystallize  readily. 
There  is  some  reason  to  suspect  that  the  alkaloid  of  the  shoots  of  potatoes  may 
be  distinct  from  that  of  the  bittersweet,  Solanum  dulcamara. 

f.  Veratrine.  C^^H^gNOg  %  This  alkaloid  is  found  in  Verairum  sabadilla,  V, 
album,  §rc.  It  is  extracted  as  atropine  is,  and  is  generally  obtained  as  a  crystal- 
line powder,  nearly  white,  very  acrid  and  poisonous,  exciting  when  introduced 
into  the  nostril  violent  and  even  dangerous  sneezing.  It  is  insoluble  in  water, 
but  very  soluble  in  alcohol,  and  may  be  obtained,  by  the  spontaneous  evaporation 
of  its  alcoholic  solution,  in  prismatic  crystals  several  lines  in  length.  It  is 
coloured  red  both  by  nitric  and  sulphuric  acid. 

Veratrine,  in  the  form  of  tincture,  and  still  more  in  that  of  ointment  (1  drachm, 
or  ^  drachm  to  1  oz.  of  lard),  is  now  much  used  as  an  external  application  in 
neuralgia  and  obstinate  rheumatic  pains.  Its  effects  in  many  cases  are  highly 
beneficial.  In  making  the  ointment,  the  veratrine  should  first  be  rubbed  with  a 
few  drops  of  alcohol  to  an  impalpable  powder,  and  the  lard  then  added.  If  this 
be  not  done,  the  gritty  particles  of  veratrine  in  the  ointment  cause  so  much  irri- 
tation when  rubbed  into  the  skin  as  to  prevent  its  use  for  any  length  of  time. 
We  are  indebted  chiefly  to  Dr.  TurnbuU  for  our  knowledge  of  the  valuable  pro- 
perties of  this  alkaloid. 

g.  Sabadilline.  This  name  has  been  given  by  Conerbe  t©  a  second  crystalline 
body  found  by  him  along  with  veratrine.  It  is  alkaline,  soluble  in  hot  water, 
insoluble  in  ether,  and  forms  crystallizable  salts  with  acids.  Conerbe  states  its 
formula  to  be  C  H  NO  ;  but,  according  to  Simon,  it  is  a  compound  of  vera 
trine  with  resin,  containing  also  resinate  of  soda. 

h.  Colchicine.  This  alkaloid  is  similar  to  veratrine,  for  which  it  was  formerly 
taken.  It  is  found  in  Colchicum  autumnale.  It  is  crystallizable,  bitter,  and 
very  poisonous.  Nitric  acid  colours  it  blue  or  violet.  It  is  soluble  in  water, 
alcohol,  and  ether.  Its  salts  are  crystallizable,  bitter,  acrid,  and  poisonous. 
They  might  probably  be  used  in  medicine  advantageously,  instead  of  the  very 
uncertain  preparations  of  colchicum  which  are  at  present  employed.     In  a  very 


712  STRYCHNINE. 

small  dose,  colchicine  causes  purging  and  vomiting.     Its  composition  is  un- 
known. 

{.  Aconiiine.  This  alkaloid,  the  composition  of  which  is  unknown,  is  found  in 
Aconilum  napelltts,  and,  probably,  also  in  A.  ferox  and  other  species.  It  is  ob- 
tained by  the  usual  method,  but,  being  very  prone  to  suffer  change,  much  is  lost. 
It  forms  a  crystalline  powder,  or  occasionally  a  vitreous  amorphous  mass.  It  is 
in  the  highest  degree  bitter,  acrid,  and  poisonous,  and  is  said  by  Geiger  to  dilute 
the  pupil.  On  the  other  hand,  the  plant  contracts  the  pupil  and  causes  numb- 
ness of  the  part  to  which  it  is  applfed,  and  Dr.  Turnbull  has  obtained  an  aconi- 
tine  possessing  these  properties  in  a  very  high  degree.  Either,  therefore,  there 
are  two  bases  in  the  aconite,  or,  as  is  much  more  probable,  the  aconitine  of  Gei- 
ger having  an  action  different  from  that  of  the  plant,  is  a  product  of  decomposi- 
tion, while  that  of  Turnbull  is  unchanged. 

Turnbull's  aconitine  is  an  invaluable  remedy  in  the  same  painful  diseases  in 
which  veratrine  is  employed.  It  is  unfortunately  obtained  in  small  proportion, 
and  as  yet  is  very  expensive.  A  cheaper  and  more  productive  method  of  pre- 
paring it  is  a  very  great  desideratum. 

k.  Delphine,  ^27^19^ ^2^  '^'^^^  alkaloid,  analogous  to  veratrine,  is  found  in 
stavesacref  Delphinum  staphyeagria.  It  has  only  been  obtained  hitherto  as  a  yel- 
lowish white  powder,  not  crystallyzed,  very  acrid,  and  poisonous.  It  forms 
neutral  salts  hitherto  little  examined.  It  may  be  used  in  the  same  affections  and 
in  the  same  manner  as  veratrine. 

/.  Staphisine.  This  is  a  substance  found  along  with  delphine,  and  said  to  be 
Cg^H^gNO^.  It  is  acrid  and  poisonous,  but  is  probably  only  a  compound  of  del- 
phine. 

m.  Emetine,  ^J  H  NO  %  This  is  the  active  principle  of  ipecacuanha,  the 
root  of  Cephaelis  ipecacuanha.  When  pure,  it  is  a  white  powder,  alkaline,  soluble 
in  alcohol  and  in  hot  water,  insoluble  in  ether.  -J^  of  a  grain  acts  as  an  emetic. 
In  a  dose  of  from  2  to  4  grains  it  i«  poisonous.     Its  salts  do  not  crystallize. 

fi.  Chiococcine  and  0,  Vtoline  are  two  very  similar  alkaloids,  found  in  Chiococca 
ramosa  and  Viola  odorata.  They  are  supposed  by  some  to  be  emetine  disguised 
by  a  little  foreign  matter. 

p.  Strychnine.  ^^J^c^j^fi^i  or  ^44^24^2^8*  ^^^^  alkaloid  is  found  in  nux 
vomica,  the  seeds  of  Strychnos  nux  nomica,  in  St.  Ignatius's  bean,  the  seed  of 
S.  Ignatii,  in  the  wood  of  S.  colubrina,  and  in  the  poison  called  Upas  iieute,  de- 
rived from  S,  tieute.  It  is  extracted  by  decoction  with  dilute  sulphuric  acid,  pre- 
cipitating the  decoction  with  milk  of  lime,  and  acting  on  the  precipitate,  after 
washing  it  with  cold' alcohol,  by  boiling  alcohol,  which  on  cooling  deposits  the 
strychnine  in  very  regular  transparent  brilliant  crystals.  If  brucine  is  present, 
it  remains  chiefly  in  the  mother  liquid,  but  the  two  bases  may  be  separated  by 
converting  both  into  nitrates,  and  crystallizing ;  the  nitrate  of  strychnine  crys- 
tallizes readily,  while  the  nitrate  of  brucine  remains  dissolved. 

Strychnine  is  very  insoluble,  requiring  7000  parts  of  water.  It  is  so  bitter, 
that  1  part  gives  a  very  strong  and  persistent  bitter  taste  to  40,000  parts  of 
water.  It  dissolves  in  hot  alcohol,  although  sparingly  if  the  alcohol  be  pure, 
and  is  insoluble  in  ether.  When  pure,  it  is  only  coloured  yellow  by  nitric 
acid  ;  a  trace  of  brucine  causes  it  to  be  reddened  by  that  acid.  It  forms  crys- 
tallizable  salts,  which  are  intensely  bitter.  Their  solutions  are  precipitated 
white  by  alkalies,  by  tincture  of  galls,  and  by  iodide  of  potassium,  in  white 


BRUCINE.    JERVINE.  71 3 

crystals  by  sulphocyanide  of  potassium,  and  as  yellow  powders  by  solutions  of 
gold  and  platinum. 

Strychnine  and  its  salts,  especially  the  latter,  from  their  solubility,  are  most 
energetic  poisons.  They  produce  spasmodic  motions,  and  are  used  in  very 
small  doses  as  remedies  in  paralysis ;  they  seem  to  have  a  specific  action  on  the 
lower  part  of  the  spinal  column.  The  average  dose  is  y^^  of  a  grain.  In  the 
event  of  an  overdose  the  best  antidote  is  infusion  of  galls  or  strong  tea,  which 
also  contains  tannine. 

q.  Brucine.  C^^H^^NgO^.  This  alkaloid  occurs  along  with  strychnine  in  nux 
vomica,  and  also  in  the  false  angustura  bark,  the  bark  of  Brucia  aniidysenierica. 
It  is  prepared  as  strychnine.  Besides  the  methods  above  mentioned  for  sepa- 
rating the  two  bases,  there  is  another,  which  is  to  boil  the  mixture  with  water 
as  long  as  it  dissolves  brucine,  or  till  the  strychnine  is  no  longer  reddened  by 
nitric  acid.  Brucine  forms  large  transparent  crystals,  which  I  have  found  to 
become  opaque  in  closely  stopped  phials.  It  is  very  bitter  and  poisonous,  but 
much  less  so  than  strychnine.  It  may  be  used  for  the  same  purposes  in  a  rather 
larger  dose.  It  is  reddened  strongly  by  nitric  acid,  and  the  red  solution  be- 
comes violet  on  the  addition  of  solution  of  tin.  It  is  thus  distinguished  from 
strychnine  and  morphine.     Its  salts,  for  the  most  part,  crystallize  with  facility. 

r.  Jervine,  ^60^45^2^3*  ^^^^  alkaloid  is  found  in  white  hellebore,  Vera- 
irum  album,  along  with  veratrine,  from  which  it  is  separated  easily,  as  it  crys- 
tallizes first  from  the  alcoholic  solution ;  and  its  sulphate  is  also  far  less  soluble 
than  that  of  veratrine.  It  forms  a  crystalline  powder,  fusible,  insoluble  in 
water,  soluble  in  alcohol,  and  forming  with  sulphuric,  nitric,  and  hydrochloric 
acids,  very  sparingly  soluble  salts,  so  that  the  solution  of  the  acetate  is  preci- 
pitated by  these  three  acids. 

s.  Curarine.  This  alkaloid  is  obtained  from  the  South  American  poison  called 
curari,  which  is  derived  from  some  plant  of  the  family  Strychnea.  It  is  a 
deadly  poison  when  introduced  into  a  wound,  but  may  be  swallowed  with  im- 
punity. The  curarine  forms  a  yellowish  amorphous  bitter  mass,  which  is  more 
poisonous  than  the  curari  which  yields  it.  Its  salts  are  bitter,  but  do  not  crys- 
tallize. 

t.  Corydaline.  ^^^^^xo  ^  Foui^cl  in  the  root  of  Corydalis  bulbosa  and  C 
fabacea.  It  forms  a  light  grey  powder,  very  soluble  in  alcohol,  which  deposits 
it  in  crystals.  It  is  reddened  by  nitric  acid,  and  forms  crystallizable  salts  with 
acetic  and  sulphuric  acids. 

M.  Carapine.  Found  in  Carapus  guianensts.  It  is  a  white  pearly  fusible  pow- 
der, yety  bitter,  soluble  in  water  and  alcohol,  insoluble  in  ether,  forming  crys- 
tallizable salts  with  hydrochloric  and  acetic  acids. 

V.  Cusparine.  Found  in  the  true  angustura  bark,  that  of  Bonplandia  trifoliata 
or  Cusparia  febrifuga:  It  forms  fusible  octahedral  crystals,  sparingly  soluble 
in  water,  very  soluble  in  alcohol. 

w.  Baphnine,  Occurs  in  the  bark  of  Daphne  gnidium  and  D.  mezereon.  It 
is  obtained  by  distilling  the  infusion  with  magnesia.  It  is  alkaline  and  acrid, 
and  forms  crystallizable  salts  with  nitric  and  sulphuric  acids,  according  to 
Vauquelin.     Baer  and  Gmelin  could  not  obtain  it. 

X.  Bebeerine  is  the  active  principle  of  the  bark  of  the  bebeeru  tree  of  Guiana^ 
which  seems  to  be  analogous  to  quinine.  It  has  not  been  obtained  crystallized 
or  colourless,  but  as  a  brown  mass,  the  composition  of  which  is  not  yet  ascer- 
tained.    Bebeerine  and  its  salts  are  bitter  and  highly  febrifuge.    Dr.  Douglas 


yg^'  BEBEERINE.    PIPERINE.      ** 

Maclagan  and  Mr.  Tilley  have  found  ^ts  composition  to  be  the  same  as  that  of 
morphine,  namely  Cg^H^gNOg. 

t/.  Sanguinarine  is  found  in  Sanguinaria  canadensis.  It  forms  a  grey  powder, 
which  is  alkaline  and  yields  red  salts.  It  excites  sneezing-,  and  is  possibly 
identical  with  chelerythrine. 

z.  Azadirine^  found  in  Mtka  azadirachta,  is  alkaline,  forms  a  cry  stall  izable 
salt  with  sulphuric  acid,  and  is  powerfully  febrifuge. 

aa,  Capsicine  is  the  active  principle  of  the  capsules  of  Capsicum  annuum  or 
cayenne  pepper.  It  has  a  resinous  aspect  and  a  burning  taste,  but  when  quite 
pure  may  be  crystallized.  It  forms  crystallizable  salts  with  acetic,  nitric,  and 
sulphuric  acids.  It  is  soluble  in  alcohol,  insoluble  (when  pure)  in  ether  and 
in  water. 

bb,  Croionine  occurs  in  the  seeds  of  Croton  tiglium,  and  may  be  obtained  from 
croton  oil  by  boiling  it  with  water  and  magnesia.  It  forms  crystals,  which  are 
fusible,  soluble  in  alcohol,  insoluble  in  water.  It  forms  crystallizable  salts  with 
sulphuric  and  phosphoric  acids. 

cc.  Buxine.  Occurs  in  Boxwood  bark.  It  forms  a  bitter,  brown,  amorphous 
mass,  soluble  in  alcohol,  alkaline,  and  forming  a  crystalline  sulphate.  It  excites 
sneezing. 

dd.  Apyrine,  Found  in  Cocos  lapidea.  It  is  a  white  alkaline  powder,  forming 
crystalline  salts  with  acids. 

ee.  Cynapine,  From  JEthusa  cynapium.  It  is  crystallizable,  soluble  in  water 
and  alcohol,  and  forms  a  crystalline  sulphate. 

ff.  Cissampeline,  or  Pelosine,  from  Cissampelos  Pareira,  is  a  white  powder, 
soluble  in  alcohol  and  ether ;  alkaline,  forming  soluble  salts,  of  which  the 
hydrochlorate  crystallizes. 

gg.  Oxyacanthint  and  Berberine  are  two  bitter  substances  found  in  the  bar- 
berry, Berberis  vulgaris.  The  former  is  decidedly  alkaline,  and  forms  crystal- 
lizable salts.  The  latter  is  bitter,  yellow,  and  feebly,  if  at  all,  alkaline.  It 
crystallizes,  and  is  used  in  dyeing.    Its  formula  is  CJ^jH^gNOj^. 

hh.  Surinamine  and  Jamaicine  are  two  alkaloids,  found  in  Gtoffrcta  Surina- 
mensis  and  G.  inermis.  Both  are  crystallizable,  and  form  crystallizable  salts ; 
those  of  the  latter  are  precipitated  by  tannine  and  corrosive  sublimate. 

u.  Fiperine,  C^^Hj^NOg.  This  compound  is  found  in  pepper,  Piper  nigrum, 
and  P.  longum.  It  is  crystallizable,  soluble  in  alcohol,  very  pungent.  It  is  a 
feeble  base,  but  does  form  salts,  especially  double  chlorides,  containing  hydro- 
chlorate  of  piperine. 

kk.  Menispermine  and  Paramenispermtne  are  found  in  tocculus  indicus,  the  seed 
of  Menispermum  cocculus.  Menispermine  is  white,  fusible,  crystallizable,  and 
forms  salts,  of  which  the  sulphate  crystallizes.     Its  formula  is  Cj^Hj^NO^. 

Paramenispermine  has  the  same  composition.  It  is  less  fusible,  but  sublimes 
at  a  high  temperature.  It  does  not  appear  to  form  definite  salts.  Both  are  insolu- 
ble in  water,  and  soluble  in  alcohol ;  and  paramenispermine  is  insoluble  in  ether. 

//.  Ilarmaltne,  C^^H^NO.  This  alkaloid  occurs  united  with  phosphoric  acid 
in  the  seeds  of  Peganum  Harmala.  It  forms  brownish-yellow  prisms,  bitter, 
astringent,  and  acrid,  very  soluble  in  alcohol,  little  soluble  in  water  or  ether.  It 
is  fusible,  and  partly  volatile.  It  forms,  with  acids,  yellow  crystallizable  salts. 
By  oxidizing  agents,  harmaline  is  transformed  into  a  red  matter,  which  forms 
red  salts  with  acids.  The  harmala  red  of  commerce  is  the  powder  of  the  seeds 
already  tranformed  into  the  phosphate  of  the  red  harmaline.     It  is  used  in  dye- 


INDIFFERENT  NON-AZOTIZED  COMPOUNDS.  715 

ing,  especially  in  giving  to  silk  every  shade  of  red,  rose-colour,  and  pink.  It  is 
produced  abundantly  in  the  steppes  of  southern  Russia,  and  is  little  known  out 
of  that  comitry. 

mm.  Theobromine,  CgH.N^O^.  This  is  a  crystalline  compound,  found  in  cacao, 
the  seed  of  Theolroma  cacao.  It  can  hardly  be  called  an  alkaloid.  It  is  very 
analogous  to  the  next  substance,  caffeine. 

nn.  Caffeine,  C  H  N  O  .  Syn.  Thiine.  Guaranine.  This  remarkable  com- 
pound is  found  in  coffee,  in  tea,  in  guarana  officinalis,  or  paullinia  sorbilis,  and  in 
ilex  paraguayensis.  It  is  best  obtained  by  adding  to  a  decoction  of  tea  a  slight 
excess  of  acetate  of  lead,  and  evaporating  to  dryness  the  filtered  liquid.  The 
dry  mass  mixed  with  sand,  is  heated  in  the  apparatus  described  for  benzoic  acid, 
when  caffeine  is  obtained  in  crystals.     Tea  yields  more  than  I  per  cent. 

Caffeine  forms  fine  white  prisms,  of  a  silky  lustre,  which  are  soluble  in  water, 
alcohol,  and  ether,  bitter,  fusible  and  volatile.  It  is  a  feeble  base,  but  forms 
with  hydrochloric  acid  and  sulphuric  acid,  salts  which  yield  very  large  crystals. 

It  is  very  remarkable,  that  caflTeine  should  approach  so  nearly  in  composition 
to  alloxan  and  alloxantine.  Anhydrous  alloxan,  plus  1  eq.  water,  is  Cj^N^H^O^^, 
and  alloxantine  is  CgN^H^Oj^,  while  caffeine  is  CgN^H^O^,  differing  from  the 
one  by  9,  from  the  other  by  8  eq.  oxygen. 

Further,  caffeine,  C  N^H^O  ,  added  to  9  eq.  water  and  9  eq.  oxygen  (that  is, 
to  HgOjg),  is  CgN  Hj^O^Q,  which  is  equal  to  2  eq.  taurine,  a  nitrogenized  prin- 
ciple derived  from  the  bile.  We  shall  hereafter  see  how  close  a  connection  can 
be  traced  between  the  bile  and  the  urine  ;  but  in  the  meantime  it  is  a  most  strik- 
ing fact,  that  tea,  coffee,  Paraguay  tea,  and  guarana,  are  all  used  by  diflTerent  and 
distant  nations  for  the  same  purpose,  namely,  as  a  refreshing  and  gently  stimu- 
lating drink,  which  notoriously  promotes  the  vital  functions,  while  all  these  plants 
contain  the  very  same  compound,  and  that  one  allied  to  the  bile  and  the  urine, 
the  chief  products  of  the  vital  metamorphosis.  The  quantity  of  caffeine  in  tea 
is  indeed  small,  but  not  too  small  to  have  a  perceptible  influence  on  the  system. 
Peligot  has  shown  that  gunpowder-tea  contains  6  per  cent,  of  theine  (caffeine). 

By  the  action  of  nitric  acid,  caffeine  yields  a  crystalline  nitrogenized  com- 
pound, nitrotheine. 

Besides  caffeine,  or  theine,  tea  contains  14  or  15  per  cent,  of  caseine,  and  the 
leaves  are  therefore  nutritious,  when  eaten,  as  they  are,  by  some  oriental  nations. 

The  following  substances  have  been  noticed  as  alkaloids,  but  are  very  little 
known  :  Castine  in  Vitex  agnus  castus  ,•  Cicutine  in  Cicuta  virosa  ,•  Chserophylline  in 
Chserophyllum  bulbosum  ,•  Esenbeckine  in  Esenbcekia  febrifuga  ,-  Digitaline  in  Digi- 
talis purpurea ;  Eupatorine  in  Eupatorium  cannabinum  ,-  Euphorbine  in  Eupkor- 
bium  ;  Convolvuline  in  Convolvolus  scammonium  ,-  and  Pereirine  in  Pereyra  bark. 

We  now  come  to  a  class  of  compounds,  very  widely  distributed  in  the  vege- 
table kingdom,  but  not  exhibiting  the  same  varieties  as  the  classes  hitherto  de- 
scribed, and  not  characterized  by  the  same  marked  properties.  This  is  the  class 
of  neutral  or  indifferent  non-azotized  bodies,  which  are  never  poisonous,  hardly 
even  possessed  of  medicinal  properties,  and  exhibit  no  striking  chemical  cha- 
acters.  It  includes  starch,  gum,  or  mucilage,  pectine  or  vegetable  jelly,  and 
woody  fibre  or  lignine,  with  their  derivatives.  We  can  only  describe  them  briefly. 

INDIFFERENT  NON-AZOTIZED  COMPOUNDS. 
1.  Starch.     C^^^qO^q. 
This  very  important  compound  is  universally  diffused  in  the  vegetable  king- 


TMT  STARCH. 

dom.  It  occurs  in  seeds,  as  in  those  of  wheat  and  other  cerealia,  and  also  in  the 
leguminosae ;  in  roots,  as  in  the  tubers  of  the  potato ;  in  the  stem  or  pith  of 
many  plants,  as  in  Sagus  Rumphii ;  in  some  barks,  as  that  of  cinnamon ;  and  in 
pulpy  fruits,  such  as  the  apple.  Finally,  it  is  contained  in  the  expressed  juice 
of  most  vegetables,  such  as  the  carrot,  in  a  state  of  suspension,  being  deposited 
on  standing. 

It  is  chiefly  extracted  from  wheat  flour  {common  starch),-  from  potatoes  (potato 
starch);  from  the  root  oi  Jatropha  manihot,  {tapioca);  from  that  of  Maranta  arun- 
dinacea  [arrow  root);  from  the  stem  and  pith  of  Sagus  farinifera  Rumphii  {sago); 
the  substances  known  by  these  different  names  being  all  essentially  the  same. 

When  flour  is  kneaded  with  water  in  a  cloth,  the  water  carries  off  the  starch 
in  suspension,  and  deposits  it  on  standing,  leaving  behind  the  gluten.  By  a 
similar  process  starch  is  purified  from  the  cellular  substance  and  other  matters 
mixed  with  it  in  potatoes,  which  are  rasped,  and  then  treated  with  water  as 
above.  Sago,  being  finally  dried  at  a  somewhat  high  temperature,  acquires  a 
homy  and  translucent  appearance. 

Pure  starch  is  a  snow-white  powder,  of  a  glistening  aspect,  which  makes  a 
crackling  noise  when  pressed  with  the  finger.  It  is  composed  of  transparent 
rounded  grains,  the  size  of  which  varies  in  different  plants.  Those  of  the  potato 
are  the  largest,  those  of  the  leguminosae,  as  peas,  are  very  small,  and  those  of 
wheat  and  rice  are  the  smallest.  Starch  is  insoluble  in  cold  water,  alcohol,  and 
ether;  but  when  heated  with  water  it  first  becomes  viscid,  and  is  then  converted 
into  a  kind  of  solution,  which,  however,  is  not  complete,  but  is  rather  formed  by 
the  swelling  of  the  grains  of  starch  into  a  mucilaginous  mass.  On  cooling,  the 
whole  forms  a  stiff,  semi-opaque  jelly.  If  dried  up,  this  yields  a  translucent 
mass,  which  softens  and  swells  into  a  jelly  with  water,  like  tragacanth.  The 
solution,  or  mixture  of  starch  and  water,  has  the  remarkable  property  of  striking 
a  deep  blue  colour  with  free  iodine.  This  appears  to  be  owing  not  so  much  to 
a  chemical  or  definite  combination,  as  to  the  mechanical  division  of  the  iodine ; 
there  is  even  reason  to  think  that  the  blue  colour  is  that  of  iodine  finely  divided, 
adhering  to  the  starch  as  a-  dye  does  to  the  fibres  of  cloth. 

When  starch  is  warmed  with  water,  to  which  has  been  added  either  some  in- 
fusion of  malt  or  some  diluted  acid,  the  viscidity  of  the  mixture  disappears,  and 
the  fluid  solution  is  no  longer  coloured  blue  by  iodine.  As  soon  as  this  is  the 
case,  the  whole  of  the  starch  has  disappeared,  and  has  been  converted  into  a  so- 
luble gum  called  dextrine,  from  its  power  of  causing  the  plane  of  polarization  to 
deviate  to  the  right.  According  to  the  proportion  of  malt  or  of  acid,  and  the 
temperature  employed,  the  change  is  more  or  less  rapid ;  and  when  the  action  is 
continued  the  dextrine  is  in  its  turn  converted  into  glucose^  or  grape  sugar,  which 
from  this  circumstance  is  also  called  starch-sugar. 

In  contact  with  oil  of  vitriol,  starch  appears  to  form  a  compound  or  coupled 
acid,  sulphoamidic  acid.  Strong  nitric  acid,  rubbed  up  with  potato  starch,  dis- 
solves it,  forming  a  viscid  liquid,  from  which  water  precipitates  a  white  com- 
pound, called  xyloidine.  This  compound  has  some  of  the  properties  of  gum-tra- 
gacanth,  but  it  contains  the  elements  of  nitric  acid,  and  has  not  yet  been  fully 
investigated.  According  to  Pelouze,  its  formula  is  CgH^O^+NO^ ;  according  to 
Ballot,  it  is  Cj^Hj^NO^g.  When  starch  is  distilled,  with  moderately-strong  sul- 
phuric acid,  it  yields  carbonic  acid,  formic  acid,  and  a  pungent  volatile  oil,  hith- 
erto very  little  examined. 

The  blue  compound  of  iodine  and  starch  is  best  prepared  by  adding  to  the  liquid 


INULINE.  717 

filtered  from  the  viscid  paste  obtained  by  boiling  starch  with  water,  first  iodide 
of  potassium,  and  then  solution  of  chlorine,  as  long  as  it  causes  a  blue  precipi- 
tate, which  is  to  be  washed  till  the  water  passes  deep  blue,  and  dried  in  vacuo. 
Its  colour  is  so  intense  as  to  be  nearly  black.  It  does  not  appear  to  be  a  com- 
pound in  definite  proportions.  The  best  method  of  using  starch  as  a  test  for 
iodine  in  mineral  waters,  &c.,  is  to  add  to  the  water  some  starch  paste,  and  then 
a  little  nitric  acid  or  chlorine.  The  latter  is  best  added  in  the  form  of  gas,  its 
weight  allowing  it  to  be  poured  like  water ;  while  in  this  way  we  are  less  likely 
to  add  an  excess  which  would  destroy  the  blue  colour.  Or  we  may  place  in  the 
bottom  of  a  phial  the  liquid  to  be  tested,  adding  a  little  oil  of  vitriol,  and  suspend- 
ing from  the  stopper  a  slip  of  paper  moistened  with  starch  paste.  After  a  time, 
if  iodine  be  present,  the  paper  will  exhibit  a  tinge  of  blue.  By  these  tests 
_^i^^th  part  of  iodine  in  a  liquid  may  be  detected. 

With  bromine,  starch  forms  an  orange  yellow  precipitate,  which  cannot  be 
dried  without  decomposition. 

Dextrine  is  best  obtained  by  heating  to  about  120°  a  mixture  of  20  parts  of 
starch  paste  and  1  part  of  strong  infusion  of  malt,  until  iodine  no  longer  colours 
the  mixture  blue.  The  addition  of  strong  alcohol  now  precipitates  the  dextrine 
as  a  thick  syrup,  while  any  sugar  remains  dissolved.  When  dried,  dextrine 
much  resembles  gum,  from  which,  however,  it  differs  in  the  extreme  facility 
with  which  it  is  converted  into  sugar  when  warmed  with  dilute  sulphuric  acid 
or  infusion  of  malt,  and  by  not  yielding  mucic  acid  when  acted  on  by  nitric  acid. 
The  composition  of  dextrine  is  the  same  as  that  of  starch.  In  fact,  dextrine  is 
supposed  by  some  to  be  the  substance  which  is  contained  in  the  grains  of  starch, 
inclosed  in  an  insoluble  membrane,  which  is  burst  in  the  process  of  conversion 
of  starch  into  dextrine,  or  solution  of  starch,  by  means  of  acids  and  infusion  of 
malt.  The  substance  present  in  the  malt  which  has  the  property  of  effecting 
this  change,  is  called  diastase.    It  contains  nitrogen. 

According  to  other  observers,  the  grains  of  starch  are  composed  of  concentric 
layers  of  one  and  the  same  substance  (dextrine?),  the  outer  layer  being  insolu- 
ble in  water.  As  starch  is  found  to  contain  a  small  proportion  of  a  matter  analo- 
gous to  wax  or  to  caoutchouc,  we  may  suppose  that  the  presence  of  this  matter 
in  the  outer  layer  is  the  cause  of  its  insolubility,  or  that  the  whole  mass  of  the 
grains  is,  by  its  means,  rendered  insoluble,  and  endowed  with  the  property  of 
swelling  up  with  water  to  a  paste  or  jelly.  Dextrine  will  then  be  the  purified, 
and  consequently  soluble,  matter  of  starch.  If  the  outer  coat  be  different  from 
the  contents  of  the  grains,  it  has  still  the  same  composition  ;  for  analysis  shows 
no  difference  between  starch,  dextrine,  and  the  insoluble  matter  left  on  the  filter 
when  starch  is  boiled  with  diluted  acids. 

Leiocome,  This  name  is  given  to  a  substance  having  the  properties  of  gum, 
which  is  prepared  by  simply  roasting  or  torrefying  starch  at  about  300°.  It  is, 
in  fact,  capable  of  being  used  instead  of  gum  in  calico-printing,  and  is  made  on 
the  large  scale.  It  has  a  yellowish-brown  colour.  It  is  probably  dextrine,  more 
or  less  pure,  generally  containing  some  undecomposed  starch.  When  well  made 
it  dissolves  in  cold  water  like  gum. 

Inuline,     C^H^^O^gl  C^H^^O^^I  C^^H^^^O^^l     This  is  a  substance  analogous 

to  starch  in  the  roots  and  tubes  of  inula  helenium,  dahlia  variabilis,  helianthua 

tuberosuSf  and  many  other  synantherous  plants,  which  do  not  yield   ordinary 

starch. 

It  is  extracted  from  the  roots  by  boiling  water,  and  is  deposited  by  the  con 


718  GUM. 

centrated  decoction  as  a  brittle  white  mass,  formed  of  crystalline  grains,  or  as  a 
fine  powder.  It  is  tasteless,  insoluble  in  cold,  very  soluble  in  hot  water.  Di- 
luted sulphuric  acid,  with  the  aid  of  heat,  rapidly  converts  it  into  grape  sugar, 
from  which,  like  starch,  it  differs  only  by  a  certain  amount  of  the  elements  of 
water.  This  may  be  seen  by  the  above  formulae,  which  represent  inuline  from 
diflferent  plants,  as  it  exists  in  its  compounds  with  oxide  of  lead.  It  would 
appear  to  differ  in  different  vegetables,  but  always  retaining  the  character  of  this 
class  of  bodies,  namely,  the  presence  of  hydrogen  and  oxygen  in  the  proportions 
to  form  water.     Iodine  colours  it  slightly  brown. 

Lichenine,  C^^H^^O  .  This  is  a  variety  of  starch  found  in  lichen  islandicus, 
or  Iceland  moss.  It  forms,  when  pure,  a  nearly  colourless,  tasteless  mass,  which 
swell  up  into  a  transparent  jelly  with  cold  water,  and  dissolves  entirely  in  hot 
water.  When  its  solution  is  boiled,  it  forms  pellicles,  like  milk,  which  adhere 
to  the  vessel.  Its  solution  is  not  coloured  by  iodine,  but  the  jelly  is  rendered 
blue  by  that  test.  By  diluted  and  boiling  sulphuric  acid  it  is  converted  into 
sugar ;  by  nitric  acid  into  oxalic  and  saccharic  acids.  It  has  the  composition  of 
starch. 

Saponine  is  the  name  given  to  a  variety  of  starch  obtained  from  the  root  of 
saponaria  officinalis.     Its  properties  are  little  known. 

2.  Gum. 

This  name  was  formerly  given  to  almost  all  exudations  from  plants.  It  is  now 
limited  to  certain  rather  abundant  substances,  which  are  solid,  uncrystallizable, 
transparent,  or  translucent,  colourless,  or  nearly  so,  tasteless,  inodorous,  soluble 
in  water,  or  at  least  softening  in  it,  and  insoluble  in  alcohol,  ether,  fat  and  vola- 
tile oils.  They  yield  mucic  acid  when  acted  on  by  nitric  acid.  They  may  be 
divided  into  gums,  which  dissolve  in  cold  water  (arabine,  mucilage),  and  gums 
which  only  swell  up  to  a  Jelly  (tragacanth  or  bassorine,  cerasine,  pectine).  Ara- 
bine and  cerasine  contain  oxygen  and  hydrogen  in  the  proportion  to  form  water  : 
the  other  gums  are  nearly  analogous  in  composition. 

Arahine,  or  gum  arable,  is  found  as  an  exudation  from  several  species  of  acacia. 
What  is  called  gum  Senegal  is  essentially  the  same.  It  is  nearly  colourless, 
transparent,  hard,  and  brittle,  and  has  a  mild  taste.  It  is  very  soluble  in  cold 
water,  and  forms  a  viscid  mucilage,  from  which  alcohol  precipitates  the  gum. 
The  diluted  solution  is  precipitated  by  silicate  of  potassa,  subacetate  of  lead  and 
protonitrate  of  mercury.  When  a  mixture  of  gum,  water,  and  sulphuric  acid  is 
kept  for  some  time  at  a  temperature  near  boiling,  it  is  converted  into  grape  sugar. 
The  composition  of  gum  is  CJ^jH^^O^^,  that  is,  the  same  as  that  of  cane  sugar, 
which  accounts  for  the  transformation.  Arabine  yields  2  or  3  per  cent,  of  ashes, 
containing  a  good  deal  of  lime. 

Mucilage  is  the  name  given  to  a  substance  resembling  gum,  found  in  many 
vegetables,  such  as  linseed^  allhxa,  and  others.  It  differs  from  arabine  in  being 
less  hard  when  dry,  and  less  transparent.  It  would  appear,  however,  that  the 
mucilage  of  althaea-root  is  essentially  starch  enclosed  in  cells  formed  of  woody 
fibre  or  cellulose.  The  different  mucilages  are  resolved  •into  grape  sugar  by 
being  heated  with  dilute  sulphuric  acid,  and  therefore  may  be  considered  as  con- 
taining, like  starch  and  arabine,  water  plus  carbon.  Since  all  these  mucilages 
contain  much  mineral  matter,  the  mucilage  of  linseed,  for  example,  leaving  11 
per  cent,  of  ashes  rich  in  lime,  it  is  probable  that  their  peculiar  qualities  depend 


BASSORINE.    PECTINE.  ffQ 

on  the  presence  of  phosphate  of  lime  or  other  salts  of  lime,  disguising  either 
starch  or  arabine. 

Bassorine  is  the  name  given  to  a  substance  which  forms  the  chief  part  of  gum 
iragacanth  and  of  gum  hassora,  and  also,  according  to  some,  of  salep.,  a  mucila- 
ginous substance,  obtained  from  the  bulbs  of  orchis  mascula.  According  to 
Schmidt,  however,  salep  is  really  formed  of  swelled  up  grains  of  starch. 

Pure  bassorine  resembles  arabine  in  appearance,  but  is  less  transparent,  and 
instead  of  dissolving  in  cold  water,  only  swells  up  to  a  very  great  extent,  form- 
ing a  viscid  mass.  Its  composition  is  analogous  to  that  of  arabine,  and  by  diges- 
tion with  diluted  sulphuric  acid,  it  is  transformed,  like  salep,  into  grape  sugar 
and  cellulose.  Cerasine  is  the  name  given  to  that  part  of  the  gum  of  the  cherry, 
plum  or  almond  trees,  which  is  insoluble  in  cold  water.  It  is  probably  identical 
with  bassorine,  or  with  salep. 

During  what  is  called  the  viscous  fermentation,  which  takes  place  in  certain 
sweet  vegetable  juices,  as  that  of  beet-root,  there  is  formed,  along  with  lactic 
acid  and  mannite,  a  mucilaginous  compound,  which  causes  the  viscidity.  When 
dried,  it  has  nearly  the  characters  and  composition  of  arabine. 

Fectine  is  the  substance  which  causes  the  juice  of  some  pulpy  fruits,  as  apples 
and  pears,  to  coagulate  or  gelatinize  when  mixed  with  alcohol,  by  which  the 
pectine  is  precipitated.  "When  dried,  it  resembles  gum  or  isinglass,  and  forms 
a  jelly  with  water.  By  the  action  of  nitric  acid  it  yields  oxalic  and  mucic  acids. 
It  generally  yields  about  8  per  cent,  of  ashes,  containing  much  phosphate  of 
lime.  In  contact  with  alkalies,  it  is  transfoimed  into  pectic  acid.  Pedic  acid  is 
easily  obtained  from  many  vegetables,  as,  for  example,  rasped  carrots,  by  wash- 
ing them  well  with  distilled  water,  and  then  boiling  50  parts  of  the  squeezed 
residue  with  300  of  water  and  I  of  potassa.  The  pectate  of  potassa  is  deposited 
as  a  jelly  in  the  filtered  liquid  on  cooling.  Either  this  salt  or  the  pectate  of 
lime  may  be  decomposed  by  diluted  hydrochloric  acid,  which  leaves  the  pectic 
acid  as  a  jelly,  which  dries  up  into  transparent  laminae,  insoluble  in  water  but 
very  soluble  in  alkalies.  From  these  solutions  acids  precipitate  it  as  a  jelly. 
In  this  form  it  is  slightly  soluble  in  boiling  water,  but  the  solution  gela- 
tinizes on  the  addition  of  acids,  salts,  alcohol  or  sugar.  It  is  supposed  not  to 
exist  ready  formed  in  the  plants,  but  to  be  produced  by  the  action  of  alkalies  on 
pectine. 

The  alkaline  pectates,  when  dry,  form  gummy  solids,  soluble  in  water.  Alco- 
hol causes  the  solution  to  gelatinize,  and  even  an  excess  of  potassa  or  soda  has 
the  same  effect.  The  earthy  and  metallic  pectates  are  gelatinous  and  insoluble. 
When  dried,  pectine,  pectic  acid,  and  all  the  pectates,  assume  a  cellular  structure, 
so  to  speak. 

The  jelly  formed  in  current  juice  as  well  as  other  juices  by  the  addition  of 
sugar  is  pectine  or  pectic  acid.  The  boiling  of  such  juices  probably  promotes 
the  formation  of  jelly  ;  for  it  has  been  shown  that  when  the  insoluble  part  of 
unripe  currants,  after  being  washed,  is  boiled  with  water  acidulated  with  a  vege- 
table acid,  a  considerable  quantity  of  pectine  is  formed,  probably  by  a  transfor- 
mation of  the  cellular  tissue. 

The  composition  of  pectic  acid  is  not  fully  ascertained.  According  to  Reg- 
nault  it  is  C^^HgOj^,  or  C^flfi^^yUO.  According  to  Mulder,  it  is  C^flp^^. 
But  the  researches  of  Chodnew4iave  led  him  to  adopt  the  formula  C^gH^gO^, 
SHO=C^H2Q02g.  In  all  the  formulae  there  is  an  excess  of  oxygen  over 
hydrogen. 


720  WOODY  FIBRE. 

The  whole  subject  of  the  mucilaginous  compounds,  including  pectine  and 
pectic  acid,  is  still  very  obscure  and  requires  renewed  investigations. 

Apiint  is  a  substance  analogous  to  pectine,  found  in  parsley,  apium  graveolens. 
Glycyrrhizine  is  the  name  given  to  a  substance  resembling  both  sugar  and  gum, 
which  is  the  chief  ingredient  in  liquorice,  the  juice  of  the  root  of  glycyrrhiza 
glabra.  It  is  soluble  in  hot  water,  and  gelatinizes  on  cooling.  Its  taste  is  sweet 
and  also  acrid,  but  it  does  not,  like  sugar,  undergo  the  vinous  fermentation.  Its 
formula  is  said  to  be  C^gHj^O^. 

Sarcocolline  is  a  gummy  matter  found  in  the  sococolla  of  commerce,  which  is 
the  dried  juice  of  pencea  mucronata.  It  is  soluble  in  alcohol  and  water,  and  has 
a  taste  both  sweet  and  bitter.    Formula  ^sz^jgO^^'i  or  C^Hg^O^^ ! 

I  3.  Woody  Fibre. 

The  skeleton  of  plants,  after  everything  soluble  in  water,  alcohol,  ether,  dilu- 
ted acids,  and  diluted  alkalies  has  been  removed,  is  called  woody  fibre.  It  varies 
in  aspect  and  in  composition  as  obtained  from  different  plants.  That  of  box  or 
willow,  when  dried,  is  Cj^HgOg ;  that  of  oak  is  O^^U^^O^ ;  and  that  of  beech 
is  intermediate  between  these  two.  All  varieties,  however,  may  be  represented 
as  composed  of  carbon  plus  water. 

Recent  researches  have  shown  that  wood  is  composed  of  two  parts  :  1.  cellu- 
lose, which  forms  the  parietes  of  the  vegetable  cells ;  and  2.  lignine,  which  fills 
those  cells,  or  forms  an  incrustation  on  their  walls.  The  latter  dissolves  in  strong 
nitric  acid,  the  former  is  left  undissolved.  Again,  oil  of  vitriol  dissolves  cellu- 
lose without  blackening,  and  appears  to  convert  it  into  dextrine,  with  which  it 
agrees  in  composition ;  while  lignine  separated  from  cellulose  is  said  to  contain 

By  the  continued  action  of  acids  or  of  hot  alkalies,  woody  fibre  yields  a  sub- 
stance which  is  coloured  blue  by  iodine.  Linen,  cotton,  or  paper,  all  of  them 
different  forms  of  woody  fibre,  when  moistened  with  pretty  strong  sulphuric 
acid,  are  converted  apparently  first  into  dextrine,  and  afterwards  into  grape  sugar. 
When  heated  with  a  more  diluted  acid,  linen  yields  an  amylaceous  pulp 
hardly  soluble  in  water,  the  composition  of  which  is  C  H   O  . 

When  exposed  to  air  and  moisture,  wood  undergoes  eremacausis,  being  slowly 
converted  into  a  friable  mass,  which  contains  a  larger  proportion  of  carbon  than 
the  original  wood.  It  would  appear  that  the  oxygen  of  the  atmosphere  combines 
with  the  hydrogen,  and  that  carbon  and  oxygen  are  given  off  from  the  residue 
as  carbonic  acid,  CO  .  As  the  residue  is  found  still  to  consist  of  carbon  and  water, 
it  is  evident  that  for  every  equivalent  of  carbon  removed,  there  are  separated  2  eq. 
of  oxygen  and  hydrogen,  so  that  the  proportion  of  carbon  to  water  in  the  residue  is 
constantly  increasing.  Woody  fibre  ^^g^zP^  ^^^^  ^^"^  yield  first  a  residue  of 
^35^20^20 '  ^^^^  ^34^i8^i8'^33^i6^i6'  ^"^  ®®  ^"*  When  air  is  left  in  contact  with 
moist  wood,  its  oxygen  is  removed  and  replaced  by  an  equal  volume  of  carbonic 
acid.  This  is  one  chief  source  of  the  insalubrity  of  marshy  districts ;  and  the 
effect  is  seen  still  more  strikingly  in  the  case  of  houses  which  have  been  sub- 
merged in  an  inundation,  which  are  very  unwholesome  as  long  as  the  wood  is 
moist. 

The  tendency  of  wood  to  decay  is  checked  or  destroyed  by  acids  and  many 
salts,  especially  corrosive  sublimate.  Out  of  contact  of  air,  moist  wood  putre- 
fies, yielding  a  white  friable  residue,  containing  less  carbon  than  the  wood.  One 


PRODUCTS  OF  THE  DISTILLATION  OF  WOOD.  7«J1 

specimen  yielded  C^H^^O^q,  while  the  corresponding  product  of  eremacausis 
above  mentioned  is  C^.H^qO^^,  and  the  wood  O^^UJO^. 

The  composition  of  brown  coal  is  analogous  to  that  of  wood  partially  decayed, 
but  subjected  to  changes  of  the  nature  of  putrefaction,  as  well  as  to  eremacausis. 
Two  specimens  of  brown  coal  yielded  C^^H^jOjg  and  O^Jl^p^. 

All  the  above  products  of  decomposition  of  wood  may  be  derived  from  oak 
wood,  C^H^gOg^i  by  the  fixation  of  oxygen,  and  the  separation  of  water  and 
carbonic  acid. 

When  the  substance  called  mould,  which  contains  the  debris  of  decayed  vege- 
table matter,  is  boiled  with  alkalies,  the  filtered  solution  deposits,  on  the  addi- 
tion of  acids,  a  brown  precipitate,  which  has  been  called  ulmine,  humus,  humine, 
geine,  ulmic  acid,  humic  acid,  and  geic  acid.  It  is  generally  admitted  that  this 
precipitate  is  a  product  of  the  action  of  the  alkali  on  the  decayed  vegetable  mat- 
ter, and  the  name  of  humus,  humine,  or  geine  is  given  to  the  substance  which 
is  believed  to  yield  the  humic  acid.  But  this  humus  has  not  been  isolated,  and 
is  not  known. 

Mulder  examined  the  precipitates  obtained  from  a  variety  of  different  sources, 
decayed  wood,  turf,  peat,  mould,  &c.  With  one  exception,  he  found  all  to  con- 
tain nitrogen,  varying  from  2*5  to  7  per  cent.  It  is  evident  that  these  substances 
are  vegetable  matter  in  diff||:ent  stages  of  decay.  Mulder  considers  these  pre- 
cipitates as  compounds  of  water,  or  water  and  ammonia,  with  three  different 
acids:  1.  acid  of  mould  C   H  O,  •  2.  humic  acid,  C,„HO,„:  3.  ulmic  acid, 

40      12     14  '       40      13     13 

When  sugar  is  boiled  with  diluted  acids,  it  yields  brown  substances  analo- 
gous to,  if  not  identical  with,  these  acids  of  Mudler. 

It  is  important  to  observe  the  general  presence  of  ammonia  Jin  mould,  &c. 
This  ammonia  has  no  doubt  been  absorbed  from  the  air  in  great  part ;  and  this 
will  explain  Jhe  favourable  inflyence  which  these  substances  exert  on  vegetation. 
They  act  also  in  furnishing,  by  their  slow  decay,  a  continual  supply  of  carbonic 
acid. 

Orenic  Acid  and  Apocrenic  Acid  are  two  brown  extractive  matters,  analogous  to 
the  preceding,  and  derived  from  decaying  vegetable  matter,  which  are  found  in 
certain  mineral  waters.     They  both  appear  to  contain  nitrogen. 

PRODUCTS  OF  THE  DISTILLATION  OF  WOOD. 

When  wood  is  heated  in  close  vessels,  it  gives  rise  to  an  immense  variety  of 
products,  according  to  the  kind  of  wood  and  to  the  priBsence  or  absence  of  resinous 
or  oily  matters.  In  all  cases  there  are  fornted  gaseous,  liquid,  and  solid  products, 
with  a  residue  of  charcoal. 

The  gases  are  carbonic  acid,  carbonic  oxide,  defiant  gas  and  marsh  gas.  The 
liquids  are  partly  soluble  in  water,  partly  insoluble.  The  latter  constitute  the 
tar,  and  are  of  a  semifluid  consistence. 

The  substances  soluble  in  water  are,  besides  water  itself,  acetic  acid,  acetone, 
pyroxylic  spirit  (hydrate  of  oxide  of  methyle),  acetate  of  oxide  of  methyle,  lig- 
none,  xylite  and  mesite. 

The  oily  substances,  insoluble  in  water,  are  very  numerous,  including  creo- 
sote, picamar,  eupion,  capnomor,  &c.  Along  with  these  are  the  compounds 
which  at  the  ordinary  temperature  are  solid,  such  as  paraffins,  naphthaline, 
cedriret,  pittacall,  pyrene,  chrysene,  and  pyroxanthine.  The  last  mentioned, 
being  very  volatile,  chiefly  accompanies  the  acetic  or  pyroligneous  acid. 

48 


722  -      CREOSOTE. 

1.  Volatile  Products,  soluble  in  water.  T532 

Jcetic  Acid.  This  is  one  of  the  chief  products  of  the  distillation  of  woods.  Its 
mode  of  purification  and  its  properties  have  been  already  described.  As  prepared 
from  this  source,  it  is  often  called  pyroligneous  acid.  The  crude  or  impure  acid 
is  highly  antiseptic;  not  only  because  vinegar,  like  most  acids,  is  so,  but  also 
because  it  contains  much  creosote  dissolved.  Hence  it  not  only  preserves  meat, 
but  gives  to  it  a  powerful  and  agreeable  smoked  flavour. 

Pyroxylic  Spirit.  This  name  is  given  to  the  spirituous  liquid,  distilled  from 
the  crude  pyroligneous  acid  before  the  latter  is  purified.  It  is  a  mixed  fluid,  the 
chief  component  being  hydrated  oxide  of  methyle,  which  is  accompanied  by 
acetate  of  oxide  of  methyle,  unless  it  has  been  rectified  with  quicklime,  which 
decomposes  the  latter.  Lignone  is  the  name  given  to  a  volatile  liquid,  some- 
what resembling  alcohol,  observed  in  pyifoxylic  spirit  by  Gmelin  and  Liebig. 
Its  formula  is  not  ascertained,  since  it  does  not,  as  far  as  we  know,  form  definite 
compounds,  from  which  its  equivalent  might  be  deduced.  Xylite  is  another 
similar  volatile  liquid,  which,  according  to  Schweitzer,  is  ^jfijfii='^{^2^P) 
-f  (CgHgjO^)  =  2MtO  -|-  ACgO^;  that  is  a  compound  of  2  eq.  oxide  of  methyle 
and  1  eq.  of  a  sesquiacetylic  acid.  When  acted  on  by  potassa,  it  yields  a  crys- 
talline salt,  CjgHj^O^,KO,  while  hydrated  oxide  ^  methyle  separates.  An  ex- 
cess of  patassa  causes  the  formation  of  three  prodiicts :  xylitic  naphtha,  C^^Hj^ 
O^ ;  xylitic  oil,  ^J^fi  »  ^^^  xylitic  resin,  CgHgO.  When  distilled  with  sul- 
phuric acid,  xylite,  if  moist,  yields  a  new  compcxind,  mesitene,  a  volatile  liquid, 
CgHgO^.  If  anhydrous,  it  yields,  besides,  another  compound,  methol,  a  less 
volatile  liquid,  which  appears  to  be  a  carbo-hydrogen,  C^H^;  isomeric  with  ace- 
tyle,  if  it  be  not  that  radical.  Mesiie  is  another  volatile  ethereal  liquid  found  in 
pyroxylic  spirit,  which,  according  to  Schweitzer,  is  Cflfi^;  isomeric  with 
acetone.  He  considers  it  as  composed  pf  oxide  <Df  methyle  and  oaide  of  acetyle, 
Cflp  +  C4H3O  =  MtO  +  AcO.  The  liquid  called  mesite  by  Reichenbach 
would  appear  to  be  stcetate  of  oxide  of  methyle,  MtO  -f-  AcO^,  mixed  with  a 
more  highly  carbonized  body,  apparently  composed  of  ^^g^J^i^'  This  latter  is 
resolved  by  the  action  of  lime  into  3  eq.  acetic  acid  (Cj^HgOg),  and  a  volatile 
liquid,  Oj^HjgO^.  Along  with  the  above,  another  liquid  appears  to  occur  in  the 
mesite  of  Reichenbach,  the  composition  of  which  is  C^jH^^Oj^.  In  addition  to 
all  the  liquids  above  mentioned,  as  occurring  in  pyroxylic  spirit,  acetone  is  fre- 
quently found. 

The  very  great  similarity  in  properties  of  so  many  substances,  namely,  hy- 
drated oxide  of  methyle,  acetate  of  oxide  of  methyle,  lignone,  xylite,  mesite, 
and  acetone,  is  worthy  of  notice.  Most  of  these  liquids  have  nearly  the  same 
density  and  boiling  point;  they  are  all  inflammable,  and  their  solubility  in  water 
is  nearly  equal.  Hence  they  all  occur  mixed,  and  are  with  great  difliculty  sepa- 
rated, so  as  to  obtain  each  in  a  state  of  purity ;  indeed,  in  most  of  them  we  can- 
not be  sure  that  this  has  yet  been  accomplished.  It  is  highly  probable,  that, 
like  the  two  first,  all  the  rest  will  be  found  to  be  compounds  of  methyle.  Our 
knowledge  on  the  subject  is  still  very  limited. 

The  purified  pyroxylic  spirit,  or  hydrated  oxide  of  methyle,  has  been  already 
fully  described,  along  with  its  chief  derivatives. 

2.  Volatile  Oily  Products,  insoluble  or  sparingly  soluble  in  Water. 

a.  Creosote  (from  «p«af,  flesh,  and  ffwC«,  I  preserve).    This  is  one  of  the  most 


CREOSOTE.  723 

important  products  of  the  distillation  of  wood.  It  is  found,  partly  dissolved,  in 
the  pyroligneous  acid,  partly  along  with  other  oils,  in  the  tar.  "When  the  crude 
pyroligneous  acid  is  saturated  at  167°  with  dry  carbonate  of  soda,  an  oil  sepa- 
rates, which  contains  much  creosote.  In  like  manner,  by  the  rectification  of  tar,' 
an  oil  of  tar  is  obtained,  the  heavier  portions  of  which  contain  a  good  deal  of 
creosote.  These  oils  are  neutralized  with  carbonate  of  potassa,  and  the  fluid 
thus  deprived  of  acid  is  distilled  with  water.  The  distilled  oil  is  acted  on  by 
dilute  phosphoric  acid  to  remove  ammonia  and,  probably,  traces  of  oily  bases, 
again  distilled,  and  dis^ved  in  aqua  potassae,  sp.  gr.  1*12,  which  dissolves  the 
creosote,  along  with  portions  of  other  oils,  but  separates  a  good  deal  of  eupion, 
&c.  The  alkaline  solution  is  now  supersaturated  with  dilute  sulphuric  acid, 
(after  having  been  boiled  in  the  air  till  it  has  become  dark  brown,)  j^hen  the 
impure  creosote  separates.  It  is  again  rectified,  and  the  treatment  with  potassa, 
boiling,  addition  of  sulphuric  acid,  and  rectification  repearted  till  the  rectified  oil 
dissolves  entirely  in  weak  potassa,  and  this  alkaline  solution  on  being  boiled  ac- 
quires only  a  slight  tinge  of  colour.  It  is  then  finally  rectified,  and  is  pure  when 
it  continues  colourless  on  being  kept.  The  tar  of  peat  appears  to  be  very  rich 
in  creosote,  and  it  also  occurs  in  coal  tar.  Good  tar,  from  beech  wood,  is  said 
to  contain  from  20  to  25  per  cent. 

Pure  creosote  is  a  colourless  transparent  liquid,  of  a  high  refractive  and  dis- 
persive power,  of  a  tolerably  fluid  but  oily  consistence.  Its  sp.  gr.  is  1*037, 
according  to  Reichenbach,  its  discoverer,  and  other  chemists ;  but  there  is  some 
discrepancy  on  this  point.  Dr.  Christison  having  always  found  it  as  high  as 
1*060  and  upwards.  Its  boiling  point  is  397°.  It  gradually  becomes  coloured 
brown  when  kept,  unless  absolutely  pure.  Creosote  has  a  very  strong,  peculiar, 
persistent  smell  of  smoke,  analogous  also  to  that  of  castoreum,  not  fetid,  but 
unpleasant  when  concentrated.  Its  taste  is  burning,  with  a  sweetish  aftertaste. 
It  disorganizes  the  skin,  causing  a  white  spot,  where  the  cuticle  soon  peels  off, 
without  inflammation.  When  applied  to  the  interior  of  the  mouth  and  to  the 
tongue  it  smarts  strongly,  whitening  and  disorganizing  the  cuticle. 

Internally  it  is  a  powerful  poison,  but  in  a  small  dose  may  be  employed 
advantageously  in  some  cases  of  vomiting  and  disease  of  the  mucous  membrane. 
It  is  given  much  diluted  with  water.  Externally,  it  may  be  employed,  either  in 
the  form  of  aqueous  solution,  of  ointment,  or  pure,  as  a  styptic,  and  is  a  valuable 
application  to  indolent  ulcers,  and  to  many  chronic  cutaneous  affections.  Pure 
creosote,  applied  to  the  hollow  of  a  decayed  tooth,  so  as  to  touch  the  expo^d 
nerve,  instaritly  relieves,  in  many  cases,  the  most  violent  toothache.  It  acts 
apparently  by  coagulating  the  siecretions,  and  thus  forming  a  covering  for  the 
nerve. 

Creosote  dissolves  in  about  80  or  100  parts  of  water,  and  is  exceedingly 
soluble  in  alcohol  and  in  acetic  acid.  These  solutions  have  the  smell,  taste,  and 
antiseptic  power  of  the  creosote. 

Creosote  possesses  a  singular  antiseptic  power.  Flesh  of  all  kinds,  if  steeped 
for  a  few  hours  in  a  weak  solution  of  creosote,  becomes  unsusceptible  of  putre- 
faction ;  and  the  same  effect  is  produced  when  the  flesh  is  exposed  to  the  vapour 
of  creosote.  This  is  the  reason  why  the  smoke  of  wood  possesses  antiseptic 
properties :  smoked  meat  or  fish  is  merely  meat  or  fish  which  has  absorbed  the 
vapour  of  creosote  from  the  smoke  in  which  it  has  been  suspended.  The  creo- 
sote appears  to  act  on  flesh,  &c.  in  virtue  of  its  remarkable  power  of  coagulating 
albumen,  which  also  accounts  for  its  styptic  action.     Tongues  and  hams  may 


724  CREOSOTE.    PICAMAR. 

be  smoked  and  effectually  cured  by  immersing  them  for  24  hours  in  a  mixture  of 
1  part  of  pure  creosote  and  100  of  water  or  brine;  and  when  thus  prepared, 
they  have  the  delicate  smoked  flavour  observed  in  reindeer  tongues,  as  usually 
cured  by  smoking. 

Owing  to  the  difficulty  of* obtaining  creosote  ^uite  pure,  its  composition 
is  hardly  ascertained  with  certainty.  According  to  Deville,  whose  researches 
are  the  most  recent,  it  may  be  regarded  as  the  alcohol,  so  to  speak,  of  the  series 
of  benzoyle.  His  analyses  lead  to  the  formula  ^14^^  or  C  HO  HO;  but 
I  cannot  ascertain  whether  this  is  the  formula  he  adopib. 

It  is  particularly  to  be  noticed,  that  there  is  a  very  great  resemblance  between 
creosote  and  carbolic  acid  (or  hydrate  of'-phenyle,  C^^H^O,  HO),  a  substance 
obtaine^from  coal  tar,  and  which  will  soon  be  described.  So  great  is  this  re- 
semblance, that  I  am  almost  inclined  to  consider  creosote  as  a  somewhat  pure 
carbolic  acid.  The  taste,  smell,  density,  (according  to  some),  boiling  point, 
solubility  in  water,  &c.,  poisonous  and  antiseptic  action,  of  these  two  bodies, 
are  the  same.  Both  combine  with  alkalies,  forming  cry  stall  izable  compounds, 
and,  what  is  more  important,  their  composition  in  100  parts  is  almost  identical. 
The  chief  differences  seem  to  be,  that  carbolic  acid  may  be  obtained  in  crystals, 
which,  however,  on  contact  with  the  air  instantly  liquefy  and  retain  the  liquid 
form,  without  any  appreciable  change  of  composition,  apparently  from  the  effect 
of  a  trace  of  moisture.  Also,  the  salts  of  carbolic  acid  with  bases  are  more 
easily  formed  and  more  permanent  than  those  of  creosote.  A  splinter  or  shaving 
of  fir  wood,  dipped  into  carbolic  acid  and  then  into  nitric  or  muriatic  acid,  be- 
comes first  blue  and  then  brown;  which  does  not  appear  to  be  the  case  with 
creosote.  But  Laurent  has  recently  shown,  that  creosote,  when  acted  on  by  a 
mixture  of  hydrochloric  acid  and  chlorate  of  potash,  yields  abundance  of  chlo- 
ranile,  a  character  in  which  it  agrees  with  carbolic  acid.  Both  substances  also 
yield  nitropicric  acid  when  acted  on  by  nitric  acid,  although  in  the  case  of  creo- 
sote this  acid  is  accompanied  by  others  not  yet  examined.  These  results  I  have 
myself  also  obtained ;  and  it  would  appear,  that  if  creosote  be  not  carbolic  acid, 
contaminated  with  some  foreign  matter,  these  two  bodies  are  at  least  closely 
connected,  and  belong  apparently  to  the  same  series,  which  is  either  that  of 
benzoyle  or  that  of  phenyle.  It  is  not  improbable  that  creosote  may  be  a  defi- 
nite compound  of  carbolic  acid  with  some  substance  of  closely  allied  composi- 
tion, but  of  basic  properties. 

Creosote  dissolves  many  organic  substances,  such  as  indigo,  camphor,  fats, 
essential  oils,  and  resins,  and  undergoes  numerous  changes  by  the  action  of 
acids,  alkalies,  and  other  reagents,  such  as  chlorine,  potassium  and  others.  With 
oil  of  vitriol  it  is  coloured  purple,  and  appears  to  form  a  coupled  acid.  None  of 
these  reactions  or  products  have  been  properly  investigated,  and  we  shall,  there- 
fore, not  confuse  the  reader  by  a  description  of  them,  more  especially  as  the  com- 
position of  creosote  itself  is  doubtful. 

b.  Picamar  is  the  name  given  by  Reichenbach  to  another  oil  discovered  by 
him  along  with  creosote  in  the  heavy  oil  of  tar.  It  is  purified  by  a  tedious  pro- 
cess, with  the  aid  of  potassa,  with  which  it  forms  a  crystalline  compound.  "When 
pure,  it  is  a  colourless  oil,  of  sp.  gr.  TIO,  of  a  burning  and  very  bitter  taste 
(hence  its  name  from  pix  and  amarus),  and  a  slight  smell.  It  boils  at  about  510°. 
It  combines  with  alkalies,  forming  crystallizable  salts,  and  may  therefore  be 
viewed  as  an  acid  in  some  sense,  although  it  is  quite  neutral  to  test  paper.  Its 
composition  is  unknown. 


EUPION.    PARAFFINE.  725 

c.  Capnomor  (from  xo.Hvo^,  smoke,  and  lUoTpa,  part),  is  another  oil,  discovered 
by  Reichenbach,  in  the  heavy  oil  of  tar,  along  with  creosote  and  picamar.  When 
the  creosote  is  purified  by  solution  in  weak  potassa,  the  oil  left  undissolved  con- 
tains a  good  deal  of  capnomor,  which  is  purified  by  a  tedious  process.  It  is  a 
limpid,  colourless  oil,  of  a  high  refracting  power,  with  an  aromatic  odour  of 
ginger,  and  a  somewhat  styptic  after-taste.  Its  sp.  gr.  is  0*9775 ;  it  is  quite 
neutral,  and  boils  at  365°.  With  sulphuric  acid  it  is  coloured  red,  and  yields  a 
coupled  acid.  Nitric  acid  converts  it  into  oxalic  acid,  nitropicric  acid,  and 
another  crystalline  substance  not  yet  examined. 

d,  Eupion  (from  fv,  fine,  and  rtLov^  oil  or  fat),  is  a  fourth  oily  liquid,  discovered 
by  Reichenbach  in  oil  of  tar.  Being  more  volatile  than  the  rest,  it  is  purified 
chiefly  by  rectification.  When  pure  it  is  colourless,  very  fluid,  not  greasy  to  the 
feel,  but  less  soft  than  water,  tasteless,  and  of  a  somewhat  agreeable  odour,  like 
that  of  some  flowers,  such  as  narcissus.  Its  sp.  gr.  is  0*740 ;  and  Reichenbach 
states  that  he  has  even  obtained  it  so  low  as  0*633,  being  the  lightest  known 
liquid.  It  is  volatile,  boiling  at  117°  or  lower.  It  is  in  the  highest  degree 
indifferent,  resisting  the  action  of  the  strongest  acids  and  alkalies.  In  fact,  as 
it  is  prepared  from  the  oil  of  tar  by  rectification,  and  the  action  of  potassa,  sul- 
phuric, and  nitric  acids  alternately  on  the  rectified  oil,  it  is  evident  that  it  must 
resist  these  agents.  There  is  good  reason  to  believe  that  several,  even  many 
different  liquids  have  been  described  under  this  name,  and  that  most  of  these  are 
not  ready  formed  in  the  tar,  but  products  of  the  action  of  acids,  &c.,  on  the  oil 
of  tar.  Reichenbach,  however,  by  simple  rectifications  of  the  oil  obtained  by 
distilling  rape  oil,  obtained  a  liquid  having  the  characters  of  eupion.  So  much  is 
certain,  that  similar  liquids  are  formed  by  the  action  of  oil  of  vitriol  on  oil  of  tar. 
The  whole  of  the  liquids  called  eupion  are  carbo-hydrogens,  and  their  formula 
is  either  CH,  or  some  multiple  of  this,  or  else  one  nearly  approaching  to  such  a 
multiple,  as  C^Hg,  &c.  It  is  very  remarkable  that  some  of  them  are  very  vola- 
tile, while  others,  apparently  of  the  same  composition,  require  a  strong  heat, 
from  400°  to  500°  for  example,  to  boil  them. 

The  purest  varieties  of  eupion  burn  with  the  aid  of  a  wick,  and  yield  a  very 
brilliant  luminous  white  flame,  free  from  smoke,  and  may  hereafter  be  turned  to 
account. 

3.  Solid  Products  of  the  Distillation  of  Wood. 

a.  Paraffine,  This  name  is  given  (from  parum  and  affinis,  because  its  aflinities 
are  feeble)  to  a  white  solid  volatile  substance,  very  similar  to  wax,  discovered  by 
Reichenbach  in  tar.  It  occurs  in  the  last  portions  of  the  rectification  of  the  tar, 
which  are  semisolid.  It  is  squeezed  out,  and  purified  by  one  or  two  crystalliza- 
tions in  ether,  which  dissolves  it  when  boiling,  and  deposits  it  on  cooling  in 
beautiful  silvery  scales.  These,  when  melted,  assume,  on  cooling,  the  aspect  of 
pure  white  wax. 

Paraffine  exists  in  large  quantity  in  the  Rangoon  petroleum,  and  some  other 
bituminous  mineral  products.  It  is  formed  in  large  quantity  in  the  distillation 
of  wax.  It  melts  at  110°,  and  distils  unchanged  at  a  high  temperature.  Its  sp. 
gr.  is  0*870.  It  burns,  in  a  wick,  with  a  beautiful  clear  white  light,  free  from 
smoke,  fully  equal  to  that  of  the  finest  wax,  if  not  superior  to  it.  Like  eupion, 
it  is  highly  indifferent,  and  it  is,  like  eupion,  a  carbo-hydrogen,  containing  either 
CH,  or  some  multiple  of  it,  or  a  near  approach  to  such  a  multiple.    According 


726  PYROXANTHINE. 

to  Lewy,  it  is  C^qH^^-  It  is  acted  on  by  chlorine  with  the  aid  of  heat,  but  the 
reaction  is  not  yet  studied.  The  strongest  acids  and  alkalies  do  not  act  on  it, 
even  with  the  aid  of  heat,  if  we  except  faming  sulphuric  acid. 

b.  Cedriret,  This  is  another  compound  discovered  by  Reichenbach  in  oil  of 
tar.  When  impure  creosote  is  dissolved  in  potassa,  and  acetic  acid  added,  an 
oil  separates,  which  contains  the  creosote  and  other  oils ;  but  a  certain  quantity 
of  oily  matter  remains  dissolved  in  the  acetate  of  potassa.  This  is  distilled,  until 
what  passes  over  causes  a  red  precipitate  in  a  solution  of  sulphate  of  iron.     It  is 

>then  collected  separately,  being  pure  cedriret.  It  is  a  volatile  solid,  which  crys- 
tallizes in  a  solution  of  sulphate  of  iron,  forming  a  net-work  of  orange-red  crys- 
tals, which  dissolve  in  oil  of  vitriol  with  a  blue  colour.  Much  of  the  colour  of 
oil  of  tar  is  probably  owing  to  this  substance. 

c.  Pittacal.  This  is  still  another  compound  obtained  by  Reichenbach  from 
the  heavy  oil  of  tar.  When  the  heaviest  portions  are  nearly  neutralized  by  po- 
tassa, the  addition  of  barytic  water  gives  rise  to  a  deep  blue  colour.  This  be- 
longs to  pittacal,  but  the  mode  of  its  purification  is  not  published.  When  pure, 
it  is  a  solid,  like  indigo,  of  a  very  fine  deep-blue  colour,  exhibiting  on  the  po- 
lished surface  the  aspect  of  gold.  It  admits  of  being  fixed  on  cloth,  and  would 
make  a  valuable  dye-stuff.  Its  composition  is  unknown  ;  but  it  appears  to  con- 
tain nitrogen.  Its  name  is  derived  from  ytttfa,  pitch,  and  xaxxoj,  beautiful.  It 
is  a  compound  of  very  great  interest,  although  most  probably  a  product  of  de- 
composition of  the  oil  of  tar,  and  not  ready  formed  in  it.  It  is  very  desirable  that 
it  should  be  further  investigated. 

d.  PyroxantJdne.  This  is  a  volatile  crystalline  solid,  first  observed  by  Scan- 
Ian  in  the  crude  pyroligneous  spirit.  When  this  is  rectified  with  lime,  the  lime 
becomes  dark  brown ;  and  when  this  coloured  mass  is  acted  on  by  hydrochloric 
acid,  there  is  left  undissolved  a  dark-brown  matter,  which  is  a  mixture  of  pyro- 
xanthine  and  a  resinous  matter.  The  mass  is  boiled  .with  hot  alcohol,  which, 
on  cooling,  deposits  the  pyroxanthine  in  crystals,  which  are  purified  by  recrys- 
tallization.  They  are  of  an  intense  yellow  colour,  fusible,  and  volatile  in  a  cur- 
rent of  air,  or  with  the  vapour  of  other  substances,  but  partly  decomposed  when 
heated  alone  in  a  dry  tube.  Pyroxanthine  dissolves  in  sulphuric  acid  with  a 
deep  bluish-red,  and  in  strong  hydrochloric  acid  with  a  splendid  purple  colour, 
which  soon  passes  to  dark  brown.  I  found  its  composition  to  be  very  nearly 
C  H  O  ;  but  as  it  forms  no  definite  compounds,  I  could  not  control  the  analysis. 

Such  are  the  chief  products  of  the  distillation  of  wood,  as  far  as  they  are  yet 
known.  Their  importance  is  very  great,  and  will  be  still  greater  when  they 
shall  have  been  better  studied,  as  most  of  them  will  admit  of  useful  applications. 
But  no  doubt  can  be  entertained  that  the  above  numerous  list  is  far  from  being 
complete,  and  that  more  compounds  remain  to  be  discovered  in  tar.  Indeed, 
there  is  even  now  good  reason  to  believe  that  several  or  most  of  the  substances 
characterizing  coal  tar  occur  also,  although  in  smaller  quantity,  in  wood  tar. 
Such  substances  are  naphthaline,  anthracene,  and  others.  It  is  to  be  borne  in 
mind  that  the  composition  of  wood  tar  varies,  according  to  the  kind  of  wood, 
the  presence  or  absence  of  oily  or  resinous  substances,  the  comparative  abun- 
dance of  nitrogenized  matter,  and  finally  the  temperature  at  which  the  distilla- 
tion is  carried  on. 

Wood  coal,  brown  coal,  or  lignite  yields,  when  distilled,  an  oil  of  the  consist- 
ence of  butter,  in  which  creosote,  paraffine,  and  probably  eupion,  are  found,  along 
with  other  products  not  yet  examined. 


CARBOLIC  ACID.  727 

PRODUCTS  OF  THE  DISTILLATION  OF  COAL. 

Coal  differs  from  wood  in  several  points,  although  it  is  unquestionably  derived 
from  the  decay,  under  pressure,  of  woody  fibre  and  the  other  substances  which 
made  up  the  mass  of  the  early  vegetation  of  which  our  coal-beds  are  the  remains. 
Coal  contains  much  less  water,  and  a  ^uch  larger  per  centage  both  of  carbon 
and  nitrogen,  than  wood.  Hence  it  is  decomposed  at  a  higher  temperature,  and 
yields  much  ammonia,  cyanogen,  and  other  nitrogenized  products.  We  shall 
not  here  dwell  on  ammonia  and  cyanogen,  further  than  to  mention  that  out  of 
the  aqueous  products  of  the  coal  gas-works  large  quantities  of  ammonia  are  ob- 
tained ;  and  that  so  much  hydrocyanic  acid  is  also  present,  that  a  patent  was 
taken  out  some  years  since  for  the  preparation  of  Prussian  blue  from  the  gas 
liquor.     We  proceed  to  describe  the  chief  ingredients  of  coal  tar. 

a.  Carbolic  acid.  Syn.  Hydrate  ofpheni/k.  Cj^H^OjHO.  This  remarkable 
acid  is  found  in  that  portion  of  the  oil  of  coal  of  tar  which  boils  between  300° 
and  400°.  This  is  agitated  with  twice  its  volume  of  potassa  ley,  and  the  aque- 
ous solution,  on  the  addition  of  an  acid,  yields  hydrated  carbolic  acid  (impure) 
as  a  heavy  oil.    It  is  purified  by  rectification  with  a  very  little  solid  potassa. 

When  pure,  carbolic  acid  generally  appears  as  an  oily  liquid,  colourless,  and 
of  a  high  refracting  power,  neutral  to  test  paper,  of  sp.  gr.  1*062  to  1"065.  It 
has  a  burning  taste,  and  the  odour  of  creosote,  to  which  it  has  a  very  great  re- 
semblance. In  certain  circumstances  it  forms  long  needle-shaped  crystals,  which 
very  readily  lose  the  solid  form  by  exposure  to  the  atmosphere,  and  which  also 
liquefy  in  sealed  tubes  without  any  obvious  cause.  The  crystals  melt  at  94°, 
and  boil  at  368°.  The  extraordinary  resemblance  between  carbolic  acid  and 
creosote  has  been  noticed  above ;  and  there  can  be  little  doubt  that,  if  not  essen- 
tially the  same,  they  ar^  closely  connected  and  belong  to  the  same  series,  or 
contain  the  same  radical, 

A  splinter  of  pine-wood,  if  dipped,  first  in  carbolic  acid,  and  then  in  mode- 
rately strong  nitric  acid,  becomes  of  a  deep-blue,  which  soon  passes  into  brown. 

According  to  Laurent,  carbolic  acid  is  the  hydrated  oxide  of  phenyle,  C^^H^, 
and  its  formula  is  (Cj2H^)0,H0.  This  radical,  phenyle,  gives  rise  to  a  series 
of  derived  compounds  which  may  be  represented  as  follows : 

Hydrate  of  Phenyle,  or  Carbolic  Acid         .        .        C,2        Hg,©        -J-HO 
Sulphocarbolic  Acid  (Sulphophenic  Acid)    .        .        Cij        Hg        O,    HO+2SO3 

Chlorophenesic  Acid Cjg      ^pj'         ^  0,H0 

Chlorophenisic  Acid,  identical  with  the)  ^ 

Chlojjioptenic  Acid  of  Erdmann        5  ^ 

BromogPenisic  Acid  C^j 

Nitrophenesic  Acid  C12 

Nitrophenisic  Acid,  identical  with  Nitro-  >  ^ 

picic  Acid  >  ^2 

Thus  the  carbolic  acid  is  connected  with  the  derivatives  of  indigo,  of  salicyle, 
and  other  bodies,  which  yield  nitropicric  acid.  This  connection  is  also  shown 
in  the  formation  of  chloranile,  from  carbolic  acid,  by  the  action  of  chlorate  of 
potassa  and  hydrochloric  acid.  (See  under  Indigo,  the  formation  of  chloranile 
from  aniline).  It  is  also  shown,  by  the  fact,  that  salicylic  acid,  C^^H^Og,  when 
distilled  alone,  with  lime,  or  with  pounded  glass,  is  resolved  into  carbonic  acid, 


738^  KYANOL. 

SCO^,  and  carbolic  acid,  ^^fifi^.  The  action  of  carbolic  acid,  on  organic  com- 
pounds, is  the  same  as  that  of  creosote.  Thus  it  dissolves  indigo,  &c.  and 
coagulates  albumen,  preventing  the  putrefaction  of  animal  substances. 

With  bases,  it  forms  salts,  some  of  which  crystallize,  but  which  retain  an 
alkaline  reaction.  With  oil  of  vitriol,  it  yields  a  coupled  acid,  sulpho^carbolic, 
or  sulphophenic  acid,  which  forms  a  solifble  salt  with  baryta. 

The  formulae  in  the  above  table  illustrate  the  formation,  by  substitution,  of  the 
chlorophenesic  and  chlorophenisic,  of  the  nitrophenesic  and  nitrophenisic  acids. 
It  is  not  necessary  here  to  do  more  than  point  out  their  relation  to  carbolic  acid 
and  phenyle.    The  chloiobenzide  of  Mitscherlich,  Cj^HgCl    is,  according  to 

Laurent,  hydrochlorate  of  chlorophenise,  SHCl-f-Cj^  l  r\  *     *^^^®  ^^^^  body, 

chlorophenise,  which  is  obtained  by  the  action  of  potassa  on  chlorobenzide, 
would  appear  to  be  derived  by  substitution,  not  from  phenyle  C  H^,  but  from 
benzole  Cj^H^;  although  it  may  be  derived   also  from  oxide  of  phenyle  C 

^  p.*  ;  as  may  benzole  itself.    Chlorophenise  cannot  be  obtained  directly  from 

hydrate  of  phenyle,  or  its  derivatives;  but,  on  the  other  hand,  the  series  of  ben- 
zole has  an  obvious  relation  to  that  of  phenyle.  In  fact,  Laurent  considers 
benzole  as  in  some  measure  the  fundamental  compound,  or  nucleus,  and  calls  it 
phene  =Cj3Hg. 

It  has  already  been  stated  that  nitrophenisic  acid  is  identical  with  nitropicric 
acid.  Nitrophenesic  acid  is  somewhat  similar,  and  forms  salts  which  crystal- 
lize with  facility,  and  detonate  when  heated.  The  nitrophenesate  of  baryta  is 
a  beautiful  salt,  .like  bichromate  of  potassa. 

6.  Volatile  Bases  of  Coal  Tar. 

Besides  carbolic  acid,  Runge  found  in  coal-tar  two  other  acids,  rosolic  and 
hrunoUc  acids  (of  which  little  is  known),  and  three  basic  volatile  oils,  kyanol, 
leukol,  and  pyrrol.  The  last  has  been  little  examined  ;  but  the  recent  researches 
of  Hoffmann  have  confirmed  Runge's  statements  as  to  the  first  two,  which  have 
also  been  identified  with  bases  produced  from  different  quarters.  They  have, 
therefore,  acquired  a  very  high  degree  of  interest. 

1.  Kyanoli  C^^H^N.  Syn.  Jniline,  Crystalline,  Benzidam,  This  veryjemark- 
able  base  has  already  been  described  as  a  product  of  the  distillation  of  indigo 
with  potassa,  and  of  anthranilic  acid  per  5«,  under  the  name  now  generally 
adopted,  of  aniline.  It  has  also  been  shown  to  be  identical  with  th||Crystalline 
of  Unverdorben,  an  oily  base,  extracted  from  animal  oil  of  tar;  and^mth  benzi- 
dam,  an  oil  formed  by  the  action  of  sulphuretted  hydrogen,  or  sulphuret  of  am- 
monium on  nitrobenzide.     Hoffmann  has  traced  the  production  of  aniline  in 

C  H 

various  cases,  as  when  protonitrobenzoene,  C^^  <  ,^J^     is   heated   with    lime. 

The  reaction  is  as  follows:  2  CaO  +  Cj^H^NO^=2(CaO,C02)  +  Cj^H^N.    In 

fact  protonitrobenzoene  being  isomeric  with  anthranilic  acid,  it  is  not  wonderful 
that  both  of  them  should  be  resolved  into  aniline  and  carbonic  acid. 

That  there  is  a  relation  between  aniline  and  carbolic  acid  appears  from  their 
formulae;  for  aniline  is  the  amidide  of  carbolic  acid,  oi'  phenamide,  being  thus 
deduced  from  carbolate  of  ammonia.  Cj2W^O,NH3=HO  +  Cj2H^,NOj^.  The 
relation  may  be  better  exhibited  thus  :— 


LEUKOL,  OR  QUINOLEINE.  729 

Carbolic  Acid  (anhydrous),  or  Oxide  of  Phenyle  .  .   rsCjjH.O 

Aniline,  or  phenylamide     .....  ssCijHgAd 

As  another  experimental  proof  of  this  relation  may  be  mentioned  that  salicy- 
lamide,  Cj^H^0^,NH2=Cj^H^N0^,  which  has  the  same  composition  as  protoni- 
trobenzoene  and  anthranilic  acid,  both  of  which  yield  aniline,  when  heated  with 
lime  gives  not  aniline  but  carbolic  acid,  ammonia,  and  probably  a  carbo-hydrogen. 

Aniline  is  recognized  by  striking  a  deep  violet-blue  colour  with  chloride  of 
lime  (bleaching  liquor),  hence  the  name  Jtyanol,  It  combines  with  acids,  form- 
ing salts  which  crystallize  with  the  utmost  facility,  hence  the  name  crystalline. 
It  is  easily  extracted  from  coal-tar  oil,  by  agitating  with  hydrochloric  acid,  mix- 
ing the  acid  solution  with  an  excess  of  milk  of  lime,  and  rectifying  the  basic  oil 
which  separates,  and  which  is  a  mixture  of  aniline  and  leukol.  The  former  is 
the  more  volatile,  and  when  the  distilled  liquid  ceases  to  be  coloured  blue  by 
chloride  of  lime,  the  leukol  is  coming  over  nearly  pure,  the  aniline  being  found 
in  the  first  distilled  portions. 

Aniline,  when  acted  on  by  chlorine,  yields  trichloraniline  (chlorindatmit  of 

Erdmann)  C^^  ^  nf  c  ^  along  with  chlorophenusic  acid  C^  j  ^  0,H0.  With 
chlorate  of  potassa,  and  hydrochloric  acid,  it  yields  chloranile,  C^^  \  pj*  .     With 

bromine  it  yields  tribromaniline  C^  ^  t*'*  r    N   (bromaniloide    of  Fritzche). 

Strong  nitric  acid  first  colours  aniline  blue,  and  then  yellow,  with  a  violent  re- 
action, the  result  of  which  is  the  conversion  of  aniline  into  nitropicric  acid. 

2.  Leukolf  or  Quinoleine?  Cj^HgN  (Hoffmann),  or  C^gH^N  (Laurent,  Ger- 
hardt),  is  prepared  as  above.  Its  properties  have  been  formerly  mentioned,  al- 
though under  a  different  name;  for  the  most  recent  researches  tend  to  the  con- 
clusion, that  it  is  identical  with  quinoleine,  the  oily  base  obtained  by  the  action 
of  heat,  aided  by  potassa,  on  cinchonine,  quinine,  strychnine,  and  probably  other 
bases.  This  identification  is  very  curious,  like  that  of  aniline  and  kyanol,  and 
the  occurrence  of  quinoleine  in  coal-tar  is  a  very  remarkable  fact.  The  formula 
here  given  for  quinoleine  differs  from  that  given  under  that  head,  which  is  C^g 
H  N.  As,  however,  there  may  still  be  some  doubt  as  to  the  identity  of  leukol 
and  quinoleine,  I  shall  not  alter  the  formula  first  given  for  quinoleine,  until  fur- 
ther experiments  have  decided  the  exact  composition  of  that  base,  and  have  also 
fixed  that  of  leukol. 

Of  pyrrol,  and  oi  rosolic  and  brunolic  acids,  so  little  is  known  that  we  need  not 
dwell  on  them. 

c.  Volatile  Carbo-hydrogens  in  Coal  Tar. 

a.  Naphthaline,  C^^H^,  or  C^Hg.  This  remarkable  compound  occurs  in  all 
kinds  of  tar,  but  most  abundantly  in  coal-tar,  as  being  formed  at  a  very  high 
temperature.  It  is  formed  in  additional  quantity  when  any  of  the  elements  of  oil 
of  tar,  such  as  creosote,  carbolic  acid,  &c.,  or  even  alcohol  and  ether,  are  passed 
through  tubes  heated  to  a  strong  red  heat.  It  is  easily  obtained  by  re-distilling 
coal-tar,  when  the  latter  portions  are  so  full  of  naphthaline  as  to  be  semisolid. 
It  is  well  squeezed  out,  and  purified  by  sublimation  and  crystallization  in  hot 
alcohol.  Or  the  oil  of  coal-tar  is  saturated  with  chlorine  gas,  which,  by  destroy- 
ing some  of  the  oils,  allows  the  naphthaline  to  crystallize. 


730  ACTION  OF  CHLORINE  AND 

Pure  naphthaline  is  colourless  and  volatile,  and  forms  large  tabular  transparent 
crystals,  of  a  very  peculiar  smell,  and  an  acrid  aromatic  taste.  It  boils  at  414°, 
but  distils  easily  with  the  vapours  of  water,  and  is  dissipated,  like  camphor,  if 
left  exposed  at  the  ordinary  temperature. 

It  is  acted  on  by  chlorine  and  bromine,  which  combine  with  it  in  the  first  in- 
stance, and  also  give  rise  to  a  large  number  of  compounds  formed  by  substitu- 
tion; and  by  sulphuric  and  nitric  acids,  each  of  which  produces  a  number  of  new 
compounds  with  it.  These  changes  have  been  studied  with  singular  persever- 
ance and  remarkable  sagacity,  by  Laurent,  more  especially  the  action  of  chlorine, 
bromine,  and  nitric  acid.  His  researches  have  been  attended  with  unusual  suc- 
cess, and  he  may  be  said  to  have  originated  and  established,  by  these  researches, 
the  now  received  doctrine  of  substitutions.  I  cannot  hope  to  give  even  an  accu- 
rate outline  of  all  that  Laurent  has  done  in  this  department,  because  I  have  no- 
where seen  a  complete  account  of  these  curious  results  as  they  now  stand ;  but 
until  the  author  himself  publish  a  complete  account  of  his  researches  on  naph- 
thaline, I  shall  place  before  the  reader  such  a  general  account  of  them  as  shall 
show  the  great  importance  of  the  subject,  and  some  of  the  interesting  facts  al- 
ready ascertained. 

1.  Action  of  Chlorine  and  Bromine  on  Naphthaline. 

(It  is  necessary  here  to  explain  the  principle  of  nomenclature,  provisionally 
adopted  by  Laurent,  especially  for  cases  like  this  of  substitutions,  where  the 
ordinary  nomenclature  is  entirely  inapplicable.  The  nomenclature  of  Laurent 
may  be  thought,  by  some,  uncouth  :  but  it  is  simple,  systematic,  and  consistent 
with  itself.  Beginning  with  naphthaline,  he  gives  to  the'compounds  formed  by 
the  successive  substitution  of  chlorine  for  hydrogen,  names  beginning  with  chlo, 
and  ending  with  a  syllable  in  which  the  vowels  a,  e,  i,  o,  and  u,  are  employed 
to  designate  the  replacement  of  1,  2,  3,  4,  and  5  eq.  of  hydrogen.  Thus,  if,  in 
naphthaline,  C^Hg,  1  eq.  of  hydrogen  is  replaced  by  chlorine,  we  have  the  com- 

C  H  C  H 

pound   C^  ^     ^,    This  is  called  chlonaph/asc.     The  compound     C^  j  ^6  is 

C  H 

chlona  ph/e5c  ;    C^    ^  p,*  is  chlonaph/we,  &c.    The  corresponding  compounds 

'         3 

of  bromine  are  bronaph/ase,  bronaphfesc,  and  bronaph/t«e.   When  we  get  as  far  as 

C  H 

chlonaph/M««  C^^  <  pj»  as  there  are  no  more  vowels,  we  begin  again  with  a, 

C  H  C  H 

adding  a  syllable  to  the  word.    Thus,  ^^\  r^}  is  chlonaph^a/ose,  C^^  ^  p.    is 

chlonaph<a/c»e,  and  C^qCI  is  chlonaph/a/we,  and  so  on  with  bromine.  When 
hydrogen  is  replaced,  partly  by  chlorine,  partly  by  bromine,  then  the  name  is 
so  constructed  that  the  final  syllable  indicates  the  sum  of  the  equivalents  of 
chlorine  and  bromine,  while  both  chlorine  and  bromine  are  prefixed.    Thus, 

CH  S  ^^ 

chlonaphtose  is  C     <  pj  ;  and  the  compound  C    <  Cl^  is  chlortbronaph^o5«  ,- 

^  ^^  (  Br 

is  chlorabronaph/osc.    The  former  of  these  two  may  also  be  bromachlo- 
naph/rt^e,  and  the  latter  bromichlonaph^oac.     We  shall  see,  hereafter,  that  it  may 


BROMINE  AND  NAPHTHALINE.  731 

be  necessary  to  use  both  forms  to  distinguish  different  compounds  which  are 
isomeric.    Again,  where  hydrogen  is  replaced  by  NO^,  we  have,  (NO^=X), 

C     ^  „7  nitronaphtalase,  and  so  forth.    It  is  evident  that  this  nomenclature, 

although  it  gives  rise  to  words  of  a  singular  aspect,  is  yet  easily  understood, 
and  may  even,  in  many  cases,  serve  as  well  as  a  formula  to  remind  us  of  the 
composition.  Laurent  has  applied  it  to  many  other  series,  as  we  have  seen  in 
the  series  of  phenyle,  where  we  have  chlorophenesic,  chlorophenisic,  and  chlo- 
rophenasic  acids,  &c.) 

When  chlorine  is  brought  in  contact  with  naphthaline,  the  latter  melts,  and 
there  are  are  formed  at  once  two  compounds  of  chlorine  and  naphthaline ;  the 
chloride  of  naphthaline,  C^^Hg+Cl^;  and  the  subchloride  of  naphthaline  C^qH^ 
+  CI  .  At  the  same  time  hydrochloric  acid  is  disengaged,  arising  from  the 
action  of  chlorine  on  one  of  these  chlorides.  The  former  is  a  solid,  which  is 
best  purified  by  solution  in  hot  oil  of  petroleum,  which  deposits  it  on  cooling  in 
crystals.  It  may  also  be  purified  by  means  of  boiling  ether,  which  dissolves  it 
to  a  certain  extent,  and  deposits  it  on  cooling.  Chloride  of  N.  is  decomposed 
by  heat,  yielding  no  less  than  four  different  isomeric  forms  of  chlonaphtese.  An 
alcoholic  solution  of  potassa  converts  it  into  two  more  forms  of  chlonaphtese.  It 
is  also  acted  on  by  chlorine,  bromine,  nitric  acid,  and  sulphuret  of  ammonium, 
yielding  many  new  compounds. 

Subchloride  of  N.  is  an  oily  liquid,  which  by  the  action  of  heat  is  partially 
changed  into  hydrochloric  acid,  and  one  form  of  chlonaphtase.  An  alcoholic 
sol%on  of  potassa  also  converts  it  into  chlonaphtase  and  chloride  of  potassium. 
Chlorine  converts  it  into  two  chlorides  of  chlonaphtase,  isomeric  but  distinct; 
if  the  heat  is  too  strong  there  is  formed  one  kind  of  chlonaphtise. 

When  bromine  is  made  to  act  on  naphthaline,  no  bromide  of  N.  is  formed,  but 
hydrobromic  acid  is  separated  and  bronaphtase  is  produced. 

Chlonaphtase,  C^[li^G\)  is  obtained  by  acting  on  subchloride  of  N.  by  alco- 
holic solution  of  potassa.  On  the  addition  of  water,  an  oily  liquid  separates, 
which  is  purified  by  rectification,  and  is  then  chlonaphtase.  No  isomeric  modi- 
fication of  it  is  yet  known,  but  the  existence  of  such  is  extremely  probable. 
Bromine  acts  on  it,  converting  it  into  bromide  of  chlorabronaphtese,  Br^+C^^H^ 
ClBr. 

Bronaphtase,  C  (H  Br)  is  formed  by  the  direct  action  of  bromine  on  naphtha- 
line, care  being  taken  to  avoid  excess  of  bromine,  which  would  form  bronaphtese, 
and  excess  of  naphthaline  which  would  remain  unchanged.  Bronaphtase  is  a 
colourless  oil,  decomposed  by  chlorine  and  bromine,  the  latter  converting  it  into 
bronaphtese  and  the  products  of  the  further  action  of  bromine  on  bronaphtese. 
As  yet  only  one  form  of  bronaphtase  is  known. 

Chlonaphtese,  C^QCHgCl  ),  occurs  in  no  less  than  7  different  isomeric  forms. 
These  are  distinguished  by  Laurent  as  modifications  a,  c,  ad,  e,f,  x,  and  y,  but 
I  am  not  aware  of  the  principle  on  which  these  letters  are  selected,  a,  c,f,  and 
X,  are  obtained  by  the  action  of  heat  on  the  chloride  of  N.;  ad  and  e  by  boiling 
chloride  of  N.  with  tincture  of  potassa ;  and  y  by  the  action  of  chlorine  on  ni- 
tronaphtese.  a  and  x  are  liquid,  all  the  rest  crystallize  easily.  The  solid  forms 
have  each  a  different  point  of  fusion,  and  the  whole  7  give  different  results 
when  acted  on  by  chlorine  and  bromine.  Since,  therefore,  the  composition  of  all 
7  is  the  same,  we  are  compelled  to  adopt  the  conclusion  that  it  is  not  the  same 


733  ACTION  OF  CHLORINE  AND 

2  eq.  of  hydrogen  which  are  replaced  by  chlorine,  and  that  it  is  not  indiflferent 
which  equivalents  of  hydrogen  are  thus  replaced,  but  that,  on  the  contrary,  the 
properties  of  these  compouiyis  depend  on  the-  particular  equivalents  or  molecules 
of  hydrogen  replaced  by  chlorine,  and  that  consequently  the  arrangement,  or 
relative  as  well  as  absolute  position  of  these  molecules  in  the  compound  mole- 
cule, is  a  matter  of  far  greater  importance,  in  reference  to  chemical  characters, 
than  the  properties  of  the  elements,  or  their  place  in  the  electro-chemical  ar- 
rangement. 

Referring  to  what  I  have  said  on  the  subject  of  types,  at  pp.  630,  531, 1 
would  here  point  out  that  napthaline  is  a  type,  the  molecule  of  which  is  made 
up  of  20  equivalents  (not  single  atoms,  but  molecules)  of  carbon,  and  8  equiva- 
lent molecules  of  hydrogen ;  and  that  chlonaphtese  is  a  sub-type,  in  which  the 
20  molecules  of  carbon  are  associated,  as  in  the  fundamental  type,  with  8  other 
molecules,  not  all,  as  before,  of  hydrogen,  but  6  of  hydrogen  and  2  of  chlorine, 
a  body  usually  considered  as  entirely  opposed  to  hydrogen,  chlorine  being 
strongly  negative,  and  hydrogen  strongly  positive.  Yet  the  type  remains  un- 
changed, and  we  cannot  help  seeing  that  the  2  molecules  of  chlorine,  in  virtue 
of  their  position  in  reference  to  the  20  of  carbon^  are  playing  the  part  of  2  mole- 
cules of  hydrogen. 

Further,  if  we  conceive  the  8  molecules  of  hydrogen  in  the  fundamental  type 
to  occupy  each  a  fixed  position,  in  relation  to  the  20  of  carbon,  we  see  from  the 
wonderful  phenomena  just  indicated,  from  the  existence  of  7  distinct  forms  of 
chlonaphtese,  that,  in  each  of  these,  a  different  pair  of  molecules  of  hydrogen 
has  been  replaced  by  chlorine.  If  the  8  molecules  of  hydrogen  be  supposf^  to 
be  numbered,  according  to  the  fixed  position  of  each  in  the  compound  molecule 
of  the  type,  then  we  can  see  that  in  chlonaphtese  a,  the  molecules  1  and  2  may 
be  those  replaced,  while  in  c  the  molecules  6  and  7  may  be  those  replaced  by 
chlorine,  and  so  on.  It  is  easy  to  calculate  that  in  this  way  at  least  28  different 
isomeric  forms  of  chlonaphtese  may  exist,  and  of  these  7  are  already  known. 

Our  space  will  not  admit  of  details  on  the  different  forms  of  chlonaphtese,  but 
I  have  thought  it  indispensable  to  explain  the  view  now  taken  of  these  singular 
compounds,  in  a  general  way.  It  is  evident  that  we  may  expect  much  light  to 
be  thrown  on  the  obscure  subject  of  the  molecular  arrangement  of  compounds  by 
continued  researches  in  the  same  direction.  The  recent  progress  of  those  de- 
partments of  physics  which  are  most  closely  allied  to  chemistry,  has  established 
the  existence  of  certain  relations  between  the  atomic  weight  and  constitution  of 
compounds  and  their  physical  properties,  such  as  volume  or  density,  volatility, 
state  in  regard  to  cohesion,  solidity,  fluidity,  &c.,  and  crystalline  form.  We 
now  see  a  prospect  of  tracing  the  connection  between  the  molecular  arrangement 
of  compound  bodies  and  their  chemical  properties;  and  we  may  even  hope  here- 
after to  be  enabled,  simply  by  accurate  observation  of  the  external  properties  of 
a  body,  physical  and  chemical,  to  ascertain  its  composition  and  constitution  ;  and 
also  to  predict  with  accuracy  the  properties  of  compounds  yet  unformed,  the  for- 
mation of  which  will  probably  become  a  problem,  solvable  by  a  few  rules  of 
universal  application. 

For  the  present,  we  have  only  the  distant  prospect  of  these  results ;  but  we 
have  only  assiduously  to  pursue  the  study  of  nature  on  true  inductive  principles, 
in  order  to  be  hereafter  enabled  to  bring  into  order  the  chaos,  so  to  speak,  of  in- 
teresting and  important  observations,  the  number  of  which  is  hourly  increasing, 


BROMINE  ON  NAPHTHALINE.  733 

while  a  large  proportion  of  them  have  not  yet  found  a  use  or  an  application.  We 
must  now  return  to  the  derivatives  of  naplhthaline,  which  we  have  only  space 
briefly  to  name. 

Bronaphtese,  ^2o(^6^^2)»  ^^  easily  formed  by  the  action  of  bromine  on  napth- 
thaline  or  on  bronaphtase.  It  is  a  crystallizable  solid,  and  probably  corresponds 
to  chlonaphtese,  c.  Only  one  bronaphtase  is  yet  known.  It  forms  several  com- 
pounds with  bromine. 

Chlonaphtise,  (C^qH^CI^)  occurs  in, 6  different  forms  (out  of  55  which  are 
possible),  a,  ac,  c,  g,  d,  and  ad,  all  of  which  are  crystallizable  solids.  They  are 
obtained  in  different  ways  :  a  by  boiling  with  tincture  of  potassa  the  oily  modi- 
fication of  chloride  of  chlonaphtase ;  ac  by  the  action  of  chlorine  on  chlonaph- 
tese ad,  melted ;  c  and  g,  along  with  some  of  a,  by  boiling  with  tincture  of 
potassa  the  crystallized  chloride  of  chlonaphtase  ;  d  by  distilling  the  crystallized 
chloride  of  chlonaphtase ;  and  ad  by  boiling  with  tincture  of  potassa  the  double 
chloride  of  naphthaline  and  of  chlonaphtase;  a  is  converted  by  chlorine  into 
chlonaphtose  a ;  and  bromine  converts  it  into  chloribronaphtose  a. 

Bronaphtise  ^cji^p^^  is  obtained  by  heating  the  bromide  of  bronaphtise, 
when  bromine  is  given  off.     It  is  crystallizable.     Only  one  form  is  yet  known. 

Chkmaphiose  C^(H^Cl^)  occurs  in  four  isomeric  forms,  a,  h,  c,  and  k,  out  of 
a  very  large  number  which  are  possible.  They  are  all  crystallizable.  It  is  unne- 
cessary to  mention  the  methods  employed  to  obtain  them,  which  are  analogous 
to  those  already  described  for  chlonaphtise  or  chlonaphtese. 

Bronaphtase,  ^^^(H^Br^)  appears  to  exist  in  two  forms,  a  and  h,  both  crystal- 
lizable. 

Chlonaphtuse,  ^^^(H^Cl^)  and  Bronaphiuse,  C^jjCH^Br^),  are  not  yet  known. 

Chlonaphtalase,  O^QCH^Clg)  is  obtained  by  the  action  of  chlorine  on  chlonaph- 
tise a.    It  forms  soft  flexible  prisms. 

Chlonaphtalese,  (^^{'RCl^)  is  not  yet  known. 

Chlonaphialise,  C^Clg,  the  compound  in  which  all  the  hydrogen  of  naphtha- 
line is  replaced  by  chlorine,  is  obtained  by  continuing  the  action  of  chlorine  on 
chlonaphtise  a.  It  is  also  crystallizable.  Laurent,  apparently  from  its  crystal- 
line form,  considers  it  to  correspond  with  the  modifications  c  of  chlonaphtese 
and  chlonaphtise ;  and  for  the  same  reason  he  considers  the  only  chlonaphtalase 
known,  as  chlonaphtalase  a.  In  the  case  of  chlonaphtalise,  if  different  modifi- 
cations can  occur,  they  must  depend  on  a  different  principle  from  that  which 
regulates  the  modifications  of  those  compounds  in  which  both  chlorine  and 
hydrogen  are  concerned.  But  until  Laurent  shall  publish  a  complete  account  of 
his  views,  it  is  not  easy  to  ascertain  exactly  what  those  views  are.  I  suspect 
some  error  in  the  only  account  of  these  researches  to  which.  I  could  refer. 

Besides  the  above,  there  are  a  number  of  compounds  derived  from  naphthaline, 
in  which  the  hydrogen  is  replaced  by  bromine  and  chlorine  at  once. 

Chlorebronaphtise  a,  G^J^Hfil^Bx)  is  a  crystalline  solid  very  similar  to  chlo- 
naphtise a. 

Chlorebronaphiose  h,  C^QCH^Cl^Br^)  is  obtained  by  the  action  of  bromine  on 
chlonaphtese  /.  -^ 

^Chloribronaphtose  a,  Bromachlonaphtose  a,  and  Bromachlonaphtose  b,  are  three 
isomeric  compounds.  The  first  is  obtained  by  the  action  of  bromine  on  chlo- 
naphtise a,  and  the  bromine  is,  therefore,  placed  second  in  the  name.  The  two 
others  are  both  formed  when  chlorine  acts  on  bronaphtese.    They  furnish  a  very 


734  PRODUCTS  DERIVED  FROM  NAPHTHALINE. 

beautiful  proof  of  the  truth  that  the  position  of  the  replaced  or  replacing  mole- 
cule is  all-important.    They  are  all  crystallizable. 

Bromeclilonaphtose  6,  CgpCH^Cl^Br^)  is  a  crystalline  solid,  obtained  by  boiling 
chloride  of  bromechlonaphtise  with  tincture  of  potassa. 

Chloribronaphiuse,  C^{li^C\^T^)  is  a  crystalline  solid,  formed  by  the  action 
'  of  bromine  on  chloride  of  naphthaline. 

There  remain  to  be  described  some  compounds,  analogous  to  the  chlorides  of 
naphthaline,  and  containing  consequently  chlorine  or  bromine,  in  addition  to  the 
type  or  subtype. 

Chloride  of  chlonaphtase  CA^-{-C^(ll^C\),  is  obtained  by  the  action  of  chlorine 
on  the  subchloride  of  naphthaline.  It  is  the  most  remarkable  of  the  whole 
series  from  the  great  size  and  beauty  of  its  crystals.  It  occurs  in  an  isomeric 
form  as  an  oily  liquid.  When  distilled,  these  compounds  yield  different  forms 
of  chlonaphtise  mixed  together. 

Chloride  of  chlonaphtese,  ^14+^2^(11^012)  occurs  in  three  isomeric  forms,  a 
and  X  are  oily  liquids,  derived  respectively  from  chlonaphtese  a  and  x  by  the 
action  of  chlorine,  c  is  derived  from  chlonaphtese  c  in  the  same  way,  and  is 
crystalline.     They  all  yield  chlonaphtose  when  heated,  but  in  different  forms. 

Bromide  of  chlonaptese,  'Gx ^-^ C  J^H p\^)  is  obtained  by  the  action  of  biomine 
on  chlonaphtese  c.  It  is  crystalline.  An  excess  of  bromine  produces  at  least 
five  different  compounds. 

Bromide  of  chlorabronaphtese,  Br^-i-C2jj(HgBrCl),  is  formed  when  bromine 
acts  on  chlonaphtase.    It  is  crystalline. 

Bromide  of  bronaphtese,  Br^+C^QCHgEr^)  is  formed  by  the  action  of  bromine 
on  bronaphtese.  It  is  crystalline,  and  when  distilled  yields  hydrobromic  acid 
and  bronaphtose. 

Subhromide  of  bronaphtise,  BT^-^C^(¥lfiT^  is  formed  along  with  the  preced- 
ing.    It  is  also  crystalline. 

Bromide  of  bronaphtise,  BT^-\-C^{HgBT^)  is  also  a  highly  crystalline  solid. 

Subchloride  of  bronaphtose,  Cl^-f  C2^(H^Br),  formed  by  the  action  of  chlorine 
on  bronaphtase,  crystallizes  in  regular  rhomboidal  plates. 

Chloride  of  bronaphtese,  Cl^-|- 02^(11^6 r^)  crystallizes  in  long  prisms.  Per- 
chloride  of  bronaphtise,  Cl^-|-  ^^^(H^Brg)  crystallizes  in  right  prisma  with  rhombic 
base. 

Chloride  cf  bromechlonaphtise,  Cl^-|-C2Q(HjBr2Cl)  crystallizes  in  oblique 
ihombic  prisms.  When  boiled  with  tincture  of  potassa  it  yields  bromechlonaph' 
tuse,  C„(H3Br.Cl,). 

All  the  preceding  compounds  have  been  discovered,  studied,  analyzed,  and 
described  by  Laurent,  besides  a  large  additional  number  of  derivatives  of  naph- 
thaline, under  the  agency  of  chlorine  and  bromine,  which  he  has  not  so  fully 
examined.  Those  here  named  are  sufficient  to  illustrate  the  endless  variety  of 
compounds  attainable.  Every  subtype  of  the  original  type  of  naphthaline 
admits  of  numerous  permutations,  and  where  both  chlorine  and  bromine  are 
present,  the  number  of  possible  permutations  is  enormously  increased.  In  short, 
these  remarkable  jresearches  have  only  made  us  acquainted  with  a  very  small 
selection  of  the  possible  products  of  the  action  of  chlorine  and  bromine  ^n 
naphthaline,  the  type  remaining  unchanged. 

Thus  the  subtype  chlonaphtose  Cjjp(H^Cl^),  admits  of  65  isomeric  modifica- 
tions, all  different,  as  does  of  course  brohaphtose  also.     But  these  subtypes, 


ACTION  OF  NITRIC  ACID  ON  NAPHTHALINE.  735 

may  yield  the  modified  subtypes,  chlorabronaphtose,  chlorebronaphtose,  chlori- 
bronaphtose,  bromachlonaphtose,  bromechlonaphtose,  and  bromichlonaphtose,  and 
others,  difficult  to  name,  depending  on  the  relative  proportions  and  positions,  in 
the  molecule  of  the  subtype,  of  the  4  eq.  chlorine  and  bromine.  It  is  easy  to 
imagine  14  such  modified  subtypes,  and  there  appears  no  reason  why  each  of 
them,  with  the  two  subtypes,  should  not  admit  of  at  least  G5  isomeric  forms. 
This  would  give  1040  isomeric  forms,  all  included  under  the  two  subtypes  chlo- 
naphtose  and  bronaphtose,  or  under  one  subtype  which  may  be  called  naphtose, 
C^{Y{^^.    X  is  here  put  for  chlorine  or  bromine. 

2.  Action  of  Sulphuric  Acid  on  NaphthaHne. 

When  naphthaline  is  dissolved  in  warm  oil  of  vitriol  to  saturation,  the  solu- 
tion, if  left  exposed  to  the  air,  becomes  a  semisolid  mass  of  a  dirty  purplish 
colour.  This,  dried  on  a  porous  brick,  leaves  a  quantity  of  scales,  very  soluble 
in  water  and  alcohol,  which  are  a  mixture  of  two  acids. 

a.  Hyposulphonaphthalic  acidy  C^H^^SJd^-^Il0 1  The  above  mixture,  being 
dissolved  in  water,  is  saturated  with  carbonate  of  lead,  which  forms  insoluble 
sulphate  of  lead,  and  two  soluble  salts,  one  of  which  is  soluble  in  alcohol  and 
contains  this  acid,  and  yields  it  when  decomposed  by  sulphuretted  hydrogen. 
The  acid  forms  a  hard  crystalline  fusible  mass  of  an  acid  and  bitter  taste.  Its 
salts  are  soluble  and  crystallizable.     Their  formula  is  ^ao^igS  0^,M0. 

b,  Hyposulphonaphtic  acid,  C^f{^p^^=^O^^^^^yHO'\  The  lead  salt  inso- 
luble in  alcohol  contains  this  acid,  the  salts  of  which  are  soluble,  bitter,  and 
hardly  crystallizable.  It  is  probable  that  a  third  acid  accompanies  these  two ; 
for  Faraday  obtained  a  third  salt  of  baryta  and  Berzelius  found  a  third  salt  of 
lead  in  the  mother  liquid  of  the  other  two.  Faraday's  salt,  which  remains  with 
the  sulphate  of  bfryta  formed  in  the  process  by  the  free  sulphuric  acid,  and  may 
be  extracted  by  boiling  water,  yields  about  42  per  cent,  of  sulphate  of  baryta 
when  calcined. 

The  vapours  of  anhydrous  sulphuric  acid,  passed  over  fused  naphthaline,  form 
with  it  a  red  liquid.  If  the  acid  be  in  excess,  there  is  formed  a  new  acid,  the 
hyposulphoglutinic  atid,  besides  small  quantities  of  the  preceding  acids  ;  if  there 
be  excess  of  naphthaline  there  are  formed  two  neutral  bodies,  sulphonaphthaline 
and  sulphonaphihalide. 

Hyposulphoglutinic  acid,  when  pure  and  dry,  is  a  hard  glassy  mass.  When 
precipitated  from  its  salts  by  stronger  acids,  it  forms  a  viscid  hydrate  like  tur- 
pentine. Its  salts  are  generally  soluble  and  do  not  crystallize.  Its  composition 
is  unknown. 

Sulphonaphthaline,  C^^IIgSO^?  is  a  crystalline  fusible  solid. 

Sulphonaphthalide,  ^^fli^^^^^  ^^  ^  crystalline  powder  not  fusible  at  212°. 

3.  Action  of  Nitric  Acid  on  Naphthaline,  and  its  Derivatives. 

Nitric  acid  acts  on  naphthaline,  and  gives  rise  to  a  whole  series  of  compounds  in 
which  NO^  is  substituted  for  hydrogen.  The  same  principles  apply  here  as  in 
the  action  of  chlorine  and  bromine  on  naphthaline.  It  is  to  Laurent  that  we  are 
indebted  for  our  knowledge  of  these  compounds,  which  our  space  will  only  allow 
us  to  name. 

Nitronaphtalase,  C^qH^X,  (X  is  here  put  for  NO^),  is  best  formed  by  causing 
nitrous  acid  to  pass  through  melted  naphthaline.  It  is  purified  by  means  of  al- 
cohol, and  forms  long  prisms  of  a  sulphur-yellow  colour,  fusible  at  110°.    Chlo- 


736  ACTION  OF  NITRIC  ACID 

rine  decomposes  it,  producing  chlonaphtose.  Nitric  acid  converts  it  into  niiro- 
naphtalese. 

Mtronaphtalese,  C^i^K^X^),  forms  a  crystalline  powder  fusible  at  365°,  insolu- 
ble in  water,  very  sparingly  soluble  in  alcohol. 

Naphtalase,  ^^^(H^O)  is  a  yellow  crystalline  solid  formed  by  gently  heating 
nitronaphtalase  with  10  parts  of  lime  slightly  moistened.  It  communicates  to 
oil  of  vitriol  a  magnificent  blue  colour.  It  is  insoluble  in  alcohol  as  well  as  in 
water,  otherwise  it  would  recal  pyroxanthine,  which  is  yellow  and  volatile  and 
colours  sulphuric  acid  purple. 

NitronapUakise,  ^20(^52^22)  ^  ^^  ^  crystalline  compound  formed  when  naph- 
thaline is  added  in  small  quantities  to  a  large  mass  of  hot  nitric  acid.  Nitro- 
naphtalese  is  produced  along  with  it.  It  is  pale-yellow  and  very  fusible, 
becoming  liquid  even  in  boiling  alcohol.  This  great  fusibility  prevents  us, 
notwithstanding  its  strange  formula,  from  considering  it  as  a  mixture  of  nitro- 
naphtalese  and  nitronaphtalise,  the  former  of  which  melts  at  365°,  the  latter  at 
410°,  and  which  are  very  insoluble  in  ether,  in  which  liquid  nitronaphtaleise 
readily  dissolves. 

Nitronaphtalise,  C^  (H^X^)  is  formed  along  with  the  preceding,  and  crystal- 
lizes in  rhomboidal  plates  of  a  pale-yellow  colour,  fusible  at  410°. 

Nitronaphtale,  ^19^5^3^11'  ^®  ^  crystalline  substance,  formed  by  the  long- 
continued  action  of  nitric  acid  on  the  mother  liquor  of  all  the  preceding.  It 
melts  at  420°,  and  sometimes  solidifies  in  an  amorphous  state;  a  slight  heat,  or 
touching  the  melted  substance  with  a  point,  causes  it  to  crystallize. 

Nitronaphtalesic  acid,  C ^gH^^Nj^O^  %  ^^^fi^J^fi^  '^  This  acid  is  formed  when 
nitronaphtalese  is  boiled  with  tincture  of  potassa,  and  is  separated  from  the  po- 
tassa  by  nitric  acid.  When  dry  it  is  brownish-black,  and  forms  brown  salts, 
which  are  soluble  and  uncry stall izable.  NitronaphiaUiiic  acid,  Cj^H^OgN^j,  or 
Cg^HgO^^Ng,  is  a  similar  acid,  formed  from  nitronaphtaleise.  Niironaphtalisic 
acid  is  another  brown  acid,  formed  in  the  same  way  from  nitronaphtalise. 

Oxide  of  chlorox^naphtose,  0^-f-C^  (H^Cl^O^),  is  formed  when  nitric  acid  acts 
on  crystallized  chloride  of  chlonaphtose.  It  appears  as  as  a  yellow  crystalline 
solid.  It  is  accompanied  by  chloranaphtisic  acid,  into  which  it  is  also  converted 
by  boiling  with  tincture  of  potassa. 

Chloranaphtisic  acid,  C^^H^Cl  Og,  is  formed  from  the  preceding  compound,  as 
follows  :  C3j,H^Cl20^+HO-h2KO=KCl-|-(C^H^C10g-f-KO).  It  is  separated 
from  the  potassa  by  adding  an  acid,  and  forms  yellow  crystals,  fusible  at  392°. 
Its  salts  are  for  the  most  part  insoluble,  and  exhibit  the  most  beautiful  colours, 
including  yellow,  orange,  red,  and  carmine. 

Oxide  of  chlwoxenaphlalise,  Og+CgQClgO^,  is  obtained  along  with  chlophtalisic 
acid  and  other  compounds,  when  nitric  acid  is  boiled  with  chlonaphtalase,  C^^jH^ 
CI  .     It  forms  golden  scales. 

Chloroxenaphtalesic  acid,  C^qH  Cl^O^,  is  formed  when  the  preceding  com- 
pound is  acted  on  by  potassa,  which  at  once  changes  it  into  a  fine  carmine-red 
substance,  from  which  acids  separate  the  new  acid  as  a  yellow  crystalline  pow- 
der. It  forms  beautiful  red  salts  with  potassa  and  ammonia.  It  is  formed  as 
follows:  Cj:\fi^-Yl\0-\-2  K0=(C^HC1^0g-[-K0)  +  KCl. 

Phiallc  or  naphtalie  acid,  C^^ip^,  2W0=C^^\{fi^,  is  formed  by  the  action 
of  nitric  acid  on  chloride  of  naphthaline.  It  forms  rounded  groups  of  lamellar 
crystals,  and  yields  crystallizable  salts.    When  distilled  with  lime,  it  yields 


NAPHTALIDAM.  737 

benzole  (phene),  and  carbonic  acid,  ^iQ^fis~'^^^2'^^i2^6'  ^^^^  ^^^  ^Y" 
drated   acid  is  distilled,  it  yields  the  anhydrous  acid  in  fine  elastic  needles. 

The  acid  phtalate  of  ammonia,  CjgH^Og,NH^O,HO,  when  heated  yields  water, 
4H0,  znd  phtaltynide,  G^fl^NO^. 

Phtalamide,  C  H^NO^,  is  obtained  by  acting  on  anhydrous  phtalic  acid  by 
ammonia.  It  appears  that  phtalimide  is  acid  phtalate  of  ammonia,  minus  4  eq. 
water,  while  phtalamide  is  anhydrous  phtalate  of  ammonia,  C^gH^Og-f-NH^, 
minus  1  eq.  water.  Both  are  crystalline  solids,  and  both  appear  to  form  defi- 
nite compounds  with  oxide  of  silver. 

NitropUalic  acid,  C^^^O^^^^HO,  is  derived  from  phtalic  acid  by  the  substi- 
tution of  1  eq.  NO^  for  1  eq.  hydrogen.  C^gH^O^— H+N0^=CjgH3N0j^.  It 
forms  beautiful  pale-yellow  crystals ;  and  when  gently  heated,  it  yields  the  an- 
hydrous acid  in  fine  white  needles. 

ChlopUalisic  acid^  C^gHCl  Og,  is  formed  along  with  the  oxide  of  chloroxen- 
aphtose  when  chlonaphtalase  is  boiled  with  nitric  acid.  It  is  crystallizable, 
and  represents  anhydrous  phtalic  acid,  in  which  3  eq.  hydrogen  have  been  re- 
placed by  3  eq.  chlorine. 

4.    Action  of  Sulphuretted  Hydrogen  on  the  Nitrogenized  Compounds  derived  from 

Naphthaline. 

Naphtalidam,  C^^H^jN.  This  is  a  very  interesting  base,  formed  by  the  action 
of  sulphuretted  hydrogen,  aided  by  ammonia,  on  an  alcoholic  solution  of 
nitronaphtalase.  It  may  be  obtained,  although  more  slowly,  without  the  use 
of  ammonia.  The  mixture  becomes  of  a  dirty  green,  and  the  addition  of  sul- 
phuric acid  causes  the  solution  to  become  thick  from  the  separation  ot  sulphate 
of  naphtalidam.  This  salt  is  purified,  and  decomposed  by  ammonia,  when,  the 
liquid  is  soon  filled  with  fine  white  needles  of  pure  naphtalidam.  It  is  a  very 
powerful  base,  melting  at  86°,  and  boiling  at  582°.  When  distilled,  it  is  apt  to 
continue  liquid  till  cooled  to  32°.  The  liquid  base,  if  exposed  to  the  air,  ab- 
sorbs oxygen,  and  becomes  of  a  dirty  violet  colour.  It  forms  white  crystalli- 
zable salts  with  all  the  acids,  and  its  hydrochlorate  forms  double  salts  with  the 
bichlorides  of  platinum  and  mercury. 

The  discovery  of  this  base,  and  of  the  ingenious  method  by  which  it  is 
formed,  is  due  to  Zinin,  who  has  also  found  that  the  other  nitrogenized  deriva- 
tives of  naphthaline,  treated  in  the  same  way,  form  similar  bases.  That  from 
nitronaphtalese  is  crystallizable,  and  forms  a  hydrochlorate  in  scales. 

The  formation  of  these  bases  throws  great  light  on  the  true  nature  of  the  vege- 
table alkalies.  Zinin  obtained  from  nitrobenzide,  by  the  same  method,  a  base, 
an  oil  which  he  called  benzidam ;  but  Hoffmann  has  shown  its  identity  with 
aniline. 

To  judge  from  the  action  of  chlorine  unaided  by  heat,  and  of  nitric  acid,  on 
naphthaline,  that  body,  C^qH^,  is  composed  of  two  carbo-hydrogens,  C^gH^  and 
C  H  ,  the  latter  of  which  is  more  easily  altered.    The  former,  plus  6  eq.  oxygen, 

k .yields  phtalic  acid,  C^qH^  -f  0^ ;  and  the  substitution  in  phtalic  acid  of  NO^ 
i(=X),  for  H  yields  nitrophtalic  acid,  C^^  5     3_j_  o^. 
L  j3.  Mthracene,  C^^H^^.    This  compound,  which  is  isomeric  with  naphthaline, 
^s  also  found  in  coal-tar,  and  is  sometimes  called  paranaphthaline.     It  melts  at 
356°,  and  distils  at  392°,  yielding  foliated  plates.      When  acted  on  by  nitric 

49 


738  F0S6IL  RESINS,  WAX,  OIL,  NAPHTHA,  &c. 

acid,  it  gives  rise  to  a  series  of  compounds,  in  which  oxygen  is  substituted  for 
hydrogen,  while  the  compounds  thus  formed  combine  with  hyponitrous  acid. 
Thus,  we  have 

Anthracene ^ao^n 

Hyponitrite  of  Anthracenase     ....  CaoH^O-f- NO3 

Bi-hyponitrite  of  Anthracenese  .        .        .  CJ0HJ0O2+2NO3 

Ter-hyponitrite  of  Anthracenise        .        .        .  CjoHgOg -j- SNOg  +  3H0. 

Hyponitrite  of  Anthracenose  .        .        .  CgoHgO^  -[-  NO3 

Hyponitrite  of  Anthracenuse  .        .        .  C3oH705-t-N03+HO 

Anthracenuse  C30H7O5 

Chloranthracenese     ......  CgoHjoClg 

The  second  compound  of  the  above  list  is  not  known ;  but  its  existence  is 
probable.  In  all  the  works  to  which  I  have  access,  there  appear  to  be  errors, 
probably  of  the  press,  in  the  table,  which  I  have  ventured  to  correct,  so  as  to 
bring  the  formulae  into  correspondence  with  the  systematic  names  devised  by 
Laurent,  who  discovered  all  these  substances,  on  the  same  principle  as  in  the 
case  of  naphthaline. 

y.  Chrysene,  C^H  or  C^^H^,  is  found  among  the  last  portions  of  the  rectifica- 
tion of  coal-tar.  It  is  a  yellow  crystalline  solid,  insoluble  in  most  liquids.  It 
melts  at  455°. 

S.  Pyrene,  C^^H^  or  C^^H^,  is  found  accompanying  the  preceding.  It  is  a 
good  deal  more  fusible.  When  acted  on  by  nitric  acid,  both  of  the  above  com- 
pounds yield  modifications,  called,  by  Laurent,  the  hyponitrites  of  chrysenase 
and  of  pyrenase,  C^^H^O  +  NO^  and  Cj^H^O  +  NO^.  The  former,  by  the  con- 
tinued action  of  nitric  acid,  is  converted  into  C^^H^O^  -f-  SNO^,  which  Laurent 
calls  nitrite  of  chrysenese  (properly,  of  chrysenaese  ?) 

When  bituminous  shale  is  distilled,  it  yields  a  thick  empyreumatic  oil,  com- 
posed of  several  products.  Among  these  is  an  oil  apparently  identical  with 
eupion,  and  another  very  peculiar  oil,  called  ampeline.  This  oil  has  neither  taste 
nor  smell,  but  is  in  some  points  more  analogous  to  creosote  than  to  any 
other  substance.  It  dissolves  in  water,  but  a  few  drops  of  acid  cause  it  to 
separate.  Its  composition  is  still  unknown.  It  may  possibly  be  a  product  of 
the  action  of  oil  of  vitriol,  which  is  used  in  its  preparation,  on  some  other  sub- 
stance. 

Ampelic  Acid  is  formed  by  the  action  of  nitric  acid  on  that  part  of  the  oil  of 
schist  which  distils  at  300°.  It  is  oily,  soluble  in  hot  water,  and  forms  very 
solute  salts.  Its  composition  is  not  known  with  certainty.  A  similar  oil,  ob- 
tained from  coal-tar,  was  found  to  contain  C,  H  O  .    This  would  be  isomeric 

14      6     0 

with  hydrated  salicylic  acid. 

FOSSIL  RESINS,  WAX,  OIL,  NAPHTHA,  &c. 

Reiinite  or  Retinasphalt,  is  a  fossil  resin  found  in  lignite  or  wood-coal.  It  is 
fusible  and  combustible,  and  almost  entirely  soluble  in  alcohol.  Retinic  acid, 
C^jHgOj,  was  found  by  Johnston  in  the  retinasphalt  of  Bovey. 

Ilatehetine  is  another  fossil  resin  found  in  the  lignites  of  Wales.  It  is  colour- 
less, or  slightly  yellow,  fusible  and  volatile. 

Sc?ieererite  is  a  colourless,  translucent  substance,  of  a  pearly  lustre,  found  in 


PETROLEUM.  739 

the  Swiss  lignites.    Both  Hatchetine  and  Scheererite  appear  to  be  carbo-hydro- 
gens,  and  much  resemble  paraffine,  not  quite  pure. 

Mddktonite  is  a  fossil  resin,  found,  near  Leeds,  in  coal. 

Idrialine  is  a  remarkable  solid  carbo-hydrogen,  found  in  the  quicksilver-mines 
of  Idria.  Its  composition  is  C^H,  or  perhaps  C^^H^ ;  it  colours  oil  of  vitriol  in- 
tensely blue,  forming  a  coupled  acid.  Succisterene,  a  solid  body  obtained  by 
Pelletier  and  Walter  in  the  distillation  of  amber,  has  the  same  composition,  and 
colours  sulphuric  acid  blue.  It  is,  therefore,  in  all  probability,  identical  with 
idrialine. 

Ozokerite  or  Fossil  Wax  is  found  in  large  masses  in  the  bituminous  schist  of 
Slamick  in  Moldavia.  When  distilled,  it  yields  a  substance  like  wax,  and  also 
a  good  deal  of  paraffine.  Ozokerite  is  very  fusible,  and  bums  with  a  bright 
flame. 

Fichtelite  is  a  fusible,  volatile,  crystallizable  solid,  found  in  branches  of  pine- 
trees,  in  the  peat  of  the  turbaries  in  the  Fichtelgebirge.  It  appears  to  have  the 
formula  C^^H^^,  and  is  probably  derived  from  essence  of  turpentine,  Cg^H^^. 

Tekoretine,  Phylloretine,  Xyloretinei  and  Boloretine,  are  the  names  of  four 
resinous  compounds,  found  in  the  peat  of  Denmark,  on  the  remains  of  pine-trees. 
Tekoretine  and  Phylloretine  are  both  fusible,  volatile,  and  crystallizable.  The 
former  appears  to  be  Cj^Hg,  the  latter  C^H^.  Xyloretine  is  less  fusible,  and  is 
decomposed  by  heat.  It  crystallizes,  and  its  formula  is  said  to  be  C^H^^^^, 
which  only  differs  from  that  of  sylvic  acid  by  I  eq.  hydrogen.  Boloretine  is 
fusible,  but  does  not  crystallize.  Its  formula  is  C^H^^+SHO,  but  it  occurs 
also  with  5  or  6  eq.  of  water. 

Jsphaltunii  Mineral  Pitch,  Pitch  of  Judea.  These  are  the  names  of  certain 
substances  of  similar  characters,  found  in  different  parts  of  the  world,  as  in  Tri- 
nidad, in  Hanover,  and  at  the  Dead  Sea  in  Palestine.  They  all  resemble  pitch 
in  aspect,  and  are  composed  of  a  dark-brown  resin,  mixed  with  more  or  less  of 
a  brilliant  black  matter,  asphaltene,  C^QH^gO^,  or  of  a  liquid  volatile  oil,  peiro- 
lene,  C^QH^g.  The  former  of  these  is  probably  an  oxide  of  the  latter.  The 
different  kinds  of  asphaltum  are  much  used  for  waterproof  cements,  and  for  pave- 
ments, or  roofs.  Naphteine  is  a  somewhat  analagous  substance,  found  in  the 
limestones  of  the  Maine  et  Loire. 

Petroleum  and  Naphtha.  In  certain  spots,  in  the  neighbourhood  of  the  Cas- 
pian, in  Ava,  at  the  Tegernsee  in  Bavaria,  at  Amiano  in  Italy,  and  near  Neuf- 
chatel,  as  well  as  in  other  places,  pits  dug  in  the  earth  become  filled  with  water, 
on  which  floats,  more  or  less  abundantly,  an  oily  matter,  formerly  called  rock- 
oil.  The  purer  kinds  are  little  coloured  and  very  fluid,  and  when  distilled  with 
water  leave  hardly  any  residue.  These  are  called  naphtha.  Other  kinds,  as  the 
petroleum  of  Rangoon  in  Ava,  are  dark-coloured  and  semisolid,  but  become 
liquid  at  80°  or  90°.  These  yield  by  distillation,  first,  much  naphtha,  nearly 
colourless,  and  then  much  paraffine,  which  is  easily  purified.  Naphtha,  when 
pure,  has  the  sp.  gr.  0*755,  and  its  formula  is  CgH^.  Rectified  naphtha  is  used 
for  the  purpose  of  preserving  potassium  and  sodium,  which  have  no  action  on  it 
if  water  be  not  present.  In  many  places  the  native  naphtha  is  used  to  give  light. 

Reichenbach  found  that  coal,  distilled  with  water,  yielded  a  little  of  an  oil 
very  similar  to  petroleum. 

All  the  above  substances  are  formed  by  the  decay  or  destruction  of  organic 
matter,  chiefly  wood.  It  is  not  altogether  improbable  that  those  kinds  which, 
like  the  Rangoon  petroleum,  contain  paraffine  ready  formed,  may  have  been 


740  VEGETABLE  FIBRINE  AND  ALBUMEN. 

formed  by  the  action  of  heat  on  beds  of  vegetable  remains,  situated  pretty  deep 
in  the  crust  of  the  earth. 

Soot  and  Lamp  Black  are  produced  by  the  imperfect  combustion  of  organic 
matters.  They  contain  much  carbon,  mixed,  in  soot,  with  an  acid  resinous  mat- 
ter, and  with  a  substance  analogous  to  humus,  but  containing  nitrogen,  and 
called  asboline.  Lamp-black,  besides  a  little  resin  and  oily  matter,  often  con- 
tains naphthaline,  which  may  be  extracted  by  alcohol. 

SULPHURIZED  AND  NUTRITIOUS  ANIMAL  AND  VEGETABLE  PRINCIPLES. 

*  '  We  have  already  seen  that  some  essential  oils  contain  a  large  proportion  of 
'Ifalphur,  and  it  is  probable  that  these  oils  are  derived  from  the  decomposition  of 
compounds  existing  in  the  plants  which  contain  much  sulphur,  but  the  true  na- 
ture of  which  is  not  yet  known.  But  while  such  compounds  only  occur  in  a 
few  plants,  there  is  another  class  of  sulphurized  compounds  which  occur  in  all 
plants  without  exception.  These  compounds  contain  nitrogen  and  oxygen,  both 
in  considerable  proportion  to  the  carbon  and  hydrogen,  and  a  small  proportion  of 
sulphur.  They  are  all  solid,  and  when  heated  yield  products  containing  ammo- 
nia and  sulphur.  They  have  neither  a  medicinal  nor  a  poisonous  action  on  the 
tauiimal  system,  but  are  nutritious  in  the  strict  sense  of  the  word. 

Such  are  vegetable  albumen,  vegetable  fibrine,  and  vegetable  caseine,  as  well 
as  animal  albumen,  animal  fibrine,  and  animal  caseine.  The  latter,  when  com- 
pared with  the  former  respectively,  are  found  to  differ  from  them  only  in  form, 
agreeing  with  them  in  all  essential  chemical  characters.  Every  one  of  the  six 
dissolves  in  strong  hydrochloric  acid,  gently  warmed,  with  a  purple  colour;  and 
all  of  them  likewise  dissolve  in  caustic  potassa,  forming  a  solution  which  (after 
'all  the  sulphur  has  been  converted  into  sulphuret  of  potassium  by  boiling)  gives, 
on  the  addition  of  acetic  acid,  sulphuretted  hydrogen  gas,  and  a  gelatinous  pre- 
cipitate, which  in  every  case  is  the  same  substance,  called  ProUine,  by  Mulder, 
its  discoverer.  Hence  the  above  substances  are  called  proteine  compounds, — not 
that  we  can  prove  them  to  contain  proteine  ready  formed,  but  because  they  all 
yield  proteine  in  the  same  circumstances. 

1.  Vegetable  Albumen  has  only  been  studied  as  yet  in  the  coagulated  or  inso- 
luble state.  It  occurs,  however,  dissolved,  or  in  the  soluble  form,  in  vegetables, 
and  especially  in  the  oily  seeds,  along  with  caseine.  It  is  always  combined 
with  alkali,  to  which  it  owes  its  solubility.  Its  distinguishing  character  is  that 
of  coagulating  or  becoming  insoluble  when  heated  to  from  140°  to  160°.  Once 
coagulated  it  no  longer  dissolves,  even  in  the  liquid  in  which  it  was  formerly 
qnite  dissolved.  When  a  fresh  vegetable  juice  is  filtered  and  boiled,  it  yields  a 
coagulum,  which  is  nearly  pure  albumen.  Its  solutions  are  also  coagulated  by 
acids,  by  infusion  of  galls,  by  creosotes,  and  by  corrosive  sublimate.  When 
dried,  it  is  translucent.     In  all  these  characters  it  agrees  with  animal  albumen. 

2.  Vegetable  Fibrine  is  the  essential  part  of  what  is  called  the  gluten  of  wheat. 
It  is  chiefly  found  in  the  seeds  of  the  cerealia.     When  wheat,  softened  in  water, 

'is  kneaded  under  water  in  linen  bags  to  obtain  the  starch,  and  the  residuary 
masses  are  beat  up  with  rods,  the  pure  fibrine  adheres  in  elastic,  transparent  fila- 
ments to  the  rods.  These,  after  being  treated  by  ether,  to  remove  fat  oil,  are 
pure  fibrine.  When  dried,  it  becomes  greyish  and  translucent,  like  horn.  When 
heated,  it  yields  the  usual  products  of  animal  matters ;  and  when  left  to  itself 
in  the  moist  state,  it  putrefies,  disengaging  fetid  gases.  It  is  quite  insoluble  in 
water.    Diluted  phosphoric  and  acetic  acids  dissolve  it  easily  :  these  solutions 


FERMENTATION  ON  VEGETABLE  JUICES.  741 

are  precipitated  by  fenrocyanide  of  potassium,  and  by  infusion  of  galls.  Diluted 
potassa  also  dissolves  it ;  and  this  solution,  when  neutralized  by  phosphoric  or 
acetic  acid,  yields  a  precipitate  which  dissolves  in  an  excess  of  either  of  these, 
acids. 

3.  Vegetable  Caseine.  Syn.  Legumine,  is  an  essential  part  of  the  seeds  of 
the  leguminosae,  and  also  of  the  oily  seeds.  It  is  only  known  in  combination 
with  acids  and  with  alkalies.  To  obtain  it,  kidney-beans,  lentils,  or  pease,  are 
softened  in  water,  then  brayed  in  a  mortar,  the  pulp  mixed  with  much  cold  water, 
and  strained  through  a  fine  sieve,  which  retains  the  husks,  and  allows  the  caseine 
and  starch  to  pass,  the  former  dissolved,  the  latter  suspended.  On  standing,  the 
starch  settles  to  the  bottom,  leaving  a  solution  of  caseine,  which  maf  be  decanted. 
It  is  sometimes  milky  if  much  oil  be  present,  sometimes  clear.  When  exposed 
to  the  air,  it  quickly  becomes  acid,  lactic  acid  being  formed,  and  coagulates 
exactly  as  skimmed  milk  does  when  it  becomes  sour.  The  solution  of  caseine 
does  not  coagulate  by  heat,  but,  like  milk,  forms  a  pellicle  which  is  renewed  as 
fast  as  it  is  removed.  It  is  coagulated  by  the  addition  of  an  acid,  and  the  coagu- 
lum  dissolves  in  an  excess  of  all  vegetable  acids,  except  acetic  acid,  which  with 
mineral  acids  produces  a  permanent  precipitate.  This  precipitate  is  well  washed 
with  cold  water,  alcohol,  and  ether,  dissolved  in  hot  water  with  a  little  ammonia, 
and  this  solution  is  precipitated  by  alcohol.  It  still  contains  ammonia,  but  is 
otherwise  nearly  pure. 

In  this  state  it  is  like  paste  of  starch,  and  when  dried  it  is  nearly  transparent, 
and  liquefies  when  heated.  In  water  it  softens,  and  this  paste  is  coagulated  by 
acids,  corrosive  sublimate,  infusion  of  galls,  and  creosote.  Caseine  is  very 
soluble  in  tartaric  and  oxalic  acids,  also  in  caustic  and  carbonated  alkalies  if 
diluted.  The  coagula,  or  precipitates  formed  by  mineral  acids  in  solutions  of 
caseine,  are  compounds  of  caseine  with  the  acid :  they  are  soluble  in  strong 
acids. 

4.  Emulsine^  or  Synaptase,  is  the  name  given  to  a  peculiar  compound  of' this 
class,  found  in  certain  oily  seeds,  as  in  almonds,  &c.  An  emulsion  of  these 
seeds  is  very  like  milk.  On  standing,  the  oil  rises,  like  cream,  to  the  top,  and 
the  watery  liquid  is  now  coagulated  by  acetic  acid,  as  milk  would  be.  It  coagu- 
lates also  by  boiling ;  and  in  this  case,  the  whey,  separated  from  the  coagulum, 
again  coagulates  on  standing  twenty-four  hours,  and  is  found  to  contain  lactic 
acid.  The  emulsine  agrees  with  albumen,  in  being  coagulated  by  heat,  and 
with  caseine  in  being  coagulated  by  acetic  acid.  It  exerts  a  peculiar  decomposing 
agency  on  amygdaline,  in  which  it  is  also  itself  decomposed. 

Fungine  is  the  substance  of  which  mushrooms  are  chiefly  composed.  Its  true 
nature  is  uncertain,  but  it  contains  nitrogen. 

Gliadine  is  the  name  given  to  the  viscid  ingredient  of  gluten.  It  contains 
sulphur,  and  approaches  in  composition  to  vegetable  albumen.  It  is  probably  a 
mixture. 

When  a  vegetable  juice,  containing  one  or  more  of  these  compounds  along 
with  sugar,  is  exposed  to  the  air,  oxygen  is  absorbed,  and  a  change  is  com- 
menced in  the  albumen,  fibrine,  caseine,  gluten,  &c.,  which  is  soon  communi- 
cated to  the  sugar,  causing  it  to  undergo  the  vinous  fermentation.  The  temperature 
rises,  and  occasionally  the  viscous  fermentation  takes  place,  producing  lactic 
acid,  gum,  and  mannite.  During  fermentation,  a  grey  deposit  is  formed  ;  this 
is  yeast  or  ferment.  When  the  whole  of  the  azotized  principles  have  not  been 
decomposed  or  rendered  insoluble,  the  liquid,  if  excluded  from  air,  remains 


742  DIASTASE.    MALT. 

without  farther  change :  but  if  air  be  admitted,  the  alcohol  is  converted  into 
acetic  acid,  oxygen  being  absorbed  by  the  azotized  matters,  the  contact  of  which 
jcauses  the  alcohol  also  to  absorb  oxygen.  When  the  sugar  is  in  excess,  only 
part  of  it  is  converted  into  alcohol,  and  part  of  the  azotized  matter  takes  the 
form  of  insoluble  yeast,  the  rest  being  decomposed.  The  saccarine  and  spirituous 
liquid  undergoes  no  further  alteration.  All  the  above  statements  apply  to  the 
juice  of  the  grape  and  to  the  formation  of  wines  and  vinegar. 

When  the  juice,  as  that  of  the  grape,  contains  tartaric  acid,  ethers  are  formed, 
which  give  the  liquid  a  peculiar  smell  and  flavour,  such  as  cenanthic  ether,  which 
is  characteristic  of  all  wines.  When  a  juice  contains  sugar  and  caseine,  it  is 
most  apt  to  undergo  the  viscous  fermentation,  or,  at  least,  the  caseine  favours 
the  production  of  lactic  acid  from  the  sugar.  But  at  a  high  temperature,  such 
as  100°,  butyric  acid  is  formed,  instead  of  lactic  acid. 

Vegetable  fibrine,  as  it  is  found  in  wheat  flour,  is  subject  to  continual  altera- 
tion by  contact  with  water ;  and  in  this  state  it  has  the  singular  property  of 
converting  starch  into  dextrine,  a  soluble  gum,  and  then  into  sugar.  This 
remarkable  power  is  best  seen  in  germinating  grain,  as  in  malt,  of  which  a  small 
part  mixed  with  a  large  quantity  of  starch  in  a  thick  paste,  and  warmed  to  150^ 
or  160°,  very  soon  renders  the  whole  quite  fluid  and  dissolved,  and  finally  con- 
verts it  into  grape  sugaf.  That  part  of  the  fibrine  which  acts  on  the  starch  has 
bacome  soluble  in  water.    It  is  called  diastase. 

Diastase  is  made  by  rubbing  up  malt  with  a  little  water,  expressing  the  mix- 
ture, adding  just  enough  alcohol  to  separate  the  albumen,  and  to  allow  the  liquid 
to  filter.  The  filtered  liquid,  mixed  with  more  alcohol,  deposits  the  diastase.  It 
is  purified  by  being  repeatedly  dissolved  in  water  and  precipitated  by  alcohol. 
It  is  finally  dried  at  a  temperature  of  100°  or  110°.  Thus  prepared,  diastase 
cannot  be  a  pure  compound,  but  it  possesses  in  a  high  degree  the  power  of  pro- 
moting a  solution  of  starch,  that  is,  its  conversion  into  dextrine  and  sugar.  One 
part  of  diastase  can  convert  into  dextrine,  with  a  little  sugar,  no  less  than  2000 
parts  of  starch.  Diastase  is  evidently  fibrine  altered,  and  still  more  prone  to 
change.  Its  solution  cannot  be  kept,  it  becomes  acid,  and  loses  its  action  on 
starch. 

Malt  is  made  by  softening  b^ley  in  water,  and  then  exposing  it  to  the  air  in 
moderately  thick  layers,  at  a  moderate  temperature,  turning  it  frequently.  In 
about  four  days  the  seeds  germinate,  if  they  have  not  been  allowed  to  become 
too  hot,  and  if  the  air  has  had  free  access.  As  soon  as  the  germ  has  acquired 
the  length  of  the  seed,  the  operation  is  checked  by  drying  the  seeds  in  a  current 
of  warm  air.  They  now  constitute  malt.  In  this  operation,  much  carbonic  acid 
is  given  ofi*,  oxygen  being  no  doubt  absorbed ;  the  azotized  matter  in  the  seeds 
has  undergone  a  change,  and  has  acquired  the  properties  of  diastase ;  and  the 
starch  has  in  part  disappeared,  its  place  being  supplied  by  grape  sugar  and  dex- 
trine. 

When  the  malt  is  infused  in  warm  water,  the  metamorphosis  of  the  starch  is 
completed,  and  the  whole  dextrine  passes  into  sugar,  which  dissolves,  along 
with  extractive  matter  and  salts.  The  solution  is  called  must.  When  sufficiently 
concentrated  hops  and  yeast  are  added,  and  fermentation  being  carried  on,  the 
result  is  beer  or  ale,  according  to  the  strength  of  the  must.  When  the  malt  has 
been  in  part  roasted,  the  beer  becomes  very  dark-coloured,  as  in  the  case  of 
porter. 

To  obtain  grain  spirit,  the  meal,  either  of  barley,  oats,  or  rye,  or  a  mixture,  is 


PANIFICATION.  743 

digested  in  warm  water  along  with  1  part  of  malt  for  4  of  meal,  till  the  lyiass,  at 
first  thick,  becomes  fluid,  a  proof  that  all  the  starch  has  been  metamorphosed. 
Yeast  is  then  added,  and,  after  fermentation,  the  must  or  wort  as  it  is  called,-  is 
distilled  and  rectified.  Potato  spirit  is  obtained  in  the  same  way,  only  usin* 
potato  starch,  instead  of  barley  meal  or  rye  flour. 

Many  other  vegetable  matters,  and  many  fruits,  may  be  made  to  yield  spirit, 
malt  or  diastase  being  used  in  all  cases  where  starch  is  to  be  converted  into  sugar. 

Potato  spirit  is  accompanied  by  the  hydrated  oxide  of  amyle,  or  oil  of  potato 
spirit ;  grain  spirit  by  an  oily  matter,  consisting  chiefly  of  margaric  and  cenanthic 
acids,  probably  in  part  as  margaic  and  cenanthic  ether,  and  of  a  volatile  oil,  called 
by  Mulder  oleum  siticum,  that  is,  oil  of  grain.  Wine  spirit,  that  is,  Irandy,  con- 
tains cenanthic  ether,  and  the  spirit  of  molasses,  or  rum,  owes  its  flavour  to  bu- 
tyric ether.  The  oils  which  contaminate  potato  and  grain  spirit  are  offensive 
and  even  injurious  to  health;  they  are  included  by  the  Germans  under  the  gen- 
eral term  faseleol, 

Fanijication.  Bread  may  be  made  from  any  flour  containing,  as  all  good  flour 
does,  vegetable  fibrine,  sugar,  and  starch.  The  flour  being  made  into  a  paste 
with  warm  water,  and  yeast  being  added,  it  is  set  aside  in  a  warm  place.  After 
a  time,  more  flour  is  kneaded  into  the  mass,  which  has  begun  to  rise,  and  the 
whole  is  now  heated  in  the  oven,  or  baked.  The  yeast  induces  the  vinous  fer- 
mentation in  the  sugar  of  the  flour,  and  the  alcohol  and  carbonic  acid  escaping, 
raise  the  bread  and  render  it  porous.  The  starch  in  general  is  little  changed,  but 
the  sugar  disappears,  as  well  as  a  part  of  the  gluten  or  fibrine.  To  avoid  this 
loss,  bread  is  now  raised  by  means  of  carbonate  of  soda  or  ammonia  and  a  diluted 
acid,  which  are  added  to  the  dough,  and  the  effect  is  perfectly  satisfactory. . 
Equally  good  or  better  bread  is  obtained,  and  the  quantity  of  flour  which  will 
yield  1500  loaves  by  fermentation,  furnishes  1600  by  the  new  method,  the  sugar 
and  fibrine  being  saved.  The  addition  of  a  little  alum  to  the  dough  is  useful  in 
arresting  that  decomposition  in  the  flour  which  is  apt  to  occur  if  it  have  been 
kept  in  a  moist  place.  Too  much  alum  cannot  be  introduced,  as  it  would  pre- 
vent the  fermentation. 

The  nutritive  properties  (using  the  word  in  its  strict  sense)  of  diflferent  kinds 
of  flour  or  meal  is  directly  proportional  to  the  fibrine  or  albumen  they  contain; 
because  it  is  these  substances  alone  which  can  be  converted  into  blood  or  flesh. 
Hence  a  working  man  requires  more  oat  bread  than  wheat  bread  to  restore  the 
daily  waste  of  the  body,  oatmeal  containing  much  less  fibrine  &c.  than  wheat 
flour.  The  starch  is  consumed  in  the  body,  up  to  a  certain  point,  but  beyond 
this  it  is  discharged  in  the  excrements.  We  shall  see  hereafter  what  its  func- 
tion probably  is.  Even  the  best  wheat  flour  contains  more  starch  than  is  con- 
sumed ;  and  the  excess  is  greater  in  other  grains. 

In  germination,  the  azotized  principles  of  the  seeds  become  soluble  and  prone 
to  further  change.  When  now  dissolved,  they  are  in  the  same  state  as  those  of 
the  grape  juice  which  at  once  cause  fermentation  when  air  is  admitted.  Diastase 
is  merely  gluten,  that  is,  fibrine,  in  this  soluble  form  or  period  of  change. 

When  left  in  water,  gluten  swells,  putrefies  and  disengages  carbonic  acid, 
hydrogen,  and  sulphuretted  hydrogen  gases  :  it  then  becomes  fluid  and  ropy,  the 
water  becomes  very  acid,  and  contains  a  peculiar  compound  called  caseous  oxide, 
with  acetate,  phosphate,  and  caseate  of  ammonia.     When  vegetable  caseine  pu- 


744  FERMENT.— ANIMAL  ALBUMEN. 

trefies,  it  gives  out  the  odour  of  putrid  cheese,  and  yields  sulphuretted  hydrogen 
gas. 

Ferment,  Yeast,  Lees  of  Wine.  These  are  names  given  to  the  deposit  formed 
in  fermenting  liquids,  which  possess  the  property  of  exciting  fermentation  in 
must,  wort,  grape  juice,  infusion  of  malt,  or  solution  of  sugar.  When  solution 
of  sugar  is  employed  in  excess,  the  ferment  gradually  diminishes,  till  about  15 
per  cent,  are  left,  of  a  substance  containing  no  nitrogen,  and  insoluble.  This  is 
cellulose,  or  hordeine.  On  the  other  hand,  in  grape  juice,  or  infusion  of  malt, 
the  ferment  is  reproduced  from  the  azotized  principles  present. 

Mulder  and  Schlossberger  have  shown  that  ferment  is  composed  of  regular 
cells,  formed  of  cellulose,  and  containing  an  azotized  matter,  very  easily  decom- 
posed, which  is  a  proteine  compound.  This  body  rapidly  decomposes  the  deut- 
oxide  and  persulphuret  of  hydrogen,  but  loses  this  property  after  it  has  been 
heated  to  212°.     Mulder  thinks  that,  after  boiling,  it  is  a  superoxide  of  proteine. 

The  power  of  yeast  or  ferment  to  act  on  sugar  is  destroyed  by  boiling  water, 
by  absolute  alcohol,  by  pyroligneous  acid,  salts  of  mercury,  essential  oils,  sul- 
phurous acid,  &c. 

Caseous  Oxide,  Caseic  Acid,  or  Jposepidine,  are  names  given  to  the  crystalline 
compound  formed  during  the  putrefaction  of  gluten  under  water.  It  contains 
nitrogen,  but  its  formula  is  unknown.  It  is  soluble  in  water,  insoluble  in  alcohol. 

We  now  proceed  to  the  consideration  of  the  parallel  compounds,  animal  albu- 
men, Jibrine,  and  caseine. 

5.  Animal  Albumen  is  hardly  known  in  a  state  of  purity.  The  purest  appears 
to  be  that  prepared  by  exactly  neutralizing  serum  of  blood  or  white  of  egg  with 
acetic  acid,  and  adding  a  large  quantity  of  water.  The  albumen  separates  in 
translucent  flocculent  masses,  which,  when  washed  with  water,  assume  the 
aspect  of  paste.  (Denis.)  Albumen  is  best  known  in  the  form  of  the  serum  of 
the  blood  and  that  of  white  of  egg. 

Serum  of  blood,  dried  in  a  very  gentle  heat,  leaves  a  translucent  mass,  which 
dissolves  completely  by  digestion  with  water.  Both  in  this  form,  and  in  the 
preceding,  it  dissolves  far  more  easily  in  the  most  diluted  alkaline  solutions. 

White  of  egg  consists  of  very  delicate  cells,  filled  with  a  ropy  liquid.  By 
beating  with  water,  the  cells  are  broken,  and  are  afterwards  deposited,  being 
insoluble.  Dried  at  a  gentle  heat  white  of  egg  is  yellow,  translucent,  and 
brittle.  In  water  it  again  softens  into  its  original  state.  When  calcined,  it 
leaves  6  or  7  per  cent,  of  salts,  common  salt,  carbonate,  phosphate,  and  sulphate 
of  soda,  and  phosphate  of  lime. 

The  action  of  heat  on  albumen  is  remarkable.  When  heated  alone,  or  after 
dilution  with  water,  to  between  145°  and  165°,  it  coagulates  into  the  well-known 
white  elastic  mass,  which,  when  dried,  becomes  yellow,  horny,  and  brittle.  It 
is  now  quite  insoluble  in  water ;  but  if,  after  being  coagulated  and  dried,  it  is 
placed  in  water,  it  swells  up  into  the  original  elastic  mass  of  coagulated  albu- 
men. 

The  albumen  prepared  by  the  process  of  Denis  dissolves  readily  not  only  in 
acids  and  alkalies,  but  also  in  neutral  salts,  such  as  nitrate  or  sulphate  of  potassa 
or  soda.    It  is  owing  to  the  presence  of  such  salts  in  serum  or  white  of  egg  that 


ANIMAL  CASEINE.— MILK.  745 

their  albumen  is  soluble  in  water.  When  the  pure  albumen  of  Denis  is  dissolved 
in  solution  of  nitre,  it  is  coagulated  by  boiling  exactly  like  serum. 

Solutions  of  albumen  are  coagulated  by  acids ;  the  addition  of  free  alkalies 
prevents  even  the  action  of  heat.  Serum  and  white  of  egg,  when  mixed  with 
water,  being  both  alkaline,  may  be  neutralized  carefully  by  acids,  without  coagu- 
lation. Acid  solutions  of  albumen  are  precipitated  by  corrosive  sublimate  and 
ferrocyanide  of  potassium,  by  infusion  of  galls,  by  creosote,  and  by  alcohol. 
The  real  difference  between  soluble  and  insoluble  or  coagulated  albumen  is  not 
yet  known. 

When  albumen  putrefies,  it  yields  sulphuret  of  ammonium,  sulphuretted  hy- 
drogen, and  other  products.  When  heated,  it  burns  with  the  odour  of  burnt  horn 
or  animal  matter. 

6.  Animal  Fihrine  is  found  in  blood,  chyle,  and  lymph  dissolved,  and  forms 
the  chief  part  of  the  muscles.  It  may  be  obtained  by  whipping  up  blood  with 
rods,  when  it  adheres  to  the  rods,  and  is  finally  purified  by  kneading  with  water 
to  remove  colouring  matter,  and  by  digestion  with  alcohol  and  ether,  which  dis- 
solve fatty  substances.  When  dry  it  is  somewhat  similar  to  albumen,  and  when 
heated  burns  with  the  same  smell,  leaving  from  0*77  to  2*55  per  cent,  of  ashes, 
phosphates  of  lime  and  magnesia.  Recent  fibrine  loses,  in  vacuo,  about  80  per 
cent,  of  water,  the  greater  part  of  which  it  again  takes  up  when  placed  in  water. 
When  long  boiled  with  water,  it  slowly  dissolves ;  and  when  left  long,  that  is, 
for  some  months,  under  water,  it  gradually  disappears. 

The  fibrine  of  venous  blood  dissolves,  at  a  gentle  heat,  in  solutions  of  acetate 
of  soda,  sal-ammoniac,  and  nitre.  These  solutions  are  coagulated  by  heat,  and 
exhibit  the  properties  of  dissolved  albumen.  Muscular  fibrine  may  also  be  thus 
dissolved  ;  but  neither  arterial  fibrine,  nor  the  fibrine  of  the  huffy  coat,  can  undergo 
this  change.  Venous  fibrine  loses  this  property  by  exposure  to  the  air,  when  it 
absorbs  oxygen  and  gives  off  carbonic  acid.  Fresh  fibrine  rapidly  decomposes 
deutoxide  of  hydrogen :  but  boiling  water  or  alcohol  deprive  it  of  this  property. 

The  most  striking  character  of  fibrine  is  its  spontaneous  coagulation,  as  in  the 
blood  ;  which  is  also  seen  in  vegetable  fibrine  in  some  juices.  In  regard  to 
acids  and  alkalies,  fibrine  acts  like  albumen. 

7.  Animal  Caseine  is  chiefly  found  in  milk.  It  is  not  known  in  a  state  of 
purity,  but  only  combined  with  bases  or  acids,  for  both  of  which  it  has  a  power- 
ful attraction.  Uncombined  caseine  is  insoluble :  in  milk  it  is  dissolved  by 
virtue  of  the  potassa  which  renders  that  fluid  alkaline.  If  carefully  neutralized 
by  an  acid,  milk  is  not  coagulated,  but  it  is  then  coagulated  by  boiling.  The 
coagulum  or  curd  formed  by  excess  of  acids  is  very  soluble  in  oxalic  and  tartaric 
acids,  sparingly  so  in  the  mineral  acids.  This  coagulum  contains,  along  with 
caseine,  a  good  deal  of  the  acid  employed. 

The  coagulum  caused  in  milk  by  alcohol  yields,  when  burned,  10  per  cent,  of 
ashes,  chiefly  phosphate  of  lime.  What  is  called  soluble  caseine  is  a  compound 
containing  much  potassa.  With  lime,  baryta,  &c.,  caseine  forms  insoluble 
compounds. 

Milk,  ar  any  other  solution  of  caseine,  when  evaporated  in  the  air,  forms  a 
pellicle,  which  is  renewed  as  fast  as  it  is  removed.  This  is  insoluble,  and 
yields  ashes  containing  lime  and  phosphate  of  lime. 

Milk  may  be  analyzed  by  drying  it  up  in  vacuo,  dissolving  the  butter  by  a 
mixture  of  ether  and  alcohol,  and  the  sugar  of  milk  and  salts  by  cold  water.  The 
caseine  remains  in  this  way  undissolved,  the  salts  having  been  first  removed. 


746  COMPOSITION  OF  MILK.— CHEESE. 

When  exposed  to  the  air,  milk  undergoes  a  peculiar  change.  The  caseine 
enters  into  decomposition,  and  this  decomposition  passes  to  the  sugar  of  milk, 
which  yields  a  little  lactic  acid,  and  this  causes  the  caseine  not  yet  decomposed 
to  coagulate.  But  the  decomposition  continues :  the  sugar  of  milk  is  at  last 
entirely  converted  into  lactic  acid,  mannite  and  gum ;  and  if  the  acid  be  neutra- 
lized, and  fresh  sugar  added,  it  will  undergo  the  same  change  as  long  as  any 
caseine  remains.  This  is  the  method  followed  for  obtaining  lactic  and  lactates. 
The  coagulum,  separated  from  the  whey  when  first  formed,  and  pressed  out, 
forms  cheese.  In  making  the  better  kinds  of  cheese,  the  milk,  instead  of  being 
allowed  to  coagulate  spontaneously,  is  coagulated  by  contact  with  water  in 
which  part  of  the  lining  membrane  of  a  stomach  has  been  infused.  This  infusion 
is  called  rennet,  and  it  acts  by  virtue  of  containing  albumen  or  gelatine  in  a 
state  of  decomposition,  which  is  at  once  communicated  to  the  sugar. 

When  milk,  spontaneously  coagulated,  is  exposed  to  a  heat  of  from  75°  to 
85°,  without  any  addition,  the  sugar  of  milk  passes  into  grape  sugar,  and  vinous 
fermentation  ensues.  The  fermented  milk,  distilled,  yields  a  spirit  containing 
traces  of  butyric  ether. 

If  sugar  is  made  to  ferment  with  caseine  at  about  100°,  carbonic  acid  and 
hydrogen  gases  are  disengaged,  and  butyric  acid  is  formed  in  large  quantity. 

The  chief  mineral  substances  in  milk  are  potassa  and  phosphate  of  lime, 
which  are  found  in  its  ashes.  The  ashes  also  contain  sulphates,  although  milk 
does  not.  The  sulphuric  acid  in  the  ashes  is  derived  from  the  oxidation  of  the 
sulphur  of  the  caseine. 

The  proportions  of  water,  caseine,  sugar  of  milk,  butter,  and  salts,  are  very 
variable  in  milk.  It  generally  contains  about  86  per  cent,  of  water,  4  to  7  of 
caseine,  3*5  to  5*5  of  butter,  and  3  to  5*5  of  sugar  of  milk  and  salts.  For  the 
best  method  of  analyzing  milk,  proposed  by  Haidlen,  I  must  refer  to  the  "An- 
nalen  per  Chemie  und  Pharmacie,  xlv.,  274."  By  this  method  Haidlen  ob- 
tained as  follows : — 

From  Cow's  Milk.  Human  Milk.  Do. 

Butter        . 3                3-4  1-3 

Sugarofmilk,  and  salts  sohible  in  alcohol        .        .        4-6             43  3-2 

Caseine  and  insoluble  salts 5-1              3-1  2-7 

Water 87-3           89-2  92-8 

100-0  100-0  100  0 

The  colostrum,  or  milk  given  immediately  after  parturition,  differs  from  normal 
milk  in  containing  15  to  25  per  cent,  of  albumen,  with  less  caseine,  butter,  and 
sugar  of  milk. 

The  milk  of  bitches,  according  to  Simon,  contains  from  14*6  to  17*4  of 
caseine,  16-2  to  13-3  of  butter,  and  no  sugar. 

Cheese  is  caseine  in  a  state  of  incipient  or  progressive  decomposition  or  putre- 
faction. In  the  finer  kinds  of  cheese,  there  is  a  large  proportion  of  butter,  and 
to  the  volatile  acids  of  the  butter  may  be  ascribed  the  flavour  of  cheese.  Some 
kinds  of  cheese  are  full  of  what  are  called  eyes,  that  is,  hollows,  caused  by  the 
formation  of  bubbles  of  gas ;  and  in  these  hollows  a  liquid  is  sometimes  found, 
containing  free  ammonia,  a  product  of  decomposition,  which  greatly  heightens 
the  flavour.    When  the  blue  mould  appears  in  cheese,  it  is  in  a  state  of  rapid 


COMPOSITION  OF  THE  PRECEDING  SUBSTANCES.  74X 

decay  or  eremacausis,  and  much  ammonia  is  given  off.  Little  is  yet  known  of 
the  chemical  differences  in  the  making  of  different  kinds  of  cheese.  The  richest 
are  made  almost  entirely  from  cream,  as  Stilton  and  Pe^mesan.  Others,  as 
Gruyere,  Gloucester,  Cheshire,  and  Dutch  cheese,  are  made  with  fresh  un- 
creamed  milk,  or  mixtures  of  this  with  cream ;  and  more  or  less  salt  is  used,  as 
well  as  diflferent  methods  of  coagulating,  in  different  places. 

Animal  Mucus  is  somewhat  analogous  to  albumen,  when  dry.  In  water,  it 
softens  and  swells,  like  tragacanth.  It  is  precipitated  by  picric  acid.  It  con- 
tains sulphur. 

8.  Horny  Matter.  This  name  may  be  given  to  the  substance  of  which  the 
epidermis,  hair,  wool,  silk,  feathers,  nails,  claws,  hoofs,  horns,  shell,  and  pro- 
bably also  sponge,  are  composed.  All  these  substances  dissolve  in  potash-ley 
when  heated  with  it,  giving  off  ammonia,  and  forming  a  solution  from  which,  by 
neutralization  with  acetic  acid,  a  white  gelatinous  matter  is  precipitated.  (See 
Proteine.)  They  all  contain  sulphur.  Sponge  leaves  31  per  cent,  of  ashes, 
among  which  is  found  iodide  of  potassium.  All  the  above  substances,  when 
heated  or  burned,  give  out  the  same  peculiar  and  well-known  smell,  known  as 
that  of  burnt  feathers. 

COMPOSITION  OF  THE  PRECEDING  SUBSTANCES. 

According  to  the  researches  of  Mulder,  Liebig,  Dumas,  and  many  other  che- 
mists, vegetable  albumen,  fibrine,  and  caseine,  have  all  the  same,  or  very  nearly  the 
same,  composition,  as  far  as  concerns  the  carbon,  hydrogen,  nitrogen,  and  oxy- 
gen, including  under  oxygen  the  sulphur  and  phosphorus,  which  occur  in  small 
proportion.    Thus  we  have,  in  vegetable 

Albumen.  Caseine.  Fibrine. 

Carbon 54-74  54-14  54  095 

Hydrogen 777  7-16  7-308 

Nitrogen       .                ....        15-85  15-67  15-659 

Oxygen  and  sulphur,  &c.     .        .        .        21-64  22-03  22-938 

100-00  100-00  100-000 

The  above  are  analyses,  taken  at  random  from  a  number  by  different  observers. 
Gluten,  as  being  formed  chiefly  of  fibrine  and  a  modified  albumen,  has  the  same 
composition. 

We  find,  further,  that  animal  albumen,  fibrine  and  caseine,  agree  in  composi- 
tion.   Thus  we  find,  in  animal 

Albumen.  Caseine.  Fibrine. 

Carbon 54-803 

Hydrogen 7-021 

Nitrogen 15-677 

Oxygen  and  sulphur,  &c.      .        .        .        22-499 


54-668 

54-443 

7-302 

6-997 

15-683 

15-824 

22-347 

22-726 

/ 


100000  100-000  100-000 


The  composition  of  horny  matter,  of  mucus,  of  the  inner  coat  of  arteries,  &c., 
is  analogous  to  the  above,  but  not  identical  with  it. 


748  PROTEINE.— ITS  COMPOSITION. 

PROTEINE. 

The  remarkable  similarity  in  composition  of  all  the  truly  nutritive  substances, 
whatever  their  origin,  is  not  confined  to  the  proportions  of  the  elements  in  100 
parts,  but  appears  also  to  belong  to  their  intimate  constitution.  Thus,  when 
their  solution  in  potassa,  boiled  until  the  whole  sulphur  is  removed,  is  neutra- 
lized with  acetic  acid,  there  is  formed  from  every  one  of  the  preceding,  a  gelatin- 
ous precipitate,  which  contains  neither  sulphur,  phosphorus,  nor  salts,  and 
which  Mulder  calls  Proteine,  as  being,  in  his  opinion,  the  first  or  leading  com- 
pound, from  which  all  the  others  are  derived. 

Proteine  is  very  soluble  in  acetic  and  phosphoric  acids  of  any  degree  of  con- 
centration ;  it  dissolves  in  hot  and  strong  hydrochloric  acid  with  a  deep  blue  or 
purple  colour,  which  changes  to  black  on  boiling.  The  composition  of  proteine 
is  as  follows: 

Carbon 54-848 

Hydrogen 6-959 

Nitrogen 15-847 

Oxygen 22-346 


100-000 


That  is  to  say,  exactly  the  same  as  the  organic  part  of  albumen,  &c.  It  is  evi- 
dent, therefore,  that  we  may  consider  albumen,  fibrine,  and  caseine,  both  animal 
and  vegetable,  as  formed  of  proteine,  along  with  alkaline  and  earthy  salts,  dif- 
ferent in  each  case,  and  also  along  with  a  little  sulphur  and  phosphorus,  or,  as 
in  caseine,  sulphur  without  phosphorus.  We  are  not  entitled  to  say  that  these 
bodies  are  actually  compounds  of  proteine  with  salts,  sulphur,  &c.,  for,  in  truth, 
proteine  is  rather  a  product  of  decomposition  than  a  compound  pre-existing.  But 
there  is  an  advantage  to  the  memory  in  taking  the  above  view  ;  and,  besides, 
it  is  certain  that  albumen,  &c.,  all  agree  so  closely  in  constitution,  as  to  yield 
the  same  product  of  decomposition. 

When  boiled  with  potassa,  proteine  gives  rise  to  three  new  products ;  eryihro- 
protide,  leucine^  and  protide. 

Mulder  deduces  from  the  analysis  of  proteine  the  formula  CJ^^Hg^N^Oj^;  Lie- 
big  prefers  that  of  ^^^^^q^^^i  which  agrees  as  well  with  the  results  of  analysis, 
and  throws  more  light  on  certain  transformations  which  occur  in  the  body.  Both 
formulae  are  to  be  considered  as  tentative  only. 

Mulder  obtained  by  long  boiling  of  fibrine  with  water,  a  substance  which  ap- 
peared to  be  a  binozide  of  proteine,  =^4o^3i^«^i4'  '^^^  same  substance  was 
found  by  him  in  the  buflfy  coat  of  blood  in  inflammatory  diseases  ;  and  was  also 
obtained  along  with  proteine  by  Van  Laer  among  the  products  of  the  action  of 
boiling  diluted  potassa  on  hair. 

When  fibrine  and  albumen  are  long  boiled  with  water  they  yield,  according  to 
Mulder,  a  teroxtde  of  proteine^  ^40^31^5^15* 

By  the  action  of  chlorine  on  solutions  of  the  proteine  compounds  there  is' 
formed  a  substance  in  white  flocculent  particles,  nearly  insoluble.  This  is  chlo- 
roproteic  acid,-  and  its  formula  is  ^40^31^5^  12+ ^^3*     (Mulder.) 

Leucine  crystallizes  in  brilliant  white  scales,  very  soluble  in  hot  water  and 
alcohol,  also  in  ether.  With  nitric  acid  it  forms  nitroleucic  acid.  This  acid 
crystallizes  in  needles.  The  composition  of  these  products  is  not  fully  ascer- 
tained. 


ACTION  OF  ACIDS  ON  PROTEINE  COMPOUNDS.  749 

According  to  Mulder,  eryihroprotide  is,  C^^HgNO^,  and  protide,  C^^HgNO^, 
ACTION  OF  ACIDS  ON  PROTEINE  COMPOUNDS. 

When  moist  fibrine  is  placed  in  water  acidulated  with  jjoVu  ^^  hydrochloric 
acid,  it  swells  up  to  a  jelly  which  finally  dissolves,  all  except  a  few  flocculi,  to 
which  Bouchardat  gives  the  name  of  Epidermose,  Albumen  and  vegetable  fibrine 
undergo  a  similar  change.  Bouchardat  gives  to  the  dissolved  matter  the  name 
of  albuminose  ,•  but  it  is  either  protein^,  or  binoxide  of  proteine.     (Mulder.) 

When  the  bufiy  coat  of  inflammatory  blood  is  boiled  with  water,  the  filtered 
liquid  on  cooling  forms  a  jelly.  This,  according  to  Mulder,  is  tritoxide  of  pro- 
teine, and  not  gelatine  as  supposed  by  Bouchardat. 

When  compounds  of  proteine  are  dissolved  with  the  aid  of  heat  in  strong  hy- 
drochloric acid,  they  yield  a  purple  solution,  which  becomes  black  on  exposure 
to  the  air.  It  then  contains  sal  ammoniac  and  humate  of  ammonia.  We  have, 
on  the  one  hand, 


Ill 


Proteine  .        C^gNeHggOi^  ^  ^  THumic  Acid  C48    H24O24 

Water  .  Hg  O^  | 

Oxygen  .  0.  °  I  Ammonia        .  N  H3 

Hydro-     )  [^J  Sal         ) 

chloric    >  H5  CI5    el's   Ammoniac  >  N5H20     CJ^ 

Acid       )  I  s  I  5  eq.      ) 


C^sNeH^^O^^Cls 


This  reaction  enables  us  to  see  how  proteine  might  be  formed  from  the  ele- 
ments of  sugar  and  ammonia,  water  and  oxygen  being  eliminated.  For,  abstract- 
ing from  the  hydrochloric  acid,  and  bearing  in  mind  that  humine  or  humic  acid, 
^48^24^24'  ^^  J^erely  sugar  minus  water,  grape  sugar  (dry)  being  Cj^H^^^j^?  ^^^ 
4  eq.  of  it  being  equal  to  C  H  O  ;  let  us  then  suppose  4  eq.  of  grape  sugar  to 
lose  half  the  water  they  contain,  leaving  this  variety  of  humic  acid,  and  to  take 
up  6  eq.  of  ammonia.  Let  us  further  pursue  the  process,  which  is  opposite  to 
that  above  explained,  and  subtract  4  eq.  oxygen  and  6  eq.  water,  and  proteine 
will  remain.  The  reader  will  observe  that  we  can  actually,  with  the  aid  of  hy- 
drochloric acid,  cause  proteine  to  take  up  oxygen  and  water,  and  to  produce  or 
be  resolved  into  ammonia  and  humic  acid,  and  that  this  humic  acid  only  differs 
from  sugar  by  the  elements  of  water.  So  that  we  may  expect  hereafter  to  reverse 
the  process  and  to  cause  sugar  or  humic  acid,  taking  up  ammonia  and  giving  oflf 
water  and  oxygen,  to  give  rise  to  proteine.  At  all  events  it  is  evident  that  pro- 
teine might  thus  be  derived  from  sugar  and  ammonia,  which  meet  in  plants;  and 
although  in  general  we  are  unable  artificially  to  produce  the  more  complex  sub- 
stances, and  can  only  decompose  or  resolve  them  into  less  complex  forms,  yet 
there  are,  even  now,  some  cases  in  which  more  complex  molecules  may  be  arti- 
ficially formed  by  the  coalescence  of  more  simple  ones ;  and  it  is  probably,  in 
these  very  circumstances,  that  the  vital  force  interferes  and  modifies  the  results. 
We  may  represent  as  follows  the  conceivable  change,  (the  converse  of  that  ac- 
tually observed,)  by  which  we  may  conceive  proteine  to  originate  from  sugar 
and  ammonia. 


C43    H^gOjg^  ^  Proteine 

"  >  =    <  Oxygen 
.        .  NgHja      )  J  Water 


Sugar        .        .        .        C43    H^gOja)  (Proteine        .        C43N6H3gO,4 

Ammonia 


^43^6^66048       C48N6H6604g 


750  GELATIGENOUS  TISSUES. 

The  action  of  nitric  acid  on  proteine  compounds  gives  rise  to  xantho-proteic 
acid,  an  orange-yellow  insoluble  mass,  not  crystalline.  Its  formula  is,  C  H^^^ 
N^0^2+2HO.     (Mulder). 

Muscular  fibrine,  in  contact  with  oil  of  vitriol,  becomes  gelatinous  and  dis- 
solves. This  solution,  mixed  with  2  vol.  of  water  and  boiled,  yields  sulphate 
of  ammonia,  leucine,  and  a  syrupy  substance  sweet  and  soluble  in  alcohol. 
Gelatine,  in  the  same  circumstances,  yields  sugar  of  gelatine,  and  a  fermentesci- 
ble  sugar,  probably  sugar  of  grapes. 

GELATIGENOUS  TISSUES. 

Under  this  head  we  place  several  tissues  which  yield  to  boiling  water  a  sub- 
stance which  on  cooling  forms  a  jelly,  or  may  be  called  gelatine.  They  are 
chiefly  found  in  the  cellular  membrane,  the  skin,  the  membranes  in  general,  the 
tendons,  ligaments,  bones,  cartilages,  &c. 

The  cellular  tissue  and  the  membranes  are  chiefly  formed  of  gelatinous  mat- 
ter, which  is  insoluble  in  cold  water  and  acids.  It  combines  with  salts,  as  cor- 
rosive sublimate,  persulphate  of  iron  and  alum,  forming  insoluble  compounds 
which  do  not  putrefy,  as  gelatine  itself  so  readily  does. 

The  gelatine  of  the  skin,  when  moist,  combines  with  tannic  acid,  if  steeped 
in  a  solution  of  that  acid,  and  is  converted  into  leather.  While  the  true  skin  is 
gelatinous,  the  epidermis  is  more  allied  to  horn. 

Chondrine  is  the  name  given  to  the  gelatine  of  the  cartilages. 

Gelatine  or  Glue  is  that  given  to  the  gelatine  of  the  bones  and  hoofs,  skins, 
&c.  of  animals.  Isinglass  is  made  from  the  air-bladder  of  fishes,  and  is  nearly 
pure  gelatine. 

1  part  of  pure  gelatine,  dissolved  in  100  of  hot  water,  forms  a  jelly  on  cool- 
ing.    A  solution  of  isinglass  is  completely  precipitated  by  infusion  of  nut^lls. 

Chondrine  and  gelatine,  in  solution,  are  distinguished  by  acids,  alum,  and 
salts  of  lead,  which  precipitate  chondrine  but  not  gelatine.  In  regard  to  other 
tests,  they  agree.    ^^Vo  °^  either  may  be  detected  by  tannic  acid. 

By  the  action  of  chlorine  on  gelatine,  there  is  formed  what  is  called  chlorite 
of  gelatine,  consisting,  according  to  Mulder,  of  chlorous  acid  and  gelatine. 

By  the  action  of  potassa,  gelatine  is  converted  into  sugar  of  gelatine,  or  into 
a  mixture  of  sugar  of  gelatine  and  leucine. 

Sugar  of  gelatine  crystallizes  in  prisms,  very  soluble  in  water,  and  very  sweet. 
With  nitric  acid  it  forms  an  acid,  nitrosaccharic  acid,  which  forms  white  trans- 
parent prisms,  fusible  and  very  soluble;  it  forms  salts,  which  for  the  most  part 
crystallize.  According  to  Mulder,  sugar  of  gelatine  is  ^^^PT=^fi^fig 
-|-2H0 ;  and  it  forms  with  metallic  oxides  compounds  of  the  formula  C  H  N 
O^+SMO.  Nitrosaccharic  acid  is  (CgH^N2N^4-2NOp4-4HO  ;  and  its  salts  are 
(C^H^N20^-+-2NO^)+2MO+2HO  or  (CgH^N^O^+2NOJ  +  3MO+HO.  But, 
according  to  Boussingault,  sugar  of  gelatine  is  CiQHjjjN^Oj^=CjgH  N^Oj^-j- 
3H0.  The  proportions  are  the  same  as  in  Mulder's  formula,  but  doubled,  and 
the  compound  is  supposed  to  contain  3  eq.  of  basic  water.  But  in  the  com- 
pounds of  the  sugar  with  bases,  these  3  eq.  of  water  are  replaced  by  4  of  oxide, 
giving  the  formula  CjgH^^N^0jj-i-4M0,  which  is  the  double  of  Mulder's  formula, 
plus  1  eq.  water. 

The  nitrosaccharic  acid  in  crystals,  according  to  Boussingault,  is  ^  gH^j^N^O^^ 
-t-4NO^+6HO=:CjgHj^N3033H-7HO.    When  dried  at  230°  it  is  O^^^^'Sp^^-f 


BONE.    THE  BILE.  751 

4H0,  and  its  salts  correspond,  being  as  follows,  CjgH^^Ng03^4-4MO.  If  we 
double  Mulder's  formula,  for  tbe  sake  of  comparison,  we  obtain  C^jgH^^NgO  + 
8H0  for  the  acid,  and  for  the  salts  CjgHj^Ng03^-t-4MO  +  4HO.  It  will  be 
seen  that  in  regard  to  the  nitrosaccharic  acid,  Boussingault's  formula  differs 
from  Mulder's  in  containing  1  eq.  of  water  less,  instead  of  more,  as  in  the  sugar 
of  gelatine. 

The  nitrosaccharates  crystallize  very  easily.  That  of  copper,  according  to  the 
very  recent  experiments  of  Verloren,  is  C^gHj^NgO^H-SHO+GCuO. 

Gelatine  does  not  yield  proteine  by  the  action  of  potassa,  and  therefore  does 
not  belong  to  the  series  of  the  proteine  compounds.  Liebig  adopts  for  gelatine 
the  formula  C^gH^^N^iO^g ;  and  for  chondrine,  C^gH^QNgO^Q.  The  arterial  mem- 
brane he  supposes  to  be  C^gH^gNgOj^.  The  latter  is  equal  to  proteine,  plus  2 
eq.  water;  and  chondrine  is  equal  to  proteine,  plus  4  eq.  water  and  2  eq.  oxygen. 
It  is  easy,  therefore,  to  see  that  gelatine  is  not  fitted  for  nutrition  of  the  body 
generally,  since  it  cannot  yield  blood,  which  is  only  formed  by  proteine  com- 
pounds. Gelatine  may  contribute,  however,  to  the  nutrition  or  supply  of  the 
gelatigenous  tissues. 

Bone.  The  Gelatine  and  other  animal  matters  in  healthy  bone  constitute  from 
37*5  to  44  per  cent.;  the  rest  is  earthy  matter.  In  rickets  and  mollities  ossium, 
the  cartilaginous  matter  amounts  to  from  63  or  70  to  80  per  cent.,  and  the  phos- 
phate of  lime  is  diminished  in  proportion,  not  exceeding,  in  some  cases,  12  or 
13  per  cent. 

The  proportions  of  gelatine  and  earthy  matter  vary  in  different  animal  species. 

The  earthy  ingredients  of  bone  are,  phosphate  of  lime,  carbonate  of  lime, 
fluoride  of  calcium,  phosphate  of  magnesia,  with  small  quantities  of  common  salt, 
soda,  &c. 

Bone  or  Ivor^  Black,  obtained  by  calcining  bones  in  retorts,  contains  all  the 
earthy  and  saline  matters,  with  a  large  proportion  of  charcoal  intimately  mixed 
with  them.     It  probably  contains  nitrogen.     Qu  1  as  paracyanogen  or  mellone  ? 

THE  BILE. 

This  animal  fluid,  collected  from  the  liver  in  the  gall-bladder,  is  slightly  alka- 
line, and  has  a  viscid,  oily  consistence.  It  has,  when  fresh,  a  golden  yellow 
colour  with  a  tinge  of  green,  and  becomes  darker  when  exposed  to  the  air.  Its 
taste  is  bitter  and  persistent,  with  a  sweetish  after-taste.  It  is  perfectly  miscible 
with  water,  and  its  aqueous  solution  froths  like  solution  of  soap. 

When  dried  in  the  vapour-bath,  bile  leaves  a  yellow  mass,  which  dissolves  in 
alcohol,  leaving  undissolved  a  little  mucus.  The  alcoholic  solution  is  deep  green, 
but  may  be  decolorised  either  by  animal  charcoal,  or  by  the  cautious  addition  of 
baryta,  which  forms  an  insoluble  compound  with  the  colouring  matter.  The 
decolorised  alcoholic  solution  of  bile|  still  contains  cholesterine,  which  is  sepa- 
rated by  adding  twice  its  volume  of  ether,  which  separates  the  bile  as  a  thick 
syrup,  retaining  the  cholesterine  dissolved.  The  bile,  if  now  dried  up  in  the 
vapour-bath,  leaves  a  transparent  solid  mass  like  gum  arable,  perfectly  soluble 
in  water  and  in  alcohol. 

The  solution  of  bile  is  precipitated  by  natural  acetate  of  lead,  but  the  liquid 
becomes  acid.  If  the  free  acid  be  neutralized,  acetate  of  lead  produces  a  fresh 
precipitate,  the  liquid  again  becoming  acid.    Tribasic  subacetate  of  lead  precipi- 


mt 


THE  BILE.    CHOLEIC  ACID. 


tates  at  once  the  whole  of  the  organic  matter  of  the  bile,  but  an  excess  of  the 
precipitant  is  apt  to  redissolve  a  part  of  the  precipitate,  which  is  also  soluble  in 
alcohol.      Mineral  acids  cause  a  resinoid  precipitate  in  solution  of  bile. 

Bile  in  solution  may  be  recognized  by  the  property  of  striking  a  purple  colour 
with  solution  of  sugar  and  sulphuric  acid. 

Purified  bile,  when  calcined,  leaves  a  white  ash,  composed  chiefly  of  carbonate 
of  soda,  with  traces  of  phosphate  of  soda  and  common  salt.  The  ash  amounts  to 
12  per  cent.,  of  which  upwards  of  11  consist  of  carbonate  of  soda. 

It  is,  therefore,  evident  that  bile  is  composed  of  soda  united  to  an  organic  com- 
pound, having  the  characters  of  an  acid,  although  a  feeble  one,  and  in  some  re- 
spects analogous  to  the  fatty  and  resinous  acids.  This  compound,  which  is  the 
whole  organic  or  combustible  part  of  rtie  bile,  is  called  choleic  or  bilic  acid,  and 
bile  is  the  choleate  of  soda. 

Choleic  acid  is  best  prepared  by  making  an  alcoholic  solution  of  8  parts  of 
pure  bile,  and  dissolving,  with  the  aid  of  heat,  in  this,  1  part  of  effloresced 
(monohydrated)  oxalic  acid.  The  oxalate  of  soda  separates  in  crystals.  The 
filtered  liquid,  diluted  with  a  little  water,  is  digested  with  carbonate  of  lead,  till 
all  oxalic  acid  is  removed.  Any  lead  that  may  be  dissolved  is  separated  by  sul- 
phuretted hydrogen,  and  the  filtered  solution  evaporated  in  the  water  heat. 
Choleic  acid  may  also  be  obtained  by  the  action  of  dry  hydrochloric  acid  gas  on 
a  solution  of  pure  bile  in  absolute  alcohol,  and  by  several  other  processes,  of 
which  one  may  be  noticed.  Pure  bile  is  precipitated  by  subacetate  of  lead,  and 
the  precipitate  brought  with  water  to  the  boiling  point.  Sulphuric  acid  is  now 
added,  drop  by  drop,  until  the  precipitate  has  lost  its  pec^iar  consistence.  The 
liquid  is  then  filtered,  and  any  dissolved  lead  separated  by  sulphuretted  hydro- 
gen. 

To  purify  choleic  acid  it  is  dissolved  in  a  very  small  quantity  of  alcohol,  and 
precipitated  by  ether,  which  retains  in  solution  fatty  matters.  The  probable 
formula  of  choleic  acid  is  C^fiJiO^=G^^^^^O^^,nO, 

When  dried  in  the  water-bath,  or  in  vacuo,  over  sulphuric  acid,  choleic  acid, 
if  prepared  from  decolorised  bile,  is  colourless,  or  nearly  so,  and  has  the  aspect  of 
gum.  It  is  resinous  and  friable  when  dry,  but  its  powder  attracts  moisture 
strongly,  and  becomes  agglomerated  together.  Its  solution  is  distinctly  acid  to 
test-paper.  The  addition  of  mineral  acids  causes  a  separation  of  choleic  acid  in 
oily  drops,  which  are  soluble  in  pure  water. 

Pure  choleic  acid,  when  heated  on  platinum  foil,  burns  with  flame,  leaving  a 
voluminous  coal  which  finally  burns  away  without  residue  of  ashes.  When 
choleic  acid  leaves  an  alkaline  ash,  it  is  because  it  contains  undecomposed  bile, 
choleate  of  soda ;  in  fact,  it  may  be  called  acid  choleate  of  soda,  a  substance 
which  has  been  described  as  a  distinct  ingredient  of  the  bile  by  several  chemists. 

Numerous  analyses  of  pure  bile  (deducting  the  ashes)  and  of  choleic  acid,  both 
prepared  in  many  diflferent  ways,  by  difi(erent  chemists,  as  Demargay,  Theyer 
and  Schlosser,  Kemp,  Enderlin  and  others,  agree  so  well  together  that  no  doubt 
can  be  entertained  in  regard  to  this  point,  that  the  bilic  or  choleic  acid  of  ox  bile 
is  a  substance  of  uniform  composition,  and  that  the  acid  in  bile  has  the  same 
composition  as  that  which  is  obtained  in  the  separate  state  by  the  processes 
above  given. 

Further,  if  the  choleate  of  lead,  purified  from  phosphate,  chloride,  &c.  of  lead 
by  solution  in  alcohol,  be  acted  on  by  carbonate  of  soda,  choleate  of  soda  (artifi- 


I 


DECOMPOSITION  OF  BILE.  753 

cial)  is  obtained ;  and  this  salt,  when  pure,  is  found  to  differ  in  no  one  respect 
from  pure  bile,  or  natural  choleate  of  soda,  and  is,  therefore,  regenerated  bile. 
Its  composition  is  the  same  as  that  of  bile. 

Choleate  of  soda  has  already  been  described  as  purified  bile. 

Acid  choleate  of  soda  has  been  at  different  times  known  as  biliary  matter,  and 
as  hilifellic  acid  with  excess  of  biline.  (Berzelius.)  But  the  biline  of  this  che- 
mist, and  also  his  sugar  of  bile,  are  nothing  more  nor  less  than  either  pure  bile 
or  choleic  acid.  Plainer  has  lately  obtained  the  acid  choleate  of  soda  crystal- 
lized, which  is  a  strong  additional  argument  in  favour  of  the  opinion  that  the 
bile  is  a  uniform  and  definite  compound  of  choleic  acid,  and  that  all  the  nume- 
rous compounds  described  by  Berzelius  and  others  as  constituents  of  bile,  are 
products  of  the  decomposition  of  choleic  acid.  This  is  a  consideration  of  the 
utmost  importance,  with  reference  to  the  production  of  bile  in  the  animal  body, 
to  its  functions,  and  in  short  to  chemical  physiology. 

Choleate  of  lead  (basic).  This  salt,  precipitated  by  subacetate  of  lead,  has  the 
characters  of  a  plaster,  as  choleate  of  soda  has  those  of  a  soap. 

PRODUCTS  OF  THE  DECOMPOSITION  OF  BILE. 

1.  Choloidic  acid.  This  acid  is  formed  by  the  action  of  hydrochloric  acid 
when  boiled  with  bile.  It  differs  from  choleic  acid  in  containing  no  nitrogen. 
Its  formula  is  C  H  O  .  Its  production  is  attended  with  the  formation  of  taw 
vine.  Choloidic  acid  is  resinous  or  rather  pitchy  in  aspect,  softened  by  the  heat 
of  boiling  water,  insoluble  in  water  and  ether,  soluble  in  alcohol.  Probable 
formula  C^H3„0„=C^H,,0,„,H0. 

2.  Taurine^  C^NH^Oj^.  This  substance  is  found  in  the  liquid  which  has 
deposited  the  choloidic  acid.  When  pure,  it  forms  large  prisms,  neutral,  with 
a  cooling  taste,  soluble  in  water.  It  contains  the  elements  of  binoxalate  of 
ammonia  and  of  water:  SCgOg+NH^O-f-SNO. 

[Professor  Redtenbacher  of  Vienna,  has  subjected  taurine  to  a  new  analysis,  and 
has  found  it  to  contain  26  per  cent,  of  sulphur.  This  remarkable  result  has  been 
quite  recently  confirmed  by  Professor  Gregory  ;  who  by  deflagrating  a  portion  of 
taurine  with  nitre,  dissolving  and  neutralizing  with  an  acid,  obtained  by  the  ad- 
dition of  nitrate  of  baryta  a  very  copious  precipitate  of  sulphate.] 

3.  Cholinic  acid.  This  is  another  non-azotized  acid,  formed  when  bile  is  acted 
on  by  fusion  with  caustic  alkalies,  which  disengage  the  nitrogen  as  ammonia. 
It  resembles  the  fatty  acids,  or  rather  the  resinous  acids.  It  forms  large  trans- 
parent tetrahedra,  soluble  in  alcohol  and  ether,  nearly  insoluble  in  water. 

4.  Byslisine.  This  is  the  name  given  by  Berzelius  to  a  compound  formed 
during  the  action  of  hydrochloric  acid  on  bile.  It  is  very  sparingly  soluble  in 
hot  alcohol.  (Hence  its  name,  from  Suj,  difficult,  and  ^ucrtj,  solution).  It  has  a 
resinous  aspect,  and  the  formula  C  H^gO^,  that  is,  choloidic  acid  minus  4  eq. 
water. 

The  fellic  acid  and  cholinic  acid  of  Berzelius  are  mixtures  of  some  of  the 
above,  or  of  other  products,  with  unaltered  choleic  acid.  They  do  not  exist 
ready-formed  in  bile,  according  to  Theyer  and  Schlosser. 

5.  Cholic  acid  (Gmelin).  This  is  an  acid,  containing  nitrogen,  formed  when 
choleate  of  lead  is  acted  on  by  acetic  acid.  It  forms  fine  needles  of  a  sweet 
and  pungent  taste,  very  soluble  in  alcohol  and  in  hot  water.  Its  formula  is 
unknown. 

50 


754  BILIARY  CONCRETIONS. 

6.  Cholanie  acid  is  a  resinoid  acid,  found  in  putrid  bile,  and  very  similar  to 
choloidic  acid,  if  not  identical  with  it. 

7.  Fellanic  acid  accompanies  the  preceding.  It  forms  transparent  prisms,  and 
may  possibly  be  cholinic  acid.  At  all  events,  it  is  not  established  as  a  distinct 
compound  ;  but  is  a  product,  probably  a  mixed  one,  of  some  of  the  changes  of 
80  complex  a  substance  as  choleic  acid. 

The  colouring  matter  of  the  bile  when  dry  is  reddish-brown,  but  dissolves  in 
potassa  with  a  yellow  colour,  becoming  greenish-brown  in  the  air.  Its  solution, 
mixed  with  excess  of  nitric  acid,  becomes  first  green,  then  blue,  violet,  red,  and 
finally  yellow.  The  same  changes  of  colour  are  seen  in  serum,  chyle,  or  urine 
charged  with  bile,  as  in  jaundice. 

COMPOSITION  OF  CHOLEIC  ACID. 

The  formula  of  choleic  acid  cannot  be  considered  as  ascertained  with  cer- 
tainty ;  but  the  most  recent  and  very  elaborate  researches  of  Theyer  and  Schlos- 
ser  have  led  these  chemists  to  adopt  the  formula  C^  H  NO„=C,  H,  N0,„-|- 

44      So  13  44      3o  12 

HO,  for  choleic  acid,  and  for  choleate  of  soda,  (bile)  C    H   NO   -|-NaO. 

When  fused  with  potassa,  choleic  acid  loses  1  eq.  ammonia  and  2  eq.  carbonic 
acid,  {=^C^Yifi^  and  leaves  C^H^O^.  This  is  hydrated  cholinic  acid,  or 
rather  C^fiJ)^-\-nO. 

When  boiled  with  hydrochloric  acid= 


f 


3  eq.  of  choleic  acid,  hydrated =C,32HiQgN3039 

take  up  13  eq.  water a=        H,3     Ojj 

In  all =C^H,2,N30« 

and  lose  3  eq.  taurine,  Z{Cfi^l<<Oy^       .        .        .        .        =  C^j  Hji  N3O3Q 

leaving  2  eq.  choloidic  acid,  SjCjoHjoO,,)      .        .        .        r=  C^^^^     O^ 

It  has  already  been  mentioned  that  1  eq.  choloidic  acid,  miniu  4  eq.  water,  is 
equal  to  C   H^O^,  which  is  the  formula  of  dy  sly  sine. 

BILIARY  CONCRETIONS. 

The  calculi  or  concretions  found  in  the  gall-bladder  are  generally  composed 
of  cholesterine,  with  more  or  less  colouring  matter.  Sometimes  the  cholesterine 
is  so  pure  that  alcohol  dissolves  it  entirely,  and  becomes  hardly  coloured ;  at 
other  times,  colouring  matter  alone  is  found.  The  former  case  occurs  in  the 
human  subject :  the  latter  generally  in  the  ox. 

Lithofellic  add  is  an  acid  found  constituting  the  mass  of  certain  concretions 
called  bezoar  orientale,  and  said  to  be  found  in  the  stomach  of  certain  antelopes  ; 
but  which  are,  no  doubt,  biliary  concretions. 

Lithofellic  acid  is  fusible,  gives  off  when  heated  a  fragrant  vapour,  and  has, 
when  cut  or  rubbed  in  the  concretion,  the  lustre  of  wax.  It  dissolves  in  hot 
alcohol,  and  forms  brilliant  six-sided  prisms,  insoluble  in  water.    Formula, 

^42^38^8  (^"^^"^  ^^^   ^^")  ^40^35^7'"^  (Wohlcr). 

Nitric  acid  converts  it  into  a  new  acid  containing  nitrogen.     Formula,  C^^ 

«28NO,,. 

When  distilled,  lithofellic  acid  loses  2  eq.  water,  and  yields  pyrolithofellic 
acid.  C^^H^^O,. 


GASTRIC  JUICE.  755 

BRAIN  AND  NERVOUS  MATTER. 

This  substance  consists  of  water  to  the  extent  of  about  80  per  cent. ;  of  albu- 
minous matter,  7  per  cent. ;  and  of  several  peculiar  fats,  among  which  are  choles- 
terine,  and  another  beautifully  crystalline  fat,  resembling  cholesterine,  but  dis- 
tinct from  it. 

Cerehric  Acid,  This  is  a  fatty  acid,  peculiar  to  the  nervous  matter.  It  is 
purified  by  means  of  ether,  which  removes  an  oily  matter,  and  by  crystallizap 
tion  in  hot  alcohol.  It  forms  white  granular  crystals,  slightly  soluble  in  water, 
especially  when  hot,  although  the  greater  part  is  not  dissolved  but  swells  up 
into  a  gelatinous  paste.  It  melts  when  heated,  and  when  burned  leaves  a  very 
acid  coal.  It  contains  both  nitrogen  and  phosphorus,  which  distinguishes  it 
from  the  ordinary  fat  acids.  Its  salts  are  very  insoluble  in  alcohol,  as  well  as 
in  water. 

Okophosphoric  Acid.  This  acid  is  dissolved,  in  combination  with  soda,  by  the 
ether  used  in  purifying  cerebric  acid;  but  it  is  hardly  known  in  a  state  of  purity, 
being  mixed  with  a  neutral  oil,  cerebroleine,  with  cholesterine,  and  with  cerebric 
acid,  in  small  quantity.  With  alkalies  it  forms  soaps,  exactly  similar  to  the 
salts  dissolved  from  brain  by  ether.  When  boiled  with  water  or  alcohol,  it  is 
resolved  into  cerebroleine  and  phosphoric'  acid.  Of  the  latter  it  yields  about  2 
per  cent. 

Cerebroleine  is  purified  by  cold  alcohol,  which  dissolves  the  oil,  leaving  un- 
dissolved all  cholesterine  and  cerebric  acid.  Its  composition  is  the  same  as  that 
of  the  oleine  of  human  fat. 

The  cholesterine  of  the  brain  appears  to  be  identical  with  that  of  bile.  The 
brain  also  contains  traces  of  oleic  and  margaric  acids.  When  it  putrefies,  the 
oleophosphoric  acid  disappears  entirely. 

The  most  important  point  in  the  chemical  history  af  the  brain  is  that  it  con- 
tains both  fat  and  albumen,  the  two  extremes  of  the  animal  products,  and  sub- 
stances (cerebric  and  oleophosphoric  acids)  of  a  composition  intermediate  be- 
tween that  of  albumen  and  that  of  fat.  These  bodies,  however,  appear  to  contain 
even  a  larger  proportion  of  phosphorus  than  albumen.  It  is  not  yet  known 
where  the  cerebric  and  oleophosphoric  acids  are  produced :  whether  in  or  by  a 
special  organ,  as  the  bile  is  by  the  liver ;  or  whether  in  the  circulation  generally. 
It  will  be  seen  hereafter  that  the  blood  does  contain  traces  of  cholesterine  and 
other  fatty  matters ;  and,  indeed,  as  the  blood  also  contains  bile,  it  may  be  sup- 
posed that  the  liver  does  not  form  the  bile  but  merely  separates  it  from  the  blood, 
it  having  been  previously  formed.  In  like  manner,  even  if  there  should  be  found 
an  organ  connected  with  the  formation  or  secretion  of  nervous  matter,  still  the 
function  of  that  organ  might  be  only  to  separate  cerebric  acid,  previously  formed, 
from  the  blood..  At  all  events,  we  cannot  doubt  that  the  very  remarkable  com- 
position of  the  acids  of  the  brain  has  an  important  relation  to  the  functions  of 
that  organ,  and  that  the  production  of  those  acids  forms  an  essential  part  of  the 
vital  process  going  on  in  the  body. 

GASTRIC  JUICE. 

This  juice,  as  extracted  from  the  stomach  of  executed  criminals,  is  colourless 
or  slightly  yellow,  turbid,  and  distinctly  acid.  It  contains  free  acetic  and  hydro- 
chloric acids  along  with  chlorides  of  potassium  and  sodium. 


^  SALIVA. 

The  property  of  dissolving  or  digesting  food  such  as  albumen,  fibrine,  caseine, 
&c.,  is  owing  in  part  to  the  presence  of  free  hydrochloric  acid,  and  in  part  to 
the^ presence  of  part  of  the  lining  membrane  of  the  stomach  dissolved,  and  in  a 
state  of  change.  The  gastric  juice  converts  into  chyme,  or  digests,  albumen, 
iibrine,  &c.,  out  of  the  body  as  well  as  in  it,  if  the  temperature  of  the  stomach 
be  kept  up ;  and  water  acidulated  with  a  trace  of  hydrochloric  acid,  and  after- 
-wards  left  for  24  hours  in  contact  with  the  lining  membrane  of  a  stomach,  ac- 
quires in  a  very  high  degree  the  solvent  power  of  the  gastric  juice.  Water  thus 
prepared,  dissolves  in  8  to  12  hours,  at  the  temperature  of  from  86°  to  104°,  hard- 
boiled  white  of  egg,  &c.,  which  requires  4  days  at  a  temperature  of  158°  to  176° 
to  be  dissolved  by  water  merely  acidulated  with  the  same  proportion  of  acid,  but 
not  placed  in  contact  with  the  stomach.  This  latter  fluid,  however,  dissolves 
meat  better  than  it  does  albumen,  because  the  meat  supplies  some  membranous 
matter  in  a  state  of  change,  by  which  the  solution  of  the  fibrine  is  finally  pro- 
daced. 

All  attempts  to  isolate  the  supposed  principle — pepstne  as  it  was  called,  which 
is  supposed  by  some  to  be  the  solvent  of  food  in  the  stomach — have  failed.  The 
gastric  juice  has  only  yielded  traces  of  animal  matter,  and  we  have  not  yet  any 
proof  that  its  solvent  action  depends  on  a  peculiar  compound,  and  is  not  rather 
the  effect  of  a  kind  of  fermentation  induced  in  the  food  by  contact  with  the  par- 
ticles of  the  dissolved  epithelium,  themselves  in  a  state  of  change,  and  conse- 
quently of  motion.  Indeed,  since  this  work  was  commenced,  the  existence  even 
of  free  hydrochloric  acid  in  the  gastric  juice  has  been  denied,  and  it  is  very 
doubtful  whether  any  free  acid,  such  as  lactic  or  formic  acid,  ever  exist  in  the 
gastric  juice  in  its  normal  state.  On  the  whole,  then,  taking  into  account  the 
facts  of  artificial  digestion,  it  appears  most  probable  that  digestion  is  a  process 
analogous  to  fermentation  in  the  conditions  under  which  it  takes  place,  namely, 
a  certain  temperature,  and  contact  with  azotized  matter  in  a  state  of  decomposi- 
tion ;  but  differing  from  the  usual  forms  of  fermentation  in  its  phenomena,  no  gas 
being  disengaged,  and  its  chief  result  heing  the  solution  of  an  originally  insolu- 
'ble  matter.        '-:,i9vaT/" 

SALIVA. 

Tlie  chief  use  of  the  saliva  is  to  assist  in  digestion,  whether  by  itself  contain- 
ing animal  matter  in  a  slate  of  change,  or  by  its  remarkable  power  of  inclosing 
and  retaining  bubbles  of  air,  the  oxygen  of  which  commences  the  change  neces- 
sary to  digestion,  on  coming  in  contact  with  the  food  or  the  stomach  and  gastric 
juice.  To  serve  this  purpose,  the  saliva  has  a  very  great  degree  of  viscidity,  so 
that  it  froths  up  easily,  and  the  froth  does  not  fall  readily.  It  is  alkaline,  and 
contains  hardly  more  than  1  or  2  per  cent,  of  solid  matter,  partly  mucus,  partly 
the  usual  salts,  partly  a  peculiar  soluble  matter,  ptyaline.  The  salts  of  the  saliva 
are  the  chlorides  of  potassium,  sodium,  and  calcium,  some  potassa,  and  soda, 
with  a  large  proportion  of  bone  earth.  It  appears  also  to  contain  a  trace  of  sul- 
phocyanide  of  potassium  :  at  least  it  reddens  with  persalts  of  iron ;  and  although 
acetates  do  this,  there  is  reason  to  ascribe  the  effect  here  to  sulphocyanides. 

The  pancreatic  juice  resembles  saliva,  but  appears  to  be  slightly  acid,  and 
.  contains  8  or  9  per  cent,  of  solid  matter,  including  ptyaline  and  a  matter  like 
caseine.  This  juice  is  added  to  the  chyme  in  its  passage  through  the  duode- 
num, along  with  the  bile  and  intestinal  mucus. 


757 


EXCREMENTS.    URINE. 


d^7 


The  chyme,  after  receiving  the  pancreatic  juice,  the  hile,  and  mucus,  passes 
along  the  intestine,  where  the  absorbents  or  lacteals  take  up  the  fluid  part,  leav- 
ing the  insoluble  portions.  The  chyle  or  absorbed  fluid  is  partly  conveyed  into 
the  abdominal  veins,  and  partly  made  to  pass  through  numerous  glands  (in  which 
process  it  loses  its  acid  reaction,  becoming  alkaline),  from  which  it  proceeds  to 
the  thoracic  duct,  and  is  then,  with  the  lymph,  poured  into  the  vena  cava  to  mix 
with  the  venous  blood. 

In  the  mean  time,  the  insoluble  parts  of  the  chyme  are  rejected,  and  accumu- 
late in  the  large  intestines,  various  gases  being  disengaged,  such  as  carbonic 
acid,  hydrogen,  carburetted  hydrogen,  nitrogen,  and  sulphuretted  hydrogen. 

The  solid  excrements  of  man  contain  very  little  matter  soluble  in  water,  and) 
consist  of  woody  fibre,  with  fatty,  resinous,  and  waxy  substances,  and  finally  the 
insoluble  salts  of  the  food,  namely,  phosphate  of  lime  and  magnesia,  with  traces 
of  soluble  salts,  and  some  silica. 

The  urine  of  man  contains  urea  and  uric  acid,  also  hippuric  acid,  and  other 
organic  compounds  very  imperfectly  known.  It  contains  also  phosphoric  acid, 
magnesia,  often  ammonia,  soda,  phosphate  of  soda,  common  salt,  sulphuric  acid 
or  sulphate  of  soda,  in  short,  the  soluble  salts  of  the  food,  along  with  sulphuric 
acid  formed  by  the  oxidation  of  the  sulphur  of  the  tissues.  The  addition  of  am- 
monia to  urine  causes  a  precipitate  of  phosphate  of  lime. 

Fresh  urine,  filtered  (to  separate  mucus)  into  a  perfectly  clean  vessel,  keeps 
unchanged  for  weeks  or  evftn  months  ;  but  if  in  contact  with  decomposing  animal 
matter,  the  urea  is  speedily  transformed,  by  putrefaction,  into  carbonate  of  am- 
monia, while  phosphate  of  lime  is  precipitated,  the  urine  becoming  strongly  al?? 
kaline.  uiuo 

The  urine  of  the  herbivora  contains  much  uric  acid,  also  hippuric  acid :  that 
of  the  carnivora  contains  more  urea,  and  is  strongly  acid  :  uric  acid  predominates 
very  greatly  in  the  urine  of  birds,  and  that  of  reptiles  is  nearly  pure  urate  of 
ammonia. 

When  benzoic  acid  is  administered  internally,  it  appears  in  the  urine  as  hip- 
puric acid,  which  latter  acid  is  generally  present  in  small  quantity  in  urine.  Th© 
acid  reaction  of  human  urine  is  not  owing  to  lactic  acid,  as  was  formerly  sup- 
posed, but  to  free  uric  acid  dissolved  by  the  phosphate  of  soda. 

The  salts  of  the  urine  and  of  the  excrements,  being  derived  directly  from  the 
food,  vary  according  to  its  nature,  the  soluble  inorganic  salts  of  the  food  being 
found  in  the  urine,  the  insoluble  salts  in  the  excrements.  Thus,  the  ashes  of 
the  food  of  the  carnivora  contain  no  carbonates,  but  are  rich  in  phosphates,  and 
such  also  is  the  case  with  the  salts  (or  ashes)  of  their  excreta,  liquid  or  solid. 
In  fact,  if  we  know  the  nature  and  composition  of  the  ashes  of  the  food,  we  can 
tell  at  once  the  salts  of  the  urine.  In  an  adult  animal,  the  quantity  of  salts 
excreted  is  precisely  equal  to  that  contained  in  the  ingesta,  and  therefore,  by 
altering  the  food  we  can  alter  at  pleasure  the  nature  of  the  salts  in  the  urine. 

As  an  example,  we  may  here  adduce  the  case  of  the  horse,  which  animal  con- 
sumes, in  his  food,  a  certain  quantity  of  mineral  substances,  derived  ultimately 
from  the  soil : — 

THE  HORSE. 


Consumes  of  Mineral  Substances, 

Excretes  of  Mineral  Substances, 

oz. 
In  15  lbs.  of  hay,      .     18-61) 
In  4-54  lbs.  of  oats,        2-46  S  21-49 
In  water      ....      0-42 ) 

oz. 

In  the  urine  .     .     .    3*51 )  „-  q« 
Inthefsces  .    .    .  18-36  J  ^^  ^^ 

7S8  URINARY  CALCULI. 

%i 

The  above  result  is  one  obtained  by  actual  and  very  careful  experiment,  and 
the  nature  of  the  salts  is  found  to  be  the  same,  as  indeed  must  obviously  be  the 
case,  as  long  as  the  animal  does  not  change  its  weight.  A  growing  animal  will 
retain  the  phosphates  in  part  to  aid  in  forming  bone,  and  an  old  or  wasting 
animal  will  give  out  more  salts  than  are  taken  in. 

It  is  obvious  that  analyses  of  urine  or  excrement  are  unnecessary  if  we  can 
examine  the  food;  and  that  in  general  they  must  be  useless,  since  we  can  never 
expect  the  same  result  twice,  unless  where  the  food  is  not  varied. 

Guanoy*  so  highly  prized  as  a  manure,  is  the  decayed  excrement  of  sea  fowls, 
which  was  originally,  like  that  of  reptiles,  and  indeed  also  of  birds  in  general, 
mixed  urine  and  faeces,  the  urine  being  solid  or  semisolid,  and  consisting  of  urate 
of  ammonia.  It  varies  much  in  the  proportions  of  its  ingredients,  both  because 
the  original  excrement  must  have  varied  according  to  the  food  of  the  birds  in 
different  places,  and  also  because  some  specimens  have  not  been  so  long  exposed 
to  air  and  moisture  as  others,  and  some  are  almost  fresh.  Thus  some  guano 
contains  upwards  of  30  per  cent,  of  uric  acid,  while  in  other  specimens  hardly  a 
trace  of  that  acid  is  left.  The  better  qualities  of  guano  contain  much  ammonia, 
partly  free  or  as  carbonate,  as  proved  by  its  odour,  partly  combined,  as  sal-am- 
moniac, oxalate,  urate,  and  phosphate  of  ammonia,  and  phosphate  of  ammonia 
and  magnesia.  They  also  contain  phosphate  of  soda  and  phosphate  of  lime,  the 
latter  being  derived  from  the  bones  of  the  fish  on  which  the  birds  fed.  There 
are  also  found  sulphate  of  potassa  and  soda,  and  oxalate  of  lime,  in  guano.  The 
remainder  is  water,  and  a  brown  matter  like  humus. 

It  is  easy  to  see  that  guano  must  act  chiefly  as  a  source  of  ammonia  and  of 
earthy  and  alkaline  phosphates,  so  valuable  to  growing  plants,  especially  to  those 
cultivated  for  food ;  and  that  its  value  depends  very  much  on  the  amount  of 
phosphates  it  contains.  But  while  the  value  of  guano  is  unquestionable,  let  us 
not  overlook  the  fact,  that  while  we  are  ransacking  the  most  remote  islands  for 
guano,  that  substance  supplies  us  with  nothing  but  the  mineral  salts  and  the 
ammonia  which  have  formed  crops  of  vegetables  and  races  of  animals  at  some 
former  period,  and  that  it  differs  in  no  essential  point  from  the  fresh  or  modern 
excreta  of  man  and  animals  nearer  home,  which  excreta,  at  least  those  of  man, 
the  most  valuable  of  all,  we  allow  to  be  carried  into  the  sea  in  quantities  which 
may  be  measured  by  the  food  we  consume.  In  fact  we  take  out  of  the  sea,  in 
the  shape  of  guano,  only  part  of  what  we  throw  into  it  in  the  contents  of  our 
common  sewers.  These  valuable  matters,  instead  of  being  carefully  collected 
and  preserved,  as  in  China,  are  sent  to  form  the  food  of  sea  plants :  on  these 
plants  animals  feed,  which  animals  serve  as  food  to  fish.  The  fish  are  consumed 
by  sea  fowl,  and  we  recover  in  their  excrement  a  part  of  what  we  are  constantly 
throwing  away.  Another  part  of  what  we  lose  we  recover  in  this  country,  at  a 
great  expense,  in  the  shape  of  bone-earth,  which,  however,  must  be  taken  from 
other  countries.  We  shall  return  to  this  subject :  meanwhile,  let  us  express  a 
hope  that  Europe  will  at  length  follow  generally,  as  in  some  districts  it  has 
done,  the  rational  example  set  by  the  eminently  practical  Chinese,  of  restoring 
to  the  soil,  as  nearly  as  possible,  in  the  shape  of  excreta,  what  we  take  from  it 
in  our  crops  and  cattle,  and  thus  keeping  up  its  fertility. 

URINARY  CALCULI. 
These  are  of  various  kinds,  according  to  the  peculiar  condition  of  the  urine. 

*  Found  in  large  quantities  covering  the  surface  of  many  of  the  South  Sea  islands,  and 
alio  upou  the  southern  coast  of  Africa. 


LYMPH.    BLOOD.  759 

Uric  acid  calculus  is  the  most  frequent,  being  the  usual  deposit  when  the  urine 
is  acid.  Its  origin,  as  a  calculus  or  deposit,  that  is,  in  abnormal  quantity,  is 
owing  to  deficient  aeration,  much  oxygen  being  required  to  resolve  it  into  soluble 
compounds,  such  as  urea,  carbonate  of  ammonia,  or  even  oxalic  acid.  Hence 
sedentary  habits,  highly  carbonized  food,  and  indulgence  in  strong  wine,  all 
favour  its  production  :  the  first  by  diminishing  the  supply  of  oxygen,  the  two 
latter  causes  by  seizing  on  the  oxygen  to  the  exclusion  of  the  uric  acid.  It  is 
easily  recognized  by  the  action  of  potassa,  which  dissolves  it,  and  forms  a  solu- 
tion from  which  acids  precipitate  uric  acid :  or  by  nitric  acid,  which  dissolves  it 
with  eflfervescence,  and  yields  on  evaporation  of  the  solution  a  deep  red  stain, 
becoming  purple  with  potassa.  Uric  acid  calculus  is  commonly  tinged  more  or 
less  red  or  brown.     When  pure  it  is  entirely  dissipated  before  the  blowpipe. 

Urate  of  ammonia  also  occurs,  and  is  distinguished  from  uric  acid  by  disen- 
gaging ammonia  when  dissolved  in  potassa. 

Phosphate  of  lime  is  very  frequent  when  the  urine  is  neutral  or  alkaline.  It 
is  white  and  earthy,  soluble  in  nitric  acid,  and  precipitated  by  ammonia.  It  is 
fixed  in  the  fire. 

Phosphate  of  ammonia  and  magnesia  is  also  pretty  frequent.  It  dissolves 
easily  in  acetic  acid,  and  when  heated  gives  off  ammonia,  leaving  a  solid  mass 
soluble  in  acids. 

Fusible  calculus  is  a  mixture  of  the  two  preceding.  It  melts  readily  before 
the  blowpipe. 

Oxalate  of  lime  constitutes  the  mulberry  calculus,  and  often  appears  as  minute 
crystals  in  the  urine.  When  heated,  it  leaves  carbonate  of  lime;  or  if  heated 
in  a  tube  with  oil  of  vitriol,  it  gives  off  carbonic  oxide.  It  dissolves  in  acids, 
and  is  precipitated  by  alkalies. 

Oirbonate  of  lime  occasionally,  but  very  rarely,  constitutes  a  urinary  calculus, 
which  is  easily  recognized  by  the  action  of  hydrochloric  acid,  which  dissolves 
it  with  effervescence,  and  by  a  red  heat,  which  leaves  quicklime. 

Cystic  oxide  or  cystine,  and  xa/nthic  oxide,  are  very  rare  calculi.  Their  charac- 
ters and  composition  have  been  given  under  Uric  Acid, 

LYMPH. 

This  fluid  may  be  looked  on  as  blood  devoid  of  its  colouring  matter.  When 
drawn  from  the  vessels,  it  coagulates  like  blood,  from  the  separation  of  fibrine ; 
and  the  liquid  in  which  the  coagulum  has  formed  itself,  coagulates,  when  heated, 
like  the  serum  of  the  blood.  Human  lymph  contains  about  9Q  per  cent,  of 
water,  and  variable  proportions  of  albumen,  fibrine,  and  salts,  the  salts  amount- 
ing to  nearly  2  per  cent. 

BLOOD. 

This  important  fluid,  from  which  the  whole  animal  body  is-  formed,  and  by 
which  it  is  supplied  and  nourished,  is  a  thick,  somewhat  viscid,  liquid,  of  a 
slight  saline  taste,  and  a  peculiar  faint  odour.  It  is  deep  red  and  opaque,  and 
has  a  density  of  1-0527  to  1-057. 

It  is  made  up  of  an  immense  number  of  globules  or  flattened  disks,  floating  in 
a  limpid  yellowish  fluid.  When  drawn,  it  soon  coagulates,  forming  a  trembling 
jelly,  which  gradually  contracts,  expressing  a  yellowish  liquid,  the  serum,  which 
is  occasionally  turbid,  and  is  always  alkaline  to  test  paper,  and  saline  to  the 
taste. 


760  BLOOD  GLOBULES. 

The  coagulation  consists  in  the  separation  of  the  fibrine  previously  dissolved, 
which,  owing  to  some  unknown  cause,  assumes  the  insoluble  state,  forming  a 
fine  network  or  jelly,  in  which  the  globules  are  inclosed.  If  the  blood  be  beat 
with  a  rod,  the  fibrine  separates  perfectly  and  adheres  to  the  rod  ;  but  it  is  in 
the  form  of  white  filaments,  and  the  globules  remain  suspended  in  the  serum, 
no  jelly  whatever  being  formed  in  this  case.  Or  if  the  fresh  blood  be  mixed 
with  8  times  its  bulk  of  solution  of  sulphate  of  soda,  no  coagulum  is  formed, 
the  fibrine  remains  dissolved,  and  a  sediment  is  deposited  which  contains  the 
globules  unaltered. 

The  red  globules  thus  prepared  maybe  collected  in  a  filter.  Pure  water  added 
to  them,  or  to  the  coagulum  of  blood,  rapidly  alters  their  form,  and  in  fact  dis- 
solves them  into  an  opaque  liquid.  This  action  of  water  is  thus  explained : 
the  globules  are  formed  of  a  thin,  colourless,  and  transparent  coat,  inclosing  a 
very  soluble  colouring  matter.  They  float  in  a  saline  liquid,  in  which  there  is 
equlibrium  between  the  contents  of  the  globules  and  the  fluid  surrounding  them. 
But  when  the  latter  is  diluted  with  water,  the  equilibrium  is  disturbed,  and 
endosmosis  takes  place,  by  which  the  contents  of  the  globules  acquire  so  greatly 
increased  a  volume,  that  the  globules  burst  and  their  contents  are  dissolved  in 
the  water.  The  torn  membranes  of  the  globules  may  be  detected  by  the  micro- 
scope. 

In  saline  solutions,  the  globules  do  not  absorb  water  any  more  than  in  the 
serum.  When  collected  in  a  filter,  the  globules  form  a  red  mass  of  the  consist- 
ence of  honey,  consisting  of  fibrine  and  albumen,  the  latter  in  combination  with 
the  colouring  matter.  In  a  concentrated  solution  of  chloride  of  calcium,  the 
globules  lose  water  by  exosrnosis,  and  contract  in  volume.  If  now  placed  in 
pure  water,  the  globules  again  swell,  and  burst,  forming  a  jelly  which  dissolves 
in  water.  The  solution,  on  standing,  deposits  fibrine  in  white  membranous 
masses,  and  the  supernatant  liquid,  when  boiled,  is  coagulated,  indicating  the 
presence  of  albumen. 

The  colouring  matter  of  the  blood  is  contained  in  the  globules  in  combination 
with  albumen,  but  is  unknown  in  a  state  of  purity.  The  compound  of  albumen 
and  colouring  matter  is  of  a  deep-red  colour,  becoming  bright  in  contact  with 
air  or  oxygen,  and  being  rendered  nearly  black  by  carbonic  and  sulphurous  acids, 
sulphuretted  hydrogen  and  sulphurets.  Protoxide  of  nitrogen  gives  it  a  purple 
colour. 

The  red  compound  gives  2  per  cent,  of  ashes,  of  which  |  is  peroxide  of  iron ; 
and  iron  is  uniformly  present  in  red  blood,  which  is  the  only  animal  product  in 
which  it  occurs.  This  iron  cannot  be  detected  in  the  globules  or  their  contents 
by  the  usual  tests,  but  after  passing  chlorine  through  the  red  solution  till  the 
colour  is  destroyed,  the  iron  may  be  detected  by  ferrocyanide  of  potassium. 

When  the  red  compound  of  albumen  and  colouring  matter  above  mentioned  is 
moistened  with  oil  of  vitriol,  so  gradually  as  not  to  become  warm,  a  pasty  mass 
is  obtained,  which  attracts  moisture  from  the  air  and  forms  a  red  jelly.  If  -this 
be  very  gradually  rubbed  up  with  pure  water,  it  contracts  into  a  dark- red  matter, 
which  is  surrounded  with  a  colourless  or  yellowish  liquid.  This  liquid  is  found 
to  contain  all  the  iron,  and  the  dark  matter,  when  calcined,  leaves  a  white  ash, 
entirely  free  from  iron,  if  the  operation  has  been  well  performed.  I  have  repeated 
this  interesting  experiment,  first  devised,  I  believe,  by  Sanson,  which  proves 
that,  although  the  red  compound  contains  iron,  yet  the  colour  does  not  neces- 
sarily depend  on  that  metal ;  for  the  colour  is  altogether  uninjured  by  the  com- 


I 


NUTRITION  OF  PLANTS  AND  ANIMALS.  761 

plete  removal  of  the  iron  jast  described,  although  the  colouring  matter  actually 
obtained  in  this  experiment  is  not  the  original  colouring  matter  of  the  blood,  but 
modified. 

The  Hemaiosine  of  Lecanu  is  also  a  product  of  decomposition.  It  is  prepared 
by  means  of  diluted  sulphuric  acid,  alcohol,  and  ammonia,  by  a  tedious  process. 
It  is  dark-brown,  and  forms  red  solutions  with  the  alkalies,  being  insoluble  in 
water,  alcohol,  and  ether.  It  contains  part  of  the  iron  of  the  blood,  but  as  some 
kinds  of  hematosine  contain  ^  or  -3  more  iron  than  others,  while  its  properties 
continue  the  same,  it  is  obvious  that  the  iron  does  not  contribute  essentially  to 
those  properties,  such  as  the  colour.  Hematosine  contains  6  to  8  per  cent,  of 
iron. 

But  the  iron  serves  an  important  purpose  in  the  blood  ;  and  we  have  reason  to 
think  that  it  is  present  in  the  form  of  oxide,  for  sulphuretted  hydrogen  and  solu- 
ble sulphurets  cause  the  blood  to  become  first  green  and  then  black,  owing  to 
the  formation  of  sulphuret  of  iron — a  character  indicating  either  the  oxide  or 
some  corresponding  compound,  and  not  a  compound  like  ferrocyanogen,  in  which 
the  sulphurets  cannot  detect  the  iron.  Moreover,  we  see  that  oil  of  vitriol  dis- 
solves out  oxide  of  iron ;  and  although  alkalies  and  ferrocyanide  of  potassium 
do  not  detect  it,  this  is  owing  to  the  blood  being  an  alkaline  liquid,  and  to  the 
presence  of  so  much  animal  matter. 

It  is  from  the  blood  that  are  formed  the  tissues,  the  cells,  muscular  fibre,  nerv- 
ous matter,  &c.  &c.;  and  we  may,  therefore,  expect  to  find  some  relation  between 
their  composition  and  that  of  the  blood.  In  fact,  flesh,^or  muscular  fibre,  as  it 
exists  in  the  body,  including  vessels,  nerves,  fat,  &c.,  has  exactly  the  same 
composition  as  the  blood  has  on  an  average  of  venous  and  arterial,  or  a  mixture* 
of  both.  We  may,  therefore,  look  on  muscular  fibre,  or  animal  flesh,  as  simply 
blood  more  highly  organized. 

In  addition  to  the  substances  mentioned  above,  namely,  albumen,  fibrine,  col- 
ouring matter,  and  salts,  blood  also  contains  fat,  apparently  cholesterine,  along 
with  fatty  acids  and  a  peculiar  fat,  called  seroline. 

The  normal  proportions  of  serum  and  clot  are  87  per  cent,  of  serum  to  13  of 
clot. 

1000  parts  of  human  blood  contain  869*15  of  serum,  of  which  790*37  are 
water,  67*8  albumen,  and  10*98  of  salts  and  fatty  matter:  along  with  130*85  of. 
clot,  containing  125*63  albumen  and  fibrine  of  the  globules,  and  2*27  hematosine 
(along  with  a  little  fatty  matter  and  traces  of  salts  in  all  three),  also  2*95  of 
fibrine,  separate  from  the  globules. 

Venous  blood  contains  more  water  and  fewer  globules  than  arterial  blood. 

The  blood  contains  gases,  chiefly  carbonic  acid  and  nitrogen,  which  it  gives 
off  in  vacuo,  or  in  a  current  of  hydrogen.  It  is  said  to  contain  free  oxygen,  but 
this  seems  very  improbable,  when  we  reflect  that  fibrine  absorbs  oxygen,  trans- 
forming it  into  carbonic  acid,  and  that  blood  is  instantly  altered  by  contact  with 
oxygen.  The  change  from  venous  to  arterial  blood,  from  dark  to  florid,  depends 
on  the  presence  of  oxygen,  but  also  requires  the  presence  of  a  saline  solution. 
Indeed  a  similar  change  of  colour  takes  place  in  vacuo  if  the  clot  of  venous 
blood  be  there  covered  with  a  pretty  strong  solution  of  various  salts. 

THE  NUTRITION  OF  PLANTS  AND  ANIMALS. 
The  animal  and  vegetable  kingdoms  of  nature  are  connected  together  in  a 


762  NUTRITION  OF  PLANTS  AND  ANIMALS. 

beautiful  system  of  mutual  dependence,  exhibiting  a  perpetual  circulation  of 
certain  elements  through  both,  the  mineral  kingdom  being  the  point  of  departure 
and  that  also  where  the  circulation  terminates,  to  recommence  unceasingly, 

Plants  derive  their  nourishment  exclusively  from  the  mineral  world.  It  is 
clear  that  the  first  plants  must  have  done  so,  and  although  the  decaying  remains 
of  former  plants  now  contribute  to  vegetation,  we  shall  see  that  they  do  so  under 
mineral  forms,  and  not  essentially :  they  promote  vegetation,  but  are  not  indis- 
pensable to  it. 

The  mineral  food  of  plants,  then,  consists  of  carbonic  acid,  water,  and  ammo- 
nia, all  of  which  are  obtained  from  the  atmosphere,  and  of  sulphur  (sulphuric 
acid),  phosphorus  (phosphoric  acid),  alkalies,  earths,  salts,  and  metals,  all  de- 
rived from  the  soil.  Without  the  aid  of  the  matters  derived  from  the  soil,  the 
most  abundant  supply  of  carbonic  acid,  water,  and  ammonia,  is  of  no  use.  But 
if  a  soil  contain  these  necessary  substances,  plants  will  thrive  in  it,  even  if  they 
have  no  carbonic  acid  or  ammonia  furnished  in  the  shape  of  manure  beyond  the 
usual  atmospheric  supply. 

During  germination,  oxygen  is  absorbed  and  carbonic  acid  produced :  starch 
is  transformed,  probably  by  the  action  of  disastase,  or  of  an  acid  developed  during 
germination,  into  sugar  or  dextrine,  which  being  soluble,  are  fitted  for  being  con- 
veyed to  all  parts  of  the  plant.  Meanwhile,  the  azoto-sulphurized  ingredients 
of  the  seed  also  become  soluble,  and  with  the  sugar,  &c.,  contribute  to  the  for- 
mation of  new  parts,  destined  to  collect  food  from  the  air  or  the  soil. 

The  leaves  and  roots,  as  soon  as  formed,  absorb  carbonic  acid  from  the  air 
and  from  the  soil.  Alkalies  are  at  the  same  time  taken  up  by  the  roots,  and 
with  their  aid  the  carbonic  acid,  under  the  influence  of  light,  is  decomposed,  its 
carbon  being  retained,  while  its  oxygen  is  given  off.  At  the  same  time,  water, 
ammonia,  sulphuric  acid  (or  a  sulphate),  and  phosphoric  acid  or  phosphates  are 
taken  up,  and  their  elements,  along  with  the  carbon,  give  rise  to  fibrine,  albu- 
men, caseine,  &c. 

It  is  probable  that  the  fixation  of  carbon  is  a  gradual  process,  having  succes- 
sive stages;  that  the  carbonic  acid  is  first  reduced  or  deoxidized  so  far  as  to  yield 
oxalic  acid;  thus  C^O^ — 0  =  0  0^;  that  oxalic  acid,  with  the  aid  of  water, 
is  farther  reduced,  so  as  to  yield  malic  or  citric  or  tartaric  acid;  thus,  ^fi^-h 
2HO  =  C^H20g;  and  C^H^Og  —  O^  =  C^H^O^ ;  this  last  formula  doubled  is 
that  of  anhydrous  malic  acid,  C^HJ)^.  From  this  and  similar  compounds, 
sugar,  Cj^H^Oj^,  starch,  C^fl^fi^^,  gum,  G^fi^fi^^,  and  woody  fibre,  CJi fi^ 
or  G^H^O^^j  are  easily  deduced,  by  the  addition  of  the  elements  of  water  and 
the  elimination  of  oxygen.  Thus,  3  eq.  hydrated  malic  acid,  C^^H^gO^,  plus 
6H0  and  minus  O^^,  is  equal  to  2  eq.  dry  sugar  of  grapes,  C^H^^O^.  There  is 
good  reason  to  think  that  the  chief  function  of  the  alkalies  in  plants  is  to  pro- 
mote these  metamorphoses. 

Water  not  only  acts  by  its  elements,  but  also  as  the  indispensable  solvent 
through  which  the  whole  food  of  plants,  especially  that  derived  from  the  soil, 
can  alone  enter  them. 

From  the  above  considerations  we  may  draw  several  useful  inferences. 

1 .  The  presence  of  decaying  vegetable  matter  in  the  soil  promotes  vegetation 
by  furnishing  a  steady  supply  of  carbonic  acid  gas.  The  proportion  of  decaying 
matter  or  humus  must  not  exceed  a  certain  limit ;  otherwise  there  is  too  much 
carbonic  acid  in  the  air  of  the  soil,  and  the  plant  dies  in  such  circumstances. 

2.  The  presence  of  decaying  azoto-sulphurized  matter  in  the  soil  is  very  ad- 


I 


NUTRITION  OF  PLANTS  AND  ANIMALS.  763 

rantageous,  furnishing  a  supply  of  ammonia,  which  is  essential  to  vegetation, 
and  is  scantily  supplied  by  the  atmosphere. 

3.  The  supply  of  carbonic  acid  and  of  ammonia  can  only  favour  the  develop- 
ment of  vegetation  in  so  far  as  alkalies  and  phosphates  are  supplied  by  the  soil. 

4.  Since  all  the  azoto-sulphurized  principles,  albumen,  fibrine,  caseine,  &c., 
contain  sulphur  and  phosphorus,  or  rather  phosphates,  it  is  evident  that  seeds 
and  such  other  parts  of  plants  as  contain  these  principles  can  only  be  developed 
in  so  far  as  the  soil  contains  alkaline  or  earthy  phosphates  and  sulphuric  acid  or 
sulphates. 

5.  If  the  soil  is  rich  in  alkalies,  sulphates,  and  phosphates,  and  if  it  also  con- 
tain soluble  silicates,  essential  to  the  stem  of  the  grasses  and  cerealia,  it  is  fertile 
for  all  nutritious  crops;  and  such  crops  will,  in  that  case,  derive  from  the  atmos- 
phere alone  all  the  carbon  and  nitrogen  (carbonic  acid  and  ammonia)  they  re- 
quire, provided  time  he  allowed.  The  advantage  of  decaying  organic  matter,  or 
of  manures  containing  ammonia,  in  such  a  soil,  consists  in  shortening  the  time 
necessary  for  the  development  of  the  plant ;  a  matter  of  the  last  importance  in 
Our  uncertain  climate,  but  of  far  less  consequence  in  southern  regions,  where 
summer  is  perhaps  twice  as  long. 

6.  The  ashes  of  wood,  straw,  leaves,  &c.,  consisting  entirely  of  matter  ex- 
tracted from  the  soil  by  the  plants  for  the  purposes  of  vegetation,  must  prove  a 
most  fertilizing  manure ;  and  in  all  cases,  the  ashes  of  any  crop  must  be  the  best 
manure  for  that  vegetable. 

7.  But  as  the  ashes  of  plants  are  represented  by  the  excreta  of  the  animals 
(or  the  ashes  of  these  excreta)  which  fed  on  them,  so  the  excreta  of  animals 
fed  on  turnips,  hay,  straw,  potatoes,  &c.,  must  be  the  best  manure  for  turnips, 
hay,  com,  and  potatoes,  respectively. 

8.  When  by  the  addition,  to  an  average  soil,  of  guano,  or  of  bone  earth,  a  very 
heavy  crop  is  obtained,  say  of  wheat,  we  are  not  to  expect  that  a  repetition  of 
the  same  treatment  will  produce  the  same  effect.  We  must  bear  in  mind,  that 
the  presence  of  the  increased  supply  of  phosphates  has  enabled  the  plant  to  take 
up  a  much  larger  quantity  than  otherwise  it  could  have  done,  of  alkalies,  silicates, 
and  the  other  necessary  minerals.  Since  we  have  not  added  those  substances 
in  our  guano  or  bone  earth,  it  may  happen  that  the  soil  is  exhausted  of  its  whole 
actually  available  supply  of  them  by  that  one  crop,  and  that  years  may  elapse 
before  it  becomes,  in  the  course  of  nature,  as  fertile  as  before.  " 

9.  The  only  certain  rule  is  this :  as  far  as  possible  to  restore  to  the  soil,  in  the 
shape  of  manure,  exactly  what  it  has  lost  in  the  crop  ;  if  the  soil  were  originally 
fertile,  this  will  maintain  its  fertility,  which  will  even  be  gradually  augmented 
by  the  action  of  the  weather  on  the  subsoil. 

10.  With  a  view  to  this,  every  particle  of  solid  or  liquid  manure,  especially 
human,  should  be  preserved  with  the  utmost  care.  It  is  their  mineral  elements 
which  are  the  most  valuable ;  and  since  these  have  all  come  from  the  soil,  in 
preserving  them  for  manure  we  are  only  restoring  what  we  have  taken  away. 
This  has  long  been  systematically  done  in  China,  and  is  also  generally  practised 
in  the  Netherlands ;  but  in  this  country  the  waste  of  valuable  manure  is  lament- 
able, and  is  necessarily  followed  by  a  slow  but  certain  deterioration  of  our  soil 
and  crops,  which  we  are  now  endeavouring  to  remedy  by  the  expensive,  preca- 
rious, and  partial  measure  of  importing  bone  earth  and  guano.  But  guano  will, 
ere  long,  be  exhausted,  and  when  other  countries  know  the  real  value  of  their 


764  NUTRITION  OF  PLANTS  AND  ANIMALS. 

bone  earth,  they  will  not  willingly  part  with  it,  at  all  events  not  except  at  a  very 
high  price. 

11.  If  a  soil  is  not  fertile  generally,  it  must  be  deficient  in  most  of  the  sub- 
stances above  alluded  to  ;  but  if  it  yields  good  crops  of  one  vegetable  and  not  of 
others,  it  must  be  wanting  in  the  characteristic  mineral  elements  of  the  latter, 
which  must  then  be  supplied. 

12.  The  ashes  of  plants  being  known,  the  fact  that  a  certain  vegetable,  culti- 
vated or  wild,  thrives  in  any  given  spot,  furnishes  us  with  an  analysis  of  the 
available  or  soluble  elements  of  the  soil,  and  enables  us  to  direct  our  measures 
of  improvement  according  to  the  crop  we  wish  to  raise. 

Although  certain  bases  characterize  the  ashes  of  certain  plants,  as  potassa  does 
those  of  turnips  and  potatoes,  and  lime  those  of  peas,  beans,  &c. ;  yet  in  many 
cases,  one  base  may  be  substituted  for  another,  as  soda  for  potassa,  or  magnesia 
for  lime. 

It  is  maintained  by  some  that  carbon  is  introduced  into  plants,  in  part,  as 
huirius,  humic  acid,  or  humate  of  ammonia,  dissolved  in  the  juice,  and  derived 
from  the  mould  in  the  soil.  But  there  is  no  evidence  that  fertile  soils  contain 
humus  in  a  form  soluble  in  water,  and  the  sap,  when  first  entering  the  plant,  is 
colourless,  while  all  solutions  of  humus,  &c.,  are  brown.  Besides,  in  forest  land, 
which  is  not  manured,  the  proportion  of  humus  or  of  carbon  in  the  soil,  instead 
of  diminishing,  rather  increases,  while  enormous  quantities  of  carbon  are  removed 
annually  in  the  shape  of  wood.  Here,  as  in  the  case  of  the  first  vegetables,  it  is 
plain  that  all  the  increase  of  carbon  must  be  derived  from  carbonic  acid  :  since, 
if  the  plant  does  absorb  humus  or  humic  acid,  or  humate  of  ammonia,  which  is 
not  proved,  it  must  give  to  the  soil  as  much  or  more  humus,  &c.,  as  an  excretion 
from  its  roots. 

•  It  has  also  been  argued  by  some  that  plants  may  obtain  their  nitrogen,  either 
directly  by  absorption  of  the  nitrogen  of  the  atmosphere,  or  by  causing  that  gas 
to  form  ammonia,  combining  with  hydrogen  derived  probably  from  water,  &c. ; 
or,  lastly,  from  the  decomposition  of  nitric  acid,  which  acid  is  supposed  to  be 
formed  in  the  atmosphere  by  direct  combination  of  its  elements.  But  no  evi- 
dence has  ever  been  given,  either  that  plants  can  absorb  nitrogen  directly,  or 
that  they  can  cause  the  nitrogen  of  the  atmosphere  to  combine  with  hydrogen. 
As  for  nitric  acid,  although  traces  of  it  have  been  observed  in  thunder-storms,  it 
does  not  appear  to  have  been  formed  in  sufficiently  large  quantity;*  and  if  it 
were,  no  proof  has  yet  been  offered  that  plants  can  derive  their  nitrogen  from  it. 
The  action  of  nitrate  of  potassa,  or  of  soda,  as  manure,  proves  nothing,  because 
it  may  be  due  to  the  alkalies  alone,  and  probably  is  so,  since  they  do  not  ^eeem 
to  act  better  than  other  salts  of  the  same  bases.  Moreover,  many  plants,  such  as 
tobacco,  and  sunflower,  contain  much  nitrate  in  their  juices,  and  therefore  appear 
rather  to  form  nitric  acid  than  to  destroy  it.  On  the  whole,  it  appears  nearly 
certain  that  ammonia  is  the  only  source  of  nitrogen  in  plants.    It  is  self-evident 

*  In  fact,  the  proportion  of  nitric  acid  thus  formed,  is  so  very  small  as  to  lead  to  the  con- 
clusion that  it  is  formed  only  from  the  ammonia  present  in  the  atmosphere.  Should  this 
prove  true,  as  is  highly  probable,  then  ammonia  will  be  the  source  of  all  the  nitrogen  of 
'plants,  even  if  part  of  the  nitrogen  should  be  derived  from  nitric  acid.  It  is  generally  ad. 
mitted  that  in  nitrification  the  whole  of  the  nitric  acid  is  derived  from  the  oxidation  of  am- 
monia. 


NUTRITION  OF  PLANTS  AND  ANIMALS.  765 

that  the  atmosphere  must  contain  ammonia,  derived  from  the  putrefaction  of  ani- 
mal and  vegetable  matter,  and  also  that,  however  small  the  proportion,  the  abso- 
lute quantity  in  the  air  at  any  one  time  must  be  sufficient  for  the  supply  of  the 
vegetable  world,  and  through  it  of  the  animal  world,  since  all  animals  and  vege- 
tables ultimately  putrefy,  giving  off  their  nitrogen  in  the  form  of  ammonia.  It 
is  quite  easy  to  detect  ammonia  in  rain  water,  by  which  means  it  is  conveyed  to 
the  roots  or  leaves  of  plants  ;  and  it  has  also  been  proved  that  the  juices  of  plants 
contain  abundance  of  ammonia. 

The  nutritious  principles,  albumen,  fibrine,  and  caseine,  are  formed  by  plants 
alone  from  ammonia,  sugar  (or  gum,  starch,  &c.),  sulphates,  and  phosphates. 
They  pass  into  the  body  of  animals,  and  are  there  converted  into  blood.  As  they 
cannot  be  formed  nor  exist  without  the  phosphates,  so  by  their  means  the  animal 
body  is  supplied  with  bone  earth,  and  with  the  soluble  phosphates  necessary  for 
the  other  tissues. 

In  the  animal  body,  the  leading  and  characteristic  action  is  the  absorption  of 
oxygen  and  the  oxidation  of  the  tissues  :  that  is,  of  carbon  and  hydrogen,  so  that 
animals  take  up  oxygen,  and  give  out  carbonic  acid.  This  is  the  reverse  of  what 
occurs  in  plants,  which  absorb  carbonic  acid,  and  give  out  oxygen. 

In  the  lungs,  oxygen  enters  the  blood,  and  is  carried,  apparently,  by  the  agency 
of  a  compound  of  iron,  to  every  part  of  the  body.  The  oxidation  of  the  effete, 
or  worn-out  tissues,  which  have  meanwhile  been  replaced  by  the  blood,  takes 
place  in  the  capillaries,  and  is,  in  all  probability,  the  source  of  the  animal  heat. 
The  final  result  of  this  oxidation  is  the  production  of  a  large  quantity  of  carbonic 
acid  and  water,  which  are  given  off  by  the  lungs  and  skin. 

Health,  in  the  animal  body,  consists  in  the  due  balance  or  equilibrium  between 
the  oxidizing,  or  destructive  agency  of  the  atmosphere,  and  the  process  of  nutri- 
tion by  which  the  other  is  compensated. 

Since  the  nutritious,  or  blood-forming  elements  of  food,  have  the  same  compo- 
sition as  the  albumen,  fibrine,  &c.  of  the  tissues — indeed,  in  the  case  of  animal 
food,  are  identical  with  them — we  may  consider  the  process  of  oxidation  and  de- 
struction, either  as  affecting  the  food  directly,  or,  what  is  more  probable,  those 
portions  of  the  tissues  which,  having  performed  their  functions,  are  to  be  thrown 
off.  But  we  must  not  forget  that  in  the  herbivora,  a  great  part  of  the  combustion 
which  yields  the  animal  heat  is  carried  on  at  the  expense  of  those  parts  of  the 
food  which  cannot  form  blood :  namely,  sugar,  starch,  or  gum,  fat,  &c. 

The  fat  of  the  animal  body  is,  at  all  events  in  great  part,  derived  from  the 
non-azotized  elements  of  the  food  when  these  are  in  excess,  and  oxygen  is  defi- 
cient. In  these  circumstances,  the  deficiency  of  oxygen  is  supplied  at  the  ex- 
pense of  sugar,  starch,  or  gum,  which,  by  losing  oxygen,  gives  rise  to  fat ;  for 
the  proportions  of  carbon  and  hydrogen  in  sugar,  &c.,  and  in  fat,  are  exactly  the 
same,  that  of  oxygen  alone  being  different.  Hence  the  conditions  favourable  to 
the  formation  of  fat  are,  abundant  farinaceous  food,  and  rest,  that  is,  defective 
aeration,  as  is  seen  in  stall-fed  animals,  and  in  the  fattening  of  geese  fed  on  maize 
and  deprived  of  the  power  of  locomotion.  The  formation  of  wax,  a  species  of 
fat,  from  sugar  by  the  bee,  is  another  example. 

It  is  very  interesting  to  remark  that  the  composition  of  the  chief  elements  of 
the  bile,  and  the  urine,  bears  a  close  and  simple  relation  to  that  of  the  blood  or 
tissues.  If  the  formula  of  urate  of  ammonia  be  added  to  half  that  of  choleic  acid, 
the  sum  represents  the  composition  of  blood  or  flesh,  or  differs  from  it  only  by  a 
yery  little  water  and  oxygen,  substances  which  take  part  in  almost  every  chemi- 


766  NUTRITION  OF  PLANTS  AND  ANIMALS. 

cal  change  in  the  body,  water  being  always  present  in  the  body,  and  oxygen 
being  introduced  through  the  lungs.  Now,  urate  of  ammonia  is  the  urine  of 
birds  and  reptiles,  and  represents  that  of  the  mammalia ;  for  uric  acid,  when  fur- 
ther oxidized,  yields  urea  and  carbonic  acid,  while  urea  with  the  elements  of 
water,  passes,  as  in  putrefying  urine,  into  carbonate  of  ammonia.  As  for  the  bile, 
the  other  product  of  the  destruction  of  the  tissues  (at  least  this  is  its  origin  in 
the  carnivora,  and  partly  in  the  herbivora),  it  undergoes  resorption  in  the  intes- 
tines, and  is  finally  oxidized  into  carbonic  acid  and  water,  thus  contributing  to 
keep  up  the  animal  heat.  The  final  result  is,  that  the  tissues,  which  may  be 
supposed,  with  the  addition  of  a  little  oxygen,  to  be  resolved  into  choleic  acid 
(bile)  and  urate  of  ammonia  (urine),  are  entirely  converted,  or  oxidized  into  car- 
bonic acid,  water,  and  ammonia. 

The  food  of  animals  may  thus  be  said  to  be  literally  burned  in  their  bodies, 
and  this,  as  in  the  case  of  other  combustibles,  for  the  purpose  of  producing  heat. 
The  gaseous  product  of  the  combustion  are  sent  off  through  the  skin  and  lungs, 
while  the  smoke,  soot,  and  ashes  are  represented  by  the  excrements  and  urine. 

The  food  required  by  animals  must  bear  a  certain  relation  to  the  waste  of  mat- 
ter, and  to  the  heat  required.  Thus,  a  hard-working  man,  in  whom  the  change 
of  matter  is  rapid,  requires  much  more  food  (blood,  or  proteine  compounds)  than 
a  sedentary  person ;  and  in  cold  climates,  a  much  larger  quantity  of  food  rich  in 
carbon,  especially  fat,  blubber,  and  similar  matters,  is  necessary  than  in  warm 
climates,  where,  indeed,  such  food  excites  invincible  repugnance.  Any  mispro- 
portion  in  the  amount  or  nature  of  the  food  has  a  tendency  to  induce  disease. 
Thus,  Europeans,  who  often  eat  and  drink  as  at  home  when  they  go  to  tropical 
countries,  pay  the  penalty  of  their  ignorance  in  the  very  frequent  liver  complaints 
observed  among  them.  For  the  same  reason,  hepatic  disease  is  more  frequent 
during  summer  than  during  winter. 

After  death,  the  animal  body  is  slowly,  bat  surely,  resolved  into  the  ultimate 
products  of  putrefaction,  namely,  carbonic  acid,  water,  and  ammonia,  which  rise 
into  the  atmosphere,  having  completed  the  circuit  through  which  we  have  traced 
them,  in  order  to  recommence  it  by  once  more  contributing  to  the  growth  of 
plants  on  which  animals  will  again  feed. 

The  bones  of  dead  animals  are  also  by  degrees  restored  to  the  soil  from  which 
they  were  taken ;  and  nothing  is  finally  lost.  Even  the  rich  manure  which  we 
recklessly  cast  into  the  sea,  serves  as  manure  for  sea  plants,  on  which  are  fed 
fish,  which,  in  their  turn,  become  food  for  sea  fowl,  the  excrements  of  these  last, 
in  the  shape  of  guano,  returning  to  fertilize  the  fields  from  which  their  mineral 
elements  were  perhaps  originally  taken. 

It  is  evident  that  there  must  be  a  balance  or  equilibrium  kept  up  between  the 
animal  and  vegetable  worlds.  For  the  atmosphere  in  which  both  live  does  not, 
at  least  perceptibly,  change  in  its  composition.  There  is  no  appearance  either 
of  increase  or  diminution,  in  the  proportion  of  oxygen,  or  in  that  of  carbonic 
acid.  Yet  we  know  that  animal  life  tends  directly  and  powerfully  to  increase 
the  proportion  of  carbonic  acid,  and  to  diminish  that  of  oxygen,  while  the  ten- 
dency of  vegetable  life  is  exactly  the  reverse.  Hence  if,  in  any  quarter,  popu- 
lation or  animal  life  extends,  a  corresponding  augmentation  of  vegetable  life  must 
somewhere  be  the  result;  or  if,  by  cultivation,  the  amount  of  vegetation  in  any 
quarter  is  increased,  the  inevitable  consequence  must  be  an  extension  of  animal 
life,  otherwise  the  air  would  become  richer  in  oxygen.  As  both  carbonic  acid 
and  ammonia  are  partly  supplied  to  the  atmosphere  from  the  earth  itself,  not 


NUTRITION  OF  PLANTS  AND  ANIMALS.  767 

merely  from  the  decay  of  organic  matter  at  the  surface,  but  from  great  depths, 
as  for  example  in  hot  springs,  so  we  may  conceive  the  absolute  amount  of  car- 
bonic acid  and  ammonia  on  the  surface  of  the  earth  and  in  the  atmosphere  to  be 
somewhat  greater  now  than  some  thousand  years  ago.  If  not,  then  the  increase 
of  animal  and  vegetable  life  in  one  part  of  the  globe  must  necessarily  cause  a 
diminution  of  one  or  both  in  some  other  part,  since,  at  all  events,  the  atmosphere 
becomes  neither  richer  nor  poorer  in  carbonic  acid  and  ammonia.  Should  an 
addition  of  these  substances  be  made,  they  would  instantly  be  appropriated  by 
the  vegetable  kingdom,  and  converted  into  food  for  animals,  of  which  an  addi- 
tional number  would  soon  be  produced  by  the  increased  supply  of  food ;  and 
thus  the  aggregate  amount  of  animal  and  vegetable  life  might  be  increased, 
while  the  composition  of  the  atmosphere  remained  unchanged,  the  vegetable 
world  exactly  balancing  the  animal,  because  each  produces  the  food  of  the  other, 
as  the  necessary  result  of  its  own  txistence. 

Such  is  a  very  brief  and  general  sketch  of  the  chemistry  of  animal  and  vege- 
table life,  as  far  as  we  are  at  all  acquainted  with  it.  It  is  only  within  a  very 
short  time  that  this  department  of  science  has  been  properly  cultivated,  but  the 
results  already  obtained  are  most  important  and  highly  encouraging.  When  we 
reflect  that  the  processes  by  which  carbonic  acid,  water,  ammonia,  and  the  salts 
of  the  soil  are  made  to  assume  the  forms,  first  of  vegetable  and  then  of  animal 
tissues,  as  well  as  those  by  which  these  tissues  are  again  resolved  into  the  ele- 
ments of  which  they  were  formed,  are,  and  must  be,  purely  chemical  processes 
of  combination  and  decomposition,  governed  by  the  laws  of  chemistry  as  ascer- 
tained by  observation  and  experiment,  but  modified  by  the  vital  force,  it  is  easy 
to  see  that  from  the  assiduous  study  of  the  cl^mical  changes  going  on  in  plants 
and  animals,  in  health  and  in  disease,  we  may  confidently  expect  the  most  bene- 
ficial results.  All  that  has  hitherto  been  done  has  only  pointed  out  the  path  to 
be  followed  in  order  to  obtain  valuable  and  permanent  results.  But  enough  has 
been  done  to  satisfy  all  who  are  acquainted  with  the  actual  state  of  physiology 
that,  henceforth,  it  is  chiefly  to  chemistry  that  we  must  look  for  the  extension 
and  improvement  of  physiological  science.  Already  a  knowledge  of  chemistry 
is  admitted  to  be  indispensable  to  the  physiologist,  and  before  long  this  opinion 
will  be  so  far  acted  on  that  no  one  who  is  not  well  versed  in  chemistry  will 
venture  to  write  on  physiological  subjects. 


PART   IV. 

ANALYTICAL  CHEMISTRY. 


MINERAL  ANALYSIS.* 


The  subject  of  Chemical  Analysis  is  so  comprehensive,  that  to  give  more  than 
a  general  outline  of  this  branch  of  practical  chemistry  would  be  inconsistent  with 
the  plan  of  these  Elements. 

The  few  following  observations  are  thrown  into  four  sections :  the  first  of 
which  comprises  general  instructions  concerning  the  manipulations  necessary  in 
analytical  processes ;  the  second  contains  a  few  directions  for  the  performance 
of  qualitative  analysis ;  the  third,  for  the  quantitative  estimation  of  the  most 
common  constituents  of  minerals ;  and  the  fourth,  for  the  analysis  of  mineral 
waters. 

An  analysis  may  have  for  its  object  the  estimation  of  the  weights  of  either 
the  ultimate  or  proximate  constituents  of  a  substance ;  that  is,  of  the  ultimate 
elements  of  which  a  body  is  composed,  without  reference  to  the  manner  in  which 
those  elements  are  arranged ;  or  of  the  proximate  compounds  which  form,  by 
their  immediate  union,  the  substance  in  question.  In  inorganic  analysis,  the 
proximate  constituents  are  the  substances  generally  sought ;  and  the  elementary 
composition  of  these  being  already  known,  the  ultimate  elements  of  which  the 
substance  analyzed  is  composed  are  also  ascertained. 

Before  the  composition  of  a  substance  can  be  determined  quantitatively,  it  is 
necessary  to  have  the  nature  or  quality  of  the  constituents  accurately  determined : 
and  thus  a  chemical  analysis  is  resolved  into  two  distinct  examinations ;  first, 
for  the  nature  of  the  constituents,  which  is  called  the  qualitative  analysis  ,•  and 
second,  for  the  respective  weights  of  these  constituents,  which  is  the  quaniiia- 
live  analysis.  As  an  example,  it  might  be  ascertained  merely  that  crystallized 
sulphate  of  magnesia  is  composed  of  magnesia,  sulphuric  acid,  and  water ;  or 
that  the  salt  mentioned  contains,  in  100  parts,  16*7  of  magnesia,  32*4  of  sul- 
phuric acid,  and  50*9  of  water. 

# 

*  From  the  pen  of  E.  A.  Parnell,  author  of  the  Elements  of  Chemical  Analysis,  &c. 

51 


770 


SECTION  I. 


MANIPULATIONS  IN  ANALYTICAL  PROCESSES. 


In  qualitative  analysis  the  presence  of  any  particular  ingredient  in  the  sub- 
stance under  examination  is  generally  ascertained  by  mixing  a  test-liquid  with 
the  solution  of  the  substance  operated  on,  and  observing,  by  the  occurrence  or 
non-occurrence  of  a  precipitate,  whether  the  suspected  substance  is  present  or 
not.  If  the  test-liquid  which  is  added  produces  no  precipitate  with  any  other 
substance  whatever  than  that  sought  for,  this  simple  operation  is  conclusive  as 
to  the  presence  or  absence  of  the  suspected  body :  but  if,  on  the  other  hand,  a 
test-liquid  can  produce  a  precipitate  with  more  than  a  single  substance,  it 
becomes  necessary  to  apply  other  tests  before  positive  evidence  of  the  presence 
of  a  particular  substance  is  obtamed.  For  example,  if  a  neutral  solution  is  to 
be  tested  for  sulphuric  acid,  a  solution  of  nitrate  of  baryta  or  chloride 
of  barium  is  added  to  the  liquid :  the  absence  of  a  precipitate  in  that 


Fig. 


<f 


^  case  is  conclusive  as  to  the  absence  of  sulphuric  acid.  But  if  a  pre- 
cipitate occurs,  it  might  be  produced  in  a  neutral  solution  by  other 
acids  besides  sulphuric;  namely,  boracic,  phosphoric,  hydrofluoric, 
arsenic,  and  a  few  others.  The  precipitates,  however,  which  are  pro- 
duced by  these  acids  in  solutions  of  salts  of  baryta,  are  soluble  in 
X  nitric  or  hydrochloric  acid,  while  sulphate  of  baryta  is  not.  If  either 
nitric  or  hydrochloric  acid,  therefore,  is  added  to  the  mixture  with  the 
barytic  salt  containing  the  precipitate,  the  solubility  or  insolubility  of 
the  latter  shows  whether  or  not  it  contains  sulphuric  acid. 

The  mixture  of  the  solution  of  the  substance  to  be  analyzed  with 
the  test-liquid  may  be  made  either  in  a  conical  wine-glass,  or  in  a  test- 
tube.  The  wine-glass  should  be  provided  with  a  spout  for  the  con- 
venience of  pouring  liquids  into  a  tube  or  flask,  "with  the  view  of 
applying  heat ;  an  operation  frequently  necessary.  Instead  of  a  wine- 
glass, a  test-tube  (fg.  1)  is  frequently  employed,  which  possesses 
the  advantage  of  allowing  heat  to  be  applied  without  transferring  the 
^^ — ^  liquid  to  another  vessel.  A  convenient  size  for  ordinary  use  is  four 
inches  in  length,  by  two-thirds  of  an  inch  in  diameter. 

When  it  is  necessary  to  examine  the  action  of  a  test  liquid  on  a  precipitate 
obtained  in  the  course  of  testing,  that  may  sometimes  be  done  in  the  same  glass 
or  tube;  but  often  it  is  requisite  to  separate  the  precipitate  wholly  from  the  solu- 
tion, which  is  accomplished  by  filtration.  The  process  of  filtering  is  one  on 
which  the  success  of  analyses,  both  qualitative  and  quantitative,  but  especially 
of  the  latter,  materially  depends. 

Filtration  is  eflfected  by  means  of  a  paper  filter, 
formed  by  doubling  twice  a  circular  piece  of  filtering 
paper,  so  as  to  form  a  quadrant,  and  then  opening  one 
of  the  folds,  as  shown  in  fig.  2.  The  filter  is  sup- 
ported in  a  glass  funnel,  which  is  itself  held  in  any 
convenient  manner ;  a  vessel  being  placed  below  the 
funnel  to  recive  the  filtered  liquid.  Before  pouring 
the  turbid  liquor  on  it^^the  filter  should  be  wetted 


Fig.  2. 


i 


MANIPULATIONS  IN  ANALYTICAL  PROCESSES.  77I 

with  a  few  drops  of  distilled  water,  which  has  the  effect  of  swelling  the  fibres 
of  the  paper,  without  which  precaution  the  liquid  would  not  at  first  pass  through 
clear.  As  the  loss  of  a  single  drop  of  the  liquid  might,  in  quantitative  analysis, 
render  the  operation  worthless,  its  transference  to  a  filter  must  always  be  directed 
by  a  glass  rod,  applied  to  the  lip  of  the  con-  Fig.  3; 

taining  vessel,  and  held  nearly  perpendicular, 
with  its  extremity  very  near,  but  not  touching 
the  filter  (see  Jig.  3). 

In  quantitative  analysis,  the  substance,  whose 
weight  is  to  be  determined,  is  generally  sepa- 
rated from  the  solution  in  which  it  is  contained, 
by  precipitation  in  a  solid  form,  which  is  capable 
of  being  weighed,  and  which  contains  a  known 
proportion  of  the  substance  to  be  estimated.  If, 
for  example,  the  amount  of  copper  contained  in 
a  solution  is  required,  that  metal  is  precipitated 
in  the  state  of  oxide  by  caustic  potassa  :  when 
washed  and  perfectly  dried,  the  precipitate  ox- 
ide may  be  weighed;  and  as  it  is  known  to 
contain,  in  100  parts,  79-83  parts  of  copper,  the 
quantity  of  the  metal  contained  in  any  amount  of  the  oxide  is  readily  learned  by 
calculation. 

The  whole  of  the  precipitate  having  been  collected  on  the  filter,  as  already 
described,  it  is  washed  with  pure  distilled  water  until  every  trace  of  the  origi- 
nal liquid  is  removed,  and  then  dried  on  the  filter  in  a  hot  drying-stove  at  any 
temperature  below  212°.  When  dry,  if  the  substance  is  not  decomposed  by 
being  heated  to  redness,  it  is  held,  being  still  on  the  filter,  immediately  over  a 
porcelain  or  platinum  crucible,  the  weight  of  which  when  empty  is  already 
known ;  the  paper  is  set  on  fire,  and  the  precipitate  is  allotted  to  fall  into  the 
crucible,  together  with  the  ash  of  the  filter.  The  crucible  should  be  placed 
over  a  piece  of  highly-glazed  coloured  paper,  to  retain  any  particles  of  the  pre- 
cipitate which  may.  fall  on  it,  and  which  are  afterwards  carefully  put  into  the 
crucible.  After  the  matter  has  been  heated  to  redness,  if  the  filter  has  been 
completely  burned,  the  crucible  with  its  contents  is  weighed,  and  the  weight  of 
the  empty  crucible  is  deducted  from  the  entire  weight.  The  ash  of  the  filter 
also,  the  average  weight  of  which  is  determined  by  previous  experiments,  must 
be  subtracted  from  the  weight  of  the  heated  mass. 

In  those  cases  in  which  the  precipitate  to  be  weighed  cannot  be  heated  to 
redness  without  suffering  decomposition,  the  filter  in  which  it  is  to  be  collected 
should  be  carefully  dried,  and  introduced,  folded,  into  a  platinum  crucible,  which 
is  then  covered  and  weighed.  The  necessity  of  weighing  the  filter  in  a  closed 
vessel  arises  from  the  circumstance,  that  dry  paper  rapidly  absorbs  hygrometric 
moisture  from  the  air,  which  would  prevent  its  weight  being  accurately  deter- 
mined, if  placed,  open,  on  the  pan  of  the  balance.  Having  weighed  the  filter 
and  crucible,  the  filtration  maybe  conducted  as  usual;  and,  when  the  precipitate 
is  washed  and  dried  in  the  drying-stove,  the  filter  containing  it  is  folded,  intro- 
duced into  the  same  crucible,  and  weighed.  After  the  first  weighing,  the  cru- 
cible should  be  uncovered  and  exposed  to  as  high  a  temperature  as  paper  will 
support  without  charring,  to  discover  if  any  loss  in  weight  is  experienced  through 
the  escape  of  water,  from  the  mass  not  having  been  previously  rendered  per- 


772  QUALITATIVE  ANALYSIS. 

fectly  dry.    The  weight  of  the  empty  cracible  and  filter,  deducted  from  the 
entire  weight,  gives  that  of  the  precipitate. 

Such  is  an  outline  of  the  methods  usually  followed  in  determining  the  weights 
of  the  ingredients  of  compound  bodies.  There  are,  however,  many  cases  in 
which  a  different  course  is  pursued,  varying  according  to  the  nature  of  the  sub- 
stances and  the  degree  of  nicety  required ;  but  a  description  of  these  would  im- 
properly encroach  on  space  which  is  devoted  to  another  purpose. 


SECTION  II. 


QUALITATIVE  ANALYSIS. 

In  analytical  processes  the  first  object  is  to  obtain  the  substance  in  a  prope^ 
state  of  solution.  If  soluble  in  water,  that  fluid  is  preferred  to  every  other  men" 
struum  ;  but,  if  not,  an  acid,  or  any  convenient  solvent  may  be  employed.  In 
many  instances,  however,  the  substance  to  be  analyzed  resists  the  action  even  of 
acids,  and  in  that  case  the  following  method  is  adopted  : — The  compound  is  first 
crushed  by  means  of  a  hammer  or  steel  mortar,  and  is  afterwards  reduced  to  an 
impalpable  powder  in  a  mortar  of  agate ;  it  is  then  intimately  mixed  with  three, 
four,  or  more  times  its  weight  of  potassa,  soda,  baryta,  or  their  carbonates ;  and, 
lastly,  the  mixture  is  exposed  in  a  crucible  of  silver  or  platinum  to  a  strong  heat. 
During  the  operation,  the  alkali  combines  with  one  or  more  of  the  constituents  of 
the  mineral ;  and,  consequently,  its  elements  being  disunited,  it  no  longer  resists 
the  action  of  the  Jfcids. 

The  following  brief  observations  on  qualitative  analysis  have  reference  to  the 
discovery  of  the  constituents  of  a  salt  soluble  in  water,  and  which  consists  of  a 
single  acid  and  a  single  base,  to  ascertain  which  two  distinct  operations  are  in 
general  necessary. 

The  bases,  for  the  detection  of  which  means  are  pointed  out,  are  the  following: 


1.  Oxide  of  copper. 

10.  Alumina. 

2.  Oxide  of  lead. 

11.  Magnesia. 

3.  Protoxide  of  tin. 

12.  Lime. 

4.  Peroxide  of  tin. 

13.  Strontia. 

5.  Peroxide  of  iron. 

14.  Baryta. 

6.  Protoxide  of  iron. 

15.  Ammonia. 

7.  Oxide  of  chromium. 

16.  Potassa. 

8.  Protoxide  of  manganese. 

17.  Soda. 

9.  Oxide  of  xinc. 

1.  A  portion  of  the  solution  of  the  substance  under  examination  is  strongly 
acidified  by  a  mineral  acid,  and  saturated  with  sulphuretted  hydrogen  gas,  or 
else  is  mixed  with  water  strongly  impregnated  with  that  gas. 

If  a  black  or  brownish  precipitate  is  formed,  the  base  is  one  of  the  first  three 
in  the  list,  namely,  oxide  of  copper,  oxide  of  lead,  or  protoxide  of  tin.    To  di»- 


QUALITATIVE  ANALYSIS.  ,  tTg 

tinguish  these  three  bases,  add  to  other  portions  of  the  original  solution  the  three 
following  special  tests  : 

(a.) — ^Ammonia;  which  gives  an  intense  blue  liquid  with  solutions  of  copper. 
(6.) — Iodide  of  potassium;  which  produces  a  fine  yellow  precipitate  of  iodide 

in  solutions  of  lead, 
(c.) — Bichloride  of  mercury  ;  which  gives  with  solutions  oi proto'iaJU  of  tin, 
first  a  white  precipitate  of  calomel,  and  afterwards  a  black  precipitate  of 
metallic  mercury.     The  solution  supposed  to  contain  a  proto-salt  of  tin 
should  be  added  gradually  to  the  bichloride  of  mercury,  and  not  in  the 
reverse  order,  so  that  the  bichloride  is  at  first  in  large  excess. 
If  a  yellow  or  milky-white  precipitate  is  produced  by  sulphuretted  hydrogen, 
the  bjise  may  be  either  peroxide  of  tin  or  peroxide  of  iron  :  the  precipitate  in  the 
former  case  being  the  bisulphuret  of  tin  ;  and  in  the  latter,  free  sulphur,  proceed- 
ing from  the  decomposition  of  sulphuretted  hydrogen  by  peroxide  of  iron,  the 
latter  being  at  the  same  time  reduced  to  the  state  of  protoxide. 

(a.) — If  the  base  is  peroxide  of  tr(m,'yellow  prussiate  of  potassa  gives,  with 

the  original  solution,  a  deep  blue  precipitate  of  Prussian  blue, 
(i.) — If  the  base  is  peroxide  of  tin  caustic  potassa  produces  in  the  original 
solution  a  white  precipitate  of  peroxide  of  tin,  which  may  redissolve  in 
an  excess  of  the  alkali,  and  which,  if  collected  and  ignited  strongly,  be- 
comes insoluble  in  acids. 
2.  If  sulphuretted  hydrogen  produces  no  precipitate  in  the  acid  solution  of  the 
substance,  render  another  portion  of  the  solution  alkaline  by  ammonia,  and  then 
add  an  excess  of  hydrosulphuret  of  ammonia. 

(a.) — The  formation  of  a  black  precipitate  by  hydrosulphuret  of  ammonia 
indicates  the  presence  of  protoxide  of  iron^  in  which  case  the  original  solu- 
tion gives  a  deep  blue  precipitate  with  the  red  prussiate  of  potassa. 
(&.) — If  hydrosulphuret  of  ammonia  gives  a  dull  green  precipitate,  the  base 
is  oxidt  of  chromium.    If  the  precipitate  is  collected  and  fused  with  a  bead 
of  microcosmic  salt  before  the  blowpipe,  the  bead  is  found  to  be  red  while 
hot,  but  green  when  cold, 
(c.) — If  hydrosulphuret  of  ammonia  gives  a  flesh-colour  precipitate,  the  base 
is  manganese ;  in  which  case  a  solution  of  chloride  of  lime  produces  in  the 
original  solution  a  dark  brown  precipitate  of  hydrated  peroxide  of  manga- 
nese, 
(rf.) — If  hydrosulphuret  of  ammonia  gives  a  white  precipitate,  the  base  may 
be  either  oxide  cf  zinc  or  alumina.  These  substances  may  be  distinguished 
by  ammonia  which  added  to  the  original  solution  produces  a  white  pre- 
cipitate in  both  cases ;  but  oxide  of  zinc  is  soluble  in  excess  of  the  alkali, 
while  alumina  is  not. 
3.  If  neither  sulphuretted  hydrogen  nor  hydrosulphuret  of  ammonia  produces 
a  precipitate,  add  a  solution  of  carbonate  of  soda  to  another  portion  of  the  solu- 
tion.   The  occurrence  of  a  precipitate  shows,  that  the  base  is  either  magnesia, 
lime,  strontia,  or  baryta,  to  distinguish  which  the  original  solution  is  tested  in 
the  following  manner : 

(a.) — If  a  solution  of  oxalate  of  ammonia  gives  no  precipitate,  the  base  is 

magnesia. 
(&.) — If  oxalate  of  ammonia  gives  a  precipitate,  but  dilute  sulphate  of  soda 

does  not,  the  base  is  lime. 
(c.) — If  dilute  sulphate  of  soda  gives  a  precipitate,  the  base  is  either  laryta 


774*  QUALITATIVE  ANALYSIS. 

t 
or  strontia.    These  earths  may  be  distinguished  by  a  solution  of  hyposul- 
phite of  soda,  which  precipitates  baryta,  but  not  strontia. 
4.  If  carbonate  of  soda  gives  no  precipitate,  the  base  is  then  one  of  the  three 
alkalies,  ammonia,  potassa,  or  soda. 

(a.) — If  ammonia^  the  odour  of  that  alkali  is  recognized  on  adding  caustic 

potassa. 
(&.) — A  strong  solution  of  tartaric  acid  gives  a  white  crystalline  precipitate 

of  bitartrate  of  potassa  if  the  base  is  potassa, 
(c.) — Salts  of  soda  are  best  distinguished  by  the  yellow  colour  which  they 
communicate  to  the  flame  of  alcohol. 
Tlie  base  of  the  salt  having  been  discovered,  the  examination  for  the  acid  may 
then  be  performed.   The  acids,  for  the  detection  of  which  instructions  are  given, 
are  the  following. 

1.  Carbonic.  8.  Boracic. 

2.  Sulphnrous.  9.  Hydrofluoric. 

3.  Hydrosulphuric.  10.  Iodic. 

4.  Hydriodic.  11.  Hydrochloric. 

5.  Sulphuric.  12.  Nitric. 

6.  Phosphoric.  13.  Chloric. 

7.  Arsenic. 

1.  To  the  saturated  solution  of  the  salt  in  water,  if  soluble,  or  to  the  dry  salt, 
if  insoluble,  dilute  sulphuric  acid  is  applied.  The  effervescence  of  a  gas  may 
proceed  from  carbonic,  sulphurous,  or  hydrosulphuric  acid.  A  development  of 
free  iodine  may  proceed  from  hydriodic  acid. 

Carbonic, — The  gas  evolved  is  inodorous,  and,  when  passed  through  lime- 
water,  causes  a  white  precipitate,  which  dissolves  on  transmitting  an  ex- 
cess of  the  gas. 

Sulphurous. — The  evolved  gas  has  the  pungent  smell  of  burning  sulphur. 

Hydrosulphuric. — ^The  gas  has  a  foetid  odour,  and  the  solution  of  the  sub- 
stance produces  a  black  precipitate  in  salts  of  lead. 

Hydriodic— liO  detect  hydriodic  acid  (iodides),  mix  the  solution  of  the 
substance  with  a  little  solution  of  starch,  and  allow  chlorine  gas  to  fall 
on  the  surface  of  the  liquid ;  the  blue  iodide  of  starch  is  formed.  (See 
page  237.) 

2.  If  sulphuric  acid  produces  neither  effervescence  nor  development  of  free 
iodine,  add  a  solution  of  nitrate  of  baryta  to  the  neutral  solution  of  the  substance. 
The  acids  which  may  be  precipitated  thereby  are  the  following : 

Sulphuric, — The  precipitate  is  insoluble  in  pure  hydrochloric  acid. 

Hydrofluoric, — The  powdered  substance,  gently  heated  with  oil  of  vitriol  in 
a  platinum  crucible,  evolves  a  vapour  which  corrodes  glass. 

Arsenic  {Arsenious), — Sulphuretted  hydrogen  gas,  passed  through  the  solu- 
tion of  the  substance,  strongly  acidified  by  hydrochloric  acid,  gives  a 
yellow  precipitate  of  sulphuret  of  arsenic.  This  precipitate  being  dried, 
mixed  with  a  black  flux  and  heated  to  redness  in  a  glass  tube,  gives  a 
sublimate  of  metallic  arsenic. 

Phosphoric. — Nitrate  of  silver  gives,  with  the  neutral  solution  of  the  sub- 
stance, a  yellow  precipitate  of  phosphate  of  silver,  soluble  in  nitric  acid. 

Boracic. — If  the  dry  substance  is  moistened  with  oil  of  vitriol,  and  then 
alcohol  added,  the  latter  burns  with  a  green  flame. 


QUANTITATIVE  ANALYSIS.  775 

Iodic. — Sulphurous  acid  developes  free  iodine  in  the  original  solution ;  the 
presence  of  iodine  may  then  be  ascertained  by  its  action  on  starch. 

3.  If  dilute  sulphuric  acid  produces  no  effervescence,  and  nitrate  of  barytes  no 
precipitate,  the  acid  may  be  hydrochloric,  hydriodic,  nitric,  or  chloric;  in  which 
case  add  nitrate  of  silver  to  the  solution  of  the  substance. 

(a.) — If  a  yellow  precipitate  is  formed,  the  acid  may  be  hydriodic,  which 
is  known  by  the  insolubility  of  the  precipitate  (iodide  of  silver)  in  solu- 
tion of  ammonia. 

(&.) — If  a  white  curdy  precipitate  is  formed  by  nitrate  of  silver,  the  acid  is 
hydrochloric  ,•  in  which  case  the  precipitate  (chloride  of  silver)  is  readily 
dissolved  by  ammonia. 

4.  If  nitrate  of  silver  produces  no  precipitate,  the  acid  is  either  nitric  or  chloric. 
To  detect  nitric,  add  the  dry  substance  under  examination  to  a  mixture  of  proto- 
sulphate  of  iron  and  oil  of  vitriol ;  immediately,  or  on  heating,  a  brown  colour 
is  developed,  owing  to  nitric  oxide. 

To  detect  chloric  acid,  add  oil  of  vitriol  to  the  dry  salt:  peroxide  of  chlorine 
is  evolved,  and  the  liquid  bleaches  vegetable  colours. 

QUALITATIVE  ANALYSIS  OF  GASES. 

Table  exhibiting  the  distinctive  properties  of  oxygen,  nitrogen,  protoxide  of  nitrogen,  deU^ 
toxide  of  nitrogen,  hydrogen,  carbonic  oxide,  and  carbonic  acid. 

(From  Graham's  Elements  of  Chemistry.) 
Gases. 

} 


Soluble  in  water 


Support  combustion  <„  y^®^,      »    . 

ouijpuxt^-umuusuv^u  ^  Protoxide  of  Hitrogen 


Carbonic  acid  )  Solution  disturbs  lime  water. 

Protoxide  of  nitrogen  )  Does  not. 


Combustible 


( Carbonic  oxide  )  Product    of    combustion    disturbs 


^  Carbonic  oxide  ^Product    of    t 

•^  >     lime-water. 

(Hydrogen  )  Does  not. 

Extinguish  combustion     \  j^eutoxide  of  nitrogen  )  Forms  brown  fumes  with  oxygen. 
^  (^fltrogen  3  Does  not. 


SECTION  III. 


QUANTITATIVE  ANALYSIS. 


The  following  observations  on  Quantitative  analysis  relate  chiefly  to  those 
earthy  minerals  with  which  the  beginner  usually  commences  his  labours,  the 
most  common  constituents  of  which  are  silica,  alumina,  iron,  manganese,  lime, 
magnesia,  potassa,  soda,  and  carbonic  and  sulphuric  acids. 

.Analysis  of  marble,  or  carbonate  of  lime. — The  quantity  of  carbonic  acid  con- 
tained in  marble  and  all  other  carbonates  which  are  soluble  in  hydrochloric  or 
sulphuric  acid  in  the  cold  may  be  determined  by  the  following  simple  method  : — 
A  known  weight  of  the  powdered  substance  is  introduced  into  a  flask  similar  to 


976  QUANTITATIVE  ANALYSIS. 

that  represented  in  Jig.  4.  The  flask  should  be  thin  at  the 
bottom  to  allow  of  the  application  of  heat,  and  have  the  capa- 
city of  three  or  four  ounces  of  water.  It  is  fitted  with  a  cork, 
which  has  a  perforation  to  admit  a  small  bent  tube ;  and  the 
latter  is  connected  by  means  of  another  cork  with  a  somewhat 
larger  tube,  a,  containing  fragments  of  dry  chloride  of  cal- 
cium. The  extremity  h  of  this  tube  is  drawn  out  so  as  to  be 
capillary.  The  small  tube  c  within  the  flask,  sealed  at  one 
end,  is  intended  to  hold  hydrochloric  or  sulphuric  acid  to  de- 
compose the  carbonate,  and  is  of  such  length  that  it  will  not 
fall  flat  on  the  bottom  of  the  flask,  but  rest  against  the  side  at  an  angle  of  about 
45°  with  the  bottom ;  so  that,  on  inclining  the  flask,  all  the  acid  contained  in 
this  tube  can  be  made  to  flow  out.  The  apparatus  being  arranged,  the  weighed 
carbonate  is  introduced  into  the  empty  flask  with  about  half  an  ounce  of  water ; 
the  small  tube  c,  containing  sufficient  hydrochloric  or  sulphuric  acid  to  decompose 
the  carbonate,  is  then  introduced,  taking  care  that  no  acid  comes  in  contact  with 
the  carbonate,  and  the  flask  is  closed  by  the  cork  attached  to  the  chloride  of  cal- 
cium tube  a.  The  whole  apparatus  is  now  weighed ;  after  which  the  flask  is 
inclined,  in  order  that  a  little  of  the  acid  in  the  tube  c  may  flow  out  and  come 
in  contact  with  the  carbonate,  which  is  repeated  until  the  latter  is  completely 
decomposed.  As  the  evolved  carbonic  acid  gas  is  dried  in  passing  through  the 
chloride  of  calcium  tube  a,  nothing  else  than  this  gas  escapes,  and  the  loss  in 
weight  of  the  apparatus  at  the  close  of  the  experiment  is  the  weight  of  the  car- 
bonic acid  required ;  but,  as  the  flask  is  then  full  of  carbonic  acid  gas,  which  is 
considerably  heavier  than  air,  it  should  not  be  weighed  in  its  present  state.  To 
get  rid  of  the  remaining  carbonic  acid,  the  flask  is  very  gently  heated,  so  as  to 
fill  it  with  aqueous  vapour,  and  thus  drive  out  the  gas,  the  steam  itself  not  pro- 
ceeding further  than  the  chloride  of  calcium  tube.  On  the  condensation  of  the 
steam,  air  enters  the  flask,  which,  when  cold,  is  in  the  same  condition  as  it  was 
when  weighed  before  the  decomposition  of  the  carbonate,  excepting  only  in  the 
loss  of  carbonic  acid. 

Separation  of  Lime  and  Magnesia. — The  more  common  kinds  of  carbonate  of 
lime  frequently  contain  traces  of  siliceous  and  aluminous  earths,  in  consequence 
of  which  they  are  not  completely  dissolved  in  dilute  hydrochloric  acid.  A  very 
frequent  source  of  impurity  is  carbonate  of  magnesia,  which  is  often  present  in 
such  quantity  that  it  forms  a  peculiar  compound  called  Magnesian  limestone. 
The  analysis  of  this  substance,  so  far  as  respects  carbonic  acid,  is  the  same  as 
that  of  marble.  The  separation  of  the  two  earths  may  be  conveniently  effected 
in  the  following  manner: — The  solution  of  the  mineral  in  muriatic  acid  is  evapo- 
rated to  perfect  dryness  in  a  flat  dish  or  capsule  of  porcelain;  and,  after  redis- 
solving  the  residuum  in  a  moderate  quantity  of  distilled  water,  a  solution  of 
oxalate  of  ammonia  is  added  as  long  as  a  precipitate  ensues.  The  oxalate  of 
lime  is  then  allowed  to  subside,  collected  on  a  filter,  dried,  and  decomposed  by 
a  red  heat;  and  after  moistening  the  resulting  carbonate  with  a  strong  solution 
of  carbonate  of  ammonia,  in  order  to  supply  any  particles  of  quicklime  with 
carbonic  acid,  it  should  be  dried,  heated  to  low  redness,  and  regarded  as  pure 
carbonate  of  lime.  To  the  filtered  liquid,  containing  the  magnesia,  a  mixture  of 
pure  ammonia  and  phosphate  of  soda  is  added,  when  the  magnesia  is  precipi- 
tated in  the  form  of  the  ammoniaco-phosphate.  Of  this  precipitate,  heated  to 
redness,  100  parts,  according  to  Stromeyer,  correspond  to  37  of  pure  magnesia. 


QUANTITATIVE  ANALYSIS.  777 

The  precipitation  of  magnesia  by  means  of  phosphoric  acid  and  ammonia, 
though  extremely  accurate  when  properly  performed,  requires  several  precau- 
tions. The  liquid  should  be  cold,  and  either  neutral  or  alkaline.  The  precipi- 
tate is  dissolved  with  great  ease  by  most  of  the  acids;  and  Stroraeyer  has  re- 
marked, that  some  of  it  is  held  in  solution  by  carbonic  acid,  whether  free,  or  in 
union  with  an  alkali.  The  absence  of  carbonic  acid  should  therefore  always  be 
insured,  prior  to  the  precipitation,  by  heating  the  solution  to  212°,  acidulating  at 
the  same  time  by  hydrochloric  acid,  should  an  alkaline  carbonate  be  present. 
Berzelius  has  also  observed,  that,  in  washing  the  ammoniaco-magnesian  phos- 
phate on  a  filter,  a  portion  of  the  salt  is  dissolved  as  soon  as  the  saline  matter 
of  the  solution  is  nearly  all  removed ;  that  is  to  say,  it  is  dissolved  by  pure 
water.  Hence  the  edulcoration  should  be  completed  by  water,  which  is  rendered 
slightly  saline  by  hydrochlorate  of  ammonia. 

Earthy  Sulphates. — ^The  most  abundant  of  the, earthy  sulphates  is  that  of  lime, 
the  analysis  of  which  is  easily  effected.  By  boiling  it  for  fifteen  or  twenty 
minutes  with  a  solution  of  twice  its  weight  of  carbonate  of  soda,  double  decom- 
position ensues ;  and  the  carbonate  of  lime,  after  being  collected  on  a  filter  and 
washed  with  hot  water,  is  heated  to  low  redness  and  weighed. 

Of  the  dry  carbonate,  fifty  parts  correspond  to  twenty-eight  of  lime.  The 
alkaline  solution  is  acidulated  with  hydrochloric  acid,  and  the  sulphuric  acid 
thrown  down  by  chloride  of  barium.  From  the  sulphate  of  baryta,  collected 
and  dried  at  a  red  heat,  the  quantity  of  acid  may  easily  be  estimated. 

The  method  of  analyzing  the  sulphates  of  strontia  and  baryta  is  somewhat 
different.  As  these  salts  are  difficult  of  decomposition  in  the  moist  way,  the 
following  process  is  adopted  : — The  sulphate,  in  fine  powder,  is  mixed  with, 
three  times  its  weight  of  carbonate  of  soda,  and  the  mixture  is  heated  to  redness 
in  a  platinum  crucible  for  the  space  of  an  hour.  The  ignited  mass  is  then  di- 
gested in  hot  water,  and  the  insoluble  earthy  carbonate  collected  on  a  filter. 
The  other  parts  of  the  process  are  the  same  as  the  foregoing. 

Mode  of  analyzing  Compounds  of  Silica^  Alumina^  and  Iron. — ^Minerals,  thus 
constituted,  are  decomposed  by  an  alkaline  carbonate,  at  a  red  heat,  in  the  same 
manner  as  sulphate  of  baryta.  The  mixture  is  afterwards  digested  in  dilute 
hydrochloric  acid,  by  which  means  all  the  ingredients  of  the  mineral,  if  the  de- 
composition is  complete,  are  dissolved.  The  solution  is  next  evaporated  to  dry- 
ness, the  heat  being  carefully  regulated  towards  the  close  of  the  process,  in 
order  to  prevent  any  of  the  chloride  of  iron,  the  volatility  of  which  is  consi- 
derable, from  being  dissipated  in  vapour.  By  this  operation,  the  silica,  though 
previously  held  in  solution  by  the  acid,  is  entirely  deprived  of  its  solubility ; 
so  that,  on  digesting  the  dry  mass  in  water  acidulated  with  hydrochloric  acid, 
the  alumina  and  iron  are  taken  up,  and  the  silica  is  left  in  a  state  of  purity. 
The  siliceous  earth,  after  subsiding,  is  collected  on  a  filter,  carefully  edulcorated, 
heated  to  redness,  and  weighed. 

To  the  clear  liquid,  containing  peroxide  of  iron  and  alumina,  a  solution  of  pure 
potassa  is  added  in  moderate  excess  ;  so  as  not  only  to  throw  down  those  oxides, 
but  to  redissolve  the  alumina.  The  peroxide  of  iron  is  then  collected  on  a  filter, 
edulcorated  carefully  until  the  washings  cease  to  have  an  alkaline  reaction,  and 
is  well  dried  and  ignited,  as  described  at  page  771.  This  operation,  however, 
should  be  done  with  care ;  since  any  adhering  particles  of  paper,  or  other  com- 
bustible matter,  would  bring  the  iron  into  the  state  of  black  oxide,  a  change 
which  is  known  to  have  occurred  by  the  iron  being  attracted  by  a  magnet. 


ttS  QUANTITATIVE  ANALYSIS. 

To  procure  the  alumina,  the  liquid  in  which  it  is  dissolved  is  boiled  with  hy- 
drochloric of  ammonia,  when  chloride  of  potassium  is  formed,  the  volatile  alkali 
is  dissipated  in  vapour,  and  the  alumina  subsides.  As  soon  as  the  solution  is 
thus  rendered  neutral,  the  hydrous  alumina  is  collected  on  a  filter,  dried  by  ex- 
posure to  a  white  heat,  and  quickly  weighed  after  removal  from  the  fire. 

Separation  of  Iron  and  Manganese.  —  A  compound  of  these  metals  or  their 
oxides  may  be  dissolved  in  hydrochloric  acid.  If  the  iron  is  in  a  large  propor- 
tion compared  with  the  manganese,  the  following  process  may  be  adopted  with 
advantage : — To  the  cold  solution,  considerably  diluted  with  water,  and  acidu- 
lated with  hydrochloric  acid,  carbonate  of  soda  is  gradually  added,  and  the  liquid 
is  briskly  stirred  with  a  glass  rod  during  the  effervescence,  in  order  that  it  may 
become  highly  charged  with  carbonic  acid.  By  neutralizing  the  solution  in  this 
manner,  it  at  length  attains  a  point  at  which  the  peroxide  of  iron  is  entirely  de- 
posited, leaving  the  liquid  colourless  ;  while  the  manganese,  by  aid  of  the  free 
carbonic  acid,  is  kept  in  solution.  The  iron,  after  subsiding,  is  collected  on  a 
filter,  and  its  quantity  determined  in  the  usual  manner.  The  filtered  liquor  is 
then  boiled  with  an  excess  of  carbonate  of  soda ;  and  the  precipitated  carbonate 
of  manganese  is  collected,  heated  to  full  redness  in  an  open  crucible,  by  which 
it  is  converted  into  the  red  oxide,  and  weighed.  This  method  is  one  of  some 
delicacy ;  but  in  skilful  hands  it  affords  a  very  accurate  result.  It  may  also  be 
employed  4[or  separating  ijon  from  magnesia  and  lime  as  well  as  from  man- 
ganese. 

But  if  the  proportion  of  iron  is  small  compared  with  that  of  manganese,  the 
best  mode  of  separating  it  is  by  succinate  of  ammonia  or  soda,  prepared  by  neu- 
tralizing a  solution  of  succinic  acid  with  either  of  those  alkalies.  That  this  pro- 
cess should  succeed,  it  is  necessary  that  the  iron  be  wholly  in  the  state  of 
peroxide,  that  the  solution  be  exactly  neutral,  which  may  easily  be  insured  by 
the  cautious  use  of  ammonia,  and  that  the  reddish-brown  coloured  succinate  of 
peroxide  of  iron  be  washed  with  cold  water.  When  the  precipitate  is  washed 
clean,  solution  of  ammonia  should  be  poured  on  it  to  separate  succinic  acid,  and 
the  remaining  peroxide  of  iron  may  be  dried,  cautiously  ignited,  and  weighed. 
From  the  filtered  liquid  the  manganese  may  be  precipitated  at  a  boiling  tempe- 
rature by  carbonate  of  soda,  and  its  quantity  determined  in  the  way  above  men- 
tioned. The  benzoate  may  be  substituted  for  succinate  of  ammonia  in  the  pre- 
ceding process. 

It  may  be  stated  as  a  general  rule,  that,  whenever  it  is  intended  to  precipitate 
iron  by  means  of  the  alkalies,  the  succinates,  or  benzoates,  it  is  essential  that 
this  metal  be  in  the  maximum  of  oxidation.  It  is  easily  brought  into  this  state 
by  digestion  with  a  little  nitric  acid. 

Separation  of  Manganese  from  Lime  and  Magnesia. — If  the  quantity  of  the  for- 
mer is  proportionally  small,  it  is  precipitated  as  a  sulphuret  by  hydrosulphuret 
of  ammonia  or  sulphuret  of  potassium.  The  sulphuret  is  then  dissolved  in  hy- 
drochloric acid,  and  the  manganese  thrown  down  as  usual  by  means  of  an  alkali. 
But  if  the  manganese  is  the  chief  ingredient,  the  best  method  is  to  precipitate 
it  at  once,  together  with  the  two  earths,  by  a  fixed  alkaline  carbonate  at  a  boil- 
ing temperature.  The  precipitate,  after  being  exposed  to  a  low  red  heat  and 
weighed,  is  put  into  cold  water  acidulated  with  a  drop  or  two  of  nitric  acid, 
when  the  lime  and  magnesia  will  be  slowly  dissolved  with  effervescence. 
Should  a  trace  of  the  manganese  be  likewise  taken  up,  it  may  easily  be  thrown 
down  by  hydrosulphuret  of  ammonia. 


ANALYSIS  OF  MINERAL  WATERS.  779 

Stromeyer  has  recommended  a  very  elegant  and  still  better  process  for  remov- 
ing small  quantities  of  manganese  from  lime  and  magnesia.  The  solution  is 
acidulated  with  nitric  or  hydrochloric  acid ;  bicarbonate  of  soda  is  gradually 
added  in  very  slight  excess,  stirring  after  each  addition,  that  the  liquid  may  be 
charged  with  carbonic  acid  ;  and  a  solution  of  chlorine,  or  a  current  of  the  gas, 
is  introduced.  The  protoxide  of  manganese  is  converted  by  the  chlorine  into 
the  insoluble  hydrated  peroxide,  while  any  traces  of  lime  or  magnesia,  which 
might  otherwise  fall,  are  retained  in  solution  by  means  of  carbonic  acid.  A 
solution  of  chloride  of  soda  or  lime  is  in  fact  our  most  delicate  test  for  small 
quantities  of  manganese. 

Mode  of  analyzing  an  Earthy  Mineral  containing  Silica,  Iron,  Alumina,  Man- 
ganese.  Lime,  and  Magnesia. — The  mineral,  reduced  to  fine  powder,  is  ignited 
with  three  or  four  times  its  weight  of  carbonate  of  potassa  or  soda,  the  mass  is 
taken  up  in  dilute  hydrochloric  acid,  and  the  silica  separated  in  the  way  already 
described.  To  the  solution,  thus  freed  from  silica  and  duly  acidulated,  carbonate 
of  soda,  or  still  better  the  bicarbonate,  is  gradually  added,  so  as  to  charge  the 
liquid  with  carbonic  acid,  as  in  the  analysis  of  iron  and  manganese.  In  this 
manner  the  iron  and  alumina  are  alone  precipitated,  substances  which  may  be 
separated  from  each  other  by  means  of  pure  potassa  (page  777).  The  manga- 
nese, lime,  and  magnesia,  may  then  be  determined  by  the  processes  above  de- 
scribed. 


SECTION  IV. 


ANALYSIS  OF  MINERAL  WATERS. 


Rain  water  collected  in  clean  vessels  in  the  country,  or  freshly  fallen  snow 
when  melted,  affords  the  purest  kind  of  water  which  can  be  procured  without 
having  recourse  to  distillation.  The  water  obtained  from  these  sources,  how- 
ever, is  not  absolutely  pure,  but  contains  a  portion  of  carbonic  acid  and  air,  ab- 
sorbed from  the  atmosphere.  It  is  remarkable  that  this  air  is  very  rich  in  oxy- 
gen. That  procured  from  snow  water  by  boiling  was  found  by  Gay-Lussac  and 
Humboldt  to  contain  34*8,  and  that  from  rain  water  32  per  cent,  of  oxygen  gas. 
From  the  powerfully  solvent  properties  of  water,  this  fluid  no  sooner  reaches  the 
ground  and  percolates  through  the  soil,  than  it  dissolves  some  of  the  substances 
which  it  meets  with  in  its  passage.  Under  common  circumstances  it  takes  up 
so  small  a  quantity  of  foreign  matter,  that  its  sensible  properties  are  not  mate- 
rially affected,  and  in  this  state  it  gives  rise  to  spring,  well,  and  river  water. 
Sometimes,  on  the  contrary,  it  becomes  so  strongly  impregnated  with  saline  and 
other  substances,  that  it  acquires  a  peculiar  flavour,  and  is  thus  rendered  unfit 
for  domestic  uses.     It  is  then  known  by  the  name  of  mineral  water. 

The  composition  of  spring  water  is  dependent  on  the  nature  of  the  soil  through 
which  it  flows.  If  it  has  filtered  through  primitive  strata,  such  as  quartz  rock, 
granite,  and  the  like,  it  is  in  general  very  pure ;  but,  if  it  meets  with  limestone 
or  gypsum  in  its  passage,  a  portion  of  these  salts  is  dissolved,  and  communicates 


780  ANALYSIS  OF  MINERAL  WATERS. 

the  property  called  hardness.  Hard  water  is  characterized  by  decomposing  soap, 
the  lime  of  the  former  yielding  insoluble  compounds  with  the  margaric  and  oleic 
acids  of  the  latter.  If  this  defect  is  owing  to  the  presence  of  carbonate  of  lime, 
it  is  easily  remedied  by  boiling,  when  free  carbonic  acid  is  expelled,  and  the 
insoluble  carbonate  of  lime  subsides.  If  sulphate  of  lime  is  present,  the  addi- 
tion of  a  little  carbonate  of  soda,  by  precipitating  the  lime,  converts  the  hard  into 
soft  water.  Besides  these  ingredients,  the  chlorides  of  calcium  and  sodium  are 
frequently  contained  in  spring  water. 

Spring  water,  in  consequence  of  its  saline  impregnation,  is  frequently  unfit  for 
chemical  purposes,  and  on  these  occasions  distilled  water  is  employed.  Distil- 
lation may  be  performed  on  a  small  scale  by  means  of  a  retort,  in  the  body  of 
which  water  is  made  to  boil,  while  the  condensed  vapour  is  received  in  a  glass 
flask,  called  a  recipient,  which  is  adapted  to  its  beak  or  open  extremity.  This 
process  is  more  conveniently  conducted,  however,  by  means  of  a  still. 

The  different  kinds  of  mineral  water  may  be  conveniently  arranged  for  the  pur- 
pose of  description  in  the  six  divisions  of  acidulous,  alkaline,  chalybeate,  sul- 
phureous, saline,  and  siliceous  springs. 

1.  Acidulous  springs,  of  which  those  of  Seltzer,  Spa,  Pyrmont,  and  Carlsbad 
are  the  most  celebrated,  commonly  owe  their  acidity  to  the  presence  of  free  car- 
bonic acid,  iji  consequence  of  the  escape  of  which  they  sparkle  when  poured 
from  one  vessel  into  another.  Such  carbonated  waters  communicate  a  red  tint  to 
litmus  paper  before,  but  not  after  being  boiled,  and  the  redness  disappears  on 
exposure  to  the  air.  Mixed  with  a  sufficient  quantity  of  lime  water,  they  be- 
come turbid  from  the  deposition  of  carbonate  of  lime.  They  frequently  contain 
carbonate  of  lime,  magnesia,  and  protoxide  of  iron,  in  consequence  of  the  facility 
with  which  these  salts  are  dissolved  by  water  charged  with  carbonic  acid. 

2.  Alkaline  waters  are  such  as  contain  a  free  or  carbonated  alkali,  and  conse- 
quently, either  in  their  natural  state,  or  when  concentrated  by  evaporation,  pos- 
sess an  alkaline  reaction. 

These  springs  are  rare.  The  best  instance  I  have  met  with  is  in  water  col- 
lected at  the  Furnas,  St.  Michael's,  Azores,  and  sent  to  the  Royal  Society  of 
Edinburgh  by  Lord  Napier.  These  springs  contain  carbonate  of  soda  and  car- 
bonic acid,  and  are  almost  entirely  free  from  earthy  substances.  Of  five  different 
kinds  of  these  waters  which  I  examined,  the  greater  part  also  contained  protox- 
ide of  iron,  hydyosulphuric  acid,  and  chloride  of  sodium. 

3.  Chalybeate  waters  are  characterized  by  a  strong  styptic  inky  taste,  and  by 
striking  a  black  colour  with  the  infusion  of  gall-nuts.  The  iron  is  sometimes 
combined  with  hydrochloric  or  sulphuric  acid  ;  but  most  frequently  it  is  in  the 
form  of  protocarbonate,  held  in  solution  by  free  carbonic  acid.  On  exposure  to 
the  air,  the  protoxide  is  oxidized,  and  the  hydrated  peroxide  subsides,  causing 
the  ochreous  deposit  so  commonly  observed  in  the  vicinity  of  chalybeate 
springs. 

To  ascertain  the  quantity  of  iron  contained  in  a  mineral  water,  a  known  weight 
of  it  is  concentrated  by  evaporation,  and  the  iron  is  brought  to  the  state  of  per- 
oxide by  means  of  nitric  acid.  The  peroxide  is  then  precipitated  by  ammonia 
and  weighed;  and,  if  lime  and  magnesia  are  present,  it  may  be  separated  from 
those  earths  by  the  process  described  in  the  last  section. 

Chalybeate  waters  are  by  no  means  uncommon ;  but  the  most  noted  in  Britain 
are  those  of  Tunb ridge,  Cheltenham,  and  Brighton.  The  Bath  water  also  con- 
tains a  small  quantity  of  iron. 


ANALYSIS  OF  MINERAL  WATERS.  7gi 

4.  Sulphureous  waters,  of  which  the  springs  of  Aix-la-Chapelle,  Harrowgate, 
and  Moffat  aflford  examples,  contain  hydrosulphuric  acid,  and  are  easily  recog- 
nized by  their  odour,  and  by  causing  a  brown  precipitate  with  a  salt  of  lead  or 
silver.  The  gas  is  readily  expelled  by  boiling,  and  its  quantity  may  be  roughly 
estimated  by  transmitting  it  through  a  solution  of  pure  chloride  of  mercury,  and 
weighing  the  sulphuret  which  is  generated. 

5.  Those  mineral  springs  are  called  saline,  the  character  of  which  is  caused 
by  saline  compounds.  The  salts  which  are  most  frequently  contained  in  these 
waters  are  the  sulphates  and  carbonates  of  lime,  magnesia,  and  soda,  and  the 
chlorides  of  calcium,  magnesium,  and  sodium.  Potassa  sometimes  exists  in 
them,  and  Berzelius  has  found  lithia  in  the  spring  of  Carlsbad.  It  has  lately 
been  discovered,  that  the  presence  of  hydriodic  acid  in  small  quantity  is  not 
unfrequent.  As  examples  of  saline  water  may  be  enumerated  the  springs  of 
Epsom,  Cheltenham,  Bath,  Bristol,  Bareges,  Buxton,  Pitcaithly,  and  Toeplitz. 

The  first  object  in  examining  a  saline  spring  is  to  determine  the  nature  of  its 
ingredients.  Hydrochloric  acid  is  detected  by  nitrate  of  oxide  of  silver,  and  sul- 
phuric acid  by  chloride  of  barium;  and,  if  an  alkaline  carbonate  be  present,  the 
precipitate  occasioned  by  either  of  these  tests  will  contain  a  carbonate  of  oxide 
of  silver  or  baryta.  The  presence  of  lime  and  magnesia  may  be  discovered,  the 
former  by  oxalate  of  ammonia,  and  the  latter  by  phosphate  of  ammonia.  Potassa 
is  known  by  the  action  of  chloride  of  platinum  (page  295).  To  detect  soda,  the 
water  should  be  evaporated  to  dryness,  the  deliquescent  salts  rem'oved  by  alcohol, 
and  the  matter  insoluble  in  that  menstruum,  taken  up  by  a  small  quantity  of 
water,  and  be  allowed  to  crystallize  by  spontaneous  evaporation.  The  salt  of 
soda  may  then  be  recognized  by  the  rich  yellow  colour  which  it  communicates 
to  flame  (page  300).  If  the  presence  of  hydriodic  acid  be  suspected,  the  solution 
is  brought  to  dryness,  the  soluble  parts  dissolved  in  two  or  three  drachms  of  a 
cold  solution  of  starch,  and  strong  sulphuric  acid  gradually  added  (page  239.) 

Having  thus  ascertained  the  nature  of  the  saline  ingredients,  their  quantity 
may  be  determined  by  evaporating  a  pint  of  water  to  dryness,  heating  to  low 
redness,  and  weighing  the  residue.  In  order  to  make  an  exact  analysis,  a  given 
quantity  of  the  mineral  water  is  concentrated  in  an  evaporating  basin  as  far  as 
can  be  done  without  causing  either  precipitation  or  crystallization,  and  the  re- 
sidual liquid  is  divided  into  two  equal  parts.  From  one  portion  the  sulphuric 
and  carbonic  acids  are  thrown  down  by  nitrate  of  baryta,  and,  after  collecting 
the  precipitate  on  a  filter,  the  hydrochloric  acid  is  precipitated  by  nitrate  of  oxide 
of  silver.  The  mixed  sulphate  and  carbonate  is  exposed  to  a  low  red  heat,  and 
weighed;  and  the  carbonate  is  then  dissolved  by  dilute  hydrochloric  acid,  and  its 
quantity  determined  by  weighing  the  sulphate.  The  chloride  of  silver,  of  which 
143"42  parts  correspond  to  36*42  of  hydrochloric  acid,  is  fused  in  a  platinum 
spoon  or  crucible,  in  order  to  render  it  quite  free  from  moisture.  To  the  other 
half  of  the  concentrated  mineral  water,  oxalate  of  ammonia  is  added  for  the  pur- 
pose of  precipitating  the  lime  ;  and  the  magnesia  is  afterwards  thrown  down  as 
the  ammoniaco-phosphate,  by  means  of  ammonia  and  phosphoric  acid.  Having 
thus  determined  the  weight  of  each  of  the  fixed  ingredients  excepting  the  soda, 
the  loss  is  of  course  the  quantity  of  that  alkali  required. 

The  individual  constituents  of  the  water  being  known,  it  remains  to  determine 
the  state  in  which  they  were  originally  combined.  In  a  mineral  water  contain- 
ing sulphuric  and  hydrochloric  acids,  lime,  and  soda,  it  is  obvious  that  three 

cases  are  possible.     The  liquid  may  contain  sulphate  of  lime  and  chloride  of 


783  ANALYSIS  OF  MINERAL  WATERS. 

sodium,  or  chloride  of  calcium  and  sulphate  of  soda ;  or  each  acid  may  be  dis- 
tributed between  both  the  bases.  It  was  at  one  time  supposed  that  the  lime 
must  be  in  combination  with  sulphuric  acid,  because  the  sulphate  of  that  earth  is 
left  when  the  water  is  evaporated  to  dryness.  This,  however,  by  no  means 
follows.  In  whatever  state  the  lime  may  exist  in  the  original  spring,  gypsum 
will  be  generated  as  soon  as  the  concentration  reaches  that  degree  at  which  sul- 
phate of  lime  cannot  be  held  in  solution.  The  late  Dr.  Murray,  who  treated  this 
question  with  much  sagacity,  observes  that  some  mineral  waters,  which  contain 
the  four  principles  above  mentioned,  possess  higher  medicinal  virtues  than  can 
be  justly  ascribed  to  the  presence  of  sulphate  of  lime.  He  advances  the  opinion, 
that  alkaline  bases  are  united  in  mineral  waters  with  those  acids  with  which 
they  form  the  most  soluble  compounds,  and  that  the  insoluble  salts  obtained  by 
evaporation  are  merely  products.  He  therefore  proposes  to  arrange  the  sub- 
stances determined  by  analysis  according  to  this  supposition.  (Edin.  Phil. 
Trans,  vii.)  To  this  practice  there  is  no  objection  ;  but  it  is  probable  that  each 
acid  is  rather  distributed  between  several  bases  than  combined  exclusively  with 
either. 

Sea  water  may  be  regarded  as  one  of  the  saline  mineral  waters.  Its  taste  is 
disagreeably  bitter  and  saline,  and  its  fixed  constituents  amount  to  about  three 
percent.  Its  specific  gravity  varies  from  1*0269  to  1"0285;  and  it  freezes  at 
about  28'5°  F.  A  very  complete  analysis  of  the  water  of  the  English  Channel 
was  executed  a  few  years  ago  by  Dr.  Schweitzer,  of  Brighton,  the  results  of 

which  are  subjoined : — 

Grains. 

Water 964-74372 

Chloride  of  Sodium 27-05948 

Chloride  of  Potassium 0-76552 

Chloride  of  Magnesium 3-66658 

Bromide  of  Magnesium 0-02929 

Sulphate  of  Magnesia 2-29578 

Sulphate  of  Lime             1-40662 

Carbonate  of  Lime 0-03301 

1000-00000 
The  water  of  the  Dead  Sea  has  a  far  stronger  salipe  impregnation  than  sea 
water,  containing  one-fourth  of  its  weight  of  solid  matter.  It  has  a  peculiarly 
bitter,  saline,  and  pungent  taste,  and  its  specific  gravity  is  1*211.  According 
to  the  analysis  of  Marcet,  1 00  parts  of  it  are  composed  of— muriate  of  magnesia 
10-246,  muriate  of  soda  10*36,  muriate  of  lime  3*92,  and  sulphate  of  lime  0*054. 
In  the  river  Jordan,  which  flows  into  the  Dead  Sea,  Marcet  discovered  the  same 
principles  as  in  the  lake  itself. 

6.  Siliceous  waters  are  very  rare,  and  in  those  hitherto  discovered  the  silica 
appears  to  have  been  dissolved  by  means  of  soda.  The  most  remarkable  of  these 
are  the  boiling  springs  of  the  Geyser  and  Rykum,  in  Iceland,  a  gallon  of  which, 
according  to  the  analysis  of  Black,  contains  the  following  substances ;  (Edin- 
burgh Philos.  Trans,  iii.  95  :) 

Geyser.  Rykum. 

Soda 5-56        .        .        3-0 

Alumina 2*80        .        .       0-29 

Silica 31-50        .        .      21-83 

Muriate  of  Soda        ....      1442        .        .       16-96 
Sulphate  of  Soda       ....        8-57        .        .        7-53 


ORGANIC  ANALYSIS.  783 

The  hot  springs  of  Pinnarkoon  and  Loorgoolha  in  India  are  analogous  to  the 
foregoing.  A  gallon  of  the  water  yields  about  24  grains  of  solid  matter ;  and 
the  saline  contents,  sent  to  Dr.  Brewster  by  Mr.  P.  Breton,  was  found  to  con- 
sist of  21'5  per  cent  of  silica,  19  of  chloride  of  sodium,  19  of  sulphate  of  soda, 
19  of  carbonate  of  soda,  pure  soda  5,  and  15*5  of  water.  (Edinburgh  Journal 
of  Science,  No.  xvii.  p.  97.) 

It  is  remarkable  that  nitrogen  gas  very  generally  occurs  in  hot  springs.  It  was 
found  by  Longchamp  in  various  hot  springs  of  France,  and  a  similar  observation 
has  been  made  by  Dr.  Daubeny.  Its  source  is  clearly  referable  to  atmospheric 
air  contained  in  water,  which  air  has  been  deprived  of  its  oxygen  by  chemical 
changes  in  the  interior  of  the  earth. 


ORGANIC  ANALYSIS. 


The  Analysis  of  organic  substances  has  for  its  object,  to  determine  the  nature 
and  quantity  of  the  elements  which  compose  them;  and  is  one  of  the  most  im- 
portant departments  of  analytical  chemistry.  The  method  employed  by  the 
earlier  chemists  to  obtain  a  knowledge  of  the  chemical  composition  of  organic 
bodies  had  not  the  smallest  resemblance  to  the  organic  analysis  of  the  present 
day.  They  subjected  these  bodies  to  destructive  distillation,  and  judged  of  the 
difference  in  their  composition  by  the  products  thus  obtained. 

It  is  only  within  the  last  thirty  years  that  this  department  of  chemistry  has 
been  cultivated  on  scientific  principles;  and  all  the  lately  proposed  methods 
differ  from  one  another  only  in  the  way  in  which  those  principles  are  carried  out. 
The  simplest  method  of  ascertaining  the  component  parts  of  an  organic  com- 
pound, would  seem  to  be,  to  endeavour  to  obtain  its  elements  in  a  separate 
form ;  but  it  is  obvious  that,  if  we  can  obtain,  instead  of  the  elements  in  the 
free  state,  compounds,  of  known  composition,  of  those  elements  with  others,  we 
can  determine  their  quantity  with  equal  accuracy. 

Most  vegetable  substances  contain  carbon,  hydrogen,  and  oxygen ;  a  small 
number  contain,  besides  these  elements,  nitrogen.  Of  these  four  simple  sub- 
stances, nitrogen  alone  can  be  obtained  in  a  state  of  purity  from  organic  com- 
pounds ;  but  if  all  the  carbon  be  convened  into  carbonic  acid,  and  all  the 
hydrogen  into  water,  we  can  then  calculate,  with  the  utmost  precision,  the  quan- 
tity of  carbon  and  hydrogen  from  that  of  the  carbonic  acid  and  water.  Even  if 
the  elements  of  organic  substances  could  be  separated  from  them  in  a  state  of 
purity,  we  should  be  forced  to  give  the  preference,  in  analysis,  to  the  indirect 
method  now  employed,  on  account  of  its  superior  accuracy. 

The  method,  then,  which  we  employ  to  procure  an  exact  knowledge  of  the 
composition  of  an  organic  compound,  consists  in  the  conversion  of  a  known 
weight  of  the  substance  into  carbonic  acid  and  water;  and  the  success  of  th 


784  ORGANIC  ANALYSIS. 

analysis  only  depends  on  the  apparatus  employed,  in  so  far  as  that  apparatus 
must  allow  us  to  collect  these  products  without  loss,  and  to  determine  their 
weight.  When  the  compound  contains  nitrogen,  this  element  is  collected  in  the 
separate  state;  and  the  oxygen  is  always  ascertained  indirectly. 

Gay-Lnssac,  and  Thenard,  the  first  chemists  wha  executed  organic  analysis, 
used  chlorate  of  potassa  for  the  combustion  of  organic  bodies.  The  substance 
to  be  analyzed  was  mixed  with  it,  the  mixture  formed  into  pellets,  and  intro- 
duced in  small  quantities  into  a  red  hot  tube  of  glass,  placed  vertically.  The 
gaseous  matter  disengaged  by  the  combustion  was,  by  means  of  a  lateral  tube, 
collected  in  a  jar  over  mercury. 

The  whole  gas  was  accurately  measured,  and,  the  corrections  for  barometer 
and  thermometer  being  made,  caustic  potassa  was  introduced  into  the  jar.  After 
all  the  carbonic  acid  was  absorbed,  there  remained  either  pure  oxygen  gas,  or  a 
mixture  of  oxygen  and  nitrogen.  The  relative  quantity  of  the  latter  was  ascer- 
tained by  the  eudiometer.  The  knowledge  of  the  weight  of  the  substance,  and 
that  of  the  chlorate  of  potassa ;  of  the  quantity  of  carbonic  acid  formed,  and  of 
the  oxygen  remaining,  supplied  all  the  data  necessary  for  calculating  the  com- 
position of  the  body  analyzed.  That  portion  of  the  oxygen  of  the  chlorate  of 
potassa  which  had  disappeared,  had  of  course  formed  water  with  the  hydrogen 
of  the  substance. 

The  only  objection  to  the  apparatus  of  Gay-Lussac  and  Thenard  was,  that  it 
made  the  accuracy  of  the  results  to  depend  too  much  on  the  dexterity  of  the 
operator.  The  analysis  of  substances  containing  nitrogen,  moreover,  by  means 
of  chlorate  of  potassa,  was  not  very  exact,  in  consequence  of  the  formation  of 
nitrous  acid;  and  it  was  obviously  impossible  to  employ  that  salt  in  the  analysis 
of  liquid  or  volatile  substances. 

Berzelius  endeavoured,  and  successfully,  to  render  this  method  more  conve- 
nient in  the  execution,  and  to  diminish  the  number  of  calculations  required.  He 
placed  the  tube  of  combustion  in  the  horizontal  position,  and  collected  the  water 
formed.  He  also  employed  the  chlorate  of  potassa,  mixed  with  a  large  quantity 
of  common  salt,  by  which  means  the  combustion  was  rendered  slower,  and  at 
the  same  time  the  advantage  was  gained  of  introducing  the  whole  of  the  sub- 
stance to  be  burned,  into  the  tube,  before  commencing  the  combustion. 

These  forms  of  apparatus,  which  were  applicable  only  to  a  very  limited  class 
of  bodies,  were  greatly  and  most  essentially  improved  by  the  use  of  oxide  of 
copper,  instead  of  chlorate  of  potassa ;  which  was  first  proposed  by  Gay-Lussac, 
and  employed  by  him  in  the  analysis  of  uric  acid.  At  present,  the  superiority 
of  oxide  of  copper  is  so  generally  admitted,  that  chlorate  of  potassa  is  no  longer 
employed.  Besides  oxide  of  copper,  chromate  of  lead  has  of  late  been  used  in 
the  analysis  of  many  substances  containing  a  large  proportion  of  carbon. 

De  Saussure  and  Prout  have  both  described  forms  of  apparatus  for  the  analysis 
of  organic  bodies,  which  differ  from  the  original  one  of  Gay-Lussac  and  The- 
nard, only  in  their  form,  and  in  the  substitution  of  oxygen  gas,  and  oxide  of 
copper,  instead  of  chlorate  of  potassa. 

The  apparatus  of  Prout  is  so  arranged  that  the  substance  to  be  analyzed  is 
burned,  either  alone,  or  mixed  with  some  other  body,  in  a  known  volume  of 
oxygen  gas,  and  the  volume  of  the  gas,  after  the  combustion,  is  compared  with 
its  original  bulk.  This  method  is  founded  on  the  well  known  fact,  that,  when 
carbon  is  burned  in  oxygen  gas,  the  carbonic  acid  gas  produced,  occupies  exactly 
the  same  space  as  the  oxygen  consumed,  and  consequently  does  not  alter  its 


ORGANIC  ANALYSIS.  7g5 

volume :  as  also,  that  when  hydrogen  unites  with  oxygen,  for  each  volume  of 
hydrogen,  half  a  volume  of  oxygen  disappears  by  the  condensation  of  the  water 
which  is  formed. 

Consequently,  if  the  substance  to  be  burned  consists  of  carbon,  hydrogen,  and 
oxygen,  there  are  only  three  cases  possible.  Either  the  volume  of  the  oxygen 
is  unaltered ;  and  in  this  case,  the  substance  contains  oxygen  and  hydrogen  in 
the  proportions  necessary  to  form  water;  or  the  volume  of  the  oxygen  is  di- 
minished, or  it  is  increased.  In  the  latter  cases,  the  body  either  contains  more 
hydrogen,  and  consequently  less  oxygen  than  is  sufficient  to  form  water ;  or 
there  is  less  hydrogen,  and  consequently  more  oxygen  than  is  required  for  that 
purpose.  The  diminution  or  increase  in  the  volume  of  the  oxygen  can  be  ex- 
actly measured,  and,  the  quantity  of  the  carbonic  acid  produced  being  ascer- 
tained, it  is  easy  to  express  the  composition  of  the  substance  in  numbers. 

But  this  apparatus  cannot  be  applied  to  the  anlysis  of  substances  containing 
nitrogen,  nor  to  that  of  many  other  bodies.  Lately,  Brunner  has  constructed 
an  apparatus  on  a  similar  principle.  All  these  forms  of  apparatus,  however, 
have  been  employed  by  their  inventors  alone ;  and  as  they  have  no  advantage 
over  the  one  now  commonly  employed,  it  is  unnecessary  to  describe  them*  mi- 
nutely in  this  place. 

GENERAL  METHOD  OF  PROCEEDING. 

In  the  next  section  we  shall  describe  the  instruments  and  processes  which 
are  at  present  employed  by  the  majority  of  chemists  for  organic  analysis;  and 
we  shall  here  prefix  some  general  remarks  on  the  operations  which  occur  in 
such  analyses. 

It  will  be  observed,  that  all  the  parts  of  the  apparatus  used  for  this  purpose 
are  extremely  simple,  and  for  their  employment  require  no  especial  dexterity. 
The  essential  conditions  for  performing  a  good  analysis  are,  the  greatest  accuracy 
in  weighing,  and  the  strictest  conscientiousness  in  the  execution  of  all  the  pre- 
paratory steps  of  the  process.  Let  us  not  flatter  ourselves  that  we  can  obtain 
an  accurate  result,  if  any  thing  be  neglected  that  can  secure  it.  All  the  time 
and  labour  we  bestow  are  thrown  away,  if  we  omit  any  one  of  the  precautions 
which  are  recommended. 

It  is  obvious  that  the  object  in  view  may  be  obtained  by  various  means,  and 
that  the  methods  described  in  the  following  pages  are  susceptible  of  improve- 
ment: but  all  the  so-called  improvements,  hitherto  proposed,  only  prove  that 
their  authors  are  ignorant  of  the  most  general  principles  of  what  a  method  ought 
to  be. 

Every  chemist  will  be  able,  when  he  has  acquired  some  experience  in  organic 
analysis,  to  alter  the  apparatus  here  described,  in  particular  cases,  according  to 
his  ideas,  and  to  adapt  it  to  the  object  he  has  in  view;  but  it  would  be  going 
too  far  to  consider  this  deviation  in  a  special  case,  as  an  improvement  of  the 
process  in  general,  and  to  recommend  it  as  such. 

There  is  within  the  human  mind  an  innate  desire  for  improvement — hence  the 
efforts  to  improve  what  we  possess,  and  to  discover  new  means  of  attaining  the 
desired  object.  But  we  frequently  commit  the  error  of  neglecting  to  test  the 
utility  of  the  known  methods,  or  even  to  make  ourselves  familiar  with  them. 
We  begin  by  deviating  from  the  customary  path  ;  and  if  our  efforts  be  crowned 
with  success,  the  satisfaction  we  experience  in  the  discovery  we  have  made, 

52 


786 


ORGANIC  ANALYSIS. 


leads  us  to  overlook  the  circuitous  nature  of  the  route  we  have  followed,  and 
the  difficulties  we  have  had  to  overcome,  which  we  should  not  have  encountered 
on  the  beaten  path. 

n  In  what  follows,  we  hold  to  the  rule  of  Berzelius,  the  most  experienced 
chemist  of  our  own,  and  probably  also  of  all  times ;  and  of  two  equally  good 
methods,  we  prefer  the  simple  to  the  complicated  one. 

The  first  problem  to  be  solved,  in  performing  an  organic  analysis,  is,  to  pro- 
cure the  substance  to  be  analyzed  in  the  highest  degree  of  purity.  No  means 
should  be  neglected  to  satisfy  ourselves  of  the  absence  of  foreign  matters.  The 
matter  being  supposed  pure,  we  must  attend  to  the  difficulty  of  determining  the 
weight  of  the  body  to  be  analyzed,  as  one  source  of  uncertainty  in  the  results 
of  the  analysis,  and  of  the  variations  occurring  in  different  analyses  of  the  same 
substance.  All  organic  bodies  greedily  absorb  moisture  from  the  air,  and  thus 
become  heavier.  They  must,  therefore,  first  be  deprived  of  all  hygrometric 
moisture,  and  then  weighed  in  such  a  manner  that  it  is  hardly  possible  for  them 
to  attract  moisture  during  the  time  they  are  in  the  scale. . 

When  we  consider  that  an  excess  of  water,  to  the  amount  of  youths  or  j§(jths 
of  a  grain  is  equivalent  to  a  loss  of  twice  as  much  carbonic  acid,  we  cannot 
surely  bestow  too  much  attention  on  the  accurate  determination  of  the  weight 
of  the  substance  to  be  analyzed. 

This  object  may  be  obtained  in  various  ways.  The  following  apparatus  gives 
complete  security  on  this  head.    It  consists  of  the  tnheA,fg.  1.    The  wide 

Fig.  1. 


part  below  is  about  half  an  inch  in  diameter :  the  tubes  a  and  b  are  barometer 
tubes,  one  of  one-sixth,  the  other  of  one -fourth  of  an  inch  in  diameter.  The 
substance  is  introduced  by  the  wide  tube  6,  which  is  then  connected  by  means 
of  a  cork  with  the  tube  C,  containing  fused  chloride  of  calcium.  The  opposite 
tube  a  is  joined  with  the  tube  dfjig.  2 :  c  is  an  ordinary  syphon.  The  tube  d 
is  about  an  inch  shorter  than  o',  the  external  limb  of  the  syphon. 

Fig.  2. 


By  means  of  this  arrangement  we  can  produce  a  perfectly  uniform  discharge 
of  water  from  the  three  necked  bottle ;  and  since  the  air,  which  replaces  the 


ORGANIC  ANALYSIS. 


787 


water,  must  enter  the  bottle  by  the  tube  d,  we  can  instantly  perceive  whether  all 
the  joinings  are  air-tight. 

The  bottle  is  filled  with  water ;  and,  of  course,  when  this  water  is  made  to 
flow  out  by  the  syphon,  the  continual  current  of  dry  air  thus  produced  entirely 
removes  all  moisture  from  the  substance. 

The  horizontal  part  of  the  drying  apparatus  is  placed  in  a  sand  bath,  a  water 
bath,  a  bath  of  solution  of  chloride  of  calcium,  &c.,  according  to  the  temperature 
to  which  we  wish  to  expose  the  substance.  If  we  wish  to  determine  the  amount 
of  water,  the  apparatus  A  is  weighed,  first  empty,  and  then  with  the  substance. 
It  is  then  placed  in  the  water  bath,  &c.,  and  a  stream  of  dry  air  is  made  to  pass 
through  it,  as  long  as  water  condenses  in  the  tube  cf.  By  weighing  occasion- 
ally, we  ascertain  if  it  loses  weight.  When  the  weight  becomes  constant,  a 
small  portion  of  the  substance  is  shaken  out  of  h  into  a  long  and  perfectly  dry 
test  tube,  which  is  then  heated  by  a  spirit  lamp  or  sand  bath — of  course  to  a 
degree  insufficient  to  produce  decomposition.  If  no  trace  of  water  bedew  the 
side  of  the  test  tube,  we  may  be  certain  that  the  substance  is  perfectly  dry :  if 
any  moisture  appear,  the  water  bath  must  be  replaced  by  one  of  a  solution  of 
salt,  or  of  chloride  of  calcium,  and  the  operation  repeated  at  a  higher  temperature. 

Mitscherlich  employs  a  simi-  ^^S*  ^* 

lar  apparatus  for  drying  organic       , 
substances  ;  but  instead  of  the 
bottle  and  syphon  he  connects 
with  the  tube  a  a  hand  air- 
pump,  by  means  of  which  he 

draws  air  through  the  apparatus  till  the  substance    is 
dry.     But  it  is  extremely  fatiguing  to  continue  pumping 


from  four  to  six  hours ;  and  probably  no  one  will  adopt  this 
method,  except  where  no  three  necked  bottle  is  to  be  had. 

Instead  of  the  bottle  we  may  employ,  with  still  greater 
convenience,  a  vessel  of  tin  plate,  Jig.  3,  which  holds 
about  4  gallons  of  water.  The  funnel  a  serves  for  replen- 
ishing the  vessel  when  empty,  when  the  air  escapes  by 
the  middle  opening  &,  which  is  shut  with  a  cork  at  other 
times.    The  flow  of  water  is  regulated  by  the  stopcock. 

When  the  substance  retains  water  with  great  obstinacy,  it  is  dried  in  vacuo  at 
a  high  temperature.    The  cut  fig.  4,  exhibits  this  arrangement.     A  is  a  small 

Fig.  4. 


788  ORGANIC  ANALYSIS. 

hand  air-pump,  B  a  tube  with  chloride  of  calcium,  D  a  strong  cylindrical  tube, 
sealed  at  one  end,  which  contains  the  substance  to  be  dried.  C  is  a  thermometer. 
The  tube  D  is  placed  in  an  iron  or  copper  vessel  with  a  concentrated  solution 
of  chloride  of  zinc,  and  heated  nearly  to  the  temperature  at  which  the  substance 
is  decomposed.  After  the  moist  air  has  been  removed  by  the  air-pump,  air  is 
from  time  to  time  admitted  into  the  apparatus  by  the  stopcock  a  ,•  this  air  by 
passing  through  the  chloride  of  calcium,  is  each  time  deprived  of  all  hygrometic 
moisture,  so  that  in  a  very  short  time,  at  most  in  a  few  minutes,  we  can  by  this 
means  remove  all  water,  whether  hygrometric  water  or  water  of  crystallization. 
Fig.  5.  When  the  substance  is  dry,  a  certain  quantity  of  it  must  be  weighed 
out  for  analysis.  This  is  best  done  in  a  small  narrow  tube,  open  at  the 
lend.  The  cut,  Jk;,  5,  exhibits  it  of  the  actual  size.  This  tube  may 
either  be  placed  horizontally  on  the  scale,  or  set  in  a  conical  roll  of  tin- 
plate,  which  rests  with  its  broad  end  on  the  pan  of  the  balance.  A 
stand  of  tin-plate  is  also  very  convenient.  The  tube  being  weighed,  a 
portion  of  the  substance  is  introduced  and  the  tube  is  weighed  again. 
The  increase  of  weight  gives  the  quantity  of  the  substance. 

We  may  also  counterpoise  the  tube  with  the  substance,  empty  the  tube, 
and  return  it  into  the  scale  with  any  adhering  particles.  The  weight 
necessary  to  restore  the  counterpoise,  gives  the  quantity  taken  out  of  the 
tube. 

As  a  general  rule,  we  must  avoid  all  weighing  in  a  watch-glass,  or  any 
wide  vessel.  With  the  narrow  tube  recommended,  no  appreciable  change 
of  air  can  take  place  within  it  during  the  short  time  it  lies  on  the  scale ;  and 
even  when  containing  highly  hydroscopic  substances,  this  simple  apparatus  does 
not  increase  in  weight  in  the  course  of  half  an  hour. 

We  have  now  a  known  quantity  of  the  substance.  To  determine  the  amount 
of  its  carbon  and  hydrogen,  we  must  convert  the  carbon  into  carbonic  acid,  and 
the  hydrogen  into  water,  and  we  must  ascertain  the  weight  of  both  these  pro- 
ducts. 

In  general,  the  substance,  if  dry  and  pulverizable,  is. mixed  with  oxide  of 
copper,  and  the  mixture  heated  in  a  glass-tube  by  means  of  a  charcoal  fire.  The 
tube  of  combustion  is  15  to  18  inches  long,  and  A  to  J  of  an  inch  in  diameter. 
The  closed  end  is  drawn  out  to  a  point,  which  is  bent  obliquely  upwards,  and 
sealed.  During  the  mixture  of  the  substance  with  the  oxide  of  copper,  both 
bodies  attract  moisture  from  the  air.  This  water  would  increase  the  weight  of 
that  formed  in  the  combustion,  and  must  be  most  carefully  and  completely  re- 
moved before  the  combustion. 

This  is  most  easily  effected  by  an  arrangement  similar  to  that  above  described, 
for  drying  the  substance  in  vacuo  at  a  high  temperature.  A^  fg.  6,  is  the  air- 
pump,  B  the  tube  with  fused  chloride  of  calcium,  C  the  tube  of  combustion 
filled  with  the  mixture,  which  is  placed  in  a  wedge-shaped  box  of  wood,  D, 
and  surrounded  with  sand  heated  to  250°  Fahrenheit.  Before  pumping  out  the 
air,  the  tube  with  the  mixture,  C,  must  be  subjected,  in  the  horizonal  position, 
to  several  smart  taps  on  a  table,  so  that  a  space  is  seen  to  be  empty  above  the 
mixture  all  along  the  tube.  If  this  method  of  furnishing  a  free  exit  to  the  air 
when  pumped  out  be  neglected,  as  soon  as  the  pump  is  worked,  a  part  of  the 
mixture  is  forced  into  the  tube  with  chloride  of  calcium.  We  now  produce  a 
vacuum  in  the  tube,  and  allow  dry  air  from  time  to  time  to  enter  by  the  stopcock, 
and  after  pumping  out  the  air  ten  or  twelve  times,  we  can  perceive  no  further  de- 


ORGANIC  ANALYSIS. 
Fig.  6. 


m 


position  of  moisture  at  the  point  b  of  the  tube  B,  even  when  we  surround  it  with 
cotton  wool,  and  cool  it  by  dropping  ether  upon  it.  The  mixture  may  then  be 
considered  dry. 

The  substance  is  mixed  with  pure  oxide  of  copper  in  a  clean  and  warm  mortar 
of  Wedgewood's  ware  or  porcelain.  The  more  carefully  we  divide  the  sub- 
stance and  mix  it  with  the  oxide  of  copper,  the  more  easy  and  complete  is  the 
combustion, 

Mitscherlich  leaves  the  point  of  the  tube  of  combustion  open,  joins  either  end 
with  a  tube  containing  chloride  of  calcium,  with  the  other  end  of  which  is  con- 
nected a  pair  of  bellows ;  heats  the  oxide  of  copper,  which  has  been  introduced 
so  as  to  fill  half  of  the  tube,  to  a  low  red  heat,  and  forces,  by  means  of  the  bel- 
lows, dry  air  over  the  hot  oxide.  The  point  is  then  sealed  up.  He  now  coun- 
terpoises the  tube  with  the  oxide  of  copper,  and  shakes  out  of  the  tube  in  which 
it  has  been  dried,  a  portion  of  the  substance  to  be  analyzed,  into  the  counterpoise 
tube.    The  increase  of  weight  gives  the  quantity  of  the  substance. 

He  now  mixes  it  with  the  oxide  of  copper  in  the  following  manner : — He 
bends  one  end  of  a  long  copper  wire  into  the  form  of  a  corkscrew,  screws  this 
half  way  into  the  layer  of  oxide,  and  moves  it  up  and  down  till  the  mixture  ap- 
pears sufficiently  intimate. 

This  method  is  less  convenient  and  more  troublesome  than  the  one  above  de- 
scribed. In  the  first  place  the  weight  of  the  tube  with  oxide  of  copper,  (from 
1800  to  2100  grains,)  does  not  permit  us  to  determine  the  weight  of  the  sub- 
stance to  be  analyzed  to  the  g^^jth  of  a  grain.  This  is  a  source  of  uncertainty. 
Again,  we  cannot  efiect  a  complete  mixture  by  m6ans  of  a  corkscrew  wire. 
This  is  easily  shown.  If  we  mix  some  starch  as  intimately  as  possible  with 
oxide  of  copper  in  this  manner,  and  press  the  mixture  in  a  mortar  with  the  pestle, 
we  easily  recognize  the  unmixed  or  cohering  particles  of  starch  by  a  number  of 
round  white  spots.     The  interior  of  these  particles  would  only  be  charred,  not 


790 


ORGANIC  ANALYSIS. 


burned.      Berzelius  recommends  this  method,  when  we  have  not  an  air-pump ; 
but  in  that  case  it  would  be  better  not  to  attempt  the  analysis  of  organic  bodies 
at  all. 
The  water  formed  in  the  combustion  is  collected  in  the  tube,  fig,  7,  which  is 
Yig,  7.  filled  with  chloride  of  calcium — large  frag- 

ments being  placed  in  the  bulb,  and  coarse 
powder  in  the  long  tube.  Near  the  two  open 
ends  of  this  tube,  at  a  and  6,  is  put  a  little 
cotton-wool,  in  order  to  prevent  any  chloride  of  calcium  from  falling  out.  The 
tube  b  is  fitted  tight  into  the  larger  tube  by  means  of  a  cork  :  the  cork  is  cut  off 
close  to  the  tube,  and  covered  with  sealing  wax  to  prevent  dust  from  adhering  to 
it.  The  whole  is  weighed.  Its  increase  of  weight  after  the  combustion  gives 
the  quantity  of  water  produced. 

The  tube  with  chloride  of  calcium,  thus  prepared,  is  connected  at  the  end  a 
by  means  of  a  cork  to  the  tube  of  combustion,  fig.  8.  The  cork  should  be  per- 
forated by  means  of  Mohr's  cork-borer,  and  the  aperture  filed  very  smooth,  and 
made  to  fit  the  end  a  very  tight.  It  is  then,  with  a  very  sharp  straight-edged 
knife,  cut  so  as  to  fit  closely  into  the  tube  of  combustion.  According  to  the 
shape  of  the  tube,  the  cork  should  be  cut  cylindrical  or  slightly  conical.  We 
must  avoid  perforating  the  cork  with  a  hot  wire,  as  most  corks  perforated  in  this 
way  crack,  and  become  useless. 

Fig.  8, 


The  carbonic  acid  formed  in  the  combustion  is  collected  in  the  apparatus,^.  9. 

_,.    g  which   is   filled  with   a   solution   of 

caustic  potassa,  in  such  a  manner  that 

a  small  bubble  of  air  remains  in  each 

bulb.     This  apparatus  consists  of  a 

glass    tube,   in  which    5  bulbs   are 

blown.    To  fill  this   apparatus  with 

caustic  ley,  one  end  must  be  connected 

by  a  cork  with  the  sucker,^.  10 ;  the 

\^  other  end  of  the  potassa  apparatus  is 

then  dipped  into  a  glass  containing 

the  ley,  and  the  liquid  drawn  by  suction  with  the  mouth  into  the  apparatus.  The 

end  of  the  tube  which  has  been 
'^'     *  moistened  with  the  ley  is  to  be 

dried  externally,  and  internally  : 
the  latter  is  easily  accomplished 
by  means  of  a  small  roll  of  filter- 
ing paper.  The  apparatus,  when 
quite  dry  and  clean,  is  weighed, 
\4  and  then  joined  to  the  tube  with 
the  chloride  of  calcium  by  means 
of  a  small  tube  of  caoutchouc. 

The  potassa  apparatus,  when 
filled  with  ley,  commonly  weighs 


ORGANIC  ANALYSIS.  791 

from  750  to  900  grains.  If  the  ley  have  the  sp.  gr.  1"25  to  r27,  it  does  not  pro- 
duce foam  when  bubbles  of  gas  pass  through  it ;  and  when  of  this  strength,  its 
absorptive  power  is  likewise  greatest.  Caustic  soda  ley  foams  like  soap  and 
water,  and  must  therefore  be  avoided. 

[The  ley  is  best  prepared  in  the  following  manner.  Two  parts  of  the  subcar- 
bonate  of  potassa  of  the  shops  are  dissolved  in  20  to  24  of  boiling  water.  One 
part  of  quicklime  is  slaked  by  being  covered  with  hot  water  in  any  convenient 
vessel.  In  this  way  the  whole  of  the  lime  is  converted  into  a  uniform  cream, 
without  the  formation  of  any  hard  sandy  particles,  which  occur  in  the  ordinary 
method  of  slaking,  and  which  are  not  only  useless  but  hurtful,  by  preventing, 
from  the  space  they  occupy,  and  the  increased  proportion  of  lime  they  render 
necessary,  the  separation,  by  decanting,  of  much  of  the  ley.  The  cream  of  lime 
is  added  in  small  portions  to  the  boiling  solution  of  carbonate  of  potassa,  which 
is  boiled  a  few  minutes  after  each  addition,  water  being  occasionally  added  to 
supply  the  loss  by  evaporation.  When  the  whole  of  the  lime  has  been  added, 
the  mixture  is  boiled  for  a  short  time  longer,  and  is  then  allowed  to  cool  in  the 
pan  or  goblet,  carefully  closed  with  its  lid.  After  12  hours,  nearly  the  whole  of 
the  ley  may  be  decanted  perfectly  clear,  and  quite  caustic,  especially  if  the  vessel 
has  been  nearly  full.  The  carbonate  of  lime,  when  this  process  is  followed  ex- 
actly, is  sandy,  and  occupies  a  very  small  bulk.  The  clear  liquid  is  now  to  be 
rapidly  boiled  down  in  a  clean  iron  vessel,  till  small  crystals  begin  to  separate. 
It  is  then  allowed  to  cool  in  a  stoppered  bottle  of  green  glass,  when  it  deposits 
the  whole  of  the  sulphate  of  potassa  originally  present  in  the  subcarbonate ;  that 
salt  being  absolutely  insoluble  in  a  clear  solution  of  caustic  potassa.  For  the 
above  essential  improvements  in  the  preparation  of  caustic  potassa,  we  are  in- 
debted to  the  author  of  this  treatise  and  to  Dr.  F.  Mohr  of  Coblentz.  I  find 
that  the  solution  which  has  deposited  the  sulphate  of  potassa  possesses  the  sp. 
gr.  1*25,  and  is  perfectly  adapted  for  organic  analysis.  As  all  contact  with 
organic  matter  has  been  avoided,  it  is  also  in  general  colourless,  and  yields  solid 
caustic  potassa  almost  white,  containing  no  impurity  except  a  little  chloride  of 
potassium;  which  of  course  may  be  avoided  by  using  genuine  salt  of  tartar;  but 
which  does  not  in  the  least  affect  the  use  of  the  potassa  for  most  purposes.  The 
necessity  for  using  at  least  10  or  12  parts  of  water  to  1  of  carbonate  of  potaasa 
arises  from  the  curious  fact,  noticed  by  Professor  Liebig,  that  when  less  water 
is  present,  the  potassa  takes  1back  the  carbonic  acid  from  the  carbonate  of  lime. — 
W.  G.] 

The  tubes  of  caoutchouc  are  made  out  of  thin  sheets  of  that  substance.  A  por- 
tion, IJ  inch  long,  is  doubled  up  so  as  to  form  a  tube  of  the  size  of  those  which 
it  is  to  connect.  About  a  line  in  width  is  now  to  be  cut  oflf  with  a  very  clean 
and  sharp  pair  of  scissors,  along  the  length  of  the  caoutchouc  where  the  two  sides 
meet.  We  thus  obtain  two  smooth  cut  surfaces,  which,  if  pressed  together  by 
the  thumb  nails,  adhere  so  as  to  form  a  perfect  junction.  The  tube  is  now  pulled 
lengthways,  so  as  to  stretch  it  several  times.  If  we  touch  the  fresh  cut  surfaces 
with  the  fingers,  they  do  not  cohere  where  they  have  been  touched.  It  is  right 
also  to  moisten  the  inside  of  the  caoutchouc,  before  forming  the  tube,  that  its 
sides  may  not  cohere.  The  caoutchouc  tubes  are  fastened  over  the  glass  tubes 
by  strong  threads  of  silk,  knotted  at  the  ends,  to  prevent  them  from  slipping. 

[It  is  more  effectual  to  dust  the  inside  of  the  tube  with  any  fine  powder,  such 
as  flour  or  starch — removing  all  that  is  superfluous. — W.  G.] 


^g/^  ORGANIC  ANALYSIS. 

The  furnace  in  which  the  combustion  is  carried  on,  is  exhibited  hy  Jig.  II.  It 

is  made  of  sheet  iron,  22  to  24  inches  long, 

and  3  inches  high.     The  bottom  is  3  inches 

wide,  and  furnished  with  apertures  which 

form  a  sort  of  grate;   these  apertures  are 

narrow  slits,  running  across,  at  an  half  inch 

distance  from  each  other.     The  sides  of  the 

furnace  are  inclined  outwards  so  that  at  the 

top  they  are  4J  inches  apart.    The  whole  rests  on  a  large  tile  or  paving  stone, 

e,Jig.  14,  in  such  a  manner  that  the  two  slits  nearest 

^  '      '  the  front  are  left  open,  while  the  remainder  are  closed 

W*^  <^  ffi  ^y  the  tile.  Within  the  furnace  are  placed  at  inter- 
\  ^i  ll  ^^^  supports  of  strong  sheet  iron,  of  the  form  D, 
^^^  fig.  12.  They  must  be  of  equal  height,  and  must 
correspond  with  the  round  aperture  in  the  front  of  the  furnace,  A,  fig.  12.  Their 
use  is  to  support  the  tube  of  combustion. 

When  we  wish  to  increase  the  heat,  the  furnace  is  raised  a  little  on  one  side, 
and  a  thin  bit  of  tile  is  introduced  at  two  places.  This  allows  air  to  enter  by  all 
th£  slits  in  the  bottom  of  the  furnace.  Good  charcoal  is  the  only  fuel  employed 
in  this  furnace. 

SPECIAL  DETAILS  OF  THE  METHOD. 

The  tube  of  combustion,  if  necessary,  is  washed  out  with  water,  and  dried  by 
means  of  bibulous  paper  tied  round  a  whalebone.  When  the  point  has  been 
drawn  out  and  sealed,  the  tube  is  made  very  hot,  and  a  long  narrow  tube  intro- 
duced as  far  as  the  closed  end.  By  drawing  air  through  the  narrow  tube  with 
the  mouth,  the  last  traces  of  moisture  are  soon  removed.  The  dry  tube  is  rinsed 
out.  with  a  little  hot  oxide  of  copper,  which  is  then  put  aside.  In  order  to  have 
some  measure  of  the  quantity  of  oxide  which  is  to  be  mixed  with  the  substance 
we  wish  to  analyze,  the  tube  is  now  to  be  filled  to  three-fourths  of  its  length  with 
pure  oxide  of  copper,  out  of  the  crucible  in  which  it  has  been  just  ignited,  and  while 
it  is  yet  hot.  We  must  carefully  avoid  bringing  this  oxide,  which  is  destined 
for  the  coinbustion,  in  contact  with  any  foreign  matter. 

The  mixture  of  solid  substances,  not  volatile,  witli  the  oxide  of  copper,  must 
always  be  made  in  a  mortar  of  porcelain,  (Wedgewood's  ware,)  of  a  smooth, 
but  not  polished  surface,  and  a  deep  shape.  The  mortar  is  previously  rubbed 
out  with  pure  oxide  of  copper,  which  is  put  aside.  The  weighed  substance  is 
now  shaken  out  into  the  mortar,  and  the  tube  in  which  it  was  contained  rinsed 
out  with  a  little  oxide  of  copper,  which  is  added  to  the  substance.  The  latter  is 
first  rubbed  with  a  little  oxide,  with  which  it  is  intimately  mixed,  and  by  de- 
grees the  whole  oxide  of  copper  is  added,  which  had  been  measured  in  the  tube. 

The  mixture  must  be  made  without  applying  any  great  force,  for  which  reason 
the  substance,  before  being  weighed,  and  the  oxide  of  copper,  before  the  gentle 
ignition  which  must  always  precede  its  use,  must  be  reduced  to  a  fine  powder. 
If  the  oxide  of  copper  contain  hard  particles,  the  mixture  cannot  be  made  suffi- 
ciently intimate ;  and  it  often  happens  that  the  pestle,  when  pressed  on  such 
particles,  springs  off,  whereby  portions  of  the  mixture  may  be  thrown  out  of  the 
mortar.  If  the  mortar  be  placed  on  a  sheet  of  glazed  writing  paper,  it  is  easy  to 
see  whether  any  part  of  the  mixture  has  been  lost  or  not. 


ORGANIC  ANALYSIS. 


793 


Having  first  introduced  pure  oxide  of  copper,  so  as  to  fill  about  half  an  inch 
at  the  closed  end  of  the  tube  of  combustion,  we  now  transfer  the  mixture  from 
the  mortar  to  the  tube.  The  mortar  is  rubbed  out  with  pure  oxide  of  copper, 
which  is  also  introduced  into  the  tube,  and  above  the  whole  is  put  pure  oxide  of 
copper,  till  within  one  inch  of  the  open  end  of  the  tube.    In  jig.  13  are  shown 

Fig.  13. 


the  lengths  of  the  different  layers  of  pure  oxide,  mixture,  rising  from  the  mortar, 
and  again  pure  oxide.  They  are  marked  by  the  dotted  lines,  and  serve  to  show 
nearly  the  usual  proportions. 

The  cork  which  joins  the  tube  of  chloride  of  calcium  to  the  tube  of  combus- 
tion, is  struck  with  a  light  hammer,  till  it  becomes  soft  and  elastic.  When  the 
perforation  for  the  small  tube  is  finished,  and  the  cork  accurately  fitted  to  the 
tube  of  combustion,  the  cork  is  placed  in  a  covered  crucible  in  hot  sand,  in  order 
to  expel  from  it  all  hygrometric  moisture.  It  must  fit  very  tight  into  the  tube 
of  combustion ;  but  its  softness  allows  the  employment  of  the  necessary  force, 
without  the  risk  of  breaking  the  apparatus. 

The  tube  of  combustion,  and  that  with  the  chloride  of  calcium,  must  be  hori- 
zontal, or  very  slightly  inclined  towards  the  potassa  apparatus,  so  that  the  water 
which  collects  in  the  narrow  end  of  the  tube  with  chloride  of  calcium,  may  flow 
forward  of  itself  to  the  chloride  of  calcium.  For  this  purpose,  the  farther  end 
of  the  furnace  is  made  a  little  higher  than  the  other,  by  introducing  a  thin  bit  of 
wood  or  iron  below  the  tile  at  that  end.    Fig.  14  shows  the  whole  apparatus 

Fig.  14. 


arranged  for  the  combustion;  a  is  the  tube  of  combustion,  h  the  tube  with  chlo^ 
ride  of  calcium,  c  the  caoutchouc  tube,  m  the  larger  bulb  of  the  potassa  apparatus, 
which  is  joined  to  the  tube  5,  e  is  the  tile,/ a  small  wedge  of  iron  introduced  to 
give  the  furnace  a  slight  inclination  towards  the  potassa  apparatus. 

The  tube  of  combustion,  before  being  joined  with  the  tube  6,  or  introduced 
into  the  furnace,  must  be  tapped  smartly  in  the  horizontal  position  on  a  flat  table, 
in  order  to  produce,  above  the  mixture,  [Jig.  13)  through  the  whole  length  of  the 
tube,  a  vacant  space  to  afford  a  passage  to  the  gaseous  products  of  the  combus- 
tion. Without  this  precaution,  it  often  happens  that  the  oxide  of  copper  is 
thrown  forwards,  or  that  the  tube  at  the  farther  end  becomes  choked.  Innume- 
rable analyses  have  shown  that,  with  this  arrangement,  the  combustion  is  not 
less  complete  than  when  no  vacant  space  is  left,  however  rich  in  carbon  the  sub- 
stance may  be. 


794  ORGANIC  ANALYSIS. 

Mitscherlich  screws  a  spiral  of  copper  wire  through  the  whole  length  of  the 
mixture,  and  leaves  it  in  the  tube  during  the  operation,  with  the  design  of  in- 
terrupting the  continuity  of  the  mass ;  but  we  cannot  depend  on  its  efficiency. 
I  repeat,  that  the  arrangement  described  gives  the  only  security  for  the  uniform 
success  of  the  analysis. 

The  anterior  portion  of  the  tube  of  combustion  contains  pure  oxide  of  copper, 
which  must  be  raised  to  a  red  heat  before  that  part  of  the  tube  which  contains 
the  mixture  is  surrounded  with  glowing  charcoal. 

But,  before  beginning  the  combustion  at  all,  it  is  absolutely  necessary  to  be 
assured  that  all  the  joinings  are  air-tight. 

To  ascertain  this,  a  small  quantity  of  air  is  sucked  out  of  the  apparatus,  by 
means  of  the  suction-tube  b,  (Jig.  10,)  and  the  mouth;  this  naturally  causes  the 
ley  to  rise  in  the  tube  of  the  bulb,  m.  It  is,  consequently,  from  1  to  Ij  inch 
higher  in  that  than  in  the  opposite  tube,  as  may  be  seen  in  B,  (fg.  9,)  where 
a  and  j3  mark  the  level  of  the  ley  in  both  tubes.  If  this  level  does  not  remain 
unchanged  ;  that  is,  if  the  liquid  falls  back  into  the  middle  part  of  the  appara- 
tus, A,  Jig.  9,  air  must  enter  the  apparatus  either  by  the  caoutchouc  tube,  c,  or 
the  cork.  One  or  both  must  be  changed,  till  the  liquid  raised  by  suction  to  a> 
remains  steadily  at  the  same  point. 

The  anterior  portion  of  the  tube  of  combustion  is  now  surrounded  with  red- 
hot  charcoal.  If  the  tube  be  quite  dry,  and  the  glass  free  from  knots,  there  is 
no  danger  of  its  being  cracked  by  the  heat.  If  the  oxide  of  copper  has  not 
been  thoroughly  dried,  the  first  action  of  the  heat  causes  a  more  or  less  distinct 
deposition  of  dew  on  the  cold  empty  part  of  the  tube  a,  which  projects  one  inch 
out  of  the  furnace.  In  this  case,  we  may  be  quite  certain  that  the  determina- 
tion of  the  hydrogen  will  give  an  excess. 
Fig.  15.  ^^  ^^®P  ^^®  fragments  of  charcoal  in  their  place,  and  to  prevent  the 
heat  from  spreading  to  the  remaining  parts  of  the  tube  a,  the  screen  g, 
Jig.  14,  is  employed.  It  is  made  of  strong  sheet-iron,  with  a  slit  for 
the  tube,  and  of  the  shape  of  Jig.  15,  which  fits  the  sides  of  the  fur- 
nace. 

The  screen  is  set  up  behind  the  interior  part  of  the  tube,  which  contains  pure 
oxide  of  copper.  When  this  has  been  heated  red-hot,  the  screen  is  moved  one- 
half  to  one  inch  backwards,  and  this  part  surrounded  with  red-hot  charcoal. 
The  distance  to  which  the  screen  is  to  be  moved  each  time,  depends  on  the 
rapidity  with  which  gas  is  disengaged.  So  much  red-hot  charcoal  must  be  put 
on  each  time,  that  the  part  of  the  tube,  which  must  be  completely  surrounded 
\vith  glowing  coals,  shall  be  quickly  raised  to  a  red  heat.  Even  when  the  dis- 
engagement of  gas  is  at  first  more  rapid  than  is  desirable,  we  must  not  remove 
the  charcoal  we  have  put  on.  To  do  so  would  rarely  moderate  the  disengage- 
ment of  gas,  but  might  easily  render  the  combustion  imperfect.  We  must, 
therefore,  endeavour  to  regulate  the  current  of  gas,  by  heating  shorter  portions 
of  the  tube  at  once. 

The  fore-end  of  the  tube,  which  is  empty,  and  projects  one  inch  out  of  the 
furnace,  must  be  kept  during  the  whole  operation,  so  hot  that  not  the  smallest 
quantity  of  water  can  condense  within  it.  In  this  way,  we  can  avoid  any  loss 
of  water  with  certainty. 

The  combustion  would  proceed  with  perfect  regularity,  if  we  could  deprive 
the  glass  of  all  conducting  power.  This  is  impossible,  but  we  cannot  be  too 
careful  only  to  heat  small  portions  of  the  tube  at  once.  The  bubbles  of  gas 
must  form  an  uninterrupted  and  rapid  current,  yet  not  too  rapid. 


% 


ORGANIC  ANALYSIS.  795 

When  there  are  too  few  supports  in  the  furnace,  the  tube  sometimes  bends  by 
its  own  weight;  but  there  is  no  danger  of  its  being  blown  into  holes,  as  the 
pressure  of  the  liquid  which  the  gas  has  to  overcome  in  escaping,  is  too  small 
to  act  on  the  glass,  even  when  softened  by  the  heat. 

Mitscherlich  places  the  tube  of  combustion  in  a  gun-barrel,  filed  open  the  long 
way  so  as  to  admit  the  tube.  He  thus  endeavours  to  secure  a  uniform  heating, 
without  melting  of  the  tube ;  but  in  this  way,  we  lose  all  the  advantages  of  an 
accurate  regulation  of  the  combustion.  Volatile  substances,  heated  by  the  con- 
ducting power  of  the  gun-barrel,  distil  over  without  interruption,  and  without 
undergoing  combustion ;  and  in  the  case  of  substances  difficult  to  burn,  we  can- 
not apply  the  necessary  heat.  Mitscherlich  tries  to  prevent  the  conduction  of 
the  heat  along  the  gun-barrel  by  blowing  on  it,  or  surrounding  it  with  moist 
cloths.  But,  during  the  combustion,  our  attention  is  taken  up  with  matters  of 
too  great  importance  to  permit  of  our  occupying  ourselves  with  attempting  to 
keep  the  gun-barrel  cool  by  blowing  on  it.  To  surround  it  with  moist  cloths  is 
altogether  inadmissible,  for  obvious  reasons. 

The  position  of  the  potassa  apparatus  during  the  combustion,  is  shown  in  fig. 
14.  A  bit  of  cork  is  introduced  under  r,  so  that  this  part  lies  a  little  higher 
than  the  opposite  end.     It  is  best  supported  on  a  folded  towel. 

When  the  whole  tube  of  combustion,  at  the  end  of  the  operation,  is  sur- 
rounded with  red-hot  charcoal,  the  heat  is  to  be  increased  along  the  whole  length 
of  the  furnace.  This  is  done  below,  by  admitting  air  through  all  the  slits,  and 
above,  by  blowing  the  fire  with  a  sheet  of  pasteboard,  which  is  rapidly  moved 
backwards  and  forwards.  As  soon  as  the  disengagement  of  gas  becomes  very 
slow,  the  bit  of  cork  is  removed  from  the  potassa  apparatus,  which  is  restored 
to  its  horizontal  position.    Fig,  9,  A,  page  790. 

We  can  now  see  whether  the  combustion  has  been  completely  successful  or 
not.  If  the  disengagement  of  gas  cease  all  at  once,  we  are  sure  that  the  com- 
bustion has  been  complete.  If  it  continue,  on  the  contrary,  at  intervals  for  a 
long  time,  the  mixture  with  oxide  of  copper  has  not  been  well  made.  We  may 
then  reckon  v/ith  certainty  on  a  deficiency  in  the  determination  of  the  carbon. 

As  soon  as  no  more  gas  comes  over,  the  ley  rises  into  the  bulb  m,fig.  9.  The 
size  of  this  bulb  prevents  all  chance  of  the  liquid's  rising  into  the  tube  &,  and 
allows  plenty  of  time  for  the  remaining  manipulations.  For  when  the  liquid  has 
filled  half  of  the  bulb  w,  it  ceases  to  rise.  The  middle  part  of  the  potassa  ap- 
paratus is  now  horizontal,  and  being  rendered  half  empty  by  the  rise  of  the 
liquid  in  w,  air  passes  into  the  interior.  In  Jig.  9,  y  points  out  the  height  to 
which  the  liquid  can  ascend.  When  it  has  reached  this  point  there  is  no  fur- 
ther obstacle  to  the  entrance  of  air. 

The  charcoal  which  surrounds  the  farther  end  of  the  tube  of  combustion  with 
its  sealed  point,  is  now  removed,  and  the  point  is  cut  across  with  small  pliers, 
at  the  point  ar,  fig.  8.  Over  the  point,  when  opened,  is  placed  a  tube,  A,  15  to 
20  inches  long,  open  at  both  ends,  supported  by  a  stand,  ^g.  16. 

The  suction  tube  is  now  placed  on  the  end  of  the  potassa  apparatus,  and  a  cer- 
tain quantity  of  air  is  drawn  with  the  mouth  through  the  potassa  apparatus, 
whch  is  now  placed  in  the  same  position  as  during  the  combustion ;  by  this 
means,  all  the  carbonic  acid  and  watery  vapour  which  have  remained  in  the  ap- 
paratus are  now  absorbed  by  the  ley  and  the  chloride  of  calcium.  Fig.  16  shows 
the  apparatus  at  this  period.  The  left  hand  holds  the  potassa  apparatus  at  r, 
raising  this  part  a  little  :  the  right  hand  holds  the  suction  tube  B, 


796 


ORGANIC  ANALYSIS. 
Fig.  16. 


When  the  combustion  has  been  complete,  no  taste  is  perceived  in  the  air 
drawn  through.  When  it  has  been  imperfect,  a  more  or  less  distinctly  empyreu- 
matic  taste  is  perceived.  The  latter  circumstance  is  not  always  a  proof  that  the 
analysis  has  failed ;  for  it  very  often  happens  that  two  analyses  agree  perfectly, 
in  one  of  which  an  empyreumatic  taste  is  perceived,  in  the  other  not.  This 
proves  how  minute  a  quantity  of  empyreumatic  matter  suffices  to  communicate 
a  taste  to  the  air. 

Berzelius  proposes  to  avoid  the  suction  with  the  mouth  by  employing  the  ap- 
paratus formerly  described  for  producing  a  current  of  air.  See  Jigs.  2  and  3. 
This  arrangement  is  inconvenient,  gives  unnecessary  trouble,  and  is  far  from 
supplying  the  manageable  delicacy  of  the  human  organ. 

The  air  which  is  drawn  through  the  apparatus  contains  water  and  carbonic 
acid;  and  both  are  added  to  the  products  of  the  combustion,  unless  we  take 
means  to  remove  them  from  the  air  before  it  enters  the  apparatus. 

For  this  purpose,  Ber^ielius  connects  the  point  of  the  combustion  tube,  after  it 
has  been  cut,  with  a  tube  filled  with  dry  caustic  potassa.  This  may  be  done, 
but  it  is  a  disagreeable  operation,  since  the  tube  of  combustion  must  be  kept  red 
hot  while  the  air  passes  through  it,  in  order  to  oxidize  any  traces  of  carbon  which 
may  be  deposited  on  the  reduced  copper :  while  in  order  to  attach  the  caoutchouc 
connector  to  the  point,  it  must  no  longer  be  very  hot.  Besides,  the  air,  which 
is  made  to  pass  through  the  potassa  apparatus,  if  dried,  absorbs  moisture  from 
the  ley,  which  it  carries  away;  giving  rise  to  an  apparent  loss  of  carbon. 
Now,  if  the  current  of  dry  air,  as  recommended  by  Berzelius,  be  continued  for  a 
quarter  of  an  hour,  it  is  impossible  to  neglect  this  loss,  which  must  then  be  pre- 
vented by  attaching  to  the  potassa  apparatus  another  tube  for  collecting  this 
moisture,  and  adding  its  weight  to  that  of  the  potassa  apparatus. 

All  these  troublesome  and  complicated  arrangements  may  be  avoided  by  pro- 
ceeding as  follows : — 

The  combustion  being  over,  and  the  caustic  ley  ascending  to  y,  J^.  9,  B,  the 
potassa  apparatus  is  so  inclined  that  the  angle  B  is  closed  by  the  liquid  ;  the 
point  of  the  combustion  tube  is  now  cut  off,  and  air  enters.  The  natural  result 
of  this  is,  that  the  liquid  sinks  in  the  bulb  m,  and  rises  in  n,  till  an  equilibrium 
is  established,  and  a  portion  of  liquid  remains  in  each  bulb.  The  bulb  m  is  full 
of  carbonic  acid  gas,  which  is  absorbed  by  the  caustic  ley ;  the  carbonic  acid  gas 
in  the  tube  h  takes  the  place  of  that  which  is  absorbed,  and  thus  all  the  carbonic 
acid  gas  in  the  apparatus  is  by  degrees  brought  into  the  bulb  w,  where  it  is  so 
completely  absorbed  that  not  a  single  bubble  of  gas  passes  through  the  ley. 

When  the  apparatus  has  stood  thus  for  a  few  minutes,  the  air  in  the  apparatus 
contains  no  more  carbonic  acid.  To  make  all  sure,  however,  air  is  drawn  through 


ORGANIC  ANALYSIS. 


797 


by  the  suction  tube  for  a  few  seconds ;  till  so  much  has  passed  as  is  about  equal 
in  volume  to  the  contents  of  the  tube  of  combustion,  a,  and  the  tube  with, chlo- 
ride of  calcium,  b. 

When,  as  sometimes  occurs  in  the  combustion  of  substances  very  rich  in  car- 
bon, a  trace  of  carbon  has  been  deposited  on  the  reduced  copper,  and  has  thus 
escaped  oxidation,  it  is  completely  oxidized  by  the  small  quantity  of  air  now 
drawn  through  the  red  hot  tube ;  and  the  loss  of  carbon  from  this  source  is  avoided. 

COMBUSTION  OF  VOLATILE  LIQUIDS. 

Fig.  17.  The  analysis  of  such  bodies  is  the  most  simple  and  easy ;  the  results 
are  the  most  exact ;  and  beginners  will  do  well  to  occupy  themselves 
first  with  the  combustion  of  such  substances. 

These  liquids  are  weighed  in  small  bulbs  of  glass,  with  a  long  neck, 
the  point  of  which  is  sealed.  These  bulbs  are  easily  prepared.  A 
barometer  tube,  a.  Jig,  17,  12  inches  long  and  ^  inch  in  diameter,  is 
drawn  out  before  the  blowpipe.  The  portion  drawn  out  serves  as  a 
handle,  wherewith  to  draw  out  a  small  portion  of  a  with  a  long  narrow 
neck.  The  point  c  is  then  sealed  off  at  d  ,•  the  portion  of  a  which  has 
been  drawn  off.  A,  is  softened  and  blown  into  a  bulb,  {Jig.  18.)  It  it 
then  cut  off  at  f3,  and  the  same  process  is  repeated  till  a  sufficient  number 
of  bulbs  is  procured.  The  moisture  from  the  mouth,  owing  to  the  length 
of  the  tube  from  A  to  B,  never  penetrates  into  the  bulb. 
Fig.  18.       It  ig  obvious  that  the  portion  of  tube  A,  if   wide  enough^ 

Oneed  not  be  blown  out.  Its  neck  is  1  to  Ij  inches  long ;  and 
the  sharp  edges  where  it  has  been  cut  off  must  be  rounded  in 
the  flame  of  a  spirit  lamp ;  otherwise  we  are  in  danger  of  break- 
ing off  little  splinters  after  the  bulb  has  been  weighed,  and 
while  we  are  introducing  the  liquid. 

To  fill  the  bulb  with  liquid,  it  is  warmed,  and  the  open  end 
of  the  neck  introduced  into  the  liquid.  When  by  cooling  a 
certain  quantity  of  liquid  has  entered,  the  bulb  is  again  warme'd ; 
the  vapour  which  is  formed  expels  almost  the  whole  of  the 


A 


^ 


atmospherical  air,  and  when  the  point  is 
again  dipped  in  the  liquid,  the  bulb  fills  to 
three  fourths  of  its  bulk.  The  point  is  now 
sealed  up,  the  whole  is  weighed,  and  sub- 
tracting the  weight  of  the  bulb,  when 
empty,  we  have  the  weight  of  the  liquid. 

Before  weighing  the  bulbs,  the  oxide  of 
copper  has  been  ignited,  and,  while  still 
red-hot,  introduced  into  the  tube  {jig.  19,) 
which  is  closed  with  a  dry  cork,  and 
allowed  to  become  quite  cold.  It  is  not  so 
convenient  to  allow  the  crucible  to  cool 
under  a  bell  jar  along  with  oil  of  vitriol. 

The  tube.  Jig.  19,  is  so  wide,  that  the 
tube  of  combustion  slides  easily  into  it. 
We  first  allow,  as  shown  in  j^.  20,  one  to 
one  and  a  half  inch  of  the  perfectly  dry 
oxide  to  fall  into  the  tube  of  combustion, 


Fig.  19.     Fig.  20. 


798 


ORGANIC  ANALYSIS. 


and  then  introduce  the  bulbs  alternately  with  more  oxide,  so  that  the  latter  can 
attract  no  moisture.  The  bulbs  are  scratched  with  a  sharp  file  on  the  middle  of 
the  neck,  as  in  fig.  21,  at  a.  They  are  held  by  the  point,  and  when  introduced 
into  the  mouth  of  the  tube,  broken  across,  both  bulb  and  neck  being  allowed  to 
slide  down  into  the  tube. 

Fig.  21.  The  two  bulbs,  holding  from  6  to  8  grains  of  liquid  are  suffi- 

cient ;  they  are  separated  in  the  tube  by  a  layer  of  oxide  of  cop- 
per, of  2  to  3  inches  long.  If  the  tube  of  combustion  be  18 
inches  long,  then  there  is  above  the  uppermost  bulb  a  layer  of 
oxide  11  to  12  inches  long.  Fig,  22  shows  the  bulbs  with  the 
layers  of  oxide  of  copper. 

Fig.  22. 


Mitscherlich  is  the  only  chemist  who  introduces  the  bulbs 
into  the  tube  of  combustion  sealed  up.  He  then  heats,  in  the 
course  of  the  operation,  the  part  of  the  tube  where  they  lie,  till 
they  burst;  If  the  liquid  be  not  very  volatile,  it  is  unnecessary  to 
leave  the  bulbs  closed ;  and  if  it  be  very  volatile,  this  method  is 
ill  adapted  to  practice—for  with  such  liquids  a  very  sudden  dis- 
v*^^  engagement  of  vapour  cannot  be  avoided,  especially  if  the  bulb 

^y^  be  burst  by  the  elastic  force  of  the  vapour,  and  not   by  the 

expansion  of  the  liquid.  Now  when  this  sudden  disengagement  of  vapour 
occurs,  it  is  impossible  to  prevent  a  portion  of  it  from  escaping  without  under- 
going combustion. 

When  the  liquid  boils  at  a  high  temperature,  and  is  also  rich  in  cstrbon,  it  is 
divided  into  three  portions  in  separate  bulbs,  without  however,  taking  more  than 
from  7  to  9  grains  in  all.  The  bulbs  are  separated  by  layers  of  oxide  of  copper. 
This  precaution  must  be  attended  to  in  analyzing  the  essential  oils,  because 
the  oxide  of  copper,  which  immediately  surrounds  a  bulb,  is  seldom  sufficient 
for  the  complete  oxidation  of  the  vapour,  and,  being  itself  completely  reduced 
to  the  metallic  state,  a  thin  layer  of  carbon  is  sometimes  deposited  on  its  sur- 
face. Now,  although  this  carbon  may  be  oxidized  by  the  air  drawn  through  at 
the  end  of  the  operation,  yet  it  is  better  to  avoid  the  necessity  of  this  rectifica- 
tion. 

In  the  case  of  liquids  which  are  not  very  volatile,  the  bulbs  may  be  emptied 
before  beginning  the  combustion.  The  tube  of  combustion,  after  being  filled,  is 
connected  with  the  air-pump,  as  in  fig.  7.  When  the  air  is  rarified  by  a  stroke 
of  the  piston,  the  bubble  of  air  contained  in  each  bulb  expands,  and  forces  out 
the  liquid,  which  is  absorbed  by  the  surrounding  oxide  of  copper. 

In  the  case  of  highly  volatile  liquids,  a  second  screen  at  6,  {fg.  29,)  is  placed 
between  the  spot  where  the  uppermost  bulb  lies,  and  the  heated  anterior  part  of 
the  tube.  This  part,  containing  pure  oxide  of  copper,  must,  in  such  a  case,  be 
gradually  surrounded  with  red  hot  charcoal,  beginning  at  a,  and  heating  short 
portions  at  once. 

From  the  commencement  of  the  operation,  some  bits  of  red-hot  charcoal  must 
be  placed  below  the  closed  point  of  the  tube  of  combustion  in  order  that  no  fluid 
may  distil  into  the  closed  end,  from  which  it  could  only  be  expelled  by  a  very 


ORGANIC  ANALYSIS.  799, 

strong  heat ;  the  liquid  then  boils  by  starts,  and  in  little  explosions,  whereby 
some  of  it  may  readily  pass  away  unoxidated  with  the  gaseous  products,  form- 
ing a  visible  white  cloud. 

When  the  anterior  part  of  the  tube  is  red-hot,  the  screen  h  is  removed,  and  a 
piece  of  burning  charcoal  from  time  to  time  brought  near  the  spot  where  the  first 
bulb  lies.  In  other  respects  the  combustion* is  to  be  carried  on  as  formerly 
described. 

Fixed  oils  are  weighed  in  the  small  tube,  (A,  Jig.  23,)  which  Fig.  23. 
is  supported  during  the  weighing  on  the  stand  (B,  Jig,  23,)  of 
tinned  iron.  When  2  inches  of  oxide  of  copper  have  been  intro- 
duced into  the  tube  of  combustion,  the  tube  with  the  oil  is  allowed 
to  slide  down,  with  the  open  end  upwards.  By  inclining  the  com- 
bustion tube,  the  oil  is  allowed  to  flow  out,  and  we  endeavour  to 
spread  it  over  the  sides  of  the  combustion  tube  as  far  up  as  the 
middle.  The  tube  is  then  filled,  as  formerly  directed,  with  oxide 
of  copper. 

Soft  fusible  matters  may  be  treated  exactly  in  the  same  way. 

Fusible  substances  which,  though  solid,  cannot  be  reduced  to  powder,  such  as 
wax,  are  introduced  into  the  empty  combustion  tube  in  weighed  fragments.  The 
tube  is  then  heated,  after  being  closed  with  a  cork,  till  the  substance  melts, 
when  it  is  spread  along  three  fourths  of  the  length  of  the  tube,  reckoning  from 
the  sealed  end.     When  cold,  the  tube  is  filled  with  oxide  of  copper. 

Such  substances  may  also  be  weighed  in  a  little  glass  vessel  having  the  shape 
of  a  boat,  [Jig.  24,)  which  is  easily  made  by  taking  a  tube  Fig-  24. 

\  inch  in  width,  softening  it,  and  drawing  it  out  upwards 
in  two  places,  and  then  splitting  the  tube  lengthways  by 
means  of  a  red  hot  point  of  charcoal, — {Sprengkohle,  Ber- 
zelius.)    For  the  combustion  of  such  substances  we  must  select  combustion 
tubes  somewhat  wider  and  longer  than  for  ordinary  combustions. 

COMBUSTION  OF  SUBSTANCES  VERY  RICH  IN  CARBON,  OR  OF  SUBSTANCES 
CONTAINING  CHLORINE. 

There  are  some  substances  in  which  it  is  almost  impossible  to  determine  accu- 
rately the  proportion  of  carbon  by  means  of  combustion  with  oxide  of  copper. 
Such  are :  the  different  kinds  of  coal,  indigo,  ulmine,  and  all  bodies  resembling 
these.  In  the  case  of  coal,  for  example,  the  disengagement  of  gas,  at  the  end  of 
the  operation,  does  not  cease.  It  becomes,  indeed,  gradually  slower,  but  even 
an  hour  afterwards,  when  the  heat  has  been  strong,  the  caustic  ley  does  not 
ascend. 

The  cause  of  this  is,  doubtless,  that  the  combustion  is  unequal.  The  first 
efiect  of  the  heat  is  to  disengage  combustible  gases,  which  reduce  to  the  me- 
tallic state  the  oxide  surrounding  each  particle ;  and  so  much  carbon  is  left,  that 
it  cannot  all  be  oxidized  by  cementation.  The  loss  of  carbon,  thus  occasioned, 
amounts  to  from  three  to  five  per  cent. 

When  the  substance  contains  chlorine,  the  determination  of  the  hydrogen  be- 
comes inexact.  The  chloride  of  copper  being  volatile,  it  is  impossible  to  prevent 
the  deposition  of  some  of  it  in  the  chloride  of  calcium  tube. 

For  all  such  combustions,  it  is  necessary  to  employ  the  chromate  of  lead,  of 
which  there  is  required  rather  more  than  half  the  bulk  of  the  oxide  of  copper 
which  would  have  been  required.    In  other  respects  the  process  is  the  same. 


800  ORGANIC  ANALYSIS. 

When  the  chromate  of  lead  is  used,  it  is  necessary  to  give  a  strong  heat  at 
the  end  of  the  process.  Pure  oxygen  is  then  disengaged,  in  which  the  remain- 
ing charcoal  undergoes  perfect  combustion.  But  the  increased  heat  renders  it 
necessary  to  protect  the  tube  by  covering  it  with  a  thin  sheet  of  copper,  which, 
from  its  flexibility,  may  be  easily  wrapped  round  the  tube,  and  which  may  be 
kept  in  shape  by  a  few  rings  of  iron  wire  bent  round  it. 

The  same  object  may  be  less  conveniently  attained,  when  oxide  of  copper  is 
employed,  by  placing,  in  the  closed  end  of  the  tube,  a  mixture  of  1  part  of  chlo- 
rate of  potassa,  and  8  parts  oxide  of  copper.  When,  at  the  end  of  the  operation, 
this  part  of  the  tube  is  heated,  the  remaining  charcoal  is  burnt  by  the  oxygen 
which  is  disengaged. 

For  substances  containing  chlorine,  the  chromate  of  lead  is  a  precious,  nay, 
indispensable  means  of  combustion.  Chloride  of  lead  is  formed,  which  is  not 
at  all  volatile,  at  a  red  heat. 

It  is  necessary  to  bestow  some  attention  on  the  preparation  of  the  oxide  of 
copper,  and  the  chromate  of  lead,  as  also  on  the  choice  of  combustion  tubes. 

OXIDE  OF  COPPER. 

This  oxide  may  be  prepared  by  mixing  hot  solutions  of  sulphate  of  copper 
and  carbonate  of  soda.  The  pale  blue  precipitate  of  carbonate  of  copper  is  left, 
during  from  eight  to  fourteen  days,  in  the  liquid,  and  in  a  warm  situation.  At 
the  end  of  that  time  it  loses  its  gelatinous  consistence,  becoming  green  and 
crystalline,  in  which  state  it  is  easily  washed  and  dried.  Before  being  used,  it 
must  be  strongly,  ignited,  and  carefully  tested  for  sulphuric  acid  and  soda.  If 
it  contain  even  a  minute  quantity  of  these,  it  is  unfit  for  analyses. 

The  oxide  thus  obtained  is  brownish  black,  and  forms  an  extremely  loose, 
light  powder,  which  is  in  the  highest  degree  hygroscopic.  Organic  substances, 
when  mixed  with  it,  are  burnt  with  great  facility  ;  but  occasionally  the  mixture 
in  the  tube,  when  one  part  of  it  has  been  ignited,  continues  to  burn  spontane- 
ously, in  which  case  the  analysis  is  good  for  nothing. 

It  is  better  to  use  the  oxide  of  copper  prepared  from  the  nitrate  by  calcination. 
Its  preparation  is  both  easier  and  cheaper,  and  we  are  never  doubtful  of  its  purity. 

To  prepare  it,  sheet  copper  is  ignited,  and  thrown,  while  red-hot,  into  cold 
water.  All  impurities  on  the  surface  peel  off  with  the  crust  of  oxide  formed. 
The  clean,  well- washed  metal  is  now  dissolved  in  pure  nitric  acid,  and  the  solu- 
tion evaporated  to  dryness  in  a  porcelain  capsule.  The  dry  salt  is  next  ignited 
in  a  well  covered  hessian  crucible,  (care  being  taken  not  to  introduce  too  much 
at  once,  as  the  salt  froths  up,)  and  the  calcined  mass  is  frequently  stirred  with  a 
hot  glass  rod,  or  copper-wire,  in  order  that  no  part  of  the  nitrate  may  escape  de- 
composition. Platinum  crucibles  must  not  be  employed  for  this  operation,  as 
they  are  by  degrees  attacked  and  worn  away  when  oxide  of  copper  is  ignited  in 
them. 

The  ignited  oxide  is  reduced  to  fine  powder,  and  preserved  in  a  well-stopped 
vessel.  It  is  compact,  heavy,  coal-black.  Its  hygroscopic  condition  depends 
on  the  temperature  to  which  it  has  been  exposed.  When  very  strongly  ignited, 
the  oxide  shrinks  in  bulk,  becomes  very  hard,  and  loses  almost  all  hygrometric 
properties.  In  this  form,  if  broken  into  small  fragments,  it  answers  admirably, 
when  the  finer  parts  are  removed  by  sifting,  for  the  combustion  of  liquids,  and 
of  difficultly  combustible,  fatty,  fusible,  substances.  The  tube  may.be  completely 


ORGANIC  ANALYSIS.  801 

filled  with  it,  and  no  tapping  is  required,  as  there  are  sufficient  pores  in  the  mass 
to  yield  a  free  passage  to  the  gases. 

To  attain  the  same  end,  Dumas  employs  the  oxide  obtained  by  calcining  cop- 
per turnings  on  a  muffle.  This  oxide  retains  the  form  of  the  tuinings,  and  is 
equally  well  adapted  for  the  purpose  above  mentioned. 

The  oxide  of  copper,  which  has  been  used  for  a  combustion,  may  be  again 
rendered  fit  for  use  by  moistening  it  with  pure  nitric  acid,  and  igniting  it  afresh. 
Should  the  copper  originally  have  been  contaminated  by  brass  solder,  the  oxide 
cannot  be  used  for  the  determination  of  nitrogen,  as  the  nitrate  of  zinc  is  only 
partially  decomposed  by  ignition,  but  readily  yields  nitrogen  or  nitric  oxide  when 
heated  with  organic  matter. 

If  the  substance  analyzed  have  been  a  compound  of  an  organic  substance  with 
a  fixed  base,  the  oxide,  after  the  combustion,  must  be  digested  in  cold  dilute 
nitric  acid,  well  washed  and  ignited. 

After  the  combustion  of  a  compound  containing  chlorine,  the  oxide  must  be 
redissolved  in  nitric  acid,  and  the  chlorine  precipitated  by  nitrate  of  silver.  Any 
excess  of  silver  in  the  filtered  solution  is  reduced  by  the  ignition,  and  its  pre- 
sence is  not  injurious. 

CHROMATE  OP  LEAD. 

This  substance  is  obtained  in  a  state  of  perfect  purity  by  precipitating  acetate 
or  nitrate  of  lead  with  bichromate  or  potassa,  and  washing  the  precipitate  care- 
fully with  distilled  water.  But  in  the  state  in  which  it  is  obtained  by  mere  dry- 
ing, it  is  not  adapted  for  analyses.  It  must  be  strongly  ignited  till  it  begins  to 
melt,  and  then  reduced  to  a  very  fine  powder.  The  ignition  changes  its  beauti- 
ful yellow  colour  to  a  dirty  brownish  red,  which  it  retains  on  cooling. 

The  chromate  of  lead  may  be  used  in  every  kind  of  combustion  as  well  as  the 
oxide  of  copper.  The  combustion  takes  place  easily,  and  at  a  moderate  heat.  It 
is  always  complete,  for  the  gases  after  the  combustion  are  invariably  tasteless. 

Compared  with  an  equal  weight  of  oxide  of  copper,  it  does  not  contain  so 
much  oxygen  available  for  combustion ;  but  compared  with  an  equal  bulk,  it  con- 
tains nearly  one  half  more,  since  its  density  is  more  than  twice  as  great  as  that 
of  the  oxide  of  copper. 

It  is  highly  probable  that  the  chromate  of  lead  will  be  preferred  to  the  oxide  of 
copper  in  many  cases,  where  it  is  desirable  to  determine  the  proportion  of  hydro- 
gen with  extreme  accuracy.  The  chromate  is  not  in  the  slightest  degree  hygro- 
scopic, and  the  trace  of  moisture,  which  the  substance  may  have  attracted  during 
the  mixture,  can  be  afterwards  removed  with  much  greater  facility  than  in  the 
case  of  oxide  of  copper. 

COMBUSTION  TUBES. 

The  glass  of  which  these  tubes  are  made  must  be  chosen  with  great  care. 
The  Bohemian  potassa  glass,  which  contains  no  lead,  is  the  best.  Tubes  of 
this  glass  never  crack,  even  when  suddenly  surrounded  with  red-hot  charcoal. 
It  is  extremely  difficult  to  melt,  and  when  softened,  it  is  extremely  tough.  The 
green  bottle  glass  of  Germany  cracks  easily  in  the  fire,  is  difficult  to  melt,  but, 
when  once  softened,  very  liquid.  The  softened  parts  are  blown  out  by  the 
slightest  pressure,  and  holes  are  formed  instantly  when  this  occurs. 

The  French  white  and  green  bottle  glass  must  be  rejected.    The  French  green 

53 


Q^  ORGANIC  ANALYSIS. 

glass  can  be  melted  in  a  tube  of  Bohemian  glass,  without  the  form  of  the  latter 
being  altered. 

Having  now  described  all  the  precautions  and  manipulations  which  insure  the 
performance  of  a  trustworthy  analysis,  as  far  as  concerns  the  determination  of 
carbon  and  hydrogen  by  weighing,  it  remains  for  us  to  describe  the  method  of 
determining  the  carbon  by  the  volume  of  the  carbonic  acid  produced,  as  well  as 
that  of  the  nitrogen,  which  latter  is  always  done  by  measurement.  I  have  also 
to  consider  the  degree  of  accuracy  which  is  attainable  in  the  determination  of 
the  carbon  and  hydrogen. 

CARBON. 

The  determination  of  the  carbon  by  the  process  and  apparatus  above  described 
may  be  rendered  inexact  by  several  sources  of  error.  The  first  and  most  impor- 
tant is  incomplete  combustion.  In  repeating  the  analysis,  this  may  be  avoided 
by  using  a  longer  combustion  tube  and  increasing  the  proportion  of  oxide  of 
copper.  The  latter  precaution  insures  a  greater  degree  of  division,  and  a  slower 
combustion,  which  generally  suffices. 

A  second  source  of  uncertainty,  as  formerly  mentioned,  arises  from  the  cir- 
cumstance that  the  gaseous  matter  which,  during  and  after  the  combustion, 
passes  through  the  potassa  apparatus,  carries  with  it  a  portion  of  water,  from 
the  caustic  ley,  the  weight  of  which  is  thus  diminished.  But  it  is  obvious  that 
this  loss  of  water  is,  in  part  at  least,  compensated  by  the  carbonic  acid  of  the 
air,  so  that  the  loss  of  weight  varies,  according  to  the  quantity  of  carbonic  acid 
present  in  the  atmosphere. 

This  point  has  been  satisfactorily  cleared  up  by  direct  experiments.  When 
the  combustion  tube  is  surrounded  with  red-hot  chaJrcoal,  and  the  point  broken 
ofi*,  fig.  16,  without  the  tube  h,  the  open  point  being  also  surrounded  with  char- 
coal, the  potassa  apparatus,  after  2000  cubic  centimetres  of  air  have  passed 
through  it,  not  only  does  not  lose  weight,  but  gains  18^  milligrammes  (0*275 
grain  nearly.) 

To  determine  the  amount  of  water  carried  away  by  the  current  of  air,  there 
was  connected  with  the  potassa  apparatus  a  second  similar  one  filled  with  strong 
sulphuric  acid.  It  is  clear,  that  the  water  carried  in  the  form  of  vapour  by  the 
current  of  air  from  the  caustic  ley  must  have  been  condensed  by  the  sulphuric 
acid. 

Now  the  weight  of  the  apparatus  containing  the  sulphuric  acid  had  increased 
by  14  milligrammes  (0*21  grain  nearly,)  so  that,  instead  of  a  deficiency  in  the 
carbon,  there  was,  in  this  experiment,  an  excess ;  for  the  caustic  ley  has  absorbed 
32j  milligrammes  (0*48  grain  nearly)  of  carbonic  acid  from  the  air,  and  had 
given  off  14  milligrammes  of  water. 

When  the  tube  //,  12  or  15  inches  long,  was  placed  on  the  point  of  the  com- 
bustion tube  as  in^.  16,  and  the  experiment  repeated  with  the  same  quantity 
of  air,  the  apparatus  with  sulphuric  acid  again  gained  in  weight  13.6  milli- 
grammes, and  the  potassa  apparatus  lost  5  milligrammes,  (0*075  grain  nearly.) 

It  is  obvious  that  by  this  arrangement  the  error  in  the  determination  of  carbon 
arising  from  the  loss  of  water  is  completely  compensated  by  the  absorption  of 
carbonic  acid  from  the  air. 

When  200  cubic  centimeters  (the  quantity  commonly  occurring  in  a  combus- 
tion) of  carbonic  acid  pass  through  the  potassa  apparatus,  the  loss  amounts  only 


ORGANIC  ANALYSIS.  S03 

to  half  a  milligramme  (0*0075  grain  nearly)  in  the  weight  of  carbonic  acid. 
Reduced  to  carbon,  this  amounts  only  to  0"000138  gramme,  (0'002  grain  nearly) ; 
and  this  loss  is  extended  over  from  0*4  to  0*8  gramme  (6  to  12  grains)  of  the 
substance  analyzed. 

Those  who,  at  the  end  of  the  combustion,  connect  the  point  of  the  combustion 
tube  with  a  tube  of  fused  potassa,  to  deprive  the  air  of  its  carbonic  acid,  must 
therefore  add  to  the  weight  of  the  potassa  apparatus  on  an  average  0.0013 
gramme,  (0*0295  grain  nearly,)  for  every  100  cubic  centimetres  of  gaseous 
matter  which  pass  through. 

But  the  experiments  above  detailed,  show  that  it  is  unnecessary  to  have  re- 
course to  that  method ;  and  that,  in  all  circumstances,  it  is  safer  to  follow  the 
process  I  have  recommended. 

When  the  quantity  of  carbonic  acid  produced  in  the  combustion  is  very  large, 
and  the  bubbles  follow  each  other  with  rapidity,  the  caustic  ley  becomes  warm, 
and  the  loss  of  water  is  increased. 

In  weighing  the  potassa  apparatus,  it  must  be  observed,  that  when  it  is  warm 
less  moisture  condenses  on  the  surface^of  the  glass  than  before  the  combustion, 
when  it  was  weighed  cold.  This  difference  amounts  to  0*003,  or  0*004  gramme. 
When  the  air  is  very  moist  it  may  even  reach  0*006  gramme,  (0045,  0*06,  0*09 
grain  nearly).     It  is  better  therefore  to  wait  until  the  apparatus  has  cooled  down. 

An  examination  of  the  analysis  of  one  or  two  substances  possessing  high 
atomic  weights,  will  give  the  clearest  idea  of  the  accuracy  with  which  the 
apparatus  described  enables  us  to  determine  the  carbon. 

It  is  known  with  sufficient  certainty,  that  the  atomic  weight  of  the  amygdalate 
of  baryta  is  =6738*829.  Three  analyses  of  this  salt  gave  of  carbonic  acid  163  8, 
163.5,  163.3  per  cent.  The  mean  is  163*5.  The  quantity  calculated  according 
to  the  theoretical  composition  of  the  salt  is  163*7.  The  loss  of  carbonic  acid  is, 
consequently  0*002  carbonic  acid,  (0*2  per  cent.)  which  is  equal  to  0*00055 
carbon,  (0*055  per  cent.)  There  is  no  kind  of  analysis,  in  which  greater  accu- 
racy is  attainable. 

This  is  the  proper  place  for  some  remarks  on  the  true  atomic  weight  of  carbon. 
The  earlier  determinations  of  Berzelius  give  the  number  75*33.  His  latest 
experiments  give  76*437.  I  consider  the  latter  as  the  true  atomic  weight,  deter- 
mined with  astonishing  accuracy.  Every  day's  experience  confirms  its  exact- 
ness, and  the  following  considerations  will  give  to  all  chemists  the  same 
conviction. 

The  mean  of  5  analyses  of  stearine  give,  in  100  parts  of  this  substance,  76.084 
carbon.    The  three  highest  results  gave  a  mean  of  76*306. 

From  the  products  of  the  decomposition  of  stearine  we  know  with  certainty 
that  one  equivalent  of  it  contains  146  atoms  of  carbon;  which,  taking  the  atomic 
weight  of  carbon  at  76*437,  would  give  of  carbon  in  stearine  76*21  per  cent. 
Were  the  atom  of  carbon,  as  Thomson  considers  it,  exactly  75 ;  or  75*33,  as  the 
first  experiments  of  Berzelius  made  it,  the  analysis,  supposing  stearine  to  con- 
tain 146  atoms  of  carbon,  should  have  yielded  not  more  than  75*85  and  75.98 
per  cent  of  carbon. 

The  difference,  0*36  per  cent,  carbon,  amounts  to  one  ertom  less.  But  if  we 
assume  stearine  to  contain  only  145  atoms  carbon,  all  coincidence  between  the 
composition  of  stearine  and  that  of  stearic  acid  and  glycerine,  the  products  of  its 
decomposition,  disappears ;  and  we  must  then  suppose  that  the  analysis  of  one 


■g()4  ORGANIC  ANALYSIS. 

or  of  both  of  these  substances  is  inaccurate ;  a  supposition  for  which  there  is  no 
foundation. 

In  the  combustion  of  substances  which  contain  sulphur,  as  xanthates,  sulpho- 
sinapisine,  &c.,  the  weight  of  the  carbon  generally  turns  out  too  high.  This 
proceeds  from  the  formation  of  sulphurous  acid,  which  always  occurs  when  the 
mixture  with  oxide  of  copper  has  not  been  made  sufficiently  intimate.  The  sul- 
phurous acid  is  absorbed  by  the  caustic  ley,  and  increases  its  weight.  When 
we  have  reason  to  fear  this  source  of  error,  we  must  place  between  the  chloride 
of  calcium  tube  and  the  potassa  apparatus  a  tube  with  peroxide  of  lead. 

A  concentrated  solution  of  chloride  of  calcium,  such  as  is  formed  in  the  chlo- 
ride of  calcium  tube,  does  not  retain  any  sulphurous  acid,  particularly  when  it 
is  allowed  to  lie  till  all  the  liquid  in  it  has  solidified,  that  is,  till  the  chloride  of 
calcium  has  crystallized.  The  sulphurous  acid  which  has  passed  through  the 
chloride  of  calcium  is  absorbed  by  the  peroxide  of  lead.  The  latter  must  not 
be  placed  between  the  chloride  of  calcium  and  the  combustion  tube,  unless  we 
mean  to  neglect  the  water  in  that  particular  analysis ;  as  some  water  would  be 
absorbed  by  it.  tr 

HYDROGEN. 

The  only  error  inherent  to  the  method  of  analysis  recommended,  which  affects 
the  determination  of  the  hydrogen,  arises  from  the  moisture  of  the  atmospheric 
air  which  is  drawn  through  the  apparatus  at  the  end  of  the  combustion,  with 
the  view  of  bringing  the  whole  carbonic  acid  in  contact  with  the  absorbing 
liquid. 

Innumerable  experiments  have  shown,  that  the  amount  of  moisture  absorbed 
by  the  chloride  of  calcium,  when  200  cubic  centimetres  have  passed  through, 
never  amounts  to  more  than  0*005  or  0*006  gramme  (0*075  to  0*09  grain,  nearly.) 
This  corresponds  to  0*00055  or  0-00066  gramme  (0*0075  to  0*009  grain,  neariy) 
of  hydrogen.  This  excess  is  divided  over  0*3  to  0*5  gramme  (4*5  to  7*5  grains 
nearly)  of  the  substance  analyzed ;  and  it  is  equally  great,  whether  the  sub- 
stance contain  much  or  little  hydrogen.  If  the  substance  analyzed  be  rich  in 
hydrogen,  and  have  a  small  atomic  weight,  this  error  becomes  proportionally 
smaller.  In  such  cases  we  are  in  no  doubt  as  to  the  number  of  atoms  of  hydro- 
gen.   An  example  will  illustrate  this. 

100  parts  of  pyroacetic  spirit  (acetone)  when  burned  with  oxide  of  copper, 
yield  as  a  mean  result  94*23  parts  of  water.  The  amount,  calculated  from  theo- 
retical composition,  is  92*45  parts  of  water  per  cent.  The  analysis,  therefore, 
gives  1.8  per  cent,  of  water,  or  0-2  per  cent,  of  hydrogen,  in  excess.  Now,  the 
atomic  weight  of  acetone  is  366*750.  Had  this  quantity  been  burned,  we  should 
have  had  an  excess  of  hydrogen  over  the  theoretical  quantity,  amounting  to 
07335;  but  since  the  atom  of  hydrogen  weighs  6*23978,  it  is  obvious  that  the 
error  is  far  short  of  one  atom  of  hydrogen ;  and  that  it  may  safely  be  neglected 
in  such  cases,  especially  as  we  know  the  source  of  it,  and  the  limits  within 
which  it  is  confined. 

But  this  error  cannot  be  neglected  in  substances  of  high  atomic  weight  which 
contain  much  hydrogen.  We  must  subtract  from  the  amount  of  water  obtained 
0*005  to  0*006  gramme,  (0*075  to  0*09  grain  nearly;)  or,  if  we  are  unwilling  to 
trust  to  this  correction,  we  must  break  off  the  point  before  the  caustic  ley  be- 
gins to  ascend,  remove  the  hot  charcoal  from  about  the  point,  and,  when  it  has 


ORGANIC  ANALYSIS.  805 

cooled  sufficiently,  connect  it,  by  a  tube  of  caoutchouc,  with  a  tube  containing 
chloride  of  calcium,  or  with  a  potassa  apparatus  filled  with  sulphuric  acid. 

An  example  will  render  obvious  the  necessity  for  this  correction.  0'3054 
gramme  of  stearine,  without  correction,  and  without  any  means  having  been 
taken  to  desiccate  the  air,  yielded  0'343  gramme  of  water :  100  parts,  conse- 
quently, would  have  given  11231.  According  to  the  theoretical  composition  of 
stearine,  100  parts  should  yield  only  109*63  of  water.  There  is,  therefore,  here 
an  excess  of  2*68  per  cent,  of  water,  or  0*297  per  cent,  of  hydrogen.  Now, 
this  slight  excess,  calculated  on  the  atomic  weight  of  stearine,  corresponds  lo 
somewhat  more  than  three  atoms  of  hydrogen. 

If,  however,  we  deduct,  previously  to  the  calculation,  0*006  gramme  as  hygro- 
metric  moisture,  there  remain  for  100  parts  of  stearine  110-35  of  water,  or  an  ex- 
cess over  theory  of  0*72  per  cent,  water,  or  0*08  per  cent,  hydrogen;  which 
excess,  calculated  on  the  atomic  weight,  amounts  to  less  than  one  atom  of  hy- 
drogen. 

By  following,  therefore,  the  process  of  analysis  recommended  in  this  work, 
we  must  always  be  prepared  for  an  excess  of  hydrogen  over  the  truth,  amount- 
ing to  from  0*14  pel  cent,  to  0*2  per  cent.;  and  we  can  only  consider  the  deter- 
mination of  the  hydrogen  as  exact,  when  this  excess  does  not  exceed  0*2  per 
cent.  When  the  analysis,  without  the  above  correction,  gives  exactly  the  theo- 
retical quantity  of  hydrogen,  there  is  much  reason  to  doubt  the  accuracy  of  the 
experiment ;  and  the  formula  found  for  the  composition  of  the  substance  is  erro- 
neous, when  the  results  of  repeated  analyses  yield  constantly  less  hydrogen  than 
the  formula  indicates. 

In  publishing  the  weights  obtained  in  an  analysis,  we  must  not  make  the 
above  deduction,  but  give  the  numbers  as  they  occur,  since  the  amount  of  excess, 
due  to  hygrometric  water,  furnishes  to  the  reader  a  valuable  means  of  judg- 
ing of  the  accuracy  of  the  determination  of  the  hydrogen.  It  is  only  in  calcu- 
lating the  composition  with  a  view  to  discover  the  formula  that  we  are  to  make 
the  correction  above  mentioned. 

The  determination  of  the  hydrogen  becomes  inaccurate  when  a  compound  of 
chlorine  is  burnt  with  oxide  of  copper.  The  chloride  of  copper  which  is  formed, 
sublimes  with  the  current  of  gaseous  matter,  condenses  in  the  chloride  of  cal- 
cium tube,  and  increases  its  weight.  The  more  slowly  the  combustion  goes  on, 
the  smaller  is  this  excess  of  weight;  but  it  must  never  be  neglected.  It  amounts 
in  all  to  from  0*01  to  0*015  gramme,  (0  15  to  0*225  grain  nearly.)  By  dissolv- 
ing the  chloride  of  calcium,  precipitating  the  copper  with  sulphuretted  hydrogen, 
and  determining  its  quantity,  this  source  of  error  may  be  corrected. 

In  the  analysis  of  such  bodies  we  must  be  particularly  cautious  in  moderating 
the  current  of  air  which  is  drawn  through  the  apparatus  after  the  combustion;  for 
if  the  current  be  made  rapid,  the  chloride  of  copper  may  be  seen  passing  through 
the  caustic  ley  in  the  form  of  white  vapours,  and  the  nauseous  metallic  taste  of 
the  salts  of  copper  is  perceived  in  the  mouth. 

By  the  use  of  the  chromate  of  lead,  this  source  of  error  may  be  entirely 
avoided. 

The  chloride  of  calcium  tube  must  be  emptied  immediately  after  we  have 
weighed  it,  if  we  would  not  lose  it.  If  this  be  not  done,  the  saturated  solution 
of  chloride  of  calcium  which  has  been  formed,  crystallizes,  and  infallibly  bursts 
the  tube. 


806  ORGANIC  ANALYSIS. 


DETERMINATION  OF  NITROGEN. 

When  substances  containing  nitrogen  are  analyzed,  the  carbon  and  hydrogen 
are  ascertained  by  the  method  already  described,  and  the  determination  of  the 
nitrogen  becomes  then  the  subject  of  a  separate  experiment,  in  which  every  thing 
else  is  neglected. 

We  see  at  once,  and  clearly,  whether  a  substance  contain  nitrogen  or  not,  in 
determining  the  carbon.  If  nitrogen  be  present,  bubbles  of  gas,  during  the 
whole  combustion,  escape  through  the  potassa  ley.  If  these  bubbles  towards 
the  end  of  the  combustion,  are  larger  than  an  ordinary  pin's  head,  we  may  be 
sure  that  the  substance  contains  nitrogen. 

We  may  also  ascertain  whether  a  substance  contain  nitrogen  by  melting  a 
portion  of  it  in  a  test  tube  with  4  to  10  times  its  weight  of  fused  caustic  potassa. 
Nitrogenized  substances  are  thus  decomposed  without  blackening,  and  the  whole 
nitrogen  is  disengaged  in  the  form  of  ammonia,  which  in  all  cases  may  be  easily 
recognized  by  the  smell.  If  we  are  obliged  to  have  recourse  to  turmeric  and 
other  tests  to  detect  the  ammonia,  then  the  presence  of  nitrogen  is  doubtful. 

In  the  combustion  of  most  nitrogenized  substances,  the  nitrogen  is  disengaged 
in  the  free  state,  and  in  the  form  of  gas,  mixed  with  the  carbonic  acid  and  watery 
vapour.  In  other  cases  deutoxide  of  nitrogen  is  formed ;  the  production  of  which 
renders  the  determination  of  the  nitrogen  difficult,  and  is  certain  to  render  it  in- 
accurate, if  the  utmost  care  be  not  taken  to  reduce  the  deutoxide  again  to  the 
state  of  nitrogen. 

The  nitrogen  is  always  determined  by  measurement.  Now,  since  nitrogen, 
by  passing  into  deutoxide  of  nitrogen,  doubles  its  volume,  we  are  thus  exposed 
to  a  source  of  error,  which  increases  the  apparent  quantity  of  nitrogen.  This 
error  is  obviated  by  using  a  combustion  tube  3  or  4  inches  longer  than  in  the 
determination  of  carbon,  and  placing,  above  the  anterior  layer  of  pure  oxide  of 
copper,  a  layer  of  copper  turnings,  which  have  been  ignited  till  their  surface  be- 
came black,  and  afterwards  heated  in  a  current  of  hydrogen  till  the  crust  of  oxide 
on  the  surface  has  been  completely  reduced.  Besides  this,  oxide  of  copper  may 
be  used  for  the  combustion,  which  has  already  served  for  an  analysis,  and  which 
consequently  contains  a  considerable  quantity  of  metallic  copper. 

The  following  rule  must  be  attended  to  in  the  determination  of  nitrogen : — 
The  more  carefully  and  intimately  the  mixture  with  the  oxide  of  copper  has  been 
made,  and  the  more  slowly  the  combustion  is  made  to  proceed,  the  less  danger  is  there 
df  the  formation  of  the  deutoxide  of  nitrogen.  To  give  an  idea  of  how  we  ought  to 
proceed,  it  may  here  be  remarked,  that  the  combustion  of  a  nitrogenized  sub- 
stance requires  twice  as  much  time  as  that  of  a  substance  containing  no  nitrogen. 

The  methods  to  be  pursued  in  the  determination  of  nitrogen  are  various,  and 
more  or  less  simple  according  to  the  amount  of  nitrogen  present  in  the  sub- 
stance. 

The  qualitative  analysis  of  the  gaseous  mixture  produced  in  the  combustion, 
must  in  all  cases  precede  the  quantitative  determination  of  the  nitrogen ;  for  the 
knowledge  of  the  relative  volumes  of  carbonic  acid  and  nitrogen  suffices,  in  most 
cases,  to  enable  us  to  calculate  the  amount  of  nitrogen,  that  of  carbon  having 
been  previously  ascertained.  In  these  cases  the  employment  of  a  special  process 
becomes  superfluous.  The  apparatus  employed  for  this  qualitative  analysis  is 
extremely  simple ;  the  whole  operation  lasts,  including  all  the  preparations,  about 


ORGANIC  ANALYSIS. 


807 


two  hours  ;  and  what  we  thereby  ascertain  determines  our  choice  of  another  pro- 
cess, or  renders  all  further  operations  unnecessary. 

The  substance  (weighed  or  not  weighed,  this  is  indiflfereut)  is  mixed  with 
forty  to  fifty  times  as  much  oxide  of  copper  as  would  suffice  for  its  complete  oxi- 
dation.    The  mixture  is  introduced  into  the  tube  of  combustion,  A,^.  25,  so  as 

Fig.  25. 


to  occupy  half  its  length.  Of  the  two  remaining  quarters  of  the  length  of  the 
tube,  one  is  filled  with  oxide  of  copper  from  ^  to  a,  the  other  with  copper  turn- 
ings from  a  to  the  mouth  of  the  tube.  The  combustion  tube  being  connected 
with  the  tube  B,  for  collecting  the  gas,  is  placed  in  the  furnace.  The  tube  B 
may  be  rendered  moveable  by  a  caoutchouc  connecter,  C  ;  it  reaches  into  the 
mercurial  trough,  and  is  barely  covered  with  mercury. 

The  screen  m  is  put  on  at  a,  and  then  both  the  metallic  copper  and  the  oxide 
of  copper  are  raised  to  a  full  red  heat ;  the  slits  in  the  bottom  of  the  furnace  as 
far  as  a,  being  exposed,  so  that  the  heat  may  be  strongest  in  the  anterior  half  of 
the  tube.  If  the  tube  be  not  of  Bohemian  glass,  this  part  of  the  tube  must  be 
wrapped  in  thin  sheet  copper,  tied  on  with  copper  wire  :  otherwise,  the  pressure, 
even  of  a  small  column  of  mercury,  blows  out  the  heated  part,  and  causes  a  hole 
in  the  tube. 

As  soon  as  the  copper  and  oxide  are  fully  red  hot,  the  second  screen,  f»,  is  so 
placed,  that  a  length  of  one  inch  of  the  tube, /row  the  closed  end,  is  exposed,  and 
this  is  surrounded  with  red  hot  charcoal.  The  combustion  is  thus  begun  at  the 
closed  end ;  the  gaseous  matter  disengaged  expels  all  the  atmospheric  air  from 
the  apparatus,  and  by  this  means  the  whole  is  filled  with  the  gaseous  products 
of  the  combustion  alone.  The  combustion  is  now  carried  on  as  usual,  beginning 
at  a,  and  proceeding  gradually  towards  the  closed  end,  by  moving  the  screen,  m, 
backwards  half  an  inch  at  a  time,  surrounding  each  J  inch  with  glowing  char- 
coal, &c.  The  gas,  produced  at  this  period,  is  collected  in  graduated  tubes  ^ 
inch  in  diameter,  and  12  to  15  inches  long,  accurately  graduated  into  equal  parts, 
whether  cubic  inches,  or  cubic  centimetres,  or  arbitrary  measures,  but  all  strictly 
uniform  in  each  individual  tube. 

When  the  first  tube  is  three-fourths  full  of  gas,  it  is  to  be  lifted  out  of  the 
mercury,  and  air  allowed  to  enter  it.  As  this  air,  in  a  few  seconds,  mixes  with 
the  gas,  it  furnishes  a  very  delicate  test  of  the  presence  of  deutoxide  of  nitrogen. 
Should  YQ^^^th  of  this  gas  be  present,  the  well-known  red  vapours  of  nitrous 
acid  are  instantly  seen,  which,  if  in  very  small  proportion,  give  a  yellow  colour 
to  the  gas,  when  viewed  through  a  great  thickness,  as  by  looking  through  the 
tube  horizontally  from  end  to  end. 

Sometimes  deutoxide  of  nitrogen  occur»  at  the  beginning,  and  not  after  some 
time,  because  the  oxide  at  a  is  reduced  and  assists  the  deoxidizing  agency  of  the 


808 


ORGANIC  ANALYSIS. 


turnings.  The  above*desoribed  test  of  the  purity  of  the  gas  must  be  tried  at  the 
beginning,  middle,  and  end  of  the  combustion.  If  the  formation  of  deutoxide  of 
nitrogen  has  been  observed  throughout  the  whole  operation,  either  the  mixture  of 
the  substance  with  the  oxide  has  been  imperfect,  or  the  combustion  has  been  too 
rapid,  or  else  it  is  necessary  to  increase  the  proportion  of  copper  turnings. 

It  is  not  worth  while  in  this  case  to  finish  the  experiment :  it  teaches  nothing, 
gives  rise  to  false  notions  of  the  composition  of  the  substance,  and  only  raises 
doubts  of  the  accuracy  of  the  next  better  analysis. 

We  obtain  in  all  6  or  8  tubes  of  gas,  whose  united  volumes  amount  to  from 

300  to  600  cubic  centimetres  ;  and  we  have  now  to  determine  the  relative  volume 

of  the  nitrogen  and  carbonic  acid.     For  this  purpose,  the  tubes  are  carried,  one 

Fig.  26.      Fig.  27.after  the  other,  into  the  cylinder  with  mercury,  {Jig.  26,)  which 

is  widened  out  at  the  top,  the  mercury  within  and  without  is 

brought  to  a  level,  and  the  volume  of  gas  noted. 

By  means  of  the  pipette, yig.  27,  which  is  filled  with  caustic 

ley,  and  closed  at  a  with  mercury,  the  ley  is  introduced  into 

I    the  tube  to  the  depth  of  some  lines.     This  is  generally  done 

by  applying  the  mouth  to  13,  and  producing  a  slight  pressure, 

not  more  than  sufiicient  to  force  out  some  of  the  ley. 

When  the  bent  point  of  the  pipette  is  IJ  inch  long,  and 
reaches  above  the  mercury  into  the  tube,  we  have  only  to  raise 
the  graduated  tube  in  the  mercury,  so  as  to  cause  a  slight  va- 
cuum within,  when  the  pressure  of  the  atmosphere  causes  the 
ley  to  flow  into  the  graduated  tube. 

By  gently  moving  up  and  down  the  graduated  tube,  all  the 
carbonic  acid  is  rapidly  absorbed,  and  nothing  but  nitrogen  is 
left.  The  open  end  of  the  tube  is  easily  broken,  owing  to  the  weight  of  the 
mercury.  This  accident  may  be  entirely  avoided,  by  holding  the  tube  so  that 
its  mouth  is  constantly  in  contact  with  the  side  of  the  cylinder  while  we  are 
moving  it  up  and  down.  The  mercury  without  and  within  is  now  again  brought 
to  a  level,  and  the  volume  of  gas  noted. 

Let  the  volume  of  gas  in  the  6  tubes  be  =  620,  and  let  the  remainder,  after  the 
action  of  the  caustic  ley,  be  =:  124  ;  496  vol.  of  carbonic  acid  have  consequently 
disappeared.  Hence,  in  this  case,  the  volume  of  the  nitrogen  is  to  that  of  the 
carbonic  acid,  as  124  :  496,  or  as  1  to  4. 

We  may  now  proceed,  in  a  variety  of  ways,  to  calculate  the  nitrogen  contained 
in  the  substance  from  the  relative  volumes,  it  being  presupposed^  that  the  quantity 
of  carbonic  acid  yielded  by  a  given  weight  of  the  substance  is  known.  Either  we 
convert  the  weight  of  the  carbonic  acid  into  volume,  and  divide  this  by  the  num- 
ber expressing  the  relative  proportion;  the  quotient  gives  the  corresponding 
quantity  of  nitrogen  by  volume.  For  example,  0*100  gramme  of  cafieine  yield 
by  combustion,  by  weight,  0*180  grammes  of  carbonic  acid.  The  gaseous  mix- 
ture which  caflfeine  yields  by  combustion,  contains  nitrogen  and  carbonic  acid  in 
the  proportio;!  by  volume  of  1  to  4.  Now,  1000  cubic  centimetres  of  carbonic 
acid  gas  weigh  1*97978  gramme, — 0-180  gramme  of  carbonic  acid,  therefore, 
corresponds  to  91*85  cubic  centimetres.  Dividing  this  number  by  4,  we  obtain 
the  number  22*85  cubic  centimetres,  which  are  to  91*85  as  1  to  4.  These  22*85 
cubic  centimetres  are  calculated  as  nitrogen.  We  know  that  1000  cubic  centi- 
metres of  nitrogen  weigh  1*26  gramme.  Hence,  100  parts  of  cafieine  contain 
28*834  of  nitrogen,  and  49*796  carbon. 


■V 


ORGANIC  ANALYSIS.  809 

Or,  to  avoid  this  tedious  calculation,  if  we  remember  that  1  vol.  carbonic  acid 
represents  1  atom  of  carbon,  and  1  vol.  nitrogen  gas,  2  atoms  of  nitrogen,  (1 
atom  English,)  since  the  quantity  of  carbon,  and  the  relative  volumes  of  car- 
bonic acid  and  nitrogen  are  known,  we  calculate  the  nitrogen  from  the  atomic 
weights. 

Caffeine,  according  to  the  determination  of  the  carbon,  contains  49*796  per 
cent,  of  carbon.  It  also  yields  carbonic  acid  and  nitrogen  in  the  proportion  of  4 
to  1 ;  consequently,  it  contains  carbon  and  nitrogen  in  the  proportion  of  4  atoms 
carbon  to  2  nitrogen.  (1  atom  English.) 

Therefore,  as  4  X  76'437  (the  atomic  weight  of  carbon)  is  to  2  X  88-518  (the 
atomic  weight  of  nitrogen,)  so  is  49-796  :  x.  That  is,  305-748  :  177-036  :  :  49-796 : 
X  =  28-834,  =  the  quantity  of  nitrogen  in  100  parts. 

The  above  described  qualitative  determination  of  nitrogen  furnishes  complete 
security,  and  is  exact  for  all  nitrogenized  bodies,  in  which  the  nitregen  is  to  the 
carbon  in  no  proportion  smaller  than  1  to  8. 

We  now  know  the  sum  of  the  volumes  of  nitrogen  gas  and  carbonic  acid  gas 
yielded  by  a  given  w^eight  of  the  substance.  We  know,  further,  from  a  previous 
analysis,  the  weight  of  the  carbonic  acid.  The  latter,  being  reduced  to  volume, 
is  deducted  from  the  mixed  gases  to  obtain  the  volume  of  the  nitrogen,  which  is 
then  reduced  to  weight.  The  volume  of  nitrogen  must  bear  to  the  volume  of 
carbonic  acid  a  simple  ratio,  and,  indeed,  the  same  indicated  by  the  qualitative 
analysis.  If  the  two  do  not  agree,  one  or  other  of  the  analyses  is  erroneous,  and 
must  be  repeated. 

For  example,  0-100  gramme  of  caffeine  burnt  in  this  apparatus,  yield  at  0°  C. 
and  28"  bar.  114-06  cubic  centimetres  of  gases.  The  same  quantity  of  caffeine, 
burned  in  the  apparatus,  j/Jg-.  14,  gives  0-180  gramme  of  carbonic  acid,  corre- 
sponding, at  0°  and  28"  bar.,  to  91-21  cubic  centimetres  of  carbonic  acid  gas. 
Hence,  0-100  gramme  of  caffeine  yields  114-06 — 91-21=22-85  cubic  centime- 
tres of  nitrogen=28-836  per  cent. 

The  quantity  of  substance  which  may  be  analyzed  in  this  apparatus,  depends 
on  the  size  of  the  bell-jar.  For  each  per  cent,  of  nitrogen  and  carbon  we  must 
calculate  one  cubic  centimetre  in  the  bell-jar,  and,  over  and  above,  a  free  space, 
of  from  15  to  20  cubic  centimetres,  to  allow  for  changes  of  volume  from  changes 
of  temperature.  If  the  bell-jar,  for  example,  holds  only  100  cubic  centimetres, 
we  can  only  measure  in  it  the  gases  from  0-060  gramme  (0-9  grain  nearly)  of 
caffeine,  or  of  0'09  to  0-1  gramme  of  morphine  (1-35  to  1-5  grain  nearly,)  if  the 
jar  contain  at  first  15  cubic  centimetres  of  air.  These  jars  commonly  hold  from 
200  to  250  cubic  centimetres ;  but  it  is  easy  to  see  that  in  all  these  cases,  the 
quantity  analyzed  is  very  small,  and  that  the  errors  of  manipulation  or  of  obser- 
vation have,  under  all  circumstances,  a  great  influence  on  the  amount  of  nitrogen 
obtained  ;  so  that,  when  the  quantity  of  nitrogen  in  the  substance  is  very  small, 
this  apparatus  ceases  altogether  to  give  exact  and  trustworthy  results. 

One  principal  source  of  error  here  is  the  softening  of  the  combustion  tube  by 
the  strong  heat  employed,  whereby  it  loses  its  shape,  which  of  course  affects  the 
volume  of  gas  in  the  bell-jar.  This  occurs  very  readily,  where  the  level  of  the 
mercury  has  not  been  very  carefully  regulated.  It  is  advantageous  to  enclose  the 
lower  half  of  the  tube  along  its  whole  length  in  a  half  cylinder  of  thin  sheet 
copper,  lined  with  fine  charcoal  powder  to  prevent  adhesion.  A  sheet  of  platinum 
as  long  as  the  tube,  and  only  just  broad  enough  to  keep  it  from  bending,  answers 
still  better. 


810  ORGANIC  ANALYSIS. 


JDIRECT  DETERMINATION  OF  THE  NITROGEN. 

In  the  analysis  of  substances  containing  a  very  small  proportion  of  nitrogen, 
the  whole  amount  of  the  nitrogen  gas  is  ascertained  by  a  special  operation.  For 
this  purpose  we  employ  an  apparatus,  arranged  in  the  following  manner. 
Into  the  closed  end  of  a  combustion  tube,  18  inches  long,  is  introduced  a  layer 
of  dry  hydrate  of  lin\p,  (slaked  lime)  of  2  to  2j  inches.  There  must  be  at  least 
60  to  80  grains  of  it.  Above  it  is  placed  1  inch  of  oxide  of  copper,  then  the  mix- 
ture of  the  substance  with  oxide  of  copper ;  the  other  divisions,^.  28,  point  out 

Fig.  28. 
Lime.  CuO     Mixture     CuO     Copper  a 


the  oxide  of  copper  used  for  rinsing  out  the  mortar  after  the  mixture;  above  this, 
pure  oxide  of  copper;  and,  lastly,  copper  turnings. 

The  combustion  tube  is  connected  with  another  in  the  shape  of  a  large  chloride 
of  calcium  tube  with  two  bulbs  ;  the  bulb  a  is  empty,  and  the  other  bulb  and  the 
wide  part  of  the  tube  are  filled  with  fused  hydrate  of  potassa.  By  means  of  a 
tube  of  caoutchouc,  this  apparatus,  after  the  combustion  tube  has  been  placed  in 
the  furnace,  is  connected  with  the  gas  tube  and  gasometer,  and  the  combustion 
carried  on  as  usual.  When  the  absorption  tube  is  12  inches  long,  and  the  wide 
part  of  it  I  of  an  inch  in  diameter,  it  holds  about  thirty  times  as  much  potassa  as 
is  sufficient  to  absorb  the  whole  carbonic  acid  produced,  so  that  nitrogen  alone 
enters  the  gasometer. 

If  the  hydrate  of  lime  be  gently  ignited  at  the  end  of  the  combustion,  the  water 
it  contains  is  converted  into  vapour,  and  drives  all  the  carbonic  acid  before  it 
into  the  graduated  tube.  After  the  cooling,  the  combustion  tube  contains  only 
watery  vapour  which  condenses ;  any  traces  of  carbonic  acid  being  absorbed  by 
the  quick  lime. 

Before  the  combustion  there  was  in  the  gasometer  a  known  volume  of  air,  after 
the  combustion  that  volume  is  increased,  and  the  increase  gives  exactly  the 
volume  of  nitrogen  that  has  entered  the  gasometer.  This  is  measured,  and  after 
being  corrected  to  the  normal  temperature  and  pressure,  is  reduced  to  weight. 

This  apparatus  is  exposed  to  a  constant  error,  which  is  unavoidable.  We 
always  obtain  by  it  too  little  nitrogen,  which  obviously  arises  from  this,  that  the 
oxygen  of  the  air  in  the  tube  takes  part  in  the  combustion,  and  the  volume  of  gas 
in  the  gasometer  is  thus  diminished.  By  a  series  of  the  most  careful  analyses 
of  nitrogenized  substances  of  known  composition,  the  limits  of  this  error  have 
been  ascertained,  and  when  we  add  1  per  cent,  to  the  nitrogen  obtained  in  this 
way,  the  sum  expresses  exactly  the  true  quantity  of  nitrogen  in  the  substance. 

When  the  apparatus  next  to  be  described  is  employed,  there  is  always  obtained 
an  excess  of  nitrogen,  and  this  excess,  in  good  analyses,  amounts  to  1  to  1^  cubic 
centimetres  of  the  whole  volume  obtained  ;  when  deutoxide  of  nitrogen  occurs, 
this  excess  is  greater.  But  when  a  nitrogenized  substance  is  analyzed,  both  in 
the  manner  last  described  and  in  that  about  to  be  mentioned,  the  mean  of  the  re- 
sults (one  giving  an  excess  and  the  other  a  deficiency)  approaches  as  nearly  to 
the  true  amount  of  nitrogen  as  it  is  possible  to  do  at  present,  in  cases  when  its 


ORGANIC  ANALYSIS. 


811 


quantity  is  small.  A  combustion  tube  being  chosen,  24  inches  long,  6  inches  at 
the  closed  end  are  filled  with  carbonate  of  copper ;  above  this  two  inches  are 
filled  with  pure  oxide  of  copper ;  next  the  mixture  of  the  substance  with  oxide 
of  copper ;  next,  another  layer  of  pure  oxide ;  and  lastly,  a  layer  of  copper  turn- 
ings.    In  jig.  29  these  layers  are  marked.     The  combustion  tube  is  connected 


I    i    I    M    1    I    I 


Carbonate  of 
Copper. 


Fig.  29. 


1    1    1    1    W    1 


Mixture. 


-V-h-i- 


Oxide 


1    1    1    »    I    t    M 


Copper. 


by  a  cork  with  the  three-limbed  tube,^.  30,  the  cork  being  covered  with  melted 

Fig.  30. 


sealing  wax.     One  limb  of  the  tube  is  joined  to  the  small  air  pump,  fg.  31,  B, 
the  other  with  a  bent  tube  31  inches  long.  A,  which  dips  into  a  small  mercurial 

Fig.  31. 


812  ORGANIC  ANALYSIS. 

trough,  D,  Both  joinings  are  made  with  caoutchouc  tubes.  The  three-limbed 
iubeyjig,  30,  is  somewhat  drawn  out  at  a.  The  apparatus  is  now  exhausted,  the 
mercury  rises  to  27  inches.  If  it  falls,  some  one  of  the  joinings  is  not  air  tight. 
A  screen  is  now  placed  behind  the  oxide  of  copper  at  n,  fg.  29,  and  the  half  of 
the  carbonate  of  copper  farthest  from  the  closed  end  of  the  tube  is  surrounded 
with  a  few  red  hot  bits  of  charcoal.  .Pure  carbonic  acid  is  instantly  disengaged, 
the  mercury  sinks,  gas  escapes  at  the  end  of  the  tube.  The  apparatus  is  now 
exhausted  a  second  time;  carbonic  acid  is  again  disengaged, and  this  is  repeated 
four  or  five  times,  or  till  the  bubbles  of  gas,  when  received  in  a  tube  of  caustic 
ley,  are  almost  completely  absorbed,  and  leave  a  scarcely  perceptible  trace  of  air. 
The  air  is  now  expelled  from  the  apparatus.  The  part  a!  of  the  three-limbed 
tube,  Jig.  30,  previously  drawn  out,  is  now  sealed  with  a  spirit  lamp  flame,  and 
the  air  pump,  together  with  the  S  formed  tube  of  connection  C,  removed.  A 
graduated  tube  B,  of  about  100  cubic  centimetres  capacity,  half  filled  with  mer- 
cury, and  half  with  caustic  ley,  is  now  fixed  by  the  holder  A,  fg.  31,  over  the 
mouth  of  the  long  bent  tube.  The  combustion  is  now  carried  on  as  usual ;  nitro- 
gen and  carbonic  acid  are  evolved,  the  latter  is  absorbed  by  the  ley,  and  thus 
nitrogen  alone  is  collected  in  the  graduated  tube. 

When  the  combustion  is  over,  and  the  tube  has  been  heated  as  far  as  n,  fg. 
29,  the  gas  remaining  in  the  apparatus  still  contains  some  nitrogen,  which  must 
be  brought  into  the  graduated  tube.  Jig.  31,  B'.  One  half  of  the  carbonate  of 
copper  has  served  to  expel  the  atmospheric  air,  the  other  half  now  serves  to  force 
all  the  residual  gas  into  the  graduated  tube.  The  closed  end  of  the  tube  is, 
therefore,  now  surrounded  with  red-hot  charcoal,  and  300  or  400  cubic  centime- 
tres of  gas  disengaged  and  passed  into  the  graduated  tube ;  by  which  means  the 
whole  of  the  residual  gas  is  swept  out. 

When  no  further  absorption  takes  place  in  the  graduated  tube,  especially  when 
it  is  shaken,  its  mouth  is  closed  with  a  ground  glass  plate,  and  it  is  opened  under 
water  in  a  large  jar.  The  mercury  and  caustic  ley  descend,  and  their  place  is 
occupied  by  water. 

The  gas  is  measured,  noting  the  temperature  and  pressure,  the  correction  for 
the  tension  of  water  is  made,  the  volume  reduced  to  the  normal  temperature  and 
pressure,  and  the  weight  of  the  nitrogen  calculated  from  its  volume. 

Berzelius  proposes  to  dispense  with  the  air-pump  altogether,  by  passing  a 
current  of  carbonic  acid  gas  through  the  apparatus  for  a  long  time  before  the 
combustion,  so  as  to  remove  all  the  atmospheric  air.  If  we  would  not  expose 
ourselves  to  the  risk  of  serious  error,  we  cannot  omit  the  use  of  the  air-pump  :  for, 
without  exhaustion,  the  air  contained  in  the  pores  of  the  powder  is  not  removed  by 
the  current  of  carbonic  acid.  This  air  amounts  to  from  8  to  9  cubic  centimetres 
in  the  ordinary  bulk  of  the  mixture ;  and  this  is  often  more  than  the  nitrogen 
contained  in  0*5  to  0*6  grammes  of  substance. 

Mitscherlich  proposes  to  introduce  the  mixture  into  the  tube  without  carbonate 
of  copper;  to  exhaust  the  apparatus,  to  conduct  the  combustion  as  usual,  to  re- 
ceive all  the  carbonic  acid  and  nitrogen  in  a  graduated  bell-jar,  to  measure  their 
volume,  and  to  absorb  the  carbonic  acid  by  hydrate  of  potassa.  He  thus  obtains 
the  relative  volumes,  from  which  the  weight  of  the  nitrogen  may  be  calculated. 

But  if  we  reflect  that  by  the  first  action  of  heat  on  all  organic  substances, 
volatile  products  are  formed,  which  are  only  completely  burned,  when  they  pass 
slowly  over  red-hot  oxide  of  copper;  and  if  we  consider  that  when  combustion 


ORGANIC  ANALYSIS.  813 

occurs  in  vacuo,  the  gases  evolved  expand  rapidly  therein,  we  must  expect  in- 
complete combustion  at  the  beginning  of  this  process.  Besides,  there  remains 
at  the  end  a  certain  quantity  of  nitrogen  in  the  tubes  which  is  not  measured ;  and, 
farther,  the  volume  of  the  hydrate  of  potassa  must  be  estimated  and  deducted 
from  that  of  the  gas.  This  method  was  suggested  by  the  analysis  of  uric  acid; 
but  for  this  substance,  so  rich  in  nitrogen,  it  is  not  required ;  and  it  is  hardly  to 
be  recommended  for  substances  which  contain  very  little  nitrogen. 

The  apparatus  I  have  described  may  be  also  used  for  the  combustion  of  sub- 
stances in  vacuo,  with  the  object  of  ascertaining,  by  the  qualitative  analysis  of 
the  gases,  (rejecting,  of  course,  the  first  portions,)  the  relative  volumes  of  car- 
bonic acid  and  nitrogen — and  this  with  the  exclusion  of  the  air  of  the  apparatus. 
Here  the  carbonate  of  copper  is  not  required.  But  in  substances  which  contain 
very  little  nitrogen,  we  cannot  depend  on  the  determination  of  the  relative  vol- 
umes, even  when  we  operate  with  the  utmost  care. 

We  must  never  neglect,  in  all  determinations  of  nitrogen,  to  subject  the  accu- 
racy of  our  weights  to  a  most  rigorous  scrutiny.  It  is  indifferent,  as  is  well 
known  for  ordinary  analysis  by  weight,  whether  the  weights  be  accurate  or  not, 
provided  they  agree  among  themselves.  But  when  the  weights  with  whi(A  we 
weigh  our  substances  are  not  true  to  the  standard,  we  are  exposed  to  serious 
errors  in  reducing  the  volumes  of  the  gases  to  weights. 

[MM.  Varrentrapp  and  Will  have  lately  put  in  practice  a  new  and  admirable 
process  for  estimating  the  nitrogen  in  organic  compounds.  It  has  been  already 
stated  (page  535),  that  when  neutral  organic  substances  are  heated  with  hydrated 
bases,  (i.  e.  hydrate  of  potassa  or  soda)  decomposition  occurs,  the  water  of  the 
hydrate  furnishing  oxygen  to  the  carbon  of  the  organic  body  so  as  to  form  car- 
bonic acid,  while  the  residual  hydrogen  escapes  along  with  that  proper  to  the  sub- 
stance ;  but  when  the  organic  body  contains  nitrogen,  the  whole  of  this  combines 
with  so  much  of  the  liberated  hydrogen  as  to  form  ammonia.  By  operating, 
therefore,  upon  a  known  weight  of  the  organic  substance,  and  collecting  all  the 
ammonia  which  is  evolved,  it  becomes  easy  to  determine  by  calculation  the 
quantity  of  nitrogen  which  it  contained.  We  subjoin  the  following  general 
statement  of  the  method  of  proceeding  taken  from  Fowne's  Elementary  Chemis- 
try, and  refer  the  reader  for  a  more  detailed  account  to  a  paper  by  the  authors  of 
the  process  in  the  Philosophical  Magazine,  for  March,  1842. 

"  An  intimate  mixture  is  made  of  1  part  caustic  soda,  and  2  or  3  parts  quick- 
lime, by  slaking  lime  of  good  quality  with  the  proper  proportion  of  strong  caustic 
soda,  drying  the  mixture  in  an  iron  vessel,  and  then  heating  it  to  strong  redness 
in  an  earthen  crucible.  The  ignited  mass  is  rubbed  to  powder  in  a  warm  mortar, 
and  carefully  preserved  from  the  air.  The  lime  is  useful  in  many  ways,  it  dimi- 
nishes the  tendency  to  deliquescence  of  the  alkali,  facilitates  mixture  with  the 
organic  substance,  and  prevents  fusion  and  liquefaction.  A  proper  quantity  of 
the  substance  to  be  analyzed,  from  five  to  ten  grains,  namely,  is  dried  and  accu- 
rately weighed  out ;  this  is  mixed  in  a  warm  porcelain  mortar,  with  enough  of 
the  soda-lime  to  fill  two-thirds  of  an  ordinary  combustion  tube,  the  mortar  being 
rinsed  with  a  little  more  of  the  alkaline  mixture,  and  lastly,  with  a  small  quan- 
tity of  powdered  glass,  which  completely  removes  every  thing  adherent  to  its 
surface ;  the  tube  is  then  filled  to  within  an  inch  of  the  open  end  with  the  lime- 
mixture,  and  arranged  in  the  chauffer  in  the  usual  manner.  The  ammonia  is 
collected  in  a  little  apparatus  of  three  bulbs  containing  moderately  strong  hydro- 


614  ORGANIC  ANALYSIS. 

Fig.  32. 


chloric  acid,  attached  by  a  cork  to  the  combustion  tube.  Matters  being  thus 
adjusted,  fire  is  applied  to  the  tube,  commencing  with  the  anterior  extremity. 
When  ignited  throughout  the  whole  length,  and  when  no  more  combustible  gas 
issues  from  the  apparatus,  the  point  of  the  tube  is  broken  and  a  little  air  drawn 
through  the  whole.  The  acid  liquid  is  then  emptied  into  a  capsule,  the  bulbs 
rinsed  into  the  same  with  a  little  alcohol,  and  then  repeatedly  with  distilled 
water ;  an  excess  of  pure  chloride  of  platinum  is  added,  and  the  whole  evaporated 
to  dryness  in  a  water-bath.  The  dry  mass,  when  cold,  is  treated  with  a  mixture 
of  alcohol  and  ether,  which  dissolves  out  the  superfluous  chloride  of  platinum, 
but  leaves  untouched  the  yellow  crystalline  double  chloride  of  platinum  and 
ammonium.  The  latter  is  collected  upon  a  small  weighed  filter,  washed  with 
the  same  mixture  of  alcohol  and  ether,  dried  at  212°,  and  weighed  ;  100  parts 
correspond  to  6*306  parts  of  nitrogen ;  or,  the  salt  with  its  filter  may  be  very 
carefully  ignited,  and  the  filter  burned  in  a  platinum  crucible,  and  the  nitrogen 
reckoned  from  the  w^eight  of  the  spongy  metal,  100  parts  of  that  substance  cor- 
responding to  14*25  parts  of  nitrogen; — the  former  plan  is  to  be  preferred  in  mqst 
cases. 

Bodies  very  rich  in  nitrogen,  as  urea,  must  be  mixed  with  about  an  equal 
quantity  of  pure  sugar,  to  furnish  incondensable  gas,  and  thus  diminish  the  vio- 
lence of  the  absorption  which  otherwise  occurs ;  and  the  same  precaution  must  be 
taken,  for  a  different  reason,  with  those  which  contain  little  or  no  hydrogen,"] 

METHODS  OF  CONTROL  FOR  ORGANIC  ANALYSES. 

All  the  precautions  which  insure  an  accurate  result  having  now  been  described, 
we  have  yet  to  consider  some  methods  which  are  occasionally  employed  to  check 
the  determinations  of  the  carbon  and  the  hydrogen. 

In  the  case  of  substances  having  a  small  atomic  weight,  and  in  which,  con- 
sequently, the  numbers  of  atoms  of  the  elements  stand  in  a  very  simple  relation 
to  one  another,  no  further  tontrol  is  necessary  than  the  accurate  determination  of 
the  atomic  weight.  The  case,  however,  is  very  different  with  bodies  of  consider- 
able atomic  weight — in  which  a  trifling  difference  in  the  determination  of  the 
atomic  weight  sometimes  corresponds  to  more  than  half  an  equivalent  of  carbon, 
and  often  to  more  than  3  atoms,  or  l|  equivalent  of  hydrogen.  With  such  bodies 
we  must  not  neglect  the  following  methods  of  checking  the  result: — 

Control  fur  the  Carbon. — If  the  substance  enter  into  combination  with  a  nitro- 
genized  body,  as,  for  example,  with  ammonia  or  nitric  acid,  the  combustion  of 
such  compounds,  when  the  proportion  of  the  nitrogenized  substance  is  known, 
gives,  through  the  relative  volumes  of  carbonic  acid  and  nitrogen  gases  obtained, 
a  strict  control  for  the  carbon.  The  volumes  of  the  two  gases  are  to  each  other 
as  the  equivalents  of  carbon  and  nitrogen  in  the  compound. 

A  second  method  of  checking  the  carbon  in  acids  of  high  atomic  weight,  con- 
sists in  the  combustion  of  one  of  their  salts,  whose  base  retains  carbonic  acid, 
although  ignited  with  oxide  of  copper,  as,  for  example,  baryta  does.     We  obtain 


ORGANIC  ANALYSIS.  815 

less  carbonic  acid  than  when  the  substance  itself  is  burned  with  oxide  of  copper, 
and,  of  course,  exactly  one  atom  less.  The  quantity  of  carbonic  acid  retained 
by  the  base  may  be  determined,  and  its  weight  should  be  to  that  of  the  carbonic 
acid  obtained  in  the  same  experiment  as  1  to  the  remaining-  atoms  of  the  carbon 
of  the  acid  analyzed.  Both  taken  together  should  give  the  number  of  atoms  of 
carbon  in  the  substance.  For  example,  the  acid  in  the  amygdalate  of  baryta 
contains  40  atoms  of  carbon.  This  salt,  by  combustion  with  oxide  of  copper, 
yields  a  certain  quantity  of  carbonic  acid,  which  is  to  that  retained  by  the  baryta 
39  to  1.  Added  together  they  give  40.  In  a  similar  manner  must  the  atomic 
weights  of  all  fatty  acids  be  checked. 

Control  for  the  Hydrogen. — ^The  hydrogen  of  the  organic  alkalies  may  be 
checked  by  the  analysis  of  the  salts  they  form  with  muriatic  acid.  Since  muri- 
atic acid  undergoes  no  decomposition  in  combining  with  these  bases,  the  quan- 
tity of  hydrogen  obtained  should  always  be,  if  calculated  on  the  weight  of  the 
base,  greater  by  2  atoms,  or  1  equivalent,  (the  quantity  contained  in  the  muri- 
atic acid,)  than  that  furnished  by  the  analysis  of  the  base  separately.  With  sub- 
stances like  stearic  and  oleic  acids,  there  is  always  some  uncertainty  in  the  de- 
termination of  the  hydrogen ;  and  we  must  here  choose  that  number  of  atoms 
which  corresponds  most  closely  with  the  minimum  of  hydrogen  obtained.  The 
surest  means  of  acquiring  certainty  in  such  cases,  consists  in  the  separation  of 
the  substance  into  new  products,  and  the  analysis  of  such  products.  The  hy- 
drogen of  these  must  bear  a  distinct  and  obvious  relation  to  that  of  the  substance 
from  which  they  proceed.  If  we  cannot  point  out  such  a  relation,  some  doubt 
must  still  remain. 

DETERMINATION  OF  THE  NUMBER  OF  ATOMS  OF   THE  ELEMENTS  OF  AN 
ORGANIC  COMPOUND. 

The  methods  hitherto  described  give  the  composition  of  the  substances 
analyzed  in  a  known  weight,  but  do  not  decide  on  the  number  of  atoms  of  the 
elements  of  the  compound.  We  may  indeed  ascertain  their  relative  number, 
when  we  are  able  to  decompose  the  substance  into  products  of  known  composi- 
tion. But  this  has  been  hitherto  possible  with  but  few  ;  and  the  determination 
of  the  proportion  in  which  the  substance  combines  with  the  known  atomic 
weight  of  another  body,  remains,  as  yet,  the  most  important  step  towards  ascer- 
taining the  true  composition,  and  checking  the  numerical  results  of  the  analysis. 

If  the  substance  be  an  acid,  its  atomic  weight  is  ascertained  by  the  analysis 
of  one  of  its  salts.  Its  combination  with  oxide  of  silver,  oxide  of  lead,  or  baryta, 
is  best  adapted  for  this  purpose.  Salts  of  silver,  when  they  can  be  formed,  are 
preferable  to  all  others ;  they  are  always  anhydrous,  and  leave,  when  ignited, 
pure  metallic  silver,  from  which  the  atomic  weight  may  be  easily  calculated. 
Many  salts  of  silver,  when  heated,  are  decomposed  with  a  slight  explosion;  in 
these  the  silver  must  be  determined  by  converting  the  oxide  into  chloride.  Some 
have  recommended  to  moisten  the  salt  with  oil  of  turpentine,  and  set  it  on  fire, 
which  prevents  explosion ;  but  oxalate  and  fumarate  of  silver,  besides  other  salts, 
explode  in  spite  of  this  precaution,  which  can  only  serve  its  purpose  in  few 
cases. 

Berzelius  analyzes  salts  of  lead  in  a  very  convenient  and  expeditious  way. 
He  places  the  salt  in  a  small  thin  capsule  of  porcelain,  and  heats  it  sharply  at 
the  edge,  where  the  salt  commonly  takes  fire,  and  continues  to  glow  till  nothing 
is  left  but  a  mixture  of  oxide  of  lead  and  metallic  lead.    The  weight  being  taken, 


816  ORGANIC  ANALYSIS. 

it  is  moistened  with  acetic  acid,  and  washed  by  decantation,  first  with  water,  and 
lastly  with  alcohol,  and  again  dried.  The  loss  is  oxide  of  lead,  the  final  increase 
of  weight  in  the  capsule  is  metallic  lead. 

In  forming  compounds  of  lead,  we  must  bear  especially  in  mind  the  property 
possessed  by  insoluble  salts  of  lead,  of  combining  with  salts  otherwise  soluble, 
which  may  be  present,  and  are  apt  to  be  precipitated  at  the  same  time. 

If  the  acid  form  an  acid  and  a  neutral,  or  a  neutral  and  a  basic  compound,  the 
analysis  of  such  compounds  gives  a  new  means  of  fixing  the  true  atomic  weight ; 
but  all  that  could  be  said  on  this  head  must  be  obvious  to  every  one  acquainted 
with  general  analysis. 

Compounds  of  baryta  answer  very  well.  With  bodies  of  high  atomic  weight 
the  analysis  of  salts  of  lime  is  exposed  to  serious  errors,  from  the  low  atomic 
weight  of  that  base. 

The  combustion  of  the  acid,  and  of  one  of  its  anhydrous  salts,  determines 
the  amount  of  water  present  in  the  form  of  hydratic  water. 

The  determination  of  the  water  of  crystallization  of  the  salts  analyzed,  is  of 
great  importance  in  organic  analysis,  and  must  never  be  neglected  where  it  can 
be  performed. 

The  capacity  of  saturation  of  the  organic  alkalies  may  be  ascertained  by  means 
of  the  drying  apparatus  formerly  described — {J^s.  1  and  2,  pages  786  and  787.) 
The  organic  base  is  placed  in  the  middle  portion  of  the  vessel,  and,  its  weight 
in  the  dry  state  being  known,  dry  muriatic  acid  gas  is  introduced  through  a. 
The  combination  takes  place  easily,  rapidly,  and  with  disengagement  of  heat. 
Several  of  the  bases  melt,  others  remain  porous  ;  in  all  cases  a  certain  quantity 
of  muriatic  acid,  not  essential  to  the  compound,  remains,  and  must  be  removed. 
For  this  purpose  we  proceed,  just  as  if  we  wished  to  dry  the  compound.  The 
apparatus  is  surrounded  with  boiling  water,  and  dry  air  passed  through  till  the 
weight*  becomes  constant.  The  increase  of  weight  in  the  apparatus  gives  the 
quantity  of  muriatic  acid  which  has  entered  into  combination. 

If  it  be  thought  necessary  to  ascertain  whether,  during  the  combination,  water 
may  not  have  been  given  off,  which  would  diminish  the  apparent  quantity  of  the 
muriatic  acid,  a  known  weight  of  the  salt  must  be  dissolved  in  water,  and  the 
muriatic  acid  determined  as  chloride  of  silver. 

[Note. — In  a  paper  lately  published  by  Professor  Liebig,  (Annalen  der  Phar- 
macie  XXVI.)  he  has  proposed  a  new  method  of  determining  the  atomic  weight 
of  organic  bases,  which  appears  decidedly  preferable  to  the  above.  All  the 
vegetable  alkalies  in  the  state  of  muriates,  form  double  salts  with  bichloride  of 
platinum,  analogous  to  the  compounds  of  bichloride  of  platinum  with  muriate  of 
ammonia,  and  with  the  chlorides  of  potassium  and  sodium ;  with  this  difference 
from  the  latter,  that  the  salts  formed  by  muriatic  acid  with  the  vegetable  bases 
are  true  muriates,  containing  all  the  oxygen  of  the  base,  and  all  the  hydrogen  of 
the  muriatic  acid,  thus  adding  one  more  to  the  numerous  analogies  existing 
between  the  vegetable  alkalies  and  ammonia.  These  double  salts,  which  are  easily 
obtained  pure,  are  readily  analyzed  by  ignition.  They  leave  metallic  platinum, 
from  which  their  composition  may  easily  be  calculated.  This  is  only  one  of  the 
numerous  improvements  in  organic  analysis  for  which  we  are  indebted  to  the 
author  of  this  work,  and  which  have  been  the  main  cause  of  the  astonishingly 
rapid  progress  lately  made  in  this  department  of  chemistry. — W.  G.] 

Many  organic  substances,  without  being  exactly  acids,  combine  with  oxide  of 
lead ;  and  by  this  combination  a  certain  portion  of  water  is  occasionally  sepa- 


ORGANIC  ANALYSIS.  817 

rated,  which  would  not  have  been  separated  by  heat.  By  the  analysis  of  the 
pure  substance  and  of  these  compounds  with  oxide  of  lead,  we  may  learn  all 
that  we  wish  to  know  of  the  number  of  atoms  of  the  elements  of  the  substance. 
Other  substances  combine  neither  with  acids  nor  with  oxides,  but  they  crys- 
tallize with  water.  In  such  cases  the  water  of  crystallization  must  be  deter- 
mined with  the  utmost  care.  We  can  calculate  from  it,  with  the  same  precision, 
the  single,  double,  or  half  atomic  weight  of  the  substance,  &c. — which,  of  course, 
depends  on  the  number  of  atoms  of  water  with  which  the  substance  combines. 

EXAMPLES. 

COMPOSITION  OF  AMYGDALIC  ACID— DETERMINATION  OF  ITS  ATOMIC 

WEIGHT. 
1*089  amygdalate  of  baryta,  decomposed  by  sulphuric  acid,  yield  0*234  sul- 
phate of  baryta.     The  atomic  weight  of  the  sulphate  of  baryta  is  1458*05.  That 
of  amygdalate  of  baryta  is  therefore  obtained  by  the  proportion 
0-234  :   1-089  : :  1458-05  :  6783-37. 
Control. — 1*002  amygdalate  of  baryta  yield,  by  calcination,  0*182  carbonate  of 
baryta.     Calculated  from  this,  the  atomic  weight  is  6790*00.     Mean  of  the  two 
=  6786*68. 

0*668  of  the  same  salt  yield  1*068  carbonic  acid,  or  159*88  per  cent.  0*7235 
yield  1*148  carbonic  acid,  or  158*60  per  cent.  100  parts  therefore  yield,  as  a 
mean  result  159*24  carbonic  acid. 

Further,  0*668  amygdalate  of  baryta  yield  0*302  water,  and  0*7235  yield 
0*326  water. 

When  a  salt  of  baryta  is  burned  with  oxide  of  copper,  carbonate  of  baryta  is 
left,  the  carbonic  acid  of  which  must  be  taken  into  the  calculation.  From  one 
of  the  above  experiments  it  appears  that  100  parts  of  amygdalate  of  baryta  leave, 
after  calcination,  18*17  carbonate  of  baryta.  These  18*17  parts  contain  4*0718 
carbonic  acid.  100  parts  of  amygdalate  of  baryta  yield,  therefore,  in  all,  159*24 
-J-  4-0718  =  163*3118  carbonic  acid. 

We  calculate  now  the  results  for  100  parts  amygdalate  of  baryta — what  is 
wanting  of  the  100  is  oxygen.  The  above  experiments  show  that  100  parts  of 
the  salt  contain, 

Carbon, 45-157 

^  Hydrogen,       .        .        •        .        .  5014 

Baryta, 14-098 

Oxygen, 35731 

100-000 

Next,  in  order  to  find  the  composition  of  the  acid,  and  the  number  of  atoms  of 
its  elements,  we  calculate  how  much  carbon,  hydrogen,  baryta,  and  oxygen  are 
contained  in  the  sum  of  the  atoms  of  all  the  elements,  that  is,  in  the  atomic 
weight  already  found. 
100  parts  contain 

45-157  ;  consequently  6786-68  contain  3064-660  Carbon. 
6-014;  "  6786  68       "         340-284  Hydrogen. 

14-098 ;  '«  6786-68       "         956-706  Baryta. 

35-731  ;  "  6786-68       «'       2424-948  Oxygen. 

100-000  6786-598 

3064*660  is  the  sum  of  the  weights  of  the  atoms  of  carbon  in  1  atom  of  the 

54 


3064-660 

76-437 
340-284 

6-2398 
956  706 

956-88 
2424-948 

818  ORGANIC  ANALYSIS. 

salt.    This  number,  divided  by  the  weight  of  1  atom  of  carbon,  must  give  the 
number  of  atoms  of  carbon ;  and  so  on  for  the  other  elements. 

:=  40'09  atoms  Carbon. 

=  54      atoms  Hydrogen. 

=    1       atom   Baryta. 

=  24      atoms  Oxygen. 
100 

Consequently  the  formula  for  the  salt,  as  deduced  from  the  above  analysis,  is 

C4oH54  024BaO. 

The  comparison  of  the  composition  in  100  parts,  given  by  the  formula,  v^rith 
the  numbers  obtained  experimentally,  will  now  show  how  near  the  result  of  the 
analysis  comes  to  the  theoretical  composition. 

In  100  parts. 

'    40  atoms  Carbon  .        .        .         .         =  3057-48  45-28 

54  atoms  Hydrogen      .        .        .         .        =    336-949  4-99 

1  atom   Baryta  .        .         .        .        =    956880        14-17 

24  atoms  Oxygen  ..'..=  2400-000        35  56 


Atomic  weight  of  the  formula       =  6731-309      100-00 

The  usual  method  of  calculating  the  number  of  atoms  in  the  organic  sub- 
stances analyzed,  is  exactly  that  now  explained  ;  the  formula  thus  obtained  being 
the  closest  expression  of  the  numbers  found  by  experiment.  The  acgjuracy  of 
the  formula  must  now  be  subjected  to  a  strict  examination. 

In  the  example  above  given,  the  actual  result  of  experiment  agrees  as  closely 
as  can  be  expected  with  the  theoretical  result,  according  to  the  formula  adopted. 
As  far  as  regards  the  carbon,  oxygen,  and  baryta,  or  in  short,  all  the  elements, 
except  the  hydrogen,  this  is  sufficient  security  for  the  correctness,  both  of  the 
formula  and  the  analysis ;  but  if  we  bear  in  mind  what  has  been  said  of  the 
determination  of  hydrogen,  we  perceive  that  this  exact  coincidence  proves  the 
substance  to  contain  less  hydrogen  than  that  formula  indicates. 

It  was  formerly  stated  that,  in  bodies  of  high  atomic  weight,  a  correction  is 
required  for  the  hydrogen ;  this,  in  the  above  calculation,  has  been  omitted. 

But  if  we  now  deduct,  from  the  water  actually  obtained  in  each  analysis,  6 
milligrames  (0*09  grain,  nearly)  as  foreign  to  the  substance,  we  have,  from  0*668 
amygdalate  of  baryta,  0  296  water,  and  from  0-7235,  0*320  water;  or  adding 
both  together,  from  1*3915  of  the  salt,  0*616  water.  Hence  100  parts  of  the 
salt  yield  4*91  hydrogen,  that  is,  less  than  the  formula  requires.  Adopting  now 
the  formula  C^H^^O^^BaO,  the  salt  will  contain  4*81  hydrogen  per  cent'. ;  and 
this  calculated  result  agrees  with  the  corrected  experimental  one  as  nearly  as  can 
be  expected  in  experiments  of  this  nature. 

From  what  has  been  said,  we  may  conclude,  with  sufficient  certainty,  that  the 
amygdalic  acid  does  UQt  contain  more  than  52  atoms  of  hydrogen,  and  that,  con- 
sequently, the  atomic  weight  of  the  salt  is  really  only  6738-829. 

It  is  obvious  that  the  errors  of  observation  in  this  analysis  tend  to  diminish 
the  apparent  quantity  of  carbon.  Now  if  the  salt,  with  an  atomic  weight  of 
6786*68,  only  contained  39  atoms  of  carbon,  its  composition  must  be  expressed 
by  the  formula  C^^H^^O^^BaO ;  which  would  give  for  the  atomic  weight  of  the 
salt  the  number  6874*872 ;  a  number  approaching  even  more  nearly  to  ihu  found 
by  experiment  than  the  above  calculated  one,  6738*829.     But  in  this  case,  the 


ORGANIC  ANALYSIS.  819 

salt  would  contain  only  43'35  per  cent,  carbon ;  whereas  the  quantity  obtained, 
45*157  per  cent.,  is  undoubtedly  below  the  truth. 

Here,  then,  a  difference  of  1|  per  cent,  in  the  carbon  is  equal  to  a  difference 
of  1  atom  of  that  element,  and  it  is  easy  to  see  that  the  loss  of  carbon  must 
not,  in  a  substance  like  this,  exceed  0*87  per  cent.,  if  we  wish  the  result  to  be 
free  from  doubt. 

If  we  subtract,  from  the  atomic  weight  of  the  salt  that  of  one  atom  of  baryta, 
we  obtain  the  atomic  weight  of  the  acid;  thus  6738-829 — 956-88=5781-949 ; 
from  which  number  we  can  calculate  the  composition  of  the  acid  in  100  parts. 

In  the  calculation  and  control  of  an  organic  base,  its  atomic  weight  is  ascer- 
tained by  the  quantity  of  acid  with  which  the  base  forms  a  definite  compound ; 
in  other  respects,  the  calculation  is  the  same. 

The  number  of  organic  substances  which  do  not  combine  with  some  other 
substance  of  known  atomic  weight,  and  whose  composition,  therefore,  cannot 
be  subjected  to  any  control,  is  exceedingly  small.  With  such  substances,  we 
must  be  contented  to  ascertain  the  relative  proportions  of  the  atoms  of  their 
elements,  and  to  express  these  in  the  simplest  form.  Mannite,  for  example, 
belongs  to  this  class  of  bodies.  2*735  parts  yielded  by  combustion  4*097  car- 
bonic acid,  and  1*770  water;  which  gives  for  100  parts, 

Carbon 39-7259 

Hydrogen 7-7210 

Oxygen 52-5531 

100.0000 
If  the  atomic  weight  of  mannite  were  100,  then 


'^  would  give  the  number  of  atoms  of  Carbon.'' 

76-437  ^ 


3! 

"^"^^^  the  number  of  atoms  of  hydrogen,  and 


f  ^     t^}^  the  number  of  atoms  of  oxygen. 
100-000  •'^ 

But,  as  its  atomic  weight  is  unknown,  the  quotients  express  the  relative  propor- 
tions of  the  numbers  of  atoms  of  these  elements  in  mannite.     The  quotients  are, 

0-518        ....        Carbon 
1-238        ....        Hydrogen 
0-525        ....        Oxygen 

We  see  at  once,  that  the  number  of  atoms  of  carbon  in  mannite  must  be  equal 
to  the  number  of  atoms  of  oxygen ;  for  the  numbers  0*518,  and  0*525  differ 
very  slightly.  We  observe  likewise,  that  the  number  of  atoms  of  hydrogen 
must  be  greater  than  that  required  to  make  up,  with  the  oxygen,  the  composi- 
tion of  water.  For  if  hydrogen  and  oxygen  were  present  in  the  proportion 
which  constitute  water,  525  of  oxygen  would  require  1050  of  hydrogen;  but 
we  have  1238,  that  is,  very  nearly  one-sixth  more.  For  one  atom  of  oxygen, 
therefore,  there  are  present  2*36  atoms  of  hydrogen;  or,  expressing  this  propor- 
tion in  the  nearest  whole  numbers,  mannite  contains,  for  3  atoms  oxygen,  7 
hydrogen  and  3  carbon. 
The  analysis  of  crystallized  cane  sugar  gave  the  following  results  for  100 

parts : — 

Carbon        .        .        42*301        .        .        42-301     n  553 

7  6-4  3  7 
Hydrogen  .        .  6*454   ,    .        .  fi  45  4_.2  qo^ 

6-2398 

Oxygen       .        .        51*501        .        .        51501 ^  r,- 

^^  101.000— "-^^^ 


820  ORGANIC  ANALYSIS.    ' 

Here  we  see  that  the  number  of  atoms  of  hydrogen  is  exactly  twice  as  great  as 
the  number  of  atoms  of  oxygen ;  an,d  consequently,  that  sugar  contains  these 
elements  in  the  proportion  to  form  water.  The  number  of  atoms  of  oxygen  is  to 
the  number  of  atoms  of  carbon,  as  0-515  to  0-553  ;  in  whole  numbers,  as  11  to 
12.  If  then,  we  assume  sugar  to  contain  11  atoms  of  oxygen,  (the  smallest 
whole  number)  its  composition  will  be  expressed  by  the  formula  C   H   0  . 

A  great  many  organic  bodies,  the  atomic  weight  of  which  cannot  be  directly 
determined,  are  decomposed,  when  brought  in  contact,  under  certain  circum- 
stances, with  other  substances,  such  as  acids  or  alkalies,  into  new  products, 
whose  composition  either  is  already  known,  or  can  be  easily  ascertained.  These 
decompositions  furnish  valuable  means  of  determining  the  constitution  and  con- 
trolling the  analysis  of  such  bodies.  Sugar,  for  example,  in  contact  with  fer- 
ment, is  resolved  into  carbonic  acid  and  alcohol ;  oxamide,  in  contact  with  acids 
or  alkalies,  is  resolved  into  oxalic  acid  and  ammonia.  It  is  obvious,  that  when 
we  have  determined,  in  these  instances,  the  quantity  of  carbonic  acid  and  oxalic 
acid  produced,  and  have  satisfied  ourselves  that  in  the  former  case  no  other  pro- 
duct besides  alcohol,  and  in  the  latter  none  except  ammonia,  is  formed  ;  we  can, 
from  these  data,  determine  the  composition  of  these  substances  with  absolute 
certainty. 

A  very  important  means  of  testing  the  composition  of  an  organic  compound 
of  unknown  atomic  weight,  is  furnished  by  the  hypermanganate  of  potash.  This 
salt,  gently  heated  with  a  soluble  organic  substance,  is  resolved  into  peroxide  of 
manganese,  oxygen,  and  potash.  The  oxygen  enters  into  combination  with  the 
organic  matter,  and  when  the  latter  is  in  excess,  it  rarely  happens  that  the  car- 
bon is  oxidized  so  as  to  form  carbonic  acid.  But  organic  acids  are  produced, 
and  invariably  in  the  proportion  necessary  to  neutralize  the  potash  ;  for  the  solu- 
tion remains  neutral.  The  acid  chiefly  formed  is  the  oxalic;  in  many  cases  the 
formic.  Both  are  easily  determined ;  and  from  their  quantity  and  that  of  the 
hydrated  peroxide  of  manganese,  the  composition  may  be  ascertained.  For  ex- 
ample, a  pure  solution  of  sugar,  warmed  with  this  salt,  yields  neutral  oxalate 
of  potash,  and  peroxide  of  manganese,  in  the  proportion  of  1  atom  of  the  former 
to  2  of  the  latter ;  from  which  it  is  easily  demonstrated  that  sugar  contains 
oxygen  and  hydrogen  in  the  proportion  to  form  water. 

[Note. — This  experiment  was  first  made  by  the  Translator  and  M.  Horace 
Demargay,  in  1835,  and  has  since  been  confirmed  by  the  author  of  this  work, 
and  by  M.  Pelouse.  As  the  hypermanganate  of  potassa  has  thus  become  a 
useful  re-agent  in  organic  analysis,  an  account  of  the  process  by  which  the 
translator  prepares  this  salt  will  not  be  considered  out  of  place ;  more  especially 
as  a  number  of  experimenters  have  found  some  difficulty  in  preparing  it  from 
the  account  inserted  in  the  "  Records  of  Science"  for  1836. 

Native  peroxide  of  manganese  in  very  fint  powder^  and  fused  potassa,  are 
taken  in  the  proportion  of  three  atoms  of  each ;  and  chlorate  of  potassa  in  the 
proportion  of  one  atom.  The  fused  potassa  is  dissolved  in  a  small  quantity  of 
water,  and  the  other  substances  added  to  the  solution.  The  whole  is  dried  up 
by  a  moderate  heat,  and  the  dark  green  mass  is  then  powdered,  and  heated  for 
half  an  hour  to  a  very  low  red  heat  in  a  platinum  crucible.  The  heated  mass  is 
then  dissolved  in  a  very  large  quantity  of  boiling  water,  and  when  the  solution 
has  become  of  a  pure  deep  red,  it  is  decanted  from  the  hydrated  peroxide  which 
separates,  and  evaporated  rapidly  till  small  black  crystals  appear  on  the  surface. 
On  cooling,  a  large  number  are  deposited.     They  are  easily  purified  by  recrys- 


ORGANIC  ANALYSIS.  iB21 

tallization,  when  they  become  larger  and  acquire  a  bronze  colour.  In  the  hands 
of  the  translator  this  process  never  fails,  and  from  good  oxide  of  manganese  a 
quantity  of  crystals  equal  to  half  the  weight  of  the  oxide  employed  may  easily ' 
be  obtained.  The  principal  causes  of  failure  would  appear  to  be,  impurity  of 
the  oxide  of  manganese,  or  using  it  in  a  coarse  powder,  or,  finally,  applying  too 
strong  a  heat. — W.  G.] 

Many  indifferent  azotized  substances,  in  contact  with  alkalies,  are  resolved 
into  ammonia  and  an  acid,  whose  atomic  weight  can  be  determined.  Such  bodies 
are  caffeine,  asparagine,  amygdaline,  &c.,  the  atomic  weight  of  which  may  easily 
be  deduced  from  the  quantity  of  the  acid,  or  of  a  salt  of  the  acid,  of  known 
atomic  weight,  which  is  produced.  For  example,  1'357  parts  of  amygdaline 
produce  1*592  amygdalate  of  baryta.  The  atomic  weight  of  this  salt  is 
6738-829.  Hence  1-592  :  6738-829  : :  1-357  :  5797  =  the  atomic  weight  of 
amygdaline. 

DETERMINATION  OF  THE  SPECIFIC  GRAVITY  OF  THE  VAPOURS  OF  VOL  A- 
TILE  SUBSTANCES,  AS  A  MEANS  OF  ASCERTAINING  THE  NUMBER  OF 
ATOMS  OF  THEIR  ELEMENTS. 

In  the  analysis  of  a  volatile  substance,  the  determination  of  the  specific  gra- 
vity of  the  vapour  is  a  most  valuable  means  of  control  over  the  analysis  by 
combustion.  The  process,  which  is  followed  for  this  purpose,  is  that  of  Dumas, 
first  rendered  practical  by  that  distinguished  chemist,  and  by  him  also  first 
applied,  with  the  happiest  results,  to  this  object.  The  description  of  it,  given 
by  Dumas,  in  his  "  Traite  de  Chimie,"  embraces  all  the  precautions  which  can 
ensure  an  accurate  result. 

The  apparatus  is  simple  in  a  high  degree,  and  the  whole  operation  is  easily 
performed  without  requiring  any  great  expenditure  of  time,  or  any  peculiar  dex- 
terity in  the  operator.  The  problem  to  be  solved  is  to  ascertain  the  weight  of  a 
known  volume  of  the  vapour. 

For  this  purpose,  a  convenient  vessel,  filled  with  dry  air,  at  a  known  tem- 
perature and  pressure,  is  weighed :  the  fluid  or  volatile  substance,  the  specific 
gravity  of  whose  vapour  we  wish  to  ascertain,  is  then  introduced,  and  heated  to 
from  50°  to  75°  beyond  its  boiling  point,  till  it  is  entirely  converted  into  vapour ; 
the  temperature  is  noted,  the  vessel  hermetically  sealed,  and  again  weighed. 
We  know  now  the  weight  of  the  vessel,  when  filled,  both  with  air  and  with 
vapour.  After  reducing  both  to  the  same  temperature  and  pressure,  the  weights 
of  both  are  easily  calculated,  if  the  volume,  that  is,  the  capacity  of  the  vessel, 
be  ascertained.  The  specific  gravity  of  the  vapour  is  ascertained  by  dividing 
the  weight  of  a  known  volume  by  that  of  an  equal  volume  of  air  at  the  same 
temperature  and  pressure. 

The  following  is  the  process  in  detail : — A  flask  of  the  capacity  of  20  to  35 
cubic  inches,  ^g.  33,  (10  to  18  fluid  ounces),  clean  and  dry, 
is  chosen.     It  is  connected  with  the  air  pump  and  the  appa- 
ratus, fig.  4,  p.  787.    Air  is  now  alternately  pumped  out,  and 
re-admitted,  by  which  means  it  is  soon  filled  with  dry  air. 

The  neck  of  the  flask  is  now  drawn  out  at  a,  before  the 
blow-pipe,  to  a  narrow  tube,  6  or  8  inches  long,  which  is 
bent  at  h  ,•  the  point  is  cut  across  with  a  sharp  file,  and  the 
cut  edge  rounded  in  the  flame.  The  glass  must  not  split 
when  softened,  otherwise  it  is  nearly  impossible  to  seal  it  up 


822 


ORGANIC  ANALYSIS. 


quickly  when  required.  We  have  now  got  a  bulb  or  balloon  with  a  drawn  out 
point.  It  is  now  weighed,  and  allowed  to  lie  on  the  scale  till  its  weight  no 
longer  increases  by  the  deposition  of  moisture  on  the  external  surface  of  the 
glass. 

To  introduce  the  liquid  or  the  melted  volatile  solid,  the  bulb  is  gently  warmed, 
so  as  to  expel  a  portion  of  air,  and  the  point  immersed  in  the  fluid  substance. 
As  the  heated  air  contracts,  the  liquid  rises  into  the  bulb ;  this  may  always  be 
quickly  accomplished  by  moistening  the  bulb  with  a  little  ether.  The  quantity 
of  liquid  introduced  varies  with  the  size  of  the  bulb  :  80  grains  may  be  men- 
tioned as  the  minimum,  160  as  the  maximum  quantity  required.  If  the  sub- 
stance should  solidify  in  the  neck  or  the  narrow  tube,  these  must  of  course  be 
previously  warmed. 

The  balloon  is  now  placed  in  a  bath  of  water,  chloride  of  calcium,  chloride 
of  zinc,  &c.,  which  must  always  be  heated  to  a  temperature  50°  to  75°  beyond 
the  boiling  point  of  the  substance.     The  bath  may  be  previously  heated  to  the 

re%iired  degree ;  there  is  no  fear  of 
cracking  the  bulb.  A  very  exact 
thermometer  shows  the  temperature 
of  the  bath. 

The  bulb  may  be  supported  in  the 
bath  in  a  variety  of  ways.  Fig.  34 
shows  one  method.  Fig.  35  is  the 
support  for  the  bulb. 

As  soon  as  the  temperature  of  the 
bath  rises  a  few  degrees  above  the 
boiling  point  of  the  substance,  a 
stream  of  its  vapour  issues  from  the 
point  of  the  tube.  This  gradually 
diminishes,  and  after  15  or  20  min- 
utes, a  flame  brought  near  the  point  is  not  moved  in  the  least.  Should  any 
drops  of  liquid  have  condensed  on  the  neck  of  the  tube  where  it  is  out  of  tlie 
bath,  they  must  be  removed.  This  is  easily  done  by  approaching  a  glowing 
coal ;  and  then,  by  means  of  a  spirit-lamp  and  blow-pipe,  the  point  is  suddenly 
softened,  while  the  vessel  remains  in  the  bath ;  it  closes  hermetically  with 
facility. 

The  iron  vessel  containing  the  bath  is  now  removed  from  the  fire,  the  closed 
bulb  is  taken  out,  washed,  dried,  and  weighed  with  the  precautions  formerly 
described. 

The  vapour  has  expelled  all  the  atmospherical  air,  except  a  small  quantity, 
which  must  be  ascertained.  The  volume  of  the  vapour  must  likewise  be  deter- 
mined. 

For  this  purpose  the  point  is  immersed  in  mercury,  and  is  cut  near  the  neck, 
under  the  mercury,  with  a  sharp  file.  When  the  tube  is  broken  off,  the  vacuum 
caused  by  the  condensation  of  the  vapour  at  the  ordinary  temperature,  is  instantly 
filled  by  mercury.  In  general  a  small  bubble  of  air  is  left,  but  in  many  cases 
the  mercury  entirely  fills  the  bulb.  The  volume  of  the  mercury  is  equal  to  that 
of  the  vapour  at  the  temperature  at  which  the  bulb  was  sealed.  To  determine 
it,  the  mercury  is  measured  in  a  graduated  vessel.  The  bulb  is  now  entirely 
filled  with  water,  and  the  water  measured  ,in  like  manner.  The  difference  between 
the  volume  of  the  water,  and  that  of  the  mercury,  gives  the  volume  of  the  small 
quantity  of  air,  if  any,  which  remained. 


ORGANIC  ANALYSIS.  823 

From  the  data  thus  obtained,  the  specific  gravity  of  the  vapour  may  be  calcu- 
lated. The  following  example  will  illustrate  this  calculation.  It  is  taken  from 
the  Analysis  of  Carbonic  Ether,  by  Professor  Ettling  : — 

Boiling  point  of  carbonic  ether,  258°  F.  The  balloon  with  dry  air  weighed 
47-77  grammes ;  the  temperature  of  the  air  was  65*5  F. ;  the  height  of  the 
barometer  331'8  centimetres.  The  bulb,  after  the  experiment,  was  found,  when 
filled  with  water,  to  have  a  capacity  of  290  cubic  centimetres,  =  the  volume  of 
air  contained  in  it.  290  cubic  centimetres  of  air  at  65*5°  and  331-8  B.  give,  at 
32°  and  336  bar.,  267*7  cubic  centimetres  of  air,  which  weigh  0*34776  gramme. 
Subtracting  this  weight  from  the  weight  of  the  bulb  with  dry  air,  there  remains 
47*42224  grammes  for  the  weight  of  the  bulb  alone.  The  bulb  was  heated  in  a 
bath  of  chloride  of  zinc,  and  sealed  at  the  temperature  of  292°  F.  and  331*8 
bar.,  and  it  now  weighed  48*431  grammes.  The  mercury  which  entered  the  bulb 
after  the  experiment,  measured  289*5  cubic  centimetres  at  the  temperature  of 
65*5°  F.  and  332  bar.  Subtracting  the  weight  of  the  empty  bulb  from  that  of 
the  bulb  when  filled  with  the  vapour,  we  have  for  the  weight  of  the  vapour 
1*00876  grammes.  If  its  volume,  at  292°  and  331*8  bar.,  be  assumed  to  have 
been  289*5  cubic  centimetres,  this  would  give,  at  32°  and  336  bar.,  182*98  cubic 
centimetres.  This  volume  of  vapour,  then,  weighs  1*00876  grammes;  conse- 
quently, 1000  cubic  centimetres  would  weigh  5*5129  grammes.  Now,  1000 
cubic  centimetres  of  air,  at  32°  and  336  bar.,  weigh  1*299075  grammes.  Hence, 
the  specific  gravity  of  the  vapour  of  carbonic  ether  is  =T3Si§f  5  =  4*2'*^* 

This  determination  is  certainly  exact  enough  for  controlling  the  analysis  of 
carbonic  ether ;  but  the  calculation  may  yield  a  false  result  under  certain  circum- 
stances :  for  example,  if  a  correction  be  not  made  for  the  small  quantity  of  air 
left  behind.  Since  the  mercury  which  entered  the  bulb  in  the  above  experiment 
was  only  289*5  cubic  centimetres,  while  the  capacity  of  the  bulb  was  290  c.  c, 
there  was  left  0-5  c.  c.  of  air,  which  was  weighed  along  with  the  vapour.  The 
true  weight  of  the  vapour  is  therefore  got  by  subtracting  from  1*00876  gramme 
the  weight  of  0-5  c.  c.  air,  at  32°  and  336  bar.,  which  is  0*00062  gramme.  The 
remainder  is  1*008135  gramme. 

But  the  volume  of  the  mercury  which  entered  the  bulb  does  not,  moreover, 
express  the  true  volume  of  the  vapour  at  292°  :  for  the  0*5  c.  c.  air  at  292° 
expanded  by  0*23  c.  c,  and,  therefore,  occupied  at  that  temperature  the  volume 
of  0*73  c.  c.  The  volume  of  the  vapour  in  the  above  calculation,  was,  therefore, 
taken  too  high  by  0*23  c.  c.  Its  true  volume  was,  289*5  —  0*23=289*27  c.  c. 
It  is  easy  to  see  that,  in  the  above  example,  these  corrections  hardly  affect  the 
result:  but  where  the  air  left  exceeds  2  c.  c,  it  must  be  taken  into  the  calcula- 
tion as  now  explained. 

The  process  just  described  is  not  susceptible  of  perfect  accuracy.  The  vol- 
umes which  are  measured  and  weighed  are  too  small.  If  we  take  very  large 
bulbs,  the  apparatus  becomes  difficult  to  manage,  and  requires  large  and  perfectly 
exact  balances.  But  all  this  is  unnecessary  for  the  object  in  view.  It  is  enough 
if  the  two  first  decimals  agree  with  the  calculated  theoretical  specific  gravity. 
In  no  case  can  we  reckon  on  the  accuracy  of  the  third  decimal.  For  this  reason 
it  IS  superfluous  to  take  into  account  the  expansion  of  glass  and  a  correction  of 
the  mercurial  thermometer.  The  determination  of  the  specific  gravity  of  the 
vapour  of  camphor  by  Dumas,  will  show  how  slight  are  the  changes  made  by 
these  corrections  on  the  result  of  experiment. 

Dumas  found  that  specific  gravity,  without  these  corrections,  to  be  5*356,  and 


824  ORGANIC  ANALYSIS. 

after  making  the  corrections,  to  be  5'337.  The  difference  between  the  results  of 
two  experiments  is,  however,  always  greater  than  this,  so  that  we  may  save  our- 
selves the  trouble  of  these  calculations. 

APPLICATION  OF  THE  KNOWLEDGE  OF  THE  SPECIFIC  GRAVITY  OF  A  BODY 
OF  UNKNOWN  ATOMIC  WEIGHT  AS  A  CONTROL  OVER  THE  ANALYSIS. 

The  composition  of  carbonic  ether  was  ascertained  in  the  usual  way.    The 
highest  numbers  gave  in  100  parts  51*3075  carbon,  8-5802  hydrogen,  and  40*112^^ 
oxygen.     These  numbers  correspond  to  the  formula  C^H^^Og.  "  ,  .\5 

The  specific  gravities  of  carbon  vapour,  hydrogen,  and  oxygen,  are  to  each 
other  as  their  atomic  weights.  It  is  obvious,  therefore,  that  in  one  volume  of 
carbonic  ether  vapour,  the  volumes  of  carbon,  hydrogen,  and  oxygen,  must  be 
found  in  the  ratio  of  5,  10,  and  3,  or  in  multiples  or  submultiples  of  these  num- 
bers, according  to  the  condensation  ;  the  proportions  cannot  vary. 

We  now  inquire  how  much  carbon,  hydrogen,  and  oxygen  are  contained  in 
4*243,  the  weight  of  one  volume  of  carbonic  ether  vapour. 

100  parts  contain 

51-3075  Carbon        therefore  4-243  contain  2-1769. 

8-5802  Hydrogen,  .        4-243        .       0-3645. 

401121  Oxygen,  .        4-243        .       1-7018. 

The  number  2*1769  expresses  the  sum  of  the  weights  of  the  yolumes  (the  spe- 
cific gravities)  of  carbon  vapour  in  one  volume  of  the  vapour  of  carbonic  ether. 
Dividing  this  number  by  the  weight  of  one  volume  of  carbon  vapour  (its  spe- 
cific gravity)  =  0-84297,  we  obtaki  the  number  of  volumes,  namely,  2^. 

The  specific  gravity  of  hydrogen  is  0-0683.  Hence  J /§|||  =  5  is  the  number 
of  volumes  of  hydrogen;  and  as  the  specific  gravity  of  oxygen  is  1*1026,  xy^jf 
=  1 J  is  the  number  of  volumes  of  oxygen  in  one  volume  of  carbonic  ether 
vapour.  It  is  easy  to  see  that  2^,  5,  and  1|,  are  to  each  other  as  5,  10,  and  3, 
whence  it  may  be  inferred  that  the  analysis  and  the  formula  deduced  from  it  are 
correct : 

5  volumes  Carbon       =  6x0-84279=4-2139. 

10  volumes  Hydrogen,  =  10x0-0688  =0-6880. 

3  volumes  Oxygen,     =  3x  M026  =3-3078. 

The  sum  of  all  is  .  .  8-2097. 

The  number  8*2097  is  to  the  specific  gravity  found  by  experiment,  very  nearly 
as  2  to  1.  Hence  in  one  volume  of  the  vapour  of  carbonic  ether,  there  must  be 
contained  |  volumes  carbon,  V*  volumes  hydrogen,  and  |  volumes  oxygen ;  this 
is  the  proportion  of  2|,  5,  Ij,  above  obtained.  The  weight  of  one  volume  of 
carbonic  acid  is  1*524:  that  of  one  volume  of  ether  is  2-58088.  The  sum  of 
both  is  4*10488.  Hence  one  volume  of  carbonic  ether  vapoiir  contains  one  vol- 
ume carbonic  acid,  and  one  volume  of  the  vapour  of  ether,  condensed  into  one 
volume. 


APPENDIX. 


TABLE   I. 

Table  of  Chemical  Equivalents  of  Elementary  Substances  with  their 

Symbols. 


Elements. 

a 

Equiv't. 

Elements. 

1 

a 

Equiv't. 

Elements. 

i 

Equiv't. 

Aluminium  . 

Al 

13-7 

Hydrogen    . 

H 

1 

Rhodium      . 

R 

52-2 

Antimony 

Iodine     .     . 

I 

126-3 

Selenium 

Se 

39-6 

(Stibium) 

Sb 

64-6 

Iridium   .     . 

Ir 

98-8 

Silicium .     . 

Si 

22-5 

Arsenic  .     . 

As 

37-7 

Iron,(Ferrum) 

Fe 

28 

Silver,  (Ar- 

Barium    .     . 

Ba 

68-7 

Lead,  (Plum- 

gentum,) 
Sodiumj  (Na- 

Ag 

108 

Bismuth .     . 

Bi 

71 

bum)   .     . 

Pb 

103-6 

Boron     .     . 

B 

109 

Lithium  .     . 

L 

6 

tronium)  . 

Na 

23-3 

Bromine 

Br 

78-4 

Magnesium . 

Mg 

12-7 

Strontium    . 

Sr 

43-8 

Cadmium     . 

Cd 

55-8 

Manganese  . 

Mn 

27-7 

Sulphur  .     . 
Tellurium    . 

s 

161 

Calcium .     . 

Ca 

20-5 

Mercury,  (Hy- 

Te 

64-2 

Carbon    .     . 

C 

6-12 

drargyrum) 

Hg 

202 

Thorium 

Th 

59-6 

Cerium   .     . 

Ce 

46 

Molybdenum 

Mo 

47-7 

Tin,  (Stan- 

1       '    1 

Chlorine 

CI 

35-42 

Nickel     .-  . 

Ni 

29-5 

num)  .     . 

Sn 

57-9 

Chromium   . 

Cr 

28 

Nitrogen      . 

N 

14-15 

Titanium 

Ti 

24-3 

Cobalt     .     . 

Co 

29-5 

Osmium .     . 

Os 

99-7 

Tungsten, 

Columbium, 

Oxygen  .     . 

0 

8 

(Wolfram) 

W 

99-7 

(Tantalum) 

Ta 

185 

Palladium    . 

Pd 

53-3 

Vanadium    . 

V       68-5    1 

Copper,  (Cu- 

Phosphorus 

P 

15-7 

Uranium 

U 

217 

prum)  .     . 

Cu 

31-6 

Platinum 

Pt 

98-8 

Yttrium  .     . 

Y 

32-2 

Fluorine,      . 

F 

18-68 

Potassium, 

Zinc  .     .     . 

Zn 

32-3 

Glucinium  . 

G 

26-5 

(Kalium) 

K 

39-15 

Zirconium    . 

Zr 

33-7 

Gold(Aurum) 

Au 

199-2 

'J:h 


826 


APPENDIX. 


TABLE    II.  ^ 

Table  of  the  elastic  Force  of  Aqueous  Vapour  at  (liferent  Temperatures^ 
expressed  in  Inches  of  Mercury. 


Temp. 

Force  ofVapour. 

Temp. 

Force  ofVapour. 

Force  of  Vapour. 

1 

Temp. 

Dalton.  1  Ure. 

1. 

Dalton. 

Ure. 

Dalton. 

Ure. 

32°F 

0-200 

0-200 

79°F 

0-971 

126°F 

389 

33 

0-207 

80 

1-00 

1-010 

127 

4-00 

34 

0-214 

81 

1-04 

128 

411 

35 

0-221 

82 

1-07 

129 

4-22 

36 

0-229 

83 

1-10 

130 

4-34 

4-366 

37 

0-237 

84 

1-14 

131 

4-47 

38 

0-245 

85 

1-17 

1-170 

132 

4-60 

39 

0-254 

86 

1-21 

133 

4-73 

40 

0-263 

0-250 

87 

1-24 

134 

4-86 

41 

0-273 

88 

1-28 

135 

5-00 

5070 

42 

0-283 

89 

1-32 

136 

514 

43 

0-294 

90 

1-36 

1-360 

137 

5-29 

44 

0-305 

91 

1-40 

138 

5-44 

45 

0-316 

92 

1-44 

139 

5-59 

46 

0-328 

93 

1-48 

140 

5-74 

5-770 

47 

0-339 

94 

1-53 

141 

5-90 

48 

0-351 

95 

1-58 

1-640 

142 

6-05 

49 

0-363 

9& 

1-63 

143 

6-21 

60 

0-375 

0-360 

97 

1-68 

144 

637 

51 

0-388 

98 

1-74 

145 

653 

6-600 

52 

0-401 

99 

1-80 

146 

6-70 

53 

0-415 

100 

1-86 

1-860 

147 

6-87 

54 

0.429 

101 

1-92 

148 

7-05 

55 

0-443 

0-416 

102 

1-98 

149 

7-23 

56 

0-458 

103 

2-04 

150 

7-42 

7-530 

57 

0-474 

104 

211 

151 

7-61 

58 

0-490 

105 

218 

2-100 

152 

7'81 

59 

0-507 

106 

2-25 

153 

8-01 

60 

0-524 

0-516 

107 

2-32 

154 

8-20 

61 

0-542 

108 

239 

155 

8-40 

8-500 

62 

0-560 

109 

2.46 

156 

8-60 

63 

0-578 

110 

2-53 

2-456 

157 

8-81 

64 

0-597 

111 

2-60 

158 

9  02 

65 

0-616 

0.630 

112 

2-68 

159 

9-24 

66 

0-635 

- 

113 

2-76 

160 

9-46 

9.600 

67 

0-655 

114 

2-84 

161 

9-68 

68 

0-676 

115 

2-92 

3.820 

162 

9-91 

69 

0-698 

116 

3-00 

163 

1015 

70 

0-721 

0-726 

117 

3-08 

164 

10-41 

71 

0-745 

118 

3  16 

165 

10-68 

10-800 

72 

0-770 

119 

3-25 

166 

10-96 

73 

0-796 

120 

3-33 

2-300 

167 

11-25 

74 

0-823 

121 

3-42 

168 

11  54 

75 

0-851 

0-860 

122 

3-50 

169 

11-83 

76 

0-880 

123 

3-59 

170 

1213 

12050 

77 

0-910 

124 

369 

171 

12-43 

78 

0-940 

125 

3-79 

3-830 

172 

12-73 

APPENDIX. 


827 


Force  of  Vapour. 

Temp. 

Force  of  Vapour. 

Force  of  Vapour. 

Temp. 

Temp. 

Dalton. 

Ure. 

Dalton. 

Ure. 

Dalton. 

Ure. 

173°F 

13-02 

224"F 

37-53 

275°F 

83-13 

93-480 

174 

13-32 

225 

38-20 

39-110 

276 

84-35 

175 

13-62 

13-550 

226 

38-89 

40-100 

277 

85-47 

97-800 

176 

13-92 

227 

30-59 

278 

86-50 

177 

14-22 

228 

40-30 

279 

87-63 

101-600 

178 

14-52 

229 

41-02 

280 

88-75 

101-900 

179 

14-83 

230 

41-75 

43-100 

281 

89-87 

104-400 

180 

15-15 

15-160 

231 

42-49 

282 

9099 

181 

1550 

232 

43-24 

283 

92-11 

107-700 

183 

15-86 

233 

44-00 

284 

93-23 

183 

1623 

234 

44-78 

46-800 

285 

94-35 

112-200 

184 

16-61 

235 

45-58 

47-220 

2g^ 

95-48 

185 

17-00 

16-900 

236 

46-39 

287 

96-64 

114-800 

186 

17-40 

237 

47-20 

288 

97-80 

187 

17-80 

238 

48-02 

50-300 

289 

98-96 

118-200 

188 

18-20 

239 

48-84 

290 

100-12 

120-150 

189 

18-60 

240 

49-67 

51-700 

291 

101-28 

190 

r9'00 

19-000 

241 

5050 

292 

102-45 

123-100 

191 

19-42 

242 

51-34 

53-600 

293 

103-63 

192 

19-86 

243 

52-18 

294 

104-80 

126-700 

193 

20-32 

244 

53-03 

295 

105-97 

129-000 

194 

20-77 

245 

53-88 

56-340 

296 

107-14 

195 

21-22 

21-100 

246 

54-68 

297 

108-31 

133-900 

196 

21-68 

247 

55-54 

298 

109-48 

137-400 

197 

22-13 

248 

56-42 

60-400 

299 

110-64 

198 

22-69 

'  249 

57-31 

300 

111-81 

139-700 

199 

23-16 

250 

58-21 

61-900 

301 

112-98 

200 

23-64 

23-600 

251 

59-12 

63-500 

302 

114-15 

144-300 

201 

24-12 

252 

60-05 

303 

115-32 

147-700 

202 

24-61 

253 

61-00 

304 

116-50 

203 

25-10 

254 

61-92 

66-700 

305 

117-68 

150-560 

204 

25-61 

255 

62-85 

67-250 

306 

118-86 

154-400 

205 

26-13 

25-900 

256 

63-76 

307 

120-03 

206 

26-66 

257 

64-82 

69-800 

308 

121-20 

157-700 

207 

27-20 

258 

65-78 

309 

122-37 

208 

27-74 

259 

66-75 

310 

123-53 

161-300 

209 

28-29 

260 

67-73 

72-300 

311 

124-69 

164-800 

210 

28-84 

•28-880 

261 

68-72 

312 

125-85 

167-000 

211 

29-41 

262 

69-72 

75-900 

313 

127-00 

212 

3000 

30-000 

263 

70-73 

314 

128-15 

213 

30-60 

264 

71-74 

77-900 

315 

129-29 

214 

31-21 

265 

72-76 

78-040 

316 

130-43 

215 

31-83 

266 

73-77 

317 

131-57 

216 

32-46 

33-400 

267 

74-79 

81-900 

318 

132-72 

217 

3309 

268 

75-80 

319 

133-86 

218 

33-72 

269 

76-82 

84-900 

320 

135-00 

219 

34-35 

270 

77-85 

86-300 

321 

136-14 

220 

34-99 

35-540 

271 

78-89 

88-000 

322 

137-28 

221 

35-63 

36-700 

272 

79-94 

323 

138-42 

222 

36-25 

273 

80-98 

91-200 

324 

139-56 

223 

36-88 

274 

82-01 

325 

140-70 

828 


APPENDIX. 


TABLE    III. 

Dr.  Ure's  Table,  showing  the  elastic  Force  of  the  Vapours  of  Alcohol. 
Ether,  Oil  of  Turpentine,  and  Petroleum  or  Naphtha,  at  different 
Temperatures,  expressed  in  Inches  of  Mercury. 


Ether. 

Alcohol  sp.gr.  0-813. 

Alcohol  sp.  gr.  0  813. 

Petroleum. 

Temp. 

Force  of 
Vapour. 

Temp. 

Force  of 
Vapour. 

Temp. 

Force  of 
Vapour. 

Temp. 

Force  of 
Vapour. 

34° 

6-20 

32° 

0-40 

193-3° 

46-60 

316° 

30-00 

44 

8-10 

40 

0-56 

196-3 

5010 

320 

31-70 

54 

10-30 

45 

0-70 

200 

53-00 

325 

34-00 

64 

1000 

50 

0-86 

206 

60-10 

330 

36-40 

74 

16-10 

55 

1-00 

210 

65-00 

335 

38-90 

84 

20-00 

60 

1-23 

214 

69-30 

340 

41-60 

94 

24-70 

65 

1-49 

216 

72-20 

345 

44-10 

104 

30-00 

70 

1-76 

220 

78-50 

350 

46-86 

105 

30-00 

75 

2-10 

225 

87-50 

355 

50-20 

110 

32-54 

80 

2-45 

230 

94-10 

360 

53-30 

115. 

35-90 

85 

2-93 

232 

97-10 

365 

56-90 

120 

39-47 

90 

3-40 

236 

103-60 

370 

60-70 

125 

43-24 

95 

3-90 

238 

106-90 

372 

61-90 

130 
135 

47-14 

100 

4-50 

240 

111-24 

375 

64-00 

51-90 

105 

5-20 

244 

118-20 

140 

66-90 

110 

6-00 

247 

122-10 

Oil  of  Tu 

rpentine. 

145 

62-10 

115 

7-10 

248 
249-7 

126-10 
131.40 

150 

67-60 

120 

8  10 

Temp. 

Force  of 

155 
160 

73-60 
80  30 

125 
130 

9-25 
10-60 

250 
252 

132-30 
138-60 

Vapour. 

165 

86-40 

135 

12-15 

254-3 

143-70 

304 

30-00 

170 

92-80 

140 

13-90 

258-6 

151-60 

307-6 

32-60 

175 

99.10 

145 

15-95 

260 

155-20 

310 

33  50 

180 

108-30 

150 

18-00 

262 

161-40 

315 

35-20 

185 

11610 

155 

20-30 

264 

166-10 

3-20 

3706 

190 

124-80 

160 

22-60 

322 

37-80 

195 

133-70 

165 

25-40 

3-26 

40-20 

200 

142-80 

170 

28-30 

330 

4210 

205 

151-30 

173 

30-00 

336 

45-00 

210 

166-00 

178-3 

33-50 

340 

4730 

180 

34-73 

343 

49-40 

182-3 

36-40 

347 

51-70 

185-3 

39-90 

350 

53-80 

190 

43-20 

354 
357 

360 

5660 
58-70 
60-80 

362 

62-40 

APPENDIX. 


829 


TABLE    IV. 

For  the  conversion  of  Degrees  on  the  Centigrade  Thermometer  into 
Degrees  of  Fahrenheit s  Scale. 


Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

Cent. 

Fahr. 

—50° 

— 58°0 

—6° 

21°2 

38° 

100°4 

82° 

179°6 

—49 

—56.2 

—5 

23.0 

39 

102-2 

83 

181-4 

—48 

—54.4 

—4 

24.8 

40 

1040 

84 

183-2 

—47 

—52.6 

—3 

26.6 

41 

105.8 

85 

1850 

—46 

—50.8 

—2 

28.4 

42 

107-6 

86 

186-8 

—45 

—49.0 

—1 

30.2 

43 

109-4 

87 

188-6 

—44 

—47.2 

0 

32.0 

44 

111.2 

88 

190-4 

—43 

45.4 

+1 

33.8 

45 

113.0 

89 

192-2 

—42 

—43.6 

2 

35.6 

46 

1148 

90 

1940 

—41 

—41.8 

3 

37.4 

47 

116-6 

91 

195-8 

—40 

—40.0 

4 

39.2 

48 

118-4 

92 

197-6 

—39 

—38.2 

5 

41.0 

49 

120-2 

93 

199-4 

—38 

—36.4 

6 

42.8 

50 

122.0 

94 

201-2 

—37 

—34.6 

7 

44.6 

51 

1238 

95 

203-0 

—36 

—32.8 

8 

46.4 

52 

125-6 

96 

204-8 

—35 

—30.0 

9 

48.2 

53 

127-4 

97 

206-6 

—34 

—29.2 

10 

50.0 

54 

129.2 

98 

208-4 

—33 

—27.4 

11 

51.8 

55 

131.0 

99 

210-2 

—32 

—25.6 

12 

53.6 

56 

132.8 

100 

212-0 

—31 

—23.8 

13 

55.4 

57 

134.6 

101 

213-8 

—30 

—22.0 

14 

57.2 

58 

136.4 

102 

215-6 

—29 

—20.2 

15 

59.0  . 

59 

138.2 

103 

217-4 

—28 

—18.4 

16 

60.8 

60 

140.0 

104 

219-2 

—27 

—16.6 

17 

62.6 

61 

141.8 

105 

221-0 

—26 

—14.8 

18 

64.4 

62 

143.6 

106 

222-8 

—25 

—13.0 

19 

66.2 

63 

145.4 

107 

224-6 

—24 

—11.2 

20 

68.0 

64 

147.2 

108 

226-4 

—23 

—  9.4 

21 

69.8 

65 

149.0 

109 

228-2 

—22 

—  7.6 

22 

71.6 

66 

150.8 

110 

230-0 

—21 

—  5.8 

23 

73.4 

67 

152.6 

111 

231-8 

—20 

—  4.0 

24 

75.2 

68  - 

154.4 

112 

233-6 

—19 

—  2.2 

25 

77.0 

69 

156.2 

113 

235.4 

—18 

—  0.4 

26 

78.8 

70 

158.0 

114 

237-2 

—17 

+  i.4 

27 

80.6 

71 

159.8 

115 

239-0 

—16 

3.2 

28 

82.4 

72 

161.6 

116 

240-8 

—15 

5.0 

29 

84.2 

73 

163.4 

117 

242-6 

—  14 

6.8 

30 

86.0 

74 

165.2 

118. 

244-4 

—13 

8.6 

31 

87.8 

75 

167.0 

119 

246-2 

—12 

10.4 

32 

89.6 

76 

168.8 

120 

248-0 

—11 

.      12.2 

33 

91.4 

77 

170.6 

121 

249.8 

—10 

14.0 

34 

93.2 

78 

172.4 

122 

251.6 

—  9 

15.8 

35 

95.0 

79 

174.2 

123 

253.4 

—  8 

17.6 

36 

96.8 

80 

176.0 

124 

255.2 

—  7 

19.4 

37 

98.6 

81 

177.8 

125 

257.0 

830 


APPENDIX. 


Cent. 

Fahr. 

Cent. 

Fahr 

Cent. 

Fahr. 

Cent. 

Fahr. 

126° 

258°8 

175° 

347°0 

224° 

435°2 

273° 

623°4 

127 

260.6 

176 

348.8 

225 

437-0 

274 

525.2 

128 

262-4 

177 

350.6 

226 

438  8 

275 

527.0 

129 

264.2 

178 

352.4 

227 

440.6 

276 

528-8 

130 

266.0 

179 

354.2 

228 

442.4 

277 

530.6 

131 

267-8 

180 

355-0 

229 

444.2 

278 

532-4 

132 

269.6 

181 

357.8 

230 

446.0 

279 

534.2 

133 

271.4 

182 

359  6 

231 

447.8 

280 

536-0 

134 

273.2 

183 

361.4 

232 

449.6 

281 

537.8 

135 

275.0 

184 

363-2 

233 

451.4 

282 

639.6 

136 

276-8 

185 

365-0 

234 

453.2 

283 

541.4 

137 

278-6 

186 

366.8 

235 

455.0 

284 

543.2 

138 

280-4 

187 

368.6 

236 

456.8 

285 

545.0 

139 

282.2 

188 

370.4 

237 

458.6 

286 

546-8 

140 

284.0 

189 

372.2 

238 

460.4 

287 

548.6 

141 

285.8 

190 

374.0 

239 

462.2 

288 

550.4 

142 

287-6 

191 

375.8 

240 

464.0 

289 

552.2 

143 

289.4 

192 

377-6 

241 

465.8 

290 

5540 

144 

291.2 

193 

379.4 

242 

467.6 

291 

555.8 

145 

293.0 

194 

381.2 

243 

469.4 

292 

557.6 

146 

294.8 

195 

383.0 

244 

471.2 

293 

559.4 

147 

296-6 

196 

384.8 

245 

473.0 

294 

561.2 

148 

298.4 

197 

386.6 

246 

474.8 

295 

563.0 

149 

300.2 

198 

388.4 

247 

'  476,6 

296 

564.8 

150 

302-0 

199 

390.2 

248 

478.4 

297 

566.6 

151 

303.8 

200 

392.0 

249 

480.2 

298 

568.4 

152 

305.6 

201 

393.8 

250 

482.0 

299 

570-3 

153 

307.4 

202 

395.6 

251 

483.8 

300 

572.0 

154 

.309.2 

203 

397.4 

252 

485.6 

301 

573.8 

155 

311.0 

204 

399.2 

253 

487.4 

302 

575.6 

156 

312.8 

205 

401.0 

254 

489.2 

303 

577.4 

157 

314.6 

206 

402.8 

255 

491.0 

304 

579.2 

158 

316.4 

207 

404.6 

256 

492.8 

305 

581.0 

159 

318.2 

208 

406.4 

257 

494.6 

306 

582.8 

160 

320.0 

209 

408.2 

258 

496.4 

307 

584.5 

161 

321.8 

210 

410.0 

259 

498.2 

308 

586.4 

162 

323.6 

211 

411.8 

260 

500.0 

309 

588.2 

163 

325.4 

212 

413.6 

261 

501.8 

310 

590.0 

164 

327.2 

213 

415.4 

262 

503.6 

311 

591.8 

165 

3290 

214 

417.2 

263 

505.4 

312 

593.6 

166 

330.8 

215 

419.0 

264 

507.2 

313 

595.4 

167 

332.6 

216 

420.8 

265 

509.0 

314 

597.2 

16S 

334.4 

217 

422.6 

266 

510.8 

315 

599.0 

169 

336.2 

218 

424.4 

267 

512.6 

316 

600.8 

170 

338.0 

219 

426.2 

268 

514.4 

317 

602.6 

171 

339.8 

220 

428.0 

269 

516.2 

318 

604.4 

172 

341.6 

221 

429.8 

270 

518.0 

319 

606  2 

173 

343.4 

222 

431.6 

271 

519.8 

320 

608.0 

174 

345.2 

223 

433.4 

273 

521.6 

APPENDIX. 


831 


TABLE    V. 

Dr.  Ure's  Table  of  the  Quantity  of  Oil  of  Vitriol,  of  sp.  gr.  1.8485, 
and  of  Anhydrous  Acid,  in  100  Parts  of  dilute  Sulphuric  Acid,  at 
different  Densities. 


Liquid. 

Sp.  Gr. 

Dry. 

Liquid. 

Sp.  Gr 

Dry. 

Liquid. 

Sp.  Gr. 

Dry. 

100 

1-8485 

81-54 

QQ 

1-5503 

53-82 

32 

1-2334 

26-09 

99 

1-8475 

80-72 

65 

1-5390 

53-00 

31 

1-2260 

25-28 

98 

1-8460 

79-90 

64 

1-5280 

52-18 

30 

1-2184 

24-46 

97 

1-8439 

79-09 

63 

1-5170 

51-37 

29 

1-2108 

23-65 

9Q 

1  8410 

78-28 

62 

1-5066 

50-55 

28 

1-2032 

22-83 

95 

1-8376 

77-46 

61 

1-4960 

49-74 

27 

1-1956 

22-01 

94 

1-8336 

76-65 

60 

1-4860 

48-92 

26 

1-1876 

21  20 

93 

1-8290 

75-83 

59 

1-4760 

48-11 

25 

1-1792 

20-38 

92 

1-8233 

75-02 

58. 

1-4660 

47-29 

24 

M706 

19-57 

91 

1-8179 

74-20 

57 

1-4560 

46-48 

23 

1-1626 

18-75 

90 

1-8115 

73-39 

56 

1-4460 

45-66 

22 

1-1549 

17-94 

89 

1-8043 

72-57 

55 

1-4360 

44-85 

21 

1-1480 

17-12 

88 

1-7962 

71-75 

54 

1-4265 

44-03 

20 

1-1410 

16-31 

87 

1-7870 

70-94 

53 

1-4170 

43-22 

19 

1-1330 

15-49 

86 

1-7774 

70-12 

52 

1  -4073 

42-40 

18 

1-1246 

14-68 

85 

1-7673 

69-31 

51 

1-3977 

41-58 

17 

1  1165 

13-86 

84 

1-7370 

68-49 

50 

1-3884 

40-77 

16 

1-1090 

13-05 

83 

1-7465 

67-68 

49 

1-3788 

3995 

15 

1-1019 

12-23 

82 

1-7360 

66-86 

48 

1-3697 

39-14 

14 

1-0953 

11-41 

81 

1-7245 

66-05 

47 

1-3612 

38-32 

13 

1-0887 

10-60 

80 

1-7120 

65-23 

46 

1-3530 

37-51 

12 

1-0809 

9-78 

79 

1-6993 

64-42 

45 

1-3440 

36-69 

11 

1-0743 

8-97 

78 

1-6870 

63-60 

44 

1-3345 

35-88 

10 

1-0682 

8-15 

77 

1-6750 

62-78 

43 

1-3255 

35-06 

9 

1-0614 

7-34 

76 

1-6630 

61-97 

42 

1-3165 

34-25 

8 

1-0544 

6-52 

75 

1-6520 

61-15 

41 

1-3080 

33-43 

7 

1-0477 

5-71 

74 

1-6415 

60-34 

40 

1-2999 

32-61 

6 

1-0405 

4-89 

73 

1-6321 

59-52 

39 

1-2913 

31-80 

5 

1-0336 

4-08 

72 

1-6204 

58-71 

38 

1-2826 

30-98 

4 

1-0268 

3-26 

71 

1-6090 

57-89 

37 

1-2740 

30-17 

3 

1-0206 

2-446 

70 

1-5975 

57-08 

36 

1-2654 

29-35 

2 

10140 

1.63 

69 

1-5868 

56-26 

35 

1-2572 

28-54 

1 

1-0074 

0.8154 

68 

1-5760 

55-45 

34 

1-2490 

27-72 

67 

1-5648 

54-63 

33 

1-2409 

26-91 

832 


APPENDIX. 


TABLE    VI. 

Dr.  Ure!s  Table  of  the  Quantity  of  Real  or  Anhydrous  Nitric  Acid  in 
100  Parts  of  Liquid  Acid,  at^ifferent  Densities. 


Real  acid 

Real  acid 

Real  acid 

Specific 

in  100  parts 

Specific 

in  100  parts 

Specific 

in  100  parts 

Gravity. 

of  the  Liquid. 

Gravity. 

of  the  Liquid 

Gravity. 

of  the  Liquid. 

1-5000 

79-700 

1-3783 

52-692 

1-1895 

26-301 

1-4980 

78-903 

1-3732 

51-805 

1-1833 

25-504 

1-4960 

78-106 

1-3681 

51-068 

1-1770 

24-707 

1-4940 

77-309 

1-3630 

50-211 

1-1709 

23-910 

1-4910 

76-512 

1-3579 

49-41-4 

1-1648 

23113 

1-4880 

75-715 

1-3529 

48-617 

1-1587 

22-316 

1-4850 

74-918 

1-3477 

47.820 

1-1526 

21.519 

1-4820 

74-121 

1-3427 

47-023 

1-1465 

20-722 

1-4790 

73-324 

1-3376 

46-226 

1-1403 

19-925 

1-4760 

72-527 

1-3323 

45-429 

1-1345 

19-128 

1-4730 

71-730 

1-3270 

44-632 

1-1286 

18-331 

1-4700 

70-933 

1-3216 

43-835 

1-1227 

17-534 

1-4670 

70136 

1-3163 

43  038 

1-1168 

16-737 

1-4640 

69-339 

1-3110 

42-241 

1-1109 

15-940 

1-4600 

68-542 

1-3056 

41-444 

1-1051 

15-143 

1-4570 

67-745 

1-3001 

40-647 

1-0993 

14-346 

1-4530 

66-948 

1-2947 

39-850 

1-0935 

13-549 

1-4500 

66-155 

1-2887 

39053 

1-0878 

12-752 

1-4460 

65-354 

1-2826 

38-256 

1-0821 

11-955 

1-4424 

64-557 

1-2765 

37-459 

1-0764 

11-158 

1-4385 

63-760 

1-2705 

36-662 

1-0708 

10-361 

1-4346 

62-963 

1-2644 

35-865 

1-0651 

9-564 

1-4306 

62-166 

1-2583 

35068 

1-0595 

8-767 

1-4269 

61-369 

1-2523 

34-271 

1-0540 

7-970 

1-4228 

60-572 

1-2462 

33-474 

1-0485 

7-173 

1-4189 

59-775 

1-2402 

32-677 

1-0430 

6-376 

1-4147 

58-978 

1-2341 

31-880 

1-0375 

5-579 

1-4107 

68181 

1-2277 

31-083 

10320 

4-782 

1-4065 

57-384 

1-2212 

30-286 

1-0267 

3-985 

1-4023 

56-587 

1-2148 

29-489 

1  0212 

3-188 

1-3978 

55-790 

1-2084 

28-692 

1-0159 

2-391 

1-3945 

54-993 

1-2019 

27-895 

10106 

1-594 

1-3882 

54-196 

M958 

27-098 

1-0053 

0-797 

1-3833 

53-399 

APPENDIX. 


833 


TABLE    VII. 

Table  of  Lowitz  showing  the  Quantity  of  absolute  Alcohol  in  Spirits  of 
different  Specific  Gravities. 


100  Parts. 

Sp.  Gravity. 

100  Parts. 

Sp.  Gravity. 

100  Parts. 

Sp.  Gravity. 

Ale. 

Wat. 

At  68°. 

At  60°. 

Ale. 

Wat. 

At  68°. 

At  60°. 

Ale. 
32 

Wat. 

At  68°. 

At  60°. 

100 

0 

0-791 

0-796 

66 

34 

0-877 

0-881 

68 

0-952 

0-956 

99 

1 

0-794 

0-798 

65 

35 

0-880 

0-883 

31 

69 

0-954 

0-957 

98 

2 

0-797 

0-801 

64 

36 

0-882 

0-886 

30 

70 

0-956 

0-958 

97 

3 

0-800 

0-804 

63 

37 

0-885 

0-888 

29 

71 

0-957 

0-960 

96 

4 

0-803 

0-807 

62 

38 

0-887 

0-891 

28 

72 

0-959 

0-962 

95 

5 

0-805 

0-709 

61 

39 

0-889 

0-893 

27 

73 

0-961 

0-963 

94 

6 

0-808 

0-812 

60 

40 

0-892 

0-896 

26 

74 

0-963 

0-965 

93 

7 

0-811 

0-815 

59 

41 

0-894 

0-898 

25 

75 

0-965 

0-967 

92 

8 

0-813 

0-817 

58 

42 

0-896 

0-900 

24 

76 

0-966 

0-968 

91 

9 

0-816 

0-8-30 

57 

43 

0-899 

0-902 

23 

77 

0-968 

0-970 

90 

10 

0-818 

0-823 

56 

44 

0-901 

0-904 

22 

78 

0-970 

0-972 

89 

11 

0-821 

0-825 

55 

45 

0-903 

0-906 

21 

79 

0-971 

0-973 

88 

12 

0-823 

0-827 

54 

46 

0-905 

0-908 

20 

80 

0-973 

0-974 

87 

13 

0-826 

0.830 

53 

47 

0-907 

0-910 

19 

81 

0-974 

0-975 

86 

14 

0-828 

0-832 

52 

48 

0-909 

0-912 

18 

82 

0-976 

0-977 

85 

15 

0-831 

0-835 

51 

49 

0-912 

0-915 

17 

83 

0-977 

0-978 

84 

16 

0-834 

0-838 

50 

50 

0-914 

0-917 

16 

84 

0-978 

0-979 

83 

17 

0-836 

0-840 

49 

51 

0-917 

0-920 

15 

85 

0-980 

0-981 

82 

18 

0-839 

0-843 

48 

52 

0919 

0-922 

14 

86 

0-981 

0-982 

81 

19 

0-842 

0-846 

47 

53 

0-921 

0-924 

13 

87 

0-983 

0-984 

80 

20 

0-844 

0-848 

46 

54 

0-923 

0-926 

12 

88 

0-985 

0-986 

79 

21 

0-847 

0-851 

45 

55 

0-925 

0-928 

11 

89 

0-986 

0987 

78 

22 

0-849 

0-853 

44 

56 

0-927 

0-930 

10 

90 

0-987 

0-988 

77 

23 

0-851 

0-855 

43 

57 

0-930 

0-933 

9 

91 

0-988 

0-989 

76 

24 

0-853 

0-857 

42 

58 

0-932 

0-935 

8 

92 

0-989 

0-990 

75 

25 

0-856 

0-860 

41 

59 

0-934 

0-937 

1^ 

93 

0-991 

0-991 

74 

26 

0-859 

0-863 

40 

60 

0-936 

0-939 

6 

94 

0-992 

0-992 

73 

27 

0-861 

0-865 

39 

61 

0-938 

0-941 

5 

95 

0-994 

72 

28 

0-863 

0-867 

38 

62 

0-940 

0-943 

4 

96 

0-995 

71 

29 

0-866 

0-870 

37 

63 

0-942 

0-945 

3 

97 

0-997 

70 

30 

0-868 

0-872 

36 

64 

0-944 

0-947 

2 

98 

0-998 

69 

31 

0-870 

0-874 

35 

65 

0-946 

0-949 

1 

99 

0-999 

68 

32 

0-872 

0-875 

34 

66 

0-948 

0-951 

0 

100 

1-000 

67 

33 

0-875 

0-879 

33 

67 

0-950 

0-953 

55 


334 


APPENDIX. 


TABLE    VIII. 

Tables  showing  the  Specific  Gravity  of  Liquids^  at  the  Temperature  of  35° 
Fahr.  corresponding  to  the  Degrees  of  Beaume^  s  Hydrometer. 


FOR   LIQUIDS   LIGHTER   THAN   WATER. 


Deg.  Sp.  Gr. 
10=1-000 
11   -990 


12 
13 
14 
15 
16 


•985 
•977 
•970 
•963 
•955 


Deg.  Sp.  Gr. 

17  =  .949 

18  •942 


19 

20 
21 
22 


•935 
•928 
•922 
•915 


Deg.    Sp.  Gr. 

23  =  -909 

24  ^903 


25 
26 
27 

28 


•897 
•892 
•886 
•880 


Deg.    Sp.  Gr. 

29  =  -874 

30  -867 


31 
32 
33 
34 


•861 
•856 
•852 
•847 


Deg.    Sp.  Gr. 

35  =  ^842 

36  ^837 


37 
38 
39 
40 


•832 

•827 
•822 
•817 


FOR   LIQUIDS    HEAVIER   THAN   WATER. 


Deg.  Sp.  Gr. 
0=1-000 
3  1020 
6  1-040 
9  1^064 
12  1-089 


Deg.  Sp.  Gr. 
15=1-114 
18  1-140 
21  1^170 
24  r200 
27  1-230 


Deg.  Sp.  Gr. 
30=1-261 
33  1-295 
36  1-333 
39  1-373 
42  1-414 


Deg. 

Sp.  Gr. 

45= 

=1-455 

48 

1-500 

51 

1-547 

64 

1-594 

57 

1-659 

Deg.  Sp.  Gr. 
60=1-717 
63  1-779 
QQ  1-848 
69  1-920 
72  2-000 


INDEX. 


A. 

Absinthine,  687 
Absolute  alcohol,  610 
Acetal,  619 
Acetates,  629     . 

products  of  decompo- 
sition of,  629 
Acetone,  629 

its  compounds  and  pro- 
ducts, 629 
Acetic  acid,  722,  620 

products  of  decompo- 
sition of,  629 
Acetyle,  618 

oxychloride  of,  624 

combinations  of,  618 
Acids,  definition  of,  439 

nomenclature  of,  113 

organic,  641 

coupled,  542 
Acid,  acetic  and  acetylous, 
620 

acetylous,  620 

acetylic,  620 

aconitic,  650 

adipic,  673 

aldehydic,  620 

aloeretinic,  702 

aloetic,  702 

althionic,  618 

alloxanic,  584 

ambreic,  677 

amygdalinic,  598 

anilic,  699 

anisic,  666 

anthranilic,  700 

antimonic  and  antimo- 
nious,  375 

arsenic,  369 

arsenious,  364 

aspartic,  688 

atropic,  678 

azelaic,  673 

azoleic,  673 

auric,  418 

benzilic,  596 

benzoic,  690 

bibromisatic,  695 

bichlorisatic,  695 

bilifellic,  753 

boletic,  678 

boracic,  209 

boro-hydrofluoric,  253 


Acid,  brombenzoic,  593 
bromic,  247 
bromosalicylic,  603 
butyric,   capric,   and 

caproic,  663,  664 
cafTeic,  678 
caincic,  678 
camphoric,  664 
capric,  664 
carbazotic,  699 
carbolic,  727 
carbonic,  188 
mode  of  obtaining  in  a 

solid  state,  52 
low  temperature  of,  in 

the  solid  state,  53 
cerebric,  755 
cetylic,  669 
chelidonic,  678 
chloranilic,  698 
chloric,  226 
chlorinized  chlorind- 

optenic,  698 
chlorindoptenic,  697 
chlorisatic,  695 
chloroacetic,  626 
chlorocarbonic,  230 
chlorosalicylic,  603 
chlorophenesic,  700 
chlorophenusic,  700 
chlorous,  225 
chlorovalerosic,  666 
chlorovalerisic,  666 
choleic,  754 
choloidic,  753 
cholesteric,  677 
cholic,  753 
chromic,  378 
chrysanilic,  700 
chrysammic,  702 
chrysolepic,  703 
cinnamic,  605 
citraconic,  651 
citric,  648 
columbic,  396 
crameric,  678 
crenic  and  apocrenic, 

721 
croconic,  552 
crotonic,  664 
cuminic,  667 
cyanic,  558 
cyanilic,  579 
cyanuric,  579 


Acid,  cynoxalic,  589 

draconic,  681  * 

elaidic,  678 
ellagic,  659 
equisetic,  650 
erytholeic,  690 
ethionic,  617 
ferrocyanic,  567 
fluoboric,  252 
fluochromic,  383 
fluoric,  251 
fluosilicic,  253,  250 
formic,  644 
fulminic,  561 
fumaric,  656 
fungic,  678 
gallic,  658 

glacial  phosphoric,  207 
glucic,  635 
hippuric,  593 
hircic,  664 

hydrated  salicylous,  601 
hydriodic,  237 
hydrobromic,  245 
hydrochloric,  219 
hydro-cobalto-cyanic, 

570 
hydrocyanic,  555 
hydro-ferrid-cyanic, 

570 
hydroferrocyanic,  567 
hydrofluoric,  250 
hydroleic,  675 
hydromargaric,  675 
hydromargaritic,  675 
hydromellonic,  575 
hydropersulphuric,  265 
hydroselenic,  267 
hydrosulphocyanic, 

574 
hydrosulphuric,  263 
hydrotelluric,  405 
hypochlorous,  223 
hyponitrous,  178 
hypophosphorous,  204 
hyposulphobenzidic, 

594 
hyposulphobenzoic, 

593 
hyposulphoindigotic, 

693 
hyposulphuric,  200 
hyposulphurous,  199 
indigotic,  699 


836 


INDEX. 


Acid,  iodic,  239 

iodosalicylic,  603 
iodous,  239 
isatinic,  694 
isethionic,  617 
itaconic,  651 

Iaponic,  659 
:akodylic,  631 
kinic,  661  » 

komenic,  661 
lactic,  639 
lampic,  620 
lipic,  673 
lithic,  see  Uric 
lithofellic,  754 
maleic,  656 
malic,  655 
manganic,  328 
margaric,  669 
margaritic,  674 
meconic,  660 
mechloic,  689 
melanic,  602 
melassic,  635 
mellitic,  553 
mesoxalic,  584 
metagallic,  658 
metamargaric,  675 
metaphosphoric  205,207 
methionateofbaryta,617 
methionic,  617 
metoleic,  676 
molybdic,  molybdous, 

mucic,  636 

muriatic,  219 
/       mykomelinic,  584 

naphalic,  736 

nitric,  181 

nitro-murJatic,  222 

nitronaphalesic,  736 

nitronaphthalic,  736 

nitro-picric,  699 

nitro-salicylic,  699 

nitrous,  179 

oenanthic,  666 

oleic,  672 

oleophosphoric,  755 

osmic,  428 

oxalic,  549 

oxalovinic,  615 

oxaluric,  585 

oxymuriatic,  216 

palmic,  674 

palmitic,  662 

parabanic,  585 

paraphosphoric,  205 

paralartaric,  624 
perchloric,  227 
periodic,  241 
permanganic,  328 
phocenic,  664 
phosphatic,  264 
phosphoric,  205 
phosphorous,  204 
phosphovinic,  613 
picric,  699 
pimelic,  673 
pinic,  685 
prussic,  555 
pyrocitric,  648 
pyrogallic,  658 


Acid,  pyroligneous,  620  Agriculture,  chemistry  of, 

pyromalic,  655  761 

pyromucic,  637  Air,  atmospheric,  166 

pyrophosphoric,207,205  alkaline,  255 


racemic,  654 
ricinic,  674 
rhodizonic,  552 
rocellic,  667 
rubinic,  659 
saccharic,  635 
saccharosulphuric,  634 
sacchulmic,  634 
salicylous  and  salicy- 
lic, 601,  602 
sebacic,  673 
selenic,  214 
selenious,  213 
silicic,  211 
silico-fluoric,  254 
stearic,  669 
suberic,  671 
succinic,  671 
sulphocyanic,  674 
sulphoindigotic,  693 
sulphomesitylic,  629 
sulphonaphthalic,  735 
sulphopurpuric,  694 
sulphosaccaric,  634 
sulphovinic,  613 
sulphur,  192 
sulphuric,  195 
fuming,  196 
sulphurous,  194 
sylvic,  684 
tannic,  657 
tartaric,  651 
tartralic,  653 
telluric,  404 
tellurous,  404 
thionuric,  585 
titanic,  402 
tungstic,  394 
uramilic,  686 
uric,  580 
valerianic,  666 
vanadic,  388 
veratric,  664 
xanthic,  615 
xanthoproteic,  750 
Acids,  organic,  541 


fixed,  188 
Alabaster,  464 
Albumen,  animal,  744 
vegetable,  740 
composition  of,  747 
Alcohol,  609 

absolute,  610 

action  of  chlorine,  &c. 

on,  626 
action  of  bichloride  of 

platinum  on,  628 
comp'ds   derived    from 
oxidation  of,  618 
Aldehydic  acid,  620 
Aldehyde,  618 

resin  of,  619 
Alembroth,  salt  of,  509 
Algaroth,  powder  of,  373 
Alizarine,  686 
Alkalies,  289 

metallic  bases  of,  289 
volatile,  255 
silicated,  211 
vegetable,  703 
Alkalimeter,  493 
Alkaline  air,  255 
bases,  289 
Alkaline  earths,  289 

metallic  bases  of,  289 
Alkaline  waters,  780 
Alkaloids,  703 
Alkarsine,  630 
Allanite,  399 
Allantoine,  581 
Alloxan,  582 
Alloxanates,  684 
Alloxantine,  586 
Alloys,  431 

of  arsenic,  433 

of  tin,  lead,  antimony, 

and  bismuth,  434 
of  copper,  434 
of  steel  and  silver,  436 
of  gold,  435 
Almond  oil,  672 
Aloes,  bitter  of,  702 


a  table  of  those  for  the  Althionic  acid,  617 
detection  of  which  di-  Alum,  468 
rections  are  given  in  stone,  468 

section   on   chemical  Alumen  ustum,  468 


Alumina,  or  aluminous  earth, 
316 
tests  of,  317 
mellitate  of,  553 
sulphates  of,  466 
sulphates,    double,    of, 

468 
acetate,  of,  622 
Aluminite,  466 
Aluminium    and    its    com- 
pounds, 315 
by  what  circumstances  Amalgam,  431,  433 

modified,  120  for  looking-glasses,  433 

quiescent  and  divellent,  for  electrical   machine, 

118  433 

measure  of,  125  Amalgamation  of  silver  ores, 

changes  that  accompa-  412 

ny,  118  Amule,  or  amyle,  646 


analysis,  774 
theory  of,  541 

Acidulous  waters,  780 

Aconitine,  712 

Acroleine,  674 

Aeriform  bodies,  23,  41 

Affinity,  chemical,  115 
table  of,  116 
single  elective,  116 
double  elective,  117 
disposing,  161 


INDEX. 


83T 


Amule,  compounds  of,  647 

Amarythrine,  690 

Amber,  671 

Ambergris  and  ambreine, 
677 

Amide,  258 

combinations  of,  543 

Amilene,  648 

Ammelide,  577 

Ammeline,  577 

and  acids,  577 

Ammonia,  255 

Ammonia,  liquid,   table   of 
the  strength  of  solu- 
tions of,  257 
character  of  the  salts 

of,  256 
sulphate  of,  463 
sulphates,   double   of, 

470 
sulphite  of,  470 
nitrate  of,  473 
phosphates  of,  483 
arseniates  of,  487 
carbonates  of,  495 
hydrosalts  of,  499 
sulphur  salts  of,  502 
haloid  salts  of,  509 
chlorides  with,  514 
oxalate  of,  550 
acetate  of,  622 
subcarbonate  of,  495 
bimalate  of,  656 
citrate  of,  649 
succinate  of,  672 
urate  of,  581,  759 
mellitate  of,  553 
cyanates  of,  560 
oxalurate  of,  585 
thionurate  of,  586 
benzoate  of,  599 
salicylite  of,  602 
table  of  salts  of,  499 

Ammoniacal  gas,  255 

Ammoniacal  salts,  499 

Ammoniaco-magnesian 
phosphate,  484 

Ammonium,  256 

sulpho-cyanide  of,  576 
oxide  of,  256 

Ammoniuret  of  copper,  467 

Amygdaline,  598 

Analysis  qualitative,  772 
quantitative,  775 

Analytical  chemistry,  769 
division  of  the  subject, 
770 

Anhydrite,  464 

Aniline,  692,  700,  704 

Animals,  changes  which  oc- 
cur during  the  life, 
growth,  and  nutri- 
tion  of,  761 

Anthracene,  737 

Antiarine,  688 

Antimonialis,  pulvis,  375 

Antimoniates,  375 

Antimonio-sulphurets, 
608 

Antimonites,  375 

Antimony  and  its  comp'ds, 
372 


Antimony,  butter  of,  375 
regulus  of,  372 
argentine    flowers   of, 

373 
glass,  crocus,  and  liver 

of,  376 
alloys  of,  vide  Alloys 
golden    sulphuret    of, 

377 
oxychloride  of,  376 
tartrate  of,  and  potassa 
652 
Apatite,  483 
Apparatus,  Nooth's,  189 
Aqua  fortis,  182 
regia,  222 
Aqueous  vapour,elastic  force 
of  at  different  tem- 
peratures,   table   of, 
826 
Arbor  Dianae,  414 
Saturni,  361 
Archil,  689 
Aricine,  706 

Arrangement  of  the  work,  5 
Arrow-root,  716 
Arseniates,  486 
Arsenites,  488 
Arsenic  and  its  compounds, 
364 
white  oxide  of,  364 
tests  of,  366 
alloys  of,  vide  Alloys 
fuming  liquor  of,  370 
Arsenio-sulphurets,  505 
Arseniuretted  hydrogen,  370 
Asparagine,  688 
Atmospheric  air,  166 

chemical  properties  of, 

170 
physical  properties  of, 

166 
analysis  of,  169 
weight  of,  166 
Atom,  definition  of,  136 
Atomic    theory,    Dalton's 
view  of,  135 
weights,  136 
Atropine,  711 

Attraction,    chemical,    vide 
Affinity,  115 
cohesive,  2 

terrestrial,  or'gravity,  2 
electric,  67 
Aurates,  418 
Auro-chlorides,  510 
Azobenzide,  594 
Azobenzoide,  596 
Azobenzyle,  595 
Azolitmine,  690 
Azote,  165 

Azotized    substances    com- 
mon  to  the  vegeta- 
ble   and    animal 
world,  748 

B. 

Baldwin's  phosphorus,  64 
Balsam  of  Peru,  606 

of  Tolu,  685 
Barilla,  494 


Barley,  malting,  742 
Barium   and   its  compounds 
303 

sulphur  salts  of,  438,502 

haloid  salts  of,  509 

hydrate  of,  304 

ferrocyanide  of,  569 
Baryta  or  barytes,  303 

tests  of,  304 
Baryta,  alloxanate  of,  684 

sulphate  of,  464 

nitrate  of,  473 

nitrite  of,  475 

chlorate  of,  476 

arseniate  of,  487 

carbonate  of,  496 

metaphosphate  of,  486 
Baryto-calcite,  498 
Bases,  a  table  of  those  for 
the  discoveryof  which 
directions  are  given  in 
section  on  chemical 
analysis,  772 

tests  used  for  the  dis- 
covery  of,  and  the 
modes  of  applying 
them,  773 

volatile,  704 
Beer,  742 

Bell-metal,  434,  vide  Alloys 
Benzamide,  592 
Benzhydraniide,  695 
Benzilates,  596 
Benzile,  596 

hydrocyanate  of,  596 
Benzimide,  595 
Benzoates,  591 
Benzoic  ether,  615 
Benzoinamide,  595 
Benzoine,  595 

hydrocyanate  of,  596 
Benzole,  594 

chloride  of,  694 
Benzone,  594 
Benzoyle,  590 

constitution  of  the  com- 
pounds  of,  590 

hyduret  of,  591 

formation  of,  from  bitter 
almonds,  591 

chloride  of,  592 

bromide  of,  692 

iodide  of,  592 

sulphuret  of,  592 

benzoate  of  hyduret  of, 
593 

table  of  compounds  of, 
590 

appendix  of,  598 
Berberine,  713 
Berlin  or  Prussian  blue,  569 
Bibromisatine,  695 
Bromisatine,  695 
Bile  and  biliary  calculi,  761, 

754 
Bismuth   or  wismuth  and  its 
compounds,  399 

magistery  of,  400 

butter  of,  401 

alloys  of,  vide  Alloys 
Bitter  almonds,  oil  of,  691 
Bitumen,  739 


INDEX. 


Black  dyes,  687  Camphor,  oil  of,  665 

Black  lead,  639  Camphorates,  665 

Black  oxide  of  iron,  334,  335  Cannel  coal,  vide  Coal 


copper,  256 
Bleaching,  218 
Bleaching  powder,  218 
Blende,  341 
Block  tin,  350 
Blood,  759 

analysis  of,  761 

coagulation  of,  759 

serum  of,  759 

fibrin  of,  760 
Blowpipe,  with  oxygen  and 

hydrogen,  158 
Blue,  Prussian  or  Berlin,  569 
Blue  dyes,  687 
Blue  vitriol,  466 
Bodies,  isomorphous,  454 

isomeric,  150 

plesiomorphous,  457 
Boiling  point  or  liquids,  42 
Bone  earth,  483 
Borates,  491 
Borax,  209,  491 
Boro-fluorides,  517 
Boron  and  its  acid,  208 

terchloride  of,  232 
Brain,  analysis  of,  755 
Brass,  434 

brazing,  434 
Bromates,  480 
Bromides,  245 

double,  516 

of  cyanogen,  565 
Bromine,  243 

its  compounds,  245 

chloride  of,  247 

its  attraction  for  me- 
tals, 283 
Brucine,  713 
Brunswick  green,  513 
Bryonine,  688 

of  antimony,  375 

of  zinc,  342 

C. 

Cadmium  and  its  comp'ds, 
343 

Caffeine,  715 
Calamine,  341 
Calcination,  280 
Calcium  and  its  compounds, 
308 

sulphur  salts  of,  503 

haloid  salts  of,  509 
Calculi,  urinary,  758 

biliary,  754 
Calculus,  mulberry^  759 

bone  earth,  759 

ammoniaco.magnesian 
fusible,  759 

cystic  oxide,  759 

xanthic,  759 
Calomel,  408 
Caloric,  vide  Heat 
Calorimeter  of  Lavoisier  and 

Laplace,  33 
Calx,  280 

Camera  obscura,  58 
Camphone,  665 
Camphor,  665 


Cantharadine,  683 
Canton's  phosphorus,  64 
Caoutchouc,  684 

volatile  liquid  of,  684 
Capnomor,  725 
Caramel,  635 
Carbon,  185 

chlorides  of,  229,  230 
its    compounds   with 

oxygen,  187 
with  hydrogen,  258 
with  nitrogen,  271 
with  sulphur,  273 
Carbo-sulphurets,  504 
Carbonates,  general  proper- 
ties of,  492 
double,  498 
Carbonic  oxide,  190 

ether,  614 
Carbovinate  of  potassa,  614 
Carburetted  hydrogen,  258 
Carmine,  702 
Cartilage,  750 
Caseine,  745 

identical  with    legu- 

mine,  741 
occurs  in  many  vegeta- 
bles,  741 
Cassius,  purple  of,  410 
Castor  oil,  674 
Castorine,  677 
Catechine,  659 
Catechu,  659 
Cathartine,  688 
Cedriret,  726 
Celestine,  464 
Cetrarine,  688 
Cerine,  677 
Cerium,  and  its  compounds, 

399 
Cerosine,  678 
Ceruse,  497 
Cetene,  646 
Cetyle,  646 

combinations  of,  647 
Chalk,  496 

stones,  580 
Chalybeate  waters,  780 
Charcoal,  185 

animal,  or  ivory  black, 

185 
property  of  absorbing 

gases,  186 
antiseptic  property  of, 

187 
destroys    colours     in 
fluids,  187 
Chelidonine,  710 
Chemical   analysis,  the  dif- 
ferent   objects    pro- 
posed  in,  769 
exemplification     of, 

769 
quantitative  and  quali- 

tative,  769 
directions  for  conduct- 
ing, 770 
Chemical    decomposition, 
theory  of,  110 


Chemical  action,  changes  thitt 
accompany  it,  of  den- 
sity,       temperature, 
form  and  colour,  118 
affinity  or  attraction,ll5 
symbols,  146 
equivalents,  128 

mode  of  ascertaining, 

134 
scale  of,  135 
formulae,  146 
symbols,  table  of,  146 
Chemical  equivalents  of  ele- 
mentary   substances, 
table  of,  147 
Chemistry,  organic,  521 

inorganic,  111 
Cheese,  vide  Caseine 
Chinoidine,  706 
Chinoiline,  705 
Chlorates,  226,  476 
Chloral,  626 
Chloranilam,  698 
Chloranilammon,  698 
Chloranile,  698 
Chlorides  or  chlorurets,  218 

metallic,  282 
Chlorides  with  ammonia,  614 
with  phosphuretted  hy- 
drogen, 515 
Chlorides  of  carbon,  229 
oxy-,  512 

with  double  iodides,  616 
Chloride  of  sulphur,  231 
phosphorus,  231 
boron,  232 
iodine,  241 
bromine,  247 
cyanogen,  564 
nitrogen,  228 
lime,  310 
sodium,  300 
Chlorine,  215 

Chlorine,  its  affinity  for  me- 
tals, 282 
its  compounds,  219 
nature  of,  217,  233 
bleaching     powers    of, 

218 
disinfecting  powers  of, 

218 
theories  of  constitution 
of,  216 
Chlorindamit,  698 
Chlorindine,  697 

bichlorisatyde,  696 
Chlorindopten,  697 
Chlorisatinc,  694 

bichlorisatine,  693 
Chlorisatyde,  696 
Chlorites,  247 
Chloroacetates,  626 
Chlorobenzide,  594 
Chlorocarbonic  ether,  616 
Chloronaphthalase,  733 
Chloronaphthalese,  733 
Chloronaphthalise,  733 
Chloronitrous  gas,  233 
Chlorophane,  64 
Chlorophyll,  687 
Chlorosalicine,  604 
Chlorosalicylimide,  603 


INDEX. 


839 


Chlorurets,  218 
Cholesterine,  677 
Chondrine,  750 
Chromates,  484 

of  chlorides,  490 
Chromate  of  iron,  378 
Chromium  and  its  comp'ds, 
378 

sulphate  of,  466 
Chrome  alum,  469 
Chrome  yellow,  490 
Chrysammate  of  potassa,  702 
Chrysolepate  of  potassa,  703 
Chyle,  757 
Chyme,  756 
Cinchona  bark,  706 

bases  of,  706 
Cinchonine,  706 
Cinnabar,  412 
Cinnabar,  factitious,  412 
Cinnamon,  oil  of,  680 
Cinnamule,  605 

hydurets  of,  605 
Cinnameine,  606 
Citrates,  649 
Citric  acid,  648 
Classification     of    chemical 

substances,  5 
Cleavage,  453 
Cloves,  oil  of,  680 
Coal-mines,    fire-damp    of, 
259 

wood  or  brown,  726 

gases,  726 

changes  of,  727 

nitrogen  contained  in, 
727 
Coagulation   of  the   blood, 

vide  Blood 
Cobalt  and  its  compounds, 

345 
Cyanides,  565 
Cobalto -cyanide    of   potas- 

slum,  571 
Cobalto- cyanides,  571 
Codeine,  708 
Cocculus  Indicus,  principle 

of,  711 
Cochineal,  702 
Cohesive  attraction,  2,  120 

influence  of,  over  che- 
mical action,  121 
Cold,   artificial   methods   of 

producing,  40,  48 
Colouring  matter, 

non-azotized    vegeta- 
ble, 686 

vide  Blood 

yellow,  686 

red,  686 

green,  686 
Colours  primitive,  61 
Coke,  185 
Columbin,  688 
Columbium    and    its    com- 
pounds, 395 
Combination  defined,  126 

utility  of,  131 

laws  of,  127,  128 
Combining   proportions   ex- 
plained, 128 

table  of,  134 


Combining   exemplifications 

of,  133 
Combustion,  152 

theories  of,  153,  154 
spontaneous,  vide 

Phosphuretted     hy- 
drogen   and     Pyro- 
phosphorus 
Compound  radical,  524 
Composition  of  bodies,  132 
how  determined,  134 
Conine,  705 
Conductor,  prime,  73 
Conductors  of  heat,  9 
Conduction  of  heat,  9 
Cooling  of  bodies,  18 
Copal,  685 
Copper  nickel,  348 
Copper  and  its  compounds, 
354 
test  of,  356 
alloys  of,  vide  Alloys 
pyrites,  358 
glance,  358 
sulphates  of,  466 
nitrate  of,  474 
arsenite  of,  488 
carbonate  of,  497 
tinning  of,  434 
acetates  of,  623 
black  oxide  of,  356 
white  muriate  of,  357 
sheathing,  preservation 

of,  84 
white,  of  the  Chinese, 

434 
ore,  blue,  497 
Cork,  vide  Suberic  acid 
Corydaline,  713 
Corrosive  sublimate,  409 

tests  of,  410 
Count   Rumford's   mode   of 
ascertaining     conducting 
power  of  articles  of  cloth- 
ing, 10 
Cream  of  lime,  vide  Milk  of 

lime,  309  ' 
Creosote,  722 
Crocus  of  antimony,  376 
Cryophorus,  48 
Crystallization,  446 
systems  of,  447 
water  of,  443 
Crystallography,  446 

octohedral  system  of, 

449 
square  prismatic  sys- 

tem  of,  451 
right     prismatic     sys- 
tem, 451 
oblique,     doubly    ob- 
lique,  and  rhombo- 
hedral  systems,  452 
Crystals,  simple  form  of,  447 
compound  form  of,  448 
angles,     planes,     and 

edges  of,  in,  447 
structure  of,  453 
cleavage  of,  453 
Cubebine,  689 
Cudbear,  689 
Cyanates,  559 


Cyanides,  double,  of  metals, 

567 
Cyanogen,  271,  554 

compounds  of,  554 
Cyanogen,   decomposition  of 
solution,  540 
and  carbonic  oxide,  580 
Cyanurates,  563 
Cyanurets,  metallic,  (or  Cya- 
nides,) 565 
double,  567 
Cyanuret,   red,  of  potassium 

and  iron,  670 
Cyclamine,  689 
Cystic  oxide,  calculus,  759^ 


Daguerreotype,  63 

Daturine,  710 

Dead  Sea,  analysis  of  its  wa- 
ter, 782 

Decay  of  wood,  533 

prevented  by  antisep- 
tics, 720 

Decomposition,  simple,  115 
double,  116 

Decrepitation,  445 

Definite  proportions,  doctrine 
of,  vide  Equivalents 

Deflagration,  472 

Deliquescence,  443 

Delphine,  712 

Density,  49 

Dephlogisticated  air,  vide  Ox- 
gen 
marine  acid,  vide  Chlo- 
rine 

Derbyshire  spar,  310 

Dew,  formation  of,  18 

Dew-point,  51 

Dextrine,  717 

Diamond,  185 

Diastase,  717 

Diflerential     thermometer, 
26 

Digestion,  756 

respective  action  in,  of 
gastric  juice,  hydro- 
chloric  acid,  and  oxy- 
gen, 756 

Dioxides,  133 

Disinfecting  liquor,  218 

Distilled  waters,  780 

Distillation  by  descent,  341 

Drying  oils,  674 

Dutch  gold,  434 

Dyes,  686 


Earths,  pure,  289 

metallic  bases  of,  289 
siliceous,  210 
alkaline,  289 
aluminous,  314     * 
Earthy   sulphates,    mode    of 

analyzing,  777 
Earthy  minerals,  analysis  of, 
containing  silica,  iron,  alu- 
mina, manganese,  lime  and 
magnesia,  779 


840 


INDEX. 


Ebullition,  42 
Efflorescence,  444 

influeiye  of,  over  affi- 
nity, 122 
Elaldehyde,  619 
Elasticity,  its  effects  on  che- 
mical affinity,  122 

of  vapours,  49 
Electric  attraction,  67 

repulsion,  67 

excitement,  causes  of, 
71 

intensity,  79 

current*,  98 
Electrics,  positive,  110 

negative,  110 
Electrical  battery,  74 

accumulation,  laws  of, 
79 

machine,  71 

unit  jar,  78 
Electricity,  67 

elementary  facts  of,  67 

conductor    and    non- 
conductors of,  68 

vitreous  or  positive,  69 

resinous  oruegative,69 

theories  of,  69 

induction  of,  73 

of  atmospheric,  72 

identical    with     light- 
ning, 82 

historical  notice  relat- 

*  ing  to,  81 

velocity  of,  81 

light  of,  81 

condenser  of,  74 
Electro-chemical  decompo- 
sition, theory  of,  100 

theory,  105 
Electrodes,  101 
Electro-dynamics,  96 
Electro-magnetism,  96 
Electrometer,  balance,  78 

quadrant,  77 

gold  leaf,  77 

torsion,  77 
Electrolyte,  101 
Electro-negative  and   posi- 
tive elements,  108 
Electrophorus,  75 
Electroscopes  and   electro- 
meters, 77 
Elements,  146,  147 
Elementary  substances,  che- 
mical equivalents  of,  128 
Emetine,  712 
Empyreal  air,  vide  Oxygen 
Emulsine,  741 
Epsom  salts,  465 
Equivalent,  chemical,  12S 

scale  of,  135 
Eremacausis,  473,  533 
Ergotine,  688 
Erethryne,  689 
Erythroleine,  690 
Erythrolitmine,  690 
Erythronium,  384 
Essential  oils,  678 

non- oxygenated,  678 

oxygenated,  679 

containing  sulphur ,68 1 


Ethal,  646 
Ether,  608 

theory  of  the  formation 
of,  608 

constitution  of,  and  its 
compounds,  607 

acetic,  622 

oxalic,  614 

chloric,  611 

hydriodic,  611 

hydrochloric,  611 

hydrobromic,  611 

carbonic,  614 

chlorocarbonic,  416 
Etherine,  617 
Etherole,  617 
Ethionate  of  baryta,  617 
Ethiop's  mineral,  412 

per  se,  406 
Ethule  or  Ethyle,  609 

with  oxygen,  608 

with  water,  609 

and  chlorine,  611 

bromide  of,  611 

iodide  of,  611 

sulphuret  of,  611 

compounds  of,  sul- 
phuret of,  611 

bisulphuret  of,  612 

seleniuret  of,  612 

cyanide  of,  612 

sulphocyanide  of,  6 12 

oxide  of,  and  oxalic 
acid,  614 

double  salts  of  oxalic 
acid,  with  oxide  of 
615 

oxalate  of,  with  ammo- 
nia, 615 

bicarbosulphate  of  ox- 
ide of,  815 

oxide  of,  and  hydrated 
cyanic  acid,  615 

oxide  of,  and  benzoic 
acid,  615 

compounds  of,  of  un- 
certain constitution, 
616 

salts  of,  612 

oxide  of,  and  sulphuric 
acid,  613 

double  salts  of  the  sul- 
phate of  oxide  of,613 

oxide  of,  and  phospho- 
ric acid,  613 

phosphate  of  oxide  of 
ethule  with  metallic 
oxides,  613 

oxide  of,  with  nitric 
acid,  613 

oxide  of,  with  hyponi- 
trous  acid,  614 

oxide  of,  with  carbonic 
acid,  614 

carbonate  of  oxide  of, 
614 

sulphate  of  oxide  of, 
613 
Eupione,  725 
Evaporation,  46 

circumstances  influ- 
encing, 49 


Evaporation,  cause  of,  50 
limit  to,  47 

Leslie's      method      of 
freezing  by,  48 
Excrements,  solid,  757 

ashes  of,  757 
Expansion  of  solids,  20 

force  of,  in  solids  irre- 
sistible, 20 
of  liquids,  21 
of  gases,  23 
table  of  the  expansion 
of  different  bodies,  21 
increasing  ratio  of,  in 

fluids,  22 
of  some  fluids,  by  cold, 

22 
of  some  solids,  23 
Extractive  matter,  687 
Eye,  action  of,  on  light,  58 

F. 

Factitious  cinnabar,  412 
Fat  animal,  its  origin,  766 
Feathers,  747 
Fecula,  715 
Ferment,  744 
Fermentation,  vinous,  637 
viscous,  638 
theory  of,  537 
Ferrid-cyanogen,  570 
Ferro-cyanurets,  570 
Ferro-cyanides,  568 
Ferro-cyanide   of  potassium 

and  iron,  &c.  667 
Fibre,  woody,  720 
Fibrine,  745 

of  the  blood,  745 
identity  of  vegetable  and 
animal,  747 
Filter,  770 
Filtration,  770 

Fire-damp  of  coal  mines,  259 
Fixed  bodies,  41 
Fixed  air,  188 
Fixed  oils,  674 
Flame,  vide  Combustion  and 

Carbu retted  hydrogen 
Flesh,  761 
Flint,  211 
Flowers  of  sulphur,  193 

argentine  of  antimony, 
373 
Fluoborates,  252 
Fluidity  caused  by  heat,  37 

heat  of,  37 
Fluosilicates,  254  vide  Salts 
Fluorides,  metallic,  250 
Fluorides,  double,  616 

oxy.,  519 
Fluorine,  249 

its  attraction  for  metals, 
283 

theories,  relating  to,251 
Fluor-spar,  251 
Fly  powder,  364 
Food  of  plants,  761 
Formiates,  645 
Formyle,  643 

compounds  of,  644 
Fraxinine,  689  ^ 


INDEX. 


841 


Freezing  mixtures,  40 

tables  of,  40 
Freezing  in  Tacuo,  Leslie's 

method,  48 
Friction,  heat  produced  by, 
53 
electricity  excited  by, 
67 
Frigorific      mixtures      with 

snow,  table  of,  40 
Fulminates,  561 

of  copper  and  zinc, 662 
Fulminating  gold,  418 

mercury,  561 
Fulminating  platinum,  433 

silver,  661 
Fumaramide,  657 
Fuming  liquor  of  Libavius, 
352 
of  Boyle,  501 
of  arsenic,  370 
Fusible  metal,  299 
Fusion,  watery,  444 
point  of,  279 


Galena,  368 
Gallates,  658 
Gall-nuts,  659 
Galvanic  battery,  87 
Galvanism,  82 

how  developed,  82 

eifects  of,  92 

chemical  agency  of,100 

electrical  agency  of, 
92,  101 

connection  of,  with 
magnetism,  97 

theories  of  its  produc- 
tion, 105 

magnetic  effects  of,  93 

chemical  theory  of,  105 
Galvanometer,  83,  94 
Gases,  41 

constitution  of,  with 
respect  to  heat,  52 

pressure  required  to  li- 
quefy, 52 

table  of  refractive  in- 
dices, 58 

table  of,  exhibiting 
their  distinctive  pro- 
perties, 775 

become  incandescent 
when  strongly  heat- 
ed, 63 

mode  of  finding  the 
specific  gravity  of, 
112 

condensation  of,  53 

law  of  expansion  of,  23 

diffusion  of,  171 

formula  for  correcting 
the  effects  of  heat 
on,  24 

their  bulk  influenced 
by  moisture,  and  the 
formula  for  correct- 
ing its  effects,  60 

qualitative  analysis  of, 
775 


Gases,    absorption    of,    by 
charcoal,  186 

mode  of  drying,  52 
Gastric  juice,  755 

the  action  of,  in  diges- 
tion, 756 
Gelatine,  760 

sugar,  750 
Gelatinous  tissue,  750 
Gentianine,  687 
Germination,  761 
Gibbsite,  317 
Glance  silver,  415 

copper,  358 
Glass,  various  kinds  of,  212 

of  antimony,  376 

of  borax,  491 
Glauberite,  467 
Glauber  salts,  463 
Glaucopicrine,  710 
Glucina,  318 

test  of,  319 
Glucinium  and  its  oxide,  318 
Glue,  750 
Gluten,  740 
Glycerine,  648 
Glycerule,  648 
Gold  and  its  compounds,  416 

fulminating  compound 
of,  418 

ethereal    solution    of, 
419 

alloys  of,  435 

haloid  salts  of,  510 
Golden  sulphuret  of  antimo- 
ny, 377 
Gong,  Chinese,  434 
Goulard's  extract,  623 
Grain  tin,  350 
Graphite,  339 
Gravel,  urinary,  759 
Gravitation,  2 

Gravity,  eflfect  of,  on  chemi- 
cal action,  125 

modes  of  determining, 
111 
Green,  Scheele's,  366,  488 

mineral,  497 

Brunswick,  513 
Green  vitriol,  465 
Growth  of  plants,  762 
Guaiacine,  689 
Guano,  758 
Gum,  718 

tragacanth,  719 
Gypsum,  464 

H. 

Haarkies,  345 

Haematite,  brown  and   red, 

335 
Haematosine,  761 
Haematoxylin,  686 
Hair,  747 
Haloid  salts,  509 
Harmaline,  714 
Hartshorn,  spirit  of,  254 
Heat,  7 

animal,  how  produced, 

765 
definition  of,  7 
56 


Heat,  nature  of,  7 

communication    of,   by 

contact,  8 
conduction  of,  9 
conductors  of,  table  of, 

9 
of  fluidity,  38 
slow  conductors  of,  10 
conveyed  by  liquids,  10 
effect  of  upon  liquids, 10 
effect  of  upon  gases,  11 
radiation  of,  11       • 
what  surfaces  best  suit- 
ed for  radiation  of,  12 
radiation  of,  not  affected 

by  colours,  13 
absorption  of,  14 
has  different  degrees  of 

refrangibility,  17 
polarization  and  double 

refraction  of,  17 
influence  of  upon  vege- 

tation,  19 
dimensions  and  forms  of 
bodies  influenced  by, 
19 
effect   of,  on   chemical 

action,  19 
quantity  of,  transmitted 
by  different  bodies, 15 
relation  of,  to  light,  66 
emitted  during  combus- 
tion, 156 
latent,  33,  38 
free,  33 
luminous,  65 
non-luminous,  14 
effects  of,  19 
expansion  by,  20 
expansion  of  solids,  20 
expansion  of  liquids,  21 
expansion  of  gases,  23 
exception  to  the  law  of 

expansion  by,  22 
how  conducted    by    li- 
quids and  gases,  10 
specific,  31,  32 
specific,  table  of,  34 
laws  of  distribution   by 

radiation,  12 
capacities  of  bodies  for, 

32 
sensible  and  insensible, 

33 
sources  of,  53 
radiated,  11 
reflection  of,  13 

? absorption  of,  14 
ransmission  of,  15 
theory   of,   by   Prevost 

and  Pictet,  17 
application  of  Prevost's 
theory  to  the   forma- 
tion of  dew,   by  Dr. 
Wells,  18 
Heavy  spar,  464 
Helenine,  683 
Herbivora,  bile  of,  765 
Romberg's  pyrophorus,  468 
Horn,  747 

silver,  415 
quicksilver,  406 


842 


INDEX. 


Horn,  lead,  362 

Horny  matter,  membraneous 

and  compact,  747 
Humus,  721 

Hydrargo. chlorides,  509 
Hydracids,  439 
Hydrates,  nature  of,  161 
Hydriodates,  238 
Hydro,  how  employed,  161 
Hydrobenzamide,  595 
Hydrocarburet,  258 
Hydrochlorales,  499 
Hydrogen,  156 

preparation  of,  156 
properties    of,    157, 

163 
compounds    of,     with 

sulphur,  263 
compounds    of,     with 

phosphorus,  267 
oxidation  of,  157,  158 
peroxide  of,  163 
arseniuretted,  370 
carbu retted,  258 
and    carbon,   comp'ds 

of,  258 
and  carbon,  new  com- 
pounds of,  259 
and  nitrogen,  255 
and  potassium,  297 
seleniuretted,  267 
sulphuretted,  263 
persulphuret  of,  265 
with  metals,  289 
phosphuretted,  268 
perphosphuretted,  268 
salts  of,  501 
aurochloride  of,  510 
phosphuretted,     chlo- 
rides with,  515 
platino-biniodide      of, 
516 
Hydrogurets,  orhydurets,  of 

metals,  289 
Hydrosalts,  498 
Hydrosulphurets,  502 
Hyduret  of  benzoyle,  591 
Hyduret    of    cinnamyle, 

605 
Hygrometers,  50 
Hyoscyamine,  710 
Hyponitrite     of     oxide     of 

ethyle,  614 
Hyperoxymuriates,  226 


I. 


Ice,  rid*  Water 
Imperatorine,  689 
Imponderables,  7 

influence  of,  over  che- 
mical action,  125 
Incandescence,  63 
Indigo,  691 

white,  692 

blue  and  white,  com- 
position of,  692 
action  of  sulphuric  acid 

on,  693 
products  of  oxidation 

of,  694 
commercial,  691 


Indine,  696 

Induction,  electric,  73 

magneto-electric,  98 

Inflammable  air  of  marshes, 
258    - 

Ink,  marking,  475 

sympathetic,  347 

Insolubility,  influence  of,  on 
affinity,  121 

Insulators,  electrical,  68 

Inulin,717 

lodates,  479 

Iodides,  or  iodurets,  236 

Iodides,  metallic,  282 
double,  515 
oxy-,  516 
of  cyanogen,  565 

Iodine,  235 

test  for,  237 
compounds  of,  237 
oxide  of,  239 
chlorides  of,  241 
bromide  of,  248 
attraction  of,  for  me- 
tals, 282 

Ipecacuanha,  712 

Iridio-chlorides,  512 

Iridium  and  its  compounds, 
427,  429 

Iron  and  its  compounds,  331 
ores  of,  331 
cast,  332 
rusting  of,  333 
pyrites,  339 
malleable,  332 
black  oxide  of,  333 
red  oxide  of,  333 
cyanide  of,  566 
ferrocyanide  of,  569 
ferrid- cyanide  of,  570 
pyrites,  magnetic,  339 
sulphates  of,  466 
alum,  469 
meteoric,  components 

of,  331,  347 
chromate  of,  378 
carbonate  of,  497 
alloys  of  steel,  435 

Iron  and  manganese,  aiva- 
lytical  mode  of  separat- 
ing, 778 

Isatine,  694 

Isatyde,  696 

Isethionates,  617 

Isomeric  bodies,  150 

Isomorphism,  454 

Ismorphous  substances,  ta- 
ble of,  456 

Ivory  black,  185 

J. 

Jalap,  resins  of,  685 
Jervine,  713 


K. 

Kalium  and  Kali,  293 
Kakodyle,  630 

compounds  of,  630 
Kelp,  494 
Kermes  mineral,  377 


Kinates,  661 
King's  yellow,  371 
Kino,  659 
Kinoyle,  728 
Kupfernickel,  348 


Labarraque's  soda  liquid,  218 

Lac,  685 

Lactates,  639 

Lactine,  636 

Lactucine,  688 

Lake,  702 

Lamp,  safety,  260 

Lantapium,  399 

Lapis  causticus,  293 
infernalis,  475 
lazuli,  301 

Lard,  vide  Fats 

Latent  heat,  33,  38 

Laurel-water,  599 

Laws   of  combination,    127, 
128 

Laws  of  combination  in  mul- 
tiple proportions,  128 
volumes,  138 
of   the    distribution    of 
radiant  heat,  11 

Lead  and  its  compounds,  358 
white,  360,  497 
horn,  362 
ceruse  of,  497 
nitrate  of,  474 
nitrite  of,  475 
phosphate  of,  487 
arseniate  of,  488 
carbonate  of,  497 
oxychloride  of,  514 
oxy-iodides  of,  616 
oxyfluoride  of,  519 
acetate  of,  623 
ferrocyanide  of,  569 
sulphocyanide  of,  674 
tests  of,  in  wine,  361 
alloys  of,  433 

Leather,  750 

Lecanorine,  689 

Legumine,  741 

Lenses,  achromatic,  61 
of  the  eye,  59 

Lepidolite,  302 

Leucine,  748 

Leukol,  729 

I.eyden  jar,  74 

Libavius,  fuming    liquor   of, 
352 

Ligaments,  750 

Light,  theories  of,  55 
diff"us;on  of,  55 
ordinary  ray  of,  59 
extraordinary  ray  of,  59 
reflection  of,  56 
refraction  of,  57 
refraction,  double  of,  59 
polarized,  60 
decomposition  of,  60 
calorific  rays  of,  61 
prismatic  colours  of,  60 
chemical  rays  of,  63 
magnetizing  rays  of,  63 
terrestrial,  63 


INDEX. 


843 


Light,  sources  of,  63 

laws  of  its  distribution, 

56 
velocity  of,  56 
laws  of  reflection  of,  56 
laws  of  refraction  of, 

57 
table  of  refractive  in- 
dices, 58 
dispersion  of  the  rays 

of,  61 
calorific,  rays  of,  61 
calorific  rays  of,  61 
illuminating  power  of 

different  rays  of,  61 
relation  of,  to  heat,  66 
coloured,   emitted    by 
different  substances, 
64 
Lightning,  82 
Lignine,  720 
Lignone,  722 
Lime,  or  quicklime,  308 
fluate  of,  251 
water,  milk  of,  and  hy- 
drate of,  309 
slaked,  309 
chloride  of,  310 
sulphate  of,  464 
sulphite  of,  471 
nitrate  of,  474 
phosphates  of,  483 
arseniate  of,  488 
carbonate  of,  496 
carbonates,  double  of, 

498 
oxalate  of,  550 
acetate  of,  622 
stone,  496 
Lime  and  magnesia,  analy- 
tic  mpde   of   separating, 
776 
Liquids   become    incandes- 
cent at  high  temperatures, 
63 
Liquefaction,  37 

attended  by  disappear- 
ance of  heat,  37 
Liquids,   expansion    of,   by 
heat,  21 
conducting   power  of, 
11 
Liquor  silicum,  211 
Liriodendrine,  687 
Litharge,  360 
Lithates,  vide  Urates 
Lithia,  or  Lithion,  302 
sulphate  of,  463 
tests  of,  302 
Lithium  and  its  compounds, 
302 
hydrosulphuret  of,  503 
carbosulphuret  of,  504 
arseniosulphuret       of, 

507 
molybdosulphuret    of, 

508 
hydrargo- chlorides  of, 
609 
Litmus,  689 

Liver  of  antimony,  376  j 
Luna  cornea,  415 


Lunar  caustic,  414 
Lupuline,  688 
Lymph,  759 

M. 

Madder,  purple,  red,  orange, 

&c.,  686 
Magnesia,  312 
tests  of,  312 
sulphate  of,  465 
nitrate  of,  474 
phosphates  of,  483 
carbonate  of,  496 
oxalate  of,  550 
Magnesian  limestone,  498 

mode  of  analyzing,  776 
Magnesite,  496 
Magnesium,  312 

and  its  compounds, 312 
hydrosulphuret  of,  504 
arseniosulphuret  of,505 
haloid  salts  of,  509 
Magnet,  horseshoe,  95 
Magnetic  iron  pyrites,  339 
Magnetism,  electro,  93 
Magneto-electric  induction, 

9o 
Malachite,  497 
Manganese  and  its  comp'ds, 
323 
sulphate  of,  465 
haloid  salts  of,  509 
alum,  568 
Manganesium,    or    Manga- 

nium,  323 
Manna  and  Mannite,  639 
Marble,  496 
Manipulations  in  analytical 

processes,  770 
Marble  or  carbonate  of  lime, 

mode  of  analyzing,  775 
Margarine,  669     . 
Margarone,  670 
Massicot,  360 
Mastic,  685 

Matter,  chemical  properties 
of,  3 
influence   of   quantity 
of,  over  affinity,  123 
Meconates,  660 
Meconine,  689 
Melam,  577 
Melamine,  577 
Melampyrine,  689 
Mellone,  575 

Mellonide  of  potassium,  576 
Menispermine,  714 
Mercury  and  its  compounds, 
406 
amalgams  of,  433 
fulminating  compound 

of,  561 
sulphates  of,  467 
nitrates  of,  474 
carbonates  of,  498 
oxychloride  of,  514 
cyanide  of,  566 
ferrocyanide  of,  569 
Mercaptan,  611 
Mesitylene,  629 
Mesityle,  629^ 


Mesityle,  its  compounds,  629 
Metaldehyde,  619 
Metallic  combinations,  431 
bases  of   the  alkaline 

earths,  289 
bases  of  the    alkalies, 
289 
Metallic  sulphocyanides,  574 
Metals,  276 

general    properties  of, 

276 
alloys  of,  433 
oxidation  of,  280 
alkaline  or  alkaligenous, 

289 
table    of   discovery  of, 

277 
table  of  specific  gravity 

of,  277 
malleability  of,  278 
ductility  of,  278 
crystallization  of,  279 
tenacity  of,  278 
hardness  of,  278 
structure  of,  277 
native  state  of,  280 
volatility  of,  279 
alloys  of,  380 
aflSnity  of,  380 
action  of  heat  on,  379 
action  of  electricity  on, 

276 
fusibility   of,   table    of, 

279 
reduction  of,  281 
compounds      of,     with 
chlorine,  282  , 
iodine,  282 
Metals  with  bromine,  283 
fluorine,  283 
sulphur,  283 
selenium,  285 
cyanogen,  287 
phosphorus,  288 
carbon,  289 
hydrogen,  289 
nitrogen,  289 
classification  of,  289 
Metaphosphates,  485 
Meteoric  stones,  231 
Methule,  640 

hydrate  of  oxide  of,  640 
salts  of,  641 
Milk,  745 

sugar  of,  636 
cause  of  coagulation  of, 
535 
Mindererus,  spirit  of,  622 
Mineral  chameleon,  328 
green, 497 
yellow,  514 
Mineral  waters,  analysis    of, 
780 
denominations  of,  780 
Minerals,  needful    to  plants, 
are   also   indispensable  to 
animals,  521 
Minium,  361 
Molecules,  137 
Molybdates,  392 
Molybdenum    and    its    com- 
pounds, 390 


844 


INDEX. 


Molybdo-sulphurets,  507 

Mordant,  352 

Morphia,  or  Morphine,  707 

Pseudo-morphine,  708 
Mucus,  747 
Mulberry  calculus,  vide  Cal- 

cuius 
Murexan,  589 
Murexide,  688 
Muriates,  499 
Muscular    tissue    or    fibre, 

745 
Mustard,  oil  of,  681 
Myricine,  677 

N. 

Nails  of  animals,  747 

Naphtha  from  coal  tar,  737 

Naphthalidam,  737 

Naphthaline,  729 

Naphalic  acid,  736 

Narceine,  708 

Narcotine,  708 

Natrium,  299 

Natron,  300 

Nervous  matter,  755 

contains    phosphorus, 
775 

Neutral  salts,  characters  of, 
442 

Neutralization,  119 

Nickel  and  its  compounds, 
347 
•    sulphates  of,  466 

Nicotine,  705 

Nitrates,  471 

table  of,  472 

Nitrate  of  soda,  as  a  ma- 
nure, 764 

Nitre,  472 

Nitric  oxide  gas,  175 

Nitrites,  475 

Nitrobenzide,  594 

Nitrous  ether,  614 

Nitron.iphthalase,  735 

Nitronaphthalese,  736 

Nitronaphthalise,  736 

Nitrogen,  165 

ter iodide  of,  242 
sulphuret  of,  275 

Nitrogen  gas, 

properties  of,  166 
oxides  of,  166 
protoxide  of,  174 
binoxide  of,  175 
quadrochloride  of,  228 
compounds     of,    with 
carbon,  271 

Nomenclature,  113 

Nutrition  of  animals,  761 

0. 

Oil  of  vitriol,  195 
of  wine,  517 
of  mustard,  bases  of, 

681 
fixed,  674 
Oils,   drying,    or    siccative, 
674 
volatile,   or  essential, 
678 


Oil,  vegetable,  678 
Oil  of  turpentine,  678 

of  juniper,  679 
Oils  and  fats   occurring  in 

nature,  674 
Oils,  sweet,  principle  of,  648 

occurring    in    nature, 
674 
Olefiant  gas,  261 
Oleine,  672 
Olive  oil,  672 
Olivile,  689 
Olivine,  689 
Opium,  active  principle  of, 

707 
Orceine,  690 
Orcine,  690 
Organic  chemistry,  521 

substances,    character 
of,  522 

bases  703 
Organic  acids,  648 
Orpiment,  371 
Osmio-chlorides,  512 
Osmium  and  its  compounds, 
428 

test  of,  429 
Oxalates,  550 
Oxalovinates,  615 
Oxamethane,  615 
Oxamethylane,  642 
Oxamide,  or  Oxalamide,  550 
Oxichloride  of  acetyle,  624 
Oxidation,  152 
Oxide  of  ammonium,  256 
Oxide,  carbonic,  190 
Oxides,  113 

nomenclature  of,  113 
Oxidium  manganoso-manga- 

nicum,  327 
Oxidum  ferroso.ferricum,335 
Oxygen, 150 

prefjaration  of,  151 

properties  of,  152 

necessary  to    respira- 
tion,  153 
Oxyhydrogen  blow-pipe,  158 
Oxymuriate  of  potassa,  477 
Oxiodine,  240 
Oxychlorides,  512 
Oxyfluorides,  519 

P- 

Palladio-chlorides,  511 
Palmine,  674 

Palladium  and  its  comp'ds, 
624 
cyanide  of,  566 
Panary    fermentation,    vide 

Vinoas 
Pancreatic  juice,  756 
Papin's  digester,  44 
Paracyanogen,  372 
Paraffine,  725 
Paramenispcrmine,  714 
Paranaphthaline,  737 
Particles,      integrant      and 

component,  3 
Patent  yellow,  514 
Pearlash,  493 
Perchlorates,  477 
Peruvine,606 


Petroleum,  737 
Peucedanine,  689         ' 
Pewter,  434 
Phillyrine,  689 
Phloretine,  690 
Phloridzeine,  690 
Phloridzine,  690 
Phlogiston,  156 
Phosphates,  480 
Phosphorescence,  64 
Phosphorus,  201 

iodides  of,  242 
bromides  of,  248 
combinations    of,   with 
oxygen,  203 
with  hydrogen,  267 
chlorides  of,  231 
solar,  65 
sulphuret  of,  274 
Baldwin's,  64 
Canton's,  64 
Homberg's,  64 
Phosphuret  of  nitrogen,  273 
Phosphurets,  metallic,  288 
Phosphuretted  hydrogen  gas, 
288 
salts  of,  501 
chlorides  with,  515 
Photography,  61 
Photometer,  66 
Picamar,  724 
Picrolichenine,  687 
Picrotoxine,  688 
Pinchbeck,  434 
Piperine,  714 
Pitchblende,  397 
Pittacal,  726 
Plants,  growth  of,  702 

derive     ammonia      and 
carbonic     acid     gas 
from  the  air,  762 
digestion  of,  762 
food  of,  764 
Plaster  of  Paris,  464 
Plasters,  677 
Platino-chlorides,  611 
Platinum  and  its  compounds, 
720 
a    powerful    oxydizing 

agent,  421 
spongy,  421,  423 
fulminating  powder  of, 

423 
alloys  of,  420 
Plesiomorphisra,  457 
Plumbagin,  689 
Plumbago,  339 
Polychrome,  687 
Populin,  687 
Porphyroxine,  688 
Potash,  or  pearlash,  493 
Potash,  or  potassa,  293 
cyanate  of,  559 
cyanurate  of,  663 
hydrate  of,  293 
solution  of,  294 
Potassa  fusa,  293 
tests  of,  295 
sulphates  of,  462 
sulphite  of,  470 
nitrate  of,  472 
nitrite  of,  475 


INDEX. 


845 


Potassa  fusa,  chlorate,  oxy- 
muriate,   or    hyper- 
oxymuriate  of,  476 
iodates  of,  479 
phosphates  of,  482 
Potash,  or  potassa 

arseniates  of,  487 
arsenite  of,  489 
chromates  of,  489 
carbonates  of,  493 , 
oxalates  of,  550 
acetate  of,  622 
citrate  of,  649 
tartrates  of,  656 
tartrate  of,  and  soda, 

652 
triple  prussiate  of,  567 
Potassium  and  its  comp'ds, 
291 
cyanide  of,  565 
ferro -cyanide  of,  568 
ferrid- cyanide  of,  570 
cobalto-cyanide  of,571 
sulpho-cyanide  of,  574 
mellonide  of,  576 
sulphur-salts  of,  503 
haloid-salts  of,  510 
hydrosulphuret  of,  503 
sulphocyanuret  of,  574 
carbo-sulphuret  of,504 
arsenio-sulphurets   of, 

505 
molybdo-sulphuret  of, 
507 
Precipitate,  red,  407 
Pressure,    influence   of,   on 

the  bulk  of  gases,  167 
Prism,  60 
Prismatic  or  solar  spectrum, 

60 
Proportions,  definite,  126 

combining,  127 
Proportions  in  which  bodies 

unite,  126 
Proteine   and   its  modifica- 
tions, 748 
Protide,  748 

Prussian,  or  Berlin  blue,  569 
Prussiates,  vide  Hydrocya- 

nates 
Prussiate,  triple,  567 
Pulvis  antimonialis,  375 
Purple   powder  of  Cassius, 
.     419 

Putrefaction,  539 
Putrefactive      fermentation, 

538 
Pyrites,  iron,  339 
copper,  358 
Pyrogallic  acid,  658 
Pyrometer  of  Daniell,  28 

Wedgewood,  30 
Pyrophorus  of  Homberg,468 
Pyrophosphates,  484 
Pyroxilic  spirit,  722 

Q. 

Qualitative  analysis,  direc- 
tions for  performing,  772 

Quantitative  analysis,  direc- 
tions  for  performing,  775 


Quantity,   its    influence   on 

afiinity,  123 
Quassine,  688 
Quicklime,  308 
Quicksilver,  406 

horn,  408 
Quills,  vide  Feathers 
Quina,  or  Quinine,  706 
Quinoline,  706 

R. 

Radiation,  r/(ie  Heat 
Radicals,  organic,  524,  542 
Rays  of  heat,  angles  of  in- 
cidence and  reflec- 
tion of,  13 

luminous,  15 
Realgar,  371 
Red  lead,  361 

antimony,  376 

precipitate,  407 

dyes,  686 

oxide   of   manganese, 
324 

oxide  of  copper,  356 
Reduction  of  metals,  281 
Resin  of  copper,  357 
Resin  of  aldehyde,  619 
Resins,  684 
Respiration,  765 
Rhodizonate  of  potassa,  552 
Rhodio-chlorides,  512 
Rhodium  and   its  comp'ds, 

426 
Rochelle  salt,  652 
Rouge,  687 


S. 


Sabadilline,  711 
Saccharine     fermentation, 

716 
Saccharum  Saturn!,  623 
Sacchulmine,  637 
Safety-lamp,  Sir  H.  Davy's, 
260 
improvement    of,    by 
Messrs.   Upton  and 
Roberts,  261 
Sal-ammoniac,  500 
Salicine,  601 
Salicyle,  601 
Salicylamide,  602 
Salicylites,  601 
Salifiable  base,  437 
Saliva,  766 
Salt,  common,  300 

of  Alembroth,  509 
neutral,  119 
'  of   Seignette   or    Ro- 
chelles  salt,  652 
-petre,  472 
Salts,  general  remarks  on, 
436 
nomenclature  of,  113 
classification   of,  437, 

442 
affinity  of,   for  water, 

443 
crystallization  of,  446 
double  and  triple,  459} 


Salts,  deliquescent,  443 

aqueous  fusion  of,  444 
efflorescence  of,  444 
water  of  crystallization 

of,  444 
decrepitation  of,  445 
plesiomorphism  of,  457 
isomorphous,  454 
oxy-,  458 
sulphates,  460 
table  of,  461 
double,  467 

table  of,  460 
sulphites,  470 
nitrates,  471 

table  of,  472 
cyanates,  559 
nitrites,  475 
chlorates,  476 
perchlorates,  477 
hypochlorites,  478 
iodates,  479 
bromates,  480 
chlorites,  477 
phosphates,  480 

table  of,  481 
pyrophosphates,  484 
metaphosphates,  485 

table  of,  485 
arseniates,  486 

table  of,  487 
arsenites,  488 
chromates,  489 
chlorides,  218 
borates,  491 
carbonates,  492 

table  of,  492 

double,  498 
hydro. salts,  498 
ammoniacal,  499 

table  of,  499 
of  phosphuretted   hy- 
drogen, 501 
sulphur-salts,  502 
hydro-sulphurets,  502 

table  of  503 
sulpho-cyanurets,  574 
carbo-sulphurets,  604 

table  of,  504 
arsenio-sulphurets,  505 

table  of,  506 
molybdo-sulphurets, 

507 

table  of,  508 
antimonio-sulphurets, 

508 
tungsto-sulphurets,  508 
haloid-salts,  509 
hydrargo-chlorides, 

509 

table  of,  509 
auro-chlorides,  510 

table  of,  510 
platino-chlorides,  510 

table  of,  511 
palladio-chlorides,  511 
rhodio-chlorides,   512 
iridio-chlorides,  512 
osmio-chlorides,  512 
oxy-chlorides,  512 
chlorides  with  ammo- 
nia, 514 


846 


INDEX. 


W 


Salts,  chlorides  with    phos- 
phu  retted    hydrogen, 

515 
double  iodides,  545 
oxy-iodides,  516 
double  bromides,    516 
double  fluorides,  516 
boro-fluorides,  517 
silico-fluorides,  518 
titano-fluorides,  518 
oxy-fluorides,  519 
double  cyanurets,  567 
ferro-cyanurets,  568 
cobalto-cyanurets,  511 
oxalates,  550 
acetates,  622 
lactates,  639 
of  saccharic  acid,  635 
mucates,  637 
pyromucates,  636 
formiates,  645 
meconates,  660 
citraconates,  651 
tartralates,  653 
margarates,  669 
stearates,  670 
oleates,  672 
sebates,  673 
elaidates,  673 
hydrocyanates,  558 
molybdates,  392 
vegetable   bases,  salts 

of,  703 
antimonies,  375 
antimoniates,  575 
raellitates,  553 
fulminates,  561 
cyanurates,  563  | 
cyanides,  565 
ferrocyanides,  663 
ferridcyanides,  570 
cobalto. cyanides,  571 
metallo-sulphocya- 

nides,  574 
of  melamine,  577 
of  ammeline,  677 
urates,  581 
alloxanates,  584 
thionurates,  585 
formobenzoates,  592 
hippurates,  593 
hyposulphobenzoates, 
•  593 

benzilates,  596 
cinnamates,  606 
oxalovinates,  615 
isethionates,  617 
methionate  of  baryta, 

617 
of  oxide   of   methule, 

641 
of  amule,  647 
kinates,  661 
malates,  656 
citrates,  649 
tartrates,  651 
benzoates,  591 
tannates,  657 
gallates,  658 
succinates,  672 
caniphorates,  665 
Santonine,  687 


Saponine,  688 

Scale  of  Equivalents,  135 

Scheele's  green,  488 

Scillitine,  688 

Sea  water,  analysis  of,  782 

Sebates,  673 

Seignette,  salt  of,  652 

Selenite,  464 

Selenium,  212 

its  oxide,  113 
sulphuret  of,  275 

Seleniurets,  metallic,  275 
of  phosphorus,  275 

Senegine,  689 

Serum,  759 

Silica,  or  siliceous  earth,  211 

Silica,  alumina,   and   iron, 
mode   of  analyzing 
compounds  of,  777 

Silicates,  211 

Silicatfed  alkali,  211 

Siliceous  waters,  analysis  of, 
782 

Silicium,    and    its    com- 
pounds,  210 

Silico-fluorides,  518 

Silicon,  210 

terchloride  of,  232 
terbromide  of,  249 

Silicum  liquor,  211 

Silver  and   its  compounds, 
412 

cyanurate  of,  563 
cyanide  of,  666 
fulminating  compounds 

of,  415 
glance,  415 
alloys  of  435 
amalgamation  of,  412 
sulphate  of,  467 
nitrate  of,  475 
phosphates  of,  484 
dipyrophosphate    of, 

485 
arseniates  of,  488 
granulated,  415 
horn,  415 

Sinnamine,  706 

Sinapoline,  706 

Slacked  lime,  308 

Slag  formed  in  the  reduction 
of  iron,  332 

Smalt,  346 

Smilacine,  689 

Soap,  677 

Soda,  or  Natrium,  299 
tests  of,  299 
chloride  of,  300 
sulphates  of,  463 
sulphite  of,  470 
nitrate  of,  472 
nitrite  of,  475 
perchlorate  of,  477 
phosphates  of,  481 
pyrophosphates  of,  484 
metaphosphates  of,  485 
arseniates  of,  487 
arsenites  of,  488 
borate  of,  491 
carbonate  of,  494 
acetate  of,  622 
citrates  of,  649 


Soda,  tartrate  of,  and  potassa, 

652 
Sodium,  or  Natrium,  and  its 
compounds,  299 

chloride  of,  300 

hydrosulphuret  of,  503 
Solanine,  711 
Solar  rays,  vide  i-ight 
Solders,  434 

Solids,  expansion  of,  by  heat, 
20 

liquefaction  of,  37 

conducting  power  of,  9 

specific  heat  of,  34 
Solution,  115 
Spaniolitmine,  690 
Spar,  fluor,  251 
Specific  gravity,  49 

mode    of    determining, 
111 
Specific  heat,  32 

of  gases,  34 
Speiss,  347 
Spelter,  341 
Spermaceti,  677 
Spirea   ulmaria,    volatile   oil 

of,  601 
Spirit,  proof,  611 

of  wine,  610 
Spirit  of  hartshorn,  257 
Stannates,  352 
Staphysine,  712 
Starch,  715 
Steam,  temperature  of,  44 

elasticity  of,  45 

elastic  force  of  at  differ- 
ent temperatures,  44 

latent  heat  of,  45 
Stearates,  670 
Stearine,  670 
Steel,  340 
Stramonine,  711 
Stream  tin,  vide  Tin 
Stibium,  372 
Strontia,  or  Strontites, 

tests  of,  307 

sulphate  of,  464 

sulphite  of,  470 

nitrate  of,  473 

nitrite  of  475 

carbonate  of,  496 
Strontianite,  596 
Strontium  and  its  compounds, 
306 

hydrosulphuret  of,  503 

carbo-sulphurets  of,  504 

haloid-salts  of,  509 
Strychnia,  712 
Styracine,  685 
Styrol,  679 
Suet,  vide  Fat 
Sugar,  632 

of lead,  623 

of  starch,  633 

of  grapes,  633 

of  milk,  636 

of  diabetes,  633 

compounds      of,    with 
bases,  633 

action  of  acids,  637 

preparation     of,    from 
starch,  633 


INDEX. 


847 


Sugar,  from  woody  fibre,  633 

mushroom,  637 

action  of  heat  on,  635 
Sugar-candy,  632 
Sulphates,  460 

double,  467 
Sulphesatyde,  696 
Sulphites,  470 
Sulphobenzide,  594 
Sulphocyanurets,  674 
Sulphur,  192 

its  oxides,  194 

flowers  of,  193 

hydrate  of,  193 

chlorides  of,  230 

bromide  of,  248 

compounds  of,  with  car- 
bon, 273 

iodide  of,  243 

its  attraction  for  metals, 
283 

salts,  438,  502 

bases,  438,  402 

acids,  438,  502 
Sulpho-cyanogen,  573 
Sulphovinic  acid,  613 
Sulphonaphthaline  and   sul- 

phonaphthalide,  735 
Sulphurets,  metallic,  283 
Sulphuret  of  phosphorus,274 
Sulphuretted  hydrogen,  263 
Sulphuretted  sulphites,  199 
Sulphuric  ether,  608 
Sulphurous   and   saline  wa- 
ters, 781 
Supporters   of   combustion, 

154 
Symbols,  146 
Synaptase,  599 
Synthesis  defined,  5 

T. 

Tallow,  670 
Tanghinine,  689 
Tannates,  657 
Tannin,  or  Tannic  acid,  657 
Tantalum,  395 
Tantalite,  395 
Tartar,  652 
Tartarized  iron,  652 
Tartar,  cream  of,  652 

soluble,  652 

emetic,  652 
Tartralates,  654 
Tartrates,  652 
Taurine,  753 
Telerythrine,  690 
Telescope,  construction  of, 

58 
Telluretted  hydrogen,  405 
Tellurium  and  its  comp'ds, 

403 
Temperature^  31 

at   which    bodies    be- 
come luminous,  63 

equilibrium  of,  7 
Tenacity  of  metals,  278 
Test-liquids,  their  applica- 
tion and  their  mode 
of  action,  770 

example  of,  770 


Test  tube,  770 
Tests  for  detecting  the  pre- 
sence    of      certain 
bases  and  the  mode 
of  application,  773 
effects    produced    by, 
on  the  several  sub- 
stances    to     which 
they  are  applied,  773 
Thebaine,  708 
Thermometer,    or    thermo- 

scope,  25 
Thermometer,      Centigrade 
and       Fahrenheit's, 
table  for  the  conver- 
sion of  the  degrees 
of  one  into  the  other, 
829 
Fahrenheit's,  27 
Reaumur's,  27 
Centigrade,  27 
air,  25 

differential,  26 
formula  for  converting 
the     expression     of 
one  into  another,  27 
graduation  of,  27 
Theobromine,  715 
Thiosinnamine,  706 
Thorina,  321 

Its  tests,  321 
Thorium  and  its  compounds, 

320 
Tin  and  its  compounds,  350 
alloys  of,  434 
oxychlondes  of,  513 
permuriate  of,  352 
Tincal,  401 
Titanium  and  its  compounds, 

^402 
Titanofluorides,  519 
Tombac,  434 
Transfer,  galvanic,  100 
Trona,  495 
Trough,  galvanic,  87 
Tungstates,  394 
Tungsten  and  its  comp'ds, 

393 
Tungsto-sulphurets,  508 
Turkey  red,  686 
Turpentine,  oil  of,  678 
Turpeth  mineral,  467 
Type,  metal  for,  434 

U. 

Ultramarine,  301 

Upas  poison,  688 

Uramile,  586 

Uranium  and  its  compounds, 
397 

Urates,  580 

Urea,  560       ^ 

nitrate  of,  660 

Urethane,  616 

Urethylane,  642 

Uric  acid,  580 

Urine  of  man,  757 

analysis  of,  757 
of  herbivora,  757 
of  carnivora,  757 
of  serpents,  757 


Urine,  importance  of,  as  a 

manure,  758 
Urinary  concretions  or  cal- 
culi, 758 

V. 

Vacuum,  boiling  in,  44 
evaporation  in,  49 
Vanadium  and  its  compounds, 

384 
Vaporization,  41 

cause  of,  48 
Vapour,  elastic  force  of  aque-     , 
ous,  at  different  tern-  ^ 
peratures,    table    of, 
826 
dilatation  of,  42 
density  of,  42 
elasticity  of,  or  tension 

of,  45 
latent  heat  of,  45 
presence  of,  in  gases,48 
table  of  elastic  force  of, 

44 
variable  quantity  in  the 
atmosphere,  50 
Vapours  of  alcohol,  ether,  oil 
of    turpentine,    and 
petroleum,  or  naph- 
tha, elastic    force   of 
at  different  tempera- 
tures, table  of,  828 
Varvicite,  327 
Vegetable  alkalies,  703 
Vegetables,  changes  that  oc- 
cur during   the   life, 
growth,  and  nutrition 
of,  762     . 
first  produce  albumen, 
fibrine,  and  caseine, 
762 
Vegetable     tissues,     mineral 
substances  essential  to,  762 
Veratrine,  711 
Vejtfigris,  623 
Verditter,  497 
Vermilion,  412 
Vienna  green,  623 
Vinegar,  621 

theory  of  making,  620 
qualities  of,  621 
from  wood,  621 
Vinous  fermentation,  637 
Vision,  vide  Eye,  action  of 
Vital  air,  vide  Oxygen 
Vitriol,  oil  of,  195 
blue,  466 
green,  465 
white,  466 
Volatile  alkali,  255 

bodies,  41 
Volta-electric  induction,  97 

-electrometer,  98 
Volta's  pile,  82 
Voltaic  circles,  laws  of  the 
action  of,  90 
simple,  S3 
one  described  by  Davy, 

85 
compound,  87 
that  ofVolta,  87 


848 


INDEX. 


Volumes,  theory  of,  138 

Volumes,  combining,  13S 

table  of,  139 

W. 

Water,  composition  of,  159 
Water,  rain  and  snow,  rich 
in  oxygen,  779 

spring,  well,  and  riyer, 
779 

hardness  of,  the  cause 
of,  and  how  re- 
moved, 780 

properties  of,  161 

expansion  of,  in  freez- 
ing, 23 

boiling  and  freezing 
points  of,  27 

of  crystallization,  144 
Waters,  mineral,  779 

analysis  of,  779 

acidulous,  780 

alkaline,  780 

chalybeate,  780 

sulphureous,  781 

saline,  781 

siliceous,  782 


Waters,  of  the  sea,  782 

of  the  Dead    Sea  and 
River  Jordan,  782 
Watery  fusion,  444 
Wax,  677 
Welding,  332 
White  lead,  360,  497 
White  copper,  357 
White  precipitate,  544 
White  vitriol,  466 
Wine,  oil  of,  617 
Witherite,  496 
Wood,  products  of  the  dis- 

tillation  of,  721 
Wood  coal,  or  browtt  coal, 

721 
Woody  fibre,  720 
decay  of,  720 


Xanthic  oxide  calculus,  759 
Xylites,  722 


Y. 


Yeast,  744 


Yellow,  mineral   or    patent, 
514 
king»s,  371 
Yellow,  chrome,  490 
Yellow  dyes,  686 
Yttria,  319 
Yttrium,  319 
Yttro-tantalite,  395 

Z. 

Zaffre,  345 

Zanthopicrine,  688 

Zinc  and  its  compounds,  341 
tests  of  the  presence  of, 

342 
blende,  341,  343 
brown  and  blue  blaze  of, 

341 
butter  of,  342 
alloys  of,  434,  435 
amalgam  of,  433 
sulphate  of,  466 
acetate  of,  623 

Zinc-cyanuret,  566 

Zinetum,  341 

Zirconium  and  its  comp'ds, 
321 


THE   END, 


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